API RP 577

Covers — guidance for inspectors on welding processes (SMAW, GTAW, GMAW, etc.), weld metallurgy, common discontinuities and their causes, welding inspection activities, and interpretation of welding documentation (WPS/PQR/WPQ).

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

• Procedure/welder qualification → ASME Section IX.
• Weld acceptance criteria and NDE extent → the construction/inspection code (API 570 / B31.3) and ASME Section V.
• Material verification (PMI) → API RP 578.

RP 577 builds welding understanding for inspectors; it does not replace Section IX qualification or the code acceptance criteria.

RP 577 provides guidance for welding inspection:

• Processes — characteristics and typical applications of common arc-welding processes.
• Metallurgy — weld/HAZ metallurgy, preheat/PWHT, and hardness considerations.
• Discontinuities — types, causes, and detection of common weld defects.
• Documentation — reading and verifying WPS, PQR, and welder qualification records.

API RP 577 gives inspectors the welding knowledge they need to oversee and inspect welding on refinery and process equipment: the arc-welding processes, weld and heat-affected-zone metallurgy, the discontinuities that arise and why, and how to read and verify WPS/PQR/WPQ documentation.

It bridges the welding-qualification code (ASME Section IX) and the practical inspection role, complementing RP 578 (material verification). It is guidance, not a qualification or acceptance code — procedures are still qualified to Section IX and welds accepted per the construction/inspection code and Section V.

Engineering Note: Use RP 577 to verify the WPS covers the actual base metals and thicknesses and that the PQR supports it — a weld made outside the qualified essential-variable range is nonconforming regardless of how good it looks.