Iron dissolution kinetics of API 5CT C110 carbon steel in acidic environments: A numerical modelling approach

This study investigates the reaction kinetics of API 5CT C110 carbon steel dissolution in different acidic environments using electrochemical techniques. An optimal analysis time was determined, outside the active material dissolution and transient regions. Electrochemical impedance spectroscopy (EIS) at open-circuit potential revealed two distinct reaction time steps in the different acidic environments. The effects of anion concentrations on the reaction mechanisms were determined under accelerated anodic conditions. The findings demonstrate that reaction rates are influenced by the interdependence between surface potential and solution species. An alternative numerical modelling approach was developed for EIS data analysis, achieving an accuracy of 98.8 % for a three-time-step model, representing a previously unreported mechanistic step. Furthermore, the model accounts for the reactant concentrations that influence the reaction rates. This method improves accuracy, simplifies parameter optimisation, and enhances interpretability compared to conventional equivalent circuit fitting. • Impedance data provides insight into transient corrosion mechanisms. • 24–48 h identified as optimal window for current electrochemical studies. • EIS confirmed two-time steps under OCP, consistent with the Heusler mechanism. • A third time step emerged with high anion concentration and anodic polarisation. • Formula fitting method achieved > 98 % agreement, outperforming circuit fitting.