Modeling and experimental study of CO2 corrosion on carbon steel at elevated pressure and temperature

Corrosion of carbon steel in carbonic acid environment largely depends on surrounding conditions such as CO2 partial pressure, temperature, flow velocity, and water chemistry. This article presents results of experimental and theoretical investigations conducted on corrosion of carbon steel (AISI C1045) in brine (2% NaCl solution) saturated with mixed gas containing carbon dioxide and nitrogen. Experiments were carried out in a 2-liter autoclave at 0.83 MPa varying temperature and CO2 partial pressure. Linear polarization resistance (LPR) and weight loss (WL) techniques were utilized to measure corrosion rate. Test duration was 187 h. In the presence of CO2, corrosion rate increased sharply in the first 10 h, followed by sharp reduction. Results show that temperature is the most dominant factor in affecting CO2 corrosion. The maximum corrosion with and without the presence of CO2 was observed at 43 degrees C. In addition to experimental study, a new model has been developed to predict corrosion rate of steel in corrosive environment as a function of temperature and pressure. The model is applicable for non-scale forming condition. It considers electrochemical reactions that occur at steel surface, mass transport, and homogenous chemical reaction that occurs in the bulk solution. The model uses an improved solubility model to predict concentration of dissolved CO2 and other species. Model predictions are validated using the experimental measurements. Predominantly, results show good agreement between model predictions and measurements demonstrating the validity of the assumptions made in the establishment of corrosion model. (C) 2015 Elsevier B.V. All rights reserved.