Weld Inspection, Defects and Quality Control
This domain tests visual and non-destructive inspection, defect identification and acceptance decisions. You must know what each method can and cannot find.
Core rules
- Visual inspection (VT) checks bead shape, size, undercut, spatter, cracks, fit-up and alignment before and after welding.
- Penetrant testing (PT) finds surface-breaking defects in non-porous materials. Magnetic particle testing (MT) finds surface and near-surface defects in ferromagnetic materials.
- Ultrasonic testing (UT) finds internal defects and is good for planar defects. Radiographic testing (RT) finds internal volumetric defects such as porosity and slag.
- Common defects: porosity, slag inclusion, lack of fusion, lack of penetration, undercut, overlap, spatter, cracks and wrong weld size.
Worked example
A drawing requires a 6 mm fillet leg. A fillet gauge reads 5.2 mm. The shortfall is 6.0 − 5.2 = 0.8 mm. If the acceptance standard requires at least 6 mm, the weld is undersized and must be repaired. The reasoning is that leg length controls throat thickness and load capacity.
Traps that cost marks
- Using PT to find internal porosity.
- Assuming RT is best for all cracks; tight planar cracks can be missed.
- Measuring a fillet with a ruler instead of a gauge.
- Accepting undercut because the bead “looks neat”.