Corrosion Behavior of Metallic Materials in the Reducing Environments Characteristic of a Coal-Fired MHD Generator

Metallic materials selected for the balance of plant construction of components of an open cycle coal fired magnetohydrodynamic (MHD) generator must withstand the corrosive erosive conditions encountered in these systems. The corrosion behavior of carbon steel, chromium-molybdenum ferritic steels, austenitic stainless steels, and nickel base alloys, has been evaluated after exposure to complex gas mixtures that simulate a coal fired MHD environment with substoichiometric combustion. The results show that sulfidation was the predominant mode of interaction for the alloys in this environment. In general, carbon steel and Cr-Mo steels suffered significant sulfidation attack, while the austenitic stainless steels exhibited superior resistance to corrosion. It is concluded that low cost ferritic steels with a stainless steel cladding or a ramming refractory coating can be effectively used for protection of the radiant boiler components of a typical coal fired MHD generator system. The experimental observations on the nature of corrosion products which formed on metallic materials were in good agreement with predictions based on thermochemical stability considerations.