6.1 Welding Procedure Specification (WPS)

What a WPS Is

A Welding Procedure Specification (WPS) is a formal, written document that provides direction to the welder or welding operator for making production welds in accordance with code requirements. AWS A3.0 defines it as the document that lists all the welding variables — both essential and nonessential — for a specific application. Think of it as the verified "recipe" for a weld: it tells exactly which process, base metal, filler metal, joint design, position, electrical parameters, preheat, and technique produce a sound, code-compliant weld every time, regardless of which qualified welder makes it.

The WPS exists so that welding is repeatable and traceable. Without it, two welders could weld the same joint with wildly different heat inputs, deposition rates, and bead profiles, yielding inconsistent mechanical properties. The WPS removes that variability by locking the controlling variables to ranges proven to work.

What the WPS Specifies

A complete WPS addresses every variable that affects weld quality. The table below groups the typical contents.

Two Routes to a Valid WPS

Under AWS D1.1 (Structural Welding Code — Steel) a WPS becomes valid by one of two routes:

1. Prequalified WPS — written to the conservative limits of Clause 3 (Prequalification). Because the process, base metal, filler metal, joint geometry, and preheat are all within proven prequalified limits, the code grants the WPS validity without any destructive testing — no PQR is needed.
2. Qualified-by-test WPS — any WPS that falls outside even one prequalification limit. It must be supported by a Procedure Qualification Record (PQR) generated by welding a test coupon and passing the required mechanical tests under Clause 6 (Qualification).

Note that other codes do not offer prequalification: ASME Section IX and API 1104 require every WPS to be supported by a PQR. The prequalified concept is essentially unique to the AWS D1 family.

Prequalification Limits (Clause 3)

For a WPS to ride on prequalification, every limit in Clause 3 must be met — missing one limit forces qualification by test. The headline limits are:

• Processes: only SMAW, SAW, GMAW (spray/globular/pulsed), and FCAW are prequalified. GMAW-S (short-circuit) is excluded because its low heat input risks incomplete fusion.
• Base metals: must appear in the approved-base-metal table (e.g., A36, A572 Gr. 50, A992) and be welded with a matching filler from the matching-filler table.
• Joint geometry: must conform exactly to a prequalified joint detail (CJP joints, or PJP joints per the prequalified figures) — including groove angle, root opening, and root face tolerances.
• Preheat/interpass: must meet the minimum preheat table, which scales with thickness, carbon equivalent (steel category), and hydrogen level of the electrode.
• Other limits: maximum single-pass fillet and root-pass sizes, and electrode/flux conditions.

Miss any one — say a groove angle 5° outside the figure, or an unlisted base metal — and the WPS is no longer prequalified and needs a PQR.

The CWI's Role with the WPS

The CWI does not write the WPS — that is the contractor's or engineer's responsibility. The CWI reviews and verifies it. On the job the inspector confirms that: (a) a WPS exists for the joint being welded; (b) it is either properly prequalified or backed by a supporting PQR; (c) the production variables (amps, volts, preheat, position, filler) being used in the field actually fall within the ranges on the WPS; and (d) the WPS revision in use is current. A field amperage of 250 A read on a WPS limited to 120–200 A is a documented nonconformance even if the weld looks acceptable.

The CWI commonly performs this verification at the start of a shift and during periodic in-process checks, recording observed amps, volts, gas flow, preheat, and electrode size against the WPS.

A practical inspection sequence for WPS compliance: (1) locate the governing WPS for the joint; (2) confirm it is prequalified or PQR-supported; (3) read the essential variables off the WPS; (4) compare them to the actual material certs, electrode certs, and metered field values; (5) confirm the welder's WPQ covers the WPS; and (6) flag any deviation as a nonconformance for engineering disposition. Note the CWI cannot "approve" an out-of-range condition — only the responsible engineer can disposition it via revised documentation or a new qualification.

Exam trap: The WPS lists variables as ranges (e.g., 90–150 A); the supporting PQR lists the actual single values used during the test. Do not confuse the two. Also remember GMAW short-circuit transfer (GMAW-S) is NOT prequalified — any GMAW-S WPS must be qualified by test.