Products of fuel combustion (coal, liquid hydrocarbons, black oil, etc.) contain significant amounts of connections of sulfur and the vanadium, influencing for the speed of gas corrosion. In these conditions corrosion carbonaceous and low-alloy steels the more strongly, than above factor of the charge of air on combustion of fuel. At presence in the environment of compound of sulfur ferricarbonic alloys are subject of intercrystalline attack. It is possible to explain it big number of defects in crystal lattices of sulfides, in comparison with oxide lattices, that results, in turn, in acceleration of diffusion processes and an intensification of corrosion. The mechanism of influence of compound of vanadium is those: at burning the cheap liquid fuel polluted by vanadium (black oil, oil), a plenty of the ashes containing pentaoxide of vanadium is formed. Ashes, sticking to a surface of metal, increases speed of its oxidation and causes undersurface corrosion at temperatures above of ashes.
In techniques corrosion prevention is carried out by various methods. The most rational and reliable way is manufacturing devices, machines, etc. from corrosion-proof both metal, and nonmetallic materials. However this way of protection against corrosion can be not always used by virtue of economic, technical or technological conditions. In the industry often produce products, devices, pipes from the cheap and accessible materials possessing high technological and mechanical properties, with their subsequent protection against corrosion.
Methods of protection against corrosion can be divided into three groups:
1) Influence on metal;
2) Influence on an excited environment;
3) The combined methods of protection.
To the first group of methods of protection carry:
a) Metals alloying - creation of a shielding superficial layer, introduction of the elements lowering catholic or anode activity of an alloy, introduction of the elements preventing structural corrosion;
b) Processing of the metal surface - thermal and thermochemical processing, vibrating a proskating of surface, chemical and electrochemical sputtering, machining (cold-hardening, rollers, etc.), modifying of rust on the surface;
c) Deposition of protective coatings - constant, temporary and periodic action (greasing, wax);
d) Selection of corrosion-proof materials for conditions of operation of a design;
e) Rational designing - withdrawal of separate design units from excited environments, exception of stagnant zones of aggressive liquids;
f) Electrochemical protection.
The second group of protection methods includes:
a) Application of corrosion (decelerator) inhibitor;
b) Hermetic sealing of design (full or partial);
c) Creation of artificial environments (processing of water environments, application of neutral environments, dehydration of air).
To the third group refer:
a) Complex protection measures influence on metal;
b) Complex influence of protection measures on an excited environment;
c) Complex influence on metal and an excited environment.
The decision of corrosion protection problem of complex systems (cars, the equipment chemical, an iron and steel industry, bridges, etc.) is possible only at the system approach to research and the organization of designing of protection methods.
Now various methods of coverings deposition find practical application: electrochemical sedimentation from water solutions and salts flux, chemical sedimentation from the gas phase, diffusion saturation of the surface, plasma, detonation.
Simultaneous evaporation or dispersion of several metals or alloys and the subsequent sedimentation allow receiving the various combinations of metal and nonmetallic materials practically unattainable by other methods.
Чтобы распечатать файл, скачайте его (в формате Word).
Ссылка на скачивание - внизу страницы.