Weld Inspection, Discontinuities, and Quality Control
This domain tests weld inspection, discontinuities and quality control: visual inspection, NDT methods, common defects and acceptance decisions. The exam expects you to identify a discontinuity and choose a suitable inspection method.
Core rules
- Visual inspection (VT) comes first: check cleanliness, bead profile, undercut, spatter, arc strikes and dimensions.
- Penetrant testing (PT) finds surface-breaking defects on non-porous materials; magnetic particle testing (MT) finds surface and near-surface defects in ferromagnetic steel.
- Ultrasonic testing (UT) finds internal planar defects such as lack of fusion; radiography (RT) finds internal volumetric defects such as porosity and slag.
- Acceptance is against the applicable code or drawing, not a personal opinion.
Worked example
A completed carbon steel fillet weld shows a fine surface line. Reasoning: clean the area and use VT first. If it is surface-breaking, MT or PT can help locate it; MT is suitable because the steel is ferromagnetic. If the concern is lack of fusion below the surface, UT is better than PT because PT cannot detect subsurface defects. The weld is accepted or repaired only by comparing the indication with the specified acceptance criteria.
Traps
Do not call every discontinuity a defect; defect means it fails acceptance. Do not use PT on a rough, porous surface without considering bleed-through. Do not use MT on austenitic stainless steel as if it were ferromagnetic. Do not inspect before slag and spatter are cleaned.