Effect of Cr content on steel corrosion mechanism in dynamic high-salinity supercritical CO 2 environment

Against the background of large-scale application of carbon capture, utilisation and storage-CO 2 enhanced oil recovery, the corrosion failure of wellbore tubulars in dynamic high-salinity supercritical CO 2 environments remains an urgent problem to be solved. This study investigates the effect of chromium (Cr) content on casing steel corrosion in a dynamic supercritical CO 2 environment simulating Xinjiang high-salinity formation water. Weight loss and microstructural analyses of N80, 5Cr, 9Cr, and 13Cr steels revealed a non-monotonic trend in corrosion rate: 5Cr steel suffered catastrophic corrosion (4.1465 mm/a), while 13Cr steel showed excellent corrosion resistance (0.0222 mm/a). We further confirmed that corrosion resistance in this severe environment depends on the chemical stability of the Cr-rich passive film, rather than the macroscopic mechanical strength of the corrosion product film. This work provides an important experimental basis for material selection, and 13Cr or higher-grade alloys are recommended for this working condition.