Does ASME B31.1 require ASME IX procedure qualification?

Yes. B31.1 adopts ASME Section IX as the required basis for WPS and PQR qualification. Welders and welding operators must also be qualified to ASME IX. B31.1 then adds specific service requirements on top — most notably PWHT and radiography thresholds that differ from B31.3.

What is the difference between B31.1 and B31.3 for welding?

Both codes reference ASME IX for WPS/PQR qualification, but the service conditions differ. B31.1 governs power piping (steam, high-temperature high-pressure service in power plants). B31.3 governs process piping (refineries, chemical plants). PWHT obligations and radiographic examination thresholds are generally more stringent under B31.1 for comparable materials and thicknesses.

Does a WPS qualified under B31.3 automatically work for B31.1?

Not without review. The underlying ASME IX qualification may carry over, but you must verify that your PQR test conditions satisfy B31.1's specific PWHT and examination requirements for the service class involved. A B31.3 PQR may be missing impact testing that B31.1 requires for low-temperature service.

What fab shops need to worry about B31.1?

Any shop fabricating steam-service piping, boiler-external piping, turbine inlet lines, feedwater piping, or process lines connected to power boilers. If the client's specification calls out ASME B31.1, it governs — regardless of what other codes the shop normally works to.

ASME B31.1 Power Piping WPS Requirements Explained

How ASME B31.1 power piping governs welding procedure specifications, when it applies versus B31.3, PWHT differences, and what fab shops need to qualify.

Most structural fab shops live in the AWS D1.1 world. But shops that cross into power plant construction, fossil-fuel generating stations, cogeneration facilities, or industrial boiler systems will eventually encounter ASME B31.1 — the Power Piping Code. Understanding how B31.1 governs welding procedure specifications and where it diverges from B31.3 process piping saves significant requalification cost and schedule grief.

What ASME B31.1 Covers

B31.1 applies to piping systems that fall under the definition of "power piping" — broadly, piping used in electric power generation, industrial plants, geothermal heating, and central and district heating systems. The specific scope includes steam lines, high-pressure hot-water lines, boiler external piping (beyond the boiler proper), turbine inlet and extraction lines, and feedwater piping.

If the piping is internal to a boiler — the pressure vessel itself — ASME Section I governs. If you're fabricating petrochemical process piping in a refinery, B31.3 governs. B31.1 occupies the space between: it captures the piping that connects power-generating or heat-generating equipment, where elevated temperature, cyclic thermal stress, and system criticality demand a higher level of control.

How B31.1 Governs WPS Qualification

B31.1 adopts ASME Section IX as the mandatory basis for welding procedure and performance qualification. Every WPS used on B31.1 scope piping must be supported by a qualifying PQR tested and documented per ASME IX requirements.

This means P-Numbers, F-Numbers, and A-Numbers from ASME IX apply. The P1 group (carbon steel) is the most common in power piping. P4 and P5 chromium-molybdenum alloy steels (Cr-Mo grades such as P91, P22) appear frequently in high-temperature steam service. Filler metal selection follows ASME IX F-Number and A-Number matching, not the AWS A5-series filler classification system that D1.1 shops use.

One practical implication: a shop that has always worked to AWS D1.1 with E7018 or ER70S-6 filler must develop or acquire ASME IX-qualified WPS documents using ASME P-Number and F-Number language when transitioning to B31.1 work. The two qualification systems are parallel, not interchangeable in documentation form.

For guidance on ASME IX P-Numbers and F-Numbers, see ASME IX P-Numbers and F-Numbers explained.

PWHT Requirements Under B31.1

Post-weld heat treatment is one of the areas where B31.1 and B31.3 diverge most visibly. B31.1 mandates PWHT for carbon steel (P1) welds above specific wall thicknesses, with the threshold lower than what B31.3 permits in many service classifications.

For standard carbon steel piping in steam service, B31.1 requires PWHT when nominal wall thickness exceeds approximately 3/4 inch [19 mm]. The soak temperature range for P1 material is typically 1100–1200°F [595–650°C], held for one hour per inch of thickness with a one-hour minimum. These are general values — always verify against the current edition of B31.1 and your engineering specification, which may impose tighter limits.

For chromium-molybdenum alloy steels (P4, P5B, P91), PWHT is mandatory regardless of thickness. The soak temperature and hold time requirements escalate significantly, and cooling rates must be controlled. P91 (9% Cr, 1% Mo with vanadium) demands particularly disciplined PWHT control — soak temperature, hold time, and especially the cooling rate through the martensitic transformation range all affect the final creep strength and notch toughness of the weld deposit.

Your WPS must document the PWHT cycle in detail: heating rate above a specified temperature threshold, soak temperature range, hold time, and maximum cooling rate. A WPS that shows only "PWHT: 1150°F, 1 hour" is insufficient for B31.1 work — the heating rate and cooling rate are essential variables that affect final mechanical properties.

For a comparison of PWHT documentation requirements under ASME IX, see ASME IX QW-407 PWHT essential variables.

Impact Testing and Low-Temperature Service

B31.1 requires Charpy V-notch impact testing for base metals and weld deposits intended for low-temperature service, using thresholds defined in the code. If the piping will operate below a specified minimum temperature (which varies by material and thickness), your PQR test coupon must include CVN specimens tested at the design minimum temperature.

A WPS qualified for ambient to high-temperature steam service will not automatically satisfy B31.1 requirements for cold-service lines (cryogenic liquids, refrigerant service) without a separate low-temperature PQR. This is a common source of scope creep when a power plant project includes LNG or compressed-gas systems alongside steam lines — different WPS qualification lineages may be required for the same shop.

Radiographic and Ultrasonic Examination

B31.1 specifies radiographic (RT) and ultrasonic (UT) examination requirements based on service conditions, weld category, and wall thickness. For boiler external piping and steam lines above certain pressure and temperature thresholds, B31.1 typically requires 100% RT on butt welds.

The acceptance criteria for RT and UT under B31.1 follow the code's own tables — not AWS D1.1 Table 9.25 (structural) or ASME VIII (pressure vessels). The NDE method, acceptance standard, and the qualification level of the examiner all must be documented in your inspection and test plan.

If your shop's NDE documentation templates reference AWS D1.1 criteria or ASME VIII criteria, they will need to be revised for B31.1 work. This is worth catching early — swapping acceptance criteria on an NDE report after the fact is an audit red flag.

Material Traceability and Certifications

B31.1 requires complete material traceability from mill certificate through the finished weld. Base metal must be verified against the code's listed materials; unlisted base metals require engineering approval. Mill Test Reports (MTRs) must accompany piping materials and be reviewed against the applicable ASTM specification before welding begins.

For piping welds, heat traceability of filler metals is also required in many B31.1 specifications — the heat (lot) number of electrodes or wire used on each weld must be recorded and retained. This is a level of consumable traceability that AWS D1.1 structural shops often don't track, and it requires a change to your consumable issuing and record-keeping procedures. See filler metal lot control under AWS D1.1 for a comparison of approaches.

What to Audit Before a B31.1 Project

Before accepting B31.1 scope work, a fab shop's QC manager should verify:

WPS/PQR documents are formatted using ASME IX (QW-482/QW-483 forms), not AWS Annex M or a structural shop template. ASME IX essential variables govern.
PWHT records exist and document heating rate, soak temperature, hold time, and cooling rate — not just temperature and time.
Filler metal certs show F-Number and A-Number classification, and heat traceability is built into the consumable issue process.
NDE procedures reference B31.1 acceptance criteria, not D1.1 or ASME VIII.
Welder performance qualifications are valid under ASME IX, not just AWS D1.1. A welder qualified to D1.1 Clause 4 (structural) is not automatically qualified for B31.1 work.
Impact test records exist on PQRs if the project includes low-temperature service lines.

Starting a B31.1 project with D1.1 WPS documentation is a quality system mismatch that will surface during the owner's inspector review — typically at the worst possible time. Getting qualification documents right before the first arc is struck is far cheaper than a mid-project requalification.

If your shop is managing WPS documents across multiple codes — D1.1, ASME IX, and now B31.1 — a centralized WPS library with code-specific filtering is worth investing in. See welding procedure library audit readiness for how leading fab shops organize multi-code procedure libraries, or explore our WPS management software for tooling built around this problem.

Rule library based on AWS D1.1:2025; verify against your governing edition. For ASME B31.1 requirements, consult the current edition of the ASME B31.1 Power Piping Code and ASME Section IX applicable to your project contract.