Weld Procedure Qualification (WPQ) Thickness Range Verifier Guide

Per ASME BPVC Section IX QW-202.4, the minimum qualified base metal thickness for a given WPQ is the lesser of: (a) the actual thickness of the test coupon, or (b) 5 mm — unless the test coupon thickness is ≥13 mm, in which case the minimum qualified thickness is half the test coupon thickness (but not less than 5 mm). For example, a 12 mm test coupon qualifies down to 5 mm; a 20 mm coupon qualifies down to 10 mm. This rule applies to both groove and fillet welds, but note that QW-202.4(a) explicitly excludes P-No. 10H and P-No. 11 materials, which require separate qualification. Always verify against the latest edition of ASME IX and cross-check with your Procedure Qualification Record (PQR) documentation.

Yes — provided the WPQ’s qualified thickness range explicitly covers 10 mm. Per ASME IX QW-202.4, a WPQ qualified on a 6 mm test coupon establishes a minimum qualified thickness of 5 mm (since 6 mm < 13 mm), but the maximum qualified thickness depends on the test coupon thickness: if the coupon was 6 mm, the maximum qualified thickness is 12 mm (2× coupon thickness, per QW-202.4(b)). So a 6 mm coupon qualifies 5–12 mm — making 10 mm fully acceptable. However, this assumes no other variables (e.g., P-number, F-number, or essential variable changes) invalidate the range. Always confirm via the PQR’s essential variable listing and ensure the WPS reflects the qualified limits.

According to ASME IX QW-202.4(b), the maximum qualified base metal thickness is 2× the test coupon thickness — but only if the coupon thickness is ≤19 mm. For coupons >19 mm, the maximum qualified thickness equals the coupon thickness itself. For example: a 12 mm coupon qualifies up to 24 mm; a 25 mm coupon qualifies up to 25 mm. Note that this applies to groove welds; fillet welds follow different rules (QW-202.4(c)). Also, thickness qualification is independent of weld metal thickness — it governs the base metal’s nominal thickness at the joint. Always validate against your PQR’s recorded coupon dimensions and ensure no essential variable restrictions (e.g., preheat, PWHT) limit applicability.

Yes — critically. Thickness qualification under ASME IX is material-specific and tied to P-Number groupings. A WPQ qualified on P-No. 1 (carbon steel) does not qualify welding on P-No. 8 (austenitic stainless steels), regardless of identical thickness ranges. Each P-Number requires separate procedure qualification because metallurgical behavior, thermal conductivity, and distortion characteristics differ significantly. QW-253 explicitly lists P-Numbers as essential variables — changing P-Number invalidates the WPQ for that material. Even within P-No. 8, subgroups (e.g., P-No. 8A vs. 8B) may require requalification if notch toughness is required (QW-403.5). Never extrapolate thickness ranges across P-Numbers without formal requalification.

No — not fully. A 20 mm test coupon qualifies a minimum thickness of 10 mm (half the coupon, per QW-202.4(a)) and a maximum of 20 mm (since coupon >19 mm, max = coupon thickness per QW-202.4(b)). Thus, 3 mm falls below the qualified minimum (10 mm), and 40 mm exceeds the qualified maximum (20 mm). To cover 3 mm, you’d need a separate WPQ with a ≤6 mm coupon (qualifying down to 5 mm minimum) or a dedicated thin-section qualification. To cover 40 mm, you’d need a ≥40 mm coupon (or ≥20 mm if using alternative rules for thick sections with impact testing, per QW-403.6). Always map each project’s thickness requirements to validated PQR ranges — never assume linear scalability.

Yes — indirectly but significantly. While PWHT itself is an essential variable (QW-253), its application affects qualified thickness ranges when impact testing is required. Per QW-403.6, if a WPQ includes PWHT and impact testing, the qualified thickness range is limited to twice the test coupon thickness, even for coupons >19 mm — overriding the standard ‘max = coupon thickness’ rule. For example, a 25 mm PWHT+impact coupon qualifies only up to 50 mm, not unlimited thickness. Conversely, omitting PWHT where required invalidates the WPQ entirely. Always review QW-407 (PWHT variables) and QW-403.6 together — thickness validity hinges on whether PWHT was performed and documented on the PQR, and whether toughness testing applied.

No — supplemental mechanical tests do not extend qualified thickness ranges under ASME IX. QW-202.4 defines thickness limits solely based on the original test coupon dimensions and applicable clauses — not test results. Passing additional tensile or side-bend tests on thicker material does not requalify the procedure for that thickness. To cover new thicknesses outside the qualified range, you must perform a new procedure qualification with a test coupon meeting QW-202.4’s dimensional requirements for the target thickness. Exceptions exist only for specific cases like corrosion-resistant cladding (QW-202.5), but those follow distinct rules. Relying on supplemental testing risks noncompliance during ASME audits — always requalify formally via a new PQR.