Corrosion study of candidate alloys in high temperature, high pressure supercritical carbon dioxide for brayton cycle applications

Materials performance in supercritical carbon dioxide (SC-CO₂) has been explored as part of ongoing research for the SC-CO₂ Brayton cycle. The SC-CO₂ Brayton cycle is under consideration by the Generation IV advanced nuclear reactor initiative for power generation since it allows for power plant simplification and higher power conversion efficiencies. For this study, corrosion performance was evaluated in terms of weight gain by the thermo-gravimetric method using a custom, high pressure and high temperature autoclave design capable of testing materials up to temperatures of 650°C and pressures of 20MPa. Tests were performed under isothermal conditions at temperatures of 450°C, 550°C, and 650°C at 20MPa, using research grade CO₂ (99.9998%). Weight gain measurements were made in intervals of 200 hours up to a total exposure time of 1000 hours. The alloys selected for this study consisted of two ferritic steels, NF616 and HCM12A, two austenitic alloys, 347 stainless steel and alloy 800H, and three advanced concept alumina-forming austenitic (AFA) alloys, AFA-OC6, AFA-OC7, and AFA-OC10. Scanning Electron Microscope (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDS) analyses were also conducted to further characterize the performance of the alloys after corrosion testing.