Simulation and Optimization of Cathodic Protection Designs

Early predictions of corrosion rates and estimates of adequate CP have traditionally been based on case studies and sample exposure tests. Applying these techniques to real structures usually involve extrapolations, use of large safety factors and ongoing corrections and maintenance of the system. In the late 1960s the finite element method was applied to the problem by discretization of the electrolytically conductive environment into a mesh and solving numerically with Laplace equations to define the intersection points, or nodes of this mesh [17]. 

However, creating a finite element mesh can be an extremely tedious and time-consuming process and, even when the mesh generation process is automated, it is difficult to perform a simulation when there are large geometry scale differences in the model, which is exactly the case found in most corrosion control problems where anodes are small compared to the size of the structure and the problem areas are most likely in corners and areas of complex geometry. 

In the late 1970s, boundary element (BE) methods became available. As the name implies, the BE numerical method still requires mesh elements to be created, but now only on the boimdary (or surfaces) of the problem geometry (Fig. 13.41). The main advantages of boundary elements for an ICCP analysis are [17] 

1 Modeling Ship Impressed Current Cathodic Protection 

The design goal of an ICCP system is to produce an evenly distributed protection potential on a structure as well as to reduce the power consumption of the anodes to a minimum. The available design variables are the number of anodes, their location, and the location of the reference cells. The constraints on the design are the values of the potential on the structure. In order to provide adequate protection the potential must be less than a specified value, for example, -800 mV. In order to prevent overprotection the potential must be greater than a specified value, for example, -900 mV. An optimum solution can be obtained by combining an automatic optimization procedure with the BE model of the ICCP system. In this context Eq. (13.3) describes the electrochemical corrosion profile for the wetted surface of a ship hull is [18] 

---