Hull protection, being one of the key challenges common for all stakeholders in maritime industry has seen development of various innovative solutions over the recent years.
That was the reason why World Maritime News Staff asked a specialist from Cathelco, the company that designs and manufactures equipment for ships and offshore installations, about their experience when it comes to hull protection of maritime installations especially in harsh environment conditions.
Ships operating in arctic conditions are faced with twin problems in connection with hull corrosion protection.
Firstly, the temperature of the seawater results in lower conductivity which means that a higher current density is required to protect the hull and prevent corrosion.
To overcome this, Cathelco design their Ice Class ICCP systems with a higher driving voltage which is typically 50 volts, instead of the 24 volts which would be effective in temperate waters.
In icy water there is also greater risk of mechanical damage to the ICCP anodes and their mountings. To reduce abrasion by ice as the ship moves forward, the Cathelco Ice Class anodes are recessed on the hull and come with reinforced doubler plates and cofferdams. The streamlined elliptical shape of the anode is another important factor in reducing damage caused by ice.
Cathelco’s experience in protecting vessels which operate in ice conditions stretches back for many years. One of the first vessels to be installed was the ‘Terry Fox’, a Canadian Coast Guard vessel operating in the Eastern Arctic and Gulf of St Lawrence. This was followed by an ICCP system for the ‘Arctic’, a 26,000 dwt ice class bulk carrier operating in Canadian arctic waters.
Coming up to date, some of the most recent installations have been on board the Polarcus Asima and Polarcus Alima, two Ulstein X-Bow vessels which are used for seismic surveys, together with two more newbuilds for the same company.
“Many of the same factors apply to the design of ICCP systems for the protection of offshore platforms and semi-submersibles, but as these are stationery there is also the problem of protecting the anodes against the pressure of the winter ice”, said Aneel Mumtaz, a corrosion engineer with Cathelco.
For this reason, the anodes are designed with high strength cofferdams and special angled doubler plates which deflect the ice. The current emitting faces of the anodes also have a thicker layer of mixed metal oxide for greater wear resistance.
One of the most unusual projects in recent years was the design of an ICCP system for the Akademik Lomonosov, a prototype Russian floating nuclear power station. Construction work at the Baltiysky Zavod yard in St Petersburg was completed in 2011 and it was then towed to a location in the far east of Russia.
Cathelco supplied a 300 amp ICCP system for the vessel with two elliptical anodes positioned port and starboard at the stern and further two midships. The anodes and reference electrodes were diver changeable, enabling them to be replaced without the need for drydocking.
Another important project was the supply of corrosion protection systems for two massives designed for operation in the Barents Sea.
The rigs were constructed in the Vyborg yard in Russia for Gazflot and were based on the versatile Moss Maritime CS50 design.
“The rigs had a complex geometry, especially around the bracings and riser column. Although the ICCP system provided optimum corrosion protection the whole structure, additional sacrificial anodes were placed in ‘hot spots’ to avoid the shadowing effect of structural members”, Aneel Mumtaz concluded.
World Maritime News Staff, November 2, 2012