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Feature 1 | COATINGS


offer very different resistance to electrical currents than the Black Sea. “Te sacrificial anodes needed replacing


and the owner looked at the cost of anodes and the amount they had to replace – which would have been in the hundreds – and decided to go for an ICCP system instead,” Ellis says. He adds that a typical ICCP system for a semi-submersible might have two control panels in each pontoon, four reference electrodes and an arrangement of rod and disc anodes to achieve the necessary distribution of current over the submerged hull surface, while sacrificial anodes might also be used for gaps in the coverage. Te vessel’s two pontoons were fitted with


an ICCP system comprising a 900amp, 24V thyristor control panel wired to six anodes and two reference electrodes. Because it was conducted at sea, the company had to come up with a novel way of installing the system. Cofferdams to house the anodes and reference electrodes were attached to sections of steel that were the same grade and thickness as the original hull. Firstly,


divers created a temporary cofferdam on the exterior of the hull and removed a section of plate. Te new section, with the cofferdam to house the anodes and electrodes was then welded into position. Next, divers fitted the anodes and reference electrodes, and finally, a di-electric shield made from PVC was placed around the anode and sealed into position.


FPSO and FSO configurations For FPSO vessels the requirement is different, due to the different hull shape. Two different ICCP systems, a forward and aſt, are normally employed on a vessel of over 175m length with each having control panels and an arrangement of anodes and reference cells, usually with a power ratio of 1:3, because working stern areas are much more vulnerable to corrosion due to the proximity of different metals such as propellers. However, given that FPSO and FSO vessels are mostly stationary throughout


their


operational lives, their output requirements are a more straightforward 1:1 forward and aſt, although problems can arise through


their use of anchor chains and risers. “Mooring systems on FPSO vessels


use multiple mooring chains,” says Ellis. “When the links in the chains are tight they provide a pathway for corrosion currents, but when they are slack the connection is lost.” He claims that the best solution is to design the ICCP system for the “highest demand for protection”. Cathleco recently supplied an ICCP


system for the Armada TGT 1, a 332m FPSO vessel converted at Singapore’s Keppel Shipyard for Bumi Armada Berhad. She will be deployed off Vietnam, producing up to 55,000 barrels of oil per day and storing 620,000 barrels of oil. Cathelco installed an 800 amp fore and


aſt ICCP system. Both of the systems consist of 400amp thyristor control panels wired to pairs of anodes and reference electrodes mounted on the surface of the hull. The vessel has been installed with linear loop anodes which are diver changeable, allowing them to be changed at sea, without the need to drydock. OMT


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