Tafel-Piontelli model to predict the corrosion rate of carbon steel exposed to strong and weak acids: experimental validation and application to sweet corrosion

Sweet corrosion of carbon steel represents a significant challenge to Oil & Gas production plants. This form of corrosion is caused by carbonic acid in the transported fluids, resulting in severe corrosion with high penetration rates, influenced by factors such as pH, temperature, and other environmental conditions. Developing reliable tools to predict the corrosion rate of metals in acidic environments is essential for designing effective management strategies, both during the initial stages and throughout the service life of any infrastructure. The Tafel-Piontelli model is a mechanistic framework developed to address this purpose. Its theoretical foundations are based on the Tafel law, which governs the kinetics of many corrosion processes in aqueous solutions. The model represents the environment in contact with the metal surface as an acidic electrolyte with controlled water chemistry, where hydrogen evolution is the dominant cathodic reaction. The model was validated through potentiodynamic polarization, surface analysis, and mass loss rate measurements conducted in strong and weak acids under different pH levels and temperature conditions. This study presents the model's general framework and a summary of its experimental validation. The results are promising: the model accurately predicts the corrosion rate in strong and weak acids, along with its exponential dependence on temperature and pH. Preliminary findings on the impact of water flow on corrosion rates in acidic conditions are also discussed. Additionally, the model’s predictive performance is compared with established industry corrosion models for sweet corrosion in Oil & Gas infrastructure under typical operating conditions, showing a strong correlation with experimental data.