Cathodic Protection System installed by Drake Towage

Cathodic Protection System installed by Drake Towage

Work recently completed by Drake Towage to install an Anti Corrosion System for the Steel Sheet Piles on the River Nene near Freedom Bridge in Wisbech.

Drake Towage have recently completed the installation of a Cathodic Protection System to preserve the steel sheet piling lining the River Nene at Freedom Bridge, Wisbech against corrosion. This work being on a joint venture basis with Anglia Cathodic Protection Services (ACAPS) and Skanska for Cambridgeshire Highways.

As a brief explanation to the process, any metal which is buried or immersed in water is subject to decomposition by what is commonly referred to as rust. This phenomenon is an on-going problem and costs industry millions in terms of maintenance and replacement. The sheet piles along the Nene Quay and South Brink had been identified as having accelerated low level corrosion.

As corrosion is an electrochemical process, the method applied to protect structures against such decay is to introduce another metal which can be persuaded to sacrifice itself whilst keeping the target structure in pristine condition. This is known as electrolysis and can be achieved by altering the electrical charge within the immediate environment of the structure to be protected.

By installing some one hundred equally spaced mixed metal oxide anodes on the bed of the river Nene and maintaining a good separation distance from the structure it was possible to impose a negative depression along the full length of the piling to mitigate the corrosion process. Power was introduced to the anodes via a total of six dedicated Switch Mode Power Supply Units based on the pedestrian walkway above the piling.

The Drake Towage Team were selected for the project owing to their ability and experience as a marine contractor. Having access to a wide range of specialist equipment they were able to undertake the installation of the anodes and cabling using their floating pontoons as a work station. Strategic planning enabled the team to work around the daily tides, installing anodes inside their protective concrete casing during low water and cabling for electrical supply, including all ducting, brackets etc. during high water.

The end result is that the structure is now polarising to maintain constant potentials of -0.950v DC, as opposed to the original value of 0.55v DC which was recorded prior to the works commencing.

This is a constant application and has been designed to preserve the structure for a corrosion free life of minimum 30years but with target duration of 50 years.

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