V. R. Ivashkiv

Corrosion and tribocorrosion of 17G1S-U (17Mn1Si) steel in a chloride-acetate solution bubbled with hydrogen sulfide, air, and their mixtures at a ratio of partial pressures PH2S : Pair 1:1 and 1:10 were investigated. At low oxygen concentrations, the corrosion rate of steel is lower than in a saturated hydrogen sulfide solution due to the interaction of H2S and O2 and a decrease in the conсentration of both components. At oxygen high concentrations, steel corrosion accelerates due to the oxidation of sulfide films on the surface and the deterioration of their protective properties. Hydrogenation of steel decreases with oxygen partial pressure increase due to decreasing sulfide concentration in the solution. Tribocorrosion of steel in the solution at a ratio of partial pressures 1:1 depends on a combination of anodic dissolution and hydrogen cracking, and at a ratio of 1:10 – mainly on anodic dissolution. The combined effect of pitting corrosion, iron oxides and hydroxides in the corrosion products determines the abrasive mechanism of tribocorrosion.

The influence of chemical and electrochemical polishing on the surface roughness of the Ti–6Al–3Mo alloy obtained after wire electroerosion cutting are investigated. After electrochemical polishing in mixtures of perchloric and acetic acids, the surface roughness of the alloy Ra corresponds to 0.8 mkm, but due to the inhomogeneous distribution of the electric field, rounding of the edges and macro-unevenness occurs. The composition of the electrolytes and the modes for chemical polishing of the alloy are recommended. After such treatment, the arithmetic mean of the profile deviations does not exceed 0.6 mkm.

The wear resistance of steel 45 in oil-abrasive medium with surface nanocrystalline struc­ture formed by severe plastic deformation using energy of high-speed friction with addi­tional alloying with chrome and nickel from special technological media during mecha­nical-pulse treat­ment is studied. The increase of the wear resistance of steel due to surface alloying during mechanical pulse treatment comparing with the same treatment without surface alloying is shown. This is explained by the formation of the nanostructure with less grain size and higher microhardness, as well as the effect of alloying elements on the structure formation with lower electrochemical potentials, which are more favourable for secondary structures formation due to surface activation during wear resistance tests.

Hydrogen permeability through a steel 20 membrane during corrosion in a chloride-acetate solution under the influence of dissolved CO2 and H2S and mechanical stress was investi­gated. It was established that the permeability and effective diffusion coefficient of hydro­gen are the lowest in a solution saturated with carbon dioxide. Adding hydrogen sulfide to the solution at a concentration from 100 mg/dm3 to saturation leads to an increase in the permeability of hydrogen through the membrane from 1.5 to 3.2 times, which is associated with the intensification of corrosion and hydrogenation of the charging surface. At the same time, the effective hydrogen diffusion coefficient is stable. The applied mechanical stress increases the subsurface concentration and permeability of hydrogen atoms in the metal. The penetration of hydrogen depends, first of all, on the hydrogen sulfide con­cen­tration in the solution, which determines the corrosion and hydro­genation rates of the steel.

The causes of accelerated corrosion of a coiled tubing НT-95 steel after acid washing of a gas field well in the Poltava Basin were investigated. Corrosion losses of steel in the washing solution do not exceed 3.6 mm/year due to the presence of a corrosion inhibitor in its composition. It was found that after acid treatment of a gas well, the corrosion rate of steel increased by three orders of magnitude. It is shown that the accelerated corrosion of steel occurs due to neutralization of the inhibitor effect and the change in the nature of metal corrosion caused by the high concentration of oxidizing agents such as iron (III) Fe2O3 oxides in the well. When Fe2O3 interacts with the hydrochloric acid of the washing solu­tion, iron chloride FeCl3 is formed, which partially neutralizes the inhibitor effect and accelerates corrosion of steel.