Corrosion assessment and mechanisms of stainless steel in molten salt for solar thermal power generation

Stainless steel is mainly used for components such as thermal molten salt tanks， heat transfer pipes， heat exchangers， valves， and pumps in solar thermal power generation systems. Molten salt， with its excellent thermophysical properties， serves as the heat transfer and storage medium in solar thermal power generation. However， molten salt exhibits strong corrosive properties towards metal materials. This paper provides an overview of the corrosion assessment and mechanisms of stainless steel in molten salt environments. Firstly， the application of stainless steel in solar thermal power generation systems and its corrosion evaluation in molten salt are introduced. Subsequently， the main corrosion types of stainless steel in molten salt， as well as the corrosion mechanisms in nitrate， carbonate， and chloride salts， are summarized. Austenitic stainless steel meets the corrosion rate requirements for structural materials in solar salt， aluminum-containing stainless steel exhibits superior corrosion resistance in carbonate salts， and 310 stainless steel is suitable for use in purified chloride salts under inert atmosphere protection. The corrosion of stainless steel in molten salt mainly depends on the types of salt anions. Corrosion in salts containing oxygen anions and halide salts is categorized under the molten salt acid-base theory， while chloride salt corrosion also involves the activation-oxidation theory. Finally， the electrochemical corrosion behaviors of atmosphere， impurities and temperature that affect the corrosiveness of molten salt are discussed， and it is pointed out that chloride salt purification can greatly reduce the corrosion of metal materials. Aluminum-containing stainless steel can form a more stable A12O3 passivation film in the oxygenated anionic salt， which can effectively prevent the dissolution of chromium and iron and the penetration of corrosive impurities， which is the main research direction of molten salt corrosion-resistant stainless steel.