Constructing a subsea pipeline

Building Nord Stream 2 is a feat of expert teamwork and precision engineering.

For each line of the twin pipeline, around 100,000 12 metre pipe sections will be welded together and laid over a distance of 1,200 kilometres underneath the Baltic Sea.

Every joint is rigorously examined to meet international quality standards and ensure the integrity of the pipeline. Every care is taken to minimise impacts on the marine environment. Every pipe delivery must be punctual so that pipe lay vessels can maintain their 24 hour daily production schedule.

The Nord Stream 2 team, supported by expert contractors, will plan every step of the process in detail to ensure that construction is seamless once pipe-laying begins in 2018.

The construction process begins with the fabrication of individual pipe sections. The pipes are manufactured to precise specifications, with a diameter of 1,153 mm and a wall thickness of up to 41 mm. They are then coated internally to reduce friction against the gas flow, and coated externally to prevent corrosion and add protection and stability on the seabed.

Manufactured pipes are already being delivered to the coating plants, to ensure all the pipes are ready in time to meet the construction schedule.

Pipe

Europipe GmbH is one of three pipe suppliers selected by Nord Stream 2 AG. Production of the high-quality large-diameter pipes started in August 2016 and will continue in several lots up to mid-2018 in the pipe mill in Mülheim an der Ruhr, Germany, for a total of 90,000 out of the 200,000 pipes that will be required for the pipeline. The pipes are transported entirely by rail to the Port of Mukran.

Once pipe-laying begins, the coated pipes will be shipped regularly from their storage locations around the Baltic Sea in time to meet demand from the pipe lay vessels.

Both before and during the construction phase, survey vessels will perform detailed inspection of the seabed along the pipeline route, to check for any new obstructions. Coarse gravel will be strategically placed where needed to provide a stable base for the pipeline.

In cooperation with the relevant authorities, Nord Stream 2 and its contractors will share information about the location of construction vessels and their Safety Exclusion Zones, to minimise disruption to other sea traffic.

On board the offshore pipe lay vessel, individual pipe sections (approx. 12.2 m lengths) will be bevelled and then welded together as part of a production process to construct the main pipe string which is laid on the seabed.  

All welds that join each length of pipe together will undergo ultrasonic testing to detect any flaws. Once the weld is approved, a corrosion resistant sleeve will be applied over the weld area, followed by a layer of polyurethane material which serves to encapsulate the corrosion resistant sleeve. The pipeline will then be progressively lowered from the vessel to the sea bed as a continuous pipe string. This operation is done in a carefully controlled manner using specially designed tensioners that securely hold the pipe as the vessel moves forward along the pipeline construction route.

Survey vessels will use underwater remotely operated vehicles to monitor the installation to ensure the pipeline is correctly positioned on the seabed.

Through this carefully managed process, individual lay vessels can construct the pipeline at a rate of up to three kilometres per day. The pipeline is anticipated to be completed in time for start of gas transportation at the end of 2019.