Effect of O₂, SO₂ and NO₂ Impurities on Corrosion Behavior of X52 Steel in Supercritical CO₂ Transport Environments

The differences in corrosion behavior of X52 steel exposed to supercritical CO₂-H₂O environments with the impurities of O₂, SO₂ or NO₂ were compared by combining the methods of corrosion test, surface analysis technology and water chemistry simulation calculation. The influence mechanism of various impurities and their interaction on the corrosion of the steel were discussed. The results showed that the corrosion rate of X52 steel was only 0. 007 mm/a in supercritical CO₂-H₂O environment containing 0. 02% (volumn fraction) O₂, while the rate of X52 steel was higher than 0. 300 mm/a in the environment containing 0. 02% SO₂ or 0. 02% NO₂. The interaction between O₂ and SO₂ or O₂ and NO₂ promoted the formation of corrosive substance of H₂SO₄ or HNO₃, thus leading to a significant synergistic effect on the enhancement of corrosion rate. The corrosion and film formation processes of X52 steel were mainly controlled by the impurities in supercritical CO₂-H₂O environments. The different influences of the impurities and their reaction products on the precipitation amount as well as chemical environment of aqueous phase resulted in the disparities in the corrosion degree of X52 steel.