Aqueous carbon dioxide corrosion of carbon steel is an electrochemical process involving the anodic dissolution of iron and the cathodic evolution of hydrogen. The overall reaction is shown in Equation 1 (LaTex Code):

$$ Fe + C{O_2} + {H_2}O \to FeC{O_3} + {H_2} \tag{1}$$Depending on the environmental condition, this reaction is often followed by the formation of a scale, such as iron carbonate (FeCO₃) and/or, particularly at elevated temperatures, magnetite (Fe₃O₄). The protectiveness of such scales depends on the conditions under which they form. In particular, the type of steel, temperature, solution pH, electrolyte composition (e.g. chloride content), and partial pressure of carbon dioxide (pCO₂) and hydrogen sulfide (pH₂S) all affect the nature and kinetics of the scale formation. You will find a more detailed discussion on the overall anodic and cathodic reactions during carbon dioxide corrosion of carbon steel in this post.

Example

References

1. S. Nešić, “Key issues related to modeling of internal corrosion of oil and gas pipelines – A review”, Corrosion Science 49, (2007): p.4308–4338.