One of the corrosion prevention methods is to add chemical compounds called inhibitors in corrosive environments. Inhibitors can be inorganic or organic compounds. However, these compounds are dangerous for human health and environment because of their toxicity effects. In addition to obtain them is difficult and expensive. For this reason, corrosion inhibitors that are non-toxic, biocompatible, not harmful to human health and the environment, and which can be obtained easily and cheaply, are the subject of many researches in recent years. Scientists have focused on a new class of inhibitors such as plant extracts, fruit and vegetable extracts and essential oils. Plant extracts are the most studied class of these inhibitors, called green inhibitors. The protection effects of plant extracts are due to the adsorption of their molecules on the metal surface. They provide the metal with a protective film by blocking the active sites. The formation of film provides the metal surface with a physical barrier from corrosive media, and supplies protection effects from corrosive attacks. Copper is noble metal and as a result of this property, it shows to resist against to corrosion. However, certain conditions can cause corrosion on copper, such as polluted air, oxidizing acids, oxidizing heavy metal salts, sulfur ammonia and some sulfur and ammonia compounds. Therefore, the investigation of copper corrosion is significant. In this review, studies are summarized with plant extracts, which have an inhibitory effect on the corrosion of copper.

The adsorption and protective action of sodium malonate and its alkyl derivatives (C2 and C9) on the surface of nickel in a neutral buffer solution was studied. Adsorption isotherms of malonate and its alkylderivatives on the oxidized surface of nickel were obtained and the values of free energy of adsorption 0 -DGa were determined, which lie in the range from 51 to 79 kJ/mol. The dependence of the protective effect on the hydrophobicity of alkylmalonates was revealed. The higher the hydrophobicity of the compound, the higher the protective effect. A composition of sodium malonate and laurate in a ratio of 4:1 has been developed, which has a higher protective effect than sodium malonate and laurate alone.

In the article, the chamber protection of steel with octadecylamine, benzotriazole and binary inhibitors based on them was studied by corrosion and electrochemical methods. It is demonstrated that antagonism of protective action of octadecylamine and benzotriazole in the case of their introduction into the chamber in the form of homogenised mixture is primarily associated mainly with interaction of components in the inhibitor portion. From the perspective of practical utility, the discrete introduction of octadecylamine and benzotriazole into the chamber is more advantageous than the use of a homogenised mixture. The optimal method for protecting carbon steel is the introduction of equal amounts of octadecylamine and benzotriazole into the chamber by weight. The mechanism of action of the binary inhibitor can be defined as a blocking action. The protective effect of the aforementioned chamber inhibitors is associated with the stabilisation of the passive state of steel.

The paper presents data on the corrosion resistance of coatings based on metastable phases of tungsten in the W–C system, obtained by chemical deposition from the gas phase (CVD – chemical vapor deposition) in hot concentrated solutions of hydrochloric acid and hydrogen sulfide, simulating media that can be in contact with metal surfaces of oil and gas equipment during hydrochloric acid treatment of the bottomhole zone wells. It is shown that the corrosion rate of coatings in all media does not exceed 20 microns/year, while their anticorrosive ability practically does not depend on their mechanical characteristics. Also, the extended exposure in hydrochloric acid solution showed that the penetrability of the coatings does not exceed 0.02%.

As part of the development of the concept of creating "smart" adaptive polymer anticorrosive coatings, the kinetics of electrochemical properties of thin- and thick-layer multilayer Zn-filled coatings at various temperatures from 23 to 60°C during prolonged exposure up to 150 days in 3% NaCl were studied. It is shown that at low temperatures and, consequently, low corrosion rates of zinc (Zn) filler, it is advisable to increase the thickness of highly filled composite coatings with active solid-phase additives in order to reduce porosity and create conditions for a restorative increase in impedance. Activation of the self-healing process in multilayer coatings can be realized with an increase in temperature. So already at 40°C, the impedance begins to grow over the entire frequency range. At the same time, an increase in the ohmic component in the high-frequency (HF) region is recorded, with a simultaneous drop in capacitance and an increase in the phase anglemodulus up to 86°, which indicates an increase in the hydrophobicity of the coating material. In parallel, the activation of tread properties is observed. The results obtained show that optimization of the coating design, in particular multilayering, combined with acceleration of coating’s internal diffusion and corrosion processes, make it possible to give the coating "smart" properties by implementing adaptive impedance growth and blocking defects with a corroding metal dispersed filler while significantly extending the period of antocorrosion protection.

Inhibitors and coatings, for example, obtained by chemical oxidation, can be used to prevent corrosion of aluminum alloys. The combination of these two protection methods makes it possible to obtain coatings with high protective properties. In this work, ultrathin inhibited conversion coatings were studied, which were obtained in molybdenum and tungstate converting compounds and their modifications, including well-known corrosion inhibitors of aluminum alloys. It has been shown that the subsequent treatment of coatings in a corrosion inhibitor solution has a greater effect on coatings obtained in a solution based on phosphoric acid than on coatings obtained in a solution based on molybdenum and sodium tungstate. This difference seems to be related to the structure and composition of the coatings under study. Among inorganic modifying additives, the best effect of increasing protective properties is demonstrated by sodium silicate and sodium tetraborate, and among organic ones – tannin and 5-methyl benzotriazole. According to corrosion tests in the humidity chamber, coatings obtained in converting compounds with the addition of sodium silicate demonstrate the greatest corrosion resistance.

A quantitative assessment of both the initial heterogeneity of the structure of epoxy composites and the analysis of its development under the influence of aggressive media by local X-ray spectral analysis of the distribution of particles of inorganic fillers has been carried out. Statistical processing of X-ray spectral analysis profiles makes it possible to accelerate the assessment of changes in the size of the ID and the proportion of Z of various elements of the structure of the inorganic filler framework under the influence of physically and chemically active aggressive media. When filling a system based on an adaptive epoxy-phenol-formaldehyde-furan FF matrix with chromium oxide Cr2O3, a complex effect of reducing the proportion of P and the size of ID is observed.

Metal structures, machine parts and technological equipment can be subject to corrosion due to thermodynamic instability of some metals in contact with the external environment. This applies primarily to “ferrous metals” and manifests itself both when they are found in natural conditions and in technological environments. Therefore, it is necessary to monitor their corrosion behavior during operation and use protective measures if necessary. Among the methods of corrosion monitoring stand out methods based on the principles of electrochemistry, because the mechanism of metal corrosion in contact with electrolytes is subject to the laws of electrochemical kinetics. In this case, electrical parameters (potential, current, resistance, impedance) are measured, which makes it possible to easily accomplish this using modern microprocessor technology and create hardware-software complexes for research and control of the metal corrosion state. Among the many methods and principles of the electrochemical measurement results interpretation for the assessment of the metal corrosion state known to date, it is not always easy to choose the optimal method for a particular problem. This is especially true for professionals associated with the control of the corrosion condition of objects, but who have no fundamental electrochemical training. This review summarizes the main methods of corrosion investigation based on electrochemical measurements and shows their capabilities and the relationship of the parameters used. In addition, a description of the software developed to implement the described methods using the IPC-FRA potentiostatic system is given.

A methodology for analyzing the properties and mechanisms of action of chamber corrosion inhibitors using electrochemical impedance spectra, adequately described by the equivalent Mansfeld circuit, has been developed. The suggested approach makes it possible:

         – to estimate the coefficient and degree of metal protection by the inhibitor;

          – to estimate the degree of surface coverage with corrosion-blocking layers;

          – to determine the predominant mechanism of corrosion inhibition.

The informative value of the approach was illustrated by data on the effect on the electrochemical impedance spectra:

          – of octadecylamine vapor pressure used in the chamber treatment of copper;

          – of chamber treatment of steel with octadecylamine, benzotriazole and their mixtures with different ratios of the components;

          – of time of zinc exposure in air after chamber treatment with ethylhexanoic acid.

A study of the corrosion-electrochemical characteristics of high-alloy steels 14Cr17Ni2, 12Cr18Ni10Ti and the CrNi77TiAlB alloy was carried out. The optimal laser processing mode was selected from the point of view of corrosion resistance. The corrosion-electrochemical properties of these steels were studied by the method of potentiodynamic polarization in an aqueous borate buffer solution at pH=7.4. In order to increase corrosion resistance, the studied steels were subjected to laser processing in air and argon atmospheres at the radiation powers of 4.5 and 17.9 W. It has been shown that laser processing in air with the power of 4.5 W improves the corrosion resistance of 12Cr18Ni10Ti steel and CrNi77TiAlB alloy compared to the initial data. For steel 14Cr17Ni2, processing in air with the radiation power of 17.9 W is optimal.