Search Results for UNS K03504

A cracked 356 mm (14 in.) diam slip-on flange (Ni-Cr-Mo-V steel) was submitted for failure analysis. Reported results and observations indicated that the flange was not an integral forging or a casting, as specified. It had been fabricated by welding and machining a ring insert within a flange with a larger internal diameter. The flange cracked because the welds between the flange and the insert were inadequate to withstand the bolting pressures. A warning was issued to end users of the flanges, which are being inspected nondestructively for conformance to specifications.

A carbon steel piping cross-tee assembly which conveyed hydrogen sulfide (H7S) process gas at 150 to 275 deg C (300 to 585 deg F) with a maximum allowable operating pressure of 3 MPa (450 psig) ruptured at the toe of one of the welds at the cross after several years of service. The failure was initially thought to be the result of thermal fatigue, and the internal surfaces exhibited the “elephant hide” pattern characteristic of thermal fatigue. However metallographic failure analysis found that this pattern was the result of corrosion rather than thermal fatigue. Corrosion caused failure at this location because the weld was abnormally thin as fabricated. Thus, failure resulted from inadequate deposition of weld metal and subsequent wall thinning from internal corrosion. It was recommended that the cross-tee be replaced with a like component, with more careful attention to weld quality.