Effect of pH on the corrosion inhibition of mild steel in CO₂ saturated brine solution

Work has been performed to investigate the effect of pH on the performance of a tertiary amine possessing a single carboxylic acid group. The efficiency of this inhibitor and speed at which the efficiency increased were able to show a strong pH dependency, indicating that in such systems pH monitoring is important. Measurements have revealed that when the pH was lowered from 6.5 to 3.9 different changes in corrosion potential were observed after inhibitor addition and that the efficiency of the inhibitor decreased with increasing acidity. It is believed that cause (on clean and pre‐corroded specimens) is related to variations in the chemistry of the inhibitor such that at pH 6.5 inhibition is primarily due to O^‐ adsorption at anodic sites, while at pH 3.9 decreased corrosion rates occur as a result of the inhibitor loosely lying flat at the metal solution interface. It is also proposed that between the pH range studied the steel surface consists mainly of anodic sites.