Recent Developments in Mechanistic Modeling of Mild Steel Corrosion in H2s Environments

Abstract

The corrosion of mild steel in hydrogen sulfide (H2S) environments, as a serious concern in the oil and gas transmission pipelines, has been investigated over the past decades. However, the mechanisms of corrosion of mild steel in H2S environments have been studied in more detail only in recent years. In the present study, a comprehensive mathematical model was developed based on the recent advancement in the mechanistic understanding of corrosion processes in aqueous H2S environments in order to predict the corrosion rate and the polarization response of steel in this system. In this model, the cathodic reaction was developed based on H2S dissociation and its buffering effect. The only cathodic reaction in the system is hydrogen ion reduction. The results confirmed that H2S buffering capacity can thoroughly explain the “double wave” characteristics of the cathodic polarization as well as the increased cathodic limiting current densities of steel in this system. In addition, the anodic iron dissolution reaction was revised by considering the effect of hydrogen sulfide on this reaction. On that account, a reaction pathway with the sulfide intermediates was introduced parallel to the acidic iron dissolution reaction. The developed model was then compared with the available experimental data in the literature, and it was shown that it could reasonably represent the characteristic electrochemical behaviors of H2S corrosion of steel. Furthermore, the predicted corrosion rates are shown to be in good agreement with experimental data over a wide range of experimental conditions.