Revealing the effect of O2, SO2 and H2O in supercritical CO2 on the corrosion behavior of 316L steel at elevated temperature

Closed supercritical CO2 (sCO2) power systems require steels that can resist corrosion in high temperature CO2 containing different impurities at ppm levels. However, potential impurity effects on Fe-16Cr steels are not well understood. Herein we evaluated the corrosion behavior of 316L steel in sCO2 containing 100 ppm O2, SO2 or H2O at 600 °C and 20 MPa. All investigated impurities enhanced Fe-oxide nodule formation, leading to higher carburization in underlying substrate. Presence of O2 caused transition of chromia scale into Fe-Cr spinel, because Cr supply from underlying substrate could not meet the consumption. Spallation occurred when 316L was exposed with SO2 impurity, attributed to the formation of sulfides within and beneath the oxide scales. H2O impurity showed relatively low damage to protective chromia layer with localized aggravation. Corrosion mechanisms related to impurities were unraveled based on experimental results and thermodynamic analysis.