All three sections of the first of Nord Stream’s twin 1,224 kilometre natural gas pipelines have now been joined together underwater by hyperbaric tie-ins. The completed pipeline through the Baltic Sea will now be prepared for connection to the landfalls in Russia and Germany later in the summer.
The connection by hyperbaric tie-in of these three pipeline sections was successfully carried out at the two offshore locations. The connection of the Gulf of Finland and central sections took place off the coast of Finland at a sea depth of approximately 80 metres, and the connection of the central and south western sections off the Swedish island of Gotland at a depth of approximately 110 metres. Each of the two “tie-ins” was carried out in an underwater welding habitat and was remotely controlled from a diving support vessel, the Technip Skandi Arctic. The specialised subsea equipment used to perform the tie-ins was provided by the PRS (Pipeline Repair System) pool, a pool of pipeline operators administrated by Statoil. The construction work was supported by teams of divers, who were present at all times to ensure that the equipment was correctly positioned and operated subsea.
Nord Stream’s twin pipelines each consist of 101,000 12-metre long 48-inch diameter concrete-weight coated steel pipes each weighing about 23 tonnes. The pipes of the first line were welded together on board special pipelay vessels and laid on the seabed along a precisely defined route which had been agreed with the authorities of the five countries through whose waters the pipeline passes: Russia, Finland, Sweden, Denmark and Germany. The two main pipelay vessels used for the first line, Saipem’s Castoro Sei and Allseas’ Solitaire, are currently laying the second pipeline in the Gulf of Finland.
Work on the second pipeline is progressing at the rate of about six kilometres a day, and more than 230 kilometres have already been constructed. When both lines are fully operational by the end of 2012, the Nord Stream Pipeline will be capable of transporting 55 billion cubic metres (bcm) of gas a year to Europe. No other major new pipeline with a capacity over 10 bcm is expected to come on-stream before 2015.
Source:Nord Stream , June 21, 2011;