Abstract
The mitigation of corrosion in carbon steel pipelines due to the addition of corrosion inhibitors has traditionally been described by using adsorption isotherms. Consequently, current models of corrosion mitigation by inhibitors are based on the use of adsorption isotherms to predict surface coverage, inhibitor efficiency and ultimately the corrosion rate as a function of inhibitor concentration. However, a coverage does not properly describe the underlying electrochemical mechanisms, nor can it predict the resulting change in corrosion potential. The goal of this research is to analyze and explain how the underlying electrochemical reactions are affected by the presence of adsorbed corrosion inhibitor and the shift in corrosion potential that occurs. Two CO2 corrosion inhibitors are studied here: tail oil fatty acid / diehylenetriamine imidazoline and quaternary alkyl benzyl dimethyl ammonium chloride. A mechanistic model was developed based on electrochemical kinetics and by using a mitigation factor, θ, which accounts for the overall retardation in the anodic and cathodic reactions. It was found that the retardation of the electrochemical reactions affected by these inhibitor can be modeled by using a single parameter: surface coverage factor.
