Optimum Design of Cathodic Protection for Long Pipeline

Abstract

A boundary element method (BEM) is developed for optimizing the locations and impressed currents of electrodes in a catholic protection system for a long underground structure such as a pipeline and an oil well casing. The cattodic protection system has usually been designed on the basis of past experience together with a limited number of empirical formulas applicable for a narrow range of conditions. The optimization is performed by minimizing the electric power necessary to keep the potential on the metal surface below a critical value. A long underground structure is often buried in soil with non-uniform electric conductivity. In this case, direct application of conventional multi-domain method for BEM analysis gives an unrealistic solution. To overcome this problem, the electric conductivity is modeled with a linear function of location. The polarization characteristics are also formulated to express its continuous change. A penalty function is used as a objective function which has a term taking a large value when the protection condition is not satisfied. To minimize the objective function, the Simplex method is employed. In order to demonstrate the usefulness of the method, some example problems are presented.