A corrosion failure analysis of a titanium tank used for production and storage of molten sodium sulfide

The corrosion failure of a titanium tank operating under high temperature of 220 °C for the production and storage of molten Na 2 S was thoroughly analyzed in this study. The various material characterization methods, such as visual inspection, microscopic observation, chemical analysis, and mechanical assessment, demonstrated that hydride-induced embrittlement plays a considerable role in the failure of the titanium tank. The key finding was that side products of H 2, H 2 S, and Na 2 SO 3 cause the destruction of the passive oxide film and, thus, provide the conditions for the absorption and penetration of atomic hydrogen, resulting in the formation of brittle TiH 2 and subsequent flaking on the surface. To failure prevention of the titanium tank in such environments, the selection of tank material from Monel® 400, blowing nitrogen gas into the system, and loading Na 2 CO 3 into the reactive media were proposed. By complementary electrochemical investigations, it was clarified that Na 2 CO 3 can stabilize the passive oxide film on the titanium surface and, therefore, enhance the resistance of the titanium tank against corrosion and failure. Notably, the present study can provide helpful references for enhancing the safety maintenance management of similar types of equipment.