Influence of Turbulent Flow on the Localized Corrosion Process of Mild Steel with Inhibited Aqueous Carbon Dioxide Systems

Three percent sodium chloride (NaCl) solutions saturated with carbon dioxide (CO₂) were used to study the corrosion inhibition of mild steel samples under turbulent flow conditions. The performance of cetyl trimethyl ammonium bromide (CTAB) was tested with three different concentrations (20, 60, and 100 ppm) and three different pH values (3.8, 5, and 6). The rotating cylinder electrode (RCE) was used to test different turbulent flow conditions (1,000 rpm to 5,000 rpm). It was found that the inhibitor performance is a function of concentration and pH. A localized corrosion process was found on the surface samples and further research was carried out to determine its causes. With the use of cyclic anodic polarization curves and surface examinations, it was demonstrated that the localized corrosion process does not occur at a specific rotation speed. Potentiostatic experiments simulated the effect of shear stress and the instantaneous changes in corrosion potential (E_corr) observed when the rotation speed was increased. The electrochemical measurements and surface examinations showed that changes in E_corr to more positive values are more important in producing the localized process, and removing the electrostatically adsorbed inhibitor from the surface sample, than increases in shear stress.