Weld inspection, testing and non-destructive examination
This domain covers method selection, capability and limitation of NDE, plus acceptance against standards. The exam expects you to know why a method detects a given defect, not just its acronym.
Method capability
Visual testing (ISO 17637) is the first and cheapest inspection. Penetrant testing (ISO 3452) detects surface-breaking defects in non-porous materials. Magnetic particle testing (ISO 17638) detects surface and near-surface defects in ferromagnetic materials only. Radiography (ISO 17636) is volumetric but insensitive to planar defects oriented parallel to the beam. Ultrasonics (ISO 17640) detects planar and volumetric defects and gives through-thickness location; phased array and TOFD improve coverage and sizing.
Worked example: angle-beam geometry
A 60° probe inspects 20 mm plate on first leg. Path length = t / cos 60° = 20 / 0.5 = 40 mm. Surface distance from index point to reflector = t × tan 60° = 20 × 1.732 = 34.6 mm. On second leg, path doubles to 80 mm and surface distance to 69.3 mm. These values place the reflector and set the scanning range; an incorrect trigonometric basis puts indications in the wrong location.
Acceptance and documentation
Acceptance levels follow EN ISO 5817 or the applicable product standard. Indications are sized, characterised and compared with levels; defect types are classified to ISO 6520. Records must allow traceability from report to weld and inspector certification.
Traps
Using MT on austenitic stainless; expecting PT to find buried defects; assuming RT finds lack of fusion aligned with the beam; applying acceptance criteria from the wrong standard.