API 1104: Standard for Welding of Pipelines and Related Appurtenances
Welding standard for oil and gas pipelines covering welder qualification, welding procedures, and inspection requirements. API 1104 mandates radiographic and ultrasonic inspection of welds with specific acceptance criteria. This standard is widely used in pipeline construction and operations worldwide. Welder qualifications per API 1104 are accepted internationally.
The American Petroleum Institute (API) publishes the in-service inspection standards that govern downstream and midstream petroleum equipment.
OSHA Process Safety Management (29 CFR 1910.119) and EPA Risk Management Program rules cite API inspection standards as recognised and generally accepted good engineering practice (RAGAGEP), so non-compliance is enforced indirectly through PSM audits.
API 1104 is invoked when the scope of work matches its title — standard for welding of pipelines and related appurtenances — and when the contract or regulatory regime cites it as the controlling document. On petroleum and petrochemical equipment, API 1104 usually feeds into a written mechanical-integrity program: inspection intervals, examination methods, and acceptance criteria are all traced back to a clause number in the document. In fabrication shops the standard is reproduced inside the written procedure book and referenced from every inspection report so that the auditor's paper trail leads back to the same paragraph the inspector worked from.
Methods covered
Industries
- Pipeline
- Oil & Gas
- Construction
- Personnel qualification: examinations under API 1104 must be performed by inspectors qualified and certified to a recognised scheme (typically ASNT SNT-TC-1A, CP-189, or ISO 9712 depending on jurisdiction), with documented training hours, vision tests, and a controlling written practice.
- Written procedure: every examination requires a written, controlled procedure that names the method, equipment, calibration steps, scanning pattern, and acceptance criteria — and is qualified before first use.
- Equipment verification: ultrasonic instruments must be verified against a calibration block (V1, V2, IIW, or job-specific reference) at intervals defined by the procedure — typically before use, every four hours of scanning, on operator change, and at end of shift.
- Image-quality verification: every radiograph or digital exposure carries a penetrameter / IQI of the type and thickness specified by the standard; the IQI must be visible and at the required sensitivity for the radiograph to be acceptable.
- Radiation safety: source handling, exclusion zones, dosimetry, and source recordkeeping must follow the licensing authority's rules in addition to the inspection standard itself.
- Magnetic-particle technique: magnetisation method (yoke, prods, central conductor, multidirectional), field strength verification (pie gauge, Hall-effect meter, or QQI), and demagnetisation are all specified in the written procedure.
- Acceptance criteria: indications are evaluated against the standard's tabulated limits (length, depth, alignment, frequency); any indication exceeding the criteria is recorded, dispositioned, and either repaired or evaluated for fitness-for-service.
- Documentation: examination reports must include enough information for a third party to reproduce the inspection — equipment serial numbers, calibration records, inspector ID, sketches of indications, and the controlling procedure revision.
- Inspection intervals: API 1104 sets maximum intervals between inspections based on remaining-life calculations or fixed default intervals; an authorised inspector must approve any extension based on documented risk-based-inspection analysis.
- Latest Edition
- 22nd edition (2021)
- First Published
- 1953
- Scope
- Welding of pipelines and related facilities; covers procedure qualification, welder qualification, NDE, and acceptance criteria for cross-country girth welds.
- Acceptance Criteria
- Sec. 9 tables for porosity, slag, undercut, cracks, lack of fusion/penetration; alternative criteria via Annex A (ECA).
- Calibration / Qualification
- Welding procedures per Sec. 5; welders per Sec. 6; NDE personnel per ASNT SNT-TC-1A or equivalent.
Key Clauses Inspectors Cite
- Sec. 5 — Qualification of Welding Procedures
- Sec. 6 — Qualification of Welders
- Sec. 9 — Acceptance Standards for NDT
- Sec. 11 — Repair and Removal of Defects
Companion / Parent Standards
ASME B31.4 (liquid pipelines) · ASME B31.8 (gas pipelines) · API 5L (line pipe) · BS 7910 (ECA)
Sample Contract Language
“Girth welds shall be welded and inspected per API 1104 22nd ed.; AUT acceptance per Annex A (ECA) where applicable.”
API revises its inspection codes on roughly a five-to-seven-year cycle, with addenda issued in between. Recent updates to API 1104 have continued the move toward risk-based-inspection (RBI) as an accepted basis for setting inspection intervals, expanded coverage of damage mechanisms, and updated cross-references to the latest editions of API 579 (fitness-for-service) and API 580/581 (RBI). The version cited in a written mechanical-integrity program should be tracked in the document control system so that any update flows through to the inspection plan.
A typical refinery turnaround applies API 1104 to the inspection scope for high-temperature piping and pressure vessels: corrosion-monitoring locations are read with UT thickness gauges, girth welds on repaired sections are radiographed or PAUT-scanned, and any indication outside the standard's acceptance table is dispositioned through API 579 fitness-for-service before the unit restarts.
What does API 1104 cover?
API 1104 (Standard for Welding of Pipelines and Related Appurtenances) is published by API. Welding standard for oil and gas pipelines covering welder qualification, welding procedures, and inspection requirements.
Is API 1104 mandatory or voluntary?
API 1104 is a consensus standard. It becomes mandatory when invoked by a contract, by another code that cites it (for example ASME Section V calling out an ASTM practice), or by a regulator that has adopted it into law in a specific jurisdiction.
Who is qualified to perform inspections under API 1104?
Inspections under API 1104 must be performed by personnel qualified and certified to a recognised NDT certification scheme — most commonly ASNT SNT-TC-1A or CP-189 in the United States, ISO 9712 in much of the rest of the world, and NAS 410 for aerospace work. The written practice that controls qualification must be in place before any examination is started.
How does API 1104 interact with ASME Section V?
API 1104 typically references ASME Section V for the underlying examination methods and acceptance criteria, then layers on the API-specific inspection intervals, damage-mechanism coverage, and Authorised Inspector requirements that apply to in-service equipment.
Standard Code
API 1104
Organization
API
Methods Covered
4 method(s)
Industries
3 sector(s)
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