Carbon Dioxide CO2 Corrosion Mechanism(In pipe lines of natural gas and oil transportation)

Carbon dioxide which is present naturally is also injected purposely into gas wells to enhance oil recovery. In the process of recovery it is required to sustain CO₂ environment also.

Carbon Dioxide CO₂ Corrosion Mechanism

Although a lot of reaction mechanisms exist for CO₂ corrosion, the most widely accepted

Mechanism is given as follows.

CO₂ hydration:

CO₂g ↔ CO₂ aqu --------------- (1)

CO₂ aq + H₂O (l) → H₂CO₃ aq -------------(2)

The carbonic acid dissociates into bicarbonate and carbonate ions in two cathodic steps. The cathodic reaction also includes reduction of hydrogen ions.

2 H₂CO₃+ 2e^- → H₂+ 2HCO₃^{- -----------------} (3)

2HCO₃^-+ 2e^- → H₂ + 2CO₃^2- -----------(4)

2H⁺+ 2e^- → H₂  -------------------(5)

The CO2 corrosion reaction includes the anodic dissolution of iron at the metal surface and given by,

Fe → Fe⁺²+ 2e^-  -------------------(6)

The overall electrochemical reaction of CO2 corrosion is given by,

Fe + CO₂ + H₂O → FeCO₃ + H₂ ------------------------------(7)

Thus, the overall reaction of CO₂ corrosion leads to the formation of FeCO₃ with the liberation of hydrogen gas. FeCO₃, if precipitated, could form a protective film on the metal surface and prevent the metal from further corrosive attack. The properties of the FeCO₃ layer are greatly influenced by the corrosion rate and environmental conditions.

In spite of extensive research on CO₂ corrosion over decades, it is still unclear which of the three cathodic reactions dominates the corrosion reaction in different environmental conditions. The net cathodic reaction current is assumed to be the sum of all the three cathodic reaction currents and according to mixed potential theory this sum must equal the total anodic dissolution current. From this complex corrosion mechanism it can be expected that the corrosion rate of carbon steel can be greatly affected by the environmental factors like fluid hydrodynamics which might affect the rate of the reaction.

See Also:

Carbon Dioxide CO₂ Corrosion Mechanism in steel pipe lines

Effect of pH on Carbon Dioxide CO2 corrosion on carbon steel pipe lines

Effect of temperature on Carbon Dioxide CO2 corrosion on carbon steel pipe lines


Effect of hydrodynamics on Carbon Dioxide CO2 corrosion on carbon steel pipe lines 


Effect of CO2 partial pressure on  CO2 corrosion on carbon steel pipe lines


Effect of Fe²⁺ concentration on Carbon Dioxide CO2 corrosion on carbon steel pipe lines