Effect of acetic acid on CO₂ corrosion of 3Cr low-alloy steel

The effect of acetic acid on the corrosion behaviors of 3Cr low-alloy steel in CO₂-containing sodium chloride solution was investigated by immersion test and electrochemical measurements. It is found that with addition of acetic acid the corrosion scale becomes much looser and sheds off easily. To the corrosion mechanism, the cathodic reaction will be enhanced by the direct reduction of un-dissociated acetic acid and the increase of anodic reaction rate is attributed to the fact that acetic acid degrades the protectiveness of corrosion scale and enhances corrosion of steel by decreasing the FeCO ₃ supersaturation in solution. The dissolution of Cr and the formation of Cr(OH)₃ dominate the anodic process when 3Cr low-alloy steel is immersed in CO₂-saturated solution with no acetic acid. And the dissolution of Fe is predominant in the anodic reaction and the steel is in active dissolution state in the presence of acetic acid.