The Battelle Hydrothermal Coal Treatment Process (BHCP) subjects pressure vessel and piping construction materials to severely corrosive conditions. The combination of alkaline leachant and sulfur from coal at temperatures to 325 C can promote various forms of corrosion including general attack, pitting, stress corrosion cracking (SCC), and sulfidation. Environmental conditions experienced in the BHCP are unique. Prior to this study no data on materials' behavior in these solutions were available; however, data in comparable solutions provide a basis for predicting corrosion behavior. From background information, two modes of degradation were identified as potentially limiting materials selection for BHCP service: (1) mild steels, low-alloy steels, and iron-chromium-nickel alloys are susceptible to SCC in alkaline solutions at temperatures and concentrations in the range of those experienced in the BHCP and (2) nickel and nickel alloys are susceptible to sulfidation in high-temperature solutions containing sulfur. It was recognized that an experimental program to determine corrosion of candidate construction materials in BHCP solutions was necessary to provide a sound rationale for materials selection.
