Design

The aim of the cathodic protection systems design is to define the number, the mass, sizes and the distribution of the anodes in order to be sure that the criterion of the potential at any point during the planned lifespan for the system is respected. Generally it is carried out in a simple way to be easily implemented, which especially requires the experience of the designer.

In some complex cases, using a software can be necessary. The purpose is to determine the distribution of the electrode potential at any point of the system we want to protect.

This distribution of the potential is modelled for different values of the protection current. The useful parameters for these calculations have two different origins:

• geometric: sizes and shape of the structure, shapes and positions of the anodes,
• physicochemical, depending on the environment around the structure: nature (ground, etc), electrical resistivity, chemical composition, if necessary temperature.

Calculations of the distribution of the potential are made in a numerical way by the finite element method or by the integral equations one. In the most elaborated methods, the evolution of the surface quality under protection (deposits, etc.) is taken into account. The distribution of potential is then obtained overtime: for example, just after start and a few years later.

The results of these calculations enable to locate the areas where cathodic protection may be not sufficient. They also enable to determine the possible interactions between two independent systems of cathodic protection but applied to close structures.