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19 September 2013

Goliat equipped with the world's strongest rope mooring lines

Goliat will be the first production facility on the Norwegian shelf to be held in place by ropes. To achieve this, Eni Norge has developed the world’s strongest mooring rope.

Goliat will be the first oil field to come on stream in the Barents Sea, and as part of this project, Eni Norge is continuing to develop new technologies and systems. The floating production platform will not be held in place using chains or wires, but with specially developed ropes – the strongest of their kind in the world. 

“There are very few off-the-shelf products used in the Goliat project”, says Andor Engebakken, the project’s Transport and Installation Manager. “Most systems are tailor-made and specially adapted to enable safe and stable production operations in the harsh weather conditions we face in the Barents Sea”, he says.

Multiple benefits
The mooring lines consist of a combination of steel chains and polyester rope, and each line is connected to a suction anchor located on the sea floor. The chains are attached to the hull using chain stoppers. Most of the ropes’ length consists of polyester fibre, and there will be a steel chain on the sea floor. Subsea buoyancy elements will be used to hold the polyester ropes clear of the sea floor.

The Goliat platform will be equipped with 14 mooring lines varying in length from 900 to 1800 metres, and the longest length of rope will be about 1250 metres. The use of rope in preference to chains provides many benefits, but by far the most important is weight. A polyester rope weighs only three per cent of the weight of a chain with the same breaking strength.

“Chains weigh half a tonne per metre”, says Engebakken. “We will be deploying a total of 13,000 metres of this rope, so we’re talking about considerable savings in weight which will enable us to increase oil storage capacity on the Goliat platform” says Engebakken. “Moreover, the rope is extremely flexible in response to major loads, and this will help to reduce wear and tear in harsh weather conditions. The rope has a lifetime of more than 20 years”, says Engebakken.

Polyester and dyneema
The rope has been manufactured by Lankhorst Ropes in Portugal, and is made of polyester with a dyneema jacket which gives the rope a minimum breaking strength of 2579 tonnes.

“A considerable amount of research and development has gone into the qualification and approval of the rope”, says Engebakken. “Dyneema is the same material which butchers’ gloves are made of, and is stronger than kevlar which is used in bullet-proof vests. Our studies demonstrate that the rope will be able to withstand trawling impacts caused by the largest industrial trawlers. This has been an important objective during development of the rope”, says Engebakken.