API 1104 · Pipeline Construction · Oil & Gas

Pipeline Welding Requirements — API 1104 Qualification and Inspection

Pipeline welding requirements under API 1104 govern procedure qualification, welder testing, production workmanship, and inspection for oil and gas pipeline construction. Compliance is mandatory under 49 CFR 192 for gas transmission and 49 CFR 195 for hazardous liquid pipelines in the United States.

Regulatory mandate: API 1104 is not optional for regulated pipelines. U.S. DOT regulations incorporate it by reference. A pipeline weld that does not meet API 1104 requirements is a regulatory violation, not just a quality concern. Welders, inspectors, and contractors must understand these requirements before performing or evaluating pipeline welding.

Procedure Qualification Requirements

Pipeline WPS qualification under API 1104 Section 5 requires destructive testing of test welds: tensile tests, nick-break tests, and guided bend tests. There is no prequalified WPS path. Variables include pipe diameter, wall thickness, joint design, welding process, filler metal, shielding gas, and position.

API 1104 Section 5 requires that every welding procedure used on pipeline construction or repair be qualified by destructive testing before production welding begins. There is no prequalified exemption comparable to D1.1 Clause 5 — every pipeline procedure must be tested and documented.

The procedure specification must define the welding process, base material specification, diameter and wall thickness range, joint design (groove angle, root opening, root face), filler metal classification, electrical characteristics, position, direction of welding, shielding gas (if applicable), preheat and interpass temperatures, post-weld heat treatment (if applicable), and number and sequence of passes.

Qualification testing requires the contractor to produce a test weld under controlled conditions, then cut and test specimens from the completed weld. The required destructive tests for butt welds include tensile tests (two specimens), nick-break tests (two specimens from the root and face side), and guided bend tests (two root bends and two face bends for thinner material, or four side bends for wall thickness exceeding 12.7 mm). Radiographic or ultrasonic testing is performed on the completed test weld before destructive specimen removal.

Welder Qualification Requirements

API 1104 Section 6 qualifies welders on test coupons using the specific WPS they will use in production. Qualification testing includes nick-break and bend tests or radiographic examination. Qualification is specific to pipe diameter ranges, wall thickness ranges, and welding position (fixed, rolled, or combination).

Section 6 requires each welder to demonstrate competence by producing a test weld that meets the acceptance criteria. The qualification test is specific to the welding procedure, position, and pipe diameter range. The welder must use the same process, filler metal type, and technique specified in the qualified procedure.

Pipeline welding positions include:

Rolled (1G): Pipe is rotated during welding, so all welding occurs in the flat position. Used for shop fabrication and tie-in welds where rotation equipment is available. A 1G qualification does not qualify for fixed-position field welding.
Fixed horizontal (5G): Pipe axis is horizontal and the pipe cannot be rotated. The welder must weld around the pipe from top to bottom (or bottom to top), passing through vertical and overhead positions. This is the most common field welding position for horizontal pipeline construction.
Fixed inclined (6G): Pipe axis is inclined at 45 degrees and cannot be rotated. This position combines elements of all other positions and is the most comprehensive single-position qualification. A 6G qualification covers all fixed-position welding including 5G, 2G, and restricted-access conditions.
Restricted access (branch connections): Pipeline branch connections and saddle joints present restricted access conditions where standard butt weld techniques are insufficient. API 1104 Section 6 addresses qualification for these geometries separately. The welder must demonstrate competence in multiple positions with limited access, simulating the real conditions encountered on operating pipeline systems.

Welder qualifications under API 1104 are specific to the employer. A welder changing companies must re-qualify with the new employer, even if the procedure is identical. This is more restrictive than ASME Section IX, where performance qualifications can transfer between employers under certain conditions.

Production Welding Workmanship

API 1104 Section 7 governs production welding. Requirements include surface preparation, alignment and spacing tolerances, weather protection (minimum 0 degrees F ambient for welding), and interpass cleaning. Tack welds become part of the completed weld and must meet the same quality requirements.

Sections 7 and 8 of API 1104 establish workmanship requirements for production welding. Key provisions include alignment tolerances for butt joints (internal misalignment must not exceed specified limits based on pipe wall thickness), minimum preheat requirements based on material grade and wall thickness, interpass temperature limits, cleaning requirements between passes, and restrictions on the use of hammering or peening on completed welds.

Pipeline welds are typically made using downhill progression — starting at the 12 o’clock position (top of pipe) and progressing downward to the 6 o’clock position. This differs from structural welding under D1.1, which typically uses uphill progression. Downhill welding requires faster travel speeds and produces lower heat input per pass, which affects the resulting microstructure and mechanical properties of the heat-affected zone. The choice of progression direction is an essential variable in the procedure specification.

Root pass welding on pipelines typically uses SMAW with E6010 cellulosic electrodes, producing an open-root joint without backing. This technique requires high welder skill to achieve consistent root penetration without burn-through or incomplete fusion. Fill and cap passes may use the same process or transition to FCAW, GMAW, or other processes as specified in the qualified procedure.

Inspection and Acceptance Criteria

API 1104 Section 9 defines NDT acceptance criteria for production welds. Visual inspection verifies weld profile, reinforcement height, and surface defects. Radiographic testing evaluates internal defects: inadequate penetration, incomplete fusion, porosity, slag, and burn-through. Acceptance limits are based on defect length relative to weld length.

Section 9 of API 1104 establishes inspection requirements and acceptance criteria for production welds. All production girth welds must be inspected by radiographic testing (RT), ultrasonic testing (UT), or other approved nondestructive examination methods as specified in the construction documents. Visual inspection is required for all welds before and during NDT.

The acceptance criteria in Section 9 address specific discontinuity types found in pipeline girth welds. Each discontinuity type has defined acceptance limits based on length, width, and distribution relative to the weld length:

Inadequate penetration without high-low (IP): Root penetration must be complete and continuous. Individual IP indications up to 25 mm are acceptable if the total length does not exceed 25 mm in any 300 mm of weld. Total IP in the weld must not exceed 8% of the weld length.
Incomplete fusion (IF): Fusion must be complete between the weld metal and the base metal, and between adjacent weld passes. Acceptance limits for IF are the same as for IP — individual indications up to 25 mm, total not exceeding 25 mm in any 300 mm, and not exceeding 8% of weld length.
Burn-through (BT): Burn-through occurs when the welding arc melts through the pipe wall. For new construction, burn-through indications exceeding 6 mm are not acceptable. Individual burn-through areas must not exceed specified size limits.
Slag inclusions and porosity: Elongated slag inclusions exceeding 50 mm are not acceptable. Isolated slag inclusions up to 50 mm are acceptable if width does not exceed specified limits. Porosity is evaluated by cluster size and distribution — individual pore diameter must not exceed specified limits, and the total area of porosity in any cluster must not exceed specified percentages.

In-Service Welding

API 1104 Appendix B covers welding on pipelines that are in operation, which may contain pressurized hydrocarbon product. In-service welding includes hot taps (adding branch connections while pressurized), encirclement sleeve installations, and direct deposit weld repairs. The primary safety concern is burn-through — the welding arc melting through the remaining wall thickness into the pressurized product, which can cause a release of flammable or toxic material.

Procedure qualification for in-service welding requires testing under simulated flow conditions at the minimum wall thickness expected in the field. Heat input must be carefully controlled — too high risks burn-through, too low risks hydrogen cracking due to the rapid cooling caused by flowing product acting as a heat sink. Preheat requirements may differ from new construction procedures because the flowing product reduces the effectiveness of external preheating.

In-service welder qualifications require the welder to demonstrate competence under simulated in-service conditions. The welder must show the ability to control heat input while achieving complete fusion and acceptable root penetration on thin-wall material with cooling conditions that simulate flowing product.

How Pipeline Requirements Compare to Other Codes

API 1104 governs cross-country pipelines with no prequalified WPS path. D1.1 governs steel structures with prequalified WPSs. ASME IX governs pressure equipment (plant piping, vessels). API 1104 groups base metals by specified minimum yield strength; D1.1 uses Table 5.6 steel grade categories.

D1.1 structural welding focuses on buildings and bridges using plate and shapes, with prequalified WPS exemptions and Table 8.1 acceptance criteria designed for statically and cyclically loaded connections. Pipeline welding under API 1104 focuses on circumferential butt joints in round pipe, with no prequalified exemptions and acceptance criteria designed for pressurized containment systems. ASME IX provides the qualification framework for pressure vessels and some piping systems, but pipeline-specific regulations reference API 1104 directly. For Canadian pipeline work, CSA Z662 is the governing standard rather than API 1104.

Aspect	API 1104	AWS D1.1	ASME IX
Scope	Cross-country pipelines	Structural steel	Pressure equipment
Prequalified WPS?	No	Yes (Clause 5)	No
Qualification method	Section 5 destructive testing	Clause 6 testing	QW testing + PQR
Base metal grouping	SMYS Groups I–IV	Table 5.6 categories	P-numbers
Acceptance criteria	Section 9 + ECA (Appendix A)	Table 8.1 visual	Per construction code
In-service welding	Appendix B	Clause 11 (repair only)	Not covered

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Frequently Asked Questions

What welding standard applies to pipelines?

API 1104 (Welding of Pipelines and Related Facilities) is the primary welding standard for oil and gas pipelines. It is referenced by U.S. Department of Transportation regulations 49 CFR 192 (gas transmission pipelines) and 49 CFR 195 (hazardous liquid pipelines), making it mandatory for regulated pipeline systems. API 1104 covers procedure qualification, welder qualification, workmanship, inspection, and acceptance criteria. For pipelines that also fall under ASME B31.8 (gas transmission) or B31.4 (liquid transportation), API 1104 governs the welding qualification, not ASME Section IX.

What positions do pipeline welders need to qualify in?

Pipeline welding positions under API 1104 include rolled (1G), fixed horizontal (5G), fixed inclined at 45 degrees (6G), and restricted access positions. The 6G position is the most comprehensive single qualification because it requires the welder to weld around a pipe fixed at a 45-degree angle, which includes flat, vertical, and overhead welding in a single test. A 6G qualification covers all fixed-position welding. Rolled (1G) qualification only covers the rolled position and is used for shop fabrication where pipe can be rotated during welding.

What is the difference between pipeline welding and structural welding?

Pipeline welding under API 1104 and structural welding under AWS D1.1 differ in several fundamental ways. Pipeline welds are typically circumferential butt joints on round pipe in fixed positions, while structural welds include groove and fillet welds on plate and shapes in multiple orientations. Pipeline welding uses downhill progression (starting at the top of the pipe) for most root and fill passes, while structural welding typically uses uphill progression. Pipeline welding qualifies by pipe diameter and wall thickness, while structural welding qualifies by plate thickness. Pipeline procedures often use E6010 cellulosic electrodes for root passes, which are not prequalified under D1.1.

What is a pipeline welding coupon test?

A pipeline welding coupon test under API 1104 Section 6 requires the welder to produce a complete circumferential butt weld on a pipe specimen using the qualified welding procedure. The completed test weld is then examined by radiography or destructive testing to verify the welder can produce acceptable quality. Destructive tests include nick-break specimens and root/face bend specimens cut from the test weld. The test pipe diameter and position must match or exceed the intended production work per Section 6.2.1 qualification ranges.

Can pipeline welders weld steel structures?

An API 1104 pipeline welder qualification does not automatically qualify the welder for steel structure welding under AWS D1.1, and vice versa. The two standards have independent qualification systems with different essential variables, test requirements, and acceptance criteria. A pipeline welder seeking to perform structural work must qualify separately under D1.1 (or the applicable structural code). In practice, many pipeline welders also hold structural qualifications, but each must be obtained and maintained independently. The welding processes and techniques overlap, but the qualification records are separate.