Oak Ridge National Laboratory has assisted coal liquefaction pilot plant operators by assessing materials' performance through supply and examination of corrosion samples, on-site examination of equipment, and analysis of failed pilot plant components in our laboratory. This paper describes these examinations, which have revealed chloride and polythionic acid stress corrosion cracking, water-side pitting, sulfidation, and a chloride-related acid attack. These analyses have helped identify corrosion problems and make proper materials selections or design changes, and have provided designers with information useful in selecting materials for proposed plants.