CP validation for offshore structures (NACE 2012)

C. Baeté, M. Purcar, L. Bortels, B. Van Den Bossche, J-M. Dewilde,  Elsyca n.v.

Abstract

Nowadays offshore structures are typically equipped with a sacrificial anode cathodic protection system (SACP). Design and application of SACP systems is well documented and most owners of marine equipment rely on this traditional approach. SACP systems for big structures result in a large amount of anodes increasing the mechanical load on the structure, installation cost (welding) and the release of soluble metals into the environment. Moreover, monitoring of the CP performance requires access to the anodes in order to verify the material consumption resulting in expensive ROV inspections.

An innovative and more economical way to protect such offshore structures is by fitting these structures with an impressed current system (ICCP). This relatively new approach makes use of a restricted amount of insoluble Mixed Metal Oxide (MMO) anodes positioned at strategic locations on the structure. Monitoring and adjusting of the ICCP system can easily be performed from an accessible control panel. Most of the ICCP installations are even less expensive than SACP systems. The difficulty, however, is to find a correct design in order to guarantee an adequate protection level for the complete structure and to avoid local overprotection around the MMO anodes.

In this article case studies will be discussed where a 3D simulation technology was used to evaluate the two different CP system designs for a semi-submersible oil rig. Long term effects like polarization behavior and consumption rate of sacrificial anodes is provided and simulation results are compared to current standards.