Investigation of supercritical CO2 corrosion behavior of X80 carbon steel in pipelines: An in situ experimental and DFT study

The electrochemical corrosion behavior of X80 carbon steel was investigated in a supercritical CO₂ (sCO₂) environment at 60 ℃ and 9 MPa, by in-situ experiments and density functional theory (DFT) calculations, revealing the corrosion mechanism. For in situ electrochemical measurements, two novel CO₂-rich and H₂O-rich cells were developed to replace the traditional three-electrode cell. Electrochemical impedance spectroscopy revealed distinct differences in the corrosion behavior between CO₂-rich and H₂O-rich environments during the later stages of testing. In H₂O-rich environments, as corrosion time increased, the corrosion product layer gradually changed from porous to dense, eventually forming a protective layer. In CO₂-rich environments, corrosion occurs mainly in areas where water condenses to form FeCO₃. Simultaneously, microscopic calculations provided evidence for the three-step sCO₂ hydrolysis mechanism and the formation of FeCO₃ products.