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AWS G2.3M/G2.3:2019 An American National Standard

Guide for the ing of Solid Solution Austenitic Stainless Steels

CVLC AMER G4JS-62761.indd:0.27/0.6858(offset:4.385)::17.27

AWS G2.3M/G2.3:2019 An American National Standard Approved by the American National Standards Institute August 16, 2018

Guide for the ing of Solid Solution Austenitic Stainless Steels

3rd Edition

Supersedes AWS G2.3M/G2.3:2012

Prepared by the American Welding Society (AWS) G2 Committee on ing of Metals and Alloys

Under the Direction of the AWS Technical Activities Committee

Approved by the AWS Board of Directors

Abstract This guide presents a description of solid solution austenitic stainless steels and the processes and procedures that can be used for the ing of these materials. This standard discusses the welding processes and welding parameters, qualifications, inspection and repair methods, cleaning, and safety considerations. Practical information has been included in the form of figures, tables, and graphs that should prove useful in determining capabilities and limitations in the ing of austenitic stainless steels.

AWS G2.3M/G2.3:2019

ISBN Print: 978-1-64322-016-1 ISBN PDF: 978-1-64300-017-8 © 2018 by American Welding Society All rights reserved Printed in the United States of America Photocopy Rights. No portion of this standard may be reproduced, stored in a retrieval system, or transmitted in any form, including mechanical, photocopying, recording, or otherwise, without the prior written permission of the copyright owner. Authorization to photocopy items for internal, personal, or educational classroom use only or the internal, personal, or educational classroom use only of specific clients is granted by the American Welding Society provided that the appropriate fee is paid to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, tel: (978) 750-8400; Internet: <www.copyright.com>.

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Statement on the Use of American Welding Society Standards All standards (codes, specifications, recommended practices, methods, classifications, and guides) of the American Welding Society (AWS) are voluntary consensus standards that have been developed in accordance with the rules of the American National Standards Institute (ANSI). When AWS American National Standards are either incorporated in, or made part of, documents that are included in federal or state laws and regulations, or the regulations of other governmental bodies, their provisions carry the full legal authority of the statute. In such cases, any changes in those AWS standards must be approved by the governmental body having statutory jurisdiction before they can become a part of those laws and regulations. In all cases, these standards carry the full legal authority of the contract or other document that invokes the AWS standards. Where this contractual relationship exists, changes in or deviations from requirements of an AWS standard must be by agreement between the contracting parties. AWS American National Standards are developed through a consensus standards development process that brings together volunteers representing varied viewpoints and interests to achieve consensus. While AWS isters the process and establishes rules to promote fairness in the development of consensus, it does not independently test, evaluate, or the accuracy of any information or the soundness of any judgments contained in its standards. AWS disclaims liability for any injury to persons or to property, or other damages of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, or reliance on this standard. AWS also makes no guarantee or warranty as to the accuracy or completeness of any information published herein. In issuing and making this standard available, AWS is neither undertaking to render professional or other services for or on behalf of any person or entity, nor is AWS undertaking to perform any duty owed by any person or entity to someone else. Anyone using these documents should rely on his or her own independent judgment or, as appropriate, seek the advice of a competent professional in determining the exercise of reasonable care in any given circumstances. It is assumed that the use of this standard and its provisions is entrusted to appropriately qualified and competent personnel. This standard may be superseded by new editions. This standard may also be corrected through publication of amendments or errata, or supplemented by publication of addenda. Information on the latest editions of AWS standards including amendments, errata, and addenda is posted on the AWS web page (www.aws.org). s should ensure that they have the latest edition, amendments, errata, and addenda. Publication of this standard does not authorize infringement of any patent or trade name. s of this standard accept any and all liabilities for infringement of any patent or trade name items. AWS disclaims liability for the infringement of any patent or product trade name resulting from the use of this standard. AWS does not monitor, police, or enforce compliance with this standard, nor does it have the power to do so. Official interpretations of any of the technical requirements of this standard may only be obtained by sending a request, in writing, to the appropriate technical committee. Such requests should be addressed to the American Welding Society, Attention: Managing Director, Standards Development, 8669 NW 36 St, # 130, Miami, FL 33166 (see Annex G). With regard to technical inquiries made concerning AWS standards, oral opinions on AWS standards may be rendered. These opinions are offered solely as a convenience to s of this standard, and they do not constitute professional advice. Such opinions represent only the personal opinions of the particular individuals giving them. These individuals do not speak on behalf of AWS, nor do these oral opinions constitute official or unofficial opinions or interpretations of AWS. In addition, oral opinions are informal and should not be used as a substitute for an official interpretation. This standard is subject to revision at any time by the AWS G2 Committee on ing of Metals and Alloys. It must be reviewed every five years, and if not revised, it must be either reaffirmed or withdrawn. Comments (recommendations, additions, or deletions) and any pertinent data that may be of use in improving this standard are required and should be addressed to AWS Headquarters. Such comments will receive careful consideration by the AWS G2 Committee on ing of Metals and Alloys and the author of the comments will be informed of the Committee’s response to the comments. Guests are invited to attend all meetings of the AWS G2 Committee on ing of Metals and Alloys to express their comments verbally. Procedures for appeal of an adverse decision concerning all such comments are provided in the Rules of Operation of the Technical Activities Committee. A copy of these Rules can be obtained from the American Welding Society, 8669 NW 36 St, # 130, Miami, FL 33166.

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Personnel AWS G2 Committee on ing of Metals and Alloys Midalloy ExxonMobil Production Company American Welding Society Black & Veatch ATI Wah Chang Consultant to Nickel Institute

W. Layo, Chair G. Dunn, Vice Chair S. N. Borrero, Secretary S. O. Luke R. C. Sutherlin D. J. Tillack

AWS G2E Subcommittee on Stainless Steel Alloys Black & Veatch American Welding Society Bechtel Corporation Air Products and Chemicals, Incorporated Kobelco Welding of America, Incorporated Midalloy Townley Foundry & Machine ESAB Welding and Cutting Products GE Oil & Gas National Institute of Standards and Technology Consultant to Nickel Institute Böhler Welding Group USA, Incorporated

S. O. Luke, Chair S. N. Borrero, Secretary R. L. Colwell S. M. Fragano D. W. Haynie W. E. Layo H. W. Record C. D. Ross D. Singh J. W. Sowards D. J. Tillack M. D. Yaple

Advisor to the AWS G2E Subcommittee on Stainless Steel Alloys Voestalpine Böhler Welding USA, Incorporated

R. D. Fuchs

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Foreword This foreword is not part of this standard but is included for informational purposes only.

The American Welding Society formed the G2 Committee on the ing of Metals and Alloys in 1992 in response to an industry demand for information on welding the metals and alloys that have not been covered by other documents and committees. This document is written by the G2 Committee on the ing of Metals and Alloys. NOTE: The ’s attention is called to the possibility that compliance with this standard may require use of an invention covered by patent rights. By publication of this standard, no position is taken with respect to the validity of any such claim(s) or of any patent rights in connection therewith. If a patent holder has filed a statement of willingness to grant a license under these rights on reasonable and nondiscriminatory and conditions to applicants desiring to obtain such a license, then details may be obtained from the standards developer. A vertical line in the margin or underlined text in clauses, tables, or figures indicates an editorial or technical change from the 2012 edition. Comments and suggestions for the improvement of this standard are welcome. They should be sent to the Secretary, AWS G2 Committee on ing of Metals and Alloys, American Welding Society, 8669 NW 36 St, # 130, Miami, FL 33166.

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Table of Contents Page No. Personnel ......................................................................................................................................................................v Foreword.....................................................................................................................................................................vii List of Tables................................................................................................................................................................xi List of Figures.............................................................................................................................................................xii 1. General Requirements ........................................................................................................................................1 1.1 Scope............................................................................................................................................................1 1.2 Units of Measure..........................................................................................................................................1 1.3 Safety ...........................................................................................................................................................1 2. Normative References .........................................................................................................................................2 3. and Definitions .........................................................................................................................................2 4. General Information ...........................................................................................................................................4 4.1 History .........................................................................................................................................................4 4.2 Properties .....................................................................................................................................................8 4.3 Product Forms..............................................................................................................................................8 4.4 Specifications...............................................................................................................................................8 5. Metallurgy..........................................................................................................................................................15 5.1 Ferrite Discussion ......................................................................................................................................15 5.2 The Ferrite-Sigma Phase Relationship ......................................................................................................21 5.3 Corrosion Resistance Related to Welding .................................................................................................22 5.4 Heat Tint ....................................................................................................................................................23 6. Welding and Fabrication Considerations........................................................................................................24 6.1 Weld t Design......................................................................................................................................24 6.2 Cleaning Prior to Welding .........................................................................................................................25 6.3 Thermal Arc Gouging and Grinding..........................................................................................................26 6.4 Distortion Control......................................................................................................................................27 6.5 Welding Preheat and Maximum Inter Temperature............................................................................28 6.6 Welding Position........................................................................................................................................28 6.7 Root Welding .....................................................................................................................................28 6.8 Shielding Gas and Cleanliness...................................................................................................................32 7. Weldability Considerations ..............................................................................................................................32 7.1 Solidification Cracking ..............................................................................................................................32 7.2 Reheat Cracking in Type 347-SS...............................................................................................................33 7.3 Other Forms of Weld Cracking and Prevention Strategies ........................................................................33 7.4 Reheat Cracking in FCAW Deposits .........................................................................................................34 8. Welding Processes..............................................................................................................................................34 8.1 Shielded Metal Arc Welding (SMAW)......................................................................................................34 8.2 Gas Tungsten Arc Welding (GTAW) .........................................................................................................40 8.3 Gas Metal Arc Welding (GMAW).............................................................................................................44 8.4 Flux Cored Arc Welding (GCAW) ............................................................................................................52 8.5 Submerged Arc Welding (SAW) ...............................................................................................................56 8.6 Plasma Arc Welding (PAW) ......................................................................................................................58

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Page No. 8.7 8.8 8.9

Laser Beam Welding (LBW) and Electron Beam Welding (EBW) ..........................................................59 Resistance Welding....................................................................................................................................59 Brazing.......................................................................................................................................................59

9. Postweld Operations..........................................................................................................................................60 9.1 Visual Examination....................................................................................................................................60 9.2 Weld Size ...................................................................................................................................................60 9.3 Final Visual Examination ..........................................................................................................................60 9.4 Weld Discontinuities..................................................................................................................................60 9.5 Slag Removal.............................................................................................................................................61 9.6 Grinding and Finishing Techniques...........................................................................................................61 9.7 Media Blasting...........................................................................................................................................61 9.8 Cleaning, Pickling, and ivation...........................................................................................................62 9.9 Electropolishing.........................................................................................................................................64 10. Heat Treatment..................................................................................................................................................65 10.1 Solution Annealing ....................................................................................................................................65 10.2 Stress Relief ...............................................................................................................................................65 10.3 Stabilization Anneal...................................................................................................................................66 11. Storage and Shipping Recommendations .......................................................................................................67 12. Maintenance and Repair ..................................................................................................................................67 12.1 Maintenance...............................................................................................................................................67 12.2 Repair.........................................................................................................................................................68 Annex A (Informative)—Suggested Filler Metal Selection Chart .............................................................................71 Annex B (Informative)—Informative References ......................................................................................................79 Annex C (Informative)—ASTM Base Metal Specifications for Austenitic Stainless Steels.....................................83 Annex D (Informative)—Estimating the Ferrite Content of Cast Base Materials .....................................................87 Annex E (Informative)—Engineering , Common Conversions, and SMAW Electrode Diameters.................89 Annex F (Informative)—Example Purchase Specification Topics.............................................................................93 Annex G (Informative)—Requesting an Official Interpretation on an AWS Standard..............................................95 List of AWS Documents on the ing of Metals and Alloys ..................................................................................97

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List of Tables Table 4.1 4.2 4.3 4.4 5.1 6.1 6.2 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 8.13 8.14 8.15 8.16 8.17 8.18 8.19 A.1 A.2 A.3 E.1 E.2 E.3

Page No. The Chemical Composition Limits of Common Wrought Austenitic Stainless Steel Base Materials ..........5 The Chemical Composition Limits of Common Cast Austenitic Stainless Steel Base Materials .................9 Mechanical Properties of Wrought Annealed Stainless Steel Alloys ..........................................................12 Minimum Mechanical Properties of Common Cast Austenitic Stainless Steel Base Materials ..................14 Ferrite Diagram Comparisons of Chrome and Nickel Equivalencies ..........................................................19 Typical Physical Property Comparisons of Austenitic Stainless Steels versus Carbon Steels ....................27 Purging Guidelines for Piping......................................................................................................................31 Chemical Composition of Undiluted SMAW Weld Deposits......................................................................35 All-Weld-Metal Mechanical Property Requirements Undiluted SMAW Weld Deposits (AWS A5.4/A5.4M) .....................................................................................................................................37 SMAW Electrodes: Welding Current, Position of Welding, and Operating Characteristics .......................38 SMAW Electrodes: Suggested Current Ranges for E3xx-15, -16, and -17 Type Electrodes ......................39 Tungsten Amperage Limits, GTAW.............................................................................................................41 Suggested Argon Torch Flow Rates, Manual GTAW ..................................................................................42 Suggested Gas Cup Size versus Maximum Welding Current, Manual GTAW ...........................................42 GTAW (TIG) Shielding Gas Selection.........................................................................................................43 Chemical Compositions of Bare Stainless Steel Filler Metals (AWS A5.9/A5.9M) and of Metal Cored Filler Metal Deposits (AWS A5.22/A5.22M) .........................................................................45 Nickel-Based Consumables, Chemical Composition Ranges......................................................................47 Nickel-Based SMAW Electrodes, Specified Tensile Properties ..................................................................48 GMAW (MIG) Shielding Gas Selection ......................................................................................................49 GMAW Parameters (Short Circuit, DCEP, He + 7.5%Ar + 2.5%CO2 Shielding Gas) ...............................50 GMAW Parameters (Spray Transfer, DCEP, 98%Ar + 2%O2 Shielding Gas) ............................................50 FCAW Electrodes Classification Scheme (AWS A5.22/A5.22M:2012) .....................................................52 Stainless Steel Weld Deposit Composition Requirements for FCAW Electrodes and Rods (AWS A5.22/A5.22M) .................................................................................................................................53 Stainless Steel Weld Deposit Tensile Requirements for Flux Cored Electrodes and Rods (AWS A5.22/A5.22M) .................................................................................................................................55 Shielding Gas Selection for Flux Cored Arc Welding .................................................................................55 Typical Submerged Arc Welding Parameters, DCEP ..................................................................................58 Suggested Filler Metal Selection Chart—Wrought Standard Grades..........................................................73 Suggested Filler Metal Selection Chart—Wrought Proprietary Grades ......................................................76 Filler Selection for Stainless Steel Castings ................................................................................................77 Common Engineering .......................................................................................................................89 Data ..............................................................................................................................................................89 Common Welding-Related Conversion Factors...........................................................................................90

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List of Figures Figure 4.1 5.1 5.2 5.3 5.4a 5.4b D.1

Page No. Alloying Variations of Common Austenitic Stainless Steels.........................................................................7 The Schaeffler Diagram ...............................................................................................................................16 The DeLong Diagram ..................................................................................................................................17 WRC-1992 Diagram for Stainless Steel Weld Metal...................................................................................18 Carbide Precipitation in Type 304 Austenitic Stainless Steel......................................................................23 Carbide Reaction Temperature Ranges........................................................................................................24 The Schoefer Diagram .................................................................................................................................87

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Guide for the ing of Solid Solution Austenitic Stainless Steels 1. General Requirements 1.1 Scope. This guide presents a description of solid solution austenitic stainless steels and the most commonly used welding processes and procedures for ing these materials. The most commonly used welding processes, including shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), submerged arc welding (SAW), and flux cored arc welding (FCAW), are discussed in detail; laser beam, electron beam, plasma arc, resistance, and braze welding are not covered in great detail. The welding processes discussed in this guide include recommended welding parameters, filler metals, shielding gases, and fluxes. Procedure qualifications, inspection and repair considerations and methods, and cleaning and safety considerations are also discussed. Practical information has been included as figures, tables, and graphs that should prove useful for determining the capabilities and limitations in the ing of austenitic stainless steels. This guide does not address martensitic, ferritic, or duplex stainless steels. Although this guide is not written with mandatory requirements, mandatory language, such as the use of “shall,” will be found in those portions of the document where failure to follow the instructions or procedures could produce inferior, misleading, or unsafe results. 1.2 Units of Measure. This standard uses both the International System of Units (SI) and U.S. Customary Units. The latter are shown with brackets ([ ]) or in appropriate columns in tables and figures. The measurements may not be exact equivalents; therefore, each system should be used independently. 1.3 Safety. Safety and health issues and concerns are beyond the scope of this standard; some safety and health information is provided, but such issues are not fully addressed herein. Safety and health information is available from the following sources: American Welding Society: (1) ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes (2) AWS Safety and Health Fact Sheets (3) Other safety and health information on the AWS website Material or Equipment Manufacturers: (1) Safety Data Sheets supplied by materials manufacturers (2) Operating Manuals supplied by equipment manufacturers Applicable Regulatory Agencies Work performed in accordance with this standard may involve the use of materials that have been deemed hazardous and may involve operations or equipment that may cause injury or death. This standard does not purport to address all safety and health risks that may be encountered. The of this standard should establish an appropriate safety program to address such risks as well as to meet applicable regulatory requirements. ANSI Z49.1 should be considered when developing the safety program.

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2. Normative References The standards listed below contain provisions, which through reference in this text, constitute mandatory provisions of this AWS standard. For undated references, the latest edition of the referenced standard shall apply. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. American Welding Society (AWS) standards: AWS A3.0M/A3.0, Standard Welding and Definitions, Including for Adhesive Bonding, Brazing, Soldering, Thermal Cutting, and Thermal Spraying; AWS A4.2M:2006 (ISO 8249:2000 MOD), Standard Procedures for Calibrating Magnetic Instruments to Measure the Delta Ferrite Content of Austenitic and Duplex Ferritic-Austenitic Stainless Steel Weld Metal; AWS A5.4/A5.4M, Specification for Stainless Steel Electrodes for Shielded Metal Arc Welding; AWS A5.8M/A5.8, Specification for Filler Metals for Brazing and Braze Welding; AWS A5.9/A5.9M, Specification for Bare Stainless Steel Welding Electrodes and Rods; AWS A5.11/A5.11M, Specification for Nickel and Nickel-Alloy Welding Electrodes for Shielded Metal Arc Welding; AWS A5.12M/A5.12 (ISO 6848:2004 MOD), Specification for Tungsten and Oxide Dispersed Tungsten Electrodes for Arc Welding and Cutting; AWS A5.14/A5.14M, Specification for Nickel and Nickel-Alloy Bare Welding Electrodes and Rods; AWS A5.22/A5.22M, Specification for Stainless Steel Flux Cored and Metal Cored Welding Electrodes and Rods; AWS A5.32M/A5.32 (ISO 14175:2008 MOD), Welding Consumables—Gases and Gas Mixtures for Fusion Welding and Allied Processes; AWS A5.34/A5.34M, Specification for Nickel-Alloy Electrodes for Flux Cored Arc Welding; and AWS C5.3, Recommended Practices for Air Carbon Arc Gouging and Cutting. ASTM International standard: ASTM A380, Standard Recommended Practice for Cleaning and Descaling and ivation of Stainless Steel Parts, Equipment and Systems. SAE International standard: SAE HS-1086, Metals & Alloys in the Unified Numbering System

3. and Definitions AWS A3.0M/A3.0, Standard Welding and Definitions, Including for Adhesive Bonding, Brazing, Soldering, Thermal Cutting, and Thermal Spraying, provides the basis for and definitions used herein. However, the following and definitions are included below to accommodate usage specific to this document. austenite. A solid solution phase with the face-centered cubic (FCC) crystal structure. The FCC crystal structure of austenite is nonmagnetic and remains ductile even at cryogenic temperatures. Austenite forms in stainless steels when iron is alloyed with sufficient austenite-promoting elements including nickel, carbon, nitrogen, manganese, or copper. Charpy Impact Test. A pendulum-type single blow impact test in which a notched specimen is ed at both ends as simple beam and broken by a falling pendulum. The energy absorbed is a measure of impact strength and notch toughness. Toughness of austenitic stainless steels is typically measured in of lateral expansion. Toughness may also be measured in of energy absorption in Joules [ft·lbf]. cleaning. Cleaning as discussed herein refers to the removal of surface contaminants (lubricants, soil, free iron, etc.) using cleaning solutions that range from soapy water to organic solvents to acid-based liquids, or by mechanical means. creep. The time-dependent strain that occurs under load at elevated temperature.

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ductility-dip cracking. A solid-state crack formed at elevated temperatures. Typically occurs in alloys with the austenitic face-centered cubic (FCC) microstructure and is associated with an abrupt drop in ductility. This form of cracking typically occurs with high weld restraint, such as in the thick-section weldments, and when a large austenite grain size is present. ferrite. An atomic crystal structure of a steel alloy where the atoms are arranged in a body-centered cubic (BCC) crystal structure. In the stainless steels that are primarily austenitic, ferrite can be found in some base materials and weld deposits that have sufficient amounts of ferrite-promoting elements such as Cr, Mo, Nb compared to the amount of elements that promote the formation of austenite such as C, Ni, N, and Cu. Ferrite is characterized as magnetic. Unless otherwise noted, the term “ferrite” as discussed in this document refers to the ferrite that is present after solidification and after metallurgical transformations (if any) have completed. Ferrite Number (FN). A value assigned to the ferrite content of weld metal according to its magnetic response using a scale defined by the AWS A4.2M standard. At low levels, the FN is sometimes considered to approximate the percent ferrite, but percent ferrite is much more difficult to determine and not very reproducible. Due to ease and reproducibility of measurement, FN is normally preferred as a means of expressing ferrite content. free iron. Iron particles or iron deposits on the material’s surface not originating from the stainless steel base metal. heat (of material). A finite quantity of material melted and produced at a mill at one time. heat-affected zone (HAZ). The portion of base metal that has had its mechanical properties or microstructure altered by the heat of welding, brazing, soldering, or thermal cutting. heat tint. Discoloration of the surface of metal by formation of an oxide film that occurs when metal is exposed to oxygen-containing atmosphere at an elevated temperature. hot crack. A crack formed at temperatures near the completion of solidification in weld metal or the partially melted zone. See also liquation cracking and weld metal solidification cracking. knifeline attack (KLA). Corrosion that occurs in a very narrow region directly adjacent to the weld fusion line. Stable carbides (niobium or titanium carbides) in that region are dissolved (put into solution) from the heat of welding, but do not reprecipitate with carbon during welding or cooling. Instead, chromium carbides form in that region during high-temperature exposure or when cooling rates after welding are too slow. The precipitation of chromium carbide sensitizes the region making it susceptible to KLA unless a stabilization anneal is performed. The stabilization anneal temperature is sufficient to reprecipitate the niobium or titanium carbides, thus removing the sensitization effect (see Figure 5.4b). liquation cracking. A form of hot cracking that occurs in the heat-affected zone (HAZ) of single welds, or in reheated weld metal in multi welds due to formation of liquid films along grain boundaries in the partially melted zone adjacent to the fusion line. Liquation results from the segregation of impurities to grain boundaries or by constitutional liquation (e.g., partial melting of NbC or TiC). It can be difficult to detect and typically appears as small cracks in the HAZ or “micro fissures” in prior weld es. magnetic. As used in this document, the ability of a magnet to be attracted to the material being tested. ivation. The chemical treatment of a stainless steel with a mild oxidant so as to remove free iron from the surface and speed up the process of forming a protective/ive layer. However, ivation is not effective for the removal of heat tint or oxide scale on stainless steel. phase. A portion of a material that has roughly the same composition, structure and atomic arrangement throughout, and having a distinct boundary between it and any surrounding or ading phases. pickling. The removal of highly adherent oxides using aggressive acid-based solutions. These oxides include heat tint formed adjacent to welds as well as thicker oxide layers formed during longer term, high-temperature exposure (e.g., furnace heat treatments performed without protective atmospheres, mill scales from rolling and forging operations, and high-temperature service exposure). Pickling is also effective for removing free iron. precipitate \pri-'si-p-'tt\ vb. The process of forming small, discrete particles (phases) (usually formed at elevated temperatures) within a material’s structure. precipitate \pri-'si-p-tt\ n. Small, discrete particles (phases) usually formed at elevated temperatures within a material’s structure. Depending on the alloy, their presence can either be intentional and beneficial, or, undesired and potentially detrimental.

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sensitization. The formation of chromium-depleted regions adjacent to chromium-rich carbides that nucleate and grow on austenite grain boundaries during exposure to temperatures of about 480°C to 850°C [900°F to 1560°F]. Regions depleted of chromium are susceptible to preferential attack by a corroding medium. sigma phase. A hard, brittle, nonmagnetic phase with a tetragonal crystal structure containing large amounts of chromium and iron. It can form after extended time in the temperature range of about 600°C to 925°C [1100°F to 1700°F] and can significantly reduce corrosion resistance and produces a marked reduction in room temperature ductility. It forms most readily from weld-metal delta ferrite. solid solution. A solid solution alloy is a homogeneous mixture of two or more elements. The type and proportions of alloying elements are such that the final alloy mixture is formulated to be homogenous without separating into multiple different structure types or chemical compounds. solution annealing. Heating austenitic stainless steels and holding at a temperature (typically 1040°C [1900°F] minimum) long enough to redissolve constituents to enter into solid solution. Cooling must be sufficiently rapid to hold constituents into solution. stress-relief anneal. A heat treatment performed to reduce residual stresses. See 10.2. superaustenitic stainless steel. A series of solution strengthened austenitic stainless steels typically containing high alloying levels of chromium, nickel, nitrogen, and molybdenum. These alloying additions provide superior resistance to pitting corrosion and stress corrosion cracking relative to standard austenitic stainless steel grades. Waveform controlled power sources. Terminology used to describe GMAW welding equipment that has the capability to simultaneously adjust various electrical parameters such as voltage, wave shape, or pulsing frequency when the operator adjusts wire feed speed. weld metal solidification cracking. A form of intergranular cracking occurring as the cooling weld metal transitions from liquid to solid in the simultaneous presence of low melting points compounds and shrinkage stresses. This form typically appears as either centerline or crater cracks. whiskers. Short pieces of unmelted GMAW electrode attached to the material being welded. Whiskers are occasionally found on the interior surface of pipe welds when the GMAW electrode es through the root opening then shorts out and welds itself to the weld t root face. worm tracks. A linear depression in the surface of a weld as a result of insufficient outgassing of the weld puddle.

4. General Information 4.1 History. Austenitic stainless steels were first researched by Leon Guillet in in 1904. In 1906, Guillet published a detailed study of the iron-nickel-chromium alloys; this study established the basic metallurgical characteristics of austenitic steels. Between 1908 and 1912, E. Maurer of the research department at ’s F. Krupp steel plant developed the first commercial austenitic stainless steel. From the late 1920s, different forms of austenitic stainless steels were produced. The most notable is the use of Type 302 on the roof of the Chrysler Building in New York. Until 1968, stainless steels were produced by melting the charge in an electric furnace and refining it by certain slag practices. Carbon contents were lowered by blowing the melt with oxygen; however, they were limited to about 0.05%. To produce very low levels of carbon (under 0.03% is ideal for welding), special charges were required and the resultant alloys were designated with the letter “L.” After 1968, the use of argon-oxygen decarburization refining practices began in conjunction with the electric melt furnace, producing very low levels of carbon as a matter of course. Many of today’s alloys may be dual certified to both standard and low-carbon compositions and mechanical properties. 4.1.1 Alloy Description. Austenitic stainless steels are iron-based alloys with primary alloying elements of chromium and nickel (see Table 4.1). Chromium contributes to the well-known corrosion resistance of the alloys, while nickel is one of the primary elements that contribute to its austenitic microstructure. Alloying variations of common alloys are shown in Figure 4.1.

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Table 4.1 The Chemical Composition Limits of Common Wrought Austenitic Stainless Steel Base Materials Base Metal Type

UNS Numbera

C

Cr

Ni

Mo

Mn

Si

N

Other

201

S20100

0.15

16.0–18.0

3.5–5.5

—

5.5–7.5

1.0

0.25

—

202

S20200

0.15

17.0–19.0

4.0–6.0

—

7.5–10.0

1.0

0.25

—

205

S20500

0.12–0.25

16.0–18.0

1.0–1.75

—

14.0–15.5

1.0

0.32–0.40

—

1.0

0.20–0.40

Nb 0.10–0.30, V 0.10–0.30

209

S20910

0.06

20.5–23.5

11.5–13.5

1.5–3.0

4.0–6.0

216

S21600

0.08

17.5–22.0

5.0–7.0

2.0–3.0

7.5–9.0

1.0

0.25–0.50

—

218

S21800

0.10

16.0–18.0

8.0–9.0

—

7.0–9.0

3.5–4.5

0.08–0.18

—

219

S21904

0.04

19.0–21.5

5.5–7.5

—

8.0–10.0

1.0

0.15–0.40

—

240

S24000

0.08

17.0–19.0

2.5–3.75

—

11.5–14.5

1.0

0.20–0.40

—

241

S24100

0.15

16.5–19.5

0.5–2.5

—

11.0–14.0

1.0

0.20–0.45

—

301

S30100

0.15

16.0–18.0

6.0–8.0

—

2.0

1.0

—

—

302

S30200

0.15

17.0–19.0

8.0–10.0

—

2.0

1.0

—

—

302B

S30215

0.15

17.0–19.0

8.0–10.0

—

2.0

2.0–3.0

—

—

303

S30300

0.15

17.0–19.0

8.0–10.0

—

2.0

1.0

—

S 0.15 min.

304

S30400

0.08

18.0–20.0

8.0–10.5

—

2.0

1.0

—

—

304L

S30403

0.03

18.0–20.0

8.0–12.0

—

2.0

1.0

—

—

304LN

S30453

0.03

18.0–20.0

8.0–12.0

—

2.0

1.0

0.10–0.16

—

304H

S30409

0.04–0.10

18.0–20.0

8.0–11.0

—

2.0

1.0

—

—

304HN

S30452

0.08

18.0–20.0

8.0–10.5

—

2.0

1.0

0.10–0.16

—

305

S30500

0.12

17.0–19.0

10.0–13.0

—

2.0

1.0

—

—

309

S30900

0.20

22.0–24.0

12.0–15.0

—

2.0

1.0

—

—

309Cb

S30940

0.08

22.0–24.0

12.0–15.0

—

2.0

1.0

—

Nb 10 × C min. –1.0

309H

S30909

0.04–0.10

22.0–24.0

12.0–16.0

—

2.0

0.75

—

—

309S

S30908

0.08

22.0–24.0

12.0–15.0

—

2.0

1.0

—

—

310

S31000

0.25

24.0–26.0

19.0–22.0

—

2.0

1.5

—

—

310H

S31009

0.04–0.10

24.0–26.0

19.0–22.0

—

2.0

0.75

—

—

310S

S31008

0.08

24.0–26.0

19.0–22.0

—

2.0

1.5

—

—

310MoLN

S31050

0.03

24.0–26.0

20.5–23.5

1.6–3.0

2.0

0.4

0.09–0.16

—

314

S31400

0.25

23.0–26.0

19.0–22.0

—

2.0

1.5–3.0

—

—

316

S31600

0.08

16.0–18.0

10.0–14.0

2.0–3.0

2.0

1.0

—

—

316H

S31609

0.04–0.10

16.0–18.0

10.0–14.0

2.0–3.0

2.0

1.0

—

—

316L

S31603

0.03

16.0–18.0

10.0–14.0

2.0–3.0

2.0

1.0

—

—

316LN

S31653

0.03

16.0–18.0

10.0–14.0

2.0–3.0

2.0

1.0

0.10–0.16

—

316N

S31651

0.08

16.0–18.0

10.0–14.0

2.0–3.0

2.0

1.0

0.10–0.16

—

316Ti

S31635

0.08

16.0–18.0

10.0–14.0

2.0–3.0

2.0

1.0

0.10

Ti 5 × (C+N) min. –0.7

317

S31700

0.08

18.0–20.0

11.0–15.0

3.0–4.0

2.0

1.0

—

—

317L

S31703

0.03

18.0–20.0

11.0–15.0

3.0–4.0

2.0

1.0

—

—

317LM

S31725

0.03

18.0–20.0

13.0–17.0

4.0–5.0

2.0

0.75

0.10

—

317LMN

S31726

0.03

17.0–20.0

13.5–17.5

4.0–5.0

2.0

0.75

0.10–0.20

Cu 0.75

(Continued)

5

AWS G2.3M/G2.3:2019

Table 4.1 (Continued) The Chemical Composition Limits of Common Wrought Austenitic Stainless Steel Base Materials Base Metal Type

UNS Numbera

C

Cr

Ni

Mo

Mn

317LN

S31753

0.03

18.0–20.0

11.0–15.0

3.0–4.0

321

S32100

0.08

17.0–19.0

9.0–12.0

—

321H

S32109

0.04–0.10

17.0–20.0

9.0–12.0

Si

N

Other

2.0

1.0

0.10–0.22

—

2.0

1.0

—

Ti 5 × C min.

—

2.0

1.0

—

Ti 4 × C min. –0.60

347

S34700

0.08

17.0–19.0

9.0–13.0

—

2.0

1.0

—

Nb 10 × C min.

347H

S34709

0.04–0.10

17.0–20.0

9.0–13.0

—

2.0

1.0

—

Nb 8 × C min. –1.0

348

S34800

0.08

17.0–19.0

9.0–13.0

—

2.0

1.0

—

Nb 10 × C min. Ta 0.10 Co 0.20

348H

S34809

0.04–0.10

17.0–20.0

9.0–13.0

—

2.0

1.0

—

Nb 8 × C min. –1.0 Ta 0.10 Co 0.20

N08028

0.03

26.0–28.0

30.0–34.0

3.0–4.0

2.5

1.0

—

—

N08925

0.02

19.0–21.0

24.0–26.0

6.0–7.0

1.0

0.5

0.10–0.20

—

20Cb3

N08020

0.07

19.0–21.0

32.0–38.0

2.0–3.0

2.0

1.0

—

Cu 3.0–4.0 Nb 8 × C min. –1.0

20Mo-4®, c

N08024

0.03

22.5–25.0

35.0–40.0

3.5–5.0

1.0

0.5

—

Cu 0.5–1.5 Nb 0.15–0.35

20Mo-6®, c

N08026

0.03

22.0–26.0

33.0–37.2

5.0–6.7

1.0

0.5

0.10–0.16

Cu 2.0–4.0

25-6MO®, d

N08926

0.02

19.0–21.0

24.0–26.0

6.0–7.0

2.0

0.5

0.15–0.25

Cu 0.5–1.5

27-7MO®, d

S31277

0.02

20.5–23.0

26.0–28.0

6.5–8.0

3.0

0.5

0.30–0.40

Cu 0.5–1.5

MA®, e

28 1925 (926)

253

hMo®, b

S30815

0.10

20.0–22.0

10.0–12.0

—

0.8

1.4–2.0

0.14–0.20

Ce 0.03–0.08

254 SMO®, f

S31254

0.02

19.5–20.5

17.5–18.5

6.0–6.5

1.0

0.8

0.18–0.22

Cu 0.5–1.0

SMO®, f

S32654

0.02

24.0–25.0

21.0–23.0

7.0–8.0

2.0–4.0

0.5

0.45–0.55

Cu 0.30–0.60

31

N08031

0.015

26.0–28.0

30.0–32.0

6.0–7.0

2.0

0.3

0.15–0.25

Cu 1.0–1.4

RA-330®, e

N08330

0.08

17.0–20.0

34.0–37.0

—

2.0

0.75–1.5

—

Cu 1.0 Pb 0.005 Sn 0.025

AL-6XN®, g

N08367

0.03

20.0–22.0

23.5–25.5

6.0–7.0

2.0

1.0

0.18–0.25

—

800

N08800

0.10

19.0–23.0

30.0–35.0

—

1.5

1.0

—

Al 0.15–0.60 Ti 0.15–0.60

825

N08825

0.05

19.5–23.5

38.0–46.0

2.5–3.5

1.0

0.5

—

Al 0.2 Ti 0.60–1.2

904L

N08904

0.02

19.0–23.0

23.0–28.0

4.0–5.0

2.0

1.0

—

Cu 1.0–2.0

654

a

SAE HS-1086, Metals & Alloys in the Unified Numbering System. 1925 hMO is a ed trademark of ThyssenKrupp VDM GmbH. c 20Mo-4 and 20Mo-6 are ed trademarks of Carpenter Technology Corporation. d 25-6MO and 27-7MO are ed trademarks of Special Metals. e RA-330, 253 MA are ed trademarks of Rolled Alloys, Inc. f 254 SMO and 654 SMO are ed trademarks of Outokumpu. g AL-6XN® is a ed trademark of Alleghany Ludlum Corporation. b

Notes: 1. Composition limits are shown in wt %. Specific product material standards should be referred to for the exact composition limits. A single value denotes a maximum limit except where “min.” (minimum) is indicated. Composition maximum limits for the impurities phosphorous and sulfur are not listed in this table. 2. Columbium (Cb) = Niobium (Nb).

6

AWS G2.3M/G2.3:2019

Source: Reprinted, with permission, from the Specialty Steel Industry of North America, “Design Guidelines for the Selection and Use of Stainless Steel,” Austenitic Figure, page 3.

Figure 4.1—Alloying Variations of Common Austenitic Stainless Steels

Steel alloys are termed “stainless” when the chromium content exceeds 10.5% to 12%. The presence of at least 10.5% chromium provides for the development of a “ive” chromium-enriched film on the surface that resists oxidation and corrosion. This film is just a few angstroms thick and will spontaneously regenerate, if disrupted, as long as oxygen is present. The austenitic alloys derive their name because of their predominantly “austenitic” microstructure. The term “stainless” was adopted because the alloy could not be etched using the common etchants that were used for carbon steels. In early years, etching was termed “staining”; hence, the new alloys were then termed “austenitic stainless steels.”

7

AWS G2.3M/G2.3:2019

The different alloys in the solid solution austenitic family have different compositions and properties, but many common characteristics. They can be hardened by cold working, but not by heat treatment. In the annealed condition, wrought base materials are essentially nonmagnetic, although some might exhibit a slight magnetic attraction because of variations in chemical composition or the extent of cold working after annealing. Cast alloys, depending on the alloy type and the specific composition of the casting, can range from nonmagnetic to strongly magnetic, depending on the casting’s ferrite content. Weld metals can also exhibit varying levels of magnetic attraction depending on weld metal ferrite content. The austenitics are readily formed, fabricated, and welded. They generally have a good combination of corrosion resistance, toughness even at cryogenic temperatures, and strength. Some stainless alloys such as Types 304H, 316H, 321, and 347 are used often in high-temperature applications because of their improved creep strength. Wrought alloys were identified in the old American Iron and Steel Institute (AISI) system as Type 300 series. Today the Unified Numbering System for Metals and Alloys (UNS) is widely used, and stainless steel is identified by a letter followed by a five-digit number (e.g., Type 304 is S30400). Alloys containing over 2% manganese as a minimum requirement, along with deliberate nitrogen addition, are often identified as 200 series alloys. Type 304 (UNS S30400), sometimes referred to as 18-8 stainless, is the most widely used alloy of the austenitic group. It has a nominal composition of 18% chromium and 8% nickel. Type 304 has excellent corrosion resistance in general aqueous or atmospheric service environments and has good mechanical properties. Molybdenum is added to various alloys, including Types 316 and 317, for improved pitting and crevice corrosion resistance compared to Type 304. Type 317 has improved resistance in increasing chloride environments. Table 4.1 lists the chemical composition limits of some commonly used wrought austenitic grades. Cast alloy designations were originally established by the Alloy Casting Institute and have since been adopted by ASTM International. Alloy designations beginning with the letter C are most commonly used for their corrosion-resistant characteristics in aqueous environments and in vapors below 650°C [1200°F]. Alloy designations beginning with the letter H are most commonly used above 650°C [1200°F]. The higher carbon content of the H-alloys makes them stronger at elevated temperatures than the corrosion resistant types. Table 4.2 lists the chemical composition limits of some commonly used cast austenitic grades. 4.2 Properties. Since different grades of austenitic stainless steels have different allowable chemical compositions, the austenitic stainless steels can exhibit a wide range of mechanical properties. At room temperature in the annealed condition, the wrought austenitic stainless steels typically exhibit Charpy V-notch energy absorption values well in excess of 135 J [100 ft·lbf]. These alloys also exhibit good ductility and toughness even at high strengths and at cryogenic temperatures. The mechanical properties of some common wrought, annealed austenitic stainless steels are listed in Table 4.3. The mechanical properties of some common annealed, cast austenitic stainless steels are listed in Table 4.4. At room temperature, they exhibit yield strengths between 210 MPa to 1380 MPa [30 ksi to 200 ksi], depending on composition and amount of cold work. Note: The heat of welding anneals and removes the strengthening effect of any cold working in the heat-affected zone (HAZ) with the result that strength will be reduced in the HAZ. When cold worked materials have been selected because of their elevated tensile strength properties, welding should be avoided, or, the reduced strength of the HAZ and the strength of the weld deposit (compared to the base material) should be considered in the welded design. 4.3 Product Forms. Wrought austenitic stainless steels are produced under a wide variety of industry standards including the American Iron and Steel Institute (AISI), Aerospace Materials Specifications (AMS), the American Society of Mechanical Engineers (ASME), American Society for Testing and Materials (ASTM), Military Standards (MIL), and SAE International standards. International standards include AS (Australia), CSA (Canada), GB (China), EN (Europe), AFNOR (), DIN EN (), MSZ (Hungary), IS (India), ISO (International), UNI (Italy), JIS (Japan), PNH (Poland), STAS (Romania), GOST (Russia), UNE (Spain), SIS (Sweden), BS (UK), as well as others. Various references for finding information on materials produced according to international standards can be found in Annex B. 4.4 Specifications. For a list of common ASTM standards applicable to wrought and cast austenitic stainless steels, refer to Annex C.

8

Table 4.2 The Chemical Composition Limits of Common Cast Austenitic Stainless Steel Base Materials

Gradea CE20N

CF3 CF3A

Typical ASTM UNS Microstructure Designation & Otherc Referenced Numberb J92802

J92500

Reference Wrought Grade

C

Cr

Ni

Mo

Mn

Si

Other

—

A351 A451

—

0.20

23.0–26.0

8.0–11.0

0.50

1.50

1.50

N: 0.08–0.20

4

A351 A451 A743 A744

304L

0.03

17.0–21.0

8.0–12.0

0.50

1.50

2.00

—

316L

0.03

17.0–21.0

9.0–13.0

2.0–3.0

1.50

1.50

—

J92800

4

A351 A451 A743 A744

CF8 CF8A

J92600

4

A351 A451 A743 A744

304

0.08

18.0–21.0

8.0–11.0

0.50

1.50

2.00

—

4

A351 A451 A743 A744

347

0.08

18.0–21.0

9.0–12.0

0.50

1.50

2.00

Nb: 8 × C min. –1.0

316

0.08

18.0–21.0

9.0–12.0

2.0–3.0

1.50

1.50

—

9

CF3M CF3MA

CF8C

J92710

J92900

4

CF10

J92590

4

A351

304H

0.04–0.10

18.0–21.0

8.0–11.0

0.50

1.50

2.00

—

CF10M

J92901

4

A351

316H

0.04–0.10

18.0–21.0

9.0–12.0

2.0–3.0

1.50

1.50

—

CF10MC

J92971

A351

—

0.10

15.0–18.0

13.0–16.0

1.75–2.25

1.50

1.50

Nb: 10 × C min. –1.20

CF20

J92602

4

A743

302

0.20

18.0–21.0

8.0–11.0

—

1.50

2.00

—

CF10SMnN

J92972

4

A351 A743

Nitronic 60

0.10

16.0–18.0

8.0–9.0

—

7.0–9.0

3.5–4.5

N: 0.08–0.18

CG6MMN

J93790

A351 A743

Nitronic 50

0.06

20.5–23.5

11.5–13.5

1.5–3.0

4.0–6.0

1.0

N: 0.20–0.40 Nb: 0.10–0.30 V: 0.10–0.30

(Continued)

AWS G2.3M/G2.3:2019

CF8M

A351 A451 A743 A744

Gradea

Typical ASTM UNS Microstructure Designation Numberb & Otherc Referenced

Reference Wrought Grade

C

Cr

Ni

Mo

Mn

Si

Other

10

CG8M

J93000

4

A351 A743 A744

317

0.08

18.0–21.0

9.0–13.0

3.0–4.0

1.5

1.5

—

CG12

J93001

—

A743

309

0.12

20.0–23.0

10.0–13.0

—

1.50

2.00

—

CH8

J93400

—

A351 A451

—

0.08

22.0–26.0

12.0–15.0

0.50

1.50

1.50

—

CH10

J93401

8

A351 A451 A743

309

0.04–0.10

22.0–26.0

12.0–15.0

0.50

1.50

2.00

—

CH20

J93402

8

A351 A451 A743

309

0.04–0.20

22.0–26.0

12.0–15.0

0.50

1.50

2.00

—

CK20

J94202

5

A351 A451 A743

310

0.04–0.20

23.0–27.0

19.0–22.0

0.50

1.50

1.75

—

CK3MCuN

J93254

6

A351 A743 A744

254 SMO

0.025

19.5–20.5

17.5–19.5

6.0–7.0

1.20

1.00

N: 0.18–0.24 Cu: 0.50–1.0

CN3M

J94652

6

A351 A743

—

0.03

20.0–22.0

23.0–27.0

4.5–5.5

2.00

1.00

—

CN3MN

J94651

6

A743 A744

AL6XN®, e

0.03

20.0–22.0

23.5–25.5

6.0–7.0

2.00

1.00

N: 0.18–0.26 Cu: 0.75

CN3MCu

J80020

A744 A990

20Cb-3

0.03

19.0–22.00

27.5–30.5

2.0–3.0

1.50

1.00

Cu: 3.0–3.5

CN7M

N08007

6

A351 A743 A744

20Cb-3

0.07

19.0–22.0

27.5–30.5

2.0–3.0

1.5

1.5

Cu: 3.0–4.0

CT15C

N08151

7

A351

—

0.05–0.15

19.0–21.0

31.0–34.0

—

0.15–1.50

0.50–1.50

Nb 0.50–1.50

CU5MCuC

N08826

6

A494

Inconel 825

0.05

19.5–23.5

38.0–44.0

2.5–3.5

1.0

1.0

Cu: 1.50–3.50 Nb 0.10–0.30

HE

J93403

4, 3

A297

312/CE30

0.20–0.50

26.0–30.0

8.0–11.0

0.50

2.00

2.00

—

(Continued)

AWS G2.3M/G2.3:2019

Table 4.2 (Continued) The Chemical Composition Limits of Common Cast Austenitic Stainless Steel Base Materials

Table 4.2 (Continued) The Chemical Composition Limits of Common Cast Austenitic Stainless Steel Base Materials

Gradea

Typical ASTM UNS Microstructure Designation Numberb & Otherc Referenced

Reference Wrought Grade

C

Cr

Ni

Mo

Mn

Si

Other

11

HF

J92603

7, 3

A297

302

0.20–0.40

18.0–23

8.0–12.0

0.50

2.00

2.00

—

HH

J93503

7, 8, 3

A297

309/CH20

0.20–0.50

24.0–28.0

11.0–14.0

0.50

2.00

2.00

—

HK

J94224

7

A297

310/CK20

0.20–0.60

24.0–28.0

18.0–22.0

0.50

2.00

2.00

—

HK30

J94203

7

A351 A608

—

0.25–0.35

23.0–27.0

19.0–22.0

0.50

1.50

1.75

—

HK40

J94204

7

A351 A608

—

0.35–0.45

23.0–27.0

19.0–22.0

0.50

1.50

1.75

—

HL

J94604

7, 3

A297

—

0.20–0.60

28.0–32.0

18.0–22.0

0.50

2.00

2.00

—

HN

J94213

6, 3

A297

—

0.20–0.50

19.0–23.0

23.0–27.0

0.50

2.00

2.00

—

HP

J95705

6

A297

—

0.35–0.75

24–28

33–37

0.50

2.00

2.50

—

HT

J94605

6, 3

A297

330 (15–35)

0.35–0.75

15.0–19.0

33.0–37.0

0.50

2.00

2.50

—

HU

J95405

6

A297

(19–39)

0.35–0.75

17.0–21.0

37.0–41.0

0.50

2.00

2.50

—

a

For brevity, grades listed under ASTM A451 do not show the “P” after the “C.” For example, ASTM A451 grade F3 is listed in this table simply as CF3. SAE HS-1086, Metals & Alloys in the Unified Numbering System. c Ferrite content of stainless steel cast alloys can be estimated using the Schoefer diagram (see Annex D). d ASTM A297/A297M, Standard Specification for Steel Castings, Iron-Chromium and Iron-Chromium-Nickel, Heat Resistant for General Application. ASTM A351/A351M, Standard Specification for Castings, Austenitic, for Pressure-Containing Parts. ASTM A451/A451M, Standard Specification for Centrifugally Cast Austenitic Steel Pipe for High-Temperature Service. ASTM A608/A608M, Standard Specification for Centrifugally Cast Iron-Chromium-Nickel High-Alloy Tubing for Pressure Application at High Temperatures. ASTM A743/A743M, Standard Specification for Castings, Iron-Chromium, Iron-Chromium-Nickel, Corrosion Resistant for General Application. ASTM A744/A744M, Standard Specification for Castings, Iron-Chromium-Nickel, Corrosion Resistant for Severe Service. e AL-6XN® is a ed trademark of Alleghany Ludlum Corporation. b

AWS G2.3M/G2.3:2019

Notes: 1. Composition limits were excerpted from the referenced ASTM Specifications. Limits are shown in wt %. Specific product material standards should be referred to for the exact composition limits. A single value denotes a maximum limit except where “min.” (minimum) is indicated. Composition limits for P and S are not listed in this table. P and S limits typically do not exceed 0.040 wt % with some exceptions. 2. Niobium (Nb) = Columbium (Cb). 3. Similar alloys are listed in ASTM A608: HE35, HF30, HH33, HL30, HL40, HN40, and HT50. 4. Depending on the chemical composition of the casting, the structure may range from fully austenitic-to-austenite with up to 40% ferrite. Most commonly the grades contain from 5% to 40% ferrite. 5. Predominately austenitic microstructure (with minor amounts of ferrite). 6. Completely austenitic. 7. Carbides in an austenitic matrix. 8. Carbides in an austenitic matrix with minor amounts of ferrite. 9. Ferrite content of stainless steel cast alloys can be estimated using the Schoefer diagram (see Annex D). 10. HN, HT, and HU alloys do not form sigma phase under any conditions. A ratio of 2 silicon to 1 part carbon in matching type filler metal provides the best weld properties for these grades.

AWS G2.3M/G2.3:2019

Table 4.3 Mechanical Properties of Wrought Annealed Stainless Steel Alloys Tensile Strength, min.

Yield Strength, min.

UNS No.

MPa

ksi

MPa

ksi

Elongation in 50 mm [2 in] Min. %

201-1

S20100

515

75

260

38

201-2

S20100

655

95

310

202

S20200

620

90

209

S20910

725

216

S21600

218

Type

Hardness, Maximum Brinell

Rockwell B

40

217

95

45

40

241

100

260

38

40

241

—

105

415

60

30

241

100

690

100

415

60

40

241

100

S21800

655

95

345

50

35

241

100

219 (XM-11) sheet

S21904

690

100

415

60

40

—

—

240

S24000

690

100

415

60

40

241

100

301

S30100

515

75

205

30

40

217

95

302

S30200

515

75

205

30

40

201

92

304

S30400

515

75

205

30

40

201

92

304L

S30403

485

70

170

25

40

201

92

304LN

S30453

515

75

205

30

40

217

95

304H

S30409

515

75

205

30

40

201

92

304N

S30451

550

80

240

35

30

217

95

304HN

S30452

620

90

345

50

30

241

100

305

S30500

485

70

170

25

40

183

88

309H

S30909

515

75

205

30

40

217

95

309S

S30908

515

75

205

30

40

217

95

310Cb

S31040

515

75

205

30

40

217

95

310H

S31009

515

75

205

30

40

217

95

310HCb

S31041

515

75

205

30

40

217

95

310S

S31008

515

75

205

30

40

217

95

310MoLN sheet

S31050

580

84

270

39

25

217

95

254SMo

S31254

690

100

310

45

35

223

96

316

S31600

515

75

205

30

40

217

95

316H

S31609

515

75

205

30

40

217

95

316L

S31603

485

70

170

25

40

217

95

316LN

S31653

515

75

205

30

40

217

95

316N

S31651

550

80

240

35

35

217

95

(Continued)

12

AWS G2.3M/G2.3:2019

Table 4.3 (Continued) Mechanical Properties of Wrought Annealed Stainless Steel Alloys Tensile Strength, min. UNS No.

MPa

ksi

MPa

ksi

Elongation in 50 mm [2 in] Min. %

316Ti

S31635

515

75

205

30

317

S31700

515

75

205

317L

S31703

515

75

317LM

S31725

515

317LMN

S31726

317LN

Type

a

Yield Strength, min.

Hardness, Maximum Brinell

Rockwell B

40

217

95

30

35

217

95

205

30

40

217

95

75

205

30

40

217

95

550

80

240

35

40

223

96

S31753

550

80

240

35

40

217

95

321

S32100

515

75

205

30

40

217

95

321H

S32109

515

75

205

30

40

217

95

347

S34700

515

75

205

30

40

201

92

347H

S34709

515

75

205

30

40

201

92

348

S34800

515

75

205

30

40

201

92

348H

S34809

515

75

205

30

40

201

92

28

N08028

500

73

214

31

40

—

70–90

1925 hMo

N08925

600

87

295

43

40

—

—

20Cb3

N08020

550

80

240

35

30

217

95

20Mo-4

N08024

550

80

240

35

30

—

—

20Mo-6

N08026

550

80

240

35

30

—

—

25-6MO

N08926

650

94

295

43

35

—

—

27-7MO

S31277

770

112

360

52

40

—

—

253 MA

S30815

600

87

310

45

40

217

95

254 SMO

S31254

690

100

310

45

35

223

96

654 SMO

S32654

750

109

430

62

40

250

—

31

N08031

650

94

276

40

40

—

—

RA 330

N08330

483

70

207

30

—

—

70–90

AL-6XN®a

N08367

690

100

310

45

30

—

100

800

N08800

520

75

205

30

30

—

—

825

N08825

586

85

241

35

30

—

—

904L

N08904

490

71

220

31

35

—

90

18-18-2

S38100

515

75

205

30

40

217

95

AL-6XN®

is a ed trademark of Alleghany Ludlum Corporation.

Source: Extracted from various applicable ASTM specifications for sheet and plate product forms in the solution annealed condition. Minimum specified mechanical properties may vary slightly—depending on the product specification.

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AWS G2.3M/G2.3:2019

Table 4.4 Minimum Mechanical Properties of Common Cast Austenitic Stainless Steel Base Materialsa UTS, min. UNS Numberb

MPa

ksi

MPa

ksi

% Elong. min. in 50 mm [2 in]

CF3

J92802 J92500

485 485

70 70

195 205

28 30

35 35

CF3A

J92500

530

77

240

35

35

CF3M

J92800

485

70

205

30

30

CF3MA

J92800

559

80

255

37

30

CF8

J92600

485

70

205

30

35

CF8A

J92600

530

77

240

35

35

CF8C

J92710

485

70

205

30

30

CF8M

J92900

485

70

205

30

30

CF10

J92590

485

70

205

30

35

CF10M

J92901

485

70

205

30

30

CF10MC

J92971

485

70

205

30

20

CF20

J92602

485

70

205

30

30

CF10SMnN

J92972

585

85

290

42

30

CG6MMN

J93790

585

85

290

42

30

CG8M

J93000

520

75

240

35

25

CG12

J93001

485

70

195

28

35

CH8

J93400

450

65

195

28

30

CH10

J93401

485

70

205

30

30

CH20

J93402

485

70

205

30

30

CK20

J94202

450

65

195

28

30

CK3MCuN

J93254

550

80

260

38

35

CN3M

J94652

435

63

170

25

30

CN3MN

J94651

550

80

260

38

35

CN7M

N08007

425

62

170

25

35

CT15C

N08151

435

63

170

25

20

CU5MCuC

N08826

520

75

240

35

20

HE

J93403

585

85

275

40

9

HF

J92603

485

70

240

35

25

HH

J93503

515

75

240

35

10

HK

J94224

450

65

240

35

10

HK30

J94203

450

65

240

35

10

HK40

J94204

425

62

240

35

10

HL

J94604

450

65

240

35

10

HN

J94213

435

63

—

—

8

HP

J95705

430

62.5

235

34

4.5

HT

J94605

450

65

—

—

4

HU

J95405

450

65

—

—

4

Grade CE20N

a b

YS, min.

Source: Mechanical properties were adapted from ASTM specifications listed in Table 4.2 for the annealed condition. SAE HS-1086, Metals & Alloys in the Unified Numbering System.

Note: Grades produced under some ASTM standards require tensile testing only when specified in a purchase order.

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AWS G2.3M/G2.3:2019

5. Metallurgy 5.1 Ferrite Discussion 5.1.1 Austenite- and Ferrite-Forming Elements. Many of the nominally austenitic stainless steel base metals and weld metals solidify with some ferrite in their microstructure. This ferrite, which will usually transform to austenite during hot working and extensive heat treatment, is beneficial during solidification by imparting resistance to solidification cracking. In the base metal, this ferrite can reappear in the HAZ and in an autogenous weld fusion zone when the base metal is fused during welding. Elements that promote the formation of ferrite include chromium (Cr), molybdenum (Mo), silicon (Si), niobium (Nb), titanium (Ti), aluminum (Al), vanadium (V), and tungsten (W). Elements that promote the formation of austenite include nickel (Ni), carbon (C), nitrogen (N), manganese (Mn), and copper (Cu). Base materials and filler metals are produced to provide the desired chemical composition, microstructure, properties, and corrosion resistance. Changing the quantity and ratio of one or more specific elements in austenitic alloys can significantly alter the alloy’s microstructure and properties. Base and filler metal producers can alter the proportions of austenite and ferrite by altering the amounts and the ratio of ferrite-forming elements to austenite-forming elements. Cast “austenitic” alloys, depending on the alloy type and the specific composition of the casting, can range from fully austenitic to containing up to 40% ferrite. Table 4.2 provides information on the typical microstructures found in cast alloys. The presence of ferrite in castings generally increases strength, decreases toughness, and improves the material’s weldability. Depending on the service environment, the presence of ferrite can either improve or decrease the alloy’s relative corrosion resistance characteristics. The estimation of the ferrite content of cast base materials using the Schoefer diagram is discussed in Annex D. 5.1.2 Constitution (Ferrite) Diagrams. The amount of weld metal ferrite can be estimated by using the actual filler metal chemical composition and a constitution diagram (i.e., a ferrite diagram). Ferrite diagrams can also be used to predict whether a wrought base material has the potential to contain ferrite, even though in wrought products, ferrite can be eliminated by hot-working (rolling and forging) and also by heat treatment. A ferrite diagram plots the austenite-promoting elements (called Ni-equivalents) and the ferrite-promoting elements (called Cr-equivalents); both equivalents are computed from the composition of the material. Each specific ferrite-forming or austenite-forming element has its own relative “potency” that contributes to the formation of ferrite or austenite. For example, both carbon and nitrogen are “strong” austenite promoters. Very small changes in the amounts of carbon and nitrogen can result in significant changes to the proportions of austenite and ferrite. Nickel is the principal element added to the austenitic alloys that ensures the alloy will be primarily austenitic, but nickel does not have the same “potency” as carbon or nitrogen. For example, changes as small as 0.05 wt % of nitrogen or carbon content have as great of an effect as a 1% change in nickel in determining the final austenite and ferrite content of the base material or weld metal. To use any of the ferrite/constitution diagrams, the actual chemical composition of the alloy heat analysis is used to determine both the chromium-equivalent (Creq) number and the nickel-equivalent (Nieq) number. The Creq number is calculated using a simple mathematical formula with the actual wt % of all ferrite-promoting elements. Since chromium is the principal ferrite-promoting element added to austenitic alloys, the formula used to determine the total effect of the ferrite-promoting elements is termed as a “chromium-equivalent.” Similarly, all austenite-promoting elements are used to calculate the “nickel-equivalent.” The Nieq is plotted on the vertical axis of the diagram, and the Creq is plotted on the horizontal axis. The FN may be estimated by drawing a horizontal line across the diagram from the Nieq and a vertical line from the Creq. The FN is indicated by the diagonal line that es through the intersection of the horizontal and vertical lines. Of the numerous ferrite diagrams that have been developed, the Schaeffler diagram, developed in the 1940s, is still widely used. The Schaeffler diagram (Figure 5.1) is reasonably accurate for conventional 300 series stainless steel weld deposits using the SMAW process but is less accurate when less conventional compositions are used and when a high level of nitrogen (a powerful austenite former) is present. The diagram predicts ferrite as a percentage (e.g., % ferrite).

15

AWS G2.3M/G2.3:2019

Note: The boxes illustrate where the composition of some filler metals lie but are not part of the original Schaeffler diagram. Source: Reproduced from AWS The Professional's Advisor on Welding of Stainless Steels, 1999, Figure 8-7, Miami: American Welding Society.

Figure 5.1—The Schaeffler Diagram

The ferrite diagrams developed since the Schaeffler diagram use Ferrite Number (FN) values instead of % ferrite. Originally, the ferrite content of weld metal was expressed as a percentage which presented a problem in reproducibility among testing sources. This problem was reduced by using the FN system which relied on a set of magnetic standards that could be used as universally accepted values. The FN values below 10 are believed to be very close to the % ferrite values previously used, but they are not necessarily the true absolute ferrite percentage of the weld. FNs above 10 exceed the true volume percent of ferrite in the weld, but the FNs established for the higher ferrite content welds have been developed by extensive magnetic testing and comparisons and have been universally accepted as standard values. The DeLong Diagram, Figure 5.2, was developed in the 1970s. It includes the effects of nitrogen, provides estimates for nitrogen when actual values are unknown. It also provides better correlation with GTAW and GMAW weld deposits than the Schaeffler Diagram because it includes nitrogen analysis to predict ferrite. It uses FN instead of % ferrite. This diagram allows the use of typical nitrogen levels to be used if the actual nitrogen content is unknown, albeit with the risk that the estimated nitrogen content may not closely reflect the actual content. In the late 1980s, the Welding Research Council (WRC) funded the development of an improved ferrite diagram termed the WRC-1988 Diagram (not shown). It covers a broader range of compositions than the DeLong Diagram and is considered to be more accurate for predicting ferrite content of the 300 series stainless steel weld metals. The WRC-1988 Diagram was revised and improved several years later, and the WRC-1992 Diagram took its place (see Figure 5.3).

16

AWS G2.3M/G2.3:2019

Note: Calculate the nickel and chromium equivalents from the weld metal analysis. If nitrogen analysis of the weld metal is not available, assume 0.06% for GTA and covered electrode, or 0.08% for GMA weld metals. If the chemistry is accurate, the diagram predicts the WRC Ferrite Number within ±3 in approximately 90% of the tests for the 308, 309, 316, and 317 families. Source: Reproduced from AWS The Professional’s Advisor on Welding of Stainless Steels, 1999, Figure 8-6, Miami: American Welding Society.

Figure 5.2—The DeLong Diagram

The WRC Diagram uses an FN scale instead of defining ferrite as a volume percent as in the Schaeffler Diagram. Using volume percent to characterize ferrite turned out to be relatively nonreproducible, while defining ferrite content based on the FN scale is much more reproducible.1 The FN scale is defined by a set of National Institute of Standards and Technology (NIST, formerly the National Bureau of Standards) coating thickness standards. Each standard specimen in a set has a unique thickness of nonmagnetic plating over a magnetic substrate. Each specimen is assigned an FN value, and a series of these standards is used to develop a calibration procedure. The basic test instrument used for the WRC FN system is a Magne-Gage®.2, 3, 4 Other instruments can also be calibrated according to this system using secondary standards also available from NIST. The calibration procedure is completely defined in AWS A4.2M:2006 (ISO 8249:2000 MOD), Standard Procedures for Calibrating Magnetic Instruments to Measure the Delta Ferrite Content of Austenitic and Duplex Ferritic-Austenitic Stainless Steel Weld Metal. A further refinement of the WRC-1992 Diagram incorporating the effects of 1%, 4%, and 10% manganese on martensite formation has also been published.5 1 Kotecki,

D., 2000, Stainless Q & A, Welding Journal 79(12): 64–65. is a ed trademark of Magne-Gage Sales & Service Co., Inc. 3 McKay Welding Technical Bulletin SS-300-F, Welding Stainless Steels. 4 Kotecki, D., 1997, Ferrite Determination in Stainless Steel Welds—Advances Since 1974, Welding Journal 76(1): 24-s. 5 Kotecki, D., 2000, A Martensite Boundary on the WRC-1992 Diagram—Part 2: The Effect of Manganese, Welding Journal 79(12): 346-s–354-s. 2 Magne-Gage®

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AWS G2.3M/G2.3:2019

Source: Kotecki, D. J, and T. A. Siewert, 1992, WRC-1992 Constitution Diagram for Stainless Steel Weld Metals: A Modification of the WRC-1988 Diagram, Welding Journal 71(5): 171-s–178-s.

Figure 5.3—WRC-1992 Diagram for Stainless Steel Weld Metal

Table 5.1 offers a comparison of the aforementioned ferrite diagrams. 5.1.3 Measuring Ferrite Number. The FN can be easily determined by measurements made directly on weld deposits. Several instruments are available commercially to make this measurement, such as the Magne-Gage®, Severn Gage®,6 and FERITSCOPE®.7 All the instruments are portable except the Magne-Gage® which is used primarily in laboratory conditions. Consequently, the test specimen size is limited when the Magne-Gage® is used. Manufacturer’s literature should be consulted for operating instructions. Buyers of fabricated products frequently specify restrictions for deposited weld metal ferrite content. Fabricators should be aware that the deposited ferrite content can vary from the predicted value and that purchasing welding consumables at either the extreme upper or lower limit of the allowed range (defined in the buyer or designers purchase specification) can carry some risk. Many FN determinations are based on filler metals deposited on a welded pad.8 To determine FN in as-deposited weld ts, dilution of the filler metal from the base metal should be considered. The procedure described by Kotecki and Siewert can be used.9 6 The

Severn Gage® is a ed trademark of the Severn Engineering Company. is a ed trademark of Helmut Fischer GmbH Institut für Elektronik und Messtechnik, Sindelfingen, . 8 Consult references: Annex A6 of AWS A5.4/A5.4M, Annex A7 of AWS A5.9/A5.9M, and Annex A6 of AWS A5.22/A5.22M. 9 D. J. Kotecki and T. A. Siewert, WRC-1992 Constitution Diagram for Stainless Steel Metals: A Modification of the WRC 1988 Diagram, Welding Journal Research Supplement, Vol. 71(5): 171-s–178-s. 7 FERITSCOPE®

18

AWS G2.3M/G2.3:2019

Table 5.1 Ferrite Diagram Comparisons of Chrome and Nickel Equivalencies Ferrite Predictor

Schaeffler

Creq

Nieq

Comments

%Cr + %Mo

%Ni + (30 × %C)

— Original method of calculating Ferrite in 300 series Stainless Steels

+ (1.5 × %Si)

+ (0.5 × %Mn)

— Range of Ferrite 0%–100%

%Cr + %Mo

%Ni + (30 × %C)

— Modification of the Schaeffler Diagram

+ (1.5 × %Si)

+ (30 × %N)

— Improved correlation between predicted and measured ferrite

+ (0.5 × %Nb)

+ (0.5 × %Mn)

— Allows standard Nitrogen values for various welding processes

+ (0.5 × %Nb)

DeLong

— Range of Ferrite 0 FN–18 FN

WRC-1992

%Cr + %Mo

%Ni + (35 × %C)

— Method with the closest agreement between predicted and measured ferrite

+ (0.7 × %Nb)

+ (20 × %N)

— Range of Ferrite 0 FN–100 FN

+ (0.25 × %Cu)

— Suitable for Duplex Stainless Steel

Note: Manganese and silicon are not used to calculate the Nieq and Creq equivalents for the WRC-1992 Diagram because their effects were found to be statistically insignificant at levels up to at least 10% Mn and 1% Si.

5.1.4 Welding Variables and Effect on Ferrite. Welding variables can cause a significant change in deposited ferrite content compared to the predicted deposited ferrite content. For example, carbon pickup from contaminated weld ts (e.g., inadequate cleaning of poorly arc-gouged surfaces or from residual oils and greases) and excessive nitrogen pickup from the atmosphere can cause a dramatic decrease of deposited ferrite content. The use of nitrogen in the shielding gas can also affect the resultant ferrite content. Not all filler metal manufacturers analyze consumables for nitrogen content since nitrogen is not an element required to be controlled or reported for most filler metals. Nitrogen content is essential, however, for accurately predicting weld metal ferrite. Consequently, when it is essential to control ferrite of weld deposits, requiring analysis for nitrogen of welding consumables can help the more accurately predict the FN of the final weld deposit. This requirement, however, has the potential of reducing the availability of consumables. The typical nitrogen content of weld deposits for a specific welding process can be established by analysis, and these typical nitrogen values may be used to help estimate ferrite contents in other instances when nitrogen content is unknown. Any of the following factors may result in excessive nitrogen pickup: (1) Maintaining an excessive arc length; (2) Excessively low gas shielding flow rate (which is incapable of providing adequate shielding); (3) Excessively high gas shielding flow rate (which results in aspiration of air); and (4) Loss of shielding gas coverage, e.g., from drafts (fans, wind, fume exhaust systems), or when welding certain t configurations such as outside corner ts.10 10 Kotecki,

D., 2000, Stainless Q & A, Welding Journal 79(1): 94.

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Cooling rates during the solidification process can also influence the amount of ferrite.11 For these reasons, in the development of welding procedures, it is important to know the predicted ferrite content of the filler metal as well as the influence of the welding process, techniques, and variables. 5.1.5 Hot Cracking (i.e., solidification cracking) and Ferrite. Welds produced with welding consumables that produce completely austenitic weld deposits can be prone to hot cracking. Hot cracking of many weld deposit types can be prevented or minimized by using a filler metal that produces ferrite during the solidification process and retains a minimum amount of ferrite in the solidified weld. Many of the 300 series stainless steel weld deposits contain much ferrite at the moment of solidification, and most of this ferrite transforms to austenite during cooling from the solidification temperature. What is observed at room temperature is known as retained ferrite and is actually the amount of ferrite that has not transformed. For example, a typical weld on 304-SS may initially contain up to 80% ferrite during the solidification process but during cooling the majority of ferrite transforms to austenite and only about 5%–10% ferrite typically remains at room temperature.12 Ferrite-containing weld deposits provide ferrite-austenite boundaries that are able to tolerate low melting temperature compounds of sulfur and phosphorous so that they reduce hot cracking susceptibility. It should be noted, however, that some design conditions require fully austenitic microstructures where ferrite in the final weld deposit is not permitted. These types of alloys at the point of solidification are fully austenitic and thus do not transform. Whether or not there will be ferrite during the solidification process and in the solidified weld (discussed further in this subclause) has been found to be strongly dependent on the ratio of the “Cr equivalent” to the “Ni equivalent” (Creq/Nieq) determined from the specific filler metal heat being used. Weld deposits for which Creq/Nieq is less than about 1.5 (based on the Schaeffler diagram) tend to solidify fully austenitic (without ferrite).13 This value may vary somewhat depending on the equivalency relations used (e.g., Schaeffler vs. Delong, or WRC). In some filler metal types such as types 310, 320, 330, 383, and 385, adjusting the composition to provide a small amount of ferrite is not possible because of the relatively high percentage of austenite promoters (such as nickel). Crack susceptibility in these grades is minimized by control of other variables as described below. Other methods for reducing hot cracking include reducing the restraint on the weld t (e.g., relocating the weld t to areas of lower stress or utilizing thinner base materials if the design permits), keeping the heat input as low as practical, and maintaining a 175°C [350°F] maximum inter temperature. Using filler metals with very low sulfur and phosphorous contents may also help reduce the tendency for solidification cracking. Convex weld beads are more resistant to cracking than concave weld beads. Backfilling weld craters before terminating the welding arc is also a good practice. High manganese content in some fully austenitic type weld deposits is used as an alternative means to minimize hot cracking tendencies. European and some other electrode standards recognize the benefit of relatively high manganese additions to consumables as a means for minimizing hot cracking tendencies. As a comparison, for welding type 310 stainless steel, the European Standard BS EN ISO 3581:2016, Welding Consumables—Covered electrodes for manual metal arc welding of stainless and heat-resisting steels—Classification, manganese range for alloy type 25 20 SMAW electrodes is 1.0% to 5.0% while the AWS A5.4/A5.4M manganese range for type E310 is 1.0%–2.5%. Also, the SMAW electrodes are generally more resistant to hot cracking than the comparable bare wire filler metals. Refer to 7.1 for additional discussion on hot cracking (i.e., solidification cracking). In addition to estimating the ferrite number of a weld deposit, the WRC-1992 Diagram can be used to predict the solidification mode and final structure of the weld deposit. After calculating and plotting the Cr- and Ni-equivalents on the WRC-1992 Diagram, the resulting plotted FN point will fall within a specific region of the diagram identified as “A,” 11 Vitek,

J. M., S. A. David, and C. R. Hinman, 2003, Improved Ferrite Number Prediction Model that s for Cooling Rate Effects—Part 1: Model Development, Welding Journal 82(1): 10-s. 12 V. Kujanpää, N. Suutala, T. Takalo, and T. Moisio, “Correlation Between Solidification Cracking and Microstructure in Austenitic and Austenitic-Ferritic Stainless Steel Weld,” Welding Research Intl., Vol. 9(2) (1979) pp. 55–76. 13 See footnote 12.

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“AF,” “FA,” or “F.” These regions define both the grain structure immediately after solidification and the final structure after cooling and transformations (if any) are complete. In all instances defined below, the WRC Diagram can be used to estimate the final amount of retained ferrite. Type “A” solidification regions define compositions that solidify directly to an austenitic microstructure. The austenite does not transform during cooling. When weld specimens are suitably prepared, etched, and viewed under a microscope, the microstructure will be fully austenitic. Type “AF” regions define compositions that solidify directly to an austenitic microstructure, except that some of the very last liquid to solidify will do so directly to ferrite. The microstructure remains relatively unchanged through cooling, and at its final stage will show austenitic dendrite (grains) branches with small amounts of retained ferrite located between them. Type “FA” regions define compositions that solidify directly to a ferritic microstructure, except that some of the very last liquid to solidify will do so directly as austenite. Upon cooling, the austenite remains unchanged, and most of the ferrite is transformed into austenite. The final microstructure typically shows continuous austenite along original ferrite solidification grain boundaries. The structure of the ferrite/austenite can take on several forms depending on the Creq/Nieq ratio including skeletal ferrite along the dendrite cores and lathy ferrite. Type “F” regions define compositions that solidify directly to a completely ferritic microstructure. Upon cooling in the solid state, austenite nucleates on the ferrite solidification grain boundaries and grows inward toward the dendrite cores. The final microstructure may show parallel plates of ferrite and austenite; it is often called Widmanstätten austenite. This microstructure is very unusual in austenitic stainless steels. Type “FA” solidification is very effective in minimizing or preventing hot cracking—normally a ferrite content of 4 FN minimum is sufficient to ensure that Type FA solidification has occurred. If the weldment is intended for high-temperature service or very low-temperature service, the amount of ferrite normally should not be greater than necessary to prevent hot cracking. At levels of 12 FN to 15 FN, the ferrite phase starts to be interconnected. Refer to 7.3 for additional information on controlling the solidification mode. 5.1.6 Possible Detrimental Effects of Ferrite. Weld metal ferrite can adversely affect weld metal corrosion resistance in a few environments, for example, in the production of uric acid. Examples of fully austenitic grades used in extremely corrosive environments such as fertilizer production or acidic service are grades 310, 383, and 385. In cryogenic applications, ferrite reduces toughness and is consequently kept as low as possible to optimize low-temperature ductility as reflected in Charpy V-notch testing. A desirable limit for the processes using wire flux combination is about 2 FN maximum.14 However, at least one electrode manufacturer tests and certifies their electrodes for cryogenic service with higher ferrite limits and good impact properties. For high temperature applications, excessive ferrite may result in reduced creep resistance. Thomas15 observed in type 316 deposits that resistance to creep deteriorates at high ferrite levels (e.g., in the presence of continuous ferrite networks). For these reasons, ferrite ranges are often specified by the fabricator or end . 5.2 The Ferrite-Sigma Phase Relationship. Although a small amount of weld metal ferrite is very beneficial in preventing hot cracking, too much ferrite may be detrimental. In long term service in the temperature range of 400°C to 540°C [750°F to 1000°F] alpha-prime forms causing 475°C [885°F] embrittlement. If the metal is heated within 600°C to 925°C [1100°F to 1700°F] sigma phase may form. The materials room temperature ductility can be significantly reduced by the formation of alpha-prime or sigma formation. 14 Avery,

R. E., 1995, Welding Stainless and 9% Nickel Steel Cryogenic Vessels, Welding Journal 74(11): 45. R., 1978, The Effect of Delta Ferrite on the Creep Rupture Properties of Austenitic Weld Metals, Welding Journal 57(3): 81.

15 Thomas,

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Sigma phase contains large amounts of chromium and iron and can form quite rapidly at about 600°C to 925°C [1100°F to 1700°F] with the most rapid transformation around 750°C [1380°F]. At temperatures lower than 600°C [1100°F], longer times are necessary for sigma formation. Iron will accommodate large amounts of Cr, and because of micro-segregation, the ferrite present in austenitic weldments will usually contain enough Cr to transform to sigma with a minimum amount of diffusion. Once formed, it can only be eliminated by heating to about 1010°C [1850°F] or higher (depending on alloy composition) to re-dissolve the sigma. Sigma phase is nonmagnetic while ferrite is magnetic. The formation of sigma from ferrite is accompanied by some formation of austenite as well due to diffusion of nickel, carbon, and nitrogen from the sigma region to the remaining ferrite which can then transform to austenite. As a result, the amount of ferrite that is lost considerably over estimates the amount of sigma formed. Because of this transformation to sigma, the ferrite content of welds is usually limited to about a 10 FN maximum for welded components that require a high-temperature stress relief or that will be exposed to high temperature service. Variations in weld metal composition will change the rate and temperature at which the sigma phase reaction first begins. Mo and Nb speed the sigma reaction, while Ni raises the maximum temperature at which sigma is still present. In fact, the rate of sigma phase formation in the 6% Mo superaustenitic stainless steels is rapid enough that restricted welding heat input may be required to ensure rapid cooling rates and minimum time exposure in the critical temperature zone. 5.3 Corrosion Resistance Related to Welding. One of the most significant consequences of welding many of the austenitic stainless steels is sensitization. It is caused by the formation of chromium carbides (termed precipitates) at grain boundaries in the HAZ when heated in about a 480°C to 850°C [900°F to 1560°F] temperature range with a peak formation rate occurring at about 640°C [1200°F]. Chromium-carbides form when carbon atoms migrate to grain boundary regions and combine with chromium. Consequently, chromium depletion occurs in a localized zone adjacent to grain boundaries, thereby reducing the corrosion resistance of these local areas. This problem can be minimized by using low carbon base materials. Stabilized base materials and filler metals (e.g., 347 stabilized with Nb or 321 stabilized with Ti) can also be susceptible to a form of sensitization in a narrow region of base metal close to the fusion boundary termed knifeline attack (KLA). During welding, the stabilizing carbides are dissolved, and if the region is subsequently heated into the sensitizing temperature range (see Figure 5.4a) (below the temperature range that Nb or Ti carbides form [Figure 5.4b]), chromium carbides precipitate at grain boundaries—thus sensitizing that narrow region. A stabilization anneal (as described in 10.3) may be used after welding to prevent KLA. Figure 5.4a shows the effect of carbon content and exposure temperature on the sensitization rate for Type 304 stainless steel. Note that Type 304 has a maximum carbon level of 0.08%, but Type 304L has a maximum carbon level of 0.03%. Seconds of elevated temperature exposure in Type 304 (with carbon at the upper limit of 0.08%) can result in sensitization while hours of elevated exposure may be needed to produce sensitization in Type 304L. Sensitization can also be minimized by using procedures and techniques that minimize time in the sensitization range (e.g., ensuring relatively fast cooling rates). The following conditions may be considered as examples: welding with minimal preheat and a restricted maximum inter temperature, using welding heat input that is appropriate for the base material thickness, or providing forced cooling between weld es. Generally, as the alloy content of the austenitic stainless steels increases, the effect of sensitization decreases somewhat because of the increased corrosion resistance of the bulk alloy. For example, 310 SS, with 25% Cr is less susceptible to sensitization than 304 SS, which has about 18% Cr. The effects and control of HAZ sensitization in various austenitic stainless steel alloys is discussed in depth in Welding Research Council Bulletin No. 319, Sensitization of Austenitic Stainless Steels: Effect of Welding Variables on HAZ Sensitization of AISI 304 and HAZ Behavior of BWR Alternative Alloys 316NG and 347. 5.3.1 Segregation Effects. During weld metal solidification of austenitic stainless steels, alloying elements such as Mo, Cr, and N can segregate; this is particularly problematic for high molybdenum-containing stainless steel alloys. Segregated weld metal is nonhomogenous; i.e., there are compositional variations from location to location in the weld microstructure. These compositional variations can result in a weld with diminished corrosion resistance.

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Note: Time-temperature-sensitization curves for Type 304 stainless steel in a mixture of CuSO4 and H2SO4 containing free copper. Curves show the times required for carbide precipitation in steels with various carbon contents. Carbides precipitate in the areas to the right of the various carbon content curves. Source: Reprinted, with permission, from ASM International, ASM Handbook—Corrosion, Vol. 13, 1987, p. 551, Figure 1.

Figure 5.4a—Carbide Precipitation in Type 304 Austenitic Stainless Steel

While not common practice, a full solution anneal following welding can substantially reduce segregation in weld deposits. Another method used to compensate for this segregation is to use an overmatching filler metal. For example, molybdenum is known to segregate in the 6% Mo containing superaustenitics, and a nickel-based filler metal with a greater percentage of Mo is commonly chosen to compensate for the segregation that will occur. Consequently, even when segregation occurs, the regions with the lowest Mo concentration will contain more than the minimum requirement. One of the problems with using overmatching filler metals is that the strength level of the weld zone may well exceed that of the base material. This fact should be considered in the weld design process. 5.4 Heat Tint. Heat tint (Gold to Blue discoloration) that forms on welds and alongside welds during welding or heat treatment of stainless steel, is a mixture of chromium, iron, nickel, and other oxides. These oxides are of a different composition and structure than the naturally occurring oxides of the protective ive layer. These oxides can reduce the material’s corrosion resistance depending on the amount and degree of heat tint present and the service environment. The mechanism for this reduced corrosion resistance is a chromium-reduced layer just beneath the heat tint scale. Heat tint colors are an indication of the amount (thickness and degree of severity) of heat tint. In increasing order of severity, colors can range from pale straw to pale blue to deep blue to gray to a black crusty coating with a significantly thick oxide layer. The acceptable amount of heat tint or discoloration varies with different service environments. The end is in the best position to specify the acceptable level for the intended application. In some corrosive environments, light, golden heat tint may be considered acceptable while only darker heat tint colors may be removed. AWS D18.2, Guide to Weld Discoloration Levels on Inside of Austenitic Stainless Steel Tube, provides a color photograph of various degrees of heat tint and can be a useful guide in indicating acceptable heat tint levels.

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Source: Reprinted, with permission, from ASM International, 1994, Metals Engineering Institute course, Eight Forms of Corrosion: ErosionCorrosion, Intergranular Corrosion, and Dealloying, Course 14, p. 22, Figure 36.

Figure 5.4b—Carbide Reaction Temperature Ranges

If it has been determined that heat tint would be detrimental, there are several techniques for minimizing its formation such as expanding the protective gas shielded area on the side being welded and by using an effective inert backing gas during welding. The removal of heat tint can be done by a variety of methods, including chemical, electro-chemical, and mechanical as described in 9.6 through 9.8.

6. Welding and Fabrication Considerations 6.1 Weld t Design. Weld t designs for stainless steels are similar to those used for carbon steels. Square groove butt ts are commonly used for materials < 6.4 mm [1/4 in] as well as for thicker materials when they are welded with specialized welding processes such as plasma key hole or electron beam welding or other specialized welding techniques. Acceptable butt t groove designs for thicker materials include single and double bevels, J-groove, U-groove, and Vgroove designs. Compound bevels are recommended for thicknesses exceeding 25 mm [1 in]. The t design should be optimized to minimize the amount of distortion and the amount of deposited weld metal. The bevel and grooves should be large enough to allow good electrode accessibility which will help ensure good fusion. Various t designs can be found in the following documents: ASME B16.25, Buttwelding Ends

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AWS D1.6/D1.6M, Structural Welding Code—Stainless Steel PFI Standard ES-21, Internal Machining and Fit-up of GTAW Root Circumferential Butt Welds, Pipe Fabrication Institute16 PFI Standard ES-35, Nonsymmetrical Bevels and t Configurations for Butt Welds, Pipe Fabrication Institute17 6.1.1 Weld t Preparation. Austenitic stainless steels may be cut by a variety of means, e.g., by shearing, sawing, plasma, laser, abrasive water jet, grinding, thermal arc gouging, and machining. Oxy-fuel cutting torches are not suitable for cutting stainless steels due to the refractory chromium oxide that forms and interferes with the cutting action. Plate, sheet, and bar edges that need further weld t preparation after first cutting to size (with appropriate stock allowance) can be machined, ground, and thermally cut with plasma or laser. Nitrogen-containing plasma gases should be used with caution as formation of chromium nitrides can reduce corrosion resistance and actually appear as “rust” on the edges of the t preparations. Certain thermal processes, such as mechanized laser and plasma cutting, can leave weld t edges suitable for many weld t designs and welding operations without having to final machine the weld ts. Examples are Tee ts and corner ts in plate. Frequently, however, the t edges must be machined for proper fit-up prior to welding, as in pipe ts and other critical weld applications such as electron beam welding. For example, proper weld t design and fitup are usually needed in pipe and circumferential ts to ensure that complete t penetration (CJP) will be consistently achieved with a given welding process. The selection of a welding process (or processes) for a weld t, however, can depend on a variety of factors such as corrosion concerns, base material thickness, weld t designs, available welding equipment, productivity requirements, available electrodes and filler metals for a particular alloy, distortion control, accessibility limitations, and quality requirements, among possible other factors. Optimally, weld designers and manufacturers work together prior to finalizing weld designs to ensure ease of fabrication, quality, and lowest manufacturing costs. Austenitic stainless steels are generally selected for fabrication because of their corrosion resistance, appearance, or toughness and strength at temperature. Weld ts are frequently required by designers to have CJP for any of several different reasons: (1) CJP ensures that process chemicals will not be trapped in unfused crevice areas. (2) The use of CJP designs reduces stress concentrations that are detrimental to fatigue performance. (3) Equivalent cross-sectional strength to the base material is ensured. Unfortunately, welds cannot be assumed to have equal fatigue performance as the base materials being ed; consequently, welds in critical applications should be located in areas of low stress (e.g., away from corners, etc.) whenever possible. 6.1.2 Fixtures and Fitting Devices. For critical service environments, temporary fitting devices and fixtures that are tacked to stainless steel fabrications should be of the same alloy type unless overmatched filler metals appropriate for the corrosive conditions are used for tacking. Due to dilution, welds made between dissimilar base materials, such as carbon steel fitting devices tacked to a stainless steel fabrication, can result in a different weld deposit chemical composition with reduced corrosion resistance compared to the composition of the filler metal. Accelerated corrosion can occur in the weld area in corrosive environments even if the fitting device has been removed and the weld ground is flush with the base material. 6.2 Cleaning Prior to Welding 6.2.1 Grinding and Scale Removal. Weld t grooves and the immediate surrounding area should be clean prior to welding. The degree of cleaning necessary depends on the weld quality requirements for the application and the welding process employed. For example, greater levels of cleanliness are typically required with gas-shielded welding processes because of the absence of fluxing agents. 16 PFI 17 See

standards are published by the Pipe Fabrication Institute, 511 Avenue of the Americas, Suite 601, New York, NY 10011. footnote 16.

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Contaminants such as sulfur, lead, copper, zinc, phosphorous, carbon, oils, dirt, oxide scales, sulfide scales, sand, etc. may cause weld metal cracking or porosity, or may result in incomplete fusion type discontinuities. Contaminants should be removed from the weld t area prior to welding on both new and service-exposed equipment. It is not considered necessary to remove the bright surface layer (ive film) found on mill-supplied stainless steel products. However, thick, dark oxides (scales that are the result of high-temperature exposure) should be removed from the weld area before welding. Chromium-containing oxides melt at a much higher temperature than the weld metal. These unmelted oxides inhibit weld fusion, and the oxides may not have time to float to the surface before solidification occurs, potentially causing inclusions or lack of fusion during welding. Scale removal is usually done by grinding or by use of a sanding disk to remove the scale within about 12 mm [1/2 in] of both sides of the edge of the weld t. To prevent iron contamination of the stainless steel, stainless steel wire brushes should be used. Brushes and grinding wheels previously used on carbon or low alloy steels should not be used for cleaning stainless steel welds or base materials. Direct by carbon steel tools and metals should be avoided because of the possibility of contamination by iron particles. Grinding wheels and sanding discs are normally required to be reserved only for use on stainless steel. Grinding wheels should be identified by the wheel manufacturer as to be suitable for use on stainless steels. These properly identified wheels are typically manufactured only with highly refined ingredients that do not contain iron, sulfur, or chlorine which would otherwise contaminate stainless steels. For fabrications that will be bead or media blasted, chemically cleaned, or pickled after welding (see 9.8), the use of specially-reserved grinding wheels and stainless steel wire brushes is normally not as critical. Beads and grit, however, should not be contaminated by prior use on carbon steels. Steel beads and steel grit should not be used because of the risk of iron contamination. The final surface condition of the material should always be considered when selecting a cleaning or surface preparation method since coarse surface profiles can degrade the material’s corrosion resistance in some environments as well as making cleaning of equipment surfaces more difficult. When grinding on nearby carbon steels, suitable precautions should be taken to protect stainless steels from contamination by grinding debris. Contamination of stainless steel base materials by carbon steel can cause rust spots and may initiate corrosion of the stainless steel in some environments. See 6.3 for cleaning recommendations for weld grooves prepared by carbon arc gouging. 6.2.2 Solvent Cleaning. Areas to be welded should be free of contaminants such as cutting fluids, grease, oil, waxes, soil, etc. Otherwise, carbon pickup, porosity, or weld cracking may result. Solvent cleaning of the weld t area prior to welding is normally adequate if oxide scales are not present. Suitable solvents are those that remove the majority of the possible contaminants and do not leave their own residues after drying. The use of chloride-containing solvents has been traced to chloride stress corrosion failures of stainless steel heat exchangers.18 Chloride-containing solvents should be used with caution because of the potential for chloride stress corrosion cracking. Chloride-containing solvents should only be used on smooth, crevice-free components where complete removal of the cleaning solvent can be assured before welding. 6.2.3 Production High Cleanliness Example. The degree of preweld and postweld cleaning should be commensurate with the fabrication type. For example, medical grade tubing and tubing in the semiconductor or pharmaceutical industry should be absolutely clean prior to, during, and after welding. For these types of critical applications, the cleaning method should employ solvent wiping/cleaning prior to welding. Preferably, welding should be performed in a clean room whenever possible. Base materials and filler materials for critical applications should be purchased as specially cleaned and packaged to ensure absolute cleanliness during fabrication. For purging, the internal oxygen content should be less than 50 ppm (parts per million) for both tacking and welding for most applications. 6.3 Thermal Arc Gouging and Grinding. Thermal arc gouging is commonly used to prepare the second side of a double-welded (welded on both sides) t after welding the first side. When used in this manner, the process is called “backgouging.” A skilled operator can simultaneously remove weld discontinuities to sound metal and prepare the t with groove dimensions and a profile that is suitable for subsequent welding operations. The process is also commonly used to remove weld discontinuities discovered by inspection. 18 The Nickel Institute Reference Book Series 11007, Guidelines for the Welded Fabrication of Nickel Containing Stainless Steels for Corrosion Resisting Services, p. 9, The Nickel Institute Inc., 55 University Avenue, Suite 1801, Toronto, Ontario, Canada M5J 2H7.

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A close visual inspection of arc-gouged areas should be performed to ensure that cracks, porosity, unfused regions, and lack of fusion-type discontinuities have been removed before welding (i.e., gouged or backgouged to “sound metal” prior to welding the second side). Liquid penetrant examination (PT) may be used to reveal surface-breaking discontinuities on the groove surface that a visual inspection may fail to detect. As surface roughness from grinding may mask some indications, PT may be considered to supplement visual examination. The final PT is normally performed after any grinding is complete. Due to a variety of different reasons there may be localized regions or more extensive regions with visible deposits on the arc gouged groove surface. All regions having visible deposits of carbon, copper, or oxidized material (dross) should be ground to remove all deposits. Depressions in irregularly gouged surfaces can trap contaminants, and those regions need to be carefully visually inspected to ensure that if contaminants are present the regions are properly cleaned, commonly by grinding, to remove the contaminants. Welding over such contaminants can potentially result in weld discontinuities such as porosity, lack of fusion, cracking, and/or may adversely affect the weld t’s mechanical properties and/or corrosion resistance. Grinding can also be used to smooth otherwise roughly gouged groove contours and to contour the groove profile for proper access during welding operations. Prior to arc gouging, surrounding areas should be protected (e.g., anti-spatter, blankets, etc.) as needed from sparks and dross created by arc-gouging operations as they can tightly fuse to the base material making subsequent cleanup difficult. Arc gouging techniques, equipment, parameters, troubleshooting, and safety concerns are thoroughly discussed in AWS C5.3, Recommended Practices for Air Carbon Arc Gouging and Cutting. 6.4 Distortion Control. Compared to steels, austenitic stainless steels experience greater distortion during welding because of their comparatively high rate of thermal expansion, but a comparatively low rate of thermal conductivity. Austenitics, for example, expand at a rate approximately 30% to 65% greater than steels with increasing temperature, while dissipating their heat much more slowly (nearly 300% more slowly) from the weld zone than steels. As a result, appropriate welding techniques to control distortion may be needed. The austenitic stainless steels all have relatively low thermal conductivity but a high coefficient of thermal expansion (CTE) (see Table 6.1). As a result, these steels may present some distortion problems unless the usual design and welding practices for controlling distortion are observed. Copper backing bars can be placed under weld areas to draw off the heat more quickly. The use of welding fixtures can prevent movement of base plates that would result in angular misalignment. Minimizing the number of weld es, short bead lengths, or skip welding will reduce the amount of distortion.

Table 6.1 Typical Physical Property Comparisons of Austenitic Stainless Steels versus Carbon Steels Property/Alloy

Austenitic Stainless Steels

Carbon Steels

7.8 g/cm3–8.0 g/cm3 [0.28 lb/in3–0.29 lb/in3]

7.8 g/cm3 [0.28 lb/in3]

193 GPa–200 GPa [28 Msi–29 Msi]

200 GPa [29 Msi]

Mean Coefficient of Thermal Expansion 0°C–540°C [32°F–1000°F]

17.0 µm/m·°C–19.2 µm/m·°C [9.4 µin/in·°F–10.7 µin/in·°F]

11.7 µm/m·°C [6.5 µin/in·°F]

Thermal Conductivity at 100°C [212°F]

18.7 W/m·°C–22.8 W/m·°C 10.8 Btu/h·ft·°F–12.8 Btu/h·ft·°F]

60 W/m·°C [34.7 Btu/h·ft·°F]

690 nΩ·m–1020 nΩ·m

120 nΩ·m

1400°C–1450°C [2550°F–2650°F]

1538°C [2800°F]

Density Elastic Modulus

Electrical Resistivity Melting Range °C [°F]

Source: Adapted from the AWS Welding Handbook, 8th ed., Vol. 4, Table 5.2.

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The CTE is an important factor when considering warpage. The difference in the coefficients of expansion between materials becomes especially important when two different materials are welded together. The added stress placed on the weld t area can be substantial if there is a considerable difference in CTE values. The problem is amplified as t restraint increases because the structure is less able to effectively disperse the increase in stress. Controlling distortion can be accomplished by one or more fabricating and welding techniques. Clamps, jigs, and fixtures should be used whenever possible; they help to ensure proper positioning and fit-up for welding, as well as help to minimize movement of the parts during welding. ts can sometimes be preset to compensate for angular distortion, and the use of strongbacks and stiffeners may also be considered. Proper weld t designs help ensure that weld ts are not overwelded and that complete t penetration (CJP), when required, can be achieved with minimal backgouging. Tacking for fit-up and welding should be appropriate for the base metal thicknesses. Sheet metals may have to be tacked at intervals closer than 25 mm [1 in] to control distortion, or continuous seam fixturing may be required. Tacking of plate materials requires larger but fewer tacks. Skip welding or backstep welding sequences are also frequently used to help minimize distortion. Welding process selection can also have a significant influence on the amount of distortion. Distortion in thin sheet metals, for example, is controlled by specifying welding processes such as short circuiting GMAW, GTAW using low heat inputs, or LBW, in combination with the appropriate clamping, fixturing, tacking, or welding sequence procedure. A carefully thought out welding sequence is important for distortion control. Another method used to minimize welding distortion is to specify the use of a high energy welding process such as laser, plasma, or electron beam welding, resulting in narrow weld zones. t designs for these processes are frequently square groove with no root opening. Filler metal additions can frequently be eliminated as there is no V-groove to fill. Those processes can be specified when the appropriate welding equipment is available or needed to meet product quality requirements. One of the primary disadvantages of the processes, however, is the initial cost of the welding equipment. Use of two-sided t preparations (double-V or double-U grooves) with backgouging is very helpful in limiting angular distortion. Welding on the second side before the first side is completed allows distortion from welding the second side to cancel out distortion from welding the first side to a considerable extent. Properly chosen two-sided t preparations, with proper sequencing of weld deposition on the two sides, can greatly reduce angular distortion as compared to that obtained with one-side welding. 6.5 Welding Preheat and Maximum Inter Temperature. Preheat is not normally performed or desired for welding austenitic stainless steels although preheat of complex shapes and heavy sections is used by some manufacturers to improve weldability when welding H-grade cast alloys. Preheat should normally only be performed to dry off wet base materials, or if the base material temperature is below the dew point and there is moisture condensation around the weld t area. Low inter temperatures are generally desirable to ensure that cooling rates are rapid enough to prevent or minimize sensitization (formation of chromium carbides) in the weld and HAZ. Sensitization can adversely affect the corrosion resistance of the weld and HAZ. The generally recognized maximum inter temperature (IP) specified in industry for welding austenitic stainless steels is 175°C [350°F]. Accelerated cooling between weld es is generally acceptable with precautions. Clean water or clean forced air should be used. Backside cooling is generally acceptable after the first weld is completed (even while the welding is in process on subsequent es), as long as moisture or air drafts do not interfere with the welding process. The t should be dry and clean before resuming welding. Cooling should be uniform to minimize distortion.19 6.6 Welding Position. Whenever possible, the work should be positioned to gain the advantages of speed and economy provided by flat position welding. Weld positioners, rolls, etc., are frequently used for this purpose. 6.7 Root Welding. Root welds on single-welded, complete t penetration (CJP) weld ts (e.g., pipe and tube ts) are commonly specified to be made using either the GTAW or the GMAW short circuiting process (GMAW-S) 19 Kotecki,

D., 2004, Stainless Q & A, Welding Journal 83(5): 14.

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with inert backing gas (termed “purging”). Purging is used to protect the pipe interior from sugaring and to provide an acceptable level of heat tint. High quality root surface profiles are obtainable using these processes. The root surface of welds made without inert gas backing are prone to excessive oxidation, termed sugaring. Highly oxidized welds are characterized by a dull gray color appearance or a “sugared” surface (oxidized welds resemble the appearance of partially burned sugar; a cauliflower-appearing texture commonly seen on the root surface of improperly shielded welds). Sugaring occurs when metal is in the molten state and exposed to the atmosphere (or elevated oxygen levels). Heat tint, on the other hand, can occur to both weld deposits and base materials in either the solid or molten state when exposed to oxygen at elevated temperatures. The degree (i.e., amount/level) of heat tint depends on the level of oxygen and the exposure temperature and time. Fabrication codes generally do not require use of gas backing/purging. When purging is specified, the level of discoloration should be agreed upon between the designer and the fabricator. In critical service, the procedure qualification test coupon may be required to be tested for its corrosion resistance.19 The GMAW process may be restricted from use in certain applications, however, because of the potential for unmelted electrode “whiskers” and spatter on the process side that can potentially damage downstream equipment. Slag left on a service-exposed root surface is frequently a corrosion concern with other welding processes as unremoved slag can promote the corrosion of weld t areas or can also cause damage to downstream equipment. For that reason, processes with slag systems such as SMAW, FCAW, and SAW may need to be avoided for the root in single-welded CJP weld ts especially if the root side of the t is not accessible for visual examination or for cleaning or backwelding. Options for root welding (without backing material) using the GTAW process with inert gas backing include: (1) Open root ts with filler metal added. (2) Preplaced consumable inserts for pipe ts fit with a tight fitup. Standard shapes and available classifications for consumable inserts can be found in AWS A5.30/A5.30M, Specification for Consumable Inserts; and (3) Some fabricators perform autogenous root es in pipe fit-up with no root opening and a minimal root face on alloys such as 304/304L and 316/316L. Autogenous root es in some alloys may be prone to hot cracking, especially if the predicted ferrite based on base material composition is very low and t restraint is high. Another word of caution is that autogenous root es should be avoided if the alloy is being used near the limits of its corrosion resistance unless corrosion testing has proven otherwise.20, 21 For the fitup conditions without a root opening, taping off portions of the t to contain the purge while other portions of the t are being welded is not necessary. When properly welded with inert gas backing, CJP can be achieved with uniform melt-through. Options for root welding (without backing material) using the GTAW process without inert gas backing include: (1) The use of specialized fluxes applied to the base material root areas. (2) The use of flux cored GTAW filler rods with an open root t and a keyhole welding technique. Available classifications for these rods are found in AWS A5.22/A5.22M, Specification for Stainless Steel Flux Cored and Metal Cored Welding Electrodes and Rods. Flux and slag residue left on the root side from either of these two options may not be suitable in high purity or high-temperature service environments. CJP one sided ts can also be completed using open root ts with metallic backing (when permitted by design), copper backing bars, or ceramic backup tapes (see 7.3.3 for precautions when using copper backing bars). 20 Garner, A., 1983, Pitting Corrosion of High Alloy Stainless Steel Weldments in Oxidizing Environments, Welding Journal 62(1): 27–34. 21 He H. and Hamm/Wesphalia (), No. 2, 2003, Arc Welding of Stainless Steels—Selection of Filler Metals, Welding and Cutting 55: 68–71.

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Options for root welding using the GMAW-S process include: (1) Open root with inert gas purge (2) Open root without gas purge. Success has been reported in completing CJP, open root, single-welded piping ts without the use of inert backing gas using a modified GMAW-S process. Higher than normal shielding gas flow rates were utilized, as well as “silicon” enhanced electrodes, e.g., ER316LSi. It should be recognized that the internal HAZ will have a varying amount of heat tint that may affect the corrosion resistance in some service environments. The procedure should not be used for applications where little or no heat tint is a requirement. CJP single-welded ts can also be completed using open root ts with metallic backing (when permitted by design), copper backing bars, backing fluxes, or ceramic backup tapes. Root es on double-welded CJP weld ts can be made using any welding process, including those with slag systems such as the SMAW, FCAW, and SAW processes. For double welded ts, the backside of the weld ts are commonly thermally arc gouged or ground to sound metal prior to welding the back side of the weld t. 6.7.1 Purging Recommendations. A purge is generally maintained for two to three layers minimum to prevent sugaring and limit heat tint to the required level. Detailed instructions on purging prior to and during welding are given in AWS D10.11M/D10.11, Recommended Practices for Root Welding of Pipe Without Backing, and in AWS D10.4, Recommended Practices for Welding Austenitic Chromium-Nickel Stainless Steel Piping and Tubing. The guides discuss the use of dams, venting, and purge flow rates and volumes necessary to lower oxygen levels to acceptable levels prior to welding and the flow rates during welding. Additional information is presented in the Welding Journal.22, 23 AWS D18.2, Guide to Weld Discoloration Levels on Inside of Austenitic Stainless Steel Tube, depicts the dependence of the weld discoloration level on the gas impurity level. The standard provides a visual comparison guide that can be used to specify surface discoloration (heat tint) criteria for welds in an austenitic stainless steel pipe and tube. Highly oxidized welds may experience reduced corrosion resistance or possibly reduced mechanical properties such as ductility, toughness, and strength. Purging guidelines are provided in Table 6.2. The use of a purge gas or backing gas on double-welded ts is generally considered optional since the backside of the root can be ground to sound metal prior to welding the second side. Welding over oxidized weld metal without prior grinding is not recommended because of a greater chance of porosity, inclusions, and reduced mechanical properties. Even though purging may be considered optional for double-welded ts, it may still be advantageous in certain situations; however, since purging enhances the backside weld fluidity and weld contour, its use may prevent an extra gouging and grinding step. Depending on the application, the purging of single-welded ts may not always be required. However, eliminating purging (when full penetration is desired) may affect the root side of the t as follows: (1) Corrosion resistance will be degraded in some environments, (2) Weld penetration will not be consistent, (3) Weld puddle fluidity will be reduced and may increase the welding time, (4) Root-side weld profile and appearance will be degraded, (5) Some oxide scaling and flaking may occur, and (6) The mechanical properties may be reduced. The designer/engineer should weigh all factors before deciding if purging should be eliminated as a potential cost savings. 6.7.2 Verification of Production Heat Tint Levels. As previously mentioned, inert gas backing in production is used to ensure that optimum corrosion resistance, weld penetration, weld puddle fluidity, profile, and appearance can be maintained. The actual heat tint levels (and the possible presence of sugaring) on the interior of pipe and tube ts can be difficult to inspect or . It is important then, that fabricators use purging procedures/techniques that are reproduc22 Young, 23 Irving,

B., 1995, Shielding and Purging Gases: Making the Right Selection, Welding Journal 74(1): 47. B., 1994, Trying to Make Some Sense Out of Shielding Gases, Welding Journal 73(5): 65–70.

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Table 6.2 Purging Guidelines for Piping Purge-gas flow time per unit of length versus nominal pipe size (NPS)b with six volume changesa at a gas flow rate of 25 L/min [50 ft3/hr]c NPS

Purge Time

mm

in

min/m

min/ft

<25

<1

0.3

0.1

25–50

1–2

0.7

0.2

50–75

2–3

1.6

0.5

75–125

3–5

3.3

1

150

6

5

1.5

200

8

8

2.5

250

10

13

4

300

12

18

5.5

350

14

25

7.5

400

16

33

10

450

18

40

12

500

20

50

16

600

24

75

23

750

30

115

35

a

Six volume changes will typically provide less than 1/2% (5000 ppm) oxygen, the recommended maximum for general corrosive service. Significantly less volume changes are required if turbulence and mixing can be decreased. As an alternative, measuring oxygen content of the purge using an oxygen analyzer should be considered. b To calculate the total purge time (using the flow rate specified in Table 8.9), multiply the actual length of pipe with the corresponding Purge Time. Example:

7 m length of DN 150 purged at 25 L/min: [23 ft length of NPS 6 purged at 50 ft3/hr]: 7 m × 5 min/m = 35 minutes [23 ft × 1.5 min/ft = 35 minutes]

c

Lower or higher flow rates may be used. Higher flow rates may be used on larger pipe diameters to reduce purge time. Lower flow rates reduce turbulence and are recommended on smaller pipe diameters and to achieve a high-quality purge. If other flow rates are used then to find the time required multiply: The pipe length × purge time from table × (flow rate from table ÷ desired flow rate)

Example:

6 m length of DN 75 with a desired flow rate of 9 L/min [20 ft length of NPS 3 with a desired flow rate of 20 CFH] Calculated flow rate = 6 m × 1.6 min/m × (25/9) = 25 min [20 ft × 0.5 min/ft × (50/20) = 25 min]

Example:

7 m length of DN 450 with a desired flow rate of 40 L/min [23 ft length of NPS 18 with a desired flow rate of 80 CFH] Calculated flow rate = 7 m × 40 min/m × (25/40) = 175 min (3 hrs)* [23 ft × 12 min/ft × (50/80) = 175 min (3 hrs)*] *Use of purge dams recommended.

Notes: 1. Purge dams may be used to reduce the amount of purge gas and time. 2. The purge inlet-hole at one end of pipe should be placed lower than the exit hole at other end of pipe. Since argon is heavier than air, the argon entering the assembly at the bottom will force the air out the top with minimal mixing of the two gases. 3. Once the purge has been established, the flow rate should be reduced while welding. 3 L/min–5 L/min [5 CFH–10 CFH] is recommended.

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ible. Inspectors should that purging procedures are properly implemented, and when possible, make it a point to visually inspect the root surface of pipe and tube welds. Preproduction mockups may also be considered to establish acceptable heat tint levels. 6.8 Shielding Gas and Cleanliness. With all the welding processes for the austenitic stainless steels, proper weld pool shielding is a necessity. Numerous corrosion failures have been traced to improperly shielded and oxidized welds.

7. Weldability Considerations 7.1 Solidification Cracking. Many of the austenitic stainless steel alloys are considered to be easily weldable; however, as described in 5.1.5, a type of weld metal cracking that occurs during the final stages of solidification, termed “weld metal solidification cracking,” (i.e., “hot cracking”) may be encountered in the following situations: (1) When welding austenitic alloys with fully (or nearly fully) austenitic filler metals, (2) When welding free-machining grades of base materials with high levels of sulfur or phosphorous, (3) When welding fabrications with a high degree of restraint, and (4) When welding on service exposed equipment over corrosion deposits that have not been removed before welding. The chance for solidification cracking increases if two or more of the above situations exist simultaneously. Weld metal solidification cracking results when solidification shrinkage-induced tensile stresses accumulate at grain boundaries coated with liquid films. The liquid films have a limited strain capacity and separate as the deposit solidifies and shrinks resulting in crack formation. Weld solidification cracking may pose a problem when fully (or nearly fully) austenitic weld deposits are required for example, in certain corrosive service environments or in applications where nonmagnetic materials and weld deposits are required or for cryogenic service. Examples of nonmagnetic material uses include magnetic resonance imaging (MRI) and other medical equipment, mine sweepers, and electrical generation equipment. For “H-grade cast alloys,” carbon content tends to decrease the microfissuring of austenitic welds, and alloys with carbon content at the higher end of the composition range are somewhat easier to weld; however, they are more difficult to repair weld after being exposed to high temperature service. 7.1.2 Mitigation of Solidification Cracking with Ferrite Control. Many of the austenitic-type filler metals are formulated to produce weld deposits with a sufficient ferrite level that helps prevent solidification cracking. The ferrite level of the weld deposit is primarily dependent upon the chemical composition of the deposit, and hence, can vary significantly from one AWS filler metal classification to another and from one electrode production heat/lot to another. In gas shielded welding processes, improper shielding gas coverage can lead to increased amounts of nitrogen in the weld metal which can significantly reduce the ferrite content as nitrogen is a strong austenite promoter. For some special applications, a fully austenitic weld structure is required and no or very little amounts of ferrite are allowed. In such cases, weld metal solidification cracking can be minimized by selection of base and filler materials with low impurity levels (sulfur, phosphorus, and boron) or by application of proper welding technique. These are discussed in the following subclauses. 7.1.3 Various Effects of Sulfur. Weld metal solidification cracking can also occur when welding “free machining” grades of stainless steels that have relatively high levels of sulfur or phosphorous.24 Welding of the free machining grades, such as Types 303 and 303Se, can be difficult because of the pickup of sulfur, phosphorous, or selenium that can cause cracking in the weld metal or HAZ. If welding is absolutely required, E/ER312 type filler metals with low heat input procedures are generally recommended. The same pickup of detrimental elements can occur when welding on service exposed equipment without having first properly cleaned the base metal to clean, shiny metal. 24 Lee, C. H., R. Menon, and C. D. Lundin, 1988, Ductility and Weldability of Free Machining Austenitic Stainless Steel, Welding Journal 67(6): 119.

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Sulfur has also been found to play a role in the formation of cracks and voids in autogenous GTA welds on Type 316-SS. One fabricator eliminated the discontinuities by reducing the base material sulfur content to below 0.03%. Reducing the phosphorous content also helped eliminate cracks but had little effect on reducing porosity levels. Using base metals and filler metals with a Creq/Nieq > 1.5 will reduce the cracking susceptibility by helping ensure that the first liquid to solidify is ferrite. Consequently, the presence of impurities is not as critical. On the other hand, if the composition of the weld metal is such that it solidifies primarily as austenite (Creq/Nieq < 1.5), the impurity content should be very low, for example, the total phosphorous and sulfur level should be less than 0.03% and the sulfur content below 0.003%. The solidification mode can be controlled only in certain weld deposit types, e.g., Types 308, 316, 317, and 309 stainless steel. With other types, a reduction in the impurity content may be necessary in order to minimize crack formation. The base metal sulfur content has a major effect on the weld penetration of autogenous GTAW tubular welds. Welds where the sulfur content is below about 0.005 to 0.006% tend to have low penetration. 25 For example, the ASME Bioprocessing Equipment Standard (ASME BPE) specifies a sulfur content control of 0.005 to 0.017% for tubular base materials that are autogenously welded with the GTAW process. 7.2 Reheat Cracking in Type 347-SS. Weld metal and HAZ cracking can occur during postweld heat treatment or hightemperature service in some austenitic stainless steels like Type 347, especially with increasing t thickness and restraint. Fast heating rates during postweld heat treatment can be used to minimize this “reheat cracking” phenomenon as well as to restrict the ferrite content of the welding consumables. Type 316/316H and 16-8-2 filler metals may also be considered to minimize this problem. The use of Type 316/316H filler metals, however, may result in lower high-temperature creep-rupture strength and corrosion-resistance differences compared to Type 347 filler metals. 7.3 Other Forms of Weld Cracking and Prevention Strategies. There are other weldability issues in addition to those discussed in the previous subclauses. Several other important forms of weld cracking include liquation cracking, ductility-dip cracking, and copper contamination cracking. 7.3.1 Liquation Cracking. Liquation cracking can take two slightly different forms. The first type, HAZ liquation cracking, occurs as cracking is induced by grain boundary liquation in the partially melted zone during welding. The partially melted zone is weakened by intergranular liquid films and cracking occurs as the solidifying weld metal contracts and pulls against this region. Liquid films form at high temperature due to impurity segregation along grain boundaries or by the constitutional liquation, i.e., partial melting of precipitates such as TiC (in Type 321) and NbC (in Type 347). HAZ liquation cracking can be controlled by several methods. In fully austenitic alloys, limiting impurity levels (such as sulfur and phosphorus) and controlling the grain size can be effective. Reducing the weld heat input can be effective in limiting the grain growth in the HAZ and also induces steep temperature gradients that minimize the size of the zone susceptible to liquation. Selection of alloys that have some tendency to form ferrite in the partially melted zone is also an effective control method. The second type of cracking, weld metal liquation cracking, occurs in multi welds and is prone to occur in fully austenitic weld deposits as prior weld es are reheated. Impurity control is necessary in fully austenitic multi weldments, and guidelines for minimum ferrite content have been proposed for a number of other weld deposits (including Types 308, 316, 309, and 347).26 The presence of a small amount of ferrite promotes resistance to weld metal liquation cracking since the interface of ferrite and austenite is not easily wet by liquid films. 7.3.2 Ductility-Dip Cracking. Ductility-dip cracking can occur in austenitic stainless steels and is associated with a decrease in ductility above approximately one-half the melting temperature and below the solidus temperature.27 This form of cracking typically occurs when the austenite grain size is quite large and when the weldment is under a high restraint condition (e.g., multi, thick-section t). The cracking mechanism is not completely understood; however, cracks develop along the crystallographic grain boundaries in the HAZ or weld metal at temperatures below those where solidification and liquation cracking occur. The grain boundaries most susceptible to ductility-dip cracking are those that are especially straight where grain boundary sliding can occur. The presence of some ferrite in austenitic weld deposits promotes resistance to this form of cracking as this tends to promote a very tortuous grain boundary path where ductility-dip cracks cannot as easily initiate and propagate. Use of low weld heat input can also be an effective method to reduce susceptibility by reducing residual stresses in thick-section weldments. 25 Mills,

K. C. and A. A. Shirali, 1993, The Effect of Welding Parameters on Penetration in GTA Welds, Welding Journal 72(7): 347. C. D. and C. P. D. Chou, 1985, Fissuring in the “Hazard HAZ” region of austenitic stainless steel welds, Welding Journal 58(4): 113-s–118-s. 27 Lippold, J. C. and D. J. Kotecki, 2005, Welding Metallurgy and Weldability of Stainless Steels. John Wiley & Sons, Inc. Hoboken, NJ. 26 Lundin,

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7.3.3 Copper Contamination Cracking. Copper contamination cracking is a form of cracking that occurs in the HAZ of austenitic stainless steels. Contamination by copper can occur from worn, chipped, or abused copper fixturing and tooling used to hold and fixture stainless steel while welding. Melted copper can penetrate grain boundaries by a liquid metal embrittlement mechanism and can result in cracking at the grain boundaries. Cracks due to copper contamination are intergranular and are perpendicular to the principal stress direction. 7.3.4 Welding Techniques to Minimize Weld Cracking. To prevent weld metal cracking on thick, highly restrained ts, and when using fully austenitic filler metals, the weld beads should preferably be convex and stacked, side-toside, building up the weld deposit from the bottom to the top of the t by depositing the final weld beads for each layer along the t faces. The use of deep narrow weld beads should be avoided. Weld craters should be filled prior to terminating the arc to minimize the formation of crater cracks. Weld stops can also be terminated on the t faces instead of deep in the groove. This technique will minimize shrinkage stresses on the weld stop. Welders should be instructed to visually inspect the weld stops for cracks prior to starting the next bead. This is especially important when using fully austenitic filler metals and on highly restrained weld ts. All cracks should be removed prior to beginning the next weld bead. 7.4 Reheat Cracking in FCAW Deposits. Some commercial formulations of FCAW electrodes use additions of bismuth-containing compounds for purposes of improved slag removal. These designs result in about 200 ppm (0.02 wt %) of Bi in the weld deposit. This amount of Bi has no detrimental effect upon ambient temperature properties. However, reheat cracking during PWHT, premature creep failures and drastically reduced tensile ductility at temperatures above about 550°C [1022°F] have been observed in such weld metals.28 Accordingly, less than 20 ppm of Bi in weld deposits intended for such elevated temperature exposure is recommended, and AWS A5.22 requires that filler metal producing greater than 20 ppm (0.002 wt %) of Bi in the weld metal indicate that fact on material test reports.

8. Welding Processes The austenitic stainless steels are most commonly ed by the welding processes of shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), flux cored arc welding (FCAW), gas metal arc welding (GMAW), and submerged arc welding (SAW). Other ing processes that are described in less detail in this guide are plasma arc welding (PAW), laser beam welding (LBW), electron beam welding (EBW), resistance welding, and brazing. 8.1 Shielded Metal Arc Welding (SMAW). The SMAW process, commonly referred to as “stick” welding, is a versatile, manual welding process frequently chosen because of the wide selection of electrode types, the availability of inexpensive welding equipment, and the ease in which welding cables can be routed to areas where other types of equipment cannot easily be used. Electrodes are produced in standard lengths ranging from 230 mm to 460 mm [9 in to 18 in] and standard electrode corewire diameters ranging from 1.6 mm to 6.4 mm [0.062 in to 0.25 in], although availability of 6.4 mm [0.25 in] is limited. The selection of the electrode diameter to use for a particular application is normally based on the welding position and base material thickness to be welded. Generally, the SMAW process can be used for ing base materials 1.5 mm [0.06 in] and thicker. Welding power sources for the SMAW process are normally manufactured as “constant current” power supplies as opposed to “constant voltage” power supplies. Because the process is manual and the arc length may vary slightly, the use of “constant current” power sources ensures that welding current remains constant even though the arc length and the resulting voltage can vary somewhat. AWS A5.4/A5.4M, Specification for Stainless Steel Electrodes for Shielded Metal Arc Welding, prescribes requirements for the classification of covered stainless steel electrodes for SMAW. The document classifies SMAW electrodes according to (1) Chemical composition of the undiluted weld metal (see Table 8.1) and by (2) Current type, suitable welding positions, and arc characteristics (see Table 8.3). Table 8.2 lists the minimum mechanical properties specified by AWS A5.4/A5.4M for SMAW electrodes. The annex of AWS A5.4/A5.4M is a useful guide to the application and use of the various electrode types. 28 Farrar,

J. C. M., A. W. Marshall, and Z, Zhang, 2001, Position statement on the effect of bismuth on the elevated temperature properties of flux cored stainless steel weldments. Welding in the World, V45, N5/6, pp. 25–31.

34

Table 8.1 Chemical Composition of Undiluted SMAW Weld Depositsa, b

35

UNS Numberd

C

Cr

Ni

Mo

Nb (Cb) plus Ta

Mn

Si

P

S

N

Cu

V

E209-XX

W32210

0.06

20.5–24.0

9.5–12.0

1.5–3.0

—

4.0–7.0

1.00

0.04

0.03

0.10–0.30

0.75

0.10–0.30

E219-XX

W32310

0.06

19.0–21.5

5.5–7.0

0.75

—

8.0–10.0

1.00

0.04

0.03

0.10–0.30

0.75

—

E240-XX

W32410

0.06

17.0–19.0

4.0–6.0

0.75

—

10.5–13.5

1.00

0.04

0.03

0.10–0.30

0.75

—

E307-XX

W30710

0.04–0.14

18.0–21.5

9.0–10.7

0.5–1.5

—

3.30–4.75

1.00

0.04

0.03

—

0.75

—

E308-XX

W30810

0.08

18.0–21.0

9.0–11.0

0.75

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E308H-XX

W30810

0.04–0.08

18.0–21.0

9.0–11.0

0.75

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E308L-XX

W30813

0.04

18.0–21.0

9.0–11.0

0.75

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E308Mo-XX

W30820

0.08

18.0–21.0

9.0–12.0

2.0–3.0

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E308LMo-XX

W30823

0.04

18.0–21.0

9.0–12.0

2.0–3.0

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E309-XX

W30910

0.15

22.0–25.0

12.0–14.0

0.75

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E309H-XX

W30910

0.04–0.15

22.0–25.0

12.0–14.0

0.75

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E309L-XX

W30913

0.04

22.0–25.0

12.0–14.0

0.75

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E309Nb-XXe

W30917

0.12

22.0–25.0

12.0–14.0

0.75

0.70–1.00

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E309Mo-XX

W30920

0.12

22.0–25.0

12.0–14.0

2.0–3.0

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E309LMo-XX

W30923

0.04

22.0–25.0

12.0 –14.0

2.0–3.0

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E310-XX

W31010

0.08–0.20

25.0–28.0

20.0–22.5

0.75

—

1.0–2.5

0.75

0.03

0.03

—

0.75

—

E310H-XX

W31015

0.35–0.45

25.0–28.0

20.0–22.5

0.75

—

1.0–2.5

0.75

0.03

0.03

—

0.75

—

E310Nb-XXe

W31017

0.12

25.0–28.0

20.0–22.0

0.75

0.70–1.00

1.0–2.5

0.75

0.03

0.03

—

0.75

—

E310Mo-XX

W31020

0.12

25.0–28.0

20.0–22.0

2.0–3.0

—

1.0–2.5

0.75

0.03

0.03

—

0.75

—

E312-XX

W31310

0.15

28.0–32.0

8.0–10.5

0.75

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E316-XX

W31610

0.08

17.0–20.0

11.0–14.0

2.0–3.0

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E316H-XX

W31610

0.04–0.08

17.0–20.0

11.0–14.0

2.0–3.0

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

(Continued)

AWS G2.3M/G2.3:2019

AWS Classificationc

UNS Numberd

C

Cr

Ni

Mo

Nb (Cb) plus Ta

Mn

Si

P

S

N

Cu

V

E316L-XX

W31613

0.04

17.0–20.0

11.0–14.0

2.0–3.0

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E316LMn-XX

W31622

0.04

18.0–21.0

15.0–18.0

2.5–3.5

—

5.0–8.0

0.90

0.04

0.03

0.10–0.25

0.75

—

E317-XX

W31710

0.08

18.0–21.0

12.0–14.0

3.0–4.0

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E317L-XX

W31713

0.04

18.0–21.0

12.0–14.0

3.0–4.0

—

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E318-XX

W31910

0.08

17.0–20.0

11.0–14.0

2.0–3.0

6 × C min. to 1.00 max.

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E320-XX

W88021

0.07

19.0–21.0

32.0–36.0

2.0–3.0

8 × C min. to 1.00 max.

0.5–2.5

0.60

0.04

0.03

—

3.0–4.0

—

E320LR-XX

W88022

0.03

19.0–21.0

32.0–36.0

2.0–3.0

8 × C min. to 0.40 max.

1.5–2.5

0.30

0.020

0.015

—

3.0–4.0

—

E330-XX

W88331

0.18–0.25

14.0–17.0

33.0–37.0

0.75

—

1.0–2.5

1.00

0.04

0.03

—

0.75

—

E330H-XX

W88335

0.35–0.45

14.0–17.0

33.0–37.0

0.75

—

1.0–2.5

1.00

0.04

0.03

—

0.75

—

E347-XX

W34710

0.08

18.0–21.0

9.0–11.0

0.75

8 × C min. to 1.00 max.

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E349-XXf

W34910

0.13

18.0–21.0

8.0–10.0

0.35–0.65

0.75–1.20

0.5–2.5

1.00

0.04

0.03

—

0.75

—

E383-XX

W88028

0.03

26.5–29.0

30.0–33.0

3.2–4.2

—

0.5–2.5

0.90

0.02

0.02

—

0.6–1.5

—

E385-XX

W88904

0.03

19.5–21.5

24.0–26.0

4.2–5.2

—

1.0–2.5

0.90

0.03

0.02

—

1.2–2.0

—

E16-8-2-XX

W36810

0.10

14.5–16.5

7.5–9.5

1.0–2.0

—

0.5–2.5

0.60

0.03

0.03

—

0.75

—

E2209-XX

W39209

0.04

21.5–23.5

8.5–10.5

2.5–3.5

—

0.5–2.0

1.00

0.04

0.03

0.08–0.20

0.75

—

36

AWS Classificationc

a

Single values are maximum percentages. Analysis for Bi is required only if intentionally added or known to be present at levels greater than 0.002%. c The AWS Classification suffix (-XX) may be -15, -16, -17, or -26 (see Table 8.3). e E309Nb and E310Nb were formerly named E309Cb and E310Cb. The change was made to conform to the worldwide uniform designation of the element niobium. d SAE HS-1086, Metals & Alloys in the Unified Numbering System. f 0.10% to 0.30% vanadium, 0.15% titanium, 1.25% to 1.75% tungsten. b

Source: Adapted from AWS A5.4/A5.4M:2012, Specification for Stainless Steel Electrodes for Shielded Metal Arc Welding, Table 1, American Welding Society.

AWS G2.3M/G2.3:2019

Table 8.1 (Continued) Chemical Composition of Undiluted SMAW Weld Depositsa, b

AWS G2.3M/G2.3:2019

Table 8.2 All-Weld-Metal Mechanical Property Requirements Undiluted SMAW Weld Deposits (AWS A5.4/A5.4M) Tensile Strength, Min. Classification

MPa

ksi

Elongation Min. %

E209-XX

690

100

15

E219-XX

620

90

15

E240-XX

690

100

15

E307-XX

590

85

30

E308-XX

550

80

35

E308H-XX

550

80

35

E308L-XX

520

75

35

E308Mo-XX

550

80

35

E308LMo-XX

520

75

35

E309-XX

550

80

30

E309H-XX

550

80

30

E309L-XX

520

75

30

E309Nb-XX

550

80

30

E309Mo-XX

550

80

30

E309LMo-XX

520

75

30

E310-XX

550

80

30

E310H-XX

620

90

10

E310Nb-XX

550

80

25

E310Mo-XX

550

80

30

E312-XX

660

95

22

E316-XX

520

75

30

E316H-XX

520

75

30

E316L-XX

490

70

30

E316LMn-XX

550

80

20

E317-XX

550

80

30

E317L-XX

520

75

30

E318-XX

550

80

25

E320-XX

550

80

30

E320LR-XX

520

75

30

E330-XX

520

75

25

E330H-XX

620

90

10

E347-XX

520

75

30

E349-XX

690

100

25

E383-XX

520

75

30

E385-XX

520

75

30

E16-8-2-XX

550

80

35

E2209-XX

690

100

20

Note: Minimum mechanical properties specified by AWS A5.4/A5.4M:2012 for SMAW electrode deposits.

37

AWS G2.3M/G2.3:2019

Table 8.3 SMAW Electrodes: Welding Current, Position of Welding, and Operating Characteristics AWS Classification AWS A5.4/A5.4Ma

Welding Currentb

Welding Positionb

Notes

EXXX(X)-15

DCEP

All

a1, c

EXXX(X)-16

DCEP or AC

All

a2, c

EXXX(X)-17

DCEP or AC

All

a3, c

EXXX(X)-26

DCEP or AC

H, F (fillet welding)

a4

a

AWS SMAW electrode classifications include one of four different usability designations (e.g., -15, -16, -17, or -26) to define the electrode's general operability characteristics. 1. A -15 designation describes electrodes generally produced with a “basic” flux coating type consisting of lime and fluorspar. This type of coating generally produces a convex bead shape and consequently helps minimize weld metal solidification cracking when there is insufficient ferrite. -15 coatings are generally considered to produce higher Charpy impact “toughness” of all the flux coating types. The -15 electrodes have the easiest out of position welding characteristics of the different coating types. 2. A -16 designation describes electrodes that tend to produce a slightly convex fillet weld bead shape, with slightly improved surface appearance, spatter level, and slag removal than -15 coatings. 3. A -17 designation describes electrodes that tend to produce more of a spray arc and a finer rippled weld-bead surface than -16 coated electrodes. The -17 electrodes tend to produce a flat to slightly concave fillet weld bead shape. The slower freezing slag of -17 electrodes compared to -16 electrodes permits improved handling when employing a drag technique. Vertical position welding requires a slight weave technique to produce the proper bead shape. 4. A -26 designation describes electrodes with heavier flux coatings that tend to produce fillet welds that are flat to concave. The -26 electrodes are recommended for flat and horizontal fillet positions only. b Abbreviations: DCEP = direct current electrode positive; AC = alternating current; H = horizontal; F = flat. c Electrode sizes 4.8 mm [3/16 in] and larger are not recommended for vertical or overhead welding. Source: Adapted from A5.4/A5.4M:2012, Specification for Stainless Steel Electrodes for Shielded Metal Arc Welding, Table 2, American Welding Society.

Tables 8.10 and 8.11 of this document provide chemical composition and mechanical property requirements for nickelbased welding consumables indicated herein for welding austenitic stainless steels. While composition of the flux is not specified by AWS, the usability of an electrode is determined by the composition of the flux covering. The flux composition ultimately determines how the electrode operates (e.g., electrode arc characteristics) the optimum electrical welding current and the optimum welding position(s) for the electrode. Operating characteristics can vary significantly when comparing different brands of electrodes even with the same AWS and usability classification. The optimum current range can vary from brand to brand. Voltage, while not usually adjustable for the SMAW process, can also vary from one brand to another and from one usability designation to another. This can be an important consideration when the heat input must be controlled during production. Operator appeal and electrode performance trials may be performed to compare brands or other various factors such as arc starting characteristics, fume generation, out-of-position welding characteristics, the amount and adherence of spatter, ease of slag removal, bead appearance, porosity, cracking tendencies, operator preference, etc. Each electrode diameter and usability classification has an optimum current range that produces appropriate arc characteristics when operated using the specified electrical polarity. Outside of the range, the arc can become unstable, or the electrode may overheat, or both. Some approximate current settings for flat position welding are shown in Table 8.4. Slight reductions in current from the values shown are necessary for overhead welding, while vertical welding typically requires 10% to 15% less current compared to flat position welding. Note that not all usability classifications are suitable for out-of-position welding. Some manufacturers list the appropriate operating current range on their electrode containers, product catalogs, and internet web sites. Selection of an electrode for a specific application is commonly based on “matching composition” criteria, where the weld composition needs to closely approximate the base metal composition; Tables A.1, A.2, and A.3 in this document list the recommended electrode for a specific base material type. The should also that the desired electrode

38

AWS G2.3M/G2.3:2019

Table 8.4 SMAW Electrodes, Suggested Current Ranges for E3xx-15, -16, and -17 Type Electrodesa Electrode Diameter

a

mm

in

Operating Range

1.6

1/16

20–40

2

5/64

30–50

2.5

3/32

50–80

3.2

1/8

60–110

4

5/32

90–150

5

3/16

130–190

6.4

1/4

200–300

Welding current may be significantly higher for electrodes with a usability designation of -26 listed in AWS A5.4/A5.4M.

Notes: 1. Listed ranges are approximate. Flat and horizontal fillets are typically operated at the high end of the range. Vertical (upward progression) welds are typically operated at the low end of the range. Overhead welds are typically made at mid to the high end of the suggested range. When burnthrough is a concern on thin base materials, smaller diameter electrodes are preferred as well as maintaining the current at the low end of the range for a given electrode size as well as maintaining a short arc length. 2. Optimum operating current can vary significantly for a given electrode size depending on the flux coating type and manufacturer's brand. 3. Voltage is not usually deliberately controlled or monitored when welding with the SMAW process except when fabrication codes require control of heat input to ensure weld toughness. Voltage is primarily determined by arc length. Short arc length practice is preferred.

can be operated on the available equipment. For example, electrodes with a “usability” designation of E3xx-15 are designed to operate on direct current electrode positive (DCEP), but not alternating current (AC). If the available power supply is strictly AC, an electrode classification ending with a -16, -17, or -26 should be selected. Prior to use, electrodes should be left in their original sealed, moisture-proof containers in a dry storage area. A survey of several electrode manufacturers recommended that electrodes from opened containers be stored in a rod oven at a minimum temperature of approximately 110°C [225°F] to prevent moisture pickup in the coating. A maximum holding temperature of 120°C to 215°C [250°F to 420°F] was recommended depending on the manufacturer and the electrode type. AWS D1.6/D1.6M, Structural Welding Code—Stainless Steel, specifies a holding temperature of 120°C to 150°C [250°F to 300°F] for stainless steel SMAW electrodes from opened containers. Hydrogen cracking due to excessive moisture is normally not a concern for austenitic stainless steel alloys; however, moist electrodes may result in weld porosity or poor operating characteristics that may lead to other types of weld discontinuities such as lack of fusion or excessive spatter. Electrodes that have absorbed moisture can be reclaimed by baking in accordance with the electrode manufacturer’s recommendations. 8.1.1 General SMAW Recommendations. SMAW welding techniques are similar to those of the low-hydrogen type carbon steel electrodes such as E7018, except that the E3XX electrodes operate with a slightly less fluid weld pool than E7018. Use of a close arc helps ensure adequate protective gas/fume coverage of the weld pool. A short arc length also helps to minimize spatter, arc wander, and electrode overheating. Increasing the current beyond the manufacturer’s recommended operating range for the particular size of electrode to increase penetration or to compensate for the lack of fluidity is not recommended. The E3XX electrodes can overheat more easily than an E7018 electrode because of the fact that E3XX electrodes have an approximate 600% greater electrical resistivity than a carbon steel electrode. Overheating of electrodes as a result of excessive current can result in an electrode stub loss of up to 33% because the final one-third of each electrode may be unusable—resulting in significantly greater electrode costs and increased welding time. Defect-free welds are best achieved by proper weld t design, weld bead placement, and electrode manipulation. Weld beads should be properly “stacked” to avoid tight crevices between weld beads and layers. Weave widths are commonly

39

AWS G2.3M/G2.3:2019

restricted to a maximum of three times (3x) the electrode core wire diameter to minimize welding over solidified slag. Weld deposits in grooves should be flat or slightly convex, with the end craters filled to help minimize weld cracking. Slag should be chipped off between weld es and layers before depositing another . 8.2 Gas Tungsten Arc Welding (GTAW) 8.2.1 GTAW General Description. The GTAW process, commonly referred to as “TIG” (tungsten inert gas) welding (a nonstandard term), is a versatile all-position welding process used for production and repair welding. It can be used manually or adapted to automatic equipment and is applicable for ing both thin sheet and plate materials. In the hands of a skilled welder, the process can provide excellent weld bead appearance and, in many instances, post-weld finishing operations are not required. The welding process is frequently chosen because of the wide selection of filler metal types and the ability to produce clean, slag-free welds on materials 0.75 mm [0.030 in] thick and greater. Materials thinner than 0.75 mm [0.030 in] can be welded using special equipment or techniques. Specific welding power sources can provide very stable, low current levels required for welding thin sheet metals. Manual welding of thin sheet metals generally requires greater skill than for welding thicker materials. For manual welding operations, GTAW deposition rates are comparatively low when compared to other welding processes. In many situations, however, GTAW is used for quality reasons. For example, root es in critical pipe welds are frequently made using the GTAW process because welds are slag, spatter, and “whisker” free; and, complete t penetration (CJP) can be easily achieved. The GTAW process uses a nonconsumable tungsten-alloy electrode in a torch body. An arc is struck between the electrode and the base material being welded. The tungsten electrode and the molten weld pool are shielded from the atmosphere with a protective, inert shielding gas such as argon. AWS C5.5/C5.5M, Recommended Practices for Gas Tungsten Arc Welding, is a highly recommended reference covering all aspects of the GTAW process. Any of the tungsten alloy electrodes such as thoriated, lanthanated, ceriated, or zirconiated may be used for welding stainless steels. Certain electrode manufacturers also produce proprietary grades of tungsten-alloy electrodes. AWS A5.12M/A5.12 (ISO 6848:2004 MOD), Specification for Tungsten and Oxide Dispersed Tungsten Electrodes for Arc Welding and Cutting, governs the manufacture and identification of the different types of tungsten welding electrodes. The specification also describes the operating characteristics, benefits, limitations, and safety concerns of the various tungsten electrodes. s of the electrodes have observed operating characteristic differences when comparing different batches (heats) of the same electrode classification, even if the different electrode batches were produced by the same manufacturer. One significant quality difference is the ability of an electrode to remain sharp without forming whiskers. Noticeable quality differences between electrode manufacturers are not uncommon; brand comparisons are advisable. Tungsten-alloy electrodes are generally ground to a conical shape with an included angle ranging from 30° for 2.4 mm [3/32 in] diameter electrodes to 60° for 3.2 mm [1/8 in] diameter electrodes with a small flat 0.8 mm to 1.5 mm [0.03 in to 0.06 in] ground at the point. GTAW power supplies are preferably equipped with high frequency or “lift-start” technology, pre- and post-purge shielding gas controls, and upslope/downslope (or foot pedal) controls. Without high frequency or “lift-start” controls, “scratch” starting is required which can result in electrode and weld metal contamination. The GTAW welding torch should be equipped with a gas cup size that is adequate to protect the size of the weld pool. A gas diff screen (gas lens) may be used to reduce turbulence of the shielding gas coverage. The protective shielding gas atmosphere can be disrupted by drafts, fans, or generators, excessive tungsten electrode stickout, or excessive torch angles relative to the workpiece. Lack of proper shielding can cause porosity, excessive oxide formation, electrode and weld metal contamination, shallow penetration, poor arc starting, or poor weld metal fluidity. 8.2.2 GTAW Parameters and Welding Techniques. A consistent, close arc length is important especially on thin sheet metals. Electrical current and polarity for welding stainless steels is almost always direct current electrode negative (DCEN), except when occasionally welding very thin sheet materials. In this case, direct current electrode positive (DCEP) or an alternating current (AC) is sometimes used to reduce weld penetration. Pulsing electrical current is used in applications where greater control of melt-through characteristics is desired or in orbital type welding applications for better control of the weld bead solidification characteristics for out of position welding. Suggested amperage limits for GTAW tungsten alloy electrodes are given in Table 8.5. Weld penetration dependence upon electrode geometry, arc length, base metal sulfur content, welding speed, arc energy, shielding gas composition, and welding position are summarized in the Welding Journal research supplement entitled

40

AWS G2.3M/G2.3:2019

Table 8.5 Tungsten Amperage Limits, GTAW Tungsten Diameter mm [in]

Max. Amperage

0.30 [0.010]

15

0.50 [0.020]

20

1.00 [0.040]

75

1.60 [0.060 (1/16)]

150

2.40 [0.093 (3/32)]

250

3.2 [0.125 (1/8)]

330

Source: Adapted from AWS A5.12M/A5.12:2009 (ISO 6848-2004 MOD), Specification for Tungsten and Oxide Dispersed Tungsten Electrodes for Arc Welding and Cutting, American Welding Society.

“The Effect of Welding Parameters on Penetration in GTA Welds.”29 Methods to ensure uniform weld penetration and weld profiles (i.e., the use of optimized weld procedures) on varying heats and varying levels of residual elements of 300 series base materials are discussed in the Welding Journal.30 Stringer bead techniques or narrow weave techniques are recommended for manual operations. Stringer, weave, or arc oscillation methods can be used in mechanized operations. Mechanized operations can be established with or without automatic filler metal feed using spooled filler metal. Mechanization is most often used to increase production (e.g., deposition rates) or to improve weld quality. Mechanized GTAW welding using unheated filler metal additions is termed as “cold-wire” automatic GTAW. Filler metal additions for “cold-wire” automatic GTAW welding are typically at the front of the weld pool. In order to increase deposition rates over “cold-wire” applications, the filler metal may be resistance heated (I2R) to near its melting point using alternating current (AC) immediately before feeding the filler metal into the weld pool. Consequently, most of the arc energy can be used to melt the weld zone base metal and very little of the welding arc energy is needed to melt the filler metal. Less total arc energy is needed resulting in a more efficient process. Very high deposition rates (5 kg/h to 8 kg/h [10 lb/h to 18 lb/h]) are possible with hot-wire welding. Filler metal additions for “hot-wire” automatic GTAW welding are typically at the rear of the weld pool. Automatic voltage-sensing equipment is needed to control the welding operation.31 Welding equipment manufacturers should be ed for more detailed information on cold- or hot-wire applications. For automated welding and corrosion resistant overlay welding hot wire GTAW can improve the deposition rates, increasing productivity. Square wave pulsed current is used for mechanized applications to lower heat input. To avoid the distortion of thin sheet metal when performing manual GTAW welding, minimal current and low heat input is typically used, combined with weld bead sequencing techniques (e.g., by applying welds in a backstep sequence or intermittent welding), clamping, and fixturing whenever possible. Small diameter tungsten electrodes (2.4 mm [3/32 in] and less) are normally recommended. Small diameter filler metals (1.6 mm [1/16 in] diameter and less) are also recommended as less welding current is needed for melting the filler metal. If large diameter filler metals are used, the current needed to melt the filler metal is excessive for the base material and can easily result in excessive burn-through. The use 29 Mills,

K. C. and A. A. Shirali, 1993, The Effect of Welding Parameters on Penetration in GTA Welds, Welding Journal 72(7): 347. J. A., 1991, Cast-to-Cast Variability in Stainless Steel Mechanized GTA Welds, Welding Journal 70(5): 41. 31 The Lincoln Electric Company, 1994, 13th ed., The Procedure Handbook of Arc Welding: 7.5.3. 30 Lambert,

41

AWS G2.3M/G2.3:2019

of a short arc length (2.4 mm [3/32 in] or less) is also critical. The close arc length concentrates the arc in the weld t area instead of allowing the arc to spread out if longer arc lengths are used. Weld bead sizes should also be kept to a minimum to minimize distortion when welding sheet metals. 8.2.3 GTAW Shielding Gases. Argon shielding gas produced and classified in accordance with AWS A5.32M/A5.32 (ISO 14175:2008) MOD) has a minimum purity of 99.99% with a maximum dew point temperature of –50°C [–58°F] and a moisture content of 40 ppm max. moisture (volume) content.32 Flow rates vary with cup sizes but are normally in the 12 L/min [25 CFH] range for a number 8 cup size. See Table 8.6 for recommended shielding gas flow rates versus gas cup size, with or without shielding lens and Table 8.7 for the recommended gas cup size versus welding current. Shielding gas flow rates need to be controlled to ensure quality welds. Low flow rates will not properly shield the molten weld pool, while excessively high flow rates can cause turbulence and aspirate air into the gas shield, causing weld pool contamination. Helium, argon-helium, or argon-hydrogen shielding gas mixtures are frequently used in automated high speed GTAW welding operations or when trying to achieve greater penetration (see Table 8.8 for guidance in shielding gas selection). 32 AWS

A5.32M/A5.32:2011 (ISO 14175:2008 MOD), Welding Consumables—Gases and Gas Mixtures for Fusion Welding and Allied Processes.

Table 8.6 Suggested Argon Torch Flow Rates, Manual GTAW Flow Rate L/min [ft3/hr] With or without Gas Lens

Gas Nozzle Size

Number

I.D. mm [in]

Min.

Max.

4

6 [1/4]

3 [5]

5 [10]

6

10 [3/8]

5 [10]

10 [20]

8

13 [1/2]

8 [15]

13 [25]

10

16 [5/8]

10 [20]

15 [30]

Source: Adapted from M. Shaw, 1997, Practical Guide to Gas Flow Rates for GTA Welding, Welding Journal 76(4): 75.

Table 8.7 Suggested Gas Cup Size versus Maximum Welding Current, Manual GTAW Maximum Current

Minimum Cup Size mm [in]

100

6 [1/4]

150

10 [3/8]

200

13 [1/2]

300

16 [5/8]

42

AWS G2.3M/G2.3:2019

Table 8.8 GTAW (TIG) Shielding Gas Selection Shielding Gas

Comments

Argon

Most common shielding gas used for GTAW. Can be used in manual or mechanized operations. Also used for purge/backing gas.a

Argon + (2%–15%) Hydrogen

Hydrogen additions are generally limited to 10% max. to minimize arc starting problems although up to 35% has been used. H2 improves wetting and can provide cleaner welds and allow increased welding speeds. For manual welding, an H2 content of 2%–5% is sometimes used (especially 5%). 10 H2% is commonly used for mechanized welding of sheet metal & tubing for increased weld speeds, reduced undercutting, and improved weld contour at low current levels. 15% H2 has been used but arc starting problems occur with this composition. Hydrogen additions increase penetration and depth-to-width ratio due to increased arc resistance. There can be a positive influence on corrosion resistance when used as a backing gas. Hydrogen additions do not lead to hydrogen induced cracking.b, c, d, e, f, g, h

(75%–80%) Helium + (20%–25%) Argon

Primarily for mechanized welding for higher welding speeds and superior bead shape that reduces the risk of undercutting. 75% He-25% Ar (SG-AHe-25) is used in mechanized hot wire GTAW. Helium-rich gases can reduce the variation in weld bead penetration arising from compositional differences in material casts or heats.i

Helium

Primarily for mechanized welding when speed is important on “thicker” base materials because of greater arc voltage and resultant increased heat input at equivalent current compared to argon. Helium requires greater flow rates and is more expensive than argon.a, c

Argon + (0.02%–1.0%) Nitrogen

N2 addition can enhance arc starting ability and weld penetration during mechanized welding.

Nitrogen

Not used as primary shielding gas. Generally acceptable as a purge/backing gas for nonstabilized grades. Some risk of reduction in weld metal ferrite for open-root ts. There is a positive influence on improving pitting resistance when used as a backing gas.a, b, j, k

a

Young, B., 1995, Shielding and Purging Gases: Making the Right Selection, Welding Journal 74(1): 47–49. Irving, B., January 1999, Shielding Gases are the Key to Innovations in Welding, Welding Journal 78(1): 40. c O’Brien, R. L., ed., 1991, Welding Processes, AWS Welding Handbook, 8th ed., Vol. 2, p. 89. d Lyttle, K., 1993, ASM Handbook, 10th ed., Shielding Gases, pp. 67–68. e Larson, N., and W. Meredith, 1998, Linde’s Shielding Gas Selection Manual, p. 15. f Castner, H. R., 1993, What You Should Know About Austenitic Stainless Steels, Welding Journal 72(4): 56. “Additions of helium or hydrogen to argon have been found to be effective in overcoming variable penetration. Ar +5%H2 is very effective.” g Onsoien, M., R. Peters, D. Olson, and S. Liu, 1995, Effect of Hydrogen in an Argon GTAW Shielding Gas: Arc Characteristics and Bead Morphology, Welding Journal 74(1): 10. h Louthan Jr., M., 2005, Impact of H in Shielding Gas for Welding Austenitic Stainless Steels, Welding Journal 84(4): 38–42. 2 i Lucas, W., June 1992, Shielding Gases for Arc Welding, Welding & Metal Fabrication: 220–221. j Saggau, R., H. Pries, and K. Dilger, No. 1, 2005, Corrosion on Stainless-Steel Components as a Result of Temper Colors, Welding & Cutting 4. k Shirwaikar, C. and G. P. Reddy, 1975, Purging with Nitrogen in the Welding of Austenitic Stainless Steels, Welding Journal 54(1): 12. b

When using helium, it should be noted that the arc voltage for a given arc length is approximately 40% greater and as a result, heat input is greater. Adding “hydrogen to argon or helium gives an arc a wider temperature distribution, a larger heat input and a slightly reducing atmosphere, and that hydrogen additions to the argon shielding gas during GTA welding can achieve increases in penetration over fifty percent.”33 Root welding and inert gas purging recommendations are discussed in 6.7 and 6.7.1 of this document. 33 Onsoein, M., R. Peters, D. L. Olson, and S. Liu, 1995, Effect of Hydrogen in an Argon GTAW Shielding Gas: Arc Characteristics and Bead Morphology, Welding Journal 74(1): 10-s.

43

AWS G2.3M/G2.3:2019

8.2.4 Filler Metals for the GTAW Process. AWS A5.9/A5.9M, Specification for Bare Stainless Steel Welding Electrodes and Rods, prescribes requirements for the classification of bare electrodes and rods that are used with the GTAW process and other processes. It classifies the filler metals only according to chemical composition and includes filler metals used for ing various types of stainless steels such as austenitics, martensitics, and duplex stainless steels. Annex A of AWS A5.9/A5.9M is a useful guide for the purchase and intended use of the filler metals. The annex also discusses ferrite determination and controls for the different filler metal classifications. Tables A.1, A.2, and A.3 in this document list the recommended filler metal selections for welding austenitic base materials. See Table 8.9 for the chemical composition limits of the bare stainless steel welding electrodes and rods. Tables 8.10 and 8.11 of this document provide chemical composition and mechanical property requirements for nickelbased welding consumables indicated herein for welding austenitic stainless steels. AWS A5.22/A5.22M, Specification for Stainless Steel Flux Cored and Metal Cored Welding Electrodes and Rods, prescribes in part, requirements for the classification of flux-cored filler rods that can be used with the GTAW process. It classifies the GTAW filler rods according to welding position, shielding gas, and chemical composition. The flux-cored filler rods are most often used in root applications where the use of a backing gas is not possible or when purging is difficult. The use of the rods may be unacceptable in some corrosive environments or where damage to downstream equipment is a concern if the slag cannot be completely removed from the root face. Also, when a backing purge is omitted, the weld HAZ will develop a heat tint oxide that reduces corrosion resistance in some environments. Annex A of AWS A5.22/A5.22M is a useful guide for the purchase and intended use of the filler rods. The annex also discusses ferrite determination and controls for the different filler metal classifications. 8.3 Gas Metal Arc Welding (GMAW). The GMAW process, commonly referred to as “MIG” (metal inert gas) welding (a nonstandard term), uses a spooled wire electrode that is continuously fed into an arc created between the electrode and the weld pool. Shielding gas is required to protect the weld pool from atmospheric contaminants. The electrode is consumed continuously as it is fed into the arc. Electrodes are produced as either a solid alloy wire or by adding powdered alloy elements in the core of a tubular metal sheath. Cored electrodes used with the GMAW process do not have fluxing agents in contrast to the flux-cored electrodes used with the FCAW process. The use of constant voltage equipment allows the voltage and arc length to remain relatively constant for reasonable adjustments to wire feed speed. The GMAW process is normally operated on direct current electrode positive (DCEP). The GMAW process can be set up either as semiautomatic or fully automatic. Welding operations utilizing currents in excess of 400 amperes (A) may require the use of water cooled guns to avoid overheating. Welding guns in tandem are used to increase deposition rates. A wide variety of GMAW electrodes are available for welding the austenitic stainless steels. AWS A5.9/A5.9M classifies the electrodes according to chemical composition only. Annex A of the specification is a useful guide for the purchase and intended use of the filler metals. The annex also discusses ferrite determination and controls for the different electrode types. See Table 8.9 for chemical composition limits of bare stainless steel welding electrodes and rods. There are three possible types of arc transfer modes with the GMAW process: short circuiting transfer, spray transfer, and globular transfer. Pulsed spray transfer is a variation of spray transfer. 8.3.1 Short Circuiting Transfer. Short circuiting transfer, i.e., short arc, is a low heat input GMAW welding application that typically exhibits shallow penetration with relatively low deposition rates. The filler metal is transferred to the weld zone by direct when the electrode, with an attached molten droplet of filler metal, short circuits against the material. Short circuiting transfer is frequently used for welding sheet metal from 0.60 mm to 3.60 mm [0.025 in to 0.145 in] where shallow penetration is desirable to avoid excessive burn-through. Short circuiting transfer is also frequently used for the welding of root es in complete t penetration (CJP), open root, and single- or double-welded ts. Because of the low heat input of the short circuiting transfer process, the process can be used in the vertical, horizontal, and overhead positions. CJP welds made with the process may be restricted from being used in certain applications because of the shallow penetration characteristics and the chance of unfused “whiskers” poking through on the backside of single-welded ts. Whiskers may be the source of corrosion or cause downstream mechanical failure if they break off in the process stream of specific process applications. Electrodes with a diameter of 1.1 mm [0.045 in] or less are typically used in most short circuiting transfer applications. Electrodes 0.9 mm [0.035 in] in diameter and smaller are preferable for welding thin sheet metals.

44

Table 8.9 Chemical Compositions of Bare Stainless Steel Filler Metalsa (AWS A5.9/A5.9M) and of Metal Cored Filler Metal Deposits (AWS A5.22/A5.22M) Composition, wt %b, c, d AWS UNS Classificationd Numbere

C

Cr

Ni

Mo

Mn

Sif

P

S

N

Cu

Element

Amount

ER209

S20980

0.05

20.5–24.0

9.5–12.0

1.5–3.0

4.0–7.0

0.90

0.03

0.03

0.10–0.30

0.75

V

0.10–0.30

ER218

S21880

0.10

16.0–18.0

8.0–9.0

0.75

7.0–9.0

3.5–4.5

0.03

0.03

0.08–0.18

0.75

—

—

ER219

S21980

0.05

19.0–21.5

5.5–7.0

0.75

8.0–10.0

1.00

0.03

0.03

0.10–0.30

0.75

—

—

ER240

S24080

0.05

17.0–19.0

4.0–6.0

0.75

10.5–13.5

1.00

0.03

0.03

0.10–0.30

0.75

—

—

ER307

S30780

0.04–0.14

19.5–22.0

8.0–10.7

0.5–1.5

3.30–4.75

0.30–0.65

0.03

0.03

—

0.75

—

—

45

ER308

S30880

0.08

19.5–22.0

9.0–11.0

0.75

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER308Si

S30881

0.08

19.5–22.0

9.0–11.0

0.75

1.0–2.5

0.65–1.00

0.03

0.03

—

0.75

—

—

ER308H

S30880

0.04–0.08

19.5–22.0

9.0–11.0

0.50

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER308L

S30883

0.03

19.5–22.0

9.0–11.0

0.75

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER308LSi

S30888

0.03

19.5–22.0

9.0–11.0

0.75

1.0–2.5

0.65–1.00

0.03

0.03

—

0.75

—

—

ER308Mo

S30882

0.08

18.0–21.0

9.0–12.0

2.0–3.0

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER308LMo

S30886

0.04

18.0–21.0

9.0–12.0

2.0–3.0

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER309

S30980

0.12

23.0–25.0

12.0–14.0

0.75

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

S30981

0.12

23.0–25.0

12.0–14.0

0.75

1.0–2.5

0.65–1.00

0.03

0.03

—

0.75

—

—

S30983

0.03

23.0–25.0

12.0–14.0

0.75

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER309LSi

S30988

0.03

23.0–25.0

12.0–14.0

0.75

1.0–2.5

0.65–1.00

0.03

0.03

—

0.75

—

—

ER309Mo

S30982

0.12

23.0–25.0

12.0–14.0

2.0–3.0

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER309LMo

S30986

0.03

23.0–25.0

12.0–14.0

2.0–3.0

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER310

S31080

0.08–0.15

25.0–28.0

20.0–22.5

0.75

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER312

S31380

0.15

28.0–32.0

8.0–10.5

0.75

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER316

S31680

0.08

18.0–20.0

11.0–14.0

2.0–3.0

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER316Si

S31681

0.08

18.0–20.0

11.0–14.0

2.0–3.0

1.0–2.5

0.65–1.00

0.03

0.03

—

0.75

—

—

ER316H

S31680

0.04–0.08

18.0–20.0

11.0–14.0

2.0–3.0

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER316L

S31683

0.03

18.0–20.0

11.0–14.0

2.0–3.0

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER316LSi

S31688

0.03

18.0–20.0

11.0–14.0

2.0–3.0

1.0–2.5

0.65–1.00

0.03

0.03

—

0.75

—

—

(Continued)

AWS G2.3M/G2.3:2019

ER309Si ER309L

Composition, wt %b, c, d AWS UNS Classificationd Numbere

C

Cr

Ni

Mo

Mn

Sif

P

S

N

Cu

Element

Amount

ER316LMn

S31682

0.03

19.0–22.0

15.0–18.0

2.5–3.5

5.0–9.0

0.30–0.65

0.03

0.03

0.10–0.20

0.75

—

—

ER317

S31780

0.08

18.5–20.5

13.0–15.0

3.0–4.0

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER317L

S31783

0.03

18.5–20.5

13.0–15.0

3.0–4.0

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

ER318

S31980

0.08

18.0–20.0

11.0–14.0

2.0–3.0

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

Nbg

8 × C min./1.0 max.

ER320

N08021

0.07

19.0–21.0

32.0–36.0

2.0–3.0

2.5

0.60

0.03

0.03

—

3.0–4.0

Nbg

8 × C min./1.0 max. 8 × C min./0.40 max.

ER320LR

N08022

0.025

19.0–21.0

32.0–36.0

2.0–3.0

1.5–2.0

0.15

0.015

0.02

—

3.0–4.0

Nbg

ER321

S32180

0.08

18.5–20.5

9.0–10.5

0.75

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

Ti

9 × C min./1.0 max.

ER330

N08331

0.18–0.25

15.0–17.0

34.0–37.0

0.75

1.0–2.5

0.30–0.65

0.03

0.03

—

0.75

—

—

0.75

Nbg

10 × C min./1.0 max.

—

0.75

Nbg

10 × C min./1.0 max.

ER347

46

ER347Si

S34780 S34788

0.08 0.08

19.0–21.5 19.0–21.5

9.0–11.0 9.0–11.0

0.75

1.0–2.5

0.30–0.65

0.03

0.75

1.0–2.5

0.65–1.00

0.03

0.03 0.03

—

ER383

N08028

0.025

26.5–28.5

30.0–33.0

3.2–4.2

1.0–2.5

0.50

0.02

0.03

—

0.70–1.50

—

—

ER385

N08904

0.025

19.5–21.5

24.0–26.0

4.2–5.2

1.0–2.5

0.50

0.02

0.03

—

1.2–2.0

—

—

ER2209

S39209

0.03

21.5–23.5

7.5–9.5

2.5–3.5

0.50–2.00

0.90

0.03

0.03

0.08–0.20

0.75

—

—

Nbg

0.05

Ti

0.05

—

—

W

2.0–3.5

ER19–10H

S30480

0.04–0.08

18.5–20.0

9.0–11.0

0.25

1.0–2.0

0.30–0.65

0.03

0.03

—

0.75

ER16–8–2

S16880

0.10

14.5–16.5

7.5–9.5

1.0–2.0

1.0–2.0

0.30–0.65

0.03

0.03

—

0.75

a

Ferritic and martensitic grades are not included in this table. Only austenitic grades and occasionally duplex grades used for welding austenitics are reported herein. For classification of the electrode, AWS A5.9/A5.9M requires that if analysis is made by the electrode producer for elements not required by the table, then the total of those elements, excluding iron, must not exceed 0.50%. c Single values shown are maximum percentages. d In the designator for composite, stranded, and strip electrodes, the “R” is deleted, and in its place the designator “C” is used for composite and stranded electrodes and the designator “Q” is used for strip electrodes. For example, ERXXX designates a solid wire and EQXXX designates a strip electrode of the same general analysis and the same UNS number. However, ECXXX designates a composite metal-cored or stranded electrode and may not have the same UNS number. The requirements for metal cored electrodes were added to AWS A5.22/A5.22M:2010, Specification for Stainless Steel Flux Cored and Metal Cored Welding Electrodes and Rods. e SAE HS-1086, Metals & Alloys in the Unified Numbering System. f For special applications, electrodes and rods may be purchased with less than specified silicon content. g Nb may be reported as Nb + Ta. b

Source: Adapted from AWS A5.9/A5.9M:2012, Specification for Bare Stainless Steel Welding Electrodes and Rods, Table 1, American Welding Society.

AWS G2.3M/G2.3:2019

Table 8.9 (Continued) Chemical Compositions of Bare Stainless Steel Filler Metalsa (AWS A5.9/A5.9M) and of Metal Cored Filler Metal Deposits (AWS A5.22/A5.22M)

Table 8.10 Nickel-Based Consumables, Chemical Composition Rangesa C

Ni

Cr

Mo

Co

W

Nb (Cb) plus Ta

Mn

Si

Fe

Cu/Other

P

S

ENiCrFe-2b

W86133

0.10

62.0 min.

13.0–17.0

0.5–2.5

—

—

0.5–3.0

1.0–3.5

0.75

12.0

0.50

0.03

0.02

ENiCrFe-3b

W86182

0.10

59.0 min.

13.0–17.0

—

—

—

1.0–2.5

5.0–9.5

1.0

10.0

0.50

0.03

0.015

ERNiCr-3b

N06082

0.10

67.0 min.

18.0–22.0

—

—

—

2.0–3.0

2.5–3.5

0.50

3.0

0.50 Ti: 0.75

0.03

0.015

ENiCrMo-3

W86112

0.10

55.0 min.

20.0–23.0

8.0–10.0

—

—

3.15–4.15

1.0

0.75

7.0

0.50

0.03

0.02

ERNiCrMo-3b

N06625

0.10

58.0 min.

20.0–23.0

8.0–10.0

—

—

3.15–4.15

0.50

0.50

5.0

0.50 Al: 0.40 Ti: 0.40

0.02

0.015

ENiCrMo-4

W80276

0.02

Rem.

14.5–16.5

15.0–17.0

2.5

3.0–4.5

—

1.0

0.2

4.0–7.0

0.50 V: 0.35

0.04

0.03

ERNiCrMo-4

N10276

0.02

Rem.

14.5–16.5

15.0–17.0

2.5

3.0–4.5

—

1.0

0.08

4.0–7.0

0.50 V: 0.35

0.04

0.03

ENiCrMo-10b

W86022

0.02

Rem.

20.0–22.5

12.5–14.5

2.5

2.5–3.5

—

1.0

0.2

2.0–6.0

0.50 V: 0.35

0.03

0.015

ERNiCrMo-10

N06022

0.015

Rem.

20.0–22.5

12.5–14.5

2.5

2.5–3.5

—

0.50

0.08

2.0–6.0

0.50 V: 0.35

0.02

0.010

ENiCrMo-13

W86059

0.02

Rem.

22.0–24.0

15.0–16.5

—

—

—

1.0

0.2

1.5

0.50

0.015

0.01

ERNiCrMo-13

N06059

0.01

Rem.

22.0–24.0

15.0–16.5

0.3

—

—

0.5

0.10

1.5

0.50 Al: 0.1–0.4

0.015

0.010

ENiCrMo-14

W86686

0.02

Rem.

19.0–23.0

15.0–17.0

—

3.0–4.4

—

1.0

0.25

5.0

0.50 Ti: 0.25

0.02

0.01

ERNiCrMo-14

N06686

0.01

Rem.

19.0–23.0

15.0–17.0

—

3.0–4.4

—

1.0

0.08

5.0

0.50 Al: 0.5 Ti: 0.25

0.02

0.02

ENiCrCoMo-1b

W86117

0.05–0.15

Rem.

21.0–26.0

8.0–10.0

9.0–15.0

—

1.0

0.3–2.5

0.75

5.0

0.50

0.03

0.015

ERNiCrCoMo-1

N06117

0.05–0.15

Rem.

20.0–24.0

8.0–10.0

10.0–15.0

—

—

1.0

1.0

3.0

0.50 Al: 0.8–1.5 Ti: 0.60

0.03

0.015

a b

Compositions for SMAW electrodes are based on AWS Specification A5.11/A5.11M. A compositionally-equivalent version of the indicated consumable is available in an FCAW electrode (AWS A5.34/A5.34M).

Note: Single values indicate maximum permissible amount unless otherwise indicated.

AWS G2.3M/G2.3:2019

UNS Number

47

AWS Classificationa

AWS G2.3M/G2.3:2019

Table 8.11 Nickel-Based SMAW Electrodes, Specified Tensile Properties Tensile Strength, Min. Classification

MPa

ksi

Elongation Min. %

ENiCrFe-2

550

80

30

ENiCrFe-3

550

80

30

ENiCrMo-3

760

110

30

ENiCrMo-4

690

100

25

ENiCrMo-10

690

100

25

ENiCrMo-13

690

100

25

ENiCrMo-14

690

100

30

ENiCrCoMo-1

620

90

25

Note: Minimum mechanical properties specified by AWS A5.11/A5.11M:2010 for SMAW electrodes.

One of the most common shielding gases used for welding stainless steels in the short circuiting transfer mode is 90%He-7.5%Ar-2.5%CO2. A summary of the different gases typically used in short circuiting transfer applications is provided in Table 8.12. Other possible short circuiting transfer gas mixtures and applications are described in AWS A5.32M/A5.32 (ISO 14175 MOD):2011. Shielding gas producers may also be consulted for proprietary blends that they have developed for specific applications. Typical short circuiting transfer parameters are shown in Table 8.13. Short circuiting transfer welding equipment may employ the use of inductance controls to reduce the amount of spatter during the short circuiting transfer weld cycle. See 6.7 for using waveform-controlled welding power sources for root welding with and without purging. 8.3.2 Spray Transfer. Spray transfer, i.e., spray arc, is a transfer mode that is used for welding base materials typically 6 mm [0.25 in] and thicker and is used primarily only in the flat position because of the high fluidity of the weld pool. This process can be characterized as a moderate to high heat input welding process with a relatively high deposition rate. The weld penetration is typically deeper when compared to the short circuiting transfer process; consequently, spray transfer is usually unsuitable for welding materials less than 6 mm [0.25 in] thick because of excessive burnthrough without using special techniques or backing materials. The welding equipment needs to be able to provide a suitable spray transfer current level as the weld metal is transferred across the arc as extremely small droplets. Stainless steels welded using the GMAW spray transfer mode are commonly welded using argon-oxygen (either 1% or 2% O2) shielding gases although other gas blends are well proven to be effective. A summary of the different gases typically used in spray transfer applications is provided in Table 8.12. Other possible gas mixtures suitable for spray transfer welding of austenitic stainless steels are described in AWS A5.32M/A5.32 (ISO 14175 MOD):2011. Typical parameters for spray transfer welding the 300 series stainless steels are shown in Table 8.14. 8.3.3 Globular Transfer. Globular transfer, i.e., globular arc, is less preferred than spray transfer or short circuiting transfer because of an irregular arc and excessive spatter. Globular transfer occurs as a relatively large molten droplet of filler metal propelled across the arc toward the base metal. The droplet size is typically larger than the diameter of the electrode. Globular transfer is achieved by operating at current and voltage levels between short circuiting transfer and spray transfer levels. Globular transfer, when used, is limited to a flat welding position.

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AWS G2.3M/G2.3:2019

Table 8.12 GMAW (MIG) Shielding Gas Selection Commentsa, b

Shielding Gas

Transfer Mode: Short Circuiting Transfer

90%He + 7.5%Ar +

Commonly used for short circuiting transfer welding of austenitic stainless steels. Helium improves wetting. No effect on corrosion resistance, small HAZ, no undercutting, minimum distortion, minimal carbon pickup. Has been used for GMA welding of piping without backing gas.e

2.5%CO2c, d

Ar + (1%–3%)O2

Less commonly used shielding gas than He-Ar-CO2 blends. Especially useful for thin (<1 mm [0.040 in] sheet, gaps, etc. due to low sustainable arc voltage, low arc energy, low weld penetration (useful to prevent burn-through).a, f

97%Ar + (2%–5%) CO2c, d

Beneficial for reduced distortion, burn-through, and weld oxidation. CO2 exceeding 5% will increase carbon content of weld deposit.a, g 98/2 popular Europeanc

90%Ar + 7.5%He + 2.5%CO2d

Popular European mix.h Transfer Mode: Pulsed Spray Transfer or Spray Transfer

Ar +(2%–5%)CO2

Better wetting, weld profile, and less surface oxide than argon oxygen mixes. Up to 5%CO2 can be used on L-grade stainless and still maintain L-grade composition. 25% travel speed increase achievable with 5%CO2 compared to Ar + 1%O2a, i 98/2 popular Europeanc

99%Ar + 1%O2c, d, j

Good arc stability with a fluid and controllable weld pool. Good coalescence and reasonable bead contour. Some surface oxide. Minimal undercutting on heavier stainless steels.

98%Ar + 2%O2c, d, j

Better arc stability, coalescence, and welding speed than 1% oxygen mixture. Some surface oxide.

55%He + 43%Ar + 2%CO2

Good operability.f

90%Ar + 7.5%He + 2.5%CO2

See table footnotes d, h, k

Ar + He + CO2 Ar + CO2 + H2

Ar + 30%–40%He + 1%–3%CO2, and Ar + 3%–5%CO2 + 1%–2%H2 blends are considered “” blends for ing SS with pulsed or spray transfer. The latter blend is used where bead surface appearance is particularly critical. The reducing atmosphere generated by the hydrogen addition is a benefit. Ar + 25%–35%He + 1%–2%CO2 can provide a 20% or more increase in travel speed compared to most two-part blends.i, k, l

Ar + (10%–40%He) + (1%–15%) CO2

Used most often on heavy sections in positions other than flat. Good mechanical properties and weld pool control are characteristic of these mixtures.m

Ar + CO2 + N2 blends

These specialized blends can be used for the higher alloy austenitics as well as duplex stainless steels where increased corrosion resistance is important.

a

Craig, E., September 1994, GMAW Shielding Gases: Simplifying Selection, Welding Design & Fabrication; 97%Ar–3%CO2 is discussed as a universal gas mix. b Chemical abbreviations: Argon (Ar), Helium (He), Carbon Dioxide (CO ), Oxygen (O ), Hydrogen (H ). 2 2 2 c Irving, B., 1994, Trying to Make Some Sense Out of Shielding Gases, Welding Journal 73(5): 65–70; Cost comparisons of shielding gases are discussed in the feature article. d AWS C5.10/C5.10M:2003, Recommended Practices for Shielding Gases for Welding and Cutting, Table 6. e Messer, B., et al., 2002, Welding Stainless Steel Piping with no Backing Gas, Welding Journal 81(12): 32-34. Cost savings are described by eliminating backing gas when GMA welding 300 series piping materials using high silicon filler metals, inverter power sources, and tri-mix shielding gases. f Irving, B., 1999, Shielding Gases are the Key to Innovations in Welding, Welding Journal 78(1): 37; Cost and quality comparisons of shielding gases are discussed in the feature article. g Lucas, W., July 1992, Choosing a Shielding Gas, Welding & Metal Fabrication: 275–“High CO levels can cause excessive carbon pickup in the weld 2 pool; typically, between 0.010% and 0.020% will be added to the weld metal carbon content when welding with Ar+2%CO2 shielding gas.” This will contribute to weld metal sensitization problems. CO2 concentrations exceeding 3% should normally be avoided; however, up to 25%CO2 additions in argon have been used in noncritical, noncorrosive applications. h Nickel Institute Reference Book, Series No. 11007, “Guidelines for the Welded Fabrication of Nickel-Containing Stainless Steels for Corrosion Resistant Services,” p. 19.

(Continued)

49

AWS G2.3M/G2.3:2019

Table 8.12 (Continued) GMAW (MIG) Shielding Gas Selection i

Lyttle, K. and G. Stapon, June 2004, Selecting a Shielding Gas for ing Stainless Steel, The Fabricator: 36. AWS Welding Handbook, 7th ed., Vol. 2, Table 4.5. k AWS Welding Handbook, 7th ed., Vol. 2, p. 136: Mixtures of Ar, He, & CO are favored for pulsed arc welding and with Short Arc and pulse arc welding of stainless steels. “Mixtures in which argon is the primary constituent are used for pulse arc. When helium is the primary constituent it is for short arc welding.” l Lyttle, K. A. and W. F. G. Stapon, 1990, Select the Best Shielding Gas Blend for the Application. “Stainless steels are frequently welded with threepart mixes containing helium to improve weld quality through better bead appearance, improved weld pool fluidity and higher potential travel speeds.” Welding Journal 69(11): 24. mAWS A5.32M/A5.32 (ISO 14175 MOD):2011, Specification for Welding Shielding Gases, 7.3.2.1 and 7.3.2.2. j

Table 8.13 GMAW Parameters (Short Circuit, DCEP He + 7.5%Ar + 2.5%CO2 Shielding Gas)a Base Material Thickness mm [in]

a b

Electrode Diameter mm [in]

Wire Feed Speed m/min [ipm]

Current

Voltageb

1.6–3.2 [1/16–1/8]

0.8 [0.030]

4.7–7.1 [185–280]

85–125

21–24

1.2 [0.047] [18 gage]

0.9 [0.035]

3.0–3.8 [120–150]

55–75

19–20

1.5 [0.059] [16 gage]

0.9 [0.035]

4.6–5.2 [180–205]

85–95

19–20

1.9 [0.075] [14 gage]

0.9 [0.035]

5.8–7.0 [230–275]

105–110

20–21

2.7–3.5 [0.106–0.138] [12-10 gage]

0.9 [0.035]

7.6–8.3 [300–325]

125–130

20–21

4.8 [3/16]

0.9 [0.035]

8.9–9.5 [350–375]

140–150

21–22

2.7 [0.106] [12 gage]

1.1 [0.045]

2.5–3.2 [100–125]

100–120

19–20

3.5 [0.138] [10 gage]

1.1 [0.045]

3.8–4.4 [150–175]

135–150

21

4.8 [3/16]

1.1 [0.045]

5.6–6.4 [220–250]

170–175

22

6.4 [1/4]

1.1 [0.045]

6.4–7.0 [250–275]

175–185

22–23

Short circuit welding parameters using other shielding gas types may vary. For Argon + 2%O2, reduce voltage approximately 6 V. Welding parameters using other shielding gas types may vary.

Note: Electrode extension range is from 9 mm to 18 mm [3/8 in to 3/4 in] with an optimum range of 9 mm to 15 mm [3/8 in to 5/8 in]. Source: Adapted from AWS Welding Handbook, 8th ed., Vol. 2, p. 140 and Lincoln Electric Gas Metal Arc Welding Guide, GS-100, pp. 32 and 33, Tables 16 and 17.

Table 8.14 GMAW Parameters (Spray Transfer, DCEP, 98%Ar + 2%O2 Shielding Gas)a Base Material Thickness mm [in]

Electrode Diameter mm [in]

Wire Feed Speed m/min [ipm]

Current

Voltageb

Commentsb

Up to 3.2 [1/8]

0.9 [0.035]

3.3–8.1 [125–320]

125–150

15–21

—

3.2 [1/8] and over

0.9 [0.035]

10.2–12.1 [400–475]

180–210

23–25

Note c

3.2 [1/8] and over

1.1 [0.045]

6.1–9.1 [240–360]

195–260

24–26

Note c

3.2–6.4 [1/8–1/4]

1.6 [1/16]

3.3–6.1 [130–240]

225–300

24–28

Note d

6.4 [1/4] and over

1.6 [1/16]

5.1–7.6 [200–300]

300–390

29–32

Note c

a

Spray arc welding parameters using other shielding gas types may vary. For flat position or horizontal fillets. Listed ranges are approximate. Welding parameters for thin base materials are usually operated at the low end of the range. c Parameters adapted from Lincoln Electric Gas Metal Arc Welding Guide, GS-100, p. 31, Table 15. d AWS Welding Handbook, Welding Processes, 8th ed., Vol. 2, Parameters adapted from Table 4.10, p. 139. b

50

AWS G2.3M/G2.3:2019

8.3.4 Pulsed-Spray Gas Metal Arc Welding. The GMAW pulsed spray (GMAW-P) process may be selected for any of the following situations or reasons: (1) To reduce arc fume emissions34 and spatter. (2) To weld on metals that are too thin for the GMAW spray transfer process. (3) To offer greater out-of-position capabilities than with the spray transfer process. (4) To weld materials that are thicker than what would be suitable for the short circuiting transfer process. (5) To reduce heat input compared to the spray transfer process, which results in reduced distortion and dilution and enhanced HAZ properties. (6) Ease of use when using waveform-controlled power source equipment (preprogrammed welding schedules). (7) To possibly improve deposition rates. In the GMAW-P variation, the power source provides two output current levels at regular intervals: (1) A “background current” too low in magnitude to produce metal transfer but sufficiently high to maintain the arc; and (2) A pulsed, highoutput, “peak” current that causes melting of droplets from the electrode, which are then transferred across the arc to the weld zone. The process operates in the spray transfer mode only on the peak current portion of the pulse cycle. Ideally, one droplet is transferred during each pulse. As mentioned previously, controlling the background current helps maintain the arc and lowers the average heat input. The current can be cycled between a high and low value at up to several hundred cycles per second. Setting and adjusting parameters can be difficult in older GMAW pulsing equipment that does not have programmed (waveform-controlled power source) capabilities because of the comparatively large number of pulsing parameter variables. The net result of operating in pulsed spray transfer mode is to produce a spray transfer with average current levels much below the typical transition current required for a particular electrode diameter and type. For example, using a 1.1 mm [0.045 in] diameter stainless electrode with 99%Ar+1%O2 shielding gas, the minimum spray transfer current is 225 A compared to 104 A (average) when pulsing.35 This allows the ing of thinner base metals than is normally possible with standard spray transfer. Pulsed spray welding may be used in all positions. Welding fume levels are the lowest obtainable with solid wire GMAW.36 Most modern waveform-controlled power source welding machines allow for the development and storage of pulsing parameters that are different from the factory installed programs. This option may be needed for specific welding applications where the factory installed programs are not optimum for the situation. Pulsing occurs at regular intervals. The pulsing rate can be varied depending on the base material, thickness, wire diameter, shielding gas, and welding position. Pulsing parameters include: pulse frequency, peak time, peak current, background time, background current, and voltage. Because of the large number of pulsing parameters/variables, specific operating parameters for pulse GMAW welding are not provided in this document. It is recommended that the preprogrammed parameters available in waveform-controlled power source welding equipment be used, or, that new programs be developed within the welding equipment manufacturer’s recommendations. Selection of a shielding gas for pulsed spray welding is typically based on the following factors: (1) The shielding gas needs to be able to spray transfer. (2) The shielding gas needs to protect the weld pool from absorbing deleterious elements that may cause porosity, excessive oxidation, or cracking. (3) The shielding gas should be compatible with the particular waveform-controlled power source program selected for the application. 34 Castner,

H. R., 1996, Fume Generation Rates for Stainless Steel, Nickel, and Aluminum Alloys, Welding Journal 75(12): 393-s– 401-s. 35 Miller Electric, GMAW-P, Pulsed Spray Transfer, p. 5, Figure 5. 36 Praxair, Shielding Gases Selection Manual: 32.

51

AWS G2.3M/G2.3:2019

For example, a welding equipment manufacturer may have pre-established welding parameters for stainless steels that are based on only a few shielding gas choices. The end would select the preferred gas from one of the pre-established options. Other shielding gases could potentially be used with the corresponding parameters for a specific shielding gas/parameter program; however, the parameters for these new gases may need to be modified for optimum operability. The common shielding gases that are used for welding the austenitic stainless steels in the GMAW pulsed spray transfer mode are shown in Table 8.13. 8.4 Flux Cored Arc Welding (FCAW). The FCAW process is a variation of the GMAW process. The FCAW process, commonly referred to as “flux core,” uses a spooled tubular (i.e., flux-cored) electrode that is continuously fed into the arc created between the electrode and the weld pool. The tubular electrodes are produced by adding powdered fluxing agents in the core of a tubular metal sheath. Depending on the manufacturer, the electrode core may also contain principal alloying elements in powdered form. The FCAW process is commonly used in production because the process is capable of providing high deposition rates. The process has the potential for increased productivity compared to the GTAW and SMAW processes. The FCAW process is ideally suited for welding plate and sheet metal over 3 mm [0.12 in] thick, although thinner materials can also be welded. The FCAW process can be further defined by the electrode type and whether or not external gas shielding is utilized. Gas-shielded FCAW (FCAW-G) is a variation of the FCAW process that requires supplementary gas shielding. Selfshielded FCAW (FCAW-S) is a variation that uses electrodes specifically produced to operate without the need for supplementary gas shielding. A wide variety of FCAW electrodes are available for welding austenitic stainless steels. AWS A5.22/A5.22M prescribes requirements for the classification of the electrodes. It classifies the electrodes according to chemical composition, the position of welding, shielding medium, and the type of welding current used. It also indicates the minimum mechanical property requirements for weld deposits for the various alloys. Annex A of AWS A5.22/A5.22M provides useful information on the intended use of the various filler metals as well as a discussion of ferrite in weld deposits. Classification schemes for AWS A5.22/A5.22M are summarized in Table 8.15. Tables A.1, A.2, and A.3 in this document provide filler metal recommendations for welding the most common austenitic base materials. The chemical composition limits of stainless steel flux-cored electrodes are listed in Table 8.16. Table 8.17 lists the minimum mechanical properties specified by AWS A5.22/A5.22M for FCAW electrodes and rods. Base

Table 8.15 FCAW Electrodes Classification Scheme AWS A5.22/A5.22M:2012 AWS Classificationa

External Shielding Mediumb

Welding Polarity

EXXXTX-1

CO2

DCEP

EXXXTX-3

None (self-shielded)

DCEP

EXXXTX-4

75%–80%Ar/remainder CO2

DCEP

EXXXTX-Gc

Not Specified

Not Specified

a

The letter “E” indicates electrode. The letters “XXX” indicate the chemical composition. The letter “T” indicates the electrode is a tubular product form (e.g., flux-cored). The “X” after the “T” indicates the intended welding position (“0” = flat or horizontal, “1” = all position operation). b External shielding the manufacturer uses during classification tests to classify the electrode. This shall not be construed to restrict the use of any other medium for which the electrodes are found suitable for any application other than the classification tests. c The “G” indicates a general classification scheme to allow production and classification of a electrode varying in one or more respects (e.g., in regards to chemical composition, polarity, external or shielding medium). Source: Adapted from AWS A5.22/A5.22M:2012, Specification for Stainless Steel Flux Cored and Metal Cored Welding Electrodes and Rods, Table 2, American Welding Society.

52

Table 8.16 Stainless Steel Weld Deposit Composition Requirements for FCAW Electrodes and Rods (AWS A5.22/A5.22M) Weight Percenta C

Cr

Ni

Mo

Nb + Ta

Mn

Si

P

S

N

Cu

E307TX-X

W30731

013

18.0–20.5

9.0–10.5

0.5–1.5

—

3.30–4.75

1.0

0.04

0.03

—

0.5

E308TX-X

W30831

0.08

18.0–21.0

9.0–11.0

0.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E308LTX-X

W30835

0.04

18.0–21.0

9.0–11.0

0.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E308HTX-X

W30831

0.04–0.08

18.0–21.0

9.0–11.0

0.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E308MoTX-X

W30832

0.08

18.0–21.0

9.0–11.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E308LMoTX-X

W30838

0.04

18.0–21.0

9.0–12.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E309TX-X

W30931

0.10

22.0–25.0

12.0–14.0

0.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E309LNbTX-X

W30932

0.04

22.0–25.0

12.0–14.0

0.5

0.70–1.00

0.5–2.5

1.0

0.04

0.03

—

0.5

E309LTX-X

W30935

0.04

22.0–25.0

12.0–14.0

0.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E309MoTX-X

W30939

0.12

21.0–25.0

12.0–16.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E309LMoTX-X

W30938

0.04

21.0–25.0

12.0–16.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E309LNiMoTX-X

W30936

0.04

20.5–23.5

15.0–17.0

2.0–3.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E310TX-X

W31031

0.20

25.0–28.0

20.0–22.5

0.5

—

1.0–2.5

1.0

0.03

0.03

—

0.5

E312TX-X

W31331

0.15

28.0–32.0

8.0–10.5

0.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E316TX-X

W31631

0.08

17.0–20.0

11.0–14.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E316LTX-X

W31635

0.04

17.0–20.0

11.0–14.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E317LTX-X

W31735

0.04

18.0–21.0

12.0–14.0

3.0–4.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E347TX-X

W34731

0.08

18.0–21.0

9.0–11.0

0.5

8 × C min. 1.0 max.

0.5–2.5

1.0

0.04

0.03

—

0.5

E307T0-3

W30733

0.13

19.5–22.0

9.0–10.5

0.5–1.5

—

3.30–4.75

1.0

0.04

0.03

—

0.5

E308T0-3

W30833

0.08

19.5–22.0

9.0–11.0

0.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E308LT0-3

W30837

0.03

19.5–22.0

9.0–11.0

0.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E308HT0-3

W30833

0.04–0.08

19.5–22.0

9.0–11.0

0.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E308MoT0-3

W30839

0.08

18.0–21.0

9.0–11.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

AWS Classificationb

53

(Continued)

AWS G2.3M/G2.3:2019

UNS Numberc

Weight Percenta UNS Numberc

C

Cr

Ni

Mo

Nb + Ta

Mn

Si

P

S

N

Cu

E308LMoT0-3

W30838

0.03

18.0–21.0

9.0–12.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E308HMoT0-3

W30830

0.07–0.12

19.0–21.5

9.0–10.7

1.8–2.4

—

0.04

0.03

—

0.5

E309T0-3

W30933

0.10

23.0–25.5

12.0–14.0

0.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E309LT0-3

W30937

0.03

23.0–25.5

12.0–14.0

0.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E309LNbT0-3

W30934

0.03

23.0–25.5

12.0–14.0

0.5

0.70–1.00

0.5–2.5

1.0

0.04

0.03

—

0.5

E309MoT0-3

W30939

0.12

21.0–25.0

12.0–16.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E309LMoT0-3

W30938

0.04

21.0–25.0

12.0–16.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E310T0-3

W31031

0.20

25.0–28.0

20.0–22.5

0.5

—

1.0–2.5

1.0

0.03

0.03

—

0.5

E312T0-3

W31231

0.15

28.0–32.0

8.0–10.5

0.5

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E316T0-3

W31633

0.08

18.0–20.5

11.0–14.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E316LT0-3

W31637

0.03

18.0–20.5

11.0–14.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E316LKT0-3d

W31630

0.04

17.0–20.0

11.0–14.0

2.0–3.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E317LT0-3

W31737

0.03

18.5–21.0

13.0–15.0

3.0–4.0

—

0.5–2.5

1.0

0.04

0.03

—

0.5

E347T0-3

W34733

0.08

19.0–21.5

9.0–11.0

0.5

8 × C min. 1.0 max.

0.5–2.5

1.0

0.04

0.03

—

0.5

E2209T0-X

W39239

0.04

21.0–24.0

7.5–10.0

2.5–4.0

—

0.5–2.0

1.0

0.04

0.03

0.08–0.20

0.5

R308LT1-5

W30835

0.03

18.0–21.0

9.0–11.0

0.5

—

0.5–2.5

1.2

0.04

0.03

—

0.5

R309LT1-5

W30935

0.03

22.0–25.0

12.0–14.0

0.5

—

0.5–2.5

1.2

0.04

0.03

—

0.5

R316LT1-5

W31635

0.03

17.0–20.0

11.0–14.0

2.0–3.0

—

0.5–2.5

1.2

0.04

0.03

—

0.5

R347T1-5

W34731

0.08

18.0–21.0

9.0–11.0

0.5

8 × C min. 1.0 max.

0.5–2.5

1.2

0.04

0.03

—

0.5

AWS Classificationb

1.25–2.25 0.25–0.80

54 a

Single values are shown as maximum. The “X” following the “T” in the electrode AWS classification refers to the position of welding (-1, -4, or -5). In A5.22-80, the position of welding was not included in the classification. Accordingly, electrodes classified herein as either EXXXT0-1 or EXXXT1-1 would both have been classified EXXXT-1 and so forth. c SAE HS-1086, Metals & Alloys in the Unified Numbering System. d This alloy is designed for cryogenic applications. b

Source: Adapted from AWS A5.22/A5.22M:2012, Specification for Stainless Steel Flux Cored and Metal Cored Welding Electrodes and Rods, Table 1FC, American Welding Society.

AWS G2.3M/G2.3:2019

Table 8.16 (Continued) Stainless Steel Weld Deposit Composition Requirements for FCAW Electrodes and Rods (AWS A5.22/A5.22M)

AWS G2.3M/G2.3:2019

Table 8.17 Stainless Steel Weld Deposit Tensile Requirements for Flux Cored Electrodesa and Rods (AWS A5.22/A5.22M) Tensile Strength, Min. AWS Classification

a

MPa

ksi

Elongation, Min. %

E307TX-X

590

85

30

E308TX-X

550

80

35

E308LTX-X

520

75

35

E308HTX-X

550

80

35

E308MoTX-X

550

80

35

E308LMoTX-X

520

75

35

E308HMoT0-3

550

80

30

E309TX-X

550

80

30

E309LNbTX-X

520

75

30

E309LTX-X

520

75

30

E309MoTX-X

550

80

25

E309LMoTX-X

520

75

25

E309LNiMoTX-X

520

75

25

E310TX-X

550

80

30

E312TX-X

660

95

22

E316TX-X

520

75

30

E316LTX-X

485

70

30

E316LKT0-3

485

70

30

E317LTX-X

520

75

20

E347TX-X

520

75

30

E2209TX-X

690

100

20

R308LT1-5

520

75

35

R309LT1-5

520

75

30

R316L5 1-5

485

70

30

R347T1-5

520

75

30

Minimum mechanical properties as-specified in AWS A5.22/A5.22M:2012, Table 6.

Table 8.18 Shielding Gas Selection for Flux Core Arc Welding Shielding Gas

Comments

N/A Self-shielded

Shielding coverage is provided by vaporization of fluxing agents and by molten slag coverage of weld pool.

CO2

CO2 is typically less expensive than Ar/CO2 mixes. CO2 provides better cooling of the tip and nozzle compared to Ar/CO2.

Ar+(25%–30%)CO2

Commonly used shielding gas mix. Depending on electrode brand, generally provides lower spatter than CO2 gas. Good arc stability.

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material composition and mechanical property limits are provided in Tables 4.1, 4.2, 4.3, and 4.4. The most common shielding gases are provided in Table 8.18. Generally, welds made using self-shielded FCAW electrodes produce more fumes than their externally-shielded counterparts, have somewhat lower deposition rates, and typically involve more postweld cleanup. As a result, FCAW-G welds generally have a better appearance than welds made with the self-shielded types and may be of higher quality. Self-shielded electrodes are less sensitive to wind and drafts than their gas shielded counterparts and are sometimes selected for field construction for that reason. Utilizing self-shielded electrodes also eliminates the need and cost of gas. Because the operability of self-shielded electrodes is generally considered less desirable than the gas shielded counterparts, the gas shielded versions are commonly used in shop environments. Depending on the electrode classification, welding parameters, base material thickness, and operator’s skill, the FCAW process can be operated out-of-position (i.e., vertical and overhead). Electrodes classified for flat or horizontal welding may not be suitable for vertical or overhead welding because of their higher weld pool fluidity characteristics. Positioning fabrications during welding so that welds can be performed in the flat (down-hand position) can increase production rates and provide welds with optimum appearance and quality. All-position electrodes should be considered if out-ofposition welding will be performed, or if a mix of flat, horizontal, and out-of-position welding will be performed. Many FCAW electrode manufacturers produce electrodes that have exceptional operating characteristics. Some electrode brands produce weld deposits with a smooth weld bead appearance with little or no surface ripple. Prior to production welding, weldability comparisons between electrodes of different manufacturers are recommended to compare operating characteristics such as: electrode feedability, weld appearance and profile, smoke and fume generation, spatter, out-of-position welding characteristics, slag removal, operability, and weld deposit mechanical properties. Brand differences can be significant. Because labor costs typically for more than three-fourths of welding costs, consideration should be given when purchasing electrodes that have potential for increasing productivity (i.e., electrodes with optimum operability), maintaining or increasing weld quality, and reducing postweld cleaning operations. Transfer modes for the FCAW process are normally either spray transfer or globular transfer. Short circuiting transfer is not appropriate for FCAW because of the insufficient heat for melting the flux. Some companies are investigating the use of pulsing power supplies for FCAW. Due to variations in the makeup of different flux-cored electrode brands, parameter ranges can vary from one manufacturer or electrode brand to the next. For optimum parameter ranges, consult the electrode manufacturer. 8.5 Submerged Arc Welding (SAW) 8.5.1 SAW Process Description. The SAW process, commonly referred to as “sub arc,” uses one or more bare electrodes continuously fed into the arc created between the electrode and the weld pool. Because the electrode is consumed, it also serves as the filler metal for the t. Electrodes can be solid or tubular (also referred to as “composite” or “metalcored”) and are provided in spools, coils, or drums. Both the weld pool and the arc are shielded by granular or powdered flux that is automatically fed on top of the weld t as welding progresses. Flux in immediate with the molten weld pool melts and solidifies to form a protective slag layer while the remaining unmelted/unfused flux is typically vacuumed and recycled into the flux hopper. The slag is then chipped from the solidified weld. Slag can be self-peeling with proper welding parameter selection, t design, bead-stacking sequence, and proper selection of flux type/brand. When properly performed, the process can provide a high quality weld with excellent weld bead appearance and, in many instances, postweld finishing operations are not required. While deposition rates can vary significantly depending on operating parameters (electrode size, forms such as solid versus metal-cored, extension, current, and voltage), the SAW process is commonly selected because of its high deposition rate compared to other welding processes. While the SAW process has the potential to provide high quality weld deposits with an exceptional weld profile, the process also has the potential to trap slag for the entire weld length when the process is not properly monitored for each and weld layer, and when weld beads are not optimally located. 8.5.2 SAW Process Considerations. While deposition rates (kgs/h or lbs/h) for the SAW process can vary significantly depending on the operating parameters, the process is capable of much higher deposition rates compared to other common welding processes.

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Commonly used electrode sizes are 1.2 mm [0.045 in], 1.6 mm [1/16 in], 2.0 mm [5/64 in], 2.4 mm [3/32 in], 3.2 mm [1/8 in], and 4.8 mm [3/16 in] diameter; however, stocking and using one or two diameters may be sufficient for most welding applications. Because the process has the potential to be operated at high heat input rates, welding parameters should be controlled when necessary to ensure that weld zone cooling rates are fast enough to minimize the potential for sensitization. Slow cooling rates can promote the sensitization and formation of heat tint on austenitic stainless steels. When sensitization needs to be avoided because of possible corrosion concerns, the need to avoid slow cooling rates increases as the carbon content of the material increases (see Figure 5.4a). Generally, weld zone cooling rates are faster for thicker materials because of the increased heat sink. Cooling rates can be increased by decreasing the welding heat input (e.g., by decreasing current and voltage and by increasing travel speed), by using lower preheats, and by ensuring that the inter temperature is not excessive. Besides flux for a backing material, nonconsumable backing materials (e.g., copper or ceramic) may also be used where appropriate for controlling burn-through. 8.5.3 SAW Flux. Various flux manufacturers produce fluxes manufactured specifically for welding stainless steels. Flux manufacturers and the literature they distribute should be consulted prior to selecting a flux for a particular application. There is no specific AWS document for submerged arc flux to aid in flux selection. Weld metal composition is highly dependent upon flux type, electrode composition, and welding parameters (primarily voltage). Weld metal ferrite levels, for example, can change dramatically depending on any of the previously mentioned factors. Because of this, fluxes used in production should be restricted to those previously qualified by testing. Various flux brands may be evaluated to compare their different characteristics and their effects on final weld metal properties prior to weld procedure qualification testing. Since welding parameters, such as welding voltage, can affect the amount of flux consumption and final weld chemical composition, production parameters in critical applications should be maintained within reasonable limits to that qualified or tested. Active fluxes designed for the single- welding of carbon steels can increase the manganese content of the stainless weld deposits, while neutral fluxes may not compensate for the chromium losses that can occur during welding. A reduction of the chromium content may reduce the corrosion resistance and ferrite content of the weld deposit. Some fluxes used for welding carbon steels can significantly increase the carbon content of the weld deposit, even to the extent of changing an L-grade weld wire to an H-grade weld deposit. If fluxes designed for welding carbon steel are used with stainless steel welding consumables, then complete mechanical testing including Charpy toughness testing, chemical analysis, and ferrite checks should be considered during procedure qualification testing. Chemical analysis test results of the undiluted weld deposit should be compared to the bare filler composition. Submerged arc fluxes are made as either agglomerated (bonded) or fused. In general, the as-deposited oxygen content of weld metal made with agglomerated fluxes will be lower than that of the corresponding fused flux. Higher oxygen contents in the weld metal could have an adverse effect on the corrosion resistance and mechanical properties because of increased levels of oxide inclusions in the deposited weld metal. Complete blending of the component ingredients by the flux manufacturer is important during the production of agglomerated fluxes. Improper blending could result in variations in deposit composition that could adversely affect the properties. The flux layer depth should be controlled within the limits specified by the flux manufacturer. Too shallow of flux depth offers inadequate weld pool protection, while excessive flux depth adversely affects the weld bead shape and prevents gases from escaping from the weld pool; it can also result in porosity or in weld surface “worm tracks.” Specific flux brands can alter the as-deposited Ferrite Number compared to what is predicted from using the bare filler metal chemical composition and the WRC diagram or other method. Besides consulting with the flux manufacturer, inhouse testing can be used to establish whether a specific flux brand increases, decreases, or doesn’t change the deposited FN compared to the predicted FN, 8.5.4 SAW Electrodes. Electrodes can be purchased as solid or metal cored (composite). Composite electrodes are produced by adding the principal alloying elements in powdered form in the core of a tubular metal sheath. The sheath can be manufactured from an alloy similar in composition to the desired weld deposit or from a plain carbon steel material. Composite electrodes have the advantage of higher deposition rates compared to solid electrodes. A wide variety of SAW electrodes are available for welding the austenitic stainless steels. AWS A5.9/A5.9M prescribes requirements for the classification of the electrodes. It classifies the electrodes according to chemical composition only.

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Annex A of the specification is a useful guide for the purchase and intended use of the filler metals, discussing ferrite determination and controls for the different electrode types. See Table 8.9 for chemical composition limits of bare stainless steel welding electrodes and rods. Tables A.1, A.2, and A3 in this document are a useful resource for selecting filler metals for welding specific austenitic alloys in specific operating environments. Typical electrode diameters range from 1.6 mm to 4.0 mm [1/16 in to 5/32 in] diameter. Larger diameter electrodes are best suited for welding on thicker base materials (e.g., 25 mm [1 in] and greater) because of the greater heat input and deposition rates associated with the larger diameter electrodes. 8.5.5 SAW Parameters. Typical SAW parameters are shown in Table 8.19. The process can be operated with single arc or multiple arcs. The SAW process is normally operated using direct current electrode positive (DCEP) for single arc welding; and DCEP and AC for multiple arcs to prevent arc blow. 8.6 Plasma Arc Welding (PAW). During plasma arc welding, arc transfer from the torch body to the workpiece is through a column/stream of high-temperature ionized gas particles called “plasma.” A nonconsumable, alloyed tungsten electrode is recessed within a copper nozzle that is positioned within the torch body. Plasma is produced and forced through a relatively small diameter nozzle orifice when an electrical arc is initiated and gas (commonly argon) is simultaneously introduced into the copper nozzle. Supplementary shielding gases such as argon, argon-2%–5%H2, and helium are also required to shield the weld pool from atmospheric contamination during solidification similar to the shielding requirements necessary for the GTAW process. The process can be operated autogenously or with filler metal additions. Equipment and operating parameter variations allow for the welding of materials that range from very thin sheet metal and spot welding of small-diameter wires, to the autogenous welding of single-, complete t penetration square-groove ts in material up to 13 mm [0.5 in] thickness. Welding of the latter t design is typically performed using the keyhole method utilizing inert gas backing. This method pierces and maintains a hole through the t via the plasma stream. Molten metal flows from the sides and leading edge to the trailing edge of the keyhole as the welding progresses. The molten metal fills the t at the trailing edge and then resolidifies. This technique can significantly reduce welding costs and distortion and still produce high quality weld ts. Some of the variations of plasma welding include: micro-plasma (<20 A) for welding materials down to 0.5 mm [0.02 in] in thickness, fusion welding, and keyhole welding, as mentioned previously. Plasma has excellent arc stability; it exhibits a greater tolerance to variations in arc length compared to the GTAW process. Plasma arc cutting, plasma arc gouging, plasma weld overlay, and plasma arc spraying are all variations of plasma welding equipment, consumables, and operating parameters. All materials that can be welded using the GTAW process can

Table 8.19 Typical Submerged Arc Welding Parameters, DCEP Diameter mm [in]

Current (A)

Voltage (V)

Travel Speed cm/min [in/min]

1.2 [0.045]

100–250

22–28

30–50 [12–20]

1.6 [1/16]

150–300

24–30

40–50 [16–20]

2.0 [5/64]

180–350

21–32

40–50 [16–20]

2.4 [3/32]

250–400

25–32

40–55 [16–22]

3.2 [1/8]

300–550

28–32

40–55 [16–22]

4.0 [5/32]

400–600

28–32

40–55 [16–22]

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AWS G2.3M/G2.3:2019

also be welded using the PAW process. Filler metal type product forms for the PAW process for welding the austenitic stainless steels are the same as those used with the GTAW process. When used for cutting, the plasma gas flow is increased so that the deeply-penetrating plasma jet cuts through the material, removing molten material as cutting dross. PAC differs from oxy-fuel cutting in that the plasma process operates by using the arc to melt the metal, whereas in the oxy-fuel process, the oxygen oxidizes the metal and the heat from the exothermic reaction melts the metal. Unlike oxy-fuel cutting, the PAC process can be applied to cutting metals that form refractory oxides such as stainless steel, cast iron, aluminum, and other nonferrous alloys. 8.7 Laser Beam Welding (LBW) and Electron Beam Welding (EBW). Austenitic stainless steels are readily ed by laser beam (LB) and electron beam welding (EBW) processes. The deep and narrow beads and rapid solidification of laser beam and electron beam welds can make them susceptible to solidification cracking for compositions that are normally predicted to be crack-free if arc welded.37 The AWS Welding Handbook, 9th ed., Vol. 3, Chapter 13 is an excellent reference for the EBW process as is AWS C7.1M/C7.1, Recommended Practices for Electron Beam Welding. AWS C7.2, Recommended Practices for Laser Beam Welding, Cutting, and Drilling, is a useful reference for LBW practices. 8.8 Resistance Welding. Stainless steel is readily welded by resistance welding because of its high electrical resistivity. The faying surfaces should be clean and free of contaminants that can cause inconsistent welds. In addition, some contaminants might contain a low melting point element such as sulfur or lead that can cause hot cracking in the welds. Machined surfaces and mill descaled rolled-sheet surfaces may be welded after solvent or vapor degreasing. Some solvents are toxic, and breathing the fumes can cause dizziness. Other solvents are flammable and require good ventilation; therefore, proper precautions should be taken. The resistance welding of stainless steels is discussed in AWS C1.1M/C1.1, Recommended Practices for Resistance Welding. 8.9 Brazing. Brazing is defined as the ing of materials using a filler metal that has a melting point above 450°C [840°F] and below the melting point of the base metal. During brazing, the filler metal flows between the closely fitting faying surfaces (typically with a gap of 0.05 mm to 0.10 mm [0.002 in to 0.004 in] for stainless steels) by capillary action. Brazing processes include torch (TB), furnace (FB), induction (IB), resistance (RB), dip (DB), infrared (IRB), and diffusion brazing (DFB). Most of the austenitic stainless steels can be brazed. Base material cleanliness and brazing procedures are essential to achieve a quality braze t. Copper-, silver-, and nickel-based filler metal compositions, as well as compositions based on precious metals have all been used to braze the stainless steels. Brazing is beyond the scope of this guide; therefore, additional detailed information on the brazing of stainless steels can be found in the AWS Brazing Handbook. Additional brazing information is available in the following references: AWS A5.8M/A5.8, Specification for the Filler Metals for Brazing and Braze Welding AWS A5.31M/A5.31, Specification for Fluxes for Brazing and Braze Welding AWS B2.2, Specification for Brazing Procedure and Performance Qualification AWS C3.2M/C3.2, Standard Method for Evaluating the Strength of Brazed ts AWS C3.3, Recommended Practices for the Design, Manufacture, and Examination of Critical Brazed Components AWS C3.4M/C3.4, Specification for Torch Brazing AWS C3.5M/C3.5, Specification for Induction Brazing AWS C3.6M/C3.6, Specification for Furnace Brazing AWS C3.8M/C3.8, Specification for the Ultrasonic Pulse-Echo Examination of Brazed ts AWS C3.9M/C3.9, Specification for Resistance Brazing 37 Castner,

H. R., 1993, What You Should Know About Austenitic Stainless Steels, Welding Journal 72(4): 53.

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9. Postweld Operations 9.1 Visual Examination. The simplest and least expensive welding inspection technique is to visually examine the finished weld and surrounding area for conformity to the applicable fabrication code and any contract specification requirements. In the absence of any governing requirements, fabricators frequently develop their own visual acceptance criteria by adopting criteria from various fabrication codes such as from the AWS D1.6/D1.6M, Structural Welding Code— Stainless Steel. As a minimum, the weld should be visually examined by the welder while welding progresses. While not all surface discontinuities can be easily identified, welders should be able to see a large majority of them before depositing the next bead or layer. These types of surface discontinuities include: porosity, cracks, undercut, under-fill, overlap, and lack of penetration (if the root side of the weld is accessible). When identified, the discontinuities can be removed rather than potentially covering the discontinuities with the next weld bead or layer. If, however, weld discontinuities are covered up by successive weld layers, the discontinuities cannot be subsequently identified by visual examination. Also, when the welder performs his or her own visual examination and discovers discontinuities, welding techniques and procedures can then be modified (within the limits permitted by the welding procedure) to minimize the formation of discontinuities on subsequent weld layers. For example, if crater cracks are forming, then pausing the welding progression at the weld stop/crater in order to fill the crater can frequently eliminate them. 9.2 Weld Size. Welders should also be trained to be able to measure fillet weld size and to achieve the required weld size (and weld fill) in the least number of weld es (within the limits permitted by the welding procedure). For example, if an 8 mm [5/16 in] fillet weld is required but only measures 6 mm [1/4 in] once completed, then it needs to be determined if a 6 mm [1/4 in] weld is acceptable or if the fillet size needs to be increased in accordance with the original design requirements. Depending on the welding process, an additional one to two weld es may be required and the final weld size may be larger than required. The final result, after additional welding, may be a 10 mm [3/8 in] fillet size rather than the 8 mm [5/16 in] fillet that was originally specified. This would result in approximately 44% additional filler metal, a doubling of the welding time, increased distortion, and likely a less preferable weld appearance. The additional manufacturing costs could be avoided if the welder slightly modified his or her welding technique to apply the 8 mm [5/16 in] fillet in a single . 9.3 Final Visual Examination. Depending on the contract requirements, in-process and final visual examination may be required to be performed using trained personnel. Examples include an inspector specially trained by the fabricator or a Certified Welding Inspector. The American Welding Society has a certification program (AWS QC1) for welding inspectors. 9.4 Weld Discontinuities. As a result of welding, the surface of the stainless steels can be affected by slag from coated electrodes, heat tint, arc strikes, welding stop points, and weld spatter. All of these have been known to initiate corrosion in aggressive environments that normally do not attack the stainless steel base metal. Arc strikes damage the stainless steel’s protective film and create small crack-like imperfections that should be removed by light grinding. Weld stop points can create small discontinuities in the weld metal. Inadvertent arc strikes, weld stop crater cracks, and embedded iron cause damage—they occur where the protective film has been somewhat weakened by the heat of welding. Weld stop cracks can readily be avoided by using run-out tabs (extensions at the end of a weld) or by beginning just ahead of the stop point and welding over each intermediate stop point. Arc strikes should be kept within the weld t area but not on the base material. Initially, the arc can be struck on the run-out tab or on previously deposited weld metal. Weld spatter creates a tiny weld where the molten slug of metal touches and adheres to the surface. The protective film is penetrated and tiny crevices are created where the film is weakened the most. Such problems can be minimized by using welding processes, filler metals, and techniques that do not produce significant amounts of spatter. A commercial spatterprevention paste may also be applied when necessary to either side of the t to be welded. The paste and spatter are washed off during cleanup. With chlorides and other aggressive chemicals, corrosion initiation sites can also be created by heavy/coarse grinding after welding, the welding of attachments on the outside surfaces, rough machining, shearing, and other operations that roughen the surface. In mild environments, stainless steel can normally tolerate surface imperfections. Heat tint can affect the ability of the stainless steel to resist corrosion. See 5.4 for more details on heat tint.

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9.5 Slag Removal. Slag can be difficult to remove completely, but it is important to do so. It is especially important if the structure is to be used in corrosive or high-temperature service where the slag particles create crevices and can cause corrosion problems and premature failure. In high-temperature oxidizing environments/service, over 540°C [1000°F], the fluoride in slags (or the environment) fosters fluoride attack on stainless steels. In reducing sulfur-bearing environments, slag absorbs sulfur, even if present at low concentrations. This results in the sulfidation of the underlying surface, which leads to corrosion and potentially failure. In even mildly corrosive media, slag, scale, and iron particles can set up active corrosion cells. Slag can be removed by appropriate means such as grinding, wire brushing, or media blasting. Refer to 9.6 and 9.7. 9.6 Grinding and Finishing Techniques. Because of the aesthetic value of many stainless weldments, it is desirable and sometimes necessary to refinish welds to blend with the parent metal. Finishing may be by grinding or by the use of sanding disks or flexible-backed pads, drums, disks, or belts to accomplish blending. Rough welds may be ground with a coarse-grit abrasive followed by successively finer grits until they are as smooth as or smoother than the parent metal. No operation in the weld-metal grinding sequence should leave scratches below the surface of the parent metal. This is necessary to allow sufficient material for the final finishing operation of the weld, which should leave the weld flush with the base material. Disks should be clean and, therefore, frequently replaced. The best method is to limit the use of coarser disks and employ progressively finer grades to smooth the surface. For optimum material removal rates and a corrosion-resistant surface profile, excessively worn or clogged discs should not be used as they tend to burnish and cold work the surface instead of removing material. To prevent chatter and to provide a generally smoother surface finish (compared to grinding discs), rubber-bonded wheels or flexible-backed abrasives are preferred for the final finishing step. 9.6.1 Grinding Wheel and Wire Brush Requirements. Free iron can be inadvertently deposited by wire brushing with carbon steel brushes or by grinding or wire brushing with contaminated grinding wheels or stainless brushes previously used on carbon steels. Fabricators should properly segregate and identify wheels and brushes for use on stainless steel only. Aluminum oxide and silicon carbide wheels are both commonly used for grinding stainless steels. Grinding wheels should not contain iron, iron oxides, zinc, or sulfides. Some grinding disks and wheel manufacturers produce specially identified grinding wheels manufactured from contaminant-free materials. Carbon steel and Series 400 stainless steel make stiff wires but contaminate the surface and should not be used. Only Series 300 wire brushes should be used on austenitic stainless steels. Even so, metal transfer from Types 302 and 304 stainless steels to the surface of more highly alloyed stainless steels occurs especially during aggressive brushing. This leaves the surface contaminated with a less corrosion-resistant material. For critical service, operators should follow brushing with local pickling or glass-bead blasting. 9.6.2 Aesthetics. Base material product forms are commonly furnished with a shiny luster or matte surface finish. This aesthetically appearing finish can otherwise be degraded by excessive or unnecessary grinding or heavy-handed power wire brushing. One of the most common reasons for iron contaminated (rusted) surfaces is the inadvertent use of contaminated grinding wheels and brushes. By instructing craft to avoid all unnecessary grinding/brushing, the aesthetic appearance of the mill’s surface finish can be largely maintained. Final surface finish expectations should be defined in contract documents and discussed in prefabrication kickoff meetings. 9.7 Media Blasting. Media blasting using shot, grit, or bead blasting will rapidly and effectively remove colored and black scale, as well as heat tint from stainless surfaces. A wide variety of different grit and shot media are available. Each media has its own advantages and disadvantages, such as removal rate, surface roughness and appearance, and recyclability. Because corrosion resistance depends on the material’s surface condition, the effect of the blast media and procedure should be closely pre-evaluated to confirm its suitability for a particular application. Some media examples include glass bead, ceramic bead, plastic beads, olivine, walnut shells, clean silica sand, copper slag, aluminum oxide, stainless steel shot, etc. Beads and shot produce smoother surface profiles than grit media. Silica sand should be used with caution as it is difficult to ensure that only clean sand is being used. Steel or iron-containing grit and shot should be avoided as well as blast media contaminated with iron. These types of media (especially grit) will embed iron particles on the surface which can lead to rusting. If these contaminants are not removed by a suitable cleaning or pickling treatment (see 9.8), they can lead to rust spots and pitting. A thorough, clean

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water rinse to remove any traces of acid is essential. If shot blasting is used, clean, noncontaminated stainless steel shot is recommended. Unless the stainless surface will be coated after fabrication, the maximum surface profile permitted by media blasting should be defined in contract documents. Some types of media and coarse grit can produce very coarse surface profiles. These coarse profiles tend to accumulate deposits in certain process environments, are more difficult to clean, and are generally less aesthetically appealing than a smooth surface profile. Caution is advised when blasting light gauge materials since distortion can result from local surface straining. Care should be taken to prevent excessive cutting by keeping the blast in motion. 9.8 Cleaning, Pickling, and ivation. Maintaining the corrosion resistance of stainless steels requires that the surface be clean and that the surface maintain its protective, ive film.38 Depending on the service environment, scale, heat tint, iron contamination, and other surface contaminants (e.g., dirt, chlorides, sulfides, welding slag and spatter, lubricants, oils, fingerprints, permanent marker inks/paints, crayon marks, adhesives, pickling and cleaning products) should be cleaned from the material surface as soon as practical after fabrication. Maintaining cleanliness during the manufacturing process may reduce or eliminate the amount of postfabrication cleaning. Examples of cleanliness control methods used during fabrication are discussed in 6.2. Maintaining cleanliness during manufacturing cannot always be achieved. Unfortunately, corrosion problems and iron contamination resulting in surface rusting is not always identified until after the equipment is installed. The cost of subsequent cleaning and repair can be substantial. Consequently, the designer, manufacturer, and end should evaluate the need for postfabrication cleaning operations. TIP 0402-35, Post-Fabrication Cleaning of Stainless Steel in the Pulp and Paper Industry, published by TAPPI is an excellent resource document that can be used for establishing requirements for cleaning other types of stainless equipment even besides pulp and paper equipment. For example, the document can be used to help establish rules for cleaning different types of surfaces/locations such as wetted surfaces, fully dry surfaces, process- surfaces, aesthetic surfaces, high temperature surfaces, etc. The document also provides guidance on the corrosion-resistance characteristics of surfaces prepared by: pickling vs. grinding, rough versus fine surface finishes, media blasting, etc. The effectiveness and precautions of different common cleaning methods and the skill level and labor needed for each method is also discussed. It offers the reader an overview of U.S. safety and environmental compliance regulations for chemical cleaning methods and disposal. 9.8.1 Identification of Contaminated Areas. Because iron-contaminated areas are not always identifiable until after shipment when the surfaces have been exposed to moisture or the service environment, it may be necessary to check for iron contamination while the component is in the shop. When corrosion resistance is of utmost concern, iron-contaminated areas may be identified by methods described in ASTM A380, Standard Recommended Practice for Cleaning, Descaling, and ivation of Stainless Steel Parts, Equipment, and Systems. The methods described in the standard include water-wetting and drying, high humidity test, copper sulfate test, and a ferroxyl test. When either the water-wetting or humidity tests are used, iron contamination will show up as rusted areas. When the copper sulfate test is used, copper will deposit on free iron. When the ferroxyl test is used, iron contamination will show up as an intense blue color on the material surface. After the degree of contamination is determined, the cleaning method may then be decided upon. 9.8.2 General Cleaning Recommendations. For fabrications that will be exposed to low-to-moderate corrosive environments, the fabrication may not require any cleaning or only require cleaning or scrubbing with a nontoxic solvent such as soap and warm water or nontoxic solvents (e.g., aliphatic hydrocarbons and d-Limonene). Other acceptable cleaning solvents include organic solvents such as acetone, alcohol, white spirits, and thinners.39 Local rules for the disposal of organic solvents, acids, and other chemicals should be followed. A written disposal procedure should be followed and proper personal protective equipment should be used. The cleaning of fabrications for aggressive environments is discussed in the February 1993 issue of the AWS Welding Journal under the Welding Research supplement section. Reported corrosion problems in specific environments and the importance of using clean stainless steel wire brushes, specially-reserved grinding wheels, and over grinding and coarse grinding are discussed, as well as the benefits and limitations of pickling to restore corrosion resistance. Additional 38 Gooch, 39 Hill,

T. G., 1996, Corrosion Behavior of Welded Stainless Steel, Welding Journal 75(5): 135-s–154-s. J. W., 2002, Chemical Treatment Enhances Stainless Steel Fabrication Quality, Welding Journal 81(5): 40–43.

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grinding, cleaning, and corrosion control methods are discussed in the Nickel Institute Technical Series Publication No.10026, Fabrication and Metallurgical Experience in Stainless Steel Process Vessels Exposed to Corrosive Aqueous Environments. Various acid-cleaning/ivating solutions are described in ASTM A380, Table A2.1. These solutions range from nitric-hydrofluoric, nitric, and citric acid-based solutions. Chlorinated solvents and abrasive scouring powders have been used, but the should be aware that chlorides can cause chloride stress corrosion cracking in the austenitic stainless steels. Avoiding chlorinated solvents is especially important if there are crevices that can trap the solution, if the solution cannot be completely removed or rinsed from the material’s surface immediately after cleaning, and when there is a potential for high residual welding stresses. If chlorinated solvents are used, then the duration of the exposure to any chlorinated solvents should be kept to a minimum; the base material and solution temperature during cleaning should not be excessive (e.g., 60°C [140°F]). The surface should be thoroughly rinsed and scrubbed using clean, soapy water followed by a thorough clean water rinse and thorough drying. If surface contamination is more severe, simple solvents may not be adequate to clean the surface. In those instances, phosphoric, or nitric acid-based solutions may be used to remove surface rusting and embedded iron.40 However, these solutions are not particularly effective for removing heat tint or heavier oxide scales. An example solution for cleaning free iron is a phosphoric acid-based (1 pH–2 pH at 55°C to 65°C [130°F to 150°F]) solution with surfactants and emulsifiers. Since acids will not remove oils and waxes, the oils and waxes should be removed prior to acid cleaning. Such oils and waxes can be removed with various cleaning solvents, or a hot aqueous solution containing surfactants and emulsifiers can be used. Cleaning the weld t area with flapper disks and wheels (coated abrasives) may also be considered as a method for cleaning surface contamination. Field experience has shown that these methods are relatively effective because contaminated sanding grit is continually removed from the disk or wheel while new abrasive is exposed. Smooth blending of the material surface is better accomplished with flapper disks, wheels, and drums than with grinding disks (bonded abrasives) with a grit that leaves a suitable finish. Blending for corrosive environments should preferably be performed in multiple steps using progressively finer grit. An excessively coarse final surface finish affects appearance and can degrade corrosion resistance. Specialty finishing products (e.g., nonwoven abrasives typically manufactured with nylon fibers bonded with synthetic resins and impregnated with abrasives such as 3M pads) can also be used to clean and finish surfaces. The relatively nonaggressive nature of nylon and the abrasive grit makes them an excellent finishing tool. These nonwoven products are manufactured in product forms such as hand pads, rolls, disks, belts, and wheels. Grinding, sanding, and finishing grit created from the abrasive cleaning process should be blown off the material surface to prevent recontamination. Abrasive cleaning may be followed by acid cleaning if determined necessary. It should also be noted that there are instances when using abrasives is undesirable because of the degradation of the material’s surface appearance, smoothness, and uniformity. When abrasive cleaning is used, the cleaning effectiveness should be verified by methods described earlier (e.g., waterwetting and drying, high humidity test, copper sulfate test, or ferroxyl test). 9.8.3 General Pickling Recommendations. For fabrications with heat tint or heavy oxide scales, aggressive cleaning operations may be required if the fabrication will be exposed to highly corrosive environments. Scales and heat tint may be removed by the use of sanding disks, drums, or by 3M pads, as previously described. However, when mechanical cleaning is impractical, costly, or not an appropriate cleaning method, postfabrication acid pickling may be required to maximize the material’s corrosion resistance. Pickling is frequently considered when large areas of scale or heat tint must be cleaned or when it is undesirable to abrasively finish the surface. It is also generally preferable to grinding when corrosion resistance is of utmost importance. Pickling, when performed, should be done as a final fabrication step (e.g., after slag removal, grinding, heat treatment, and finishing operations). Pickling with a nitric/hydrofluoric acid solution is a much more aggressive cleaning solution than the solutions that are typically used for surface cleaning of rust and free iron. The nitric/hydrofluoric acid solution is 40 Moller, G. E. and R. E. Avery, Nickel Institute Technical Bulletin 10026, “Fabrication and Metallurgical Experience in Stainless Steel Process Vessels Exposed to Corrosive Aqueous Environments.”

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used to remove high-temperature oxides, including the underlying chromium-depleted layer and any iron contamination. Contaminants such as oils, waxes, soil, etc. must be removed prior to pickling. When size permits, pickling by immersion (e.g., in nitric/hydrofluoric acid) is the simplest way to remove heat tint as well as other surface imperfections. For large or field-fabricated vessels, a nitric-hydrofluoric acid pickling paste spray or gel can be applied to heat tinted areas. However, such an application can initiate corrosion of the stainless substrate unless the paste is promptly removed according to the manufacturer’s directions. Pickling media applied near the end of one shift and left on to be removed by the next one or on the next day can initiate considerable discoloration and corrosion of the stainless steel. Strict adherence to manufacturer’s instructions will ensure desired results. Other techniques for removing heat tint include local electropolishing and glass bead blasting. A chemical ivation may be desirable after removal of heat tint. ASTM A380 should be referenced before attempting pickling or ivating. Extreme caution must be used when using pickling solutions because of their toxicity. Manufacturer’s handling, neutralization, and disposal directions must be adhered to, as well as all state, local, and federal regulations. Additionally, the s should be aware of the potential for intergranular corrosion of sensitized alloys or severe corrosion attack from prolonged exposure. Colored or black oxides (heat tint) can form in areas adjacent to welds as a result of exposure to the air or inadequate inert gas protection while at high temperatures. For light scale, usually a 10% to 15% nitric acid with 1/2% to 3% hydrofluoric (HF) acid is used at 50°C to 60°C [110°F to 125°F]. Heavier scales and heat tint may be removed using a 15% to 25% nitric, 1% to 8% HF solution as described in ASTM A380, Table A1.1. The HF solution is the active ingredient and the nitric acid, being a ivating agent, acts as an inhibitor to protect the already clean areas. The time of exposure is determined by periodically examining the surface. Excessive time will lead to overetching. Heavy scale is frequently removed (prior to pickling) by abrasive blasting, treating with 8% to 11% sulfuric acid at 65°C to 80°C [150°F to 180°F] for 5 minutes to 45 minutes, or by a nitric-HF solution as described in ASTM A380. A final scrubbing and rinse should be followed by nitric acid-HF pickling. For applications in aggressive environments, it may be advisable to develop full corrosion resistance by a ivation treatment subsequent to the pickling operation using a nitric acid-based gel or solution.41 Postcleaning and ivation of high purity tubing systems is described in issue No. 5 of Welding and Cutting.42 The technique includes flushing the system with water, followed by a detergent rinse to remove organics, followed by a water wash to remove the detergent. Other areas of potential debris accumulation are swabbed and inspected under UV and white light to the removal of organics. A nitric acid solution is circulated to dissolve iron oxide and other contaminants. The system is finally flushed with pure demineralized water to remove all traces of the nitric acid. Another commonly used ivation treatment uses citric acid for its easier disposal. Any acid treatment should be followed by a thorough rinsing in clean water to remove any traces of acid. 9.8.4 General ivation Recommendations. As identified in the and Definitions in this document, ivation refers to a chemical ivation treatment. A clean stainless steel surface, free of exogenous iron or iron compounds, automatically forms a ive surface layer. However, the ive layer is further enhanced by a chemical treatment. The three most widely used chemical ivation treatments use nitric acid, citric acid, or a mild oxidant such as hydrogen peroxide. There are various concentrations and procedures commonly used with these products, and are detailed by the various manufacturers. 9.9 Electropolishing. Electropolishing (EP) is essentially the opposite of electroplating a metal. Rather than depositing a metallic layer onto the surface of a metal, it is removed. Stainless steel is often a sound candidate for electropolishing because it creates a smooth textured, glossy surface. This is a common requirement found in many architectural and art type structures. When removing metal from a surface, contaminants such as oxides (heat tint) and free iron are extracted, as well as any “altered surface” resulting from cold working operations such as machining, grinding, or mechanical polishing. This leaves the surface with an optimum corrosion resistance, and with an excellent cleanability factor. It is this feature that distinguishes electropolishing as a widely used application in hygienic services. 41 Hill,

J. W., 2002, Chemical Treatment Enhances Stainless Steel Fabrication Quality, Welding Journal 81(5): 40–43. S., No. 5, 2003, Peterborough/UK, How to Achieve a Clean Process Pipeline, Welding and Cutting: 55.

42 Purnell,

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10. Heat Treatment Most austenitic stainless steel weldments do not require postweld heat treatment; however, a heat treatment is sometimes used to improve corrosion resistance or to relieve stresses. The three primary heat treatments used for austenitic stainless steels include the following: (1) Full (solution) annealing followed by rapid cooling from elevated temperatures, (2) Stress relieving, and (3) Stabilization anneal for stabilized grades such as Type 347-SS. 10.1 Solution Annealing. For solution annealing, the furnace should be capable of heating the entire weldment to the annealing temperature. Localized heating methods, such as induction or resistance heating, can produce sensitized zones adjacent to the heat treated zone. Residual stresses up to the material’s yield strength can also develop if sharp thermal gradients are present. The optimum solution annealing temperature depends on the type of stainless steel. The soaking time is determined by the section thickness. The steel manufacturer should be ed for precise annealing information, but the solution annealing temperatures for austenitic stainless steels are quite high, exceeding 1040°C [1900°F]. A short time at the annealing temperature is preferred to avoid grain growth. As a general rule, the soaking time at temperature should be 12 minutes for each 10 mm [0.4 in] of thickness. The weldment should be cooled rapidly and uniformly, at least through the temperature range of approximately 900°C to 425°C [1650°F to 800°F] to retain carbon in solid solution. Water quenching or spraying is necessary for thick sections, while air cooling is suitable for thin sections. For many weldments, there can be problems performing a solution heat treatment. For example, large annealing furnaces require adequate heating and cooling capabilities. Special handling methods should be considered if removal from the furnace is required for accelerated cooling. High-temperature oxide scale will form during solution anneal unless a protective atmosphere is used. Sagging and distortion of some fabrications can occur unless the fabrication is adequately braced and ed during heat treatment. Grain growth can occur unless the time at temperature is kept as short as possible. Weld metal properties should be verified through weld procedure qualification and testing as solution annealing will alter the mechanical properties compared to the as-welded (no postweld heat treatment performed) condition. 10.2 Stress Relief. Thermal treatments performed below the solution annealing temperature are sometimes used to reduce residual stresses, especially if the weldment will be final machined. However, properties of some austenitic stainless steels or welds can be degraded by sensitization or by sigma phase formation from PWHT (see 5.2, 5.3, and 10.3). When PWHT is necessary, selection of base materials, filler metals and heat treatment parameters (time at temperature), and cooling rates should be based in part considering any potential for sensitization or formation of sigma phase. For example, Figure 5.4a may be used to develop a stress relief treatment to avoid Cr-carbide precipitation if Type 304 is used.43 The selection of an appropriate heat treat temperature may avoid the need to perform additional supplementary Charpy tests during procedure qualification testing and during production welding. For example, fabrications built to ASME Section VIII requirements (part UHA) require impact testing of fabrications/weldments if austenitic stainless steels are thermally treated between 482°C and 900°C [900°F and 1650°F]. Types 304, 304L, 316, and 316L are exempt from impact testing for minimum design metal temperatures of –29°C [–20°F] and warmer if thermally treated between 482°C and 704°C [900°F and 1300°F]. However, the applicable year and addenda of the code of construction should always be consulted for qualification requirements and allowable exemptions. 10.2.1 PWHT of Incoloy® 800, 800H, 800HT®. The ASME B&PV Code, Section VIII, Rules for Construction of Pressure Vessels, Division 1 Part UNF, Clause UNF-56 mandates PWHT of UNS Nos. N08800 (Incoloy® 800), N08810 (Incoloy 800H), and N08811 (Incoloy 800HT®) alloys for design temperatures exceeding 1000°F [540°C]. ASME VIII1 specifies two alternatives for PWHT: (1) 1625°F [885°C] minimum PWHT temperature, or (2) the fabrication may be solution annealed in accordance with the material specification. ASME VIII-1 indicates that heating and cooling rates shall be by agreement between the and the manufacturer.44 43 Avery,

R. E., January/February 1999, Welding and Fabricating Nickel-Containing Stainless Steels and Nickel Alloys, Practical Welding Today: 30. 44 Incoloy® and 800HT® are ed trademarks of the Special Metals Corporation group of companies.

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At elevated temperatures, Nb-carbides form predominantly in grain interiors of weld deposits that are produced with Nbbearing filler metals, and Ti-carbides form predominantly in grain interiors of base metal HAZs and weld deposits that are produced with Ti-bearing filler metals. The formation of these carbides (and possibly Cr-carbides) tends to strengthen the grain interiors more so than at the grain boundaries. Under conditions of “high restraint” or “thick” materials, relaxation of residual stresses during high temperature service (or during PWHT) tends to occur more so at grain boundaries. This very localized stress relaxation at grain boundaries may potentially result in a form of grain boundary cracking termed “reheat cracking.” While ASME codes for pressure piping such as B31.1, Power Piping, and B31.3, Process Piping, do not mandate PWHT for alloys 800, 800H or 800HT, PWHT should be considered at least for “high restraint” or “heavy wall thickness” fabrications (that are destined for high temperature service) in order to potentially alleviate the potential for reheat cracking. However, since cracking could also potentially occur during heating to the PWHT temperature, the heating rate to the PWHT temperature (1625°F [885°C] minimum) should be controlled so that relaxation of residual stresses occurs at a faster rate than the rate of carbide formation. The tensile strength of alloys 800/800H/800HT tends to decrease at a significant rate above approximately 1100°F [600°C], and consequently, it is considered that the heating rate above this temperature should be maximized as much as practicable to the PWHT temperature. 10.3 Stabilization Anneal. A stabilization anneal is a heat treatment used to enhance the corrosion resistance of stabilized grades of stainless steels. This heat treatment, performed at a lower temperature than a solution annealing heat treatment, dissolves any chromium carbides that have formed during welding, and ensures that all the carbon has precipitated out as either Nb (i.e., Cb) or Ti carbides (refer to Figure 5.4b). A stabilization anneal is commonly specified for stabilized grades used in hot gas service containing hydrogen sulfide which when cooled may form polythionic acid if moisture is present. This heat treatment is used to prevent in-service corrosion attack of the heat-affected zone (HAZ) of stabilized grades of austenitic stainless steels (e.g., those alloyed with Nb or Ti such as Types 309Cb, 309HCb, 310Cb, 310HCb, 316Ti, 316Cb, 321,321H, 347, 347H, 348, and 348H). These grades are normally supplied in the solution annealed condition, with the stabilization heat treatment normally performed after welding. This heat treatment can also be used to prevent sensitization of base materials if they will be exposed to temperatures within the sensitization regime (refer to Figure 5.4a). Welding of stabilized alloys that have received a stabilization anneal dissolves the Ti/Nb-carbides in a very narrow zone of the HAZ adjacent to the weld fusion line. If the weldment is subsequently heated into the sensitizing range Cr carbides will form in this narrow zone in preference to Ti/Nb-carbides. This sensitization can result in a form of corrosion in the HAZ called knifeline attack (KLA) under some corrosive conditions. The presence of chromium carbides at the grain boundaries may lead to IGA (Intergranular Attack) or IG SCC (Intergranular Stress Corrosion Cracking). The term KLA comes from the common observation that the corroded zone is only one grain wide. In high-temperature service, high-carbon (H-grade) stabilized grades of stainless steels are commonly chosen because of their higher allowable design stresses. H-grades can be particularly sensitive to sensitization and KLA unless a stabilization anneal is performed after welding. In critical corrosive service, a stabilization anneal may be necessary for both unwelded base materials as well as welded fabrications. A stabilization anneal also provides significant stress relief. The appropriate temperature for a stabilization anneal is partially dependent on grade and end use. A common stabilization anneal temperature for 347H is 900°C [1650°F]. For 321 stainless the stabilization anneal is 850-900°C [15501650°F]. These temperatures are above the range that Cr-carbides form and are sufficiently high enough to dissolve any Cr-carbides that may have been previously developed. Furthermore, it is within the temperature range at which Nb/Ti combines with carbon to form desirable Nb or Ti carbides. In some thick, high-restraint fabrications, fast heating rates above about 600°C [1100°F] may be needed to prevent weld cracking during the stabilization anneal. Multi-step heat treatments have been used to reduce the possibility of this form of cracking. Limiting ferrite content to 10 FN maximum is also important in reducing the chance of cracking during the heat treatment of high-restraint weldments.

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11. Storage and Shipping Recommendations Proper, storage, handling, and shipping of materials prior to, during, and after fabrication is important to minimize or avoid iron contamination. Plate materials should be stored off the ground. Stacked plate materials should be protected from moisture, which may otherwise initiate premature corrosion especially in the presence of road salts. Carbon steels should not be stored on top of or with stainless steels without some type of clean suitable barrier material. Specialized packaging and coverings may be required depending on the application.

12. Maintenance and Repair 12.1 Maintenance. The maintenance of stainless steel weldments depends to a large degree on the service application. In many services, stainless steels are maintenance-free except for the routine cleaning needed for the particular application. Stainless steels perform best when the surfaces are maintained clean, free of deposits, free of embedded particles, or any condition that might damage or disrupt the ive film. Thorough cleaning should be the first maintenance rule. It is helpful to understand that the ive film in stainless steels exits only on the surface and is instantly renewed when oxygen in the atmosphere is present. If conditions exist where oxygen is not present, the ive film is not renewed and corrosion resistance is compromised. It is then important for optimum corrosion resistance to remove all slag, spatter, and other contaminations as well as avoiding crevices in the design of the weldment. Good maintenance practice includes a scheduled visual inspection of the equipment or component. As a rule, properly designed stainless steel weldments seldom experience structural failures. Problems are more likely to be corrosionrelated and unfortunately many corrosion problems are close to welds. Therefore, weld areas should be a primary inspection target. Visual inspection is normally adequate, along with liquid penetrant inspection for suspicious discontinuities. Stainless steels seldom experience general corrosion, except in the case of high-temperature oxidation losses. Corrosion is most commonly in the form of pitting (including that from microbiologically-influenced corrosion (MIC)), crevice, or chloride stress corrosion cracking. The following subclauses provide suggestions when inspecting for these types of corrosion. 12.1.1 Pitting and MIC. In extreme cases, pits may be completely through the material thickness and evident on the opposite side, causing a leak. The pits are often only on the product side and vary from initial stage pits to pits of considerable depth. In the case of MIC, the pit diameter at the surface is usually very small but progresses to a much larger diameter below the surface. MIC may occur away from welds but more often is near welds, particularly in areas where heat tint has not been removed. Pits should be probed with a sharp tool to determine the shape and depth as an aid in developing a repair procedure. 12.1.2 Crevice Corrosion. Crevice corrosion may occur in the space between similar metals, between a metal and a nonmetal, or very often under deposits. Inspections should focus on surface deposits, under gaskets, or deposits resulting from evaporation on any surface. The design of crevices in the weldment should be avoided (e.g., lack of seal welds in tube to tubesheet in heat exchangers). 12.1.3 Stress Corrosion Cracking (SCC). The most common form of SCC in stainless steels is chloride stress corrosion cracking (CSCC). It may take place in environments containing chlorides, elevated temperatures above about 66°C [150°F], and areas of applied or residual tensile stress. This type of corrosion progresses rapidly, so immediate repair is necessary to avoid failure of the component. When inspecting stainless steels in services where CSCC might be a factor, the likely areas of high stress are near welds (there are residual stresses near all welds) or in areas of applied stress, such as vessel or equipment s. 12.1.4 Rust Spots. It should be recognized that not all signs of corrosion (such as rust spots) are an indication of a corrosion problem, but rather may be caused by embedded iron. Subclause 6.2.1 offers guidelines to prevent iron contamination during fabrication. However, during the course of fabrication, installation, or in service, iron contamination may occur. Rusting from free iron deposits can be more of a cosmetic concern rather than a cause for alarm after a proper evaluation is made. The prevention and removal for free iron is discussed in 9.8.2.

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12.2 Repair. Some preventive maintenance repair work can be relatively simple and a detailed analysis is unnecessary. An example might be rebuilding the base metal thickness due to wear or erosion. Before undertaking a major repair, a thorough analysis should be made into the cause of the problem, the magnitude of the repair, and a well-thought-out repair procedure. 12.2.1 Cause. The first step should be to determine why the failure occurred, particularly if it relates to a fabrication defect or a service failure. Determining the cause of the failure could preclude a repeat failure if the same design or welding procedure is used. The investigation should include sketches with dimensions and photographs. Nondestructive and destructive examinations may be needed to determine the failure cause. Structural failures usually call for a design reassessment and require engineering design involvement. When there is a mechanical failure, for example in a groove weld, there is sometimes a tendency to increase the weld reinforcement. This is usually a mistake and may compound the problem, resulting in an earlier failure. When the cause is identified as an incorrect material selection, for example where a higher alloy grade of stainless steel should have been used, there are limited options short of replacing the complete component with a higher alloy. One exception might be where the weld metal suffered significantly greater corrosion than the stainless steel base metal. A repair could be made with higher alloy weld metal with greater corrosion resistance for that environment. When a particular area experiences corrosion or wastage, a higher alloy may be applied only to that area. The repair could be made by sheet lining the area with a higher alloy. This technique is widely used in the petroleum industry and power industry for flue gas desulfurization units.45 The applied sheet liner is typically about 1.6 mm [1/16 in] thick and fillet welded to the base metal. An alternative to sheet lining is to weld overlay the area using a higher alloy filler metal when the base material thickness allows. Another consideration when analyzing the cause should be the length of service before repair is necessary. The shorter the service life before repairing is required, the more critical it is to establish the cause of the problem. Conversely, if the unit has provided a long service and is finally wearing out, then a cost-benefit analysis may be appropriate. 12.2.2 Magnitude of Repair. The first assessment should be whether the component is beyond repair or if it would be more cost-effective to replace the component. Unfortunately, replacements are not always readily available and, if the unit must be back on line as soon as possible, temporary repairs are the only option. The remarks in this subclause are applicable to solid solution austenitic stainless steels. If there is any question about material identity, a material analysis should be made before attempting any repair. Before developing a detailed welding procedure, there are other factors that need to be addressed since they have an influence on the final weld procedure, namely the following: (1) Will the repair be made on site or can the component be moved to a shop for welding? (2) How accessible is the area for welding? (3) Will distortion from welding be a problem? (4) Are codes or specification requirements properly addressed? (5) Will there be a safe environment for the welders? 12.2.3 Weld Repair Procedure. Having examined the cause and magnitude of the repair, the next step is the design of the repair welding procedure. If the weldment is a part of the original manufacturer’s equipment and the repair is of significant magnitude, it may be advisable to the manufacturer for assistance. Since there are many types of failures, it is usually necessary to develop a welding procedure for each individual application. Two examples are the repair of a cracked weld and the repair of leaks from pitting attack. Additional information on maintenance and repair welding can be found in the AWS Welding Handbook, Materials and Applications—Part 1, 8th ed., Vol. 3. 45 NACE Standard RP0292-03, Standard Recommended Practice—Installation of Thin Metallic Wallpaper Lining in Air Pollution Control and Other Process Equipment.

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12.2.3.1 Procedure for the Repair of a Cracked Weld. A typical repair usually begins by completely removing the crack and preparing the groove surface for welding. The tip of a crack is the point of highest stress and can lead to ultimate component failure if not removed and properly repaired. Cracks never improve, they only grow with time. Repairs should never be attempted by simply welding over cracks; this does not remove the crack nor does it contain it. If cracks have a tendency to travel or increase in length during the excavation process, drilling a hole slightly past the end of the crack ends has been used successfully to prevent crack growth past the drilled hole locations. Excavation is normally made by grinding, although some thermal arc processes followed by grinding may be used in some instances. The groove profile needs to provide suitable access for welding. The excavated area should be visually examined and by liquid penetrant to ensure complete removal of the defect. In repair welding, distortion can be a very important factor and the control of distortion should be an integral part of the welding procedure. When distortion must be controlled, there are a number of helpful techniques that can be used for each particular case. The techniques include external fixtures, heat input control, sequence welding, and block sequence welding. Peening weld layers is beneficial in reducing weld stress, although it should not be performed on the root . When control of distortion is an important factor, dimensional measurements should be made during the welding operation so that corrective measures can be employed during the operation (e.g., weld sequencing or peening). Be aware of iron contamination if peening is considered. Other aspects of the weld repair procedure are essentially the same as the techniques discussed in Clauses 6 and 7. 12.2.3.2 Repair of Pits. An example of a procedure to repair pits might be pits in a stainless steel vessel as a result of microbiologically-influenced corrosion (MIC). Characteristically with MIC attack, some sites are through-wall penetration resulting in leaks if fluids are contained in the vessel. Less mature sites would not have through-wall penetration. Both types usually have very small diameters on the side on which the corrosion started. Also, the attack may travel horizontally below the surface and the void may not be evident from the outside. Weld procedure details can vary with particular situations, but guidelines to developing a successful repair procedure would usually include the following elements: (1) Thoroughly clean the surfaces to be repaired, e.g., by abrasive blasting, removing any tubercles at the pits. (2) Identify the spots of MIC attack by visual or liquid penetrant inspection (LPI). If the sites are all located along welds, radiography is also very effective in locating the areas of attack and revealing the size of subsurface attack. Mapping segments to be repaired provides an orderly approach to the inspection. (3) Use the gas tungsten arc welding (GTAW) process. This is often a trial and error approach with a skilled welder working on discontinuities in the vessel or, if possible, on scrap material that has been removed. The welder may have all the proper GTAW qualifications, but this repair technique approaches an “art” rather than a mechanical operation. The need for welder practice cannot be overemphasized. (4) Prior to welding, remove all corrosion products to the extent possible and dry the areas. Grinding into the void prior to welding may be useful, depending on factors such as material thickness and size of the subsurface void. A common technique would be to initiate the arc away from the pit opening, move into the pit area (allowing corrosion products to float to the surface), add filler metal, and apply current decay to the arc. (5) Ensure that the weld repairs are ground using a fine grit abrasive. Visual and LPI inspections should be used as final inspections.

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Annex A (Informative) Suggested Filler Metal Selection Chart This annex is not part of this standard but is included for informational purposes only.

A1. General Selection Notes The following filler metals are suggested based on common industry practice. Guarantees as to the suitability for any particular application, however, cannot be made because of application and process differences. It should not be assumed that filler metals having similar or equal chemical composition levels to the base metals will have adequate corrosion resistance and strength properties in highly corrosive environments or extreme service environments. Alloying elements in filler metals can segregate during weld metal solidification and can adversely affect weld metal corrosion resistance and strength properties.46 Molybdenum, for example, often segregates during welding, and overmatched filler metals are frequently specified to compensate. Other elements, such as phosphorous and sulfur, can segregate and cause weld metal solidification cracking if the levels are excessively high in the weld metal. Weld metal pickup of phosphorous (P) and sulfur (S) from free-machining base materials can lead to solidification cracking even if the as-purchased filler metals have very low P and S contents. Even in the absence of segregation, equivalent chemical composition weld metal can have properties significantly different than the base material because of the metallurgical microstructural differences between wrought products and a “cast” weld metal structure. Properties of the deposited weld metal (e.g., strength, corrosion resistance) are normally, but not always, specified to be equal to or greater than the base metal for a specific environment. Filler metal selection is typically based on comparisons to the applicable base material properties. Filler metals/deposited weld metal may be selected based on any of the following factors (where applicable): (1) Strength, e.g., ultimate tensile strength or yield strength at room temperature or the specific operating temperature; (2) Impact toughness properties at temperature; (3) Corrosion resistance properties at high temperatures against oxidation, carburization, sulfidation, etc.; (4) Aqueous corrosion resistance properties against pitting, general corrosion, chloride or sulfide stress corrosion cracking, etc.; (5) Sensitization resistance; (6) Low magnetic permeability, e.g., for electrical equipment; (7) Ductility; (8) Creep and stress-rupture properties; (9) Solidification cracking resistance; (10) Color; (11) Abrasion or erosion resistance; (12) Galling resistance; (13) Available electrodes for a given welding process; or (14) Cost. 46 Tuthill,

A. H. and R. E. Avery, 1993, Corrosion Behavior of Stainless Steel and High-Alloy Weldments in Aggressive Oxidizing Environments, Welding Journal 72(2): 41-s–49-s.

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Filler metals should be chosen based on desired final properties. It may be preferable, for example, to weld Type 304 base materials for cryogenic service with 316L type filler metals instead of the standard Type 308/308L fillers. Type 316L with a 2 FN maximum would result in better impact properties at cryogenic temperatures than 308 type filler metals. Previous studies have shown that carbon, nitrogen, and ferrite are detrimental to toughness; consequently, those values should be controlled.47, 48, 49 The 316L filler metals, especially E316L-15, would be more crack-resistant than Type 308L fillers.50 DC-lime (-15 type) coatings typically produce better cryogenic toughness than the rutile (-16 or -17 type) coatings because the DC-lime coatings produce a weld deposit with lower oxygen content than the rutile-coated electrodes. Weld metal oxygen is mostly present as oxide inclusions, which help to nucleate and grow the fracture in a Charpy V-notch test, or in real service fractures.51 It should be noted, however, that many manufacturers will manufacture and pretest their filler metals to specific requirements such as ferrite content. Useful information on the corrosion resistance of stainless steels in numerous corrosive environments is found in the Welding Journal.52 Some factors to consider for filler metal selection for improved weld metal toughness53 at cryogenic temperatures are low carbon, low ferrite, low nitrogen, higher nickel, lime-type SMAW electrodes, and a low weld metal inclusion content. For high-temperature applications, properties such as creep rupture, high-temperature strength, and corrosion resistance may be the primary considerations for selecting a filler metal. It should be noted that the creep-rupture strengths of weld metals are often less than those of wrought base metals with similar compositions. A study using Type 308 electrodes showed that increasing filler metal carbon levels caused an increase in creep-rupture strength and a decrease in ductility.54 H-grade filler metals are typically selected for high-temperature service applications. ASME code limits the use of austenitic stainless steels at temperatures above 538°C [1000°F] with a carbon content of 0.04% minimum; this applies to filler metal 308H. The detrimental effect of bismuth on high-temperature creep of Type 308 weld metals is discussed in the Welding Journal.55 API RP 582, Welding Guidelines for the Chemical, Oil and Gas Industries, restricts bismuth for Type 347 flux core weld deposits for high-temperature service due to reductions in weld metal creep strength. Bismuth is a common flux ingredient in flux-cored electrodes and may be used by some consumable manufacturers for other types of consumables. For heavily restrained fabrications that will be exposed to PWHT temperatures or high-temperature service, consideration for purchasing consumables with “no intentional additions of bismuth” should be considered for any consumable having mineral type fluxes, e.g., SAW fluxes, and SMAW and FCAW electrodes. A variety of sources should be researched before selecting a filler metal for severely corrosive or other extreme service environments. Useful descriptions and intended uses of filler metals are listed in the annexes of AWS A5.4/A5.4M, AWS A5.9/A5.9M, and AWS A5.22/A5.22M. Base material and filler material producers and suppliers may be consulted for their welding recommendations as well as welding consultants specializing in welding for corrosive environments. In many instances the customer will specify the desired filler metal. When welding to a code, the requirements for weld procedure qualification must be complied. Most codes, however, only address room-temperature properties, and the designer and engineer should evaluate the base materials and filler metals for their suitability for specific service environments. AWS D1.6/D1.6M, Structural Welding Code—Stainless Steel, is a useful document for structural welding applications. It provides requirements for writing and the application of prequalified WPSs covering weldments in thicknesses of 2 mm [1/16 in] or greater for the temperature range of –75°C to +430°C [–100°F to +800°F]. The WPSs apply only to austenitic stainless steels and to filler metals containing delta ferrite of at least 3.0 FN. 47 ESAB,

Quality Solutions for Welding and Cutting: 8-5. T., H. Satoh, Y. Wadayama, and F. Hataya, 1987, Mechanical Properties of Fully Austenitic Weld Deposits for Cryogenic Structures, Welding Journal 66(4): 120. 49 Kotecki, D., 2001, Stainless Q & A, Welding Journal 80(2): 82. 50 AWS A5.4/A5.4M:2006, Specification for Stainless Steel Electrodes for Shielded Metal Arc Welding, Annex Clause A9. 51 Kotecki, D., 2002, Stainless Q & A, Welding Journal 81(5): 76. 52 Gooch, T. G., 1996, Corrosion Behavior of Welded Stainless Steel, Welding Journal 75(5): 135-s–154-s. 53 Avery, R. E. and D. Parsons, 1995, Welding Stainless and 9% Nickel Steel Cryogenic Vessels, Welding Journal 74(11): 45–50. 54 Klueh, R. L. and D. P. Edmonds, 1986, Chemical Composition Effects on the Creep Strength of Type 308 Stainless Steel Weld Metal, Welding Journal 65(1): 1-s–7-s. 55 Konosu, S., A. Hashimoto, H. Mashiba, M. Takeshima, and T. Ohtsuka, 1998, Creep Crack Growth Properties of Type 308 Austenitic Stainless Steel Weld Metals, Welding Journal 77(8): 322–327. 48 Matsumoto,

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Table A.1 Suggested Filler Metal Selection Chart—Wrought Standard Grades The electrode listed first in a given space below is commonly selected for welding the referenced base material. Other listed electrodes have been specified for specific applications. For other specific applications, filler metal types other than those listed below may be suitable or preferable. Where no filler metal is shown, the base metal supplier for recommended filler metal. Base Metal

UNS Number r

SMAW Electrodess, t

Bare Electrodes and Rodsu Flux Core Electrodesv

Notes

201

S20100

E209 E219 E2209 E308

ER209 ER219 ER2209 ER308

E2209T E308T

a, b, n

202

S20200

E209 E219 E2209 E308

ER209 E0R219 ER2209 ER308

E2209T E308T

a, b, n

205

S20500

E240 E2209

ER240 ER2209

E2209T

n

209

S20910

E209 E2209

ER209 ER2209

E2209T

k, n

216

S21600

E209 E2209

ER209 ER2209

E2209T E316T

a, n

218

S21800

E2209

ER218 ER2209

E2209T

n

219

S21904

E219 E2209

ER219 ER2209

E2209T

n

240

S24000

E240 E2209

ER240 ER2209

E2209T

n

241

S24100

E240 E2209

ER240 ER2209

E2209T

n

301

S30100

E308

ER308

E308T

a, b

302

S30200

E308H E308

ER308H E308

E308HT E308T

a, b

302B

S30215

E308 E309

ER308 ER309

E308T E309T

303/303 Se

—

b

E312

ER312

E312T

e

304

S30400

E308 E309 E16-8-2 E316

ER308 ER309 ER308Si ER316 ER16-8-2

E308T E309T E316T

a, b, d, f, g, m, x

304L

S30403

E308L E309L E316L

ER308L ER309L ER316L ER308LSi ER316LSi

E308LT E309LT E316LT

b, d, x

304LN

S30453

E308L E2209

ER308L ER2209

E308LT E309LT E2209T

n

304H

S30409

E308H E309 E316H E16-8-2

ER308H ER309 ER316H ER16-8-2

E308HT E309T E316HT 16-8-2

b, f, i, m b, x

304N

S30451

E308 E2209

ER308 ER2209

E308T E2209T

b, n

305

S30500

E308

ER308

E308T

a, b, l

(Continued)

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Table A.1 (Continued) Suggested Filler Metal Selection Chart—Wrought Standard Grades The electrode listed first in a given space below is commonly selected for welding the referenced base material. Other listed electrodes have been specified for specific applications. For other specific applications, filler metal types other than those listed below may be suitable or preferable. Where no filler metal is shown, the base metal supplier for recommended filler metal. Base Metal

UNS Number r

SMAW Electrodess, t

309

S30900

E309

Bare Electrodes and Rodsu Flux Core Electrodesv ER309

E309T

Notes a, b

309S

S30908

E309

ER309

E309T

a, b

309H

S30908

E309

ER309

E309T

q, m

309Cb

S30940

E309Nb

24.13LNb

E309LNb

a, w

310

S31000

E310

ER310

E310T-G

o

310H

S31009

E310H

ER310H

E310T-G

o

310S

S31008

E310

ER310

E310T-G

o

310MoLN

S31050

25 22 2 N L

25 22 2 N L

314

S31400

E310

ER310

E310T

316

S31600

E316 E16-8-2 ENiCrMo-3

ER316 ER308Mo ER16-8-2 ERNiCrMo-3

E316T-1 E308MoT 16-8-2

316H

S31609

E316H E16-8-2 ENiCrMo-3

ER316H ER16-8-2 ERNiCrMo-3

E316HT

316L

S31603

E316L E308LMo ENiCrMo-3

ER316L E308LMo ERNiCrMo-3

E316LT ENiCrMo3T

316LN

S31653

E316L E317L ENiCrMo-3

ER316L ER317L ERNiCrMo-3

E316LT E317LT

b, h, j, n, y

316N

S31651

E316 E317 E318 ENiCrMo-3 E318

ER316 ER317 ER318 ERNiCrMo-3 ER318

E316T E317T

b, h, j, y

316Ti

S31635

ENiCrMo-3

ERNiCrMo-3

—

—

317

S31700

E317 ENiCrMo-3

ER317 ERNiCrMo-3

E317T

a, h

317L

S31703

E317L E385 ENiCrMo-3

ER317L ER385 ENiCrMo-3

E317LT ENiCrMo3T ERNiCrMo-3

h

317LM

S31725

ENiCrMo-3 ENiCrMo-4 ENiCrMo-10

ERNiCrMo-3 ERNiCrMo-4 ERNiCrMo-10

ENiCrMo3T ENiCrMo4T ENiCrMo10T E317LT

—

317LMN

S31726

ENiCrMo-3 ENiCrMo-4 ENiCrMo-10

ERNiCrMo-3 ERNiCrMo-4 ERNiCrMo-10

ENiCrMo3T ENiCrMo4T ENiCrMo10T E317LT

y

317LN

S31753

ENiCrMo-3 ENiCrMo-4

ERNiCrMo-3 ERNiCrMo-4

ENiCrMo3T ENiCrMo4T

y

321

S32100

E347 E16-8-2

ER347 ER321 ER347Si ER16-8-2

E347T

(Continued)

74

—

o, p b, c, f

f, i

b, c, f, h

b, f, i, m

AWS G2.3M/G2.3:2019

Table A.1 (Continued) Suggested Filler Metal Selection Chart—Wrought Standard Grades The electrode listed first in a given space below is commonly selected for welding the referenced base material. Other listed electrodes have been specified for specific applications. For other specific applications, filler metal types other than those listed below may be suitable or preferable. Where no filler metal is shown, the base metal supplier for recommended filler metal. UNS Number r

SMAW Electrodess, t

321H

S32109

E347 E16-8-2

ER347 ER16-8-2

E347HT

f, i, m, q

347

S34700

E347 E16-8-2

ER347 ER347Si ER16-8-2

E347T

b, f, i, m

347H

S34709

E347 E16-8-2

ER347 ER16-8-2

E347HT

f, i, m, q

348

S34800

E347

ER347

E347T

i, m

348H

S34809

E347

ER347

E347T

i, q, m

Base Metal

Bare Electrodes and Rodsu Flux Core Electrodesv

a

Notes

L-grades (low carbon) are generally acceptable. For high service temperatures, L-grade base materials and filler metals are not typically used because of reduced creep strength. b Si-grades (silicon enhanced) are available for the GMAW process for improved weld pool fluidity and weld appearance. c 308Mo/308MoL will result in higher ferrite levels than 316/316L. d 309/309L may be considered for severe corrosion conditions. e Welding of this and other “free-machining” grades (303, 303Se, 316F) may result in severe hot cracking because of phosphorous, selenium, or sulfur additions to the base metal. The increased ferrite of Type 312 filler metals helps but may not always work. f E16-8-2 may be considered for steam plant use or other high-temperature applications. AWS Welding Handbook, 7th ed., Vol. 4, Table 2.13. 16-8-2 consumables have good hot-ductility properties that offer relative freedom from weld or crater cracking, even under high-restraint conditions. The weld metal is usable in either the as-welded or solution-treated condition. Corrosion tests indicate that 16-8-2 weld metal may have less corrosion resistance than Type 316 base metal, depending on the corrosive media. g Type 316L fillers (2 FN max.) may be considered for cryogenic applications (ESAB, Quality Solutions for Welding and Cutting: 8-5). h The use of E/ERNiCrMo-3 filler metals for improved corrosion resistance for 316L/317L base materials used in aggressive oxidizing environments (e.g., paper mill bleach plants) is discussed in the Welding Journal 72(2), “Corrosion Behavior of Stainless Steel and High-Alloy Weldments in Aggressive Oxidizing Environments.” i Refer to Annex A, General Selection Notes for possible bismuth concerns in flux ingredients for highly restrained weldments which will be exposed to high temperatures. j Kotecki, D., 2001, Stainless Steel Q & A, Welding Journal 80(7): 90. k 8FN may be needed to prevent solidification cracking; Kotecki, D., 2003, Stainless Steel Q & A, Welding Journal 82(11): 80. l GTAW filler metal additions or consumable inserts for root welding may be needed to prevent solidification cracking when welding Type 305 base metals. Kotecki, D., 2002, Stainless Steel Q & A, Welding Journal 8 1(9): 88. mIf using for high-temperature service applications, ferrite should be restricted to 10 FN maximum to minimize the transformation of ferrite to sigma phase which would otherwise adversely embrittle the weld. n Duplex filler metals may be a good choice for 200 series alloys as they also contain higher levels of nitrogen and have comparable yield and tensile strengths. Duplex microstructures, however, are approx. a 50/50 mix of ferrite and austenite and should not be used if the service temperature is higher than 300°C [570°F] or below –40°C [–40°F] or if the corrosive environment selectively attacks ferrite. Duplex alloys are also suitable in some applications for 300 Series. o Consult electrode manufacturers for their proprietary E 310T-G FCAW electrode versions. p European Standard EN ISO 143. q In cases where H grades are not in the AWS filler metal specification, 0.04 min carbon may be requested. r SAE HS-1086, Metals & Alloys in the Unified Numbering System. s Refer to Table 8.3 for useability guidelines for SMAW stainless steel electrodes for welding current, position of welding, and operating characteristics. t AWS Specifications A5.4/A5.4M and A5.11/A5.11M for nickel-based SMAW electrodes. u AWS Specifications A5.9/A5.9M and A5.14/A5.14M for nickel-based bare wire and electrodes. The AWS electrode classification for bare metalcored stainless steel electrodes produced under AWS specification A5.22/A5.22M begins with the letters “EC” instead of “ER.” v AWS Specifications A5.22/A5.22M and A5.34/A5.34M for nickel-based FCAW electrodes. Refer to Table 8.15 for usability guidelines for FCAW stainless steel electrodes for welding current, position of welding, and shielding gas. w 24.13LNb is a ed trademark of Sandvik Materials Technology that meets E309Nb. x 316/316L filler metals are sometimes used for welding type 304/304L base materials for general corrosive service. For severe corrosive service where molybdenum-bearing filler metals are indicated for type 304/304L base materials, the should that the corrosive conditions do not selectively attack molybdenum bearing alloys. For example, type 316/316L is reportedly less corrosion resistant in highly concentrated H2SO4 and hydrazine than 304/304L base materials and 308/308L weld deposits. y When welding nitrogen-bearing austenitic stainless steels with niobium [Nb(Cb)]-bearing welding consumables (refer to Table 8.10), there is a strong tendency for nitrogen to diffuse (migrate) from the HAZ and combine with niobium in the weld deposit (forming niobium nitrides).This leaves the fusion line strengthened by niobium nitride precipitates, while the HAZ is simultaneously weakened and potentially more susceptible to corrosion because of the nitrogen depletion. The strength differences between weld deposit, fusion line, HAZ and base material may adversely affect weld procedure qualification bend test results. For severe corrosive service or when the strength of the weld region must be controlled, niobium-free consumables (example: E/ER NiCrMo-10) may be considered.

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Table A.2 Suggested Filler Metal Selection Chart—Wrought Proprietary Grades The electrode listed first in a given space below is commonly selected for welding the referenced base material. Other listed electrodes have been specified for specific applications. For other specific applications, filler metal types other than those listed below may be suitable or preferable. Where no filler metal is shown, the base metal supplier for recommended filler metal. Base Metal

UNS Numbera

SMAW Electrodesh

Bare Electrodes and Rodsi Flux Core Electrodesj

Notes

20 (20Cb-3)

N08020

E320LR, E320, ENiCrMo-3

ER320LR, ER320, ERNiCrMo-3

ENiCrMo-3

b

800

N08800 N08810 N08811

ENiCrFe-2, ENiCrCoMo-1

ERNiCr-3, ERNiCrCoMo-1

ENiCr3Tx-y, ENiCrFe2Tx-y, ENiCrFe3Tx-y, ENiCrCoMo1Tx-y

—

825

N08825

ENiCrMo-3, ENiCrMo-14

ERNiCrMo-3, ERNiCrMo-14

ENiCrMo3Tx-y

—

RA 330®

N08330

E330 ENiCrFe-2, ENiCrFe-3

ER330, ERNiCr-3

ENiCr3Tx-y, ENiCrFe2Tx-y

e

253 MA

S30815

EN 1600 alloy type 22 12 H

—

—

c, d, f

31

N08031

ENiCrMo-10, ENiCrMo-13, ENiCrMo-14

ERNiCrMo-10, ERNiCrMo-13, ERNiCrMo-14

ENiCrMo10Tx-y

—

1925 hMo (926)

N08925

ENiCrMo-13 ENiCrMo-3, ENiCrMo-10

ERNiCrMo-13 ERNiCrMo-3, ERNiCrMo-10

ENiCrMo3Tx-y, ENiCrMo10Tx-y

—

254 SMO

S31254

ENiCrMo-3, ENiCrMo-10

ERNiCrMo-3, ERNiCrMo-10

ENiCrMo3Tx-y, ENiCrMo10Tx-y

k

654 SMO

S32654

ENiCrMo-13, ENiCrMo-14

ERNiCrMo-13, ERNiCrMo-14

—

—

28

N08028

E383

ER383

—

g

904L

N08904

E385, ENiCrMo-3, ENiCrMo-4, ENiCrMo-10

ER385, ERNiCrMo-3, ERNiCrMo-4, ERNiCrMo-10

ENiCrMo3Tx-y, ENiCrMo4Tx-y, ENiCrMo10Tx-y

—

AL-6XN

N08367

ERNiCrMo-3, ENiCrMo-10

ERNiCrMo-3, ERNiCrMo-10

ENiCrMo3Tx-y, ENiCrMo10Tx-y

k, m

20Mo-4

N08024

ENiCrMo-3

ERNiCrMo-3

ENiCrMo3Tx-y

—

20Mo-6

N08026

ENiCrMo-3, ENiCrMo-10

ENiCrMo-3, ERNiCrMo-10

ENiCrMo3Tx-y, ENiCrMo10Tx-y

k

25-6Mo

N08926

ENiCrMo-10, ENiCrMo-3, ENiCrMo-14

ERNiCrMo-10, ERNiCrMo-3, ERNiCrMo-14

ENiCrMo10Tx-y, ENiCrMo3Tx-y

k

27-7MO

S31277

ENiCrMo-10, ENiCrMo-14

ERNiCrMo-10, ERNiCrMo-14

ENiCrMo10Tx-y

—

a

SAE HS-1086, Metals & Alloys in the Unified Numbering System. 320LR is manufactured with low-residual elements such as sulfur, phosphorous, and silicon to help minimize hot cracking and microfissuring when welding fully austenitic stainless steels. Low carbon improves corrosion resistance. c Proprietary grades available. d European Standard EN ISO 14343. e RA330 is a ed trademark of Rolled Alloys. Matching grade consumables (e.g., type 330) may be used, with possible risk of hot cracking. For specific welding guidelines, refer to the Rolled Alloys website. The nickel-based filler metals are capable of producing sound welds but may not provide equivalent oxidation resistance as the base material in high-temperature service. f Base material and electrode manufacturers should be consulted prior to selecting a filler material. 253 MA is designed for its high-temperature characteristics, e.g., for its creep and corrosion resistance in various environments e.g., oxidizing, reducing, nitriding, sulfidizing, or carburizing. Ferrite should be limited to minimize the formation of sigma phase during high-temperature service. b

(Continued)

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Table A.2 (Continued) Suggested Filler Metal Selection Chart—Wrought Proprietary Grades g

Types 383 and 385 are not available in flux core electrodes. AWS Specifications A5.4/A5.4M and A5.11/A5.11M for nickel-based SMAW electrodes. i AWS Specifications A5.9/A5.9M and A5.14/A5.14M for nickel-based bare wire and electrodes. The AWS electrode classification for bare metalcored stainless steel electrodes produced under AWS specification A5.22/A5.22M begins with the letters “EC” instead of “ER.” j AWS Specifications A5.22/A5.22M and A5.34/A5.34M for nickel-based FCAW electrodes. Refer to Table 8.15 for usability guidelines for FCAW stainless steel electrodes for welding current, position of welding, and shielding gas. k When welding nitrogen-bearing austenitic stainless steels with niobium [Nb(Cb)]-bearing welding consumables (refer to Table 8.10), there is a strong tendency for nitrogen to diffuse (migrate) from the HAZ and combine with niobium in the weld deposit (forming niobium carbides).This leaves the fusion line strengthened by niobium carbide precipitates, while the HAZ is simultaneously weakened and potentially more susceptible to corrosion because of the nitrogen depletion. The strength differences between weld deposit, fusion line, HAZ and base material may adversely affect weld procedure qualification bend test results. For severe corrosive service or when the strength of the weld region must be controlled, niobium-free consumables (example: E/ER NiCrMo-10) may be considered. l For elevated temperature service, ENiCrCoMo-1 is suggested only for design temperature exceeding 790°C [1450°F]. For elevated temperature service below 790°C [1450°F], ENiCrCoMo-1 is considered excessively overmatched (strength wise) compared to base material properties. ENiCrFe-2 and ERNiCr-3 are typical filler selection for < 790°C [1450°F] except for low temperature corrosive service environments where E/ERNiCrCoMo-1 may be used. mAL-6XN® is a ed trademark of Allegheny Ludlum Corporation. h

Table A.3 Filler Selection for Stainless Steel Castings The electrode listed first in a given space below is commonly selected for welding the referenced base material. Other listed electrodes have been specified for specific applications. For other specific applications, filler metal types other than those listed below may be suitable or preferable. Where no filler metal is shown, the base metal supplier for recommended filler metal. ACI Designation

UNS Numbera

Reference Grade

CE20N

J92802

309

CF3

J92500

304L

CF10 CF10M CF10MC CF10SMnN

J92590 J92901 J92971 J92972

304H 316H 316Cb Nitronic 60

CF20 CF3M

— J92800

302 316L

CF8

J92600

304

CF8C

J92710

347

CF8M

J92900

316

CG12 CG6MMN

J93001 J93790

309 Nitronic 50

CG8M

J93000

317

ASTM Reference

AWS A5.4/A5.4M

A351 E309-XX A451 A351 E308L-XX A743 A744 A351 E308H-XX A351 E316H-XX A351 — A351 — A743 A743 E308-XX E316L-XX A351 A743 A744 A351 E308-XX A743 A744 A351 E347-XX A743 A744 A351 E316-XX A743 A744 A743 E309-XX A351 E209-XX or A743 E2209-XXg A351 E317-XX A743 A744 (Continued)

77

AWS A5.9/A5.9M

AWS A5.22/A5.22M

ER309

E309TX-X

ER308L

E308LTX-X

ER308H ER316H — ER218

E308HTX-X E316HTX-X — EC218

ER308 ER316L

E308TX-X E316LTX-X

ER308

E308TX-X

ER347

ER347TX-X

ER316

E316TX-X

ER309 ER209 or ER2209g ER317

E309TX-X ER2209TX-Xg E317TX-X

AWS G2.3M/G2.3:2019

Table A.3 (Continued) Filler Selection for Stainless Steel Castings The electrode listed first in a given space below is commonly selected for welding the referenced base material. Other listed electrodes have been specified for specific applications. For other specific applications, filler metal types other than those listed below may be suitable or preferable. Where no filler metal is shown, the base metal supplier for recommended filler metal. ACI Designation

UNS Numbera

Reference Grade

CH10

J93401

309H

CH20

J93402

309

CH8

J93400

309S

CK20

J94202

310H

CK3MCuN

J93254

254SMO

CN3M

J94652

904L

CN3MCu

J80020

20Cb3

CN3MN

J94651

AL6-XN

CN7M

N08007

CU5MCuC HE

N08826 J93403

320 20Cb3 825 312

HF HH HK

J92603 J93503 J94224

304H 309 310

HK30

J94203

—

HK40

J94204

—

HL

N08604

—

HN HP HT HU

J94213 N08705 N08605 N08004

— — 330 —

ASTM Reference

AWS A5.4/A5.4M

A351 A451 A243 A743 A351 A351 A451 A351 A451 A743 A743 A744 A990 A743

A990 A744 A743 A743 A744 A494 A297 A608 A297 A297 A297 A351 A608 A351 A608 A351 A608 A297 A608 A297 A297 A297 A297

AWS A5.9/A5.9M

AWS A5.22/A5.22M

E309H-XX

ER309

E309HTX-X

E309-XX

ER309

E309TX-X

E309-XX

ER309Si

E309TX-X

E310H-XX

ER310

E310TG-X

ENiCrMo-3b, c ENiCrMo-10

ERNiCrMo-3b, d ERNiCrMo-10d

ENiCrMo3Tx-yb ENiCrMo10Tx-ye

E385-XX ENiCrMo-3c ENiCrMo-4c E320LR-XX

ER385 ERNiCrMo-3d ERNiCrMo-4d ER320LR

ENiCrMo3Tx-ye ENiCrMo4Tx-ye —

ENiCrMo-3b, c ENiCrMo-10 E320LR-XX

ERNiCrMo-3b, d ERNiCrMo-10d ER320LR

ENiCrMo3Tx-yb ENiCrMo10Tx-ye —

— E312-XX

ERNiFeCr-1d ER312

— E312TX-X

E308-XX E309-XX E310H-XX

ER308 ER309

E308LTX-X E309TX-X —

—

E310H-XX

—

—

E310H-XX

ER25/35Hf ERNiCrCoMo-1 —

— — —

— ER25/35Hf ER330 —

— — — —

— E330H — E330-XX E330

a

SAE HS-1086, Metals & Alloys in the Unified Numbering System. See 5.3.1 on segregation effects. c AWS A5.11/A5.11M, Specification for Nickel and Nickel-Alloy Welding Electrodes for Shielded Metal Arc Welding. d AWS A5.14/A5.14M, Specification for Nickel and Nickel-Alloy Bare Welding Electrodes and Rods. e AWS A5.34/A5.34M, Specification for Nickel-Alloy Electrodes for Flux Cored Arc Welding. f Proprietary, Non AWS A5.9/A5.9M grade. g Acceptable filler metal for use up to 260°C [500°F]. b

Note: Filler metal references are not all inclusive, but others may be used depending on the application and service conditions. It is advisable to check the casting producer for recommended filler metals for high-temperature castings.

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Annex B (Informative) Informative References This annex is not part of this standard but is included for informational purposes only.

ASM International, Home Page, November 16, 2007, http://www.asminternational.org. ASME B16.25, Buttwelding Ends, American Society of Mechanical Engineers. ASTM A799/A799M (A01.02), Standard Practice for Steel Castings, Stainless, Instrument Calibration, for Estimating Ferrite Content, ASTM International. ASTM A967, Standard Specification for Chemical ivation Treatments for Stainless Steel Parts, ASTM International. ASME B31.1, Power Piping, American Society of Mechanical Engineers. ASME B31.3, Process Piping, American Society of Mechanical Engineers. ASME Boiler and Pressure Vessel Code, Section VIII, Division 1—Rules for Construction of Pressure Vessels, American Society of Mechanical Engineers. Australian Stainless Steel Development Association (ASSDA), Home Page, May 23, 2011, http://www.assda.asn.au. AWS A4.2M:2006 (ISO 8249:2000 MOD), Standard Procedures for Calibrating Magnetic Instruments to Measure the Delta Ferrite Content of Austenitic and Duplex Ferritic-Austenitic Stainless Steel Weld Metal AWS A5.30/A5.30M, Specification for Consumable Inserts, American Welding Society AWS C1.1M/C1.1, Recommended Practices for Resistance Welding, American Welding Society. AWS C5.5/C5.5M, Recommended Practices for Gas Tungsten Arc Welding, American Welding Society. AWS C5.10/C5.10M, Recommended Practices for Shielding Gases for Welding and Plasma Arc Cutting, American Welding Society. AWS C7.1M/C7.1, Recommended Practices for Electron Beam Welding, American Welding Society. AWS C7.2, Recommended Practices for Laser Beam Welding, Cutting, and Drilling, American Welding Society. AWS D1.6/D1.6M, Structural Welding Code—Stainless Steel, American Welding Society. AWS D10.4-86R, Recommended Practices for Welding Austenitic Chromium-Nickel Stainless Steel Piping and Tubing, American Welding Society. AWS D10.11M/D10.11, Recommended Practices for Root Welding of Pipe Without Backing, American Welding Society. AWS D18.2, Guide to Weld Discoloration Levels on Inside of Austenitic Stainless Steel Tube, American Welding Society. AWS, 2007, Brazing Handbook, 5th ed., Miami: American Welding Society. AWS Welding Handbook series, 8th and 9th ed. Avery R. E. and A. H. Tuthill, 1993, Corrosion Behavior of Stainless Steel and High-Alloy Weldments in Aggressive Oxidizing Environments, Welding Journal 72(2): 41.

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Avery R. E. and D. Parsons, 1995, Welding Stainless and 9% Nickel Steel Cryogenic Vessels, Welding Journal 74(11): 45–50. British Stainless Steel Association (BSSA), Home Page, May 23, 2011, http://www.bssa.org.uk. CASTI Metals Blue Book—Welding Filler Metals, 4th ed., CASTI Publishing Inc. CASTI Metals Red Book—Nonferrous Metals, 4th ed., CASTI Publishing Inc. CASTI Publishing, Home Page, December 12, 2007, http://www.casti.ca. Cedinox (Spanish), Home Page, May 23, 2011, http://www.cedinox.es. Centro Inox (Italian), Home Page, May 23, 2011, http://www.centroinox.it. ESAB, Quality Solutions for Welding and Cutting: 8-5. Euro Inox, Home Page, May 23, 2011, http://www.euro-inox.org. Gooch, T. G., 1996, Corrosion Behavior of Welded Stainless Steel, Welding Journal 75(5): 135-s–154-s. Indian Stainless Steel Development Association (ISSDA), Home Page, May 23, 2011, http://www.stainlessindia.org. International Chromium Development Association, Home Page, May 23, 2011, http://www.icdachromium.com. International Molybdenum Association, Home Page, May 23, 2011, http://www.imoa.info. International Stainless Steel Forum (ISSF), Home Page, May 23, 2011, http://www.worldstainless.org. Irving, B., 1994, Trying to Make Some Sense Out of Shielding Gases, Welding Journal 73(5): 65–70. Key To Steel, Home Page, December 12, 2007, http://www.key-to-steel.com. Klueh, R. L. and D. P. Edmonds, 1986, Chemical Composition Effects on the Creep Strength of Type 308 Stainless Steel Weld Metal, Welding Journal 65(1): 1-s–7-s. Konosu, S., A. Hashimoto, H. Mashiba, M. Takeshima, and T. Ohtsuka, 1998, Creep Crack Growth Properties of Type 308 Austenitic Stainless Steel Weld Metals, Welding Journal 77(8): 322. JIS Handbook, Ferrous Materials and Metallurgy, Books I and II, Tokyo: Japanese Standards Association. Lambert, J. A., 1991, Cast-to-Cast Variability in Stainless Steel Mechanized GTA Welds, Welding Journal 70(5): 41. Lundin, C. D. and C. P. D. Chou, November 1983, Hot Cracking Susceptibility of Austenitic Stainless Steel Weld Metals, Welding Research Council Bulletin 289. Lundin, C. D., C. H. Lee, R. Menon, and E. E. Stansbury, November 1986, Sensitization of Austenitic Stainless Steels: Effects of Welding Variables on HAZ Sensitization of AISI 304 and HAZ Behavior of BWR Alternative Alloys 316 NG and 347, Welding Research Council Bulletin 319. Matsumoto, T., H. Satoh, Y. Wadayama, and F. Hataya, 1987, Mechanical Properties of Fully Austenitic Weld Deposits for Cryogenic Structures, Welding Journal 66(4): 120-s–126-s. MatWeb, Home Page, December 13, 2007, http://www.matweb.com. National Association of Corrosion Engineers, Home Page, May 23, 2011, http://www.nace.org. Nickel Institute, Home Page, May 23, 2011, http://www.nickelinstitute.org. Onsoein, M., R. Peters, D. L. Olson, and S. Liu, 1995, Effect of Hydrogen in an Argon GTAW Shielding Gas: Arc Characteristics and Bead Morphology, Welding Journal 74(1): 10. PFI ES21, Internal Machining and Fit-up of GTAW Root Circumferential Butt Welds, Pipe Fabrication Institute. PFI ES35, Nonsymmetrical Bevels and t Configurations for Butt Welds, Pipe Fabrication Institute. Praxair, Shielding Gases Selection Manual: 32. Specialty Steel Industry of North America, Home Page, May 23, 2011, http://www.ssina.com.

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Stainless Steel Council of China Specialist Steel Enterprises Ass. (CSSC), Home Page, May 23, 2011, http://www.cssc. org.cn. Steel Construction Institute, Home Page, May 23, 2011, http://www.steel-sci.org. Wegst, C. W., Stahlschlüssel (Key to Steel), ASM International. TIP 0402-35, Post-Fabrication Cleaning of Stainless Steel in the Pulp and Paper Industry, TAPPI. Worldwide Guide to Equivalent Nonferrous Metals and Alloys, 2001, 4th ed., ASM International. Young, B., 1995, Purging Gases: Making the Right Selection, Welding Journal 74(1): 47.

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Annex C (Informative) ASTM Base Material Specifications for Austenitic Stainless Steels This annex is not part of this standard but is included for informational purposes only.

C1. Plate, Sheet, and Strip (ASTM Book of Standards Volume 01.03) A167: Stainless and Heat-Resisting Chromium-Nickel Steel Plate, Sheet, and Strip A240/A240M: Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and General Applications A264: (ASTM Book of Standards Volume 01.04) Stainless Chromium-Nickel Steel-Clad Plate. A480/A480M: General Requirements for Flat-Rolled Stainless and Heat-Resisting Steel Plate, Sheet, and Strip (and applies to each of the following: A167, A240/A240M, A264, A666, A793, and A895) A666: Annealed or Cold-Worked Austenitic Stainless Steel Sheet, Strip, Plate, and Flat Bar (replaces A177 and A412) A793: Rolled Floor Plate. Stainless Steel A895: Free-Machining Stainless Steel Plate, Sheet, and Strip A946: Chromium, Chromium-Nickel, and Silicon Alloy Steel Plate, Sheet, and Strip for Corrosion and Heat Resisting Service

C2. Tube (ASTM Book of Standards Volume 01.01) A213/A213M: Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes A249/A249M: Welded Austenitic Steel Boiler, Superheater, Heat-Exchanger, and Condenser Tubes A269: Seamless and Welded Austenitic Stainless Steel Tubing for General Service A270: Seamless and Welded Austenitic Stainless Steel Sanitary Tubing A450/A450M: General Requirements for Carbon, Ferritic Alloy, and Austenitic Alloy Steel Tubes (references the following: A213/A213M, A249/A249M, A269, A270, A271, A688/A688M, A771, A789/A789M, A791/A791M, A803/ A803M, A826, A851) A511: Seamless Stainless Steel Mechanical Tubing A554: Welded Stainless Steel Mechanical Tubing A632: Seamless and Welded Austenitic Stainless Steel Tubing (Small-Diameter) for General Service A688/A688M: Welded Austenitic Stainless Steel Feedwater Heater Tubes A778: Welded Unannealed Austenitic Stainless Steel Tubular Products

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A789/A789M: Seamless and Welded Ferritic/Austenitic Stainless Steel Tubing for General Service A1012: Seamless and Welded Ferritic, Austenitic and Duplex Alloy Steel Condenser and Heat Exchanger Tubes with Integral Fins A1016/A1016M: General Requirements for Ferritic Alloy Steel, Austenitic Alloy Steel, and Stainless Steel Tubes

C3. Bar (ASTM Book of Standards Volume 01.03) These standards cover hot-finished or cold-finished bars including rounds, squares, hexagons, and hot-rolled or extruded shapes, such as angles, tees, and channels in the more commonly used types of stainless steel. A276: Stainless Steel Bars and Shapes A479/A479M: Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels A484/A484M: General requirements for Stainless Steel Bars, Billets, and Forgings A582/A582M: Free-Machining Stainless Steel Bars A955/A955M: (ASTM Book of Standards Volume 01.04) Deformed and Plain Stainless Steel Bars for Concrete Reinforcement A968/A968M: Chromium, Chromium-Nickel, and Silicon Alloy Steel Bars and Shapes for Corrosion and Heat-Resisting Service

C4. Forgings (ASTM Book of Standards Volume 01.03) These standards cover forgings and billets or other semi-finished material (except wire) for forging. A276: Stainless Steel Bars and Shapes A479/A479M: Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels A484/A484M: General Requirements for Stainless Steel Bars, Billets, and Forgings A582/A582M: Free-Machining Stainless Steel Bars A955/A955M: (ASTM Book of Standards Volume 01.04) Deformed and Plain Stainless Steel Bars for Concrete Reinforcement A968/A968M: Chromium, Chromium-Nickel, and Silicon Alloy Steel Bars and Shapes for Corrosion and Heat-Resisting Service

C5. Pipe (ASTM Book of Standards Volume 01.01) A312/312M: Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes A358/358M: Electric-Fusion-Welded Austenitic Chromium-nickel Stainless Steel Pipe for High-Temperature Service and General Applications A376/A376M: Seamless Austenitic Steel Pipe for High-Temperature Central-Station Service A409/A409M: Welded Large Diameter Austenitic Steel Pipe for Corrosive or High-Temperature Service A813/A813M: Single- or Double-Welded Austenitic Stainless Steel Pipe A814/A814M: Cold-Worked Welded Austenitic Stainless Steel Pipe A999: General Requirements for Alloy and Stainless Steel Pipe

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C6. Fittings (ASTM Book of Standards Volume 01.01) A403/A403M: Wrought Austenitic Stainless Steel Pipe Fittings A733: Welded and Seamless Carbon Steel and Austenitic Stainless Steel Pipe Nipples A774/A774M: As-Welded Wrought Austenitic Stainless Steel Fittings for General Corrosive Service at Low and Moderate Temperatures A988/A988M: Hot Isostatically-Pressed Stainless Steel Flanges, Fittings, Valves, and Parts for High Temperature Service

C7. Castings (ASTM Book of Standards Volume 01.02) A297/A297M: Standard Specification for Steel Castings, Fe-Cr, and Fe-Cr-Ni, Heat Resistance for General Application A351/A351M: Standard Specification for Castings, Austenitic for Pressure Containing Parts A451/A451M: Standard Specification for Centrifugally Cast Austenitic Steel Pipe for High Temperature Service A494/A494M: Standard Specification for Castings, Nickel and Nickel Alloy for Corrosion Resistance Service A608/A608M: Standard Specification for Centrifugally Cast Fe-Cr-Ni High Alloy Tubing for Pressure Application at High Temperature A743/A743M: Standard Specification for Castings, Fe-Cr, Fe-Cr-Ni, Corrosion Resistant for General Application A744/A744M: Standard Specification for Castings, Fe-Cr-Ni, Corrosion Resistant for Severe Service

C8. Miscellaneous A941: (ASTM Book of Standards Volume 01.01) Terminology Relating to Steel, Stainless Steel, Related Alloys, and Ferroalloys A947M: (ASTM Book of Standards Volume 01.03) Textured Stainless Steel Sheet (Metric) A959: (ASTM Book of Standards Volume 01.03) Standard Guide for Specifying Harmonized Standard Grade Compositions for Wrought Stainless Steels General: The ASTM International web site (www.astm.org) has an excellent search engine for finding most ASTM specifications that address corrosion testing, cleaning, and ivation topics.

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Annex D (Informative) Estimating the Ferrite Content of Cast Base Materials This annex is not part of this standard but is included for informational purposes only.

The ferrite content of castings can be estimated using the Schoefer Diagram (see Figure D.1) if the actual chemical composition of the base material is known. The chemical composition can be obtained from the foundry’s certified material test report or by performing a chemical composition analysis of the casting.

Source: ASTM A800/A800M-01 (2006), Standard Practice for Steel Casting, Austenitic Alloy, Estimating Ferrite Content Thereof.

Figure D.1—The Schoefer Diagram

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The Schoefer Diagram is considered useful for alloys within the following composition ranges: C: Mn: Si: Cr:

0.20 max. 2.00 max. 2.00 max. 17.0–28.0

Ni: Mo: Cb: N:

4.0–13.0 4.0 max. 1.00 max. 0.20 max.

First calculate the composition ratio (Cre)/Nie) of “chromium equivalent” (Cre) to “nickel equivalent” (Nie) using the actual composition of the casting and the following formula: Elements in the chromium equivalent part of the formula are elements that promote the formation of ferrite. Elements in the nickel equivalent part of the formula are elements that promote the formation of austenite.

Cr  %   1.5Si  %   1.4Mo  %   Cb  %   4.99   Cre  /  Nie     Ni  %   30C  %   0.5Mn  %   26  N  0.02%   2.77  Plot a horizontal line through the calculated [(Cre)/(Nie)] value (on the diagram’s vertical axis). Next, plot vertical lines at the intersection of the horizontal line with the individual curves (two outer dashed lines and a central solid line). The intersection of the vertical lines with the diagram’s horizontal axis provides an estimation of the castings ferrite content in volume percent. The casting’s nominal ferrite content is represented by the middle solid line. The possible range of ferrite within the casting is represented within the two outer dashed lines. This method of estimating ferrite is thoroughly discussed in ASTM A800/A800M, Standard Practice for Steel Casting, Austenitic Alloy, Estimating Ferrite Content Thereof.

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Annex E (Informative) Engineering , Common Conversions, and SMAW Electrode Diameters This annex is not part of this standard but is included for informational purposes only.

Table E.1 Common Engineering Mass

Density

Force

Stress

a

SI

Quantity of mattera kg = kilogram

U.S.

lb = pound (international avoirdupois unit)

SI

Mass per unit volumea g/cm3 = grams/cubic centimeter of kg/m3

U.S.

lb/in3 = pounds/cubic inch

=

Mass × Acceleration

SI

N = Newton

U.S.

lbf = Pound force

SI

Force per unit area 1 Pa = 1 N/m2 (1 Pascal = 1 Newton/meter2) 1 MPa = 1N/mm2

U.S.

psi = pound(s) per square inch

“mass” and “weight” are that are commonly interchanged since a quantity of matter (mass) is commonly measured by weighing material in earth's relatively constant gravitational field.

Table E.2 Data Standard acceleration of gravity

SI

9.807 m/s2

U.S.

32.174 ft/s2 Rate at which work is done or rate energy is used or transferred. Power = Work (or energy) ÷ time

Power Unit of Power

SI

Watt, 1 W = 1 J/s

U.S.

ft lb/min, foot pound(s) per minute

Work

Force × Distance

Work and Energy Unit of energy (or work) Force (mass × acceleration)

The same units can be used interchangeably, e.g., W·S = 1 J = 1 N·M SI

1 Watt-Second = 1 Joule = 1 Newton-meter, 1 W·S = 1 J = 1 N·M

U.S.

ft·lb, foot pound(s) 1 kgf = 9.807 N 1 lbf

Note: SI = International System of Units, U.S. = U.S. Customary Units.

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Table E.3a Common Welding-Related Conversion Factors Weight Convert from: g kg lb lb

to: lb lb g kg

Multiply by: 0.0022046 lbs/g 2.2046 lbs/kg 453.6 g/lb (453.59237 g/lb exact) 0.4536 kg/lb

Length Convert from: in cm m in ft m

to: cm in in m m ft

Multiply by: 2.54 cm/in (exact) 0.3937 in/cm 39.37 in/m 0.0254 cm/m (exact) 0.3048 m/ft 3.28083 ft/m

Density Convert from: g/cm3 lb/in3 lb/ft3

to: lb/in3 g/cm3 kg/m3

Multiply by: 0.0373 27.68 16.0185

Stress or Pressure Convert from: Pa MPa MPa psi psi

to: psi (lb/in2) psi ksi Pa MPa

Multiply by: 0.000145038 145.038 Quick rough estimate: divide MPa value by 7 6894.76 0.00689476

Force Convert from: N lbf kgf N

to: lbf N N kgf

Multiply by: 0.22481 lbf/N 4.448222 N/lbf 9.80665 N/kgf 0.1020 kgf/N

Weight per unit length Convert from: lb/ft kg/m

to: kg/m lb/ft

Multiply by: 1.488 0.672

Energy Convert from: J ft·lbs

to: ft·lbs J

Multiply by: 0.737562 ft·lbs/J 1.355818 J/ft·lbs

Temperature Convert from: T°F T°F T°C T°C TK (Kelvin) TK (Kelvin)

to: T°C TK (Kelvin) T°F TK (Kelvin) T°C T°F

Use Equation: T°C = (T°F – 32) ÷ 1.8 TK = (T°F + 459.67) ÷ 1.8 T°F = (T°C × 1.8) + 32 TK = T°C + 273.15 T°C = TK – 273.15 T°F = (TK × 1.8) – 459.67

Temperature Interval

(Note: Delta = change, i.e., 1.8 ΔT°F = 1ΔT°C)

Convert from: Δ T°F Δ T°C

to: Δ T°C Δ T°F

Use Equation: Δ T°C = Δ T°F ÷ 1.8 Δ T°F = Δ T°C × 1.8 (Continued)

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Table E.3a (Continued) Common Welding-Related Conversion Factors

a

Flow Rates Convert from: L/min ft3/hr

to: ft3/hr L/min

Multiply by: 2.11888 0.47195

Pressure Convert from: atm atm atm atm atm bar bar bar bar torr Pa

to: psi Pa mmHg bar torr Pa psi mmHg torr mmHg lb/in2

Multiply by: 14.696 psi/atm 101 325 Pa/atm 760 mmHg/atm 1.01325 bar/atm 760 torr/atm 100 000 Pa/bar 14.504 psi/bar 750.06 mmHg/bar 750.06 torr/bar 1 mmHg/torr 0.000145038 lb/in2/Pa

Speed Convert from: in/min in.min ft/min ft/min mm/s mm/s m/h

to: m/min m/s mm/s m/h in/min ft/min ft/min

Multiply by: 0.0254 0.0004233 5.08 18.288 2.3622 0.1969 0.0547

Heat Input Convert from: kJ/in kJ/m

to: kJ/m kJ/in

Multiply by: 39.37 in/m 0.0254 m/in

Miscellaneous Convert from: Percentage ppm

to: ppm Percentage

Multiply by: 1 × 104 1 × 10–4

Power Prefixes Prefix: Giga Mega Kilo Centi Milli Micro nano

Symbol: G M k c m µ (mu) n

Factor: 109 106 103 10–2 10–3 10–6 10–9

References to “pound” are based on the international avoirdupois pound unit.

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Annex F (Informative) Example Purchase Specification Topics This annex is not part of this standard but is included for informational purposes only.

Fabrication Codes/Standards do not necessarily address all measures that otherwise may be considered important to ensure that equipment will meet the Purchaser’s expectations. Following are examples of miscellaneous topics—some of which may be considered to include in contract language—keeping in mind that imposing additional requirements may incur additional cost. Depending on the type of fabrication and end service requirements, not all topics below are necessarily needed and some may not be practical to impose. For example, pickling of internal surfaces of completed piping systems may not be possible, and pickling of external surfaces (nonprocess side) may not be needed. The selection and contract language of the various topics below would be the responsibility of the designer or Purchaser. (1) Fabrication Code or Standard and edition year (2) Inspection and Test Plan (ITP) review and approval (3) Root welding requirements for single-welded, complete t penetration (CJP) welds (made without backing materials), e.g., GTAW, GMAW-S permitted (SMAW, FCAW, SAW prohibited), etc. (4) Acceptable/prohibited types of permanent or temporary weld-t backing materials (5) Purging during welding (to provide acceptable heat tint levels/colors and to prevent sugaring) (6) Filler metal vs. base material requirements and type of service (e.g., corrosive, cryo, elevated temp. creep, etc.) (7) Ferrite requirements and methods of determining ferrite (WRC diagram, FERITSCOPE, Severn Gage, etc.) (vs. service type: cryo, elevated temp., etc.). Ferrite checks after welding (8) Restrictions of certain types of welding processes (e.g., GMAW-S permitted only for sheet metal or open-root root welding, vertical welding progression: uphill/downhill, etc.) (9) Maximum permitted inter temperature (10) Restrictions on heat straightening (11) Heat treat requirements (none, solution anneal, stress relief, stabilization anneal, etc.) (12) Fabrication, storage, handling and shipping controls to prevent contamination (13) Cleaning of slag, spatter (14) Surface finish requirements vs. location (service considerations: aesthetics, corrosion resistance, ability to clean the area) (15) Minimization of disrupted surfaces (e.g., from excessive or coarse grinding, power brushing, media blasting, etc.) (16) Use of segregated tools including stainless wire brushes (not previously used on CSs) (17) Heat tint limits vs. location (e.g., pipe interior vs. exterior) with reference to a heat tint color standard (e.g., AWS D18.2) (18) Permitted heat tint removal methods (19) Chloride limit/purity requirements of cleaning solutions, chemicals, marking pens, tapes

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(20) Postfabrication removal of tape, adhesives, markings, fluids, contamination, etc. after fabrication (21) Final fabrication free from iron contamination (verification tests prior to shipment) (22) Requirements for “pickling” or “pickling and ivation” or “ivation” (if any) versus location (e.g., base metal or weld zones) and pickling and ivation requirements for shop fabrications versus requirements for final field assemblies and weld ts. (23) 100% visual examination of all welds by competent personnel and any certification requirements (24) Other types of weld inspection and acceptance criteria and certification requirements of NDE personnel (25) Material traceability and positive material identification (PMI) (26) Submittal/review of procedures: Weld maps, WPSs (with purging procedure), PQRs, heat treatment, NDE, pickling, ivation, handling practices (27) Welder performance qualification records (28) Hydrotest, water quality, draining, drying to prevent contamination, and MIC (29) Review and acceptance of nonconformances

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Annex G (Informative) Requesting an Official Interpretation on an AWS Standard This annex is not part of this standard but is included for informational purposes only.

G1. Introduction The following procedures are here to assist standard s in submitting successful requests for official interpretations to AWS standards. Requests from the general public submitted to AWS staff or committee that do not follow these rules may be returned to the sender unanswered. AWS reserves the right to decline answering specific requests; if AWS declines a request, AWS will provide the reason to the individual why the request was declined.

G2. Limitations The activities of AWS technical committees regarding interpretations are limited strictly to the interpretation of provisions of standards prepared by the committees. Neither AWS staff nor the committees are in a position to offer interpretive or consulting services on (1) specific engineering problems, (2) requirements of standards applied to fabrications outside the scope of the document, or (3) points not specifically covered by the standard. In such cases, the inquirer should seek assistance from a competent engineer experienced in the particular field of interest.

G3. General Procedure for all Requests G3.1 Submission. All requests shall be sent to the Managing Director of AWS Standards Development. For efficient handling, it is preferred that all requests should be submitted electronically through [email protected]. Alternatively, requests may be mailed to: Managing Director Standards Development American Welding Society 8669 NW 36 St, # 130 Miami, FL 33166 G3.2 Information. All inquiries shall contain the name, address, email, phone number, and employer of the inquirer. G3.3 Scope. Each inquiry shall address one single provision of the standard unless the issue in question involves two or more interrelated provisions. The provision(s) shall be identified in the scope of the request along with the edition of the standard (e.g., D1.1:2006) that contains the provision(s) the inquirer is addressing. G3.4 Question(s). All requests shall be stated in the form of a question that can be answered ‘yes’ or ‘no’. The request shall be concise, yet complete enough to enable the committee to understand the point of the issue in question. When the point is not clearly defined, the request will be returned for clarification. Sketches should be used whenever appropriate, and all paragraphs, figures, and tables (or annexes) that bear on the issue in question shall be cited. G3.5 Proposed Answer(s). The inquirer shall provide proposed answer(s) to their own question(s).

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G3.6 Background. Additional information on the topic may be provided but is not necessary. The question(s) and proposed answer(s) above shall stand on their own without the need for additional background information.

G4. AWS Policy on Interpretations The American Welding Society (AWS) Board of Directors has adopted a policy whereby all official interpretations of AWS standards are handled in a formal manner. Under this policy, all official interpretations are approved by the technical committee that is responsible for the standard. Communication concerning an official interpretation is directed through the AWS staff member who works with that technical committee. The policy requires that all requests for an official interpretation be submitted in writing. Such requests will be handled as expeditiously as possible, but due to the procedures that must be followed, some requests for an official interpretation may take considerable time to complete.

G5. AWS Response to Requests Upon approval by the committee, the interpretation is an official interpretation of the Society, and AWS shall transmit the response to the inquirer, publish it in the Welding Journal, and post it on the AWS website.

G6. Telephone Inquiries Telephone inquiries to AWS Headquarters concerning AWS standards should be limited to questions of a general nature or to matters directly related to the use of the standard. The AWS Board Policy Manual requires that all AWS staff respond to a telephone request for an official interpretation of any AWS standard with the information that such an interpretation can be obtained only through a written request. Headquarters staff cannot provide consulting services. However, the staff can refer a caller to any of those consultants whose names are on file at AWS Headquarters.

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List of AWS Documents on the ing of Metals and Alloys Designation

Title

G2.1M/G2.1

Guide for the ing of Wrought Nickel-Base Alloys

G2.3M/G2.3

Guide for the ing of Solid Solution Austenitic Stainless Steels

G2.4/G2.4M

Guide for the Fusion Welding of Titanium and Titanium Alloys

G2.5/G2.5M

Guide for the Fusion Welding of Zirconium and Zirconium Alloys

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