Soaking it up like a sponge
Polyurethane foam protects Nord Stream Pipeline through the Baltic Sea
Since April of this year, the crew on the first pipe-laying ship has been working hard on the Baltic Sea, laying the gas lines of the Nord Stream Pipeline Project, which is to run between Vyborg in Russia and Greifswald in the eastern part of Germany. Approximately 200,000 pipes will have to be welded together, and so 200,000 weld seams will have to be sheathed and thus protected against damage. Elastopor® H, an open-cell polyurethane rigid foam, has been selected to accomplish this mission. The product’s strength and processing speed have been refined and optimized by BASF Polyurethanes from Lemfoerde, Germany. Consequently, this rigid foam is contributing to the success of the project, not only quantitatively but also qualitatively.
Nord Stream, a consortium of four companies – OAO Gazprom, BASF SE/Wintershall Holding, E.ON Ruhrgas and Nederlandse Gasunie – plans for its pipeline to connect Russia to the European Union via the Baltic Sea. The goal is to securely supply businesses and households with natural gas in the future. Over next two years, the two pipe-laying companies Saipem and the Allseas Group will deploy three ships to lay two 1220 kilometer-long pipeline conduits on the bottom of the Baltic Sea. The big challenge for the Nord Stream Project is the logistics involved: three pipe-laying ships, five marshalling yards and five countries. In such an endeavor, trust between the contractors and the suppliers is paramount. In addition, efficient and flawless work is a prerequisite for this type of project.
In April 2010, Saipem’s “Castoro Sei” set out to sea with the mission of building a pipeline. It carries aboard polyurethane components made by BASF Polyurethanes. It is anticipated that approximately 2.5 kilometers of pipeline will be laid per day. Starting in August of 2010, the Allseas vessel “Solitaire” is scheduled to join the team. Here, too, BASF’s polyurethane will be on board.
Quickly and uniformly distributed in the hollow space
The optimized Elastopor H was developed over the past two years. The polyurethane systems consist of two liquid components that are mixed together on site using special metering machines and then filled into the hollow space in the sleeve. Subsequently, an exothermal reaction turns the reaction mixture into the actual polyurethane, which is expanded by means of a foaming agent that is also present in the mixture. Thanks to its good flow properties, the polyurethane system is quickly and uniformly distributed throughout the hollow space. In order to prevent the polyurethane rigid foam from being buoyant, it is configured to be open-celled so that hydrostatic pressure causes it to fill up completely with water. Its dimensional stability is crucial here. The material stands out for its high dry density of 160 kilograms per cubic meter, which ensures the sophisticated physical properties of this product. A decisive factor during the laying operation is the fast hardening, since only after that the foam can withstand the stress encountered while the pipeline is being lowered into the sea. Then the weld seam of the pipeline is protected from all sides and can be lowered into the water by the vessel’s so-called “stinger”. Once the pipeline is finally resting on the seabed, the polyurethane rigid foam can perform its full protective function against mechanical stress.
For instance, the Nord Stream pipeline might come into contact with the weights used in large dragnets or with the anchors of ships. However, the rigid foam is formulated to be so flexible that it can withstand and absorb such a massive impact. The destructive force is not transmitted to the pipe. In order to check this property, the foam has to undergo a so-called impact test in which several test sleeves are fixed and subjected to massive blows by a hammer weighing more than two tons. The test demonstrated that the foam is able to withstand even higher forces than required without any damage occurring to the steel pipe.
Polyurethane rigid foam protects welded sites
The construction of the Nord Stream pipeline also makes very strict demands of the other materials and production processes. The pipes, each measuring approximately 12 meters in length, are made of high-strength steel that is suitable for underwater applications. They have a diameter of 48 inches and have an anticorrosion coating made of polyethylene. Over the coating, the pipe is sheathed by a layer of steel-reinforced concrete that is 60 to 110 millimeters thick. On the one hand, this sheathing protects the pipeline against mechanical damage and, on the other hand, its weight prevents the pipeline from floating so that it will stay safe and sound at the bottom of the sea.
The steel pipes are welded automatically on the ship during the pipe-laying operation. In the area of the weld seam, however, there is no corrosion protection and, since the concrete sheathing is interrupted at this place, there is no protection against external effects either. Therefore, this sensitive part of the pipeline has to be painstakingly protected. With this in mind, shrink tubing is pulled over the weld site and the interruption of the anti corrosion layer is thus sealed. A sleeve is put over the concrete sheathing and thus an annular hollow space is formed: This is where the Elastopor H springs into action. The optimized foam is filled into this hollow space. Since approximately 200,000 sleeves have to be filled this way, approximately 9,000 tons of Elastopor H are earmarked for the entire project.
Pipeline tested for tightness
In 2012, the pipeline is scheduled to be fully operational, accounting for a total capacity of 55 billion cubic meters of gas per year. The internal design pressure in the pipes varies along the pipeline length, from 220 bar in Russia to 170 bar in Germany. Prior to the start-up, the pipeline will be filled with water and will have to withstand a pressure test. This concluding test will ascertain whether the pipeline is 100 percent tight and complies with all of the safety requirements. The pipeline is expected to remain in operation for at least 50 years.