51316-7454-How Interference Can Impact The Life Of CP Systems. An FPSO Case Study

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Product Number: 51316-7454-SG

ISBN: 7454 2016 CP

Author: Robert Adey

Publication Date: 2016

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The design rules used to design CP systems in the main do not take into account the interference between the anodes provided to protect a structure or interactions between the structures themselves. CP systems will always interact with each other to some extent when they are in the same electrolyte even when there is no metallic electrical connection and this can radically affect the protection provided to the structure and the life of the CP system.This effect can be most clearly seen when anodes are closely grouped for example around a monopile or an anode sled where the effective output of the anodes can be radically reduced when compared to the classical anode resistance calculations. In these cases modelling has to be used in order to accurately determine the configuration required to protect the structure.A similar problem can occur when structures are in close proximity and electrically connected to each other. Even if the individual CP systems are well designed interference can degrade the performance of the CP system as the coatings degrade as the structure ages.A case study is presented involving the design of the CP system of an FPSO. The aim of the study was to verify the performance of the CP system to ensure that the structure was protected for the design life and the anodes had sufficient capacity. Computer modelling was used to simulate the performance of the CP system which comprised of an ICCP system and sacrificial anodes. The study identified some interesting and unexpected interactions which required the design of the CP system to be modified.