FCAW Procedure Qualification with Shielding Gas Change
A fabricator submits a WPS supported by a PQR made with FCAW-G, E71T-1C electrode, 100% CO2 shielding, 3/8-in A36 plate, single-V groove, 3G uphill, with Charpy V-notch tests at 0°F. The project requires CVN toughness at 0°F for 1-in A572 Grade 50 plate. Production will use E71T-1M electrode with 75% Ar/25% CO2 shielding, same process and position, and will include a 2-in thick flange. The fabricator's welding engineer says the electrode classification is still E71T-1 and that the existing PQR covers the range because the test was run uphill and production is uphill. The contractor wants to start production Monday. You are reviewing the WPS/PQR package.
1. Identify the essential variables that change between the PQR and the proposed production welding. Explain why each matters.
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Several changes are not routine. The shielding gas change from 100% CO2 to 75% Ar/25% CO2 is an essential variable for FCAW-G because gas composition affects arc stability, transfer mode, cooling, and toughness. The electrode suffix change from E71T-1C to E71T-1M is also significant: the C and M designations indicate different shielding-gas requirements and usability characteristics, and the manufacturer's classification is not interchangeable without qualification. The base metal change from A36 to A572 Grade 50 must be checked against the D1.1 base-metal grouping; even if the group is the same, the higher strength and thickness can affect heat input and toughness. The production thickness of 1 in and 2 in is outside the range supported by a 3/8-in test coupon unless the PQR demonstrates a broader qualified thickness range. The CVN requirement is a supplementary essential variable; impact testing must represent the production electrode, gas, thickness, and heat input. The fact that both are uphill does not neutralize these changes.
2. Does the existing PQR support the 1-in and 2-in production thickness with the required CVN toughness? Justify your answer.
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No. The PQR was made on 3/8-in plate, so its qualified base-metal thickness range must be determined from the D1.1 thickness rules for the test coupon. A 3/8-in coupon does not automatically qualify 1-in or 2-in production; the qualified range may be limited to thinner material. The 2-in flange is a further departure and may require a separate qualification or a qualified range that expressly covers it. More importantly, the PQR's CVN results apply to the tested combination: E71T-1C with CO2 on 3/8-in A36. Changing to E71T-1M with Ar/CO2 on 1-in A572 Grade 50 means the toughness data do not represent production. The contractor must either qualify a new PQR using the production electrode, gas, thickness, and heat input, or demonstrate by the code's revalidation provisions that the existing PQR remains valid. That demonstration must include CVN testing where required. A statement that the electrode is 'still E71T-1' is not enough.
3. What actions should you require before approving the WPS for production?
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Require a written WPS/PQR review against the D1.1 essential and supplementary essential variables. The contractor must identify the qualified thickness range, the qualified base-metal group, the qualified electrode and shielding gas, and the qualified position. Because the production changes both gas and electrode designation, a new PQR or a documented revalidation is required. The PQR must include mechanical testing and CVN testing at 0°F for the production combination, and the test thickness must cover the thickest production joint. The WPS must be supported by that PQR and must specify preheat, interpass, heat input, and pass sequence. Before Monday, the inspector should verify that the WPS is approved, that the welders are qualified for the new combination, and that production electrodes and gas are as qualified. If the contractor cannot complete qualification, do not approve production welding; a provisional approval without qualification would be unsupported.