Corrosion Behavior of Pipeline Steels X65 and X70 in CO₂-saturated Produced Water

Corrosion behavior of X65 and X70 in CO2-saturated medium simulating Henan oilfield produced water was studied using static weight-loss tests, electrochemical tests and morphology observation. The results indicated that X70 and X65, whose microstructures were “PF+P” and “AF+QF+M/A island” respectively, could both form a corrosion product film with a form of “porous outer layer + uniform dense inner layer + no pitting basic layer”, which possesses certain protective effect. The corrosion rates of X70 and X65 changed with time, pH and Cl- concentration, following a similar regularity. X70 exhibits better comprehensive corrosion resistance than X65. The electrochemical corrosion mechanism of X65 and X70 is that anode is controlled by activation while cathode by diffusion of HCO3-. The effects of CO2, Cl- concentrations and pH on the law and mechanism of electrochemical corrosion reactions are somewhat different.