Modeling of cathodic protection systems by the finite element method

A numerical approach for the determination of potential and current distributions in corroding systems by application of the finite element method was used to obtain solutions to the potential field equations in two and three-dimensional domains. Computer simulations were performed with this mathematical method to model the potential and current distributions of power plant steam condensers that use natural marine water for cooling. The required material polarization behavior was determined for the system conditions from experiments with rotating cylinder electrodes. Simplification of complex geometries, such as tube arrays, allowed smaller meshes to be used for these analyses.;Results of the simulations were used to estimate corrosion rates on these structures and to evaluate the effectiveness in controlling corrosion by cathodic protection. The design of sacrificial anode type cathodic protection systems for a number of units was facilitated by such computer simulations. Installation of corrosion monitoring and data acquisition instrumentation for the modeled units permitted a comparison to be made between predicted and observed performance. Tubesheet potentials, anode currents, and circulating water conductivity and temperature were recorded. Field data for the operating cathodic protection systems supported the results of the computer simulations.;Separate simulations on selected subdomains produced a detailed study of the kinetic and geometric variables which influence the current entering a tube. These results led to the development of correlations to estimate tube currents for galvanically-coupled and cathodically-protected tubes.