Investigation of SO2-induced corrosion of X65 steel in gaseous, liquid, and supercritical CO2 environments through experimental and thermodynamic approaches

Laboratory experiments and thermodynamic simulations were performed at 25 °C (8 MPa) and 35 °C (4, 8 MPa) to investigate the effects of SO₂ on the corrosion of X65 steel and water chemistry during liquid, gaseous, and supercritical CO₂ transportation. Results indicated that less than 100 ppm SO₂ significantly influenced corrosion processes. In the water-saturated CO₂ environment, higher SO₂ concentrations led to elevated general corrosion rates. Interestingly, in the CO₂-saturated water environment, the general corrosion rate decreased at 35°C, 4 and 8 MPa, whereas it increased with rising SO₂ levels at 25°C, 8 MPa. SO₂ worsened water chemistry by reducing the contents of CO₃^2- and HCO₃^-, but enhancing the contents of H⁺, SO₃^2- and HSO₃^-in the CO₂-saturated water phase at each CO₂ phase state. In the gaseous and supercritical CO₂-saturated water environment, a thin or absent corrosion product was observed, with the adsorption of SO₂ and its derivatives being the dominant factor. In the liquid CO₂-saturated water environment, the corrosion product competed with SO₂, HSO₃^-, and SO₃^2- for adsorption sites, accelerating the corrosion rate.