PQR Essential Variable Changes for GMAW Production
A fabricator has a procedure qualification record for GMAW short-circuiting on 3/8 in A36 plate, flat position, using 0.045 in ER70S-6, 100% CO2, 22 V, 180 A, with steel backing. The production weld is a 3/4 in thick A36 moment connection, welded vertical-up without backing, using the same wire but 90% Ar/10% CO2 at 26 V and 240 A in spray transfer. The fabricator wants to use the existing PQR because the base metal and filler metal are unchanged. The CWI must determine whether a new procedure qualification is required and what the welder qualification covers.
1. Identify the essential variable changes and whether a new PQR is required.
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Several essential variables have changed: transfer mode from short-circuiting to spray, shielding gas from 100% CO2 to 90% Ar/10% CO2, backing to no backing, position from flat to vertical-up, base-metal thickness from 3/8 in to 3/4 in, and current/voltage beyond the original PQR range. The filler metal classification alone is not enough. Under AWS D1.1, these changes require a new procedure qualification record and supporting WPS. The existing PQR cannot be used merely because the base metal and wire are unchanged.
2. Explain why these changes affect weld integrity.
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Transfer mode and gas composition change arc stability, penetration, heat input, and cooling rate. Spray transfer with argon-rich gas behaves very differently from short-circuiting with CO2. Removing backing changes root penetration and root soundness; the welder must control the root without burn-through. Vertical-up welding changes heat input and bead shape and is not qualified by a flat-position PQR. The thicker 3/4 in section increases restraint and cooling rate, which affects hydrogen risk and toughness. The higher current and voltage also change heat input beyond the qualified range. These are not cosmetic changes.
3. What should be done before production, including welder qualification?
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Qualify a new WPS/PQR using a 3/4 in test coupon in the vertical-up position, without backing, with the production gas mix, transfer mode, and current/voltage range. Perform the required mechanical tests, such as tension, bend, and any toughness tests specified by the governing code. Then qualify the welders to the new WPS, including position and backing conditions. Do not allow production to proceed on the old PQR. The CWI should verify the PQR essential variables, the WPS ranges, and each welder’s qualification before accepting production welds.