Abstract
The governing differential equation for the potential field in a typical electrolyte encountered in cathodic protection (e.g. seawater) is Laplace's equation. Green's second identity allows this equation to be written in Boundary Integral form which may be reduced to a system of linear algebraic equations using the techniques of Finite Elements. The resulting method is known as the Boundary Element Method. Since all the unknowns are on the boundary the system of equations is much smaller than that obtained using domain techniques such as the Finite Element or Finite Difference methods. Data preparation is similarly greatly reduced.
Although the governing differential equation is linear, the boundary conditions are typically non-linear and time dependent due to the nature of the polarization curves which relate the potential and current density on anode and cathode. Fortunately, although the Boundary Element Method cannot easily model non-linearities within the domain, non-linear boundary conditions are easily incorporated.
An example of the method applied to analyse the current density dis tributions on a real structure, a design for an oil production platform now under construction for the Worth Sea, gives some idea of the power and practicality of the method.
