Hot corrosion studies of boiler steels exposed to different molten salt mixtures at 950 °C

Abstract

High-temperature oxidation behavior of different power plant steels (P22, P91, and SS304L) was investigated under the exposure of different molten salt mixtures at a temperature of 950 °C. Cyclic corrosion study of 50 h were performed on the different specimens by applying 3–5 mg/cm2 salt mixtures (Na2SO4 + 60% V2O5, K2SO4 + 60% NaCl, Na2SO4 + 50% NaCl, 10% NaCl +10% KCl + 40% Na2SO4 + 40% K2SO4) on the surface. XRD, SEM, and EDS analysis were performed on the post corroded specimens. The results indicate that steel with low Cr content undergoes a heavy oxide scaling leading to higher weight gain due to the absence of protective Cr2O3 inner scale. Thus, steel with higher Cr content possesses better corrosion resistant properties. Moreover, addition of chlorine to the alkali salt causes an immediate drop in the melting temperature of the salt mixture, which increases the melt and leads to a more corrosive environment. Salt mixtures with higher chlorine content severely affects the corrosion resistance of each alloy. Additionally, higher weight gain was observed for the steel specimens which were exposed to the salt mixture containing a higher amount of chlorine in combination with Na2SO4.