An effective boundary element method is developed for predicting corrosion and corrosion protection of a complicated structure. In this method, the region to be analyzed is divided at first into a target sub-region and other adjacent sub-regions. Then, equivalent- boundary-
condition related to an adjacent sub-region, which is defined as the
relationship between the potential and the current density on the interface dividing the adjacent end the target sub-region, is obtained by analyzing the adjacent sub-region with an appropriate model, e.g., a closed 3D model or an open axisymmetric model. Finally, the target sub-region is analyzed using these equivalent-boundary-conditions with an appropriate model, which can be of a type different from those for the adjacent other sub-regions. It is easy for this method to perform a trial and error type design of the target sub-region, because the same equivalent- boundary- conditions ean be used repeatedly. An example analysis is carried out for a cathodic protection system of seawater pump to demonstrate the wumey ad usefulness of this combined method. Keywords: boundary element method (BEM), combined analysis, 2D, 3D, axisymmetry, potential, current density, cathodic protection, galvanic corrosion, polarization curve, seawater, pump