Welding Defects, Inspection and Testing of Welds
What this domain tests
Defect naming, cause tracing, and selecting the correct inspection method for the defect type and location.
Core rules
- Common defects. Porosity, slag inclusion, incomplete fusion, incomplete penetration, undercut, overlap, spatter, burn-through, misalignment, arc strike, and cracks (hot, cold/hydrogen, lamellar tearing).
- Cause patterns. Porosity - damp electrodes, dirty metal, gas flow too high or too low, draughts. Undercut - excessive current, arc too long, wrong work angle, travel too fast. Slag inclusion - poor interpass cleaning, low current, wrong electrode angle. Incomplete penetration - root face too large, gap too small, current too low. Cold cracking - hydrogen plus restraint plus a hard HAZ; controlled by preheat, low-hydrogen electrodes and PWHT.
- Surface methods. Visual, dye penetrant (PT) for non-porous surfaces of any material, magnetic particle (MT) for surface and near-surface flaws in ferromagnetic steel only.
- Volumetric methods. Radiography (RT) shows porosity and slag well but is weak on tight planar cracks aligned with the beam; ultrasonics (UT) detects planar and subsurface flaws and gives depth but needs a trained operator and a smooth surface.
- Destructive tests. Tensile, bend, nick-break, impact, hardness, macro-examination.
Worked example
A 10 mm fillet shows a continuous undercut of about 0.9 mm along the vertical leg; leg size is 6 mm against 8 mm specified. Reasoning: leg size short plus undercut together point to excessive current combined with too fast a travel - the arc gouges the vertical member and the puddle freezes before filling. The long arc and a drag angle below about 20° would add spatter and make undercut worse. Remedy: reduce current about 10%, shorten the arc, hold a 45° work angle with slight push, slow travel so the puddle wets both legs, then verify leg size with a fillet gauge.
Traps
Choosing MT for austenitic stainless; expecting RT to find a tight lamellar crack parallel to the beam; treating spatter as a cosmetic issue on a machined face; ignoring arc strikes, which are stress raisers.