Materials Performance

MAY 2015

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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38 MAY 2015 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 54, NO. 5 CATHODIC PROTECTION ESSENTIALS Continued f rom page 37 ICCP Retroft Modeled for an Offshore Jacket Complex An ofshore jacket complex consisting of fve platforms is protected by a conven- tional sacrifcial anode cathodic protection (CP) system. Te jacket complex is located in the North Sea at a water depth of 35 m and includes a subsea valve station and eight subsea pipelines. Te platforms date from 1967 to 1975 except for one recently installed structure. Te jacket structures are all bridge linked and electrically intercon- nected. Recent CP potential measurements and anode inspections of the existing plat- forms indicated that a signifcant amount of anodes have a remaining lifetime of less than 20 years, and extending the end-of-service life would require a signifcant retroft efort in the near future. Due to the high cost and safety risks during the installation of a retro- ft CP system with sacrifcial anodes, an al- ternative impressed current CP (ICCP) anode sled system was investigated. Remote ICCP anode sleds are relatively easy to install, but designing such a CP sys- tem is more challenging. Correct positioning of the sleds is critical for obtaining proper protection and avoiding overprotection. Using a three-dimensional computer-aided design (CAD) model of the ofshore jacket complex and computational modeling, a graphical representation of the IR-free poten- tials on the structure was developed so the feasibility of the conceptual retroft ICCP sys- tem design could be validated and optimized. First the existing CP status of the com- plex was simulated using the condition of the sacrifcial anodes as observed during the lat- est survey. Second, an ICCP system was mod- eled and various anode sled positions were investigated until an optimal design was obtained. Te remaining life of the existing anodes was calculated to keep the number of anode sleds to a minimum. Trough model- ing, the CP efectiveness of the combined system was validated and a cost-efective solution was proposed. Te simulation results are discussed in CORROSION 2015 paper no. 6012, "ICCP Retroft Challenges for an Ofshore Jacket Complex," by C. Baeté. The simulated IR-free potentials of an individual jacket with the sacrifcial anode system.

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