Evaluation of Flow Coupled CO2 Corrosion Using CFD: Kinetics Hydrodynamics

摘要

A Comprehensive numerical model has been developed for computing corrosion rates generated by CO_2 saturated aqueous solutions in an internal flow configuration. The fundamental fluid flow is characterized by numerical solutions to Navier-Stokes conservation equations for mass, momentum and energy, accompanied by models to capture turbulence generated by the flow. Particularly, the near-wall flow is captured using advanced wall treatment approaches to accurately track the viscous sub layer behavior generated by the turbulent flow. The corrosion rates are then computed by modeling the electrochemical processes occurring at the metal substrate such as the cathodic reduction of carbonic acid, hydronium ions and the anodic oxidation of the metal component. Ionic species in the solution, such as the H~+, H_2CO_3, Fe~(2+) are explicitly tracked for their dissolution and generation during the overall corrosion process. Both charge and mass transfer components of limiting current components are computed while calculating the overall corrosion current. While CFD provides the species convection and diffusion information near the metal surface to characterize the mass transfer limiting current density, exchange current density computed using Tafel's correlation are used for charge transfer current limitations. The flow coupled corrosion model is validated against recorded corrosion rates occurring under tested pipe flow conditions at different pH, flow velocity, pressure and temperature conditions. Model is also tested against data generated by flow variations induced by geometrical non-uniformity, such as pipe geometry involving constriction, protrusion and expansion, to test the ability of the numerical model to integrate variations in hydrodynamics into the corrosion predictions. In all the cases presented, very satisfactory trends in the corrosion data are predicted. In sum, the overall predictive capability of a CFD coupled corrosion calculation process is demonstrated.