Cathelco are supplying an impressed current cathodic protection (ICCP) system for the FPSO OKHA which is being converted by Single Buoy Moorings.
After conversion, the OKHA will be operated in oil fields off the North West Shelf of Australia by Woodside Energy Ltd, replacing the FPSO Cossack Pioneer.
Conversion work will take place at the Keppel Shipyard in Singapore. During the installation of the ICCP system, local support will be provided by Cathelco S.E.A., also based in Singapore.
"Before designing the system a study was undertaken by Force Technology, using computer modelling, to determine whether 'interference' from the sacrificial anodes on the riser column would have an effect on the performance of the ICCP equipment", said Aneel Mumtaz, a corrosion engineer, based at Cathelco's headquarters in Chesterfield, United Kingdom.
The study identified the potential risk of 'interference' with the ICCP system and as a result the design was modified to achieve the most effective form of corrosion protection. It was also proposed to utilise silver/silver chloride reference electrodes due to their higher stability at negative potentials.
The reference electrodes provide efficient monitoring of 'potential' at the hull/seawater interface and send a signal to the control panel which raises or lowers the anode output. In this way, the hull receives the optimum level of corrosion protection at all the times.
Cathelco will be supplying a new 1,000 amp ICCP system for the OKHA. The forward unit will consist of a control panel wired to two 250 amp linear loop anodes and the aft unit will be of an equivalent size. The advantage of linear loop anodes is that they provide a high output from a relatively small surface area making them ideal for this type of application.
Cathelco have also received an order from Saipem Energy Services SpA for ICCP equipment to protect an oil tanker which is being converted into an FPSO for use in the Aquila Oil Field off Brindisi, Italy.
After conversion, the FPSO will be operated by ENI SpA and will have a storage capacity of 700,000 barrels and a production capacity of 12,000 barrels per day.
The equipment supplied by Cathelco will provide the vessel with a 150 amp forward ICCP system and a 300 amp aft system. The forward system will utilise two 75 amp linear loop anodes and an arrangement of reference electrodes connected to a control panel, whilst the aft system will use four anodes.
In addition to providing corrosion protection for the hull over a 20 year period, the Cathelco system will also protect the rudder, propeller and mooring chains.
Cathelco ICCP systems are increasingly being installed on FSOs, FPSOs and semi-submersibles. The OKHA project will be the fourth to be carried out for Single Buoy Moorings since 2005 and Cathelco have also supplied equipment for Moss Maritime and the SeaDragon II project.