Study on the Time-Dependent Evolution of Pitting Corrosion in Flowing Environment

Abstract

Pitting corrosion is one of the most destructive forms of localized corrosion in oil-gas pipelines. Due to being obscured by corrosion products and little loss of material with small effect on the surface, this kind of corrosion is extremely insidious. In this work, a novel multi-physics model is proposed to investigate the growth behavior of pitting corrosion in the presence of fluid flow. Various physical and chemical phenomena are taken into account in a coupled scheme, including chemical reactions, electrochemical reactions, flow disturbance and the mass transport of species. The mass transport is attributed to diffusion, electro-migration and convection. The time-dependent evolution of the pit morphology is implemented via an arbitrary Lagrangian-Eulerian method. The mechanism of the pitting corrosion is revealed with the integration of flow field, local chemical environment and the electrochemical behavior within the pit hole. Special emphasis is put on the relationship between the flowing fluid and the corrosion behavior. The results show that the flowing fluid would result in an asymmetric distribution of the species concentration and corrosion current density within the pit hole. It is found that the pit growth dynamics is determined by the combined effect of solution chemistry and electrical field. It is also indicated that the pH in the bulk solution and the flow rate have a significant coupling influence on the pitting corrosion behavior.