CO2 corrosion behavior and atomic processes at the corroding interface of a high strength low alloy tempered martensite tubular steel were investigated for 177 h at 70 and 80 °C using electrochemical and surface evaluation techniques. Linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) were applied to assess the corrosion rate and evolution of atomic processes and interfacial phenomena. The corrosion rate increased at the beginning to a maximum, then, it declined with time at both temperatures. Variation of pH was monitored for the test duration, and it changed from 3.78 at the beginning to 5.82 and 5.94 for 70 and 80 °C respectively. EIS measurements and equivalent circuit modeling demonstrated the formation of a porous scale upon beginning the experiments. Increase in charge transfer resistance with time indicated a decrease in porosity of scale, increasing its protectiveness. X-ray diffraction analysis did not detect formation of iron carbonate in these conditions.

Subject
Cementite, Electrochemical impedance spectroscopy, Steel surfaces, Precipitation (solids), Corrosion rate, Iron, Acidity, Corrosion products, Constants, Sodium chloride solution, Steel, Linear polarization resistance, Martensite
Keywords:
Downhole Tubular Steels, CO2 Corrosion, Polarization Resistance, Electrochemical Impedance Spectroscopy
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2012
Association for Materials Protection and Performance (AMPP)
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