It is a quite complicated and heavy work to calculate potential distribution in a regional cathodic protection system with boundary element method (BEM). The node numbers of the model for calculation can be reduced and computer operation time can be shortened by using cylindrical element discreting method, if the geometric shape of the object to be protected is suitable for partitioning into cylindrical elements and the potentials on cross-section periphery are approximately equal. In previous work, the variable error polyhedron method was used to optimize the model. Since the fitting of the cathodic polarization curve was simplistic, the stability of the optimization was poor. In this paper, the piecewise linear fitting is applied, thus the stability of the optimizing process is improved. This improved calculation method has been used for the cathodic protection design of some oil well cases.
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