One of the most frequent QC failures in structural fab shops is using a WPS outside its qualified range without recognizing that a requalification has been triggered. The welder doesn't flag it, the foreman doesn't know to check, and the CWI only catches it during a post-production audit — or doesn't catch it at all until a third-party review surfaces the nonconformance.

This article is a working checklist of essential variable changes under AWS D1.1:2025 that require WPS requalification. Use it when reviewing WPS packages before a project, when a welder requests a process or parameter change, and during internal pre-audit checks.

How Essential Variables Work

AWS D1.1:2025 defines two tiers of variables on a WPS:

Essential variables (Table 6.6): Changes beyond qualified limits require a new PQR qualification test. The existing WPS cannot be revised to cover the change — you must test, document, and issue a new or revised WPS supported by the new PQR.

Nonessential variables (unlisted): Can be changed without requalification, but should still be documented in a WPS revision. Examples include pass count, cleaning method between passes, and electrode diameter within the same F-number class.

Supplementary essential variables (Table 6.8): Apply only when CVN Charpy impact toughness is required by the contract or project specification. These trigger requalification only for CVN-required procedures.

Understanding this tier structure prevents two common mistakes: over-requalifying (spending money on PQR tests for nonessential changes) and under-requalifying (missing real essential variable changes).

Requalification Trigger Checklist — Table 6.6 Variables

Work through each category when reviewing a proposed production change against the current WPS and supporting PQR.

Process and Transfer Mode

  • Change in welding process (SMAW → FCAW, GMAW → SAW, etc.) — always triggers requalification. A PQR supports only the process used during testing.
  • Change in GMAW transfer mode (spray to short-circuit, or pulse to spray) — short-circuit and spray are treated as separate processes for qualification purposes. This catches shops running spray-qualified WPS in joints where short-circuit is easier to control.

Base Metal

  • Change in base metal group beyond the qualified range — AWS D1.1:2025 Table 6.6 row 3. Group I to Group II coverage typically requires requalification if the original PQR was tested on Group I only. Consult the base metal group table (AWS D1.1:2025 Table 5.3 or equivalent) for your materials.
  • Change in minimum base metal thickness below the qualified range — a PQR qualified on 3/8 in [10 mm] plate covers thinner plate only to 1/8 in [3 mm] minimum (half the test thickness, with limits). Going below that threshold requires retesting on thinner material.
  • Change in maximum base metal thickness above the qualified range — typically 2T (twice the test thickness) is the max qualified range. If your new joint is 1 in [25 mm] plate and the PQR test was done on 3/8 in [10 mm], you may be outside coverage.

Filler Metal

  • Change in filler metal F-number — AWS D1.1:2025 Table 6.6, row 5. E7018 (F-4) is not interchangeable with E6013 (F-3) without requalification. The F-number grouping governs which electrodes are considered equivalent.
  • Change in filler metal A-number (weld metal chemistry) — affects mechanical properties and is essential for tensile- or CVN-qualified procedures.
  • Change in filler metal classification dropping or adding a designator that affects usability characteristics — the 2025 edition added a specific rule on –G designators (Table 6.6, row 8): a filler metal with the –G suffix (properties guaranteed by agreement) requires its own qualification if the original PQR used a fully classified electrode. This is a 2025 change from prior editions.
  • Change in electrode-to-supplemental-filler ratio beyond ±10% (GTAW hot wire, SAW with supplemental filler) — Table 6.6, row 7 in the 2025 edition specifies ±10% as the threshold.
  • Addition or deletion of supplemental filler metals — using a supplemental filler in production when none was used in the PQR, or vice versa, requires requalification.

Electrical Parameters

  • Change in current type or polarity (AC to DC, DC+ to DC–) — listed as essential (Table 6.6, row 9). Process behavior differs significantly; a DC+ qualified PQR does not cover DC– production welding.
  • Change in single vs. multiple electrode configuration for SAW — adding a second wire to a single-wire SAW PQR triggers requalification.

Position

  • Change to a position not covered by qualification — critical for field welding where the same WPS used in the shop (horizontal) gets applied overhead. AWS D1.1:2025 Table 6.6 row 15 and the position coverage table in Clause 6.

Preheat and Interpass Temperature

  • Decrease in minimum preheat temperature below the PQR minimum — Table 6.6, row 25. Common scenario: shop preheat was at 200°F [93°C] during PQR in winter; summer production crew reduces preheat because "the steel is warm." That's a requalification trigger if it drops below the PQR minimum.
  • Increase in maximum interpass temperature above PQR maximum is a supplementary essential variable for CVN procedures (Table 6.8) — see the next section. For standard non-CVN procedures, interpass temperature increase is generally not an essential variable, but many shop WPS documents set interpass limits based on engineering judgment; violating those limits is a procedure violation even if not strictly a requalification trigger.

PWHT

  • Addition or deletion of post-weld heat treatment — Table 6.6, row 26. A WPS qualified without PWHT cannot be used with PWHT (or vice versa) without requalification. This catches situations where a project spec adds a stress-relief requirement that wasn't part of the original PQR.
  • Change in PWHT temperature or holding time — any change to the PWHT parameters used during PQR qualification triggers requalification.

Groove Joint Design

  • Change from CJP to PJP or adding joint backing — Table 6.6, row 22. A CJP qualification does cover PJP in most cases, but adding or removing backing changes the root condition and requires review.
  • Change in groove type (V-groove to U-groove, bevel to J) beyond what the PQR geometry supports.

Rule library based on AWS D1.1:2025; verify against your governing edition.

Requalification Trigger Checklist — Table 6.8 (CVN Procedures Only)

These apply only when CVN Charpy impact testing is required. Know before the project starts whether CVN is required — it's typically called out in the project specification or the contract documents. AWS D1.8 (Seismic Supplement) and AWS D1.5 (Bridge Welding Code) are common sources of CVN requirements for structural work.

  • Increase in heat input above the maximum heat input used in the PQR test — Table 6.8, row 1. A welder who slows down or increases amperage on a CVN joint can exceed this limit. See our article on arc energy and heat input calculation under AWS D1.1 for the formula and monitoring approach.
  • Increase in maximum interpass temperature above PQR maximum — Table 6.8, row 8 (2025 edition; note that the 2025 revision removed preheat from Table 6.8 scope — only interpass maximum increase triggers requalification now).
  • Change in filler metal classification (CVN-specific F-number/A-number changes) — impacting the deposit toughness properties.
  • Base metal thickness below 1/2 in [12 mm] if not qualified on thinner material — Table 6.8, row 2(a) in the 2025 edition sets the floor at 1/2 in [12 mm] (previously 5/8 in [16 mm] in the 2020 edition), meaning CVN requirements now apply to a wider range of thicknesses.

Common Scenarios That Get Shops in Trouble

Scenario 1: Electrode substitution without checking F-number. A foreman switches from E71T-1C to E71T-9C-H4 because the supplier was out of stock. Both are flux-cored, both are common, but they have different classifications. If the WPS and PQR were qualified on E71T-1C and the F-number grouping doesn't cover E71T-9C, that's an essential variable change. Check F-numbers before approving any electrode substitution.

Scenario 2: GMAW short-circuit in a spray-qualified procedure. The WPS says GMAW, qualified with spray transfer at 250A, 28V. A welder in a tight joint uses short-circuit transfer (low amperage, dip contact). Spray and short-circuit are considered different processes for qualification. The welder's setup is outside the WPS coverage.

Scenario 3: Cold morning preheat shortfall. The PQR was run at 150°F preheat. The winter morning crew is rushed, the part reads 100°F on the contact thermometer before they start. If the WPS minimum is 150°F and they weld at 100°F, that's a requalification trigger — and a hydrogen cracking risk on the same pass.

Scenario 4: Adding PWHT to a project. The original contract had no PWHT. An engineer adds a stress-relief requirement mid-project. Every WPS must now be re-evaluated — the ones qualified without PWHT need new PQRs with PWHT, which takes time and money to run. Address PWHT requirements at contract review, not mid-project.

How to Manage This in Practice

The most reliable approach is systematic: before a project kicks off, your QC manager should review each WPS against the project's base metals, filler metals, positions, and any special requirements (CVN, PWHT). Run the checklist above for each WPS in the package.

When a change is proposed during production, the change goes through the same review. If it's a nonessential variable, revise the WPS and re-issue. If it's essential, either use a different WPS that covers the new condition or run a PQR.

Software that links WPS to PQR records and flags when production parameters drift outside qualified ranges makes this systematic rather than dependent on individual memory. See WPS and PQR qualification management software for how a purpose-built tool handles this.

For additional reading: when a PQR requires requalification under AWS D1.1, multiple WPS from a single PQR, and essential variables vs nonessential variables explained.