The 1,224-km (760-mi) long pipeline is now complete and will be de-watered and dried prior to being joined to the onshore landfall sections in Russia and Germany in August.
Both lines have been constructed in three sections with progressively reduced pipe-wall thicknesses as the design pressure of the gas drops from 220 bar to 200 bar (3,191-2,900 psi) and from 200 to 177.5 bar (2,900 – 2,574 psi), eventually arriving at mainland Germany at 100 bar (1,450 psi).
For the second line, the three sections were joined together underwater inside a hyperbaric welding habitat on the seabed at two locations offshore Finland and off the Swedish island of Gotland in June.
As with Line 1, diving contractor Technip deployed equipment from the Pipeline Repair System (PRS) Pool operated by Statoil. Underwater welding operations were remotely controlled from theDSV Skandi Arctic.
The PRS equipment had to be adapted to accommodate the diameter of the Nord Stream pipelines, according to Jan Olav Berge, Statoil’s Pipeline Repair Pool manager.
“The overall tie-in equipment had to be upgraded: the pipe handling frames and the welding habitat had to be enlarged, because such 48-in. (122-cm) diameter pipelines had not been handled before. The same system as used for the tie-ins will be ready to carry out any repairs to these or other large-diameter pipelines in the future if needed.”
Following the underwater tie-ins, all the water will be removed from the second pipeline this month and the pipeline will then be dried. The onshore and offshore sections will be connected in August, and following testing, this second line should come onstream as part of an integrated twin pipeline system during 4Q 2012.
When fully operational, the pipelines will have capacity to transport 55 bcm/yr (1.9 tcf/yr) of gas from fields onshore northern Russia to countries in the European Union.