Numerical Modelling of CP Systems for Marine Offshore Structures—Life Extension and Optimisation

A great number of offshore marine structures such as jacket platforms, monopiles, FPSOs and subsea pipelines are reaching the original design life and several alternatives for retrofitting are available to extend their service life. Typical retrofitting approaches are based on impressed current or sacrificial anodes. This chapter presents an overview of the mathematical framework for galvanic corrosion and CP simulation, based on the boundary element method (BEM). Then, it describes how this type of modelling tool is used to conduct numerical optimisation of CP systems in marine offshore structures, using response surfaces and model surrogates to speed up and "optimise" the optimisation process. Finally, the concept is illustrated with a real-life example for the optimal design of a retrofit anode system for three offshore jacket structures electrically connected to each other, and in the presence of interfering subsea flowlines. The presence of such interfering objects makes it impossible to achieve satisfactory results if we only consider independent (non-interacting) designs for the flowlines and the jacket structures.