On the extension of CP models to address cathodic protection under a delaminated coating

Cathodic protection models for pipeline and other metallic structures developed to address the presence of coating flaws or holidays do not account explicitly for the presence of a delaminated region surrounding a holiday. The potential drop in the delaminated region was obtained by solving the coupled, non-linear, partial differential, governing equations that describe transport and electrochemical reactions within the delaminated region. The results were used to develop an analytic expression for the potential drop across the delaminated region as a function of delaminated region length and the resistivity of the bulk environment exterior to the holiday. Expressions developed using this approach can be utilized by existing cathodic protection models to deliver improved potential distributions along protected metallic surfaces. The simulations were used to test the commonly employed assumption that transport by diffusion can be neglected in the delaminated region. The influence of diffusion on current was shown to be significant.