3/8 in Coupon, 1-1/4 in Work, and a 'PWHT When Required' Note
A fabricator's WPS W-101 is supported by PQR P-101: 3/8 in (9.5 mm) SA-516 Gr. 70 plate, single-V groove, GTAW root with ER70S-2 (F-No. 6) plus SMAW fill/cap with E7018 (F-No. 4), 200 °F minimum preheat, PWHT at 1150 °F for 1 hour. As typed, the WPS lists base metal thickness "1/16 in through 1-1/2 in," preheat "200 °F minimum," PWHT "when required by the referencing code," and groove angles "45°–75°." Production now requires 1-1/4 in thick SA-516-70 shell welds. The referencing code does not require PWHT for this joint, impact testing is not required, and the detail drawing shows a 37.5° bevel. The shop plans to start welding Monday with W-101 exactly as written.
1. Do the 1-1/4 in shell welds fall within the qualification behind W-101? If not, what is the minimum test coupon thickness that would cover them?
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No. Thickness coverage comes from the test coupon, not from what the WPS says.
- What the PQR supports: a 3/8 in coupon qualifies a base metal thickness range of 1/16 in through 2T = 3/4 in (QW-451.1). The WPS's stated "1/16 in through 1-1/2 in" is already an overreach.
- The production joint: 1-1/4 in is roughly 1.7 times the maximum qualified thickness, so W-101 cannot be used.
- What would cover it: the maximum qualified thickness is 2T, so a coupon of at least 0.625 in is needed. A 5/8 in coupon gives a qualified range of 3/16 in to 1-1/4 in (lower limit 3/16 in applies once the coupon is 3/8 in or thicker). A 3/4 in coupon would give more margin.
- Sequence: qualify a new PQR on the thicker coupon (tension and guided bend specimens), certify it, then revise W-101 so its listed range is inside the new 2T limit. The old PQR cannot simply have its thickness range edited.
2. Is 'PWHT when required by the referencing code' an acceptable WPS entry? What is required for the 1-1/4 in joints, which the code says need no PWHT?
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It is not acceptable as written. Postweld heat treatment is an essential variable for procedure qualification (QW-407.1): adding or deleting PWHT, or changing the temperature/time range outside the qualified range, requires a new PQR.
- PQR P-101 was qualified with PWHT at 1150 °F for 1 hour. That PQR therefore supports welds given a PWHT within the range it established - it does not support an as-welded joint, and it does not support an open-ended "whatever the code says."
- The WPS must state a definite PWHT temperature range and holding-time range that the PQR supports, or state "none" if the PQR was run as-welded. A conditional entry puts production outside qualification in one direction or the other.
- Because the 1-1/4 in welds will be left as-welded, the new 5/8 in qualification coupon must itself be tested as-welded. Requalifying with PWHT and then welding production without it would repeat the same defect in a new document.
- Practical check: confirm the referencing code really waives PWHT at 1-1/4 in for this material; that determination belongs to the construction code, not to Section IX.
3. The drawing calls for a 37.5° bevel while the WPS lists 45°–75°. Can the shop simply revise the WPS, or does this trigger requalification?
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A WPS revision only is sufficient here, provided nothing else moves.
- Groove angle, root gap, land, and similar joint-detail dimensions are nonessential variables for welding procedure qualification (QW-402). They must be described in the WPS, but a change does not invalidate the PQR, so the revision can be issued under the shop's normal WPS control procedure with the same approval authority.
- The line is crossed only if the change alters the joint type (for example single-V to double-V, or butt to corner) or forces a change in an essential variable - different process, different F-Number, added or deleted PWHT, thickness outside 2T.
- When revising, keep the essential variables consistent with the PQR (processes, F-Numbers, preheat minimum, PWHT condition, thickness range) and remove the unsupported 1-1/2 in entry at the same time so one revision fixes both problems.