Development of an expert system for analyzing galvanic corrosion problems by using the Boundary Element Method

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In order to reduce the economic loss due to galvanic corrosion, it is desired to develop an expert system based on a quantitative analysis of the corrosion behaviors. In this research, a method of the quantitative analysis was developed. A three-dimensional boundary element method was introduced for predicting electrogalvanic field responses resulting from anodic/cathodic interaction. Although the governing equation is linear (Laplace), the boundary condition, which is enforced based on experimentally determined polarization curves, is generally non-linear. Therefore, Newton-Raphson iterative procedure was employed. The validity and usefulness of the present prediction method were demonstrated by comparing the calculated results and the experimental data.To examine the computational accuracy of the boundary element method for predicting galvanic corrosion and cathodic protection in the actual complicated field, the galvanic field with a screen plate was analyzed by using single and mul … More tiple region methods. It was found that the difference between the computational results by the two methods increased with increasing screen height. However, the results by the two methods agreed well with each other by reducing the mesh size.A boundary element method was applied to determine the optimal impressed current densities in a cathodic protection system. In this system, enough current must be impressed to lower the potential distribution on the metal surface to the critical values. The optimal impressed current densities were determined in order to minimize the power supply for protection. The solution was obtained by using the conjugate gradient method in which the governing equations and the protecting conditions were taken into account by the penalty function method.The electrochemical polarization curves of the materials considered are not always available. In this case, the inverse approach, in which the current density across the materials is estimated from the potential values in the electrolyte, is necessary. This inverse problem generally yields an ill-conditioned system of linear equations. A regularization method was introduced using the singular value decomposition of the coefficient matrix, and a criterion for determining an effective rank of matrix was presented. A numerical example of coating damage detection was presented to illustrate the usefulness of the method. Less