Weld Quality Inspection, Destructive Testing, and Defect Analysis
Inspection is where the repair is proved. The exam tests visual criteria, the destructive tests used on coupons and salvage parts, and the defect-to-cause links that let you correct a process instead of guessing.
Visual criteria
Check weld size and length, count and spacing against the procedure, undercut, porosity, spatter, burn-through, crater fill, and toe profile. For STRSW, check tip marks, electrode alignment, and that the nugget sits on the flange rather than off the edge.
Destructive tests
Peel and chisel tests load the joint mechanically; a weld that separates at the interface shows incomplete fusion. The plug test on STRSW pulls a button that you then measure. Macro-etch sections a coupon to reveal nugget diameter and penetration, and bend tests reveal ductility and lack of fusion.
Defect-to-cause links
Porosity points to gas coverage, contamination, or wet wire. Lack of fusion points to low current, fast travel, wrong angle, or coating left between sheets. Undercut points to excess current, a long arc, or wrong angle. Burn-through points to a gap, thin metal, or too much heat. Crater cracks point to missing crater fill or abrupt termination.
Worked example
A chisel test on new-panel welds fails at the faying surface. Reasoning: separation at the interface, rather than a torn button, means the nugget never formed - check the current path (shunting), tip condition and force, coating between sheets, and whether the machine schedule matches the OEM. Appearance alone would have passed these welds.
Traps
Passing a weld by appearance; measuring a plug without the correct gauge; running destructive tests on visible customer panels instead of coupons; failing to record results.