Weld Examination, Testing, and Code Compliance
Weld Examination, Testing, and Code Compliance
This domain tests method selection, acceptance criteria, and documentation. The inspector must know what each test can and cannot detect and must apply the code's acceptance criteria instead of personal judgment.
Core rules
- Visual examination (VT) is first and applies to every weld; it finds surface profile, undercut, overlap, spatter, and gross discontinuities.
- Penetrant testing (PT) finds surface-breaking discontinuities in nonporous materials. Clean and dry the surface; use proper dwell and developer; do not use PT on rough, porous, or leaking surfaces.
- Magnetic particle testing (MT) finds surface and near-surface discontinuities in ferromagnetic materials. It is not effective on austenitic stainless steel or aluminum.
- Radiographic testing (RT) finds volumetric discontinuities and density changes. Ultrasonic testing (UT) is strong for planar and subsurface flaws but depends on calibration, couplant, and technique.
- A discontinuity is not automatically a defect. Acceptance criteria are code-specific. Cracks are generally rejectable; porosity, slag, and undercut are judged by type, size, and length.
- NDT personnel should be qualified under the employer's written practice, such as ASNT SNT-TC-1A, and equipment must be within calibration.
Worked example
A fabricator requests magnetic particle testing on an austenitic stainless steel weld. MT relies on ferromagnetic behavior, so it is not effective in austenitic stainless. The inspector rejects the method selection and uses PT for surface examination or RT or UT for volumetric examination, as the code requires. The reasoning is method capability, not convenience. The inspector also verifies the technician's certification and equipment calibration before accepting results.
Traps
Using PT on porous or painted surfaces without proper cleaning; using MT on stainless steel; treating a relevant indication as a defect without applying the code's acceptance table; accepting NDT from an uncertified technician; and applying acceptance criteria from a different code edition or product.