Modeling in selection, design and optimization of cathodic protection retrofit systems of offshore facilities

The paper deals with the retrofit of cathodic protection (CP) systems of in service offshore facilities (offshore platforms, subsea pipelines). The need of CP replacement, or retrofit, can be originated by a number of reasons, the most common one being the depletion of the original galvanic anode system. Design of CP retrofit systems has specific issues which differentiate this type of application from the case of new structures. In fact the facility to be retrofitted is at site and operating, not in the yard as for new structures. In addition, in-service structures are normally covered with a stable calcareous deposit which strongly affects protection current requirements. Modeling of the electrical field is an essential tool to predict the current demand of the structure to be retrofitted and to select the anode system configuration. The paper presents a number of examples of application of the Finite Element and Boundary Element Method modeling, taken from CP retrofit projects.