Investigation of Cathodic Reaction Mechanisms of H2S Corrosion Using a Passive SS304 Rotating Cylinder Electrode

The internal corrosion of pipeline steel in the presence of hydrogen sulfide (H2S) represents a significant problem in the oil and gas industry. Its prediction and control pose a challenge for the corrosion engineers. In previously published research by the same authors, an electrochemical model of H2S corrosion was developed in both pure H2S and H2S/CO2 aqueous systems. An additional electrochemical cathodic reaction, direct H2S reduction, was uncovered based upon the carbon steel corrosion experimental results. However, in the carbon steel corrosion experiments, the Tafel's region of cathodic reactions experienced interference by the anodic iron dissolution reaction, making the electrochemical kinetics of cathodic reactions unclear. In the present study, experimentation was conducted to better resolve the direct reduction of H2S while minimizing the effect of the anodic reaction by using a passive stainless steel working electrode. The electrochemical kinetics parameters for H2S reduction (i. e., Tafel slope, exchange current density, and reaction order with H2S concentration) were determined. Moreover, the electrochemical kinetics parameters for H+ reduction were also revisited.