INTRODUCTION:
ABSTRACT: This paper presents a 3D software tool for the design and optimization of cathodic protection systems for submerged structures. It provides the corrosion engineer an intelligent tool for managing operational costs, significantly reducing expensive commissioning surveys and costly repairs, adding major value to the cathodic protection business. A Finite Element Model (FEM) is used to solve the potential model taking into account ohmic drop effects in the electrolyte and cabling and non-linear polarization behaviour at both the cathode and anode. From the resulting potential field in the seawater electrical and magentic signatures can be obtained. In this paper several examples will be presented including oil platform, ballast tank and a marine vessel for which the ICCP has been optimized in order to minimize the underwater electrical potential and corrosion related magnetic signature.
Cathodic Protection (CP) systems are widely applied to buried and offshore structures, as they compensate (by electrochemical means) for the loss in physical protection due to the degradation of the applied coating over time. Most often, these CP systems contain a series of impressed current and/or sacrificial anodes, sometimes placed at a remote distance from the structure. The entire configuration of the CP system and the structures has some particular characteristics that necessitate and justify the use of numerical simulations. First, the low accessibility of these structures make installation, maintenance and repair very expensive. Also, the geometry of most steel structures that are subject to cathodic protection is too complex to allow analytical or even empirical estimations for the determination of the local protection level. Numerical modeling provides significant benefit by identifying insufficiently protected regions - possibly subject to corrosion, and overprotected regions - subject to excess gas evolution and hence coating disbonding. As a consequence, numerical modeling allows simplification and optimization of installation, maintenance and repair. Moreover, models provide reference values for measurements on operational sites, enabling to trace .Most of the publications dealing with the computation of the CP of both buried and submerged structures are based on the well known Boundary Element Method (BEM) [1]. Orazem et al. [2,3] use a 3D BEM approach to compute the protection level of large coating defects on pipelines. Results are presented for a pipe segment of limited length (10 feet), in presence of a parallel anode system. Riemer and Orazem [4] produced results for a larger pipeline (> 6 km) with coating defects of varying size and investigated the ability of coupons in the vicinity of the defects to measure off-potentials. Adey [5] applied a full 3D approach to calculate the potential field in the neighborhood of jacket joints under cathodic protection of sacrificial anodes. The present authors [6] used a 3D coupled multi-domain BEM approach to simulate the protection level of a buried pipe segment surrounded by a concrete vault. Aoki et al. [7] applied the BEM to detect a coating defect on a ship hull. DeGiorgi [8] made a significant contribution to the modeling work of the CP of ships.