Effect of impurity ratios on the high-temperature corrosion of Inconel 617 and Incoloy 800H in impure helium

Abstract

Helium is utilized to be the coolant of the high-temperature gas-cooled reactor (HTGR), which contains trace impurities in the primary circuit. The impurities may cause various corrosion behaviors of superalloys at elevated temperatures. In this study, the oxidation and carburization of Inconel 617 and Incoloy 800H at 950 °C in impure helium were investigated. According to thermodynamics and kinetics, the different ratios PH2/PH2O and PCH4/PH2O were set in this research, which leads to different oxidation and carburization behaviors of alloys at 950 °C. When PH2O is at a constant concentration, high PH2 would reduce the oxidation capacity of the atmosphere, and high PCH4 will cause severe carburization. Due to the presence of the silicon oxide interlayer, the oxide layer of Incoloy 800H has poor adhesion and it is easier to be destroyed at high temperatures. It may be the reason that Incoloy 800H has weaker resistance to carburization.