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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Page 34 of 100

32 MAY 2015 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 54, NO. 5 CATHODIC PROTECTION A There are 437 steel tubular piles in the coal terminal and trestle bridge of a coastal power plant. Corrosion protec tion consists of a combination of cor rosion allowance, heavy anticorrosion epoxy coating, and sacrifcial anode cathodic protection (CP). This article presents the results of an investigation of the CP system for these piles. A coastal power plant in China includes a coal terminal and a trestle bridge. The terminal has a wharf platform and two water-collecting wells (A and B). The wharf platform is 480 m long and 28 m wide. The trestle bridge is 3,405 m long and 28 m wide. Steel tubular piles, pretensioned high-strength concrete tubular piles, and cast-in-place piles were used as the founda- tions of the terminal. There are a total of 437 steel tubular piles: 289 in the wharf platform (included in 51 bents), six in water-collecting Well A, eight in water- collecting Well B, and 134 in the trestle bridge (included in 39 bents). The piles are constructed of Q345 carbon steel . The diameters of the piles in the terminal and in the trestle bridge are 1,200 and 1,000 mm , resp ectively. Constr uction of th e t e r m i n a l a n d t h e t re st l e b r i d g e w a s completed between November 2006 and November 2008. The design service life of the piles is 50 years. Corrosion protection consists of a combination of corrosion allowance, heavy anticorrosion epoxy coating, and sacrificial a n o d e c a th o di c pro t e c ti o n (C P) . Th e designed dry film thickness (DFT) of the coating is 1,100 μm in the water level fluc- tuation (tidal) zone and above, and 600 μm in the submerged zone to a depth of 6 m in the seabed. The designed service life of the sacrificial anode CP system is 30 years. Sac- rificial anode CP systems were constructed for the piles in the terminal between April and June of 2008 and for the piles of the trestle bridge between July and August of 2008. In 2013, after five years of CP opera- tion, the piles were inspected. Description of Sacrificial Anode Cathodic Protection System Material and Electrochemical Properties of Sacrificial Anodes Hi g h - e f f i c i e n c y a l u m i n u m a n o d e s (Al-Zn-In-Mg-Ti) were selected . Anode electrochemical properties were expected to satisfy the requirements specified in the GB/T 4948-2002 standard 1 (Table 1). Type of Sacrificial Anodes Three types of anodes were installed on the steel tubular piles. Table 2 shows their sizes and weights. Arrangement of Sacrificial Anodes In the terminal there are eight CP units: six in the wharf platform, one in water- collecting Well A, and one in water-collect- ing Well B. Table 3 shows the quantities of the piles in each CP unit and the anode types installed on the piles of each CP unit. Sacrifcial Anode Cathodic Protection at a Coastal Power Plant G. Yan and L. Yan, Nanjing Hydraulic Research Institute, Nanjing, China Zhu XichanG, Research Center on New Materials in Hydraulic Structures, Ministry of Water Resources, Nanjing, China ZhanG Xiaoben and ouYanG Wei Wei, Jiangsu Datang International Lvsigang Power Generation Co., Ltd., Jiangsu, China

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