Engineers are working on one of the world’s largest undersea pipelines to bring gas from Russia to western Europe. Challenges include disposing of unexploded mines, preserving marine life and laying over 1,200km of pipeline. Martina Booth reports.
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Building a mammoth sub-sea gas pipeline between Russia and Germany is a difficult enough brief. Throw in the fact that its home, the Baltic Sea, has up to 150,000 mines resting on its seabed, and an already ambitious project is made even more challenging.
During the First and Second World Wars the Baltic Sea was a regular dumping ground for munitions. Thus, before work commenced on Nord Stream − a pipeline linking the Russian gas transmission system to the gas network of the European Union − its route had to be thoroughly surveyed, to ensure it was clear of any mines that could wreak havoc on the safe construction and operation of the pipeline.
A Remotely Operated Vehicle (ROV), equipped with a gradiometer and cameras, was used to detect and record objects as small as 100mm in size along the route.
Approximately 80 munitions sites were identified. British explosive ordnance disposal firm Bactec was enlisted by the Nord Stream consortium to clear the munitions.
Nord Stream is a joint venture between four companies: Russia’s Gazprom, Germany’s Eon Ruhrgas and BASF/Wintershall and the Dutch Nederlandse Gasunie. The Russian and German members of the consortium united to build and operate the pipeline in 2005, with Gasunie joining as the fourth shareholder in 2008.
Since November 2009, it has been clearing an area along the Gulf of Finland and has so far cleared 45 mines. Bactec has been employing innovative solutions to carry out controlled detonations of the mines, which are in water-depths of 200m and nestled near marine life.
“During the survey, lots of mines were identified − torpedos, detonated charges and airdrop bombs − that needed to be disposed of. We have been using as small an amount of explosive charge as possible to clear them, because the majority are unsafe to move,” says Bactec managing director Kevin Kneebone.
“A traditional method to dispose mines is to use a bulk charge explosive on or adjacent to the mine. A bulk charge is bulk explosive −or a lump of explosives − that is initiated.
The blast effect is omnidirectional, meaning the energy is not focused. Therefore, to have the desired effect you would need to use larger amounts than a shaped charge,” says Kneebone.
“We use a small amount of explosive charge to clear the mines because most are unsafe to move”
“The problem with this method is that it is not always effective, because you may have a water gap which reduces the effect. Also, it is very difficult to place a bulk charge against the mine, as if you touch the mine it could function,” says Kneebone.
“We devised a shape charged explosive, using explosives in a container with an inverted copper cone, so when the explosives are initiated the cone forms a plasma jet that is focused onto its target − meaning using less explosives is more effective. As the net explosive quantity is reduced, the impact on the seabed environment is reduced.
“The shaped charge system − deployed by ROV − also allows you to place the explosive up to one metre away, thus eliminating the risk of an uncontrolled explosion,” he adds.
Bactec has 30 workers on-site, working on two vessels. Kneebone says work is progressing well and is due to be completed ahead of schedule next month. However, there have been challenges along the way.
“The main challenges have been with the environmental measures that we have put in place to protect the sea life,” he says. “We are using specially developed equipment to listen to marine animals in the area, so that they are not affected by the explosions.
“We are also using technology called seal scarers, which are acoustic devices that emit high intensity sounds and deter sea mammals. Smaller explosive charges are also used to move fish away from the area to reduce the amount of fish killed. That can be quite challenging,” he adds.
While Bactec is working hard to clear the waters in the Gulf of Finland, construction of the 1,200km pipeline − one of the longest sub-sea pipelines in the world − has already commenced in Swedish waters.
In April 2010, a barge commenced offshore pipe-laying near the island of Gotland, 675km from the pipeline’s starting point on the Russian Baltic sea coast near Vyborg.
Nord Stream will connect Vyborg with the German Baltic Sea shore near Greifswald. It will run through the Exclusive Economic Zones and/or territorial waters of five countries: Russia, Finland, Sweden, Denmark and Germany.
From the landing point, natural gas will be piped via the European gas network to markets, including Germany, Denmark, the UK, the Netherlands, Belgium, France and the Czech Republic.
The project consists of two parallel lines, each approximately 1,200km in length. The first pipeline, with a transmission capacity of 27.5bn.m³ a year, is due for completion in 2011. The second is due to be completed in 2012, bringing annual capacity to 55bn.m³.
In Russia, Gazprom is building a 917km onshore pipeline to connect Nord Stream to the Russian gas transmission system. Eon Ruhrgas is building two onshore connections from Greifswald on Germany’s north coast to the south and west of Germany, totalling 850km.
The project is being constructed at a staggering pace, with approximately 2.5km of pipeline being laid per day. Each pipeline comprises 1.1M t of steel, made up of 100,000 pipe sections, each measuring 12m long with a diameter of 1.4m.
On pipe laying vessels, two 12m pipe joints are welded together to form a 24m “double joint”. These sections are then lowered to the sea bed in a continuous line on a stinger.
For most of the offshore route, the pipeline will rest on the seabed − but in some areas near landfalls, or where there is heavy ship traffic, the pipe will be buried and backfilled with sand to ensure adequate stability and protection.
When the second pipeline is complete in 2012, Nord Stream will supply 55bn.m³ of gas annually, going some way to bridging the 195bn.m³ supply gap that Europe faces by 2025.
Developer Nord Stream
Value £6.4bn (€7.4bn)
Construction start date April 2010
Completion Date 2012
Consortia Members Gazprom, Eon Ruhrgas, BASF/Wintershall, Nederlandse Gasunie
Gas capacities 55bn.m³ per annum (Two pipelines with 27.5bn.m3 capacity each)
Pipeline length 1,220km
No. of pipelines 2
Maximum water depth 210m
Gas supply resources Yuzhno-Russkoye reserve, Yamal Peninsula, Ob-Taz bay Shtokmanovskoye fields
Munitons clearance contractor Bactec
Russian gas for Western homes: The Nordstream gas pipeline