LAUSR

Abstract The corrosion behavior of X65 steel in water-saturated supercritical CO 2 system containing NO 2 with or without O 2 , H 2 S and SO 2 impurities was investigated using weight loss measurement and surface analysis techniques. The interactions between NO 2 and O 2 , SO 2 or H 2 S promoted the formation of extra corrosive species and subsequently changed the corrosion film characteristics. In water-saturated supercritical CO 2 -NO 2 -O 2 -SO 2 -H 2 S system, FeSO 4 and S preferentially formed in the early corrosion stage due to the impurity interactions. As the corrosion time prolonged, (NH 4 )Fe 3 (SO 4 ) 2 (OH) 6 and FeOOH formed due to the subsequent reactions of the impurity interaction products, and S disappeared in the corrosion scale via participating in the subsequent corrosion reactions during long-term corrosion. Localized corrosion was initiated by the inhomogeneous precipitation of acid-rich water in the presence of NO 2 . However, the propagation rate of the corrosion pit in depth direction greatly reduced with time, and the corrosion morphology of X65 steel shifted from localized corrosion towards general corrosion during long-term corrosion.