Reusing a PQR for a Tougher Job
PQR-118: FCAW-G, 1 in A36 plate, 3G, 0.045 in E70T-1 with 100% CO2, six passes, measured heat input 42 kJ/in (carried as the WPS maximum), no Charpy testing. A new contract calls for 3/4 in A572 Gr 50 CJP groove welds in tension members, and the specification requires Charpy V-notch testing at 0 deg F with 20 ft-lb minimum for all groove welds in material 1/2 in and thicker. The superintendent proposes to (a) reuse PQR-118 with a note that A572 is 'similar to A36', and (b) raise the heat input limit to 60 kJ/in with a wider weave, because last month's job had lack-of-fusion rejects. First production welds are due in 12 days.
1. Can PQR-118 support a WPS for 3/4 in A572 Gr 50 as proposed? Identify every essential variable issue.
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No. The proposal fails on two independent grounds.
- Base metal group. A36 and A572 Gr 50 are not interchangeable for procedure qualification. They sit in different base metal groups (A36 in Group I, A572 Gr 50 in Group II). A change from one group to a higher group is an essential variable and requires a new PQR, not an engineering note.
- Toughness. The contract requires 20 ft-lb at 0 deg F for groove welds 1/2 in and thicker. PQR-118 has no Charpy data, so there is no evidence of weld metal or HAZ toughness. Toughness cannot be inferred from strength or from 'similar' chemistry; it is established only by testing specimens cut from a production-representative plate.
Two things do line up and should be kept in the new work: 3/4 in product from a 1 in test coupon falls inside the qualified thickness range, and 3G matches if production is 3G. Neither rescues the group change or the missing toughness.
Also verify before writing anything: filler classification, shielding gas (100% CO2), and that the heat input you will permit is actually demonstrated by the PQR data.
2. The superintendent wants the heat input limit raised from 42 to 60 kJ/in with a wider weave to fix the lack-of-fusion rejects. Assess that proposal.
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The diagnosis may be right; the method of fixing it is not.
- Where toughness is required, heat input is an essential variable. You cannot raise a WPS maximum above the value demonstrated in the PQR without requalification, because higher heat input generally coarsens the HAZ and lowers toughness. The 60 kJ/in number needs to be tested with Charpy specimens, not asserted.
- The requalification you already need for A572 Gr 50 and for toughness is the correct vehicle. Build the test plate at the higher heat input, test it, and if it passes 20 ft-lb at 0 deg F you have legitimately widened the operating window.
- Do not treat heat input as the only lever. Check weave-width limits in your WPS, travel angle, interpass cleaning, joint fit-up, and whether the operator was actually achieving the 42 kJ/in the old WPS assumed. If the real energy was running 30 kJ/in, the fix is technique and monitoring, not a new limit.
Fixing a lack-of-fusion trend by memo is how a shop ends up with a toughness failure on a tension member.
3. Production starts in 12 days. Lay out the compliant path and the decisions that must be made now.
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- New PQR. Weld a test plate in A572 Gr 50 (or 1 in, to retain the widest thickness range) with the production process, gas, filler classification and position, at the highest heat input you intend to permit.
- Testing. Cut CVN specimens, weld metal and HAZ, 0 deg F, 20 ft-lb minimum, tested at an accredited laboratory. Book the lab today. Machining and testing, not welding, is the schedule risk.
- Write the WPS from the new PQR: qualified heat input range, preheat and interpass, pass sequence, and thickness range.
- Use the waiting time for welder qualification on the same configuration and for WPS briefing of the crew.
Decisions required now: 3/4 in or 1 in test plate; who signs the PQR; whether the contract permits any waiver (ask, do not assume); and whether the 12-day date is real.
Do not start production on PQR-118 hoping the paperwork catches up. That creates nonconforming welds in tension members with no defensible basis, and the removal cost lands on the fabricator.