Weld Inspection, Testing, and Defect Identification/Correction
This domain tests inspection across the weld cycle and the identification and correction of common GTAW defects.
Core rules
- Inspect before welding: material identity, joint fit-up, cleanliness, WPS availability, filler, and equipment. Inspect during welding: current, polarity, gas flow, interpass temperature, and technique. Inspect after welding: profile, dimensions, and surface condition.
- Visual inspection identifies undercut, overlap, porosity, cracks, arc strikes, spatter, incomplete penetration at the root, and heat tint. Use gauges for fillet size, crown height, and undercut depth where required.
- Liquid penetrant testing finds surface-breaking defects in stainless steel and aluminum. Radiography finds volumetric defects such as porosity, tungsten inclusions, and incomplete fusion. Ultrasonic testing can find internal planar defects. Bend tests evaluate procedure or welder qualification.
- Common GTAW defects include porosity from gas problems, incomplete fusion from low heat or poor cleaning, incomplete penetration from poor fit-up or current, tungsten inclusion from electrode contact, cracks from restraint or contamination, and oxidation from lost shielding.
- Correct defects only by an approved method. Remove the defect to sound metal, verify removal, reweld per the WPS, and re-inspect. Do not cover defects with paint or a cosmetic pass.
Worked example
A liquid penetrant test shows a linear indication on a stainless steel cap. The inspector marks the area, and the welder grinds the indication to sound metal. The area is re-tested to confirm removal, then rewelded with the qualified WPS and inspected again. Grinding and rewelding without confirmation could leave the crack tip behind, and painting over the area would hide rather than correct the defect.
Traps that cost marks
- Treating a visual pass as complete inspection when NDT is specified.
- Confusing surface and volumetric methods.
- Grinding a defect without verifying removal.
- Ignoring tungsten inclusions or arc strikes.
- Repairing without the WPS or without re-inspection.