Evaluation of the uniform current density assumption in cathodic protection systems with close anode‐to‐cathode arrangement

Abstract

AbstractCathodic protection modelling often involves making assumptions about geometric features and material characteristics that directly impact accuracy of solutions. In the present paper, predictive power of the model using approximate uniform current boundary condition on the cathode is validated against the model using nonlinear cathode polarization curves representative of low‐carbon steel structure of common geometry, buried in soil or immersed in seawater. In order to explore the worst case scenario, the present example deals with a large diameter pipeline (Ø 1.2 m) and a wire anode (Ø 0.05 m), separated by a distance d, both embedded in an infinite space of conductivity κ. The calculation is performed for the two sets of parameters – κ and limiting current density of oxygen reduction, il. For simulation of CP systems in seawater κ = 4.79 S/m and il = −86 µA/cm2 and for CP system in soil, κ = 10−3 S/m and il = −1.1 µA/cm2. The other physical parameters were identical for both systems (Tafel slopes ba = 60 mV/dec, bc = 120 mV/dec and equilibrium potentials $\phi _{\rm e}^{\rm a} = - 700\,{\rm mV}$, $\phi _{\rm c}^{\rm a} = - 800\,{\rm mV}$). The results were visualized to best exemplify the general trends in potential and current distributions that appear upon switch between uniform and nonlinear cathodic boundary conditions.