The Nord Stream Pipeline will link the European Union (EU) to Russia’s sizeable gas reserves via the Russian gas network. The design, material and laying of roughly 1,220 km of offshore transmission line represents major planning challenges.

Construction of the first line is planned to start at the beginning of 2010 and is due to commence operation in 2011. The 55 billion cubic metres (Bcm) will be available on completion of the second line in 2012. With its own production in decline, Europe will need to import more natural gas in the coming decades. The Nord Stream Pipeline will be able to supply approximately one quarter of the additional import volumes needed in the future.

The project has been planned down to the last detail. The careful selection of materials is as important for the safe operation of the system as the technical design. Comprehensive research into the environment, risk assessment studies and detailed surveys to determine the pipeline’s optimal routing on the sea bottom have preceded its construction.

Nord Stream design

The design of the pipeline is based on the principle of segmented wall thickness. The wall thickness of the 12 m pipe sections reduces in three stages following the direction of the natural gas flow, in line with falling gas pressure in the pipeline and the resulting reduction in load. The segmented construction principle has already been applied to several North Sea pipelines (for example, the Langeled and Europipe pipelines) and facilitates substantial savings on materials. Reducing the wall thickness by 1 mm over the whole length of the pipeline saves around 80,000 tonnes of steel.

The pipes for the Nord Stream Pipeline have an internal diameter of 1,153 mm. They are manufactured from high-tensile steel (DNV Offshore Standard OS F101) and have a maximum wall thickness of 41 mm.

German company EUROPIPE will produce approximately 75 per cent (860,000 tonnes) of the pipes for the first of the two pipelines. OMK, a Russian specialist mill, will produce some 25 per cent (280,000 tonnes).

Special X70 steel has been chosen as the material for the pipes. In several aspects, it proved to be the best solution. The offshore industry lacks adequate experience of using X80 and thicker steels. X70 steel is widely used – along with X65 – in the pipeline industry, but it is more pressure resistant and thus better suited than X65 for use in large-diameter, high-pressure lines. In addition, it has the advantage of wall thicknesses approximately eight per cent smaller than X65 steel. This saves not only material, but also time.

The thickness of the pipes determines the length of the individual pipe welding process on board the pipelay vessel. A weld of X70 steel can be completed in only six minutes. This provides the basis for calculating the speed of pipelaying and thus the length of the construction period. Adding just one minute to the time taken to weld one double joint would add about one and a half months to the entire pipelaying process.

In order to ensure that the pipeline can withstand an internal pressure of up to 220 bar when it is in operation, the pipe joints are subject to a number of inspections and quality checks during their production by the manufacturer, independent pipeline specialists, and Nord Stream AG experts. Ultrasonic tests, magnetic particle inspection and X-ray examinations are undertaken to check for material defects that are not externally detectable. The steel’s strength properties are continuously tested during pipe manufacture.

The internal walls of the Nord Stream Pipeline are given an anti-friction coating of epoxy resin. The external walls receive passive anti-corrosion protection involving a triple-layered coating sealed by a polyethylene coat with a minimum thickness of 4.2 mm. In addition, the steel pipes are given a 60–110 mm thick concrete coat that increases the weight of the pipeline and thus ensures its stability on the seabed. Sacrificial aluminium and zinc anodes are applied to provide additional active cathodic protection. These anodes protect the pipes against rust in areas where passive protection is less than 100 per cent effective.

Laying the pipe

The technical engineering preparations for the pipeline’s construction are already in full swing.

Following an international tendering process in which companies from several countries took part, Nord Stream appointed Italian company Snamprogetti to undertake the job of technical construction planning.

The contract with Snamprogetti comprises:

• The drawing up of detailed construction plans and calculations, including hydraulic and thermal analyses;
• Calculations regarding the pipeline’s wall thickness and stability;
• Solutions for bridging free spans – these are sections where the pipeline cannot be laid on the sea bottom due to crevices or irregularities in the seabed; and
• Technical proposals for bringing the ends of the pipeline onshore.

As soon as the precise routing has been fixed and the required permits have been obtained, preparatory work on the seabed can begin. Near the coast and in some other areas, the pipeline will be sunk into a trench, which will then be backfilled. In deeper waters – from water depths of about 15 m – the line will lie on the seabed. Where the route crosses maritime cables, special construction measures will be needed in some cases.

Small transport ships will bring the individual pipes, which have already been concrete coated onshore, to the lay barge. There they will be checked for damage during transport, cleaned and both ends of each section bevelled, so that they can be lined up end-to-end.

The next step is to weld two 12 m lengths into a 24 m ‘double joint’. Every weld is subjected to ultrasonic testing so that even the smallest defect can be detected and rectified before the double joint in the process line – known as the ‘firing line’ – is connected to the already completed section of the pipeline.

When the weld has been inspected and shown to be perfect, the entire area of the unprotected joint linking the two pipe sections will be wrapped in a heated, corrosion-proof shrink sleeve. As the sleeve cools, it will form a waterproof seal by shrinking and wrapping around the welded joint. Around that, a steel collar will be applied and secured with steel belts. Then, polyurethane foam is poured into a mould which serves to protect the shrink sleeve especially during pipelaying.

The pipeline will be lowered to the bottom of the sea in the form of an S-shaped curve. During this process, the pipeline will be held in the right position for installation by a number of durable tensioners. The tensioners control the movement of the line and keep it under tension, so that it slides via an additional extension (known as a ‘stinger’) over board the stern slowly onto the sea bottom. Under normal conditions, up to 3 km a day of pipeline can be laid using this procedure.

Commissioning and maintenance

When construction is complete, the pipeline will be filled with water and subjected to a minimum 24 hour pressure test. For this, the water pressure will be higher than the eventual gas pressure, and it is conducted to confirm the integrity of the pipeline. Subsequently, the water is completely removed from the pipeline, which is then dried before gas is introduced for the first time.

When construction work has been completed, all preparations have been finalised, and the pipeline has been approved by the authorities, the line can be filled with gas and commercial operations can begin.

To launch gas transmission, a part of the pipeline is filled with a buffer gas (nitrogen) to prevent the air in the pipeline coming into contact with the natural gas. When it has been filled with the buffer gas, natural gas from Vyborg in Russia will be fed into the line. At the natural gas receiving facility in Lubmin near Greifswald, air, then nitrogen, and then a mixture of nitrogen and natural gas will be bled off into a secure area. This ventilation process ends when the pipeline contains only natural gas that meets the purchasers’ specifications. Thereafter, gas will be pumped in at Vyborg and the pipeline pressurised.

Pipeline operation will commence when the pressure has reached the minimum required level in Germany. At zero throughput (i.e. if there is no gas offtake in Lubmin), only sufficient gas will be fed into the pipeline to ensure, after pressure equalisation, that pressure in the pipeline nowhere exceeds 170 bar – the minimum design pressure of the final section. An online monitoring system ensures that this maximum pressure level is observed.

The pipeline will be remotely controlled from a dispatching centre where specialists will monitor the system around the clock, 365 days a year. In an emergency, the specialists will be able to immediately activate safety devices, such as isolation valves. Alternatively, these are self-activated if certain specified criteria are exceeded. In addition, procedures developed by Nord Stream for regular checking and maintenance will ensure that the system will operate throughout its life as reliably as when first commissioned.

Regular runs through the pipeline by pigs will be undertaken to examine for corrosion or other flaws. These intelligent pigs are equipped with a high-resolution magnetic flux leak technology, which can recognise the slightest flaw caused by corrosion or other damage. In addition, subsea vessels – remotely operated vehicles (ROVs) equipped with cameras – will provide regular checks of the pipeline exterior.

The advantages of an offshore pipeline

The fundamental decision to opt for an offshore pipeline was based on a series of economic, environmental, technical and safety considerations. Compared with a purely onshore route, transporting gas from gas fields in Russia to the consumers in Europe via Nord Stream saves €45 billion over a period of 50 years. Not only is the route via the Baltic Sea shorter, it can also operate at a higher pressure. This means fewer compressor stations have to be built and the system needs less fuel gas, saving costs and up to 200 MMt of greenhouse gas emissions over the course of the pipeline’s lifetime.

Offshore pipelines are based on proven technology. Some brief environmental impacts during pipelaying are unavoidable, but offshore oil and gas pipelines transport gas when in operation with virtually no negative effects on the maritime ecosystem. The world’s oceans are home to thousands of kilometres of underwater lines. Not one single major disruption has occurred in recent decades.

Seabed examination

The Baltic Sea is a sensitive ecosystem with a complex seabed morphology. Nord Stream has undertaken detailed studies of the seabed along the whole of the pipeline route using the most up-to-date inspection equipment and procedures.

Starting in 2006, the route has been optimised several times. Extensive examinations of the seabed along the entire route have resulted in minimising the amount of work needed on the seabed to ensure a stable location for the pipeline. Minimising seabed construction work reduces both the environmental effects and the costs of installation, meaning that environmental and economic interests, in this case, are in accord.