Design of sacrificial anode cathodic protection (SACP) systems to achieve uniform anode mass loss rates is desirable, since it helps avoid early installation of costly retrofit systems which may be needed if some anodes are consumed more quickly than others.
Such optimized design is only practically possible through the use of mathematical modeling performed using numerical techniques. A range of numerical methodologies can be applied to simulation of galvanic effects and cathodic protection, and of these it is the boundary element method that is applied in this work. The simulation requires an accurate model of the structure which is to be protected, as well as the anodes, and any other metallic structures which may act as current drains (even though they may not need to be cathodically protected).
The optimization process first involves design and simulation of an initial SACP system design. Performance of the design is assessed against criteria which may include anode mass loss rate, most positive allowed potential and remaining anode mass, not only at start of life, but also throughout the design life of the structure. The results of previous assessments are used to guide the selection of the next trial SACP system design, which usually involves changing the number, position or size of anodes, while adhering to user-defined rules (e.g. “keep-out areas”). The process is repeated until satisfactory results are obtained.
The objective of this paper is to explore such simulation techniques, and show how they can be combined to provide a practical toolset for SACP system design optimization. This provides the user with new and significantly more powerful design capabilities which are based on real physics rather than standardized design rules. The use of these tools both reduces the risk of the CP design not meeting its required life and ensures an economical design.
The paper illustrates performance of the design and optimization processes using a jacket structure for which long-term “sigmoidal” polarization curves provide an appropriate representation of calcareous deposits.
Keywords: SACP, Design, Optimization, Cathodic Protection, Modeling
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