An Integrated Prediction Model for H2S/CO2 Corrosion in the Pipe of Refinery

Corrosion of equipment is one of the most vital factors that results in serious process safety incidents. Though various types of equipment are subject to corrosion issues to different extent depending on the process conditions, the pipe and the piping network connecting units and equipment are relatively more vulnerable to corrosion. The vulnerability of a pipe to internal corrosion is predominantly due to the process conditions. Among the factors contributing to the internal corrosion, substances creating corrosive conditions in the pipe, such as CO2 and H2S, are the most common factors, followed by the flow condition of processes (flow rate and temperature). In this paper, a single-phase integrated prediction model for H2S/CO2 corrosion is developed to study a holistic effect of most important variables. The model investigates the electrochemical kinetics of corrosive substances, the scale formation conditions, and the flow conditions that have impact on the mass transport of corrosive species. The COMSOL software based on finite element method is used to simulate all these. The prediction results of present model are in good accordance with the measured field data. Additionally, it is found in the present model that the charge transfer current density has significant contribution to the corrosion rate, which is ignored in some other models. Apart from that, other comparisons have been made to investigate the impact on corrosion rate as a function of flow region, H2S and CO2 concentration, and temperature. Finally, the present model is able to provide the information on if there are FeS (or FeCO3) protective scales formed at steel surface