The results of the failure analysis of the gasifier distributor cone thermocouple sheaths (TE-268) from the Synthane high Btu conversion pilot plant are presented. The thermocouples are used to monitor the distributor cone temperature, and the sheaths housing the thermocouples are normally exposed to a steam and oxygen environment (600 psig and 650 exp 0 F) in the plenum below the cone. The failures of the sheathing material (Incoloy 800) are associated with sulfur-related corrosion cracks and plastic deformation and tearing, due in part to expansion of the MgO insulating material. A combination of corrosive environment, off-process temperatures, methods used in fabrication, and possible cold working contributed to the failures. (ERA citation 03:000006)
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