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Construction begins on world's longest subsea pipeline.

Construction is under way on the world's longest subsea pipeline to bring Norwegian natural gas to Britain via the 1,200-kin Langeled Pipeline System. The route of the Langeled Pipeline stretches from a land-based gas treatment plant at Nyhamna, Norway via the Sleipner platform in the North Sea, to a gas-receiving plant at Easington in northeast England.

The combination of extreme water depths, highly irregular seabed terrain, strong underwater currents, sub-zero temperatures and challenging wind and wave conditions, have imposed considerable challenges on all parties involved in the project.

Two of the world's largest pipelay vessels, Stolt Offshore's LB200 and Allseas' Sofitaire, have begun work on possibly the world's most demanding pipe-laying project.

The LB200 is laying pipe from the Sleipner platform and is heading south toward Easington, while the Solitaire began work in early June to lay the first 33 kms of Langeled and the production lines from Nyhamna. Plans call for work on the main segment of the northern leg of the line to be conducted next year.

Construction of Langeled will require 100,000 pipe joints that are being painted inside and covered with asphalt and concrete at Bredero Shaw's yard in Farsund, Norway. This work alone will require over 1 million tons of concrete and 25,000 tons of steel reinforcements.

To reduce the number of lengths of suspended pipeline, a complex route through passageways and with curves around subsea obstacles has been chosen so that the pipe can be laid in the least problematic terrain.

In preparation for the pipelay work, 2.8 million tons of rock will be installed to support and stabilize the seafloor where pipeline construction will take place. For this, Hydro awarded Van Oord b.v. of the Netherlands a subsea rock installation construct which runs from 2004-2007.

By year-end 2004, Van Oord's flexible fallrock vessel Tames had installed 90,000 tons of seabed rock in water ranging from 50 to 270 meters.

This year, Tames will be joined by a second Van Oord flexible fallpipe vessel, Rockness. Over the next two years, the vessels are scheduled to install 2 million tons of rock.

The landfall pipeline installation for the project also poses challenges. It will require the pull-in of a 380-meter long, 44-inch diameter pipeline section into a curved two-meter diameter micro-tunnel; installation of 150 meters of 44-inch trenched pipeline from the tunnel entrance up to the battery limit with the gas-receiving facilities; pressuring testing of the tunnel; and final line tie-in between the near shore section and landfall section.

Hydro has designed the pipeline to carry more than 70 million m3/d of natural gas, meaning the Easington terminal could be providing more than 20% of UK gas needs for years to come.

UK-based Nexans, a leader in the cable industry, has been awarded a contract valued at EUR 22 million for trenching services at Ormen Lange.

The contract covers trenching for two six-inch Mono Ethylene Glycol (MEG) pipelines and two umbilicals, each line being approximately 122 km long, as well as trenching of one in-field MEG pipeline and umbilical cable, each approximately 3.5 kin in length.

The MEG pipelines and umbilical cables will link Ormen Lange's subsea production stations, in 1,100 m of water to the onshore gas processing plant at Nyhamna on the west coast of Norway.

Nexans plans to use its specially developed Capjet water-jetting system to bury the lines one meter below the seabed. Trenching will be carried out during summer 2006 with two of Nexans' specially developed Capjet water-jetting systems operating in parallel from two vessels.

There will also be trenching performed in 2007.
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Title Annotation:OFFSHORE
Comment:Construction begins on world's longest subsea pipeline.(OFFSHORE)
Author:Tubb, Rita
Publication:Pipeline & Gas Journal
Geographic Code:4EUUK
Date:Jun 1, 2005
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