ASME Section IX

Covers — qualification of welding, brazing, and fusing procedures and the performance of welders, brazers, and operators, for construction under the ASME BPVC and the B31 piping codes. Organized as QW (welding), QB (brazing), and QF (fusing) articles.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Weld acceptance criteria and required examination extent → the construction code (B31.3 / B31.1 / Section VIII).
• NDE methods used to examine welds → ASME Section V.
• Structural (non-pressure) steel welding → AWS D1.1; pipeline welding → API 1104.

Section IX qualifies who welds and how; the construction code decides whether the finished weld is acceptable.

Section IX sets minimum requirements for weld qualification:

• Procedure Specification (WPS) — documents the welding process, materials (P/F/A numbers), joint, preheat, PWHT, and electrical parameters.
• Procedure Qualification Record (PQR) — records the actual test weld and its mechanical-test results supporting the WPS.
• Performance Qualification (WPQ) — proves each welder/operator can produce sound welds within a defined range.
• Essential Variables — changes beyond stated limits invalidate the qualification and require requalification.

ASME Section IX is the universal ASME framework for qualifying welds. The WPS defines how a joint is to be welded; the PQR is the test evidence that a weld made that way passed mechanical testing; and the welder/operator performance qualification proves the person can execute it. Together they make a weld's integrity traceable and defensible.

"Essential variables" are the heart of the system: changing a P-number grouping, filler classification, preheat, or PWHT beyond stated limits requalifies the procedure. Section IX is invoked by the construction codes but does not itself judge the finished weld — that acceptance comes from B31.3/Section VIII plus Section V examination.

Engineering Note: Before welding, confirm the WPS covers the actual base metals (P-numbers), thickness range, and PWHT — a mismatch between the job and the qualified range is the most common welding-documentation nonconformance.