High-temperature corrosion observed in austenitic coils and tubes in a direct reduction process

The subject of this study is related to the performance of austenitic steel coils and tubes, in a range of temperatures between 425 and 870 degrees C for the transport of reducing gas, in an installation involving the direct reduction of iron-ore by reforming natural gas. Evidence is presented that metal dusting is not the only unique high-temperature corrosion mechanism t hat caused catastrophic failures of austenitic 304 (UNS S304 00) coils and HK-40 (UNS J94204) tubes. Sensitization as well as stress corrosion crackin g occurred in 304 stainless steel coils and metal dusting took place in HK- 40 tubes, a high resistance alloy. The role of continuous injection of H2S into the process is suggested to avoid the high resistance metal dusting co rrosion mechanism found in this kind of installation.