Tube To Tube Sheet 5b2k5h

DEFINITION - HEAT EXCHANGER  Heat exchanger is a device built for efficient heat

transfer from one fluid to another, where the fluids are separated by a solid wall, so that they never mix. OR

 Heat exchanger is defined as a device used to

transfer heat from a fluids on one side of a barrier to another fluid, flowing on the other side of the barrier.

TYPES OF SHELL AND TUBE HEAT EXCHANGER SHELL AND TUBE TYPE

HEAT EXCHANGER

FIXED TUBESHEET

FLOATING TUBESHEET

“U” BUNDLE WITH SINGLE TUBE SHEET

FIXED TUBESHEET

SUMMARY  Two tube sheets with tube bundle assembled in between, are

fixed to both ends of the shell.

 Tube sheets are either directly welded to shell or bolted to

flanges which are welded to shell ends.

 Differential expansion if any, will develop stresses in tubes &

shell material.

 To take care of differential expansion, shell may require

expansion bellows.

FLOATING TUBESHEET

SUMMARY  One tubesheet is fixed to one end of the shell.  Other tubesheet is floating within the shell with

a floating head cover.  This facilitates tube & shell to expand independently

without inducing any stresses due to differential expansion.  No expansion bellow is required on the shell to take

care of differential expansion.

“U” BUNDLE WITH SINGLE TUBESHEET

“U” TUBE BUNDLE, KETTLE TYPE EXCHANGER

SUMMARY  “U” bent tube bundle assembled on one tubesheet.  Assembled tube bundle is inserted into the shell.  Tube sheet is bolted to shell flange.  “U” tubes can expand freely inside the shell.  No stresses due to differential expansion.  No expansion bellow is required on shell to take

care of differential expansion.

STANDARD CLASSIFICATION AS PER TEMA CODE  TEMA Class “R” for severe requirements of

petroleum / petroleum related application

 TEMA Class “C” for moderate requirements of

Commercial and General process application

 TEMA Class “B” for Chemical process service

MAJOR COMPONENTS  SHELL  NOZZLES  CHANNEL  D’END  TUBESHEET  TUBES  BAFFLES  TIE RODS

FUNCTION OF BAFFLES  They guide the shell side flow in back & forth

as well as up & down direction, across the tube field, increasing the velocity & the heat transfer coefficient.  They the tubes and hold them in proper position during assembly & operation.  Prevent vibration of the tubes caused by flow induced eddies.

TYPES OF BAFFLES  Single Segmental Baffle Cuts  Multi - Segmental Baffle Cuts

– Double Segment – Triple Segment  Disc & ring type

SINGLE SEGMENTAL BAFFLES VERTICAL

HORIZONTAL

ROTATED

MULTI - SEGMENTAL BAFFLE

DOUBLE SEGMENTAL CUTS

MULTI - SEGMENTAL BAFFLE

TRIPLE SEGMENTAL CUTS

DISC & RING TYPE BAFFLE

TUBE # TUBESHEET WELDING

 Tube # tubesheet welding is defined as

“process of ing tube to tubesheet in a heat exchanger by welding”.

VARIOUS TYPES OF TUBE # TUBESHEET TS  Strength Expanded – Exp. Grooves in Tube holes  Strength Expanded – Without Exp. Grooves in Tube holes  Seal Welded & Strength Expanded (With or Without Expansion Grooves)  Strength Welded (Groove Weld t) & Light Expanded

EXPANSION GROOVES

TUBE

TUBE SHEET

EXPANDED T

EXPANDED & SEAL WELDED T

WELD GROOVE

STRENTH WELD. MINIMUM 2 ES TUBE

LIGHT EXPANDED AFTER WELDING TUBE SHEET

T#TS Set up for Strength Weld

Strength Welded & Light expanded

STRENGTH WELDED T

WELDER QUALIFICATION PROCEDURE SCOPE  This procedure covers

the requirements for welding & testing of tube # tubesheet t qualification

Reference documents  Article F-3 of ASME

SEC.IX(QW193,page-9).  ASME SEC.VIII  Customer specification

PREPARATION OF MOCK UP BLOCK  The tubesheet block shall be prepared on

a plate/forging of similar base material (Thickness = or > 50 mm) for qualification of welding procedure.  For qualification of welder the tubesheet

block shall be prepared a plate/forging of similar base material (Thickness = or > 38 mm).  After machining, tube holes shall be drilled as per block

shown in fig-1.The hole size, pitch & weld edges shall be identical to tubesheet of the equipment

WELDER TRAINING & QUALIFICATION 

1) 2) 3) 4)

At the beginning, welder shall be given practice on mock up block to achieve acceptable bead finish as mentioned below : Control of welding arc to avoid melt through in tube wall. Proper arc manipulation Staggering of restart points Acceptable bead finishes without excessive reinforcement

IMPORTANT NOTE  For procedure qualification 10 mock up welds

are to be produced within acceptable standards, as mentioned in ASME SEC IX, QW-193.1.  After adequate practice welders are allowed to weld in a qualification block. The number of ts in welder qualification block will be 5 nos as per ASME SEC IX, QW-193.2.

PRECAUTIONS BEFORE TUBE # TUBESHEET WELDING  Uniform welding should be carried out while

welding tubesheet # shell .  Excessive bow will lead to difficulties while in tube insertion stage.

Ovality should be maintained at minimum

level, to allow smooth baffle assembly.

OPERATIONAL SEQUENCES FOR TUBE # TUBESHEET WELDING  Inside touchup  Baffle insertion  Tube insertion  Setup of tube # tubesheet  Welding of ts  Tube trimming  Leak test

INSIDE TOUCHUP  Inside touchup of entire shell is to be done to

avoid any restrictions during baffle insertion.  All inside seam should be checked for minimum reinforcement.

BAFFLE INSERTION  While drilling the baffles, the drill bit usually

gets deflected from the centre line of the hole throughout entire stack.  Hence, it is advisable to install the baffles in the direction of drilling with respect to the tubing direction.  Baffles are inserted into the shell with the help of fixture.

FIXTURE FOR BAFFLE INSERTION

TUBE INSERTION  Cleaning of tube & tube sheet is the most

primary requirement before tube insertion. Utmost care is to be given for the cleaning process according to the standard practices.  Tube insertion is done with the help of pilots which provides ease in tube insertion.

STANDARD L&T PRACTICES  The tube holes and out side surface of tube

shall be cleaned thoroughly to remove any oil, grease, rust, dust from surfaces.  Tube ends should be cleaned minimum upto

200 mm of length at both ends by wire wheeling.

SETUP OF TUBE # TUBESHEET  Setup is to be done in accordance to the

projection mentioned in the drawing.  Projection rings are utilized to ensure the

projection of tubes with respect to tube sheet.

PREPARATORY ARRANGEMENT BEFORE WELDING 

After insertion of tubes in tube holes, the tube ends shall be pulled outside for cleaning of tube OD. The corresponding hole ID on opposite end shall be cleaned (35mm, minimum). In a row, one tube shall be pulled forward and ading tube shall be pushed backward for cleaning of tube OD and hole ID alternatively.

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Availability of high purity argon cylinder duly cleared by welding engg. For purity check, bead-on-plate deposit shall be carried out. After grinding the bead to remove the half thickness, PT check shall be performed. Each tested and cleared cylinder shall bear signature of welding engineer.

 Thoriated Tungsten (3.0 dia.)  High frequency unit in welding m/c is working.  Pre and post flow of shielding gas is properly     

adjusted. Welders are qualified to weld that particular t and cleared RT of t on mock -up piece before start of welding. Gas cup with gas lenses. Leakage of shielding gas in connections Water cooling system and water circulation is in order. t shall be cleaned with acetone just before start of tack welding

PRECAUTIONS WHILE WELDING       

Follow the welding parameters as specified in WPS. Welding to be performed with shortest possible arc. Only vertical up progression is to the used. Projection of tungsten electrode from gas cup shall be kept max 6.0 mm. Tungsten inclusion to the avoided. In case of any doubt the point shall the dressed before proceeding for further welding. Arc initiation shall be using high frequency limit. Restart point in a shall be kept at least 4mm before the crater point of the bead. The restart of successive es shall be staggered w.r.t previous es.

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During PT after root it shall be ensured that the penetrant (dye) is not entering the un-welded ts. If the dye has entered the in welded ts, the t shall be cleaned thoroughly by pulling the tubes forward and backward. Weld shape & size shall be controlled to meet the requirement of visual inspection. For weld size correct fillet gauge shall be used. Only one welder shall the allowed to complete a t. Mix up in a t shall be avoided. Welding record of each T#TS ts shall be maintained with data and welder stamp. The argon cylinder shall be replaced when there is positive pressure. ( 10 kg per sq.cm)

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Filler wire shall be cleaned with emery paper followed by acetone cleaning. After cleaning, it shall be handled using cleaned cotton hand glove While using inconel filler wire, the arc shall be kept on CS tubes to avoid excessive melting of SS cladding. ts shall be thoroughly cleaned after PT before depositing next es. Oxidized ends of filler wire shall be cut before reusing it.

WELDING DEFECTS

TUBE TRIMMING  Tube trimming is required to be done after

welding root of all tubes in one tubesheet.  It is done to remove excessive tube length by machining on job.  Supervisor should observe that minimum tube length trimming ( < 10mm ) is required.

LEAK TEST  Air and soap solution leak test.  Helium leak test.  Kerosene leak test.  Hot oil test.  Halogen leak test.

USEFUL CALCULATIONS  Welder output.  Counterweight calculation.  Shell trimming.

WELDER OUTPUT  Calculate welder output for a job with 10000 nos of tube with

20mm dia per shift?

 Assume that efficiency of average welder for tube # tubesheet 

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welding is 25mtr/12hrs. Circumference of tube = 2*pie*r = 2*3.14159*10 = 62.83mm = 63mm approx. Welder output/shift = Average efficiency/circumference = 25*1000 / 63 = 397 es (approx). No of es/tube = 2 es / tube Total nos of tube which could be welded/shift = 397/2 = 199 nos (approx)

COUNTER WEIGHT CLACULATION

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Counter weight = x X * RHS span = Weight of baffle * LHS span X * 5 = 10*5 Hence, counterweight X = 10 ton

SHELL TRIMMING Shell trimming for A-type weld configuration.  X = L-2P-T1-T2-B1-B2+S

SHELL TRIMMING Shell trimming for B-type weld configuration  X = L-2P-T1-T2-B1-B2-2H-2R+S

ABBREVATIONS  X = Distance from the edge of tubesheet to         

shell edge (actual). T1 = Thickness of tierod tubesheet (actual). T2 = Thickness of second tubesheet (actual). P = Required tube projection L = Length of tubes (actual) H = Height of lip on second tubesheet R = Root gap between tubesheet & shell B1 = Bulge on tie rod tubesheet after welding (actual) B2 = Expected bulge on second tubesheet S = Shrinkage of tubesheet