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 Na2S was thoroughly analyzed in this study. The various materialcharacterization methods, such as visual inspection, microscopic observation, chemical analysis, and mechanical assessment, demonstrated that hydride-inducedembrittlement plays a considerable role in the failure of the titanium tank. The key finding was that side products of H2, H2S, and Na2SO3 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 TiH2 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 Na2CO3 into the reactive media were proposed. By complementary electrochemical investigations, it was clarified that Na2CO3 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.