The rates of electrochemical and precipitation reactions taking place on the steel surface are dependent on the chemistry of the aqueous phase in contact with the substrate. While the bulk speciation is often used to characterize the severity of the environment, large differences can exist between bulk and surface chemistries, leading to inaccurate representation of the corrosion phenomena. This issue requires a better understanding of the surface speciation. Given the fact that directly measuring surface speciation is a very challenging task, corrosion models must be employed to calculate these surface parameters based on the bulk chemistry. In the present work, an electrochemical model was developed for that exact purpose and used to predict corrosion behavior not only at the corrosion potential, but also under applied polarization, where surface and bulk chemistries differ greatly. This model has been extensively calibrated against experimental results in both corrosion product free conditions as well as in conditions where corrosion product layers form.