Modeling Cathodic Protection in the Presence of Interference

Understanding the interactions between CP systems is becoming more complex particularly in the marine and offshore industry. The search for oil and gas in deeper waters and remote environments has resulted in engineering designs with many components on the seabed as well as at the sea surface. However, traditional design methods are inadequate in these situations due to the important interactions that may occur between CP systems [19]. 

It was common in the early CP models to make the assumption that the internal resistance of the structure through which the current returns was negligible compared with that of the electrolyte and the electrode kinetics. Therefore it was possible to ignore the metal resistance when formulating the modeling equations and hence assume that there was no IR drop in the return path. Pipelines present a typical situation where this assumption is not valid as over a long pipeline there is significant drop in the potential due to the internal resistance of the pipeline metal. 

Another important situation for which the traditional assumptions are not valid is in new large-scale deep water oil and gas developments where not only there are long pipelines present but where hundreds of individual flowlines and connections introduce electrical connection paths that must be considered. Standard BE modeling tools are inadequate in these situations as interference will occur between the 

CP systems, causing significant currents (and therefore voltage drops) to occur in the flowlines connecting the components. 

For equilibrium the current flowing along the flowline to either the SPM or the FPS must balance. The currents flowing into or out of the metal surfaces on the SPM and the FPS can be determined by integrating the normal current density calculated by the BE over the 

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