API 1104 — Welding of Pipelines and Related Facilities
API 1104 is the American Petroleum Institute standard governing welding procedures, welder qualification, and inspection requirements for pipelines transporting oil, natural gas, and other fluids. It applies to new construction and in-service welding of carbon and low-alloy steel pipe regulated by 49 CFR 192 and 49 CFR 195.
Regulatory context: API 1104 compliance is mandatory for pipeline systems regulated under U.S. Department of Transportation rules. 49 CFR 192.225 (gas transmission) and 49 CFR 195.214 (hazardous liquids) both incorporate API 1104 by reference for welding qualification and inspection.
What Is API 1104?
API 1104 governs welding of cross-country pipelines and related facilities. It covers carbon and low-alloy steel pipe used in compression, pumping, and transmission of crude petroleum, petroleum products, fuel gases, and carbon dioxide. The 22nd edition (2021) is the current version.
API Standard 1104, “Welding of Pipelines and Related Facilities,” covers the welding of piping used in compression, pumping, and transmission of crude petroleum, petroleum products, fuel gases, carbon dioxide, and nitrogen. The standard applies to both new construction and in-service repair welding on pressurized systems. It addresses arc welding, oxyfuel gas welding, and flash butt welding of butt, fillet, and socket welds in carbon and low-alloy steel pipe.
The standard is organized into thirteen sections. Sections 1 through 4 cover scope, references, definitions, and specifications. Section 5 establishes procedure qualification requirements. Section 6 covers welder qualification. Sections 7 and 8 address design and workmanship of production welds. Section 9 covers inspection and testing of production welds. Section 10 provides acceptance standards for nondestructive testing. Sections 11 and 12 cover repair procedures and procedures for automatic welding. Section 13 addresses mechanized welding with filler metal additions.
The current edition is API 1104, 22nd Edition, 2021. API 1104 is developed independently from both ASME Section IX and AWS D1.1, though many fabricators and pipeline contractors maintain qualifications under multiple standards depending on the jurisdictional requirements of their projects.
Procedure Qualification Under API 1104
API 1104 Section 5 requires every WPS to be qualified by testing. There is no prequalified WPS path. The fabricator produces test welds on pipe specimens matching the intended production diameter and wall thickness range. Destructive testing includes tensile, nick-break, and bend tests. Radiographic testing may substitute for some destructive tests.
API 1104 Section 5 requires that welding procedures be qualified by destructive testing before production welding begins. The qualification process requires producing test welds on pipe specimens using the intended procedure, then cutting and testing specimens to demonstrate adequate mechanical properties.
The required destructive tests for butt welds include two tensile specimens, two nick-break specimens, and either root bend plus face bend tests (for thinner walls) or four side bend specimens (for wall thickness over 12.7 mm). The test weld must also pass either radiographic testing or ultrasonic testing before destructive specimen removal.
API 1104 defines essential variables that govern when re-qualification is required. The essential variables specific to API 1104 include:
- Welding process
- A change in welding process or combination of processes requires a new qualification. SMAW, GMAW, FCAW, GTAW, and SAW are the commonly qualified processes for pipeline applications. Combinations such as GTAW root with SMAW fill are qualified as a single procedure.
- Base metal group
- API 1104 groups base metals by specified minimum yield strength (SMYS). A procedure qualified on a material in one SMYS group may have limited applicability to materials in other groups. This differs from ASME IX P-numbers, which group by composition and weldability rather than strength alone.
- Joint design
- Changes in joint design beyond the qualified range — including groove angle, root opening, and root face — require re-qualification. Pipeline joints are typically V-groove or compound bevel configurations sized for the pipe wall thickness.
- Wall thickness range
- The qualified wall thickness range is determined by the test coupon thickness. Qualification on thinner material does not automatically qualify thicker material. The qualified range is specified in Section 5.4 based on the test weld dimensions.
- Pipe diameter range
- Qualification is limited by the test coupon diameter. The diameter ranges are specified in Section 5.4. Qualification on larger diameters may cover smaller diameters within the specified range, but not vice versa without separate testing.
- Position
- Pipeline welding positions are designated as rolled (1G), fixed horizontal (5G), fixed inclined (6G), or multiple positions. Qualification in the 6G position qualifies all fixed-position welding. Rolled-position qualification does not qualify fixed positions.
Welder Qualification Under API 1104
API 1104 Section 6 requires each welder to qualify on a test coupon using the specific WPS they will use in production. Qualification variables include pipe diameter, wall thickness, welding position, and joint design. Qualification tests include destructive testing (nick-break and bend tests) or radiographic examination of the completed test weld.
Section 6 requires each welder to demonstrate the ability to produce sound welds using the qualified procedure. The welder qualification test produces a test coupon that is examined by radiography or destructive testing. Single-qualification tests qualify the welder for the specific procedure, position, and pipe diameter group tested.
Welder qualifications are specific to the employer. A welder who changes employers must re-qualify with the new company, even if the welding procedure is identical. This is stricter than ASME Section IX, where performance qualifications can transfer between employers under certain conditions. API 1104 welder qualifications do not expire due to inactivity, but the company must have records demonstrating the welder has used the process within the required timeframe.
In-Service Welding (Appendix B)
API 1104 Appendix B covers welding on pipelines that are in service — carrying product under pressure during welding. In-service welding requires additional precautions: burn-through prevention (minimum wall thickness verification), hydrogen cracking prevention (low-hydrogen processes), and flow rate consideration to manage heat dissipation.
API 1104 Appendix B addresses welding on pipelines that are in operation and may contain pressurized product. In-service welding includes hot taps (adding branch connections while the pipeline is pressurized), encirclement sleeves, and direct deposit repairs. The primary safety concern is burn-through — the welding arc melting through the remaining pipe wall into the pressurized product.
Procedure qualification for in-service welding requires testing at simulated flow conditions to demonstrate the procedure can be safely performed at the minimum wall thickness encountered in the field. Heat input control is critical — low heat input reduces the risk of burn-through but increases the risk of hydrogen cracking in the heat-affected zone. Preheat requirements for in-service welding may differ from new construction because the flowing product acts as a heat sink, increasing cooling rates and hydrogen cracking susceptibility.
How API 1104 Compares to Other Welding Codes
API 1104 governs pipelines; D1.1 governs steel structures; ASME IX governs pressure equipment. API 1104 has no prequalified WPS path. It groups base metals by SMYS (specified minimum yield strength) into Groups I through IV. Acceptance criteria include both workmanship-based limits (Section 9) and fitness-for-service methods (Appendix A).
API 1104 vs AWS D1.1
D1.1 applies to structural steel, while API 1104 applies to pipelines. D1.1 qualifies procedures by plate thickness, while API 1104 qualifies by pipe diameter and wall thickness. D1.1 allows prequalified WPSs under Clause 5, while API 1104 requires qualification testing for every procedure. D1.1 uses Table 5.6 base metal groups, while API 1104 groups by SMYS. The acceptance criteria in API 1104 Section 9 are specific to girth welds in pipe, while D1.1 Table 8.1 criteria are for structural connections.
API 1104 vs ASME Section IX
Both standards require procedure qualification testing, but the essential variable rules and test requirements differ. ASME IX uses P-numbers for base metal grouping, while API 1104 uses SMYS-based groups. ASME IX guided bend and tension tests differ from API 1104 nick-break and root/face bend tests. When a pipeline also falls under ASME B31.8 (gas transmission) or B31.4 (liquid transportation), the relationship between API 1104 and ASME Section IX must be carefully managed — B31.8 references API 1104 directly for welding qualification, not ASME IX.
| Aspect | API 1104 | AWS D1.1 | ASME IX |
|---|---|---|---|
| Scope | Pipelines (cross-country) | Structural steel | Pressure equipment |
| Prequalified WPS? | No | Yes (Clause 5) | No |
| Base metal grouping | Groups I–IV (by SMYS) | Table 5.6 categories | P-numbers |
| Preheat method | Per WPS | Table 5.11 | Per WPS/PQR |
| Acceptance criteria | Workmanship + ECA (Appendix A) | Table 8.1 (visual) | Per construction code |
| Edition | 2021 (22nd) | 2025 (25th) | 2025 |
Acceptance Standards for NDT
API 1104 Section 9 defines acceptance criteria for radiographic, magnetic particle, liquid penetrant, and ultrasonic testing of production welds. Section 9 provides specific criteria for inadequate penetration, incomplete fusion, internal concavity, burn-through, slag inclusions, and porosity. The acceptance criteria are based on the length and distribution of indications relative to the weld length and pipe wall thickness.
API 1104 also includes provisions for alternative acceptance criteria in Appendix A, which allows engineering critical assessment (ECA) methods based on fracture mechanics. Under Appendix A, defect acceptance is based on fitness-for-service analysis rather than workmanship-based limits, potentially allowing larger defects when stress analysis demonstrates the defect will not grow to critical size during the design life of the pipeline.
Related Standards Guides
Frequently Asked Questions
API 1104 is the American Petroleum Institute standard for welding of pipelines and related facilities. It covers welding procedure qualification, welder qualification, and inspection requirements for pipelines used to transport petroleum, natural gas, and other fluids. API 1104 applies to new construction and in-service welding of carbon and low-alloy steel pipe. The standard is referenced by pipeline regulations including 49 CFR 192 (gas transmission) and 49 CFR 195 (hazardous liquids), making compliance mandatory for regulated pipeline systems in the United States.
API 1104 applies to pipeline welding (pipe transporting fluids under pressure), while AWS D1.1 applies to steel structures (buildings, bridges, towers). API 1104 classifies base metals by SMYS (specified minimum yield strength) rather than D1.1 Table 5.6 groups. API 1104 qualification is based on pipe diameter and wall thickness ranges, while D1.1 qualifies by plate thickness. API 1104 has specific provisions for in-service welding on pressurized pipelines, which D1.1 does not address. Both require procedure qualification testing, though D1.1 also allows prequalified WPSs under Clause 5.
No. API 1104 uses its own material grouping system based on specified minimum yield strength (SMYS) rather than ASME IX P-numbers. API 1104 Section 5.4 defines material groups by SMYS ranges. A procedure qualified on a higher-strength material group may or may not qualify for lower-strength groups depending on the essential variable rules. When pipeline projects reference both API 1104 and ASME B31.8 or B31.4, the API 1104 material grouping governs the welding qualification, not the ASME P-number system.
API 1104 Section 5 requires destructive testing of the procedure qualification test weld. The required tests include tensile tests (two specimens), nick-break tests (two specimens), and root bend and face bend tests (two each for smaller diameters) or side bend tests (four specimens for wall thickness over 12.7 mm). For in-service welding (hot taps, sleeve repairs on live pipelines), additional qualification per API 1104 Appendix B is required, including burn-through risk assessment and hardness testing due to accelerated cooling. Radiographic or ultrasonic testing of the completed test weld is performed before destructive specimen removal.
In-service welding is welding performed on a pipeline that is in operation and may contain pressurized product. API 1104 Appendix B covers in-service welding, including hot taps (branch connections made while the pipeline is pressurized) and sleeve repairs. The primary concern is burn-through, where the welding arc melts through the pipe wall into the pressurized product. Procedure qualification for in-service welding requires testing at simulated flow conditions and wall thickness minimums to demonstrate the procedure can be performed without burn-through risk.