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 SO 2 on the corrosion of X65 steel and water chemistry during liquid, gaseous, and supercritical CO 2 transportation. Results indicated that less than 100 ppm SO 2 significantly influenced corrosion processes. In the water-saturated CO 2 environment, higher SO 2 concentrations led to elevated general corrosion rates . Interestingly, in the CO 2 -saturated water environment, the general corrosion rate decreased at 35°C, 4 and 8 MPa, whereas it increased with rising SO 2 levels at 25°C, 8 MPa. SO 2 worsened water chemistry by reducing the contents of CO 3 2- and HCO 3 - , but enhancing the contents of H + , SO 3 2- and HSO 3 - in the CO 2 -saturated water phase at each CO 2 phase state. In the gaseous and supercritical CO 2 -saturated water environment, a thin or absent corrosion product was observed, with the adsorption of SO 2 and its derivatives being the dominant factor. In the liquid CO 2 -saturated water environment, the corrosion product competed with SO 2 , HSO 3 - , and SO 3 2- for adsorption sites, accelerating the corrosion rate. • Less than 100 ppm SO 2 can take leading role and alter corrosion of mild steel. • General corrosion rates in CO 2 -rich phase rose with SO 2 content at each CO 2 state. • CO 2 state affected variation of corrosion rate with SO 2 content in water-rich phase. • The adsorption of SO 2 , HSO 3 - and SO 3 2- affected corrosion in water-rich phase.