Codes, Standards, and Acceptance Criteria (Part C)
Finding the governing requirement
Read the hierarchy before answering. Contract documents (drawings and specifications) normally govern where they conflict with the code, and the code governs where it conflicts with a referenced standard; always confirm the precedence clause in the edition you are testing against. A code sets minimum requirements - a specification may be stricter, and the stricter requirement then applies.
Prequalified versus qualified procedures
In AWS D1.1, Clause 3 lists prequalified joints: specified base metal groups, thickness ranges, groove details, processes, positions, and preheat conditions. If a WPS stays wholly inside those limits, no qualification testing is needed - but the WPS must still exist, be written, and be followed. If anything falls outside (process, thickness, joint detail, position, base metal), the WPS must be qualified by test under Clause 4 with a PQR supported by mechanical tests such as reduced-section tension, guided bends, and Charpy impact testing when required.
Essential variables
Process, filler metal classification (F-number and A-number), current type and polarity, position, preheat and interpass range, thickness range, joint detail, and significant technique changes. Change one outside its qualified range and the procedure is no longer supported.
Welder performance qualification is separate from procedure qualification: it records the individual welder's ability within position and thickness ranges, and continuity requirements must be tracked.
Acceptance criteria
Acceptance tables group requirements by category: cracks (rejected outright), fusion, crater fill, undercut, porosity, weld profile, weld size, and arc strikes. Criteria often differ for statically versus cyclically loaded structure, and much NDT is required only when the contract documents demand it - though the code itself mandates specific testing for certain applications.
Worked example: given a 3/8 in groove weld in a base metal outside the prequalified list, stop and require a qualified WPS rather than applying engineering judgment.