How the pipes for the Nord Stream are laid in the Baltic Sea

How is it possible - to lay hundreds of kilometers of steel pipes to a great depth, on the bottom with difficult relief? How to ensure that this whole structure withstands enormous pressure, does not move, is not destroyed by corrosion, withstand the blows of ship anchors and fishing equipment, and finally, just work as it should? The most recent example of the construction of the underwater mega pipeline was the famous Nord Stream, which ran along the Baltic bottom and connected the Russian and German gas transmission systems. Two pipelines, each more than 1200 km long - almost 2.5 million tons of steel, absorbed by the sea according to the will of man. Using the example of Nord Stream, we will try to briefly talk about technologies for creating underwater pipelines.
As in the Baltic Sea are laying pipes for

The two gas lines consist of 199,755 twelve-meter pipes made from high-grade carbon steel.But since it comes to contact with such a chemically aggressive environment as sea water, the metal needs protection. To begin with, a three-layer coating of epoxy and polyethylene is applied to the outer surface of the pipe - this is done directly at the manufacturing plant.
As in the Baltic Sea are laying pipes for

Is it possible to lay such a pipe on the seabed? No, it needs to be further protected and strengthened against water pressure and electrochemical processes. A so-called cathodic protection is installed on the pipes (imposing a negative potential on the surface to be protected). With a certain step, electrodes are welded to the pipes, which are interconnected by an anode cable, which is connected to a constant current source. But the main thing that still needs to be done with the pipe before it is ready to sink to the bottom is the coating. In special factories, the outer surface of the pipe is covered with a layer of concrete 60–110 mm thick. After the concreting, the pipe gains a weight of about 24 tons. It has serious protection against mechanical effects, and the additional mass allows it to lie stably on the bottom.
As in the Baltic Sea are laying pipes for

But we must remember that even the bottom of such a relatively shallow sea, like the Baltic Sea, will not in itself provide a convenient and safe bed for the gas pipeline.There are two factors that inevitably had to be taken into account by the designers and builders of Nord Stream: anthropogenic and natural.
As in the Baltic Sea are laying pipes for

The history of shipping in the North European region dates back thousands of years, and therefore a lot of all kinds of rubbish accumulated on the bottom of the sea, as well as fragments of sunken ships. The twentieth century made its terrible contribution: during the World Wars, active hostilities were fought in the Baltic, hundreds of thousands of sea mines were laid, and after the wars at sea, ammunition, including chemical, was disposed of. For the monitoring of ammunition, ships were equipped with echolocation equipment, as well as a special ground robot (ROV), connected by a cable to the TMS base station.
As in the Baltic Sea are laying pipes for

Another factor, natural, is associated with the features of the bottom relief. The bottom of the sea is composed of various rocks, it has protruding ridges, depressions, crevasses, and it is not always possible to lower the pipes directly onto all this geological diversity. If we allow a large sagging of the gas pipeline between two natural supports, the structure may eventually collapse with all the troubles that result from this.Therefore, the bottom relief for laying must be artificially corrected.
As in the Baltic Sea are laying pipes for

Now, perhaps the most interesting thing: how are the pipes at the bottom? Of course, it is difficult to imagine that each individual 12-meter pipe is welded to a gas pipeline directly into the sea at depth. This means that this procedure must be done before installation. What actually happens on board a pipe-laying vessel. Here it is necessary to briefly return to the design of the pipe itself and notice that after applying anti-corrosion protection and heavier concreting of pipe on it, the pipe ends remain open and unprotected, otherwise welding would be difficult. Therefore, sections of the joints are protected from corrosion after welding.
As in the Baltic Sea are laying pipes for

Next comes the laying of the S-shaped way. In the process of laying, the whip welded from pipes acquires a shape resembling the Latin letter S. The scourge at a small angle leaves the stern of the ship, drops sharply down and reaches the bottom, where it takes a horizontal position. The hardest thing to imagine is that a thread of steel, concrete-coated 24-ton pipes is capable of such sharp bends without breaking, but everything happens that way.
As in the Baltic Sea are laying pipes for

Before using the gas pipeline to transfer fuel, it was tested ... with water. A seawater that was previously filtered from suspensions and even bacteria was pumped into the sections using a piston module. The fluid injected from a special vessel created a pressure in the lash that exceeded the working pressure, and this mode was maintained for 24 hours. Then the water was pumped out and the section of the pipeline was dried. Even before natural gas appeared in the pipeline, its pipes were filled with nitrogen.
As in the Baltic Sea are laying pipes for

The laying of the pipeline on the seabed is only part of the Nord Stream project. It took a lot of effort and cost to equip the coastal infrastructure. A separate story is the stretching of a gas pipeline to the shore using a powerful winch or the creation of a mechanism to compensate for the seasonal compression-expansion of the 1,200-kilometer line.
As in the Baltic Sea are laying pipes for

The construction of the Nord Stream has sparked a lot of discussions on various political issues ranging from ecology to the excessive role of raw materials exports in the Russian economy. But apart from politics, one cannot help noticing: the trans-Baltic gas pipeline is an excellent example of how advanced technologies and international cooperation are capable of working modern miracles in a completely working routine.
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As in the Baltic Sea are laying pipes for

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