Effect of O2 contamination on carbon steel pseudo-passive scales in CO2 aqueous solutions

Waters containing CO2 can lead to the formation of a “pseudo passive” protective corrosion product layer on carbon steel, however an oxygen contamination can significantly alter the corrosion behavior. The carbon steel API 5 L X65 specimens were tested in a CO2 saturated solution with small concentrations of O2 (90−270 ppb). Electrochemical techniques, Raman spectroscopy and SEM were used for determining the corrosion product layer properties. Oxygen contamination induces pits that result in a significant increase and instability of the open circuit potential. Removing the oxygen contamination, stops pits propagation and the carbon steel surface regains its “pseudo-passive” behavior.