Does ASME B31.8 require WPS qualification by API 1104 or can we use ASME IX?

Both are permitted under ASME B31.8. API 1104 is the industry standard for field pipeline girth welds because it was written specifically for field welding conditions. ASME Section IX is commonly used for fabricated piping spools, facility piping, and compressor station piping where shop welding is practical.

What makes direction of welding an essential variable in API 1104 pipeline WPS?

API 1104 classifies uphill (6G→12G) and downhill (12G→6G) progression as separate essential variables because each produces a distinctly different heat input, cooling rate, and weld microstructure—particularly in the root pass. Changing direction requires a completely new WPS qualification by test.

Can a structural AWS D1.1 WPS be used for B31.8 pipeline work?

No. AWS D1.1 governs structural steel connections and has no jurisdiction over pressure piping. A B31.8 pipeline girth weld WPS must be qualified per API 1104 or ASME IX regardless of how similar the base metal and filler metal look.

What is a nick-break test and when does pipeline welding require it?

A nick-break test involves notching across a weld coupon and breaking it open to expose the full weld cross section. This allows direct visual evaluation of fusion, penetration, porosity, and slag inclusions. API 1104 requires nick-break specimens as part of both procedure qualification and welder performance qualification.

ASME B31.8 Gas Pipeline WPS and PQR Requirements

ASME B31.8 gas transmission pipelines use API 1104 or ASME IX for WPS qualification. Learn how essential variables, test requirements, and welder qualification differ from AWS D1.1 structural practice.

When a fabricator with a solid AWS D1.1 WPS library takes on a natural gas transmission pipeline project for the first time, the qualification system looks similar on the surface—procedure qualification record, essential variables, mechanical tests—but the underlying code framework is different enough that every WPS and welder qualification in the shop's structural program is unusable. Understanding where ASME B31.8 draws from API 1104, and why API 1104 treats pipeline girth welding as a fundamentally different discipline, saves both project delay and requalification cost.

ASME B31.8 Scope and the Welding Code Reference

ASME B31.8 governs pressure piping for natural gas and other gas transmission and distribution systems. It covers pipelines operating above 15 psig from gas production and gathering to the customer meter. The code does not itself contain a detailed welding qualification procedure; instead, its welding section directs users to an external qualification standard.

ASME B31.8 accepts two qualification paths:

API 1104, Welding of Pipelines and Related Facilities — the dominant choice for field girth welds on transmission pipelines
ASME Section IX, Welding, Brazing, and Fusing Qualifications — more common for facility piping, compressor station piping, and prefabricated piping spools

Most transmission pipeline operators specify API 1104 for girth welds. The reason is practical: API 1104 was written around the conditions of field pipeline construction—welding in a ditch, fixed-position pipe, variable weather, and crews working in production progressions. ASME IX was designed around the shop environment of pressure vessel and process piping fabrication.

Why API 1104 Is Different from AWS D1.1 and ASME IX

A structural fabricator used to AWS D1.1 will notice several fundamental differences immediately.

No prequalified WPS. Every girth weld procedure must be qualified by test under API 1104. There is no prequalified WPS path analogous to AWS D1.1 Clause 5. If you do not have a tested PQR supporting the WPS, you cannot weld.

Direction of welding is an essential variable. This is perhaps the biggest surprise. In structural welding, vertical progression (uphill vs. downhill) affects pass sequence and bead shape, but switching direction does not by itself invalidate a WPS. Under API 1104, uphill and downhill progression are separate essential variables. A downhill WPS (the traditional cellulosic E6010 "stovepipe" method) cannot be used for uphill welding, and vice versa. The microstructure and hydrogen management of the root pass differ enough that the code treats them as different procedures.

Pipe OD and wall thickness define qualification range. Unlike AWS D1.1, which uses base metal group and test plate thickness, API 1104 qualifies a WPS within ranges defined by the pipe outside diameter and wall thickness of the test pipe. Each combination of OD range and wall thickness range must be covered by a tested PQR.

Nick-break testing. AWS D1.1 PQR testing uses tensile specimens and guided-bend specimens. API 1104 adds nick-break specimens—strips cut from the weld, notched transversely at the weld centerline, and broken open to expose the cross section. The examiner looks at fusion, penetration depth, slag inclusions, and porosity. No API 1104-qualified procedure is complete without passing nick-break results documented on the PQR.

Essential Variables Under API 1104

API 1104 Section 5 defines the essential variables that, when changed beyond specified limits, require a new procedure qualification. The key groups are:

Process and equipment: Welding process (SMAW, GMAW, FCAW, GTAW, SAW), power source type (AC vs. DC), and electrode polarity. Adding a process to a single-process WPS is an essential variable.

Base material: The pipe material group (API 1104 uses a group system based on specified minimum yield strength—Group I covers yield strengths up to 42 ksi, Group II up to 52 ksi, and so on through higher-strength grades). Welding a higher-strength group generally requires requalification.

Filler metal: The AWS filler metal classification. Changing from E6010 to E7010 on the root pass, or from E8010 to E9010, requires requalification. The high-cellulosic E6010/E7010 series is the traditional choice for downhill mainline welding; low-hydrogen E7018 and GMAW processes are common for uphill and for fill and cap passes.

Joint design: The groove geometry—included angle, root opening, and root face dimensions. Changes outside the tested range require requalification.

Direction of welding: Uphill versus downhill, as discussed above.

Position: Fixed position (5G equivalent, pipe horizontal) versus rolled position (1G equivalent). Most transmission girth welds are in fixed position; rolled welding at a fabrication facility has a separate qualification range.

Preheat and interpass temperature: Minimum preheat and maximum interpass temperature are essential variables. For high-strength pipe grades (X65, X70, X80), adequate preheat to control hydrogen-assisted cracking is critical. The carbon equivalent of modern high-strength line pipe steels and the cellulosic electrodes' inherent hydrogen contribution make preheat non-negotiable on thick-wall pipe.

Shielding gas: For GMAW and FCAW girth welding (increasingly common with internal lineup clamps and semi-automatic equipment), the shielding gas composition is an essential variable.

Mechanical Test Requirements for API 1104 PQR

A procedure qualification test weld under API 1104 requires the following minimum test specimens:

Tensile specimens (nick-break type or reduced-section): Evaluate tensile strength of the weld. The weld must not fracture in the weld metal at a value below the specified minimum tensile strength of the pipe base material.
Nick-break specimens: Evaluated visually for complete fusion, adequate penetration, and freedom from unacceptable porosity and slag inclusions.
Guided-bend specimens: Root bend and face bend specimens to evaluate ductility and fusion. Cracks exceeding specified limits are cause for rejection.
Hardness survey (when required by the operator specification or for sour-service pipelines per NACE MR0175/ISO 15156): Controls weld metal and HAZ hardness to prevent sulfide stress cracking.

The test pipe length must be sufficient to provide all required specimen sets. Unlike AWS D1.1, where a single test plate typically yields all specimens for one process and position, a girth weld PQR test pipe must be fully welded around its circumference.

Welder Performance Qualification Under API 1104

Welder qualification follows a similar structure to structural WPQ but with pipeline-specific distinctions.

A welder who qualifies on a fixed-position test in the horizontal position (5G) qualifies for all positions. Qualifying on rolled pipe (1G equivalent) qualifies only for rolled pipe production welding. The 5G test is the standard qualification for field pipeline crews.

Qualification by process: Like AWS D1.1, a welder qualified on SMAW is not automatically qualified on GMAW. Each process requires its own test.

Direction of welding: Downhill qualification covers downhill production welding only. Uphill qualification is separate.

Continuity requirement: API 1104 includes a continuity provision—a welder who has not welded on the specific process in a defined period must requalify. Operators typically specify the continuity period (often six months, mirroring the AWS D1.1 Clause 6.4.1 standard that structural shops know well).

Destructive testing: Welder performance qualification uses the same nick-break and guided-bend specimen requirements as procedure qualification. There is no visual-only welder qualification path.

Location Class and NDE Requirements Under ASME B31.8

One element with no structural welding equivalent is the ASME B31.8 location class system. Pipelines in more densely populated areas are assigned higher location classes (Class 1 through Class 4), and the radiographic testing frequency for girth welds increases with location class. A Class 1 offshore or remote pipeline may require RT on a percentage of girth welds; a Class 3 or Class 4 pipeline in a populated corridor typically requires 100 percent radiographic or AUT inspection of all girth welds.

This means a pipeline contractor's quality plan must tie the inspection frequency directly to the pipeline's location class map, not just a flat inspection rate. WPS documentation packages for B31.8 projects typically include the applicable location class, the NDE method and procedure, and the acceptance criteria standard (API 1104 Section 9 for RT or AUT acceptance).

Practical Implications for Structural Fabricators Adding Pipeline Work

If your fab shop is adding B31.8 pipeline fabrication to your structural welding program, several steps are non-negotiable before the first production weld:

Qualify new WPS procedures under API 1104 — none of your D1.1 PQRs transfer.
Requalify welders on pipeline test pipe — structural WPQ records do not satisfy API 1104 performance qualification requirements.
Review preheat requirements for the specific pipe grade ordered. X65 and higher grades in thicker walls may require preheat levels higher than comparable structural steel thicknesses would suggest.
Establish a continuity tracking program for pipeline welders separately from your structural welder continuity records.
Confirm the operator's NDE specification and procurement plan for radiographic or AUT inspection before bidding a per-joint cost.

For shops already running a compliant welder continuity program for structural work—see our article on AWS D1.1 welder continuity tracking—the administrative discipline transfers directly. The qualification content does not.

Rule library based on AWS D1.1:2025; verify against your governing edition. ASME B31.8 and API 1104 requirements are independent standards — consult the current edition of each for your specific project.

For an overview of how API 1104 procedure qualification compares to AWS D1.1 for structural pipe and tube, see our comparison article on API 1104 vs. AWS D1.1 WPS differences. Ready to manage your pipeline WPS and welder qualification records in a purpose-built system? See our pricing.