Essential criterion for evaluating the corrosion resistance of 3Cr steel in CO2 environments: Prepassivation

The low corrosion rate of 3Cr steel is caused by prepassivation, which is believed to be related to the formation of a Cr(OH)3 layer on the surface of the steel, thus modifying the anodic reaction. The open-circuit voltage (OCP) of 3Cr steel exhibited a tendency to increase over time from −0.67 to −0.48 V. Simultaneously, the solution pH near the substrate decreased, which affected the cathodic reaction with the possible participation of the direct reduction of H+. Modifying both anodic and cathodic reactions maintains the OCP in the desired potential range, causing spontaneous prepassivation to occur.