Impact of Solar Salt aging on corrosion of martensitic and austenitic steel for concentrating solar power plants
Abstract This work addresses the influence of molten nitrate salt chemistry on the corrosion behavior of a martensitic high temperature steel and an austenitic stainless steel. It is one of the first addressing controlled degradation of Solar Salt by controlling the gas atmosphere on top of the melt, thus driving the formation of corrosive ions, mainly oxide ions but also nitrite ions. The stainless steel and high temperature steel samples are subjected to the different operating conditions to demonstrate the variations in corrosivity as a function of gas atmosphere and additionally of artificially added chloride impurities. The results indicate that the atmosphere has a direct impact on the formation of corrosive oxide and nitrite ions. The low Cr steel is found to be more sensitive to chloride impurities, while the stainless steel corrosion is enhanced by the presence of nitrites and oxide ions. All studies are supported by profound molten salt analysis throughout the experiments including the analysis of nitrate, nitrite, oxide and chromate ions as well as cation compositions. Steel samples are analyzed by scanning electron microscopy methods and corrosion rates are extrapolated from 1200 h experiments.