Welding Inspection and Nondestructive Examination
NDE supports, but never replaces, visual inspection. The inspector confirms method selection, timing, procedure, personnel certification, surface condition, and acceptance criteria. Common methods are VT for surface and profile, PT for surface-breaking defects on most materials, MT for surface and near-surface defects in ferromagnetic steel, UT for internal planar and volumetric defects, and RT for internal volumetric defects.
Sequence and controls
- Complete welding and allow cooling before final NDE.
- Perform VT first; PT and MT after appropriate surface preparation.
- Use qualified procedures and certified personnel; record method, level, equipment, and results.
- Evaluate against the governing code, not “good enough.”
- Re-inspect repairs with the same method and extent.
Worked example
A completed complete-joint-penetration groove weld in carbon steel shows a surface-breaking indication at the toe. VT and MT are appropriate for the surface or near-surface indication; UT or RT would be used if internal defects are suspected. A crack is rejectable under typical structural criteria. Reasoning: method choice follows defect location and material; a surface method cannot prove internal soundness.
Traps
- PT on rough, painted, or as-welded surfaces without cleaning.
- MT on austenitic stainless steel.
- Accepting an NDE report without method and personnel level.
- Inspecting before final weld cooling.
- Skipping re-inspection after repair.