The prediction of proper repair times for reinforced concrete structures in marine environments is an important task for structural maintenance and safety. Chloride attack is the primary threat to marine reinforced concrete structures. Chloride attack can be expressed using a diffusion equation based on Fick’s second law. However, for structures that are strongly affected by the shape of the structural sections, or in the case of a surface with repaired concrete, one-dimensional analytical solutions are not sufficient for predicting long-term chloride ion penetration because of shape effects and domain discontinuity. The purpose of this study is to predict the proper repair time of reinforced concrete structures in marine environments that are exposed to long-term chloride attack. In this research, a chloride attack simulation program involving application of a two-dimensional finite difference method was developed to predict chloride ion penetration. Each discretized element of the finite difference method was implemented as an object to allow us to store the required parameters and to calculate the chloride content value independently in order to enable simulation of the discontinuity of the problem domain. The simulation program was applied to the Saemangeum tide gate bridge piers, and the results are presented herein. The results show that the deterioration of steel bars in marine reinforced concrete structures is strongly affected not only by the concrete material but also by the shape of the structures. © 2016 American Society of Agricultural and Biological Engineers.