Observation and analysis of pseudopassive film on 6.5%Cr steel in CO2 corrosion environment

• Corrosion rate of 6.5%Cr steel was considerably lower than that of 3%Cr steel.
• Pseudopassivation was observed in the anodic polarization curve of 6.5%Cr steel.
• Formation and flaking off of pseudopassivation film on 6.5%Cr steel surface during potentiodynamic polarization were recorded.
• The pseudopassivation behavior and pseudopassivation breakdown was caused by the formation and damage of the Cr(OH)3 film.
• Pseudopassivation reduces the corrosion rate of 6.5%Cr steel.

Corrosion rate of 6.5%Cr steel was considerably lower than that of carbon steel and 3%Cr steel. Current density underwent a drop in certain potential range when potentiodynamic polarization curve was tested. Microscope with camera was used for in situ recording of the change in steel surface. The flaking off of the film, which occurred at a certain potential range, was recorded. The results of electrochemical measurements indicated that the film, which mainly consisted of Cr(OH)3, was a pseudopassive film. When 6.5%Cr steel was polarized or corroded, pseudopassive film formed. Pseudopassivation of 6.5%Cr steel was closely related to low corrosion rate.