Nord Stream Line 2 Hits the Seafloor
The Nord Stream Project took another major step forward today with the completion of offshore pipelay of the second of its twin 1,224-kilometre gas pipelines through the Baltic Sea ahead of schedule.
Following extensive pre-commissioning and commissioning, Line 2 is scheduled to begin transporting gas towards the end of 2012 as part of a fully automated twin-pipeline gas transport system capable of transporting 55 billion cubic metres (bcm) of gas per year from Russia to the European Union, for at least 50 years.
The last of the 99,953 steel pipes for Line 2 was made in Germany by Europipe, concrete-weight-coated at EUPEC’s plant in Mukran, shipped to the Slite marshalling yard on the coast of the Swedish Island of Gotland and transported by a pipe-carrying vessel to Saipem’s Castoro Sei laybarge, where it was welded onto the pipeline and lowered to the seabed on April 18, 2012. This marked also the completion of the logistics activities for the Nord Stream Project.
In total, the two completed pipelines consist of 199,755, 12-metre concrete-weight-coated steel pipes each weighing about 24 tonnes. The pipelines were laid along an agreed, carefully-planned route on the seabed of the Baltic Sea by three pipelay vessels – Saipem’s Castoro Sei and Castoro Dieci, and the Allseas’ Solitaire. Altogether, some 138,850 welds were performed for both lines to join together the pipes laid by the Castoro Sei (C6), which has been working on the Nord Stream project since April 2010.
Nord Stream’s Deputy Project Director Construction, Ruurd Hoekstra commented: “Saipem’s Castoro Sei has done an excellent job for us. The vessel has been working 24/7 on this project for two years with its crew of 330 persons with only a one month planned maintenance break in May 2011. Her average lay-rate has been significantly faster than expected, the quality of welds has been exceptionally high and the safety record is outstanding. We are very pleased to have completed pipelay for Line 2 well in advance of the planned schedule. It is another major milestone for Nord Stream.”
“The fact that we were able to complete our complex construction schedule involving three pipelay vessels working simultaneously on different sections of the pipeline was made possible by years of detailed and careful planning. The expertise of our staff and contractors – technical, logistics, safety, environmental and operational – allowed for a smooth-running construction programme that met all environmental and safety considerations,” Hoekstra added.
At any one time, a minimum of 12 ships worked on the project in different parts of the Baltic Sea, and everything fitted into place. Nord Stream’s construction plans proved to be resilient enough to cope with periods of enforced downtime due to some very adverse weather conditions in the Baltic Sea.
The twin pipelines were laid in three sections. Nord Stream was able to design its offshore pipelines to operate without an intermediate compressor station. The pipelines were developed with three different design pressures and pipe wall thicknesses as the gas pressure drops over the long journey from Russia to landfall in Germany.
Pre-commissioning activities for Line 2 have already started. Each of the three sections will be flooded with seawater, cleaned and gauged and thoroughly pressure tested. Following the completion of the pressure tests, these three sections will be connected by underwater hyperbaric tie-ins in May and June off the coasts of Finland and Sweden where the design pressure changes from 220 to 200 bar and from 200 to 177.5 bar respectively.
After de-watering and drying, the completed pipeline will then be linked to the landfalls in Russia and Germany and put into operation towards the end of the year as part of Nord Stream’s fully-automated twin pipeline system. Line 1 started transporting gas in November, 2011.
Source: Nord Stream , April 18, 2012