Multi-physics coupling analysis on the time-dependent localized corrosion behavior of carbon steel in CO₂-H₂O environment

Localized corrosion of carbon steel in CO₂-H₂O environment is a long-standing challenge faced by the oil and gas industry, because of its unfeasible detection and high propagation rate. Numerical modelling can overcome the limitations of the spatial and temporal scales in the experimental studies, thus becoming a valuable complement. A multi-physics coupling model is established to investigate the evolution of localized corrosion of carbon steel in CO₂ aqueous environment. The complex interactions among the kinetics of electrode reactions, multicomponent reactions, mass transfer and the deposition of corrosion products are coupled into the model, achieving a comprehensive and physically realistic description of the actual corrosion process. The arbitrary Lagrangian-Eulerian method is implemented to track the moving metal/solution interface. Special emphasis is put on the coupling mechanism among the underlying processes at different time and length scales. This study characterizes quantitatively the time-dependent corrosion behavior, including the distributions of potential and species concentration within the corroding pit, corrosion current density and pit morphology. The inherent relationship between the corrosion behavior and the local corrosive environment within the pit is revealed. The results indicate that the competition between the chemical effect and electrical effect determines the trend and distribution of corrosion current density. The pit shape and cathode/anode area ratio have a great influence on the corrosion behavior due to the coupled role of local solution chemistry and electrical field.