Welding Defects 1i545v
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WELDING DEFECTS
WELDING DEFECTS OBJECTIVE • DEFINITON • CAUSES • REMEDIES
WELDING DEFECTS DEFINITION OF A DEFECT • A defect is one which does not allow the finished t to withstand the required strength.
WELDING DEFECTS
TERMINOLOGIES
MACRO ETCH TEST
WELDING DEFECTS DEFINITION OF A DEFECT • A defect is one which does not allow the finished t to withstand the required strength.
WELDING DEFECTS TYPES OF DEFECT: • Crack • Undercut • Blow hole and porosity • Overlap • spatter • Lack of Fusion and Penetration • Excessive convexity • Slag inclusion
WELDING DEFECTS CRACK: • A hairline separation exhibits in the root or middle or surface and inside of the weld metal or parent metal.
WELDING DEFECTS crack CAUSES: • Wrong selection of electrode. • Presence of localized stress. • A restrained t. • Fast cooling. • Improper welding technique/sequence. • Poor ductility. • Absence of preheating and post heating of the t. • Excessive sulphur in base metal.
WELDING DEFECTS crack There are various types of weld cracking • Solidification cracking (hot cracking) • Hydrogen cracking (cold cracking) • Liquid cracking
WELDING DEFECTS Solidification cracking (Hot cracking) • Similar to casting, solidification cracking can also occur in welding. • It happens at the terminal stage of solidification due to contraction of solidifying metal and thermal contraction. (Intergranular crack) • The less ductile the weld metal is, the more likely solidification cracking to occur.
WELDING DEFECTS cracking Residual stresses in weldment • Residual stresses (internal stresses) are stresses that would exist in a body after removing all external loads (normally due to non uniform temperature change during welding in this case).
WELDING DEFECTS Residual stresses in weldment Weld metal and adjacent base metal Areas further away from weld metal
Residual tensile stresses
Residual compressive stresses
WELDING DEFECTS Residual stresses in weldment
WELDING DEFECTS Solidification cracking (Hot cracking)
• Restraining The weldment is restrained after the first weld, causing solidification cracking in the second weld in T ts .
WELDING DEFECTS Solidification cracking (Hot cracking) REMEDY • Controlling composition of the metal to be welded. • Using filler metal with proper composition. • Controlling Mn and S content in carbon and low alloy steels. • Controlling solidification structure: grain refining, arc oscillation, arc pulsation, etc.
WELDING DEFECTS Solidification cracking (Hot cracking) • Controlling weld geometry: concave fillet weld suffers higher tensile stress on the face than the convex fillet weld, deep weld is more susceptible to solidification cracking.
WELDING DEFECTS Hydrogen cracking (Cold cracking)
WELDING DEFECTS Hydrogen cracking (Cold cracking) Hydrogen cracking occurs when • Hydrogen in the weld metal sources moisture from metal surface, tools, atmosphere, flux, • High stresses • Susceptible microstructure : martensite (HAZ of carbon steels due to lower diffusion coefficient of hydrogen in austenite than in ferrite) • combination of hydrogen + martensite promotes hydrogen cracking. • Relatively low temperature. (-100/-200oC) cold cracking or delayed cracking.
WELDING DEFECTS Hydrogen cracking (Cold cracking)
Remedies for hydrogen cracking • Controlling welding parameters: proper preheat and inter temperature • Postweld treatment: stress relief. • Use proper welding processes and Materials (consumables), Low hydrogen electrodes.
WELDING DEFECTS • Liquation cracking form if weld metal develops sufficient strength to pull away while Grain Boundary is still liquid
WELDING DEFECTS liquation cracking Remedies for liquation cracking • Use proper filler metal. • Reducing the heat input to lower the size of PMZ (partially melted zone). • Reducing the degree of restraint, lowering the level of tensile stresses. • Controlling impurities, suppressing micro segregation at grain boundaries. • Smaller grain size is better
WELDING DEFECTS UNDERCUT UNDERCUT: • A groove or channel formed in the parent metal at the toe of the weld
WELDING DEFECTS UNDERCUT CAUSES OF UNDERCUT: • Current too high • Use of a very short arc length • Welding speed too fast • Overheating of job due to continuous welding • Faulty electrode manipulation • Wrong electrode angle
WELDING DEFECTS UNDERCUT UNDERCUT Preventive action: • Ensure: • Proper current is set • Correct welding speed is used • Correct arc length is used • Correct manipulation of electrode is followed Corrective actions: • Deposit a thin stringer bead at the top of the end using a 2 mm • diameter electrode to fill up the undercut.
WELDING DEFECTS BLOW HOLE AND POROSITY BLOW HOLE AND POROSITY: • Blow hole or gas pocket is a large diameter hole inside a bead or on the surface of the weld caused by gas entrapment . • porosity is a group of fine holes on the surface of the weld caused by gas entrapment. CAUSES: • Presence of contaminants/impurities on the job surface or on the electrode flux, presence of high sulphur in the job or electrode. • Trapped moisture between ing surface • fast freezing of weld metal. • Improper cleaning of the edges.
WELDING DEFECTS BLOW HOLES AND POROSITY:
WELDING DEFECTS BLOW HOLE AND POROSITY PREVENTIVE ACTION: • Remove oil, grease, rust, paint, moisture etc. from the surface • use fresh and dried electrodes. Use good flux coated electrodes • avoid long arcs. CORRECTIVE ACTION: • If the blow hole or porosity is inside the weld then gouge the area and re-weld . • If it is on the surface then grind it and reweld
WELDING DEFECTS OVERLAP OVERLAP: • An overlap occurs when the molten metal from the electrode flows • over the parent metal surface without fusing into it.
WELDING DEFECTS OVERLAP CAUSES: • Low current • Slow arc travel speed • Long arc • Too large a diameter electrode • REMEDIES: • Correct current setting • Correct arc travel speed • Correct arc length • Correct diameter electrode as per metal thickness • Proper manipulation of electrode.
WELDING DEFECTS SPATTERS SPATTERS: • Small metal particles which are thrown out of the arc during welding along the weld. CAUSES • Welding current too high. • wrong polarity ( in DC ). • use of long arc • uneven flux coated electrode.
WELDING DEFECTS SPATTERS REMEDIES: • Use correct current • Use correct polarity • Use correct arc length • Use good flux coated electrode.
WELDING DEFECTS Lack of Penetration and Fusion Lack of Penetration
: • Failure of weld metal to reach the root of the t. • This type of defect tends to be sub surface and is therefore detectable only by ultrasonics or X-ray methods
Lack of Fusion • – Lack of side wall fusion which penetrates the surface may be detected using magnetic particle, dye or fluorescent penetrant inspection. CAUSES: • Edge preparation too narrow • Welding speed is too much • Less current • Use of larger diameter electrode. • Wrong angle of electrode. • Insufficient root gap.
WELDING DEFECTS Lack of Fusion and Penetration REMEDIES: • Correct edge preparation is required. • Ensure correct angle of bevel and required root gap. • Use correct size of electrode. • Correct welding speed is required. • Correct current setting required
Defects due to wrong fit ups • Misalingment 1.thickness misalignment 2.length & width wise misaligment 3.un-even root gap
• Proper seating of items flat surface un-even surface should be ground
What to ensure: • Proper clamping • Edge preparation types of ts bevel angle root face in case of fillet – leveling of thickness machining / gas cutting & grinding • Avoid arc cutting
Some best practices • checking the diagonal
• Proper tacking 150 mm (depending on the thicness • Use Air plasma cutting / gas cutting instead of arc cutting • Use proper bridging piece / rod incase of excess gaps in the fitment. • Use of tie rods
• Use of tie rods
Thank you all
WELDING DEFECTS OBJECTIVE • DEFINITON • CAUSES • REMEDIES
WELDING DEFECTS DEFINITION OF A DEFECT • A defect is one which does not allow the finished t to withstand the required strength.
WELDING DEFECTS
TERMINOLOGIES
MACRO ETCH TEST
WELDING DEFECTS DEFINITION OF A DEFECT • A defect is one which does not allow the finished t to withstand the required strength.
WELDING DEFECTS TYPES OF DEFECT: • Crack • Undercut • Blow hole and porosity • Overlap • spatter • Lack of Fusion and Penetration • Excessive convexity • Slag inclusion
WELDING DEFECTS CRACK: • A hairline separation exhibits in the root or middle or surface and inside of the weld metal or parent metal.
WELDING DEFECTS crack CAUSES: • Wrong selection of electrode. • Presence of localized stress. • A restrained t. • Fast cooling. • Improper welding technique/sequence. • Poor ductility. • Absence of preheating and post heating of the t. • Excessive sulphur in base metal.
WELDING DEFECTS crack There are various types of weld cracking • Solidification cracking (hot cracking) • Hydrogen cracking (cold cracking) • Liquid cracking
WELDING DEFECTS Solidification cracking (Hot cracking) • Similar to casting, solidification cracking can also occur in welding. • It happens at the terminal stage of solidification due to contraction of solidifying metal and thermal contraction. (Intergranular crack) • The less ductile the weld metal is, the more likely solidification cracking to occur.
WELDING DEFECTS cracking Residual stresses in weldment • Residual stresses (internal stresses) are stresses that would exist in a body after removing all external loads (normally due to non uniform temperature change during welding in this case).
WELDING DEFECTS Residual stresses in weldment Weld metal and adjacent base metal Areas further away from weld metal
Residual tensile stresses
Residual compressive stresses
WELDING DEFECTS Residual stresses in weldment
WELDING DEFECTS Solidification cracking (Hot cracking)
• Restraining The weldment is restrained after the first weld, causing solidification cracking in the second weld in T ts .
WELDING DEFECTS Solidification cracking (Hot cracking) REMEDY • Controlling composition of the metal to be welded. • Using filler metal with proper composition. • Controlling Mn and S content in carbon and low alloy steels. • Controlling solidification structure: grain refining, arc oscillation, arc pulsation, etc.
WELDING DEFECTS Solidification cracking (Hot cracking) • Controlling weld geometry: concave fillet weld suffers higher tensile stress on the face than the convex fillet weld, deep weld is more susceptible to solidification cracking.
WELDING DEFECTS Hydrogen cracking (Cold cracking)
WELDING DEFECTS Hydrogen cracking (Cold cracking) Hydrogen cracking occurs when • Hydrogen in the weld metal sources moisture from metal surface, tools, atmosphere, flux, • High stresses • Susceptible microstructure : martensite (HAZ of carbon steels due to lower diffusion coefficient of hydrogen in austenite than in ferrite) • combination of hydrogen + martensite promotes hydrogen cracking. • Relatively low temperature. (-100/-200oC) cold cracking or delayed cracking.
WELDING DEFECTS Hydrogen cracking (Cold cracking)
Remedies for hydrogen cracking • Controlling welding parameters: proper preheat and inter temperature • Postweld treatment: stress relief. • Use proper welding processes and Materials (consumables), Low hydrogen electrodes.
WELDING DEFECTS • Liquation cracking form if weld metal develops sufficient strength to pull away while Grain Boundary is still liquid
WELDING DEFECTS liquation cracking Remedies for liquation cracking • Use proper filler metal. • Reducing the heat input to lower the size of PMZ (partially melted zone). • Reducing the degree of restraint, lowering the level of tensile stresses. • Controlling impurities, suppressing micro segregation at grain boundaries. • Smaller grain size is better
WELDING DEFECTS UNDERCUT UNDERCUT: • A groove or channel formed in the parent metal at the toe of the weld
WELDING DEFECTS UNDERCUT CAUSES OF UNDERCUT: • Current too high • Use of a very short arc length • Welding speed too fast • Overheating of job due to continuous welding • Faulty electrode manipulation • Wrong electrode angle
WELDING DEFECTS UNDERCUT UNDERCUT Preventive action: • Ensure: • Proper current is set • Correct welding speed is used • Correct arc length is used • Correct manipulation of electrode is followed Corrective actions: • Deposit a thin stringer bead at the top of the end using a 2 mm • diameter electrode to fill up the undercut.
WELDING DEFECTS BLOW HOLE AND POROSITY BLOW HOLE AND POROSITY: • Blow hole or gas pocket is a large diameter hole inside a bead or on the surface of the weld caused by gas entrapment . • porosity is a group of fine holes on the surface of the weld caused by gas entrapment. CAUSES: • Presence of contaminants/impurities on the job surface or on the electrode flux, presence of high sulphur in the job or electrode. • Trapped moisture between ing surface • fast freezing of weld metal. • Improper cleaning of the edges.
WELDING DEFECTS BLOW HOLES AND POROSITY:
WELDING DEFECTS BLOW HOLE AND POROSITY PREVENTIVE ACTION: • Remove oil, grease, rust, paint, moisture etc. from the surface • use fresh and dried electrodes. Use good flux coated electrodes • avoid long arcs. CORRECTIVE ACTION: • If the blow hole or porosity is inside the weld then gouge the area and re-weld . • If it is on the surface then grind it and reweld
WELDING DEFECTS OVERLAP OVERLAP: • An overlap occurs when the molten metal from the electrode flows • over the parent metal surface without fusing into it.
WELDING DEFECTS OVERLAP CAUSES: • Low current • Slow arc travel speed • Long arc • Too large a diameter electrode • REMEDIES: • Correct current setting • Correct arc travel speed • Correct arc length • Correct diameter electrode as per metal thickness • Proper manipulation of electrode.
WELDING DEFECTS SPATTERS SPATTERS: • Small metal particles which are thrown out of the arc during welding along the weld. CAUSES • Welding current too high. • wrong polarity ( in DC ). • use of long arc • uneven flux coated electrode.
WELDING DEFECTS SPATTERS REMEDIES: • Use correct current • Use correct polarity • Use correct arc length • Use good flux coated electrode.
WELDING DEFECTS Lack of Penetration and Fusion Lack of Penetration
: • Failure of weld metal to reach the root of the t. • This type of defect tends to be sub surface and is therefore detectable only by ultrasonics or X-ray methods
Lack of Fusion • – Lack of side wall fusion which penetrates the surface may be detected using magnetic particle, dye or fluorescent penetrant inspection. CAUSES: • Edge preparation too narrow • Welding speed is too much • Less current • Use of larger diameter electrode. • Wrong angle of electrode. • Insufficient root gap.
WELDING DEFECTS Lack of Fusion and Penetration REMEDIES: • Correct edge preparation is required. • Ensure correct angle of bevel and required root gap. • Use correct size of electrode. • Correct welding speed is required. • Correct current setting required
Defects due to wrong fit ups • Misalingment 1.thickness misalignment 2.length & width wise misaligment 3.un-even root gap
• Proper seating of items flat surface un-even surface should be ground
What to ensure: • Proper clamping • Edge preparation types of ts bevel angle root face in case of fillet – leveling of thickness machining / gas cutting & grinding • Avoid arc cutting
Some best practices • checking the diagonal
• Proper tacking 150 mm (depending on the thicness • Use Air plasma cutting / gas cutting instead of arc cutting • Use proper bridging piece / rod incase of excess gaps in the fitment. • Use of tie rods
• Use of tie rods
Thank you all
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