Corrosion of alumina‐forming austenitic steel in molten nitrate salts by gravimetric analysis and impedance spectroscopy

摘要

In recent years, the study of renewable energies and its practical application has increased significantly. Solar energy feasibility entails the development of energy storage systems since solar power plants need to be working in unfavorable weather or night periods. The main heat transfer fluid (HTF) used on these plants is a salt mixture of 60% NaNO_3/40% NaNO_3 which must be kept above 220 ℃ to prevent freezing. This high operating temperature causes corrosion problems for steels in contact with the HTF, reducing the lifetime of the solar plants. The present research studies the potential of an alumina forming austenitic (AFA) stainless steel (OC-4, Fe-25Ni-14Cr-3.5Al-2.5Nb wt% base) as a candidate material for solar plant heat exchangers and pipes. Corrosion behavior of OC-4, relative to 304 stainless steel and T22 steel, was studied by gravimetric analysis and electrochemical impedance spectroscopy (EIS). The AFA OC-4 exhibited better corrosion resistance in HTF at 390℃ than the currently used 304 austenitic stainless steel.