Offshore pipeline across Baltic will secure Europe gas supply

Tag : Gas Flow Valves

 With European gas import needs projected to grow by about 200bcm bythe year 2015, Nord Steam will meet about 25percent of thisadditional requirement. After completion in 2012, the pipelineacross the Baltic Sea will connect the world’s largest gasreserves, located in Russia, with the European gas pipelinenetwork, securing natural gas supplies for the continent over thecoming decades.

The Nord Stream system is being meticulously planned down to thesmallest technical detail. This includes everything from thecarrying-out of risk assessment studies, to the exact determinationof the seabed route, to the selection of materials for thepipeline, to the technical design for a safe operation of thesystem.

The pipes for the pipeline will be manufactured from high-tensilesteel in accordance with DNV Offshore Standard OS-F101. The pipe wall thickness will vary from approximately 27mmto approximately 41mm in accordance with the dropping pressurealong the route. Inside, the pipes will be covered withantifriction coating in order to increase performance.

On the outside they will be coated with an anti-corrosion layer. Togive them extra weight and ensure their stability on the seabed,the steel pipes will be coated externally with concrete of athickness of between 60mm and 110mm. Each pipe joint is 12m long.

To ensure that the pipeline can withstand the high internalpressure of over 200bar, independent checks and quality controlwill be carried out both by the pipe mills, by independent pipelineexperts as well as by experts from Nord Stream AG. Duringmanufacturing in the pipe mills, the pipes will be thoroughlyinspected with non-destructive methods like ultrasonic testing,magnetic particle testing and radiographic testing to detectpossible material defect which are not visible from outside. Themechanical properties of the steel material will also be testedcontinuously during the manufacturing of the pipes. That way, onlypipes with the specified strength and material toughness will beused. Finally, each of the finished pipes will be subjected to anumber of quality checks before they are released from the pipemill for further use. As part of this process each pipe will befilled with water to a pressure substantially higher than themaximum operational pressure.

Before engineering work starts, the seabed will be thoroughlysurveyed along the whole pipeline route for potential obstacles.Side scan sonars will search for metallic objects in and on theseabed. Investigation of the soil, the water current, the seatemperatures and waves parameters are also part of the surveys andare pre-requisite for the engineering works. The engineers willthen determine in detail where it is necessary to prepare theseabed before pipeline laying to avoid long free spans. Further, itwill be decided where the pipeline must be buried and how obstaclesor particularly sensitive areas can be avoided.

The steel pipes will be coated in specialised coating yards andstored on land before being shipped with pipe carrier vessels tothe large pipe-laying vessel. The pipe-laying vessels have a large storagecapacity and are manned and equipped to lay pipes 24 hours a day ifthe weather conditions allow doing so. On board the pipe-layingvessel, the pipes will be inspected again for transport damagesbefore they are released for welding. The pipes will be lined upand welded together. Upon completion, each weld will be inspectedby ultrasonic testing to identify possible welding defects.Acceptable welds will be covered with an anti-corrosion coating.The pipeline will be then lowered from the vessel into the watervia the ‘stinger’ which is attached in the stern of the pipe-laying vessel and supports the pipeline. That way, stress onthe pipeline during laying remains within controlled and acceptablelimits.