Unqualified nozzle weld and premature radiography before hydrotest
A fabricator is finishing a 16 mm SA-516-70 pressure vessel. The dossier contains a PQR on 10 mm plate, GTAW root plus SMAW fill, impact tested at -20 °C, and welder W-12 qualified in 3G on a 10 mm coupon with backing. Production includes a 22 mm nozzle-to-shell groove weld made in the 4G position by W-12. Radiography of that weld was performed 4 h after welding and shows a 6 mm rounded indication and a 12 mm slag line. The client's inspector also finds that a repair is needed on the inside of the shell, 1.8 m from a 450 mm manhole, and the vessel is scheduled for hydrotest tomorrow. The project specification requires ASME IX qualification and radiography after 48 h for thickness above 20 mm.
1. Assess whether the PQR and welder qualification cover the 22 mm 4G production weld.
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PQR range. The PQR is on 10 mm plate. Under ASME IX QW-451, a 10 mm groove test coupon qualifies base-metal thickness from 1.5 to 20 mm. A 22 mm production weld is therefore outside the qualified range.
Welder range and position. The welder is qualified on a 10 mm coupon in 3G. The thickness range from that coupon is also limited to 20 mm. Position 3G covers flat, horizontal and vertical, not overhead 4G. The production weld is both too thick and in the wrong position for the welder's qualification.
Conclusion. Both the procedure and the welder are unqualified for this weld. The impact test supports the PQR only within its qualified range. The weld cannot be accepted on the existing dossier; a new PQR or a qualified extension and a welder performance qualification in 4G are required before further production. The completed weld must be treated as unqualified and evaluated.
2. What is the significance of radiography at 4 h, and how should the indications be handled?
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Radiography at 4 h is too early for a 16–22 mm ferritic steel weld where delayed hydrogen cracking is possible. The project specification requires 48 h. A crack may not have initiated at 4 h, so the film gives a false sense of security.
The 12 mm slag line is a linear, volumetric indication and is likely to exceed acceptance. The 6 mm rounded indication may be porosity, but its nature must be confirmed. Both areas should be investigated with UT and surface NDT, and the weld should be re-radiographed after 48 h. Do not hydrotest tomorrow. Repair the unacceptable indications under a qualified repair procedure, then repeat RT/UT after the required delay.
3. Plan the internal repair, including confined-space controls and documentation.
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Treat the vessel as a confined space: isolate and lock out, clean and purge, test the atmosphere for oxygen, flammability and toxic gases before entry and continuously during work. Provide forced ventilation, an attendant at the manhole, a rescue plan and harness, low-voltage lighting, and fume extraction at the arc. The welder must be qualified for the repair position and procedure.
Use a qualified repair WPS with preheat and low-hydrogen consumables. Excavate the defect, confirm removal by PT/MT, weld, and inspect after 48 h. Record the repair on the vessel drawing, update the dossier, and only then schedule hydrotest. The inspector should issue a nonconformance report and obtain client approval before the repair.