Effect of O₂ on Corrosion Behaviour of X80 Steel in Environment of Oil Field Medium Containing CO₂

Effect of O₂ on the corrosion behaviour of X80 steel in the environment of oil field medium containing CO₂ and the relative corrosion mechanism were investigated through electrochemical test and immersion test. The results show that O₂ mainly affected the cathodic polarization process of X80 steel. Under low partial pressure of O₂(0-12 kPa), the free corrosion potential and free corrosion current density of X80 steel basically remained the same. But with the increase of partial pressure of O₂ (17-22 kPa), the corrosion rate of X80 steel increased; the free corrosion potential shifted positively; the electric double layer capacitance increased; and the polarization resistance, diffusion resistance and charge transfer resistance reduced. This resulted from the localized corrosion because the O₂ destroyed CO₂ corrosion product film on X80 steel surface.