Arctic pipelines

ARCTIC PIPELINES (EN: Arctic pipelines; DE: arktische Rohrleitungen; FR: conduites arctiques, tuyauteries arctiques; ES: conductos articos, tuberias articas; RU: арктические трубопроводы) are the trunk pipelines (transport lines for the gas, oil, and oil products), which are constructed on the territory, which is limited with the Arctic circle (66 degrees 33 minutes of the northern latitude).

The division of pipelines into the Arctic and located to the south of the Arctic circle is conventional, because both of them have all the features of the trunk pipelines. The major peculiarities of the Arctic pipelines are determined by the speciality of climatic conditions, which are characteristical for this territory: low radiative balance, zero summer average and negative annual average temperatures, large areas of the permafrost soil, flooding, and strong swamping of the flat plain terrains. The most important of these factors, which are determining the basic constructive and technological distinctions of the Arctic pipelines, are the permafrost soils and low temperatures of the air.

The selection of the scheme of the laying down of the pipeline (underground, overground, or terrestrial) is determined by the thermal interaction of the pipes with soil and environment. At the negative temperature of the product, which is transported, the bearing capacity of the permafrost soil is sufficient for the normal work of pipeline of any design. At the positive temperature of the product, the soil around the pipes thaws (there forms the so-called halo of thawing), and the pipeline either floats up (positive buoyancy), or settles down. Then there are possible the failures of the pipelines, which are accompanied by the large losses of the products, which are transported.

During the underground laying down of the Arctic pipelines, there are undertaken the measures for the prevention of the thawing of the permafrost soil. This is achieved with the cooling of the product, which is pumped, to the temperature of 1-2 degrees Celsius, or with the cooling of the soil, which is surrounding the pipes, with the help of the special refrigeration devices (thermal piles). For the cooling of the gases, which are having the temperature of 40-50 degrees Celsius at the output of the compressor stations, they construct the special installations with the air cooled apparatuses and with the refrigeration machines. The cooling of the oil is not performed, because then its viscosity significantly increases, and its transportation becomes impossible without the increasing of the pressure. They lay down the underground oil pipelines only with the thermal insulation of the pipes, and with the construction of thermal piles. For the stabilization of the position of the pipelines, and for the prevention of their floating up during the summer time, when, under the influence of the solar radiation, frozen soils thaw down to the depth of 1 metre, and the surface of the soil covers itself with water, they perform the ballasting of the pipelines, or they conduct the laying down of them with the usage of the anchored supports. There is provided the special protection of the thermal insulation against the moisture.

The overpasses of the Arctic pipelines are constructed on the pile supports. During the construction of such pipelines, they install the compensating devices for the compensation of the longitudinal deformations (see the "Beam overpasses of pipelines" article), and there are undertaken the measures for the prevention of the oscillations of the pipelines because of the action of the wind (see the "Hanging pipelines" article). The construction of the overground overpasses of the Arctic pipelines is associated with the complications of the installing of the support devices on the permafrost, flooded, and swamped soils, of the laying down of the underground sections, in order to free the space for the passage of the herds of the deers, and also with the changes of the properties of the steel of the pipes at the temperatures of up to -15-30 degrees Celsius. The ordinary steels at these temperatures become brittle, and destruct themselves because of the action of the internal pressure within the pipeline. Sometimes there proceed the destructions of the pipes at the places of up to 1-2 kilometres of length. For the construction of the Arctic pipelines, they use the pipes of the special (for the pipes) steels, which are having the great (toughness) strike viscosity, and also the pipes of the special design (multilayered, combined). This increases the cost of the Arctic pipelines by 2-3 times in comparison with the pipelines, which are laid down under the ordinary conditions.

Within the USSR, the Arctic pipelines have been constructed, and are operated at the north of the Komi ASSR, within the Tyumen province of the RSFSR, the Arctic pipelines operate also within the USA, Canada, Denmark, Norway.