The Synthane high-Btu coal-conversion pilot plant was shut down following the discovery of a leaking crack in a Type 304 stainless steel weld neck flange that is part of a preheat line of the gasifier. The flange was exposed to approximately 2.9 Ms (approximately 800 h) of operation at 4.3 MPa (600 psig) steam at 399 exp 0 C (750 exp 0 F). Several additional nonleaking intergranular cracks were also found at the inside diameter surface of the weld neck. The cracks are believed to be due to intergranular stress corrosion. Also, the heat-affected zone near the weld and/or chlorides may have contributed to the cracking. Metallography revealed that slip and precipitation on slip planes and grain boundaries had occurred. This suggests that the region of the flange near the leak had undergone considerable plastic deformation prior to a heat treatment. (ERA citation 03:000007)
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