Aker Marine’s decommissioning technology focuses on removing jackets, which are the steel substructures that stand in the sea and support the platform topsides containing the production facilities.

The method involves attaching buoyancy tanks to the four corner legs of the jacket, so that when the legs are cut, the jacket will float in the water. Following this, the structure can be towed to land.

Aker Marine has designed and constructed four buoyancy tank assemblies (BTAs), each comprising two buoyancy tanks joined by a mid-section.

The BTAs are large structures, standing 67m high and weighing over 1200 tons.

Rubber elements delivered by Trelleborg Viking are fitted to the buoyancy tank assemblies where they will be in contact with the jacket legs.

They act as deflection elements, absorbing any impacts within the clamps mounted at the top and bottom of the assemblies and at places along the length of the assemblies.

Aker Marine said Trelleborg Viking’s rubber elements were an important contribution to the new method.

“[Trelleborg’s] offer was cost effective and the company was able to meet our very short delivery schedule,” Aker Marine’s Bjørn Andre Jarli said.

“They also proposed the best solution; it is essential that the rubber elements provide good grip between the clamp and the jacket to ensure there is no slippage while the clamp is holding the leg.

“In addition, the elements could not be too heavy, because it was important to keep the overall weight of the BTAs down.”

The big test for Aker Marine’s jacket removal technology will come in mid 2008, when the method will be used to refloat the jacket of a redundant North Sea platform.

If successful, Aker Marine said it would be well positioned to compete for more such assignments with its new technology.

According to Aker Marine, the decommissioning market is forecast to grow substantially within the next few years, as international guidelines require oil companies to remove almost all the oil and gas platforms they have installed in the North Sea.

Floating offshore platforms can be towed back to shore, but platforms fixed to the seabed present a special challenge.

To date, floating cranes have been mainly used to remove the production equipment on the deck and then lift the substructure or jacket.