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Nord Stream: Last Section of Line 2 Now on the Seabed
18.04.2012 + + + In the early morning of April 18, 2012, pipe number 99,953, the last pipe of Line 2, was welded onto pipeline, which was lowered onto the seabed.
"Saipem's Castoro Sei has done an excellent job for us. 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," said Deputy Project Director Construction, Ruurd Hoekstra.
The Castoro Sei Completes Her Job
The Castoro Sei has been working on the Nord Stream project since April 2010, laying 70 percent, or 853.5 kilometres, of each of the two pipelines. "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," explains Hoekstra. "Her average lay-rate has been significantly faster than expected, the quality of welds has been exceptionally high and the safety record is outstanding."
Multiple Vessels Used Throughout the Project
The twin pipelines were laid in three sections. On April 18, the Castoro Sei completed the southern section of Line 2 which runs from Kilometre Point (KP) 675 to the landing point at the German landfall. The pipelines were built in three sections as the pressure at is highest at the start in Russia, and lowest in Germany. As the pressure in the pipeliens reduces, so to does the wall thickness of the of the pipes used. Tapering the wall thickness of pipeline walls saved not only vast amounts of steel, it also enabled Nord Stream to maintain its strict construction schedule, allowing for three lay vessels to work simultaneously work on the pipelines back in 2010. The pipelines were laid along an agreed, carefully-planned route on the seabed of the Baltic Sea by Saipem's Castoro Sei and Castoro Dieci, and the Allseas' Solitaire.
"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 explains.
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. A total fleet of 148 vessels were deployed for Nord Stream for surveys, construction and logistics operations.
Almost 200,000 Pipes Were Needed
Nord Stream’s two completed pipelines consist of 199,755, 12-metre concrete-weight-coated steel pipes each weighing about 24 tonnes. Altogether, some 138,850 welds were performed for both lines to join together the pipes laid by the Castoro Sei.
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 the Castoro Sei, where it was welded onto the pipeline and lowered to the seabed on April 18.
Logistics Activities Completed
This completion of Line 2 also marked also the completion of the logistics activities for the Nord Stream Project. The complex logistics concept was the backbone of the project, and enabled the timely construction of both pipelines. This green logistics concept of short pipe transport distances was first developed in 2006, four years prior to the start of construction of Line 1.
Pressure Testing Is Underway
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 toward the end of the year as part of Nord Stream’s fully-automated twin pipeline system. Line 1 started transporting gas in November, 2011.
Line 2 to Transport Gas by Year's End
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 a year from Russia to the European Union, for at least 50 years.
Source: Nord Stream online magazine eFACTS
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