Corrosion of Nickel and Iron Based Superalloys in High Temperature Gas Environments

High-temperature gas-cooled reactors (HTGRs) with helium gas asthe primary coolant have been considered as Generation IV nuclearpower reactor systems. Several iron- and nickel-based superalloys,including Incoloy 800H, Hastelloy X, and Inconel 617, arepotential structural materials in pressure boundary components,such as the intermediate heat exchanger (IHX) in an HTGR.Impurities in a helium coolant, such as H2O and O2, can interactwith structural materials at working temperatures of >900 oC,causing serious degradation. This study investigates the oxidationbehavior of three selected alloys (Hastelloy X, Incoloy 800H, andInconel 617) in high-temperature, gaseous environments withvarious levels of O2 and H2O. A series of corrosion tests wereconducted at test temperatures of 650 oC, 750 oC, 850 oC and 950oC under various coolant compositions of dry air, 1% O2, 10%humidity, and 50% humidity.