AWS D1.1 prequalified WPS: rules, limits and common mistakes

AWS D1.1, the Structural Welding Code for steel, offers two routes to a welding procedure specification: a prequalified WPS, which you can use without a test coupon, or a WPS qualified by testing and supported by a PQR. Prequalification saves coupons, lab work and weeks of lead time. The price is that every condition of the code must be met: process, base metal, filler metal, joint detail, preheat and welding parameters.

For fabricators outside the US working for American clients, offshore operators or international EPC contractors, this is often the first stumbling block. A WPS that looks prequalified but deviates on a single point is not prequalified. Below we set out the limits and the mistakes we see most. For a wider comparison, see AWS D1.1 versus the EN standards.

Prequalified or qualified by testing

A prequalified WPS is exempt from procedure qualification testing. The code accepts that the defined combinations of process, material, joint and parameters produce sound welds, based on long experience. Exempt from testing does not mean exempt from paperwork: the manufacturer or contractor writes the WPS and makes it available to welders, inspectors and the Engineer.

If any variable falls outside the conditions, the WPS must be qualified by test: weld a coupon, have it tested and record the actual values and results in a PQR. Either way, welders must be qualified separately. Prequalification covers the procedure, never the person.

Which processes can be prequalified?

• SMAW, shielded metal arc (stick) welding.
• SAW, submerged arc welding.
• GMAW, except short-circuit transfer (GMAW-S).
• FCAW, gas-shielded or self-shielded.

GTAW (TIG), ESW, EGW and GMAW-S are code-approved but require a WPS qualified by testing. GMAW-S is often underestimated: at low current and voltage, GMAW slips into short-circuit transfer, even when the WPS states spray or globular transfer.

Base metals and filler metals

The code lists prequalified base metals in strength groups, with familiar grades such as ASTM A36, A572 Grade 50 and A992. Each group has matching filler metals classified to the AWS A5 specifications. Minimum preheat and interpass temperatures follow from a table based on material category and the thickness of the thickest part in the joint.

This is where fabricators working with European steel often go wrong. EN 10025 grades such as S355J2 are not on the list, so a WPS on S355 is not prequalified, however similar the properties. The same applies to consumables classified only to ISO 2560 or ISO 14341. Many European wires and electrodes carry dual classification; check that the AWS classification appears on the certificate.

Joint details and tolerances

Prequalified joints appear as details in the code: complete joint penetration (CJP) and partial joint penetration (PJP) groove welds, fillet welds, and plug and slot welds. Each detail fixes thickness, groove angle, root opening, root face, positions and permitted processes, with tolerances for both the drawing and the shop fit-up.

A joint that is correct on paper but fitted with an oversized root opening or undersized groove angle falls outside prequalification. Watch the back-gouging requirements for double-sided CJP welds and the rules for steel backing. Tubular T-, Y- and K-connections have separate details with their own limits.

Parameters and bead sequence

Within a prequalified combination, the code still limits execution: maximum electrode diameter per position, maximum SAW current, maximum root and fill pass thickness and maximum single-pass fillet size. For GMAW and FCAW, the shielding gas must match the filler metal classification. State real ranges for current, voltage, wire feed speed and travel speed, in line with the consumable manufacturer's data. A WPS that merely refers to the code is useless to the welder and cannot be checked by the inspector.

When you need a PQR after all

• The base metal is not listed, as with EN steels.
• The process is GTAW, GMAW-S, ESW or EGW.
• The joint detail or fit-up falls outside tolerance.
• Parameters, layer thickness or shielding gas fall outside the limits.
• The contract documents require CVN toughness values to be demonstrated by testing.

After visual inspection, the coupon is tested as the code requires, for example tensile tests, bend tests, macroetch and CVN tests where specified. Actual values then set the WPS range through the essential variables. See our article on the procedure qualification record (PQR).

Common AWS D1.1 WPS mistakes

• No written WPS, on the assumption that prequalified means nothing needs recording.
• European steel or ISO-only consumables in a WPS presented as prequalified.
• GMAW running in short-circuit, especially on thinner plate and out of position.
• Fit-up outside tolerance, discovered after the joint is welded.
• Preheat based on the thinner plate instead of the thicker one.
• Unqualified welders, because the WPS needed no coupon.
• Wrong edition: clause numbering has moved between editions, so reference the edition in the contract.

Reviewing WPSs against the code before production starts prevents rejection at the first inspection; it is a standard step in WPS and WPQR qualification.