Many fabrication shops don't do just one type of work. A shop qualified for structural steel fabrication under AWS D1.1 takes on a piping skid project that falls under ASME B31.3. The WPS library, the PQRs, the welder certifications — can any of them cross over? The answer is almost entirely no, and misunderstanding this distinction causes compliance failures at the worst time: during a third-party inspection or code authority review.
This article maps the critical differences between ASME B31.3 and AWS D1.1 welding requirements for shops navigating both standards.
Code Scope and Authority
AWS D1.1 is a structural welding code — it governs welding of structural steel used in buildings, bridges, and similar load-bearing applications. It is published by the American Welding Society. Project applicability is specified by the design, contract, or authority having jurisdiction; AISC certification programs, structural drawings, and structural steel purchase specifications typically invoke AWS D1.1.
ASME B31.3 is the Process Piping code — it covers piping in chemical plants, petroleum refineries, pharmaceutical facilities, and similar process installations. It is published by ASME (the American Society of Mechanical Engineers). B31.3 delegates welding qualification entirely to ASME Section IX; B31.3 itself covers design, materials, fabrication, testing, and examination requirements, but welding procedure and welder qualification details live in ASME IX.
These are structurally different in one fundamental way: AWS D1.1 is self-contained with its own welding qualification requirements, while ASME B31.3 delegates qualification to a separate document (ASME IX). A shop must work both documents when complying with B31.3.
Rule library based on AWS D1.1:2025; verify against your governing edition.
WPS Qualification: Prequalified vs. All-PQR-Required
This is the sharpest practical difference between the two systems.
AWS D1.1 allows prequalified WPS procedures under Clause 5. If a WPS uses only prequalified base metals from Table 5.3, a recognized welding process (SMAW, SAW, GMAW, FCAW, GTAW), joint geometry from Annex A, and stays within all the limits specified in Clause 5, no PQR test weld is required. The WPS is written, signed by a responsible engineer or CWI, and is immediately usable. This path is widely used in structural fabrication because it eliminates PQR cost for common joints and common materials.
ASME B31.3 with ASME IX has no equivalent. Every welding procedure used on B31.3 work must be supported by a PQR — a Procedure Qualification Record in which a test weld was deposited and mechanical test specimens were extracted, tested, and documented. ASME IX does allow the use of Standard Welding Procedure Specifications (SWPSs) under AWS B2.1 if the owner accepts them, but these are pre-tested procedures published by AWS, not a "no-test" route. Without owner acceptance of SWPSs, every procedure needs its own PQR.
For shops coming from structural work, the absence of a prequalified WPS path in the piping world is the single biggest cost and schedule impact when entering B31.3 work. Budget for PQR testing as part of piping project mobilization.
See also ASME Section IX standard welding procedure specifications for the SWPS option under ASME IX.
Essential Variables and Requalification Triggers
Both systems use the concept of essential variables — parameters that, when changed, require a new PQR. But the specific essential variable lists differ between D1.1 Table 6.6 and ASME IX QW-250 series tables.
AWS D1.1:2025 Table 6.6 lists essential variables for each process (SMAW, SAW, GMAW/FCAW, GTAW) covering base metal group changes, filler metal classification changes, position changes, preheat and interpass temperature changes, PWHT changes, shielding gas composition changes, and other process-specific parameters. The table structure was renumbered from the 2020 edition — Table 6.6 in 2025 was Table 6.5 in 2020.
ASME IX QW-250 tables list essential variables, supplementary essential variables (required when impact testing applies), and nonessential variables for each process. The essential variable categories cover similar concepts but are organized by process in QW-252 through QW-290 and include some parameters that D1.1 treats differently — for example, base metal grouping under ASME IX uses P-numbers (QW-422) rather than D1.1 Table 6.9 base metal groups.
ASME IX P-Numbers and F-Numbers explains the P-number base metal grouping system that governs requalification under ASME IX and B31.3.
A change that triggers requalification under one standard may or may not trigger it under the other. Shops maintaining procedures under both systems cannot assume that a parameter change affecting one set of WPS records leaves the other set unaffected. Each standard must be evaluated independently when process or material parameters change.
Welder Qualification: Separate Systems, No Crossover
AWS D1.1 welder qualification is governed by Clause 6 of the standard. Qualification is by process, position, and base metal type, and it is demonstrated by welding a test plate or pipe coupon and passing visual, bend, and/or tensile tests as specified. Qualification remains valid as long as the welder has used the process within the continuity period required by the standard.
ASME IX welder qualification is governed by QW-300 series requirements. Qualification is by process, position, base metal P-number, and filler metal F-number, and it is demonstrated by a performance qualification test weld with mechanical test requirements per QW-302. Qualification continuity is governed by QW-322, which requires that the welder have used the process within six months to maintain qualification — similar in concept to the AWS D1.1 rule but with different specific provisions. See ASME Section IX welder qualification: QW-322 explained for a detailed comparison.
The qualifications are not transferable in either direction. An ASME IX-qualified welder is not automatically qualified under AWS D1.1 and vice versa. Shops doing both types of work must qualify welders under both systems if those welders will perform both structural and piping welds. This means separate test records, separate continuity tracking, and often separate test welds.
Practically, many shops run both D1.1 and ASME IX qualification tests on the same day for the same welder, using test welds that satisfy both standards — reducing duplicate cost while maintaining separate records. Coordinate the test specimen design and position requirements between both standards before scheduling to make this work.
Inspection and NDE Requirements
AWS D1.1 specifies inspection hold points, visual inspection requirements for all welds, and volumetric NDE requirements for certain CJP groove weld categories. The specific inspection program for a project is defined by the applicable category designations on the structural drawings and the contract document's QC/QA specification. A qualified CWI typically performs or leads inspection. NDE method selection under AWS D1.1 covers the method-specific requirements.
ASME B31.3 structures its examination requirements by fluid service category:
- Normal Fluid Service (the most common): visual inspection on all welds, plus random examination — typically 5% of butt welds by RT or UT using a random examination program defined in the code
- Category D Fluid Service (low-hazard): visual inspection only; no volumetric examination unless specified
- Severe Cyclic Service: 100% radiography or UT of butt welds and certain branch connections
- Category M Fluid Service (toxic materials): 100% examination requirements similar to Severe Cyclic
The examination percentages in B31.3 Normal Fluid Service are lower than inspectors from structural backgrounds sometimes expect. The acceptance criteria for examinations also differ — B31.3 references ASME standards for RT and UT acceptance, while D1.1 has its own acceptance tables.
Record Retention and Documentation
Both standards require documentation of WPS, PQR, and welder qualification records. The specific record content requirements differ because the qualification variables differ.
For shops maintaining both systems, the biggest documentation risk is commingling records. A PQR run for an AWS D1.1 structural procedure cannot be cited to support a B31.3 piping WPS, and vice versa. WPS documentation should clearly identify the applicable code on the face of the document to prevent misuse. WPS and PQR record retention requirements covers retention periods and the document control practices that keep records auditable.
Planning for Mixed-Code Work
If your shop currently holds only AWS D1.1 qualifications and is entering B31.3 piping work, the minimum startup work includes:
- Develop and qualify new WPS procedures under ASME IX — plan for PQR testing on each process-position-base-metal combination the project requires
- Qualify welders under ASME IX QW-300 — separate from existing D1.1 qualification records
- Establish a B31.3-compliant examination program — including the random examination percentage and records for Normal Fluid Service, or the 100% program if higher fluid service categories apply
- Train CWIs or inspection personnel on the applicable ASME B31.3 and ASME IX requirements — AWS CWI scope covers AWS standards; ASME work may require AWS SCWI or ASNT-level NDE personnel depending on the examination method
This startup work takes weeks, not days. Projects that discover the qualification gap after mobilization face delays and potential stop-work orders from code authorities.
WPS responsibility: fabricator, contractor, and engineer of record roles discusses how these qualification responsibilities are allocated between parties on complex projects.
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