Inspection, Testing and Defect Identification of Completed Welds
This domain tests the inspection sequence, the acceptance logic, and your ability to name a defect from a description of its appearance or its radiograph.
The inspection sequence
Before welding: material identity, fit-up, WPS, consumable. During: parameters, interpass temperature, cleaning. After: visual and dimensional, then NDT as specified. Visual inspection is the cheapest and catches most rejects, but only if the weld is cleaned first.
Common FCAW defects and causes
Porosity - gas trapped by draughts, low flow, moisture, or dirty plate. Slag inclusion - poor interpass cleaning or wrong travel angle. Incomplete fusion - low heat input, fast travel, or wire aimed away from the fusion face. Undercut - excess voltage or current, or travel too fast. Cracks - hydrogen, restraint, crater neglect.
NDT selection
PT finds surface-breaking defects. MT finds surface and near-surface defects in ferromagnetic steel. UT detects internal planar defects and is generally better than RT for tight lack of fusion aligned with the bevel. RT detects volumetric defects - porosity and slag - and misses planar defects lying parallel to the beam.
Worked example
A radiograph shows a dark, straight, sharp-edged line running along the bevel face of a V-groove. Answer: incomplete fusion, not slag. Reasoning: slag inclusions appear irregular, rounded and scattered, and are volumetric; a straight sharp line following the fusion face is planar and follows the joint preparation. Likely cause is low heat input or the arc running on the puddle rather than the fusion face.
Traps that cost marks
Calling every dark indication porosity. Inspecting before slag removal. Assuming RT covers all internal defects. Forgetting that undercut is measured against a code limit, not against zero.