Cathelco is supplying an ICCP hull corrosion protection system for a new type of jack-up vessel which is being constructed for Master Marine of Norway who specialize in the transport and installation of heavy structures for the offshore energy industry.
The vessel, known as Service Jack 2, will initially be used to install wind turbines in the Sheringham Shoal Offshore Wind Farm which is located in the Greater Wash approximately 9 miles north of the town of Sheringham in Norfolk, United Kingdom.
Master Marine has won the contract for planning and installing 88 turbines and two substations from Scira Offshore Energy Ltd and its partners Statoil and Statkraft of Norway.
With a length of 384 ft and a width of 164 ft, the vessel has a hull configuration resembling a barge, but differs significantly in having four retractable legs which enable the laden hull to be elevated.
The key to effective corrosion protection of hulls is to polarize the whole area by ensuring an even current distribution. This is achieved by placing the anodes and reference electrodes in the most appropriate positions.
It was decided that the retractable legs would be best protected against corrosion by using sacrificial anodes, whereas the hull would be most effectively protected using an impressed current cathodic protection (ICCP) system.
“The retractable legs are located within moon pools which could affect the performance of the ICCP system by creating a current drain and lowering the level of protection. To eliminate this possibility we took particular care in positioning the reference electrodes so that the system is effectively monitored and optimum output is delivered by the anodes to prevent corrosion,” said Aneel Mumtaz, a corrosion engineer at Cathelco.
The system supplied by Cathelco consists of a control panel which feeds an impressed electrical current to elliptical anodes mounted on the hull surface near each of the four moon pools. In operation, the current from the anodes ‘neutralises’ electro-chemical activity on the surface of the hull and prevents corrosion from occurring.
Positioning the reference electrodes to achieve accurate monitoring is an important aspect of the system design, as the electrodes measure the electrical ‘potential’ at the hull/seawater interface and send a signal back to the control panel which raises or lowers the anode output. In this way, the correct level of corrosion protection is constantly maintained throughout the life of the vessel.