Electrochemical Study of Corrosion Inhibition of Carbon Steel During Oil/Water Intermittent Wetting

Application of corrosion inhibitors in production systems containing oil and water is an economic method to protect carbon steel against internal corrosion. This study investigates how intermittent oil/water wetting of such a steel surface, simulating multiphase flow phenomena, impacts corrosion inhibition in exploration-production (high salinity with CO2) and refinery (low salinity without CO2) environments. The employed corrosion inhibitor was a pyrimidinium-type model compound, its effectiveness against corrosion being characterized using linear polarization resistance measurements and electrochemical impedance spectroscopy. Experimental results demonstrated that the presence of an aliphatic oil promotes corrosion inhibition in the exploration production condition, but failed to do so in the refinery condition. Electrochemical impedance spectroscopy revealed two different protection mechanisms in the presence of oil between the two environments. The inhibitor layer in refinery condition with oil was different from in the simulated exploration production environment after oil wetting. Results also demonstrated that the inhibitor in this study was physically adsorbed on the surface steel via electrostatic attraction. Anions, identified as chloride ions, played a critical role in inhibitor adsorption.