Design, Supply & Installation of an Impressed Current Cathodic Protection System for Driven H-Piles in Hong Kong

Recently, Aegion completed a project for the design, supply,installation and commission of an impressed current cathodicprotection (ICCP) system for over 240 nos. of driven H-piles.During the upgrading project for a government sewagetreatment works, it was determined that one of the treatmenttanks near seawater uses a deep foundation, which is supportedby 242 pieces of large driven H-piles. These 12-inch squareH-piles, roughly 150 lbs/ft universal bearing piles, are an averagelength of about 150 feet and are spaced between 6.5 and 16 feetfrom each other. To achieve a facility design life of 100 yearsand prevent the undue corrosion of the steel piles, an ICCPsystem was adopted to provide a cost-effective solution.

In the design stage, special considerations were takenin light of several specific project constraints:

• Increased current requirement due to large total surfacearea of the piles and assumption of bare surface exposedto corrosive environment
• Congestion of piles
• Adjacent metallic objects near the H-pilesthat may be affected by stray current
• Allowance for maintenance and replacement

After considering the factors above, an open-hole deep anodegroundbed was adopted with an MMO anode placed in 32 holesat the same depth as the piles. The holes were distributedinside the pile caps to achieve a more even current distributionand terminated on the top of the tank structure to facilitatefuture inspection and/or replacement of anodes, if required.The whole ICCP system was powered by a total of seventransformer rectifiers. To mitigate the current interferenceto adjacent objects, stray current mitigation measures usingbonding cables were adopted. Finally, performance of the ICCPsystem was monitored through silver/silver chloride and zincreference electrodes installed at representative locations.

The ICCP system for the piles was commissioned in late2015. The commissioning criteria was consistent withinternationally recognizable standards, including EN13174:2001and NACE SP0169-2007, with results showing the ICCP systemperforming satisfactorily.