DEVELOPMENT OF ANTI-CORROSION COATINGS FOR USE IN THE ARCTIC
In recent years, the development of natural hydrocarbons in the Arctic and Antarctic conditions is the important problem. Cryogenic high-alloy steels used in practice are very expensive and require import substitution. A possible solution to this important problem could be the development of new materials with new phases. These requirements are met by alloys based on Fe (Fe - Ni, Fe - Mn, Fe - Ge, etc.) possessing metastable hexagonal densely packed (HDP) phase ε - Fe. Using the method of high-frequency alternating current (conditions standard T=298 K, p=0.1 MPa) nanostructured electrochemical coatings with iron-nickel and iron-nickel-chromium alloys with the completely new HDP ε - Fe phase and intermetallide FeNi<sub>3 </sub>were obtained. The obtained alloys fully meet the requirements for cryogenic corrosion-protective coatings and are able to replace the currently used imported AISI-316 in terms of processability and cost-effectiveness in offshore trunk pipelines. The work substantiates and establishes the presence of high operational properties of the alloys. The ε - Fe phase is formed under condition of phase transition α - Fe→ ε - Fe (или α - Fe → ε - Fe → γ - Fe) or reverse transition; high pressures (from 11.3 GPa to 13.5 GPa and higher); the phase is metastable (there is a short period ~ 0.1s or at step relief of load it turns into stable form α - Fe again). The alloy coatings obtained have increased cold resistance, low cold brittleness, high value of microhardness and corrosion resistance in sea water. The authors recommend using the coatings Fe - Ni and Fe - Ni - Cr for protection of main offshore pipelines during transportation of hydrocarbons in the Arctic.