Rejected Radiograph on a Shell Butt Weld
A 25 mm thick SA-516-70 shell course has a completed full-penetration butt weld made with an FCAW root and SAW fill. The weld is 1.2 m long. RT is required by the project specification, and the film shows a linear indication about 9 mm long and 2 mm wide near the root, plus a rounded indication 3 mm across. The welder's qualification is current, but the preheat record for the joint is missing. The RT contractor reports the linear indication as acceptable because it is less than 10 mm. The project uses ASME Section VIII Division 1 acceptance criteria. The vessel will operate at 1.6 MPa and 150 degrees C in non-lethal service. The schedule is tight; the superintendent wants to stamp the joint and move on. A UT technician is available but has not been requested. The weld cap is smooth and the area has been wire-brushed.
1. Evaluate the RT indications against the project acceptance criteria. Is the contractor's less-than-10-mm rule correct?
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For 25 mm material, the common ASME Section VIII Division 1 linear acceptance limit is one-third of thickness because the thickness is greater than 19 mm: 25 / 3 = 8.3 mm. A 9 mm linear indication exceeds that limit and is rejectable. The contractor's 10 mm rule is not the applicable criterion and should not be accepted. The 3 mm rounded indication is below the usual 6 mm rounded-indication limit, so it is acceptable on its own, but it should be evaluated together with the linear indication and the film quality. Before accepting or rejecting, verify that the radiograph has proper density, sensitivity, and coverage. Because the linear indication is near the root, it could be lack of fusion, slag, or incomplete penetration; UT can help determine its depth and through-wall extent.
2. The preheat record is missing. How does that affect disposition, and what root causes should be investigated?
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Missing preheat records mean compliance with the qualified procedure has not been demonstrated. For 25 mm SA-516-70 with an FCAW root, preheat and interpass control affect hydrogen cracking and fusion. The joint cannot be accepted on the assumption that preheat was adequate. Investigate the welder's other joints, the ambient temperature and drafts, the FCAW root parameters, heat input, and whether the preheat was applied and measured before root and fill passes. The linear root indication may be lack of fusion from low heat input, moisture in the flux or gas, or poor joint access. If the same welder or procedure produced other welds on the vessel, increase the examination sample before deciding whether this is an isolated error.
3. Specify the repair and re-examination plan, including extent of examination and welder qualification considerations.
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Do not stamp the joint. Excavate the linear indication by grinding or arc gouging to sound metal, confirm removal with PT or MT, and re-weld with a qualified WPS using recorded preheat and controlled interpass temperature. Because the indication is near the root, UT should characterize depth before excavation so the repair does not leave a second unfused root. After repair, radiograph the repaired area and re-examine the adjacent weld as required by the project specification. If the repair is large or the same welder has repeated indications, review the welder's qualification and consider requalification or additional training. Complete the preheat record, NDT reports, and repair traveler before the joint is accepted.