Cathelco ICCP system to be installed on P62 FPSO

Cathelco Ltd are supplying a hull corrosion protection system for the P62 FPSO which is being converted for Petrobras Netherlands B.V. who will operate it in the Roncador field off Brazil.

This will involve the conversion of the Mt Suva, a 279,984 dwt VLCC which was launched in 1993. The work will take place at the Jurong Shipyard in Singapore with the vessel scheduled for completion in the second quarter of 2011.

The impressed current cathodic protection (ICCP) system manufactured by Cathelco Ltd will protect the underwater surface of the hull against corrosion.

The forward system will consist of an arrangement of six 150amp anodes and two reference electrodes mounted port and starboard connected to a 900 amp thyristor control panel. This is mirrored by a similar system at the aft of the vessel to provide the necessary level of corrosion protection.

As FPSOs have long intervals between drydocking, the anodes are designed to be diver changeable which means that they can be replaced, if necessary, while the vessel is at sea.

The purpose of the ICCP system is to eliminate corrosion on the surface of the hull. To achieve this the anodes emit an impressed current which ‘neutralises’ the electrochemical activity.

In operation the reference electrodes measure the electrical ‘potential’ at the hull/seawater interface and send a reading to the control panel which raises or lowers the anode output. This ensures that the hull receives the optimum protection at all times.
On large vessels such as FPSOs it is advantageous for engineers to be able to monitor the whole system from a central location such as a control room.

For this reason, the P62 has a remote monitoring unit which enables both ICCP systems to be monitored from the same location. The monitor displays individual outputs for each anode and individual readings for reference electrodes. It also allows the A.C. power supply to be monitored to ensure that it is within tolerance.

In addition to simplifying the monitoring process, this feature allows the ICCP equipment to be accurately balanced in relation to associated cathodic protection systems.

For instance, risers are usually protected by sacrificial anode systems which have a high ‘potential’ in the initial years of operation. In these circumstances, the anode output from the shipboard ICCP system can be reduced. However, as time passes and the ‘potential’ from the sacrificial anodes on the riser decreases, the output from the ICCP system can be gradually raised.

“The ability to fine tune the system has practical advantages over the 25 year design life of the vessel as it ensures that the correct level of corrosion protection is maintained and also helps to prolong the life of the anodes”, said Steve Ellis, project development manager at Cathelco Ltd.