Making of: From Pipes to Pipeline
The Nord Stream Pipeline is a major feat of engineering, involving complex logistics, along with suppliers and contractors from all over the world. The project consists of two pipelines running almost parallel to one another through the Baltic Sea.
Construction of Line 1 Completed on Schedule
In April 2010, Nord Stream's contractors began constructing the first of its two, 1,224-kilometre natural gas pipelines. Line 1 was completed in June 2011, and gas transport began in mid November 2011 following extensive pressure testing and pre-commissioning activities. Construction of Line 2 began in May 2011. Line 2, which runs parallel to Line 1, is planned to come on stream in the last quarter of 2012. Each line has a transport capacity of roughly 27.5 bcm of natural gas a year.
By the end of 2012, both lines of the Nord Stream Pipeline system will be operational. Combined, they will be able to deliver up to 55 billion cubic metres of gas annually.
Tailor-Made Plan for the Baltic Sea
Both lines of the Nord Stream Pipeline system are laid in three sections. The three sections have different wall thicknesses following the direction of the gas flow. Gas pressure reduces as it makes its way through the pipelines. Therefore, the walls are thickest at the start of the pipelines at Portovaya Bay, Russia, and thinnest at the landing point at Greifswald, Germany.
Each of the pipelines is made up of about 100,000 pipes. Along the pipeline route, five existing harbour sites supply concrete coated pipes on a continuous basis to the lay barges owned and operated by Nord Stream's contractor, Saipem, and its subcontractor, Allseas. In 2010, three vessels were used to complete the pipelines, working at different segments of the route. Through mid-2011, two vessels were used. From mid-2011 through the third quarter of 2012, Saipem's Castoro Sei will complete Line 2.
Construction of the pipelines was scheduled to minimise environmental impacts. For example, so as not to interfere with critical seal breeding and fish spawning seasons.
Pipe Laying Handled by Three Vessels
Saipem organised three laybarges; two with special requirements, for the construction of pipelines. Saipem's Castoro Dieci, which is designed to work in shallow waters, worked in the Bay of Greifswald, Germany. The Castoro Dieci laid 28 kilometres of each of the twin pipelines, working from June 2010 to October 2010. The Allsea's Solitaire – the biggest pipelay vessel in the world – laid a 342.5-kilometre segment of each of the twin pipelines, starting in September 2010, completing its work in August 2011. With its dynamic positioning system, the Solitaire was the ideal vessel for working in the congested Gulf of Finland. Saipem's Castoro Sei is laying about 70 percent or 853.5 kilometres of each of the two pipelines. It started working in April 2010, and finished work on Line 1 in May 2011. The Castoro Sei began work on Line 2 in June 2011.
How It's Done
In preparation for pipe laying, the seabed is surveyed with a remotely operated vehicle (ROV) to ensure pipelay safety and to confirm the seabed data gathered during the lengthy route planning phase. Additionally, in some locations along the route, the strategic placement of coarse gravel is necessary to create a stable base on which the pipeline can rest. Gravel is transported and placed by dedicated rock placement vessels to the specific locations where support is required prior to pipe laying. On board the pipelay vessels, the construction cycle is made up of several steps including bevelling, welding, testing and the lowering of the pipeline onto the seabed. There are exact procedures defined for each process to ensure quality and compliance with health and safety regulations. Following the laying process, the pipeline is again monitored underwater by ROV to ensure correct positioning.
After completion of the construction work, the three pipeline segments are flooded with water and pressure tested to ensure mechanical integrity. Then, the pipeline segments are connected by welding them underwater. Once connected, the pipeline is emptied of water, and is filled with nitrogen before natural gas can be safely introduced. The connection of these three pipeline sections is carried out at the two locations where the design pressure changes. The connecting of the three sections of Line 1 was completed in June 2011. Testing of Line 2 is scheduled for the spring of 2012 and underwater tie-ins for the summer.
Delivery of gas through Line 1 started in November 2011. By the end of 2012, both lines of the Nord Stream Pipeline system will be operational. Combined, they will be able to deliver up to 55 billion cubic metres of gas annually.
