Corrosion of Alloy Haynes 230 in High Temperature Supercritical Carbon Dioxide with Oxygen Impurity Additions

The corrosion of Ni-based alloy Haynes 230 in supercritical carbon dioxide at temperatures of 650 and 750 A degrees C at a pressure of 20 MPa was investigated. In high-purity research grade CO2, the corrosion performance of the alloy was excellent with a thin, uniform, protective chromium-rich oxide layer forming on the surface. Introduction of 10 and 100 ppm O-2 impurity in the CO2 environment noticeably enhanced oxidation with evidence of oxide spallation and nodule formation. In these oxygen impurity added tests, increased oxidation led to subsurface voids due to the more rapid outward diffusion of chromium as well as intergranular alumina and chromia. The oxygen concentration at the inlet and the outlet of the autoclave was measured and used to support the results of characterization of the surface oxide to develop a more holistic understanding of the role of oxygen impurity on the corrosion process. In all cases, there some carbon was observed, which manifested as slightly higher concentration of chromium-carbide phase at the grain boundaries compared to the unexposed alloy.