Multiphysics Modeling of Pitting Corrosion Evolution in Carbon Steel Under Industrial–Coastal Atmospheric Conditions

To investigate the pitting evolution behavior of carbon steel in industrial–coastal atmospheric environments, a multiphysics numerical model was established by coupling tertiary current distribution, mass transport, and deforming geometry based on electrochemical corrosion mechanisms. Based on this framework, the effects of pH, salt concentration, and relative humidity (RH) on the pitting corrosion rate were systematically analyzed, and a predictive model for the pitting rate was subsequently developed. The results indicate that the pitting morphology gradually evolves from an initial conical shape to a hemispherical morphology and eventually develops into a quasi-cylindrical form. When the pH value increases from 6.0 to 7.0, the pitting rate decreases significantly, with a maximum reduction of 23.96%. Within the salt concentration range of 0.5%–1% (mass fraction), increasing salt concentration markedly accelerates the pitting process, resulting in a maximum increase in the pitting rate of 10%. In addition, the pitting rate exhibits a pronounced peak within the RH range of 72%–77%. The corrosion rates predicted by the proposed model are in good agreement with the experimental results, with relative errors within 5%. These results indicate that the numerical model and prediction formula established in the present study can reasonably predict the pitting evolution behavior and corrosion rate of carbon steel.