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Solution method

The speed of the electrochemical corrosion process can be reduced by polarizing the metal structure. Depending on the type of polarization, cathode, anode and protector protection are available. Cathode protection is one of the most common electrochemical protection methods. This method is used to protect steel, copper, bronze, aluminum from non-aggressive environments.
Cathode protection was first proposed by Cumberland in 1913. This method is used to protect metals from corrosion cracks, intergranular corrosion, and pitting corrosion in paladin sea and soil. Cathode protection is also widely used in the protection of underground equipment (gas pipelines, cables) and metal structures from marine corrosion. The essence of cathode protection is that the structure to be protected can be connected to the negative pole of a direct current source or a tread (cathode), turning it into a cathode and preventing corrosion. The positive pole of the current source is connected to a metal plate or graphite (anode).
Figure 1 shows the scheme of cathode protection. The transfer of metal ions from the anode fields to the solution and electrons from the anode fields to the cathode fields and the reduction of depolarizers at the cathode generate an electric current. As the anode is dissolved during the process, it is replaced with a new one after a certain period of time. Cast iron, steel, coal, graphite, metal parts are used as anodes. Cathode protection is also advisable to protect structures from atmospheric corrosion.

Figure 1. Scheme of cathode protection with external current.
1 - Protected product, 2 - Connecting wire, 3 - Direct current source, 4 - Anode grounding[4]

In tread protection, the structure to be protected is connected to a metal tread with a higher electronegativity potential. Protector protection was first proposed by Devi in 1824 in the protector protection of iron nails connecting the copper plates of the ship's hull. During the years 1854-1858, B.S. Jacobi proposed a zinc tread to protect the steel bodies of mines at sea. Currently, zinc, Al-Zn alloys and magnesium alloys are used as treads to protect steel structures from soil and marine corrosion. Magnesium, zinc or treads containing 9% Al and 10% Zn are used for steel and cast iron. Because Al is covered with a very dense oxide layer, which limits the transmission of current.\

Figure 2. Scheme of tread protection

1. 
   Pipe (to be protected) 2. Cable 3. Protector 4. Key 5. Filler
   

The electrical conductivity of the electrolyte has a significant effect on the tread area. Proper application of this method of protection can completely stop or reduce the corrosion of metal structures. The tread is gradually replaced with a new one after it is resolved during the protection process. Tread protection is used to protect metal structures from corrosion in marine, soil and neutral corrosion environments. Application is limited in acidic environments due to the high solubility of the metal tread and low cathode polarization. JaSO₄, Na₂SO₄, MgSO₄ salt mixture is used as filler in treads.

Anode protection is used to protect chemical industry equipment from corrosion. The rate of electrochemical corrosion of metals can be reduced by anode polarization. In this case, the potential of the metal to be protected tends to be negative. Some metals, such as chromium, nickel, titanium, zirconium, and iron alloys containing these elements, are easily passive in an oxidizing environment. These properties are of great practical importance in the corrosion protection of metals. The formation of a coating on the metal surface tends to negatively affect the potential of the active metal, which reduces the rate of corrosion. The application of anode protection of metals is somewhat limited, because passivation is more effective in an oxidizing environment. Unlike cathode protection, anode protection is connected to the positive pole of the current source of the product to be protected. The cathode is located close to the surface of the product. Anode protection is used to protect alloy steels from corrosion. [5]
Inorganic and organic varnishes and paints. Despite the good results of varnishes and paints in protection against atmospheric corrosion, they become unusable in the soil after a few months. Varnishes and paints containing coal tar are recommended for the prevention of corrosion of underground facilities and underground pipelines. These paints require very little material cost and effectively protect the soil from corrosion. Bitumen coatings also provide reliable protection. These coatings are currently used in conjunction with other protective materials. For example, in the protection of underground pipes from corrosion, these coatings are applied in combination with 1 mm thick epoxy resin or 5 mm thick polyethylene. The 11-year experience of the American National Bureau of Standards has shown that 6 mm thick soft steel provides excellent protection against corrosion. Portland cement and fiberglass are well protected from corrosion by many years of experience. However, both protective coatings are very fragile and prone to mechanical breakdown.
Galvanizing from metal coatings shows good results. Metal coatings Large iron surfaces corrode very quickly. In this case, it is advisable to use special artificial materials that insulate the protective coatings. [6]

4. 
   Results
   

The speed of the electrochemical corrosion process can be reduced by polarizing the metal structure. Depending on the type of polarization, cathode, anode and protector protection are available. Cathode protection is one of the most common electrochemical protection methods. This method is used to protect steel, copper, bronze, aluminum from non-aggressive environments.
1. Cathode shielding metals are used to protect against corrosion cracks, intergranular corrosion, and pitting corrosion in paladin sea and soil. Cathode protection is also widely used in the protection of underground equipment (gas pipelines, cables) and metal structures from marine corrosion.
2. In tread protection, the structure to be protected is connected to a metal tread with a higher electronegativity potential. . Currently, zinc, Al-Zn alloys and magnesium alloys are used as treads to protect steel structures from soil and marine corrosion.
3. Anode protection is used to protect chemical industry equipment from corrosion. The rate of electrochemical corrosion of metals can be reduced by anode polarization. In this case, the potential of the metal to be protected tends to be negative.

5. 
   Literature
   

1. Tomashov N.D. Theory of corrosion and protection of metals. M. Academy of Sciences of the USSR, 1959, 592 p.
2. Zhuk N.P. Course of the theory of corrosion and protection of metals. M. Metallurgy, 1976. 472 p.
3. Kolotyrkin Ya.M. Advances in Chemistry, 1962, vol. 31, no. 2, 322 p.
4. Rosenfeld I.L. Atmospheric corrosion of metals. M. ed. Academy of Sciences of the USSR, 1960, 372 p.
5. Keshe G. Corrosion of metals. Per. from German. M. Metallurgy, 1984, 400 p.
6. Internet resources