Corrosion protection

CORROSION PROTECTION of mining machines, built structures (EN: rust protection of mine equipment and machinery, corrosion protection of mining machinery and equipment; DE: Korrosionsschutz von Bergbaumaschinen und -anlagen; FR: protection contre la corrosion de l'equipement minier; ES: protection contra la corrosion del equipominero; RU: антикоррозионная защита) is the complex set of the means and methods of the protection of metallic and other structures against corrosion.

For the protection of copper, there were used yet during the ancient times the hot tinning, vegetable oils, corrosion-resistant alloys (tin bronze, brass), for the protection of the iron and steel products, there were used the polishing, burnishing, tinning. At the start of 19th century, there has been discovered the electrochemical method of corrosion protection with the help of protectors. During the middle of the 19th century, there has been established the principal possibility of obtainment of metallic coatings with electrolytic method.

The corrosion protection is developing itself most intensively during the 20th century in association with the invention of the stainless steels, new corrosion-resistant alloys, polymer coatings, and others. The system of the corrosion protection is determined by the conditions of exploitation, and by the mechanism of corrosion of metals (by electrochemical or chemical one). Within the underground (underwater) conditions of work of mining equipment, the process of corrosion of metals has electrochemical character. In association with this, for the prevention of the corrosion of underground structures, drilling rigs, overpasses, sea going vessels, and others, and also of the apparatuses, which are working with aggressive electrical-conductive environments, they use the electrochemical methods of protection. So, during the cathodic (or anodic) polarization from the external source of the electrical current, or during the attachment of the protectors to the protected structure, the potential of the metal shifts to the values, at which its corrosion slows very much or stops completely. They use for the corrosion protection the inhibitors of corrosion (chromates, nitrites, benzoates, phosphates, and others), which they introduce in small quantities into the aggressive environment, and create on the surface of the metal the adsorption film, which is slowing the electrolytic processes, and is changing the electrochemical parameters of the metals. There belong to the methods of corrosion protection the alloying of the metals, and their thermal processing. There is achieved with alloying (for example, with chromium, nickel) during the electrochemical corrosion the transition of metal from the active state to the passive one; during this process, there is forming itself the film with good protective properties. The additional alloying of the stainless steels with molybdenum protects them from the dot corrosion within the marine conditions. The alloying of titanium with small quantity of palladium sharply improves the corrosion resistance within the aggressive slightly acidic environments. The thermal processing of metals eliminates structural heterogeneity, which is causing the selective corrosion, and relieves internal stresses within alloys (for example, of the austenitic stainless steels, which are not containing titanium and niobium, of the aluminium alloys, of the martensitic slightly alloyed and stainless steels, and others), thus eliminating the conditions for the development of the intra-crystalline and dotted corrosion.

They widely use for the corrosion protection the protective coatings, both metallic (pure metals and their alloys) and non-metallic. Depending on the potential of metal, the coatings may be anodic and cathodic (in relation to the protective metal). As the consequence of the bias of potential, the anodic coatings decrease or completely eliminate the corrosion of the primary metal within the pores of the coating, that is perform the electrochemical protection, while the cathodic coatings, which are enhancing the physical-mechanical properties of the metal (for example, the wear resistance, hardness), can increase the corrosion of the primary metal within the pores. There are distinguished because of the high protective properties the non-metallic coatings, namely, laquer and paint ones, plastic ones; they may be restored during the process of the exploitation. There are introduced yet more often the coatings of polyethylene, polyisobutylene, fluoropolymer, nylon, polyvinyl chloride, and other materials, which are having the great water, acid, and alkali resistance. There effectively protect against the activity of acids and other reagents the coatings on the basis of rubber (gumming). They protect against corrosion the underground structures, for example pipelines, with the help of bitumina, asphalts, polymer tapes and enamels, and also with the help of the drainage of the stray currents from the structure. They subject to conservation metallic products and spare parts during the long-term storage and transportation. During the struggle against corrosion, there has the important significance the rational design, during which there are eliminated the joints of the parts, which are subject to corrosion (slits, gaps, and others), there are excluded the unfavourable contacts of the heterogeneous metals, which are increasing corrosion, and so on.

There are also subject to corrosive destruction the concrete, building stone, wood, and other materials, which are widely used within the mining industry. The corrosion protection of the structures of concrete is provided using the increase of its density, careful choice of composition, rational placement and compaction of the concrete mixture, introduction into mixture of the components, which are enhancing the corrosion resistance, and removal from it of the substances, which are assisting the corrosion. They use also the special portland cements (pozzolanic one, sulfate resistant one, slag portland cement, and others). They widely use the protective coatings, which are insulating the structures of concrete, and also of wood and stone, from the external environment. Besides this, they change the composition of the environment, namely, they introduce into it the substances, which are slowing the corrosion, or remove the components, which are especially hazardous in relation to corrosion (neutralization, water drainage, and others).