Construction of an Impressed Current Cathodic Protection System for marine sheet piling Logistic Platform of Taranto Port, Italy
In July 2015 Tecnoseal Industry was awarded for the engineering, supply and construction of an impressed current C.P. system for the protection of a 600m long steel sheet piling wall installed as closing seal of a marine dredging disposal site in Port of Taranto – Italy.
Sludge Disposal Site
Dredging sludge in port areas are contaminated by pollutants and heavy metals, so their disposal site must ensure a complete and long lasting sealing.
The area selected for the site was closed constructing a rock dam. The land-side was sealed using suitable plastic liners, and on the sea-side it was installed a sheet piling with sealed interlocks driven into the impermeable clay layer below the seabed. Thanks to this kind of construction, the muds that will be disposed inside the area will be completely separated from the surrounding environment, avoiding the seepage of pollutants.
Mechanical integrity of the sheet piling is a key factor to guarantee a lifelong sealing, and Cathodic Protection has been selected as the most efficient system to guarantee the absence of electrolytic corrosion.
Cathodic Protection System
The proposed Cathodic Protection System is based on No.4 vertical deepwell groundbeds to be installed along the development of the dam, dimensioned and spaced to guarantee a sufficient homogeneity of the distribution of cathodic currents. Each groundbed will be equipped with a chain of Mixed Metal Oxide Titanium tubular anodes with special activation for saline environment and PVDF/HMWPE Copper cable for superior resistance to chlorine gases generated by this type of anodes. Length of each chain is 60 meters to allow uniform current distribution on the sheet piling. A 1” ventilation pipe will be installed in each groundbed to evacuate the anodic gases.
Cathodic potentials will be monitored through Zinc reference electrodes installed along the dam in close contact with the sheet piling.
Anodes and electrodes will be connected inside AISI 316L junction boxes installed on the head of the sheet piling.
Cathodic current will be supplied by No.2 oil-cooled Transformer/Rectifier units, each equipped with No.2 separate modules with controlled bridge for Constant Current and Constant Potential working mode and maximum output 50V 100A.
Installation and commissioning
The four boreholes for installation of anode chains and the four perforation for the reference electrodes were performed with core disintegration drilling with recirculation of bentonite muds. Anodic chains were tied to the PVC ventilation pipes and driven into the boreholes. Wellheads were closed using pre-cast concrete pits. All the cables from the anode chains had been connected inside a dedicated Junction box and routed to the T/R units on an 80cm-deep trench excavated along the sheet piling and backfilled with fine sand. The same work had been carried out for the reference electrodes, which are connected inside the test posts and lead to the T/R unit for automatic potentiostatic control.
Negative connections to the pipeline (No.4 for return of cathodic current and No.4 for reference measure) were performed near the junction boxes with welded studs and treated with anticorrosive finish.
T/R units had been installed on a dedicated area at about 100 meters from the end of the sheet piling.
After all the pre-commissioning checks, the C.P. system was switched ON and the current of the four modules was slowly increased to the maximum (abt. 400A total current). Due to the extension of the surfaces to be protected and the absence of any protective paint, polarization took about 10 days. Full protection of the sheet piling was assessed according the “100mV residual polarization” criterion.
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