Acceptance Criteria and Evaluation of Test Results
What is judged
Each test method has acceptance criteria in the relevant part of EN ISO 9606 (often referencing EN ISO 5817 quality levels). Typical criteria:
- VT: no cracks, no incomplete fusion, limited undercut, limited porosity, acceptable profile.
- RT: defect sizes and types within limits; no cracks; porosity within specified levels.
- Bend: no open defects exceeding the specified size in the tension zone after bending.
- Macro: fusion to the root, adequate penetration, no cracks.
- Fracture: no lack of fusion or penetration beyond limits.
Evaluation logic
A test piece fails if any required test fails. Some standards allow re-test after a failed test (often one re-test), but the rules on re-testing are specific - do not assume unlimited retakes. The examiner evaluates and records results on the QTR.
Traps
- Confusing acceptance criteria between VT and RT - a defect acceptable on the surface may be unacceptable internally.
- Assuming a single acceptable defect means pass - cumulative or critical defects fail the piece.
- Forgetting that the quality level (e.g. B, C, D) changes the criteria.
- Overlooking that the welder's technique, not the material, is being judged - but material defects still fail the test.
Rule of thumb
Cracks are never acceptable. Everything else is a matter of type, size, location and the specified quality level.
Worked example
A butt test shows a 1 mm undercut along the cap and a small internal pore on RT. Undercut within the VT limit may pass; the pore on RT is judged against the RT criteria. The piece fails only if either exceeds its own criterion - evaluate each test against its own table.