Lawrence Berkeley National Laboratory

We discuss kinetic and thermodynamic aspects of carbon steel corrosion in CO2-containing NaCl fluids up to 240 °C. Crystalline nm-thick Fe-oxide films only form at 160 °C and 240 °C providing instantaneous and moderate corrosion protection. The absence of Fe-oxide at 80 °C results in high initial corrosion rates until a moderately protective, but thick and porous, FeCO3 film forms. From the metal/film interface it grows inwards by replacing ferrite with FeCO3. TEM reveals a precursory, likely hydrated and chloride-containing, phase that predates FeCO3 formation. Thermodynamic predictions agree well with experimental results in that Fe-oxide formation is favored over FeCO3 towards higher temperatures.