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Similar to Defects in welding / Weld defects- A comprehensive presentation.pptx
Defects in welding / Weld defects- A comprehensive presentation.pptx
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- 3. Visual/Surface defects, (i) Surfacecracks, (ii) Distortion/Warpage, (iii) Incorrect or bad bead profile, (iv) Dimensional deviation/Incorrect weld size, (v) Overlaps or rolls,
- 4. (vi) Undercuts, (vii) Underfill/Suckback, (viii)Excess penetration/Excess reinforcement, (ix) Start-Stop points, (x) Interruptions, Visual/Surface defects,
- 5. (xi) Unfilled craters, (xii)Burn-through, (xiii) Surface porosity, (xiv) Surface oxidation, (xv) Uneven and Coarse ripples, Visual/Surface defects
- 6. (xvi) Pock marks/Flatspots, (xvii) Excessive spatter, (xviii) Arc strike, (xix) Bad surface appearance, (xx) High/Iow off-set. Visual/Surface defects,
- 7. Hidden or SubsurfaceWeld Defects (i) Lack of fusion, (ii) Lack of penetration, (iii) Hidden or Subsurface cracks, (iv) Blowholes/Subsurface porosity, (v) Shrinkage cavities,
- 8. Hidden or SubsurfaceWeld Defects (vi) Slag inclusion, (vii) Tungsten/copper ( Metallic) inclusions, (viii) Finger penetration, (ix) Coarse microstructure.
- 9. Causes • Improper selectionof process • Undesirable metallurgical structures • Defects caused by the interaction of the weld metal with prior defects in the base metal • Incorrect welding parameters selection
- 10. • Inferior designresulting in inaccessibility for weld inspection • Poor workmanship • Incorrect joint edge preparations and poor fit-up • Undesirable shape and size of weld bead due to overfill and/or poor profiles. Causes
- 11. • Most dangerous •Invariably unacceptable Types: 1. Surface Cracks/Hidden cracks 2. Micro/Macro cracks Cracks
- 12. Cracks Causes: (i) High contractionstresses (being greater than the hot strength of the weld or parent material) (ii) poor fit-up and incorrect welding procedures (iii) poor edge quality.
- 14. Solidification cracking • Microsegregationand resultant formation of low solidification temperature liquid films along the grain boundaries • Microfissures formed in the welding due to shrinkage propagate as microcracks • Hot cracking
- 15. Cold cracking • Occursbelow 300 °C • Localized stresses exceed the ultimate strength of the BM • Hydrogen accumulation in highly stress-concentrated zones • Formation of brittle martensite and/or cementite during welding
- 16. Reheat cracking • Occursin welded materials during or after heat treatment.
- 17. Subsurface Cracks/Internal Cracks •a.k.a Underbead cracks • Most serious when impact loading and low temperature service conditions are involved. • Must be fully chipped back and welded up.
- 18. Internal stresses • Largethermal gradient (local heating) • Uneven expansion/contraction • Residual stresses Result: Warping, distortion, cracking
- 19. Warping / distortion Correctedby • Proper jigging of joint • Controlled cooling after welding • Stress-relieving heat treatment • Peening the weld metal and HAZ
- 20. Dimensional Defects • Badbead profiles • Non-uniform width or height of a weld, irregular crests and valleys, and variations in leg length Causes: • Variation in the supply voltage, wire slippage in feed rolls, variations in the welding speed because of backlash and lost motion in traction gear, a wrong work angle, etc. • Poor skill of welder
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- 23. Overlaps and Rolls Protrusionsof weld metal beyond the bond at the toe, face or root of the weld. Causes: • Excessive welding current • Wrong electrode offset • Wrong tilt of electrode • Accompanied by lack of fusion, cracks and other defects.
- 25. Excessive Reinforcement • Stiffensthe section • Makes notches that create stress concentration. • Objectionable from an appearance point of view • Economic waste - adds to the cost of welding without gaining any worthwhile strength.
- 26. Undercuts • Grooves meltedinto the parent metal and left unfilled by weld metal • Notch effect
- 27. Undercuts Cause(s): Excessive weldingcurrent and arc voltage. • High heat input • Width of penetration increases • Excessive melting of fusion faces
- 28. Undercuts • Limited meltflow • Depends on material interactions, temperature-dependent viscosity, and surface tension • Stress riser
- 29. Underfill/Suckback • ‘a depressionon the face of a weld’ • ‘Root surface extending below the surface of the adjacent base metal’ • Reduces the cross-sectional area of the weld
- 30. Voids, holes orcavities formed by gas trapped by the solidified weld metal. • Large holes (blow-holes) • Small holes (porosity) • Wormholes (long and continuous). Porosity
- 32. Porosity Causes: • Evaporation oflow boiling point elements • Hydrogen rejection from solid phase during solidification • Shielding gas entrapment in high density welding
- 33. Decrease in solubilityof dissolved elements in the molten pool during cooling and solidification Imperfect keyhole phenomenon • Turbulent weld pool flow Porosity
- 34. Porosity (Laser welding) •Metallurgical porosity (presence of hydrogen in weld pool) • Keyhole instability
- 35. Surface Oxidation Common withreadily oxidising metals such as Al, Ti, Mg, and their alloys, processes with less or no shielding. • Reaction with atmospheric gases • Oxidation is accelerated at higher temperatures
- 36. Inclusion • Entrapment ofsolid particles • Sources: Surface oxides, sulfide, tungsten electrodes, and slag
- 37. Slag Inclusion Slag isforced below the surface of the molten metal by the stirring action of the arc (SMAW).
- 38. Causes: Insufficient weldingcurrent, an off-set of the electrode from the axis of the weld, too high a welding speed, and improper wearing procedure. • Reduces the strength of welds and makes welded structures unreliable. Lack of fusion
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- 40. • Built-in crackready to start running through the base metal, weld metal, or HAZ when the weldment is put under stress. • Notch effect Lack of penetration
- 41. Lack of penetration •Caused by low welding current, excessive travel speed, improper electrode application, or the presence of surface contaminants
- 42. Spatter Too long arc Unsuitablefiller materials • Improper shielding gas combination with regard to BMs and filler metals • Contaminations of filler metals.
- 43. Lamellar Tears • Commonlyfound in rolled structural shapes and plates • Caused by thermally induced shrinkage stresses resulting from welding
- 44. Surface Burning (spotwelding) • Melting of the metal surface in contact with the electrode • Heavy expulsion of molten metal • Accompanied by deep electrode indentation
- 45. Cracks, deep cavities,or pinholes (spot welding) • Removing the electrode force before welds are cooled from liquids • Excessive heat generation, resulting in heavy expulsion of molten metal • Poorly fitting parts requiring most of the electrode force to bring the faying surfaces into contact
- 46. Deep electrode indentation(spot welding) • Improperly dressed electrode face • Lack of control of electrode force • Excessively high rate of heat generation due to high contact resistance (low electrode force)
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- 51. Friction stir weldingdefects
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