Today in the fields pipes will be used mainly with plastic, epoxy and paint coatings. However, the enamel more effectively protects the inner surface of pipeline corrosion and wear significantly reduces the hydraulic resistance during the transportation of oil. Oil pipelines pipes with outer diameters from 76 to 426 mm (with gauge enameling technology absorption) and wall thickness 3,5-20 mm is usually produced from steel St20 (high ductility and weldability) or 9HGS (with high toughness). St20 compared with 9HGS contains 2-3 times more carbon is 2-3 times less chromium, manganese, silicon, and about the same amount of impurities sulfur and phosphorus. Therefore, steel 9HGS preferable to a cold climate as less susceptible to brittle fracture and thus better enamelled. Aggressive effect on the pipe wall has to cut oil the inside and the outside ground.
The influence of the latter factor is largely determined by climate, soil chemistry, seasonal temperature fluctuations. Corrosive elements are particularly as a source of danger and power of the vagus DC, in contact with an electrically conducting an aggressive environment leads to the destruction of cross-cutting metal. In varying degrees this applies to the epoxy and polymer Coatings having poor adhesion and continuity, such as EP-140 enamel or enamel SD-7101. Conditions for the development of the corrosion process is retained even in the presence of a well adhered plastic coating. Aggressive environment, transported through pipes, flooding is often layered with oil content of the overwhelming highly mineralized formation water and the presence of abrasive particles. Thus, the wall of the pipe is exposed to intensive the corrosive effect of two counter-destructive factors – both inside and outside. Research has shown that metal corrosion in both cases, the proceeds of an electrochemical mechanism, at least at the initial stage operation. Further anodic dissolution process is localized on the part of the soil under the influence of makrogalvanicheskih elements, and the destruction continues in the main pipe from the inside.