Fundamental Aspects of CO2 Corrosion

Abstract The paper summarizes the present day knowledge on the electrochemical corrosion of metals in oxygen-free CO2 environment. Fundamental aspects of the corrosion mechanism, kinetic factors and effects of influencing parameters on uniform and localized corrosion are discussed emphasizing problems in the oil and gas industry. The rate of uniform corrosion of bare iron surfaces is controlled by the kinetics of the hydrogen evolution which involves the heterogeneous hydration of chemisorbed CO2 as rate determining step. New experimental data are presented supporting this mechanism. However, if the metal surface is coated with corrosion product layers mass transfer can become the limiting factor. The rate of uniform corrosion and the susceptibility to localized corrosion depends on the stability and permeability of these surface layers which are a function of CO2 partial pressure, temperature, salt content of the corrosive media, presence of certain chemicals (e.g. CO, H2S), alloy, flow and mechanical stress. Experimental results are presented demonstrating the influence of important parameters on the stability of corrosion products layers with respect to uniform and localized corrosion. Evidence is given that the pure system CO2-H2O can cause stress corrosion cracking at low alloy steels under technical relevant conditions.