The Langeled pipeline (Britpipe) - World's Longest Under Water Gas Pipeline (An Engineering Feat)

• published: 29 Oct 2014
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The Langeled pipeline (originally known as Britpipe) is an underwater pipeline transporting Norwegian natural gas to the United Kingdom. Before the completion of the Nord Stream pipeline, it was the longest subsea pipeline in the world. The project was launched under the original name Britpipe. In October 2003, Royal Dutch Shell, ExxonMobil and Statoil signed agreements to supply natural gas through the Britpipe. Robots toiled 3km under the sea to build the longest sub-sea pipeline in the world, connecting the UK and Norway. The pipeline runs 1,166 kilometres (725 mi) through the North Sea from the Nyhamna terminal in Norway via the Sleipner Riser platform in the North Sea to Easington Gas Terminal in England. The pipeline is designated to bring natural gas from the Ormen Lange gas process terminal to the UK, but through the connector at Sleipner Riser it provides also an opportunity to send gas through Gassco's existing network to continental Europe. The annual capacity of the Langeled pipeline is 25.5 billion cubic metres (900 billion cubic feet). That equates to some 20% of Britain's peak gas demand. With the energy content of natural gas at 39 MJ (megajoules) per normal cubic meter, the capacity energy flux is 31.5 GW (gigawatts). The Langeled pipeline supplements the Vesterled system with annual capacity about 12 bcm, which runs from Heimdal Riser platform in the North Sea to St. Fergus in Scotland. The project cost £1.7 billion. Nyhamna-Sleipner Riser section The Nyhamna-Sleipner Riser leg has a diameter of 1,067 millimetres (42.0 in) and can operate with a pressure of 250 bar. Hub at Sleipner Riser At Sleipner Riser the Langeled has a connection to the existing Gassled transport system. Sleipner Riser-Easington section The Sleipner Riser-Easington leg has a diameter of 1,118 millimetres (44.0 in), which makes it the largest submarine pipeline in the North Sea. Its pressure is 155 bar. Sea can go several kilometers deep. Laying a pipe at the bottom is a challenge. However, 6,000 kilometers of pipelines are laid at the bottom of the North Sea. Searching for obstacles Subsea gas pipelines account for 45 per cent of natural gas exports to Europe. Seabed is carefully surveyed along its entire route before laying the gas pipeline. Specialists must identify all potential obstacles including sunk ships, ammunition, and simply large boulders. These obstacles are either removed or bypassed. At this stage, specialists also identify locations where the pipelines should be buried or backfilled. Floating houses Pipes are laid on the seabed by special pipelaying vessels. Pipelaying vessels are huge floating platforms which can accommodate several hundreds of people at a time. As a rule, several vessels participate in the process of pipe laying. Special barges continuously supply pipes to a pipelaying vessel, which is preceded by a vessel monitoring the seabed. The supplied pipes are unloaded on storage sites located directly on the deck of the pipelaying vessel. They should have a stock of pipes for 12 hours of work. How pipes are laid Special conveyor is installed on the pipelaying vessel, which receives pipes that are welded here as well. Each welded joint is then ultrasonically tested for defects. Anticorrosion coating is applied to all joints after welding. Welded pipes are moving over the conveyor towards the aft. Stinger, a special boom, immersed in the water at an angle, over which the pipes are gradually lowered onto the seabed, is located here. It defines the required deflection of the top part of the gas pipeline, which prevents metal deformation. As a rule, pipes lie on the seabed under their own weight. They don’t need to be fixed, because each pipe weighs up to several tons after the concrete coating is applied. Pipes are laid in special trenches and backfilled with ground only in some locations, e.g. at landfalls, to ensure stability of the pipe. From sea to shore The process of laying a subsea gas pipeline normally starts not on the shore, as one could think, but in the sea. Gas pipeline can consist of several sections built at different times from different vessels and then connected to each other. Gas pipeline should be able to withstand different pressures in different sections, for this purpose pipes with different wall thickness are used. Upon the completion of the subsea section construction, pipes are drawn on shore using a special winch installed on firm ground which is connected to the pipe with steel ropes and is slowly drawing it from the sea. The pipeline is then connected with its onshore section – a tie-in is made. Hydro testing of the gas pipeline is a mandatory stage. For that, the pipeline is filled with water under requisite pressure and left for some time to identify possible defects. Condition of the gas pipeline is carefully monitored after its commissioning as well. Special electronic devices for in-pipe inspection are used in this process.