METAL DUSTING FAILURES IN METHANE REFORMING PLANT

The Mossgas plant converts natural gas from sub-sea wells located 85 k m south of Mossel Bay, to synthetic fuels. The methane rich natural ga s is reformed to syngas by reaction with steam and oxygen at very high temperatures over a nickel catalyst in the secondary reformer to prov ide feedstock for the subsequent Fischer-Tropsch reaction in circulati ng bed catalyst reactors. The gas composition and temperature during r eforming are within the carburising range and metallic components in s ome parts of the reforming system are thus susceptible to degradation by a mechanism of accelerated carburisation known as ''metal dusting'' . Failure of an Alloy 600 component in the reformer neck due to metal dusting, and the subsequent catastrophic failure of the reformer shell is described. The mechanism of metal dusting is briefly reviewed with specific reference to the comparative resistance of various metallic materials to this form of degradation. The Mossgas experience in this respect appears to contradict some of the limited data that has so far been published on the topic in that Alloy 800 has been found to vastl y out-perform the high nickel Alloy 600 in this specific process envir onment. Further alloy exposure programmes have been initiated in order to try to gain a greater understanding of the practical limitations o f metallic materials to this environment.