API 1104

Covers — gas and arc welding of piping used in the compression, pumping, and transmission of crude, petroleum products, fuel gases, CO₂, and nitrogen: procedure and welder qualification, production welding, NDE, and weld-acceptance criteria (workmanship or alternative ECA), including in-service repair welding.

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

• Plant/process piping and vessel welds → ASME Section IX + B31.3/Section VIII.
• Structural steel welding → AWS D1.1.
• The pipeline systems themselves → ASME B31.4 / B31.8; line pipe material → API 5L.

API 1104 governs pipeline girth welds; ASME Section IX governs plant pressure welds — do not cross-apply their acceptance criteria.

API 1104 sets minimum requirements for pipeline welding:

• Procedure Qualification — qualify the welding procedure by test weld with tensile, bend, and nick-break/impact testing.
• Welder Qualification — performance qualification for the pipeline positions and processes used.
• Production Welding — line-up, preheat, and pass sequence for girth welds, including semi/mechanized processes.
• Inspection & Acceptance — visual and NDE (RT/UT) with workmanship acceptance criteria, or an alternative fracture-mechanics/ECA acceptance for defined conditions.

API 1104 is the world's most widely used pipeline welding standard, covering procedure and welder qualification, production welding, and weld-acceptance criteria for transmission and distribution pipelines built and repaired under B31.4/B31.8. It offers both workmanship acceptance and an alternative engineering-critical-assessment (ECA) route for girth-weld flaws.

Its acceptance criteria reflect the axial-load, high-productivity nature of cross-country girth welding, distinct from the plant-piping focus of ASME Section IX. The standard is incorporated by reference in US pipeline safety regulations.

Engineering Note: The ECA (alternative acceptance) route can accept flaws that workmanship criteria reject, but it demands defined toughness, stress, and inspection inputs — apply it only when those prerequisites are truly met.