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Wis5 welding defects 02

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Wis5 welding defects 02

  1. 1. Faisal Yusof TE Copyright © 2003 TWI Ltd Welding Inspection Defects/Repairs Course Reference WIS 5
  2. 2. Faisal Yusof TE Copyright © 2003 TWI Ltd A perfect butt weld joint, when subjected to an external force, provide a distribution of stress throughout its volume which is not significantly greater than parent metal. DefinitionDefinition
  3. 3. Faisal Yusof TE Copyright © 2003 TWI Ltd DefinitionDefinition This is achieved as long as the following features apply :- • Welds should consists of solid metal throughout a cross section at least equal to that of parent metal. • All parts of a weld should be fully fused to the parent metal. •Welds should have smoothly blended surfaces.
  4. 4. Faisal Yusof TE Copyright © 2003 TWI Ltd Defects which may be detected by visual inspection can be grouped under five headings  Cracks  Lack of solid metals  Lack of fusion  Lack of smoothly blended surfaces  Miscellaneous Weld DefectsWeld Defects
  5. 5. Faisal Yusof TE Copyright © 2003 TWI Ltd CracksCracks
  6. 6. Faisal Yusof TE Copyright © 2003 TWI Ltd Classified by Shape  Longitudinal  Transverse  Branched  Chevron Classified by Position  HAZ  Centreline  Crater  Fusion zone  Parent metal CracksCracks Cracks that may occur in welded materials are caused generally by by many factors and may be classified by shape and position, cracks are classed as planar.
  7. 7. Faisal Yusof TE Copyright © 2003 TWI Ltd Process CracksProcess Cracks HAZ hydrogen cracking  Weld metal hydrogen cracking Solidification cracking (Hot Tearing) Lamellar tearing
  8. 8. Faisal Yusof TE Copyright © 2003 TWI Ltd CracksCracks HAZ hydrogen cracking Weld metal hydrogen cracking Solidification cracking Lamellar Tearing
  9. 9. Faisal Yusof TE Copyright © 2003 TWI Ltd Transverse crack Longitudinal crack
  10. 10. Faisal Yusof TE Copyright © 2003 TWI Ltd LACK OF SOLID METALSLACK OF SOLID METALS
  11. 11. Faisal Yusof TE Copyright © 2003 TWI Ltd POROSITYPOROSITY Description : Gas pores trapped within the weld metal Causes : • Damp fluxes/ corroded electrode •Grease/hydrocarbon/water contamination of prepared surface •Air entrapment in gas shield •Too high arc voltage/arc length •Incorrect/insufficient deoxidant in electrode, filler or parent metal Preventation : • Use dry electrodes in good condition •Optimise gas flow •Use electrode with sufficient deoxidation activity •Reduce arc voltage or arc length
  12. 12. Faisal Yusof TE Copyright © 2003 TWI Ltd Gas CavitiesGas Cavities Root pipingRoot piping PorosityPorosity
  13. 13. Faisal Yusof TE Copyright © 2003 TWI Ltd Cluster porosity Herring bone porosity
  14. 14. Faisal Yusof TE Copyright © 2003 TWI Ltd Crater PipeCrater Pipe A shrinkage cavity at the end of a weld run where the arc is terminated Causes : •Lack of welder skill due to using processes with too high current. •Inoperative crater filler ( GTAW ) Preventation : • Retrain welder •Use correct crater filling technique
  15. 15. Faisal Yusof TE Copyright © 2003 TWI Ltd Crater Pipe/CracksCrater Pipe/Cracks Crater pipeCrater pipe Crater CracksCrater Cracks
  16. 16. Faisal Yusof TE Copyright © 2003 TWI Ltd RootRoot concavityconcavity A shallow groove, which may occur in the root of a butt weld Causes : •Insufficient arc power to produce positive bead •Excessive backing pressure ( GTAW ) •Lack of welder skill •Slag flooding in backing bar groove Preventation : • Raise arc energy •Reduce gas pressure •Retraint welder •Tilt work to prevent slag flooding
  17. 17. Faisal Yusof TE Copyright © 2003 TWI Ltd root concavity
  18. 18. Faisal Yusof TE Copyright © 2003 TWI Ltd UnderfillUnderfill A weld with thickness less than that of the parent metal Causes : •Insufficient weld metal •Irregular weld bead surface Preventation : • Increase number of weld run •Retrain welder
  19. 19. Faisal Yusof TE Copyright © 2003 TWI Ltd Incomplete filled groove
  20. 20. Faisal Yusof TE Copyright © 2003 TWI Ltd Slag InclusionsSlag Inclusions Slag or other matters trapped during welding. The imperfection is of an irregular shape and thus differs in appearance from a gas pore Causes : •Heavy millscale/rust on work surface •Incomplete slag removal from underlying surface of multipass weld •Slag flooding ahead of the arc •Entrapment of slag in work surface •Unfused flux due to damage coating Preventation : • Grind surface prior welding •Improve interun slag removal •Position work to gain control of slag •Dress work surface smooth •Use electrode in good condition
  21. 21. Faisal Yusof TE Copyright © 2003 TWI Ltd Elongated slag linesInterpass slag inclusions
  22. 22. Faisal Yusof TE Copyright © 2003 TWI Ltd Inter- run ImperfectionsInter- run Imperfections Irregular along the fusion line between weld beads Causes : •Low arc current resulting in low fludity of weld pool •Too high travel speed •Inaccurate bead replacement Preventation : • Increase current •Reduce travel speed •Retrain welder
  23. 23. Faisal Yusof TE Copyright © 2003 TWI Ltd Lack of FusionLack of Fusion
  24. 24. Faisal Yusof TE Copyright © 2003 TWI Ltd Incomplete root penetrationIncomplete root penetration Failure of the weld metal to extend into root of a joint Causes : •Excessively thick root face, insufficient root gap or failure to cut back sound metal in a ‘back gouging’ operation •Low heat input •Excessive inductance in GMAW dip transfer •SMAW electrode too large( low current density ) •Use of vertical down welding Preventation : • Improved back gouging and edge preparation •Increase arc power or decrease travel speed •Improve electrical settings and possibly switch to spray transfer •Reduce electrode size •Switch to vertical up procedure
  25. 25. Faisal Yusof TE Copyright © 2003 TWI Ltd Root DefectsRoot Defects Lack of root fusion Lack of root Penetration
  26. 26. Faisal Yusof TE Copyright © 2003 TWI Ltd Lack of root penetration Lack of root fusion
  27. 27. Faisal Yusof TE Copyright © 2003 TWI Ltd Lack of sidewall fusionLack of sidewall fusion Lack of fusion between weld metal and parent metal at one side of weld Causes : •Low heat input to weld •Molten metal flowing ahead of arc •Oxide or scale on weld preparation •Excessive inductance in GMAW dip transfer welding Preventation : •Increase arc energy or increase travel speed •Improve electrode angle and work position •Improve edge preparation procedure •Reduce inductance, even if this increase spatter
  28. 28. Faisal Yusof TE Copyright © 2003 TWI Ltd Lack of SmoothlyLack of Smoothly Blended SurfacesBlended Surfaces
  29. 29. Faisal Yusof TE Copyright © 2003 TWI Ltd Surface porositySurface porosity Gas pores which break the surface of the weld Causes : •Damp or contaminated surface of electrode •Low fluxing activity •Excess sulphur ( particularly free – cutting steels) producing sulphur oxide •Loss of gas shield gas due to long arc or high breezes ( GMAW ) Preventation : •Clean surface and dry electrodes •Use a high activity flux •Use high manganese to produce MnS, note free cutting should not normally be welded •Reduce arc length
  30. 30. Faisal Yusof TE Copyright © 2003 TWI Ltd Excess Weld Metal ( Reinforcement )Excess Weld Metal ( Reinforcement ) Reinforcement is the extra metal which produces convexity in fillet welds and a welds thickness than the parent metal plate in butt welds. Causes : •Excess arc energy ( GMAW,SAW ) •Shallow edge preparation •Faulty electrode manipulation •Incorrect electrode size Preventation •Reduction of energy input •Deepen edge preparation •Improve welder skill •Reduce electrode size
  31. 31. Faisal Yusof TE Copyright © 2003 TWI Ltd Excess cap reinforcement
  32. 32. Faisal Yusof TE Copyright © 2003 TWI Ltd Excessive PenetrationExcessive Penetration Projection of the root penetration bead beyond a specified limit Causes : •Weld input energy too high •Incorrect weld preparation i.e excessive root gap, thin edge preparation, lack of backing •Use electrode unsuited to welding position •Lack of welder skill Preventation •Reduce arc power/increase weld speed •Improve work piece preparation •Use correct electrode position •Retrain welder
  33. 33. Faisal Yusof TE Copyright © 2003 TWI Ltd Excessive root penetration
  34. 34. Faisal Yusof TE Copyright © 2003 TWI Ltd UndercutUndercut An irregular groove at the toe of a run in the parent metal or in previously deposited welding, cause by welding Causes : •Melting of top edge due to too high welding current ( especially at free edge) or high travel speed •Attempting an HV fillet weld leg length >9.0 MM • Excessive/Incorrect weaving •Incorrect electrode angle Preventation •Reduce power input,especially approaching a free edge where overheating can occur •Weld in a flat position or use multirun technique •Direct arc towards thicker member
  35. 35. Faisal Yusof TE Copyright © 2003 TWI Ltd Cap UndercutCap Undercut Measured in both Length & DepthMeasured in both Length & Depth
  36. 36. Faisal Yusof TE Copyright © 2003 TWI Ltd Cap undercutRoot undercut
  37. 37. Faisal Yusof TE Copyright © 2003 TWI Ltd OverlapOverlap An Imperfection at the toe of a weld caused by metal flowing on to the surface of the parent metal without fusing to it Causes : • Poor electrode manipulation • High energy input/low travel speed causing surface flow of fillet weld • Incorrect positioning of weld • Electrode having too high a fluidity Preventation •Retrain welder •Reduce the heat input or limit size of fillet weld to 9.0 mm leg by using multi run weld •Change the flat position •Change to less fluid weld metal
  38. 38. Faisal Yusof TE Copyright © 2003 TWI Ltd Profile DefectsProfile Defects Poor stop/starts
  39. 39. Faisal Yusof TE Copyright © 2003 TWI Ltd MiscellaneousMiscellaneous
  40. 40. Faisal Yusof TE Copyright © 2003 TWI Ltd MisalignmentMisalignment The non – alignment of two abutting edges in a butt joint Causes : • Inaccuracies in assembly procedures or distortion from other welds • Excessive ‘out of flatness' in hot rolled plate or sections Preventation : •Adequate checking of alignment prior to welding coupled with the use of clamps and wedges •Check accuracy of rolled section prior to welding
  41. 41. Faisal Yusof TE Copyright © 2003 TWI Ltd Arc strikesArc strikes Random areas of fused metal where the electrode, the holder, or current return clamp accidentally touched the work and produced a short duration arc Causes : • Poor Access to work • Missing insulation on electrode holder or torch • Failure to provide an insulated resting place for the electrode holder or torch when not in use • Loose current return clamp Preventation : •Improve access ( modify assembly sequence ) •Institute a regular inspection scheme for electrode holders and torches •Provide an insulated resting place •Regularly maintain current return clamp
  42. 42. Faisal Yusof TE Copyright © 2003 TWI Ltd SpatterSpatter Small droplets of electrode material can be projected clear of the weld and may fused to the parent metal Causes: • High arc power • Magnetic arc blow • Incorrect setting for GMAW process • Damp electrodes Preventation : •Reduce arc power •Reduce arc length or swith to AC power •Modify electrical settings ( but be careful to maintain full fusion •Use dry electrodes
  43. 43. Faisal Yusof TE Copyright © 2003 TWI Ltd Burn ThroughBurn Through  High Amps/volts  Small Root face  Large Root Gap  Slow Travel SpeedBurn through A localized collapse of the weld pool due to excessive penetration resulting in a hole in the root run
  44. 44. Faisal Yusof TE Copyright © 2003 TWI Ltd Burn through Burn Through Root Defects
  45. 45. Faisal Yusof TE Copyright © 2003 TWI Ltd Root Coking/Oxidized RootRoot Coking/Oxidized Root  Loss or insufficient back purging gas  Most commonly occurs when welding stainless steels  Purging gases include argon, helium and occasionally nitrogen
  46. 46. Faisal Yusof TE Copyright © 2003 TWI Ltd Mechanical DamageMechanical Damage
  47. 47. Faisal Yusof TE Copyright © 2003 TWI Ltd Mechanical DamageMechanical Damage Mechanical damage can be defined as any surface material damage cause during the manufacturing process. This can included damage caused by:  Grinding  Hammering  Chiselling  Chipping  Breaking off welded attachments (torn surfaces)  Using needle guns to compress weld capping runs
  48. 48. Faisal Yusof TE Copyright © 2003 TWI Ltd Parent Material DefectsParent Material Defects A welding inspector should also inspect the parent material for any visible defects Lamination Mechanical damage Lap Segregation line
  49. 49. Faisal Yusof TE Copyright © 2003 TWI Ltd Plate LaminationPlate Lamination
  50. 50. Faisal Yusof TE Copyright © 2003 TWI Ltd Any Questions?Any Questions?
  51. 51. Faisal Yusof TE Copyright © 2003 TWI Ltd QuestionsQuestions QU 1. Give two main causes for the occurrence of a burn through QU 2. Give two main causes for the occurrence of excessive root penetration on a single-V butt weld QU 3. Give five defects, which may occur when welding carbon steel using the MMA welding process with the current setting to low QU 4. Give three possible causes for the occurrence of lack of side wall fusion QU 5. Sketch the following defects a. Lack of root wall fusion b. Lack of root penetration c. Incomplete filled groove d. Concave root
  52. 52. Faisal Yusof TE Copyright © 2003 TWI Ltd Weld RepairsWeld Repairs
  53. 53. Faisal Yusof TE Copyright © 2003 TWI Ltd Welding RepairsWelding Repairs  Authorization for repair  Removal and preparation for repair  Testing of repair - visual and NDT In the event of repair
  54. 54. Faisal Yusof TE Copyright © 2003 TWI Ltd  A weld repair may be used to improve weld profiles or extensive metal removal  Repairs to fabrication defects are generally easier than repairs to service failures because the repair procedure may be followed  The main problem with repairing a weld is the maintenance of mechanical properties  During the inspection of the removed area prior to welding the inspector must ensure that the defects have been totally removed and the original joint profile has been maintained as close as possible Weld RepairsWeld Repairs
  55. 55. Faisal Yusof TE Copyright © 2003 TWI Ltd The specification or procedure will govern how the defective areas are to be removed. The method of removal may be  Grinding  Chipping  Machining  Filing  Oxy-Gas gouging  Arc air gouging Weld RepairsWeld Repairs Arc air gouging

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