Abstract
Corrosion inhibitors can behave as cathodic inhibitors when they mainly suppress the cathodic reaction. These can be anodic inhibitors when they mainly suppress the anodic reaction. When corrosion inhibitors interact with both cathodic and anodic reactions, they may behave as mixed inhibitors. This paper documents the electrochemical characterization of a phosphate ester based inhibitor which creates protection from oxygen corrosion. Potentiodynamic polarization is used to determine the inhibitor behavior during the anodic and cathodic processes of corrosion. A system of a carbon steel electrode in 3.5% NaCl /3% O2 in 97% CO2 with and without an inhibitor is defined and tested. The oxygen corrosion mechanism on carbon steel was established through the comparison of the cathodic and anodic currents in the presence of 3% O2 in 97% CO2 and 100% CO2. The probable mechanism of inhibition by imidazoline and phosphate esters as well as the role of a sulfiding agent was explored. In the presence of oxygen, the anodic more than the cathodic inhibition performance was more related to the overall corrosion inhibition. As expected, phosphate ester based inhibitors demonstrated to be superior to imidazoline base inhibitors to abate oxygen corrosion.