A Mechanistic Model for Predicting Localized Pitting Corrosion in a Brine Water-CO2 System

This paper proposed a mechanistic model to simulate internal pitting corrosion rate of pipeline numerically in a water-CO₂ system.  The computational domain consists of a hemispherical pit and a thin boundary layer of liquid solution.  The mesh was generated using triangular elements with Cartesian coordinates, whereas a moving mesh method was selected to track the pitting growth.  The ionic flux of chemical species is governed by the Nernst-Planck equation.  Specifically, the convection term was calculated by solving the Navier-Stokes equations.  The electric field was computed from the Poisson equation with electroneutrality.  The concentration distribution was solved through Fick’s Second Law.  Among them, the production or consumption rates of homogeneous chemical reactions were considered in the source term, whereas the electrochemical reaction rates at the anode and cathode were applied for boundary conditions.  The precipitated amount and porosity of scale were approximated in terms of local species concentration and solubility product constant.  Consequently, the growth rate of a pre-existing pit was predicted.  Furthermore, the effects of operating parameters such as pH, temperature, partial pressure of CO₂, boundary layer thickness on incubation time and pitting corrosion rates were characterized.  Experimental tests are being conducted to verify the developed pitting corrosion model.