It is estimated that around 35% of the world's offshore structures have exceeded their 30 year operational life. This means that their original cathodic protection systems are coming towards the end of their effectiveness.
Conventional cathodic protection systems can only be completely replaced at drydocking as they involve hull penetrations. This creates a problem as the platforms frequently have on-going production requirements, therefore they cannot be refitted for a number of years.
This is the case with Pride South Atlantic, a semisubmersible operated by Pride International Inc, which is 26 years old but will not be drydocked until 2012 because of its production schedule.
The solution has come in the form of a retrofit cathodic protection system which has been developed by engineers at Cathelco Brazil, based in Rio de Janeiro, working in close co-operation with Pride International.
"It was essential to provide an effective corrosion protection system which would not interrupt the production requirements of the semisubmersible and could be installed without the need for drydocking," said Alisson de Franca, managing director of Cathelco Brazil.
The impressed current cathodic protection (ICCP) system consists of 16 Nautilus anodes which will be suspended around the semi-submersible to protect the pontoons and bracings against corrosion. The anodes are suspended through conduits, which keep them at a fixed distance from the structure to achieve a good current spread.
The system also has 8 reference electrodes which measure the electrical potential and send a signal back to the control panel which raises or lowers the output to the anodes, ensuring that the structure receives the optimum level of corrosion protection at all times.
One of the main benefits of the system is that it provides flexibility in operation and does not involve welding or hull penetrations. Placement of the anodes is relatively easy and each anode is capable of delivering up to 100 amps which is sufficient to ensure complete corrosion protection.
A further advantage is that when the semi-submersible is drydocked in the future, the control panel can be utilised in the installation of a completely new hull mounted cathodic protection system resulting in significant cost savings.
"We have the capability to work alongside operators to provide customized corrosion solutions which meet the specific needs of the structure and the operational needs of the client," said Aneel Mumtaz, a corrosion engineer at Cathelco's headquarters in the United Kingdom.
Cathelco are world leaders in the design and manufacture of impressed current cathodic protection systems for ships and offshore structures. In recent months, the company has won an order to provide their largest ever ICCP system for the FPSO P57 which is being supplied by Single Buoy Moorings to Petrobras of Brazil.
In Russia, Cathelco has supplied ICCP systems for two semi-submersible rigs which are being constructed in the Vyborg yard for energy giant Gazprom.
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