WPS Qualification Range vs. Production Thickness
A fabricator is welding a pressure-retaining component from 16 mm SA-516 Grade 70 plate using SMAW with E7018 electrodes. The WPS on file was qualified by procedure qualification testing on 10 mm test coupon using the same electrode classification and process. The WPS lists a thickness range of 1.5 mm to 20 mm, based on the fabricator's reading of the code's thickness qualification rules. The production weld is a double-V groove, full penetration, welded in the 3G position. The welder's performance qualification is current and covers 3G with backing. The production weld will be visually inspected and radiographed. The applicable code is ASME Section IX.
1. Is the WPS thickness range of 1.5 mm to 20 mm correct for a 10 mm qualification coupon? Explain the qualification logic.
Read the worked answer
Under ASME Section IX, procedure qualification thickness ranges depend on the test coupon thickness and whether impact testing is required.
For a 10 mm coupon without impact testing, QW-451 permits a qualified thickness range of 1.5 mm to 2T (where T is the coupon thickness), so 1.5 mm to 20 mm - the fabricator's stated range is consistent with that rule. The upper limit of 2T = 20 mm covers the 16 mm production thickness.
However, several checks must be made before accepting the WPS as valid for this application:
- Impact testing: If the component requires notch toughness, the thickness range collapses to the coupon thickness (T to T, with a small tolerance), and a 10 mm coupon would not qualify 16 mm. The fabricator must confirm whether impacts are required.
- Essential variable changes: The production joint is a double-V groove in 3G; the qualification must cover the groove type and position. A change from a single-V to double-V is generally not an essential variable for SMAW, but position is; the PQR must show 3G or a position that qualifies 3G.
- Electrode: E7018 must match the PQR's F-number and A-number; a change in electrode classification within the same group may be permissible, but must be verified.
So the range is plausible but conditional; the inspector should verify impact requirements and position coverage before signing off.
2. The welder's qualification covers 3G with backing, but the production weld is a double-V full-penetration joint welded from both sides without backing. Does the welder qualification cover this joint?
Read the worked answer
This requires careful analysis of QW-461 (welder performance qualification ranges).
- Position: 3G qualification covers groove welds in the vertical position. The production joint is welded in 3G, so position is covered.
- Backing: The welder qualified with backing. Under QW-461.9, a welder qualified with backing is generally not qualified to weld without backing (backing is an essential variable for welder qualification). Removing backing changes the root condition the welder must control - a free root requires the welder to establish penetration from one side without a support, which is a distinct skill.
- Double-V welded from both sides: Welding from both sides is closer to a double-sided condition; the second side is welded against previously deposited metal rather than a backing strip. This is not the same as welding with a backing strip.
Conclusion: The welder's qualification with backing does not clearly cover a no-backing double-V root. The welder likely needs a supplementary qualification without backing (or the joint must be redesigned with backing) before production welding. I would raise this as a qualification gap, require the additional welder test, and hold production until resolved. This is exactly the kind of essential-variable trap that visual inspectors must catch before welding, not after.