Corrosion: types of corrosion, methods of protection. Which cars are more prone to rust?

Corrosion is the destruction of metal, ceramic, wood and other materials as a result of chemical or physico-chemical interaction. As for the causes of such an undesirable effect, they are different. In most cases, this is a structural instability to the thermodynamic effects of the environment. Let's take a closer look at what corrosion is. Types of corrosion must also be considered, and it will not be superfluous to talk about protection against it.

Some general information

We are accustomed to hearing the term "rusting" which is used in the case of corrosion of metal and alloys. There is also such a thing as "aging" - it is characteristic of polymers. Essentially, they are one and the same. A vivid example is the aging of rubber products due to active interaction with oxygen. In addition, some plastic elements are destroyed under the influence. The rate of corrosion directly depends on the conditions in which the object is located. So, rust on a metal product will spread the faster, the higher the temperature. Humidity also affects: the higher it is, the faster it becomes unsuitable for further use. It has been empirically established that approximately 10 percent of metal products are irretrievably written off, and corrosion is to blame. Types of corrosion are different and are classified depending on the type of media, the nature of the flow, and the like. Let's look at them in more detail.

Classification

Currently, there are more than two dozen rusting options. We present only the most basic types of corrosion. Conventionally, they can be divided into the following groups:

• Chemical corrosion is a process of interaction with a corrosive environment, in which the reduction of an oxidizing agent takes place in one act. Metal and oxidizing agent are not spatially separated.
• Electrochemical corrosion - the process of metal interaction with the ionization of atoms and the reduction of the oxidizing agent take place in different acts, but the rate largely depends on the electrode potential.
• Gas corrosion - chemical rusting of metal at a minimum moisture content (not more than 0.1 percent) and / or high temperatures in a gaseous environment. Most often, this species is found in the chemical and oil refining industries.

In addition, there is still a huge number of rusting processes. All of them are corrosion. Types of corrosion, in addition to those described above, include biological, radioactive, atmospheric, contact, local, target rusting, etc.

Electrochemical corrosion and its features

With this type of destruction, the process proceeds when the metal comes into contact with the electrolyte. The latter can be condensate or rainwater. The more salts and acids are contained in the liquid, the higher the electrical conductivity and, consequently, the rate of the process. As for the places of the metal structure most susceptible to corrosion, these are rivets, welded joints, places of mechanical damage. If the structural properties of the iron alloy make it resistant to rust, the process slows down somewhat, but still continues. A prime example is galvanization. The fact is that zinc has a more negative potential than iron. For this simple reason, the iron alloy recovers and the zinc corrodes. However, the presence of an oxide film on the surface greatly slows down the destruction process. Of course, all types of electrochemical corrosion are extremely dangerous and sometimes it is even impossible to fight them.

Chemical corrosion

Such a change in the metal is quite common. A striking example is the appearance of scale as a result of the interaction of metal products with oxygen. High temperature in this case acts as an accelerator of the process, and liquids such as water, salts, acids, alkalis and salt solutions can participate in it. If we talk about materials such as copper or zinc, then their oxidation leads to the formation of a film that is resistant to further corrosion. Steel products form iron oxides. Further lead to the appearance of rust, which does not provide any protection against further destruction, but rather contributes to this. Currently, all types of chemical corrosion are eliminated by galvanizing. Other means of protection may also apply.

Types of concrete corrosion

Changing the structure and increasing the fragility of concrete under the influence of the environment can be of three types:

• The destruction of parts of cement stone is one of the most common types of corrosion. It occurs if the concrete product is systematically exposed to precipitation and other liquids. As a result, calcium oxide hydrate is washed out and the structure is disturbed.
• interaction with acids. If the cement stone is in contact with acids, then calcium bicarbonate is formed - an aggressive chemical element for a concrete product.
• Crystallization of sparingly soluble substances. In fact, this refers to biocorrosion. The bottom line is that microorganisms (spores, fungi) enter the pores and develop there, as a result of which destruction occurs.

Corrosion: types, methods of protection

Billions of dollars in annual losses have led to the fact that people began to fight this harmful effect. It is safe to say that all types of corrosion lead to the loss not of the metal itself, but of valuable metal structures, the construction of which costs a lot of money. It is difficult to say whether it is possible to provide 100 percent protection. However, with proper surface preparation, which consists of abrasive blasting, good results can be achieved. Reliably protects the paintwork from electrochemical corrosion if it is applied correctly. And a special surface treatment will reliably protect against the destruction of metal underground.

Active and passive methods of struggle

The essence of active methods is to change the structure of the double electric field. To do this, use a constant current source. The voltage must be chosen in such a way that the product to be protected increases. Another extremely popular method is the "sacrificial" anode. It collapses, protecting the base material.

Passive protection involves the use of paintwork. The main task is to completely prevent the ingress of moisture, as well as oxygen, onto the protected surface. As noted above, it makes sense to use zinc, copper or nickel coating. Even a partially destroyed layer will protect the metal from rusting. Of course, these types of metal corrosion protection are effective only when the surface does not have visible defects in the form of cracks, chips, and the like.

Galvanizing in detail

We have already considered the main types of corrosion, and now I would like to talk about the best methods of protection. One of these is galvanizing. Its essence lies in the fact that zinc or its alloy is applied to the treated surface, which gives the surface certain physical and chemical properties. It is worth noting that this method is considered one of the most economical and efficient, despite the fact that about 40 percent of the world production of this element is spent on zinc plating. Steel sheets, fasteners, as well as appliances and other metal structures can be galvanized. Interestingly, with the help of plating or spraying, you can protect a product of any size and shape. Zinc does not have a decorative purpose, although with the help of some special additives it becomes possible to obtain shiny surfaces. In principle, this metal is able to provide maximum protection in aggressive environments.

Conclusion

So we told you about what corrosion is. Types of corrosion were also considered. Now you know how to protect the surface from premature rusting. By and large, it is extremely simple to do this, but where and how the product is operated is of considerable importance. If it is constantly subjected to dynamic and vibration loads, then there is a high probability of cracks in the paintwork, through which moisture will enter the metal, as a result of which it will gradually collapse. However, the use of various rubber gaskets and sealants in metal-to-metal contact areas can slightly extend the life of the coating.

Well, that's all for this topic. Be aware that premature structural failure due to corrosion can lead to unforeseen consequences. At the enterprise, large material damage and human casualties are possible as a result of rusting of the supporting metal structure.

Metal corrosion is a widespread cause that renders various metal parts unusable. Metal corrosion (or rusting) is the destruction of metal under the influence of physical and chemical factors. The factors causing corrosion include natural precipitation, water, temperature, air, various alkalis and acids, etc.

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Metal corrosion is becoming a serious problem in construction, at home and in industry. Most often, designers provide for the protection of metal surfaces from rust, but sometimes rusting occurs on unprotected surfaces and on specially treated parts.

Metal alloys are the basis of human life, they surround him almost everywhere: at home, at work, in the process of recreation. People do not always notice metal things and details, but they constantly accompany them. Various alloys and pure metals are the most produced substances on our planet. Modern industry produces various alloys 20 times more (by weight) than all other materials. Although metals are considered among the most durable substances on Earth, they can break down and lose their characteristics as a result of rusting processes. Under the influence of water, air and other factors, the process of oxidation of metals occurs, which is called corrosion. Despite the fact that not only metal, but also rocks can corrode, the processes associated specifically with metals will be considered below. Here it is worth paying attention to the fact that some alloys or metals are more susceptible to corrosion than others. This is due to the speed of the oxidation process.

Metal oxidation process

The most common substance in alloys is iron. Corrosion of iron is described by the following chemical equation: 3O 2 +2H 2 O+4Fe=2Fe 2 O 3 . H 2 O. The resulting iron oxide is that red rust that spoils objects. But consider the types of corrosion:

1. Hydrogen corrosion. It practically does not occur on metal surfaces (although it is theoretically possible). As such, it will not be described.
2. oxygen corrosion. Similar to hydrogen.
3. Chemical. The reaction occurs due to the action of a metal with some factor (for example, air 3O 2 + 4Fe \u003d 2Fe 2 O 3) and proceeds without the formation of electrochemical processes. So, after exposure to oxygen, an oxide film appears on the surface. On some metals, such a film is strong enough and not only protects the element from destructive processes, but also increases its strength (for example, aluminum or zinc). On some metals, such a film exfoliates (destroys) very quickly, for example, in sodium or potassium. And most metals are destroyed rather slowly (iron, cast iron, etc.). So, for example, corrosion of cast iron occurs. More often, rusting occurs when the alloy comes into contact with sulfur, oxygen, and chlorine. Nozzles, fittings, etc. rust due to chemical corrosion.
4. Electrochemical corrosion of iron. This type of rusting occurs in media that conduct electricity (conductors). The time of destruction of various materials during electrochemical reactions is different. Electrochemical reactions are observed in cases of contact between metals that are at a distance in a series of tensions. For example, a product made of steel has copper soldering / fastenings. When water gets on the connections, the copper parts will be cathodes, and the steel will be the anode (each point has its own electrical potential). The rate of such processes depends on the amount and composition of the electrolyte. Reactions require the presence of 2 different metals and an electrically conductive medium. In this case, the destruction of alloys is directly proportional to the current strength. The larger the current, the faster the reaction, the faster the reaction, the faster the destruction. In some cases, alloy impurities serve as cathodes.

Electrochemical corrosion of iron

It is also worth noting the subspecies that occur during rusting (we will not describe, we will only list): underground, atmospheric, gas, with various types of immersion, continuous, contact, caused by friction, etc. All subspecies can be attributed to chemical or electrochemical rusting.

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During construction, corrosion of reinforcement and welded structures is common. Corrosion often occurs due to improper storage of material or failure to perform bar processing. Corrosion of reinforcement is quite dangerous, since reinforcement is laid to reinforce structures, and collapse is possible as a result of the destruction of the rods. Corrosion of welds is no less dangerous than corrosion of reinforcement. This will also significantly weaken the seam and may lead to tearing. There are quite a lot of examples when rust on load-bearing structures leads to the collapse of premises.

Other cases of rusting that are common in everyday life are damage to household tools (knives, cutlery, tools), damage to metal structures, damage to vehicles (both land, air and water), etc.

Perhaps the most common rusty items are keys, knives and tools. All these items are exposed to rust due to the fact that the protective coating is removed by friction, which exposes the base.

The base is subject to destruction processes due to contact with aggressive media (especially knives and tools).

Destruction due to contact with aggressive media

By the way, the destruction of things that are often used in everyday life can be observed almost everywhere and regularly, at the same time, some metal objects or structures can stand rusty for decades and will perform their functions properly. For example, a hacksaw, which was often used to cut logs and left for a month in a shed, quickly rusts and can break during operation, and a pole with a road sign can stand rusty for ten or even more years and not collapse.

Therefore, all metal things should be protected from corrosion. There are several methods of protection, but all this is chemistry. The choice of such protection depends on the type of surface and the destructive factor acting on it.

To do this, the surface is thoroughly cleaned of dirt and dust in order to exclude the possibility of the protective coating not falling on the surface. Then it is degreased (for some types of alloy or metal and for some protective coatings this is necessary), after which a protective layer is applied. Most often, protection is provided by paints and varnishes. Depending on the metal and factors, different varnishes, paints and primers are used.

Another option is to apply a thin protective layer of another material. Usually this method is practiced in production (for example, galvanizing). As a result, the consumer practically does not need to do anything after purchasing the item.

Application of a thin protective layer

Another option is to create special alloys that do not oxidize (for example, stainless steel), but they do not guarantee 100% protection, moreover, some things made from such materials oxidize.

Important parameters of the protective layers are the thickness, service life and rate of destruction under active adverse effects. When applying a protective coating, it is extremely important to fit exactly into the allowable layer thickness. Usually manufacturers of paints and varnishes indicate it on the packaging. So, if the layer is more than the maximum allowable, then this will cause an overrun of the varnish (paint), and the layer may collapse under strong mechanical stress, a thinner layer may wear off and reduce the protection period of the base.

Correctly selected protective material and correctly applied to the surface guarantees 80% that the part will not be subject to corrosion.

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Many people in everyday life do not think about how to protect their belongings from rye. And they get a problem in the form of a damaged item. How to solve this problem correctly?

Removing rust from a part

In order to restore a thing or part from rust, the first step is to remove all red plaque to a clean surface. It is removed with sandpaper, files, strong reagents (acids or alkalis), but drinks such as Coca-Cola deserve special fame in this. To do this, the thing is completely immersed in a container with a miracle liquid and left for a while (from several hours to several days - the time depends on the thing and the damaged area).

Red spots on steel products

According to the UN, each country annually loses from 0.5 to 7-8% of the gross national product due to corrosion. The paradox is that the less developed countries lose less than the developed ones. And 30% of all manufactured steel products on the planet are used to replace rusted ones. Therefore, it is highly recommended to take this issue seriously.

Corrosion lends itself to many materials, such as metal, ceramic, wood, as a result of exposure to them. As a rule, this effect is achieved due to the instability of the structure, which is affected by the thermodynamics of the environment. In the article we will understand in detail what metal corrosion is, what types it has, and also how you can protect yourself from it.

Some general information

Among the people, the word "rust" is quite popular, which refers to the process of corrosion of metal and various alloys. For polymers, people use the concept of “aging”. In fact, these words are synonymous. A striking example is the aging of rubber products that actively interact with oxygen. Some plastic products can quickly become unusable due to precipitation. How quickly the corrosion process will occur depends entirely on the conditions in which the product is placed. The humidity of the environment is especially affected. The higher its value, the faster the metal will become unusable. Experimentally, scientists have found that about 10% of products in production are simply written off due to corrosion. The types of this process are different, their classification depends on the type of environment in which the products are located, the speed and nature of the flow. Next, we consider in more detail the types of corrosion. Now every person should understand what metal corrosion is.

artificial aging

The corrosion process is not always destructive and renders certain materials unusable. Often, due to corrosion, the coating has additional properties that a person needs. That is why artificial aging has become popular. Most often it is used when it comes to aluminum and titanium. Only with the help of corrosion it is possible to achieve increased strength of materials. In order to complete the destruction process correctly, it is necessary to use heat treatment. Given that the natural aging of materials under certain conditions is a rather slow process, there is no need to specify that when using this method, the material must have a special hardening. You also need to understand all the risks that are associated with this method. For example, although the strength of the material increases, but the ductility decreases as much as possible. With ease, now the reader will be able to answer the question of what is the corrosion of an artificial type of metal.

Heat treatment reviews

This method densifies the molecules of the material, respectively, the structure changes. Often, thermal protection is necessary to strengthen pipelines, as it allows you to protect the material from rust, as well as minimize the pressure that is exerted on the structure if it is underground. Users of this technique leave reviews in which they describe that this protection method is as effective as possible and really shows good results. Such processing is desirable to apply only in the industrial sector. Due to the fact that the chambers for firing and performing other processes necessary to obtain reliable protection are expensive, the method is not popular. Such protection of metal from corrosion is quite effective.

Classification

At the moment, there are more than 20 rust options. The article will describe only the most popular types of corrosion. Conventionally, they are divided into the following groups, which will help to understand in more detail what metal corrosion is.

Chemical corrosion is the interaction with a corrosive environment. In this case, the oxidation of the metal and the reduction of the oxidizing agent occur simultaneously in one cycle. Both materials are not separated by space. Consider other types of metal corrosion.

Electrochemical corrosion is the interaction of a metal with an electrolyte. The atoms are ionized, the oxidizing agent is reduced, and these two processes occur over several cycles. Their speed is completely dependent on the potential of the electrodes.

Gas corrosion is the rusting of metal with a small amount of liquid. Moisture should not exceed 0.1%. Also, this type of corrosion can occur in a gaseous environment at high temperatures. Most often this species is found in the industry associated with the chemical industry and oil refining.

In addition to the above, there are many more types of corrosion of materials. There are biological, target, contact, local and other types of rusting.

Electrochemical corrosion and its features

At electrochemical corrosion the destruction of the material occurs due to its contact with the electrolyte. As the last substance, there may be condensate, rainwater. It should be noted that the more salts in the liquid, the higher the electrical conductivity. Accordingly, the corrosion process will proceed quite quickly. If we talk about the most popular places that are susceptible to corrosion, it should be noted rivets in a metal structure, welded joints, as well as simply places where the material is damaged. It happens that an iron alloy during its creation is coated with special substances that have anti-corrosion properties. However, this does not prevent the rusting process, but only slows it down. A fairly striking example is galvanization. Zinc has a negative potential when compared to iron. Because of this, the last material will be restored, and the zinc will be damaged. If there is an oxide film on the surface, the destruction process will become lengthy. Electrochemical corrosion has several types, but it should be noted that all of them are dangerous and, as a rule, it is impossible to stop this type of metal corrosion.

Chemical corrosion

Chemical corrosion is quite common. For example, if a person notices scale, then he must understand that it appeared as a result of metal combination, that is, interaction, with oxygen. As a rule, if the ambient temperature is high, the corrosion process will be markedly accelerated. A liquid can participate in rusting, that is, water, salt, any acid or alkali, salt solutions. When it comes to chemical corrosion of metals such as copper or zinc, their oxidation leads to a stable corrosion process of the film. The rest form iron oxide. Further, all the chemical processes that will occur will lead to the appearance of rust. It will not provide protection in any way, but, on the contrary, contributes to the occurrence of corrosion. With the help of galvanizing at the moment it is possible to protect many materials. Other means of protection against chemical corrosion of metals have also been developed.

Types of concrete corrosion

The brittleness of concrete can be caused by one of three types of corrosion. Quite often there is a change in the structure of this material. Let's take a look at why this is happening.

The most common type of corrosion should be called the destruction of cement stone. As a rule, this occurs when liquid and atmospheric precipitation constantly act on the material. Because of this, the structure of the material is destroyed. Below are more detailed examples of metal corrosion:

• interaction with acids. If the cement stone is constantly exposed to these materials, then a rather aggressive element is formed, which is harmful to the coating. This is calcium bicarbonate.
• Crystallization of sparingly soluble substances. This is about corrosion. Due to the fact that fungi, spores and other substances enter the pores, the concrete coating begins to quickly collapse.

Corrosion: ways to protect

Manufacturers often suffer huge losses due to corrosion, so a lot of work is being done to avoid this process. Moreover, it should be noted that most often corrosion does not lend itself to the metal itself, but to huge metal structures. Manufacturers spend a lot of money on their creation. Unfortunately, it is almost impossible to provide 100% protection. However, if you properly protect the surface, that is, carry out abrasive blasting, you can delay the corrosion process for several years. They also fight with paintwork. It reliably protects the material. If the metal is underground, then it must be treated with special materials. This is the only way to achieve maximum protection of the metal from corrosion.

Measures to prevent aging

As mentioned above, the corrosion process cannot be stopped. But you can maximize the time during which the material will collapse. Also, in production, as a rule, they try to get rid of the factors that affect the aging process as much as possible. For example, in factories, each structure is periodically treated with solutions and polishes. It is they who save the material from the negative impact on the metal from mechanical, temperature and chemical conditions. In order to understand this in more detail, it is necessary to study the definition of corrosion of metals. If we talk about slowing down the effect of aging, then it should be noted that heat treatment can be used for this. Under normal operating conditions, this method will avoid the rapid destruction of the material as much as possible. Welders, in order to prevent the seams on the product from opening, use firing at a temperature of 650 degrees. This technique will reduce the intensity of aging.

Active and passive methods of struggle

Active anti-corrosion methods act by changing the structure of the electric field. To do this, you need to use direct current. The voltage must be such that the product has enhanced characteristics. A fairly popular method would be to use a “sacrificial” anode. It protects the material by its own destruction. The conditions for corrosion of metals are described above.

As for passive protection, a paintwork is used for this. It completely protects the product from the ingress of liquid, as well as oxygen. Thanks to this, the surface is maximally protected from destruction. Zinc, copper, nickel coating should be used. Even if the layer is severely destroyed, it will still protect the metal from rusting. Of course, you need to understand that passive protection methods will only be relevant if the surface does not have cracks or chips.

Reviews about the paint and varnish protection of metals

At the moment, paintwork protection is very popular. It is efficient, flexible to use, and inexpensive. However, if long-term use of a metal structure is necessary, then this method of protection will not work. More than 7-8 years paint and varnish coatings will not be able to protect the material. Accordingly, they will have to be updated. Most likely, it will be necessary to carry out restoration and replace the surface of the material. Among other disadvantages of this coating, limitations in terms of use should be noted. If it is necessary to strengthen pipes that are underground or water, then paint protection will not work. Therefore, it should be understood that if it is necessary for the structure to be used for more than 10 years, other methods of protection should be resorted to.

Galvanizing in detail

Having considered the main types of corrosion, it is also necessary to discuss the most effective methods of protection. One of these is galvanizing. It allows you to protect the material from severe damage by changing the physical and chemical properties. At the moment, this method is considered economical and efficient, given that almost 40% of all mined material on Earth is spent on zinc processing. It is important to treat the material with an anti-corrosion coating.

Galvanizing is carried out for steel sheets, fasteners, appliances and huge metal structures. In general, with the help of such spraying, products of any size and shape can be protected. Zinc has no decorative purpose, although it may occasionally be added to the alloy to give it a sheen. In general, you need to understand that this metal will provide maximum protection against corrosion even in the most aggressive conditions.

Rust protection features

When working with metal, any person understands that before applying protective materials, it is necessary to prepare the surface. Often all the difficulties lie precisely in this stage. In order to create a special barrier that will allow rust to reach the metal, it is necessary to introduce the concept of a compound. Thanks to him, the kit will form protection against corrosion. In this case, electrical insulation takes place. It is usually quite difficult to protect against corrosion of ferrous metals.

Due to the specifics of the use of various means of protection, it is necessary to understand the operating conditions of the material. If the metal will be located underground, then it is necessary to use multi-layer coatings that will have not only anti-corrosion properties, but also enhanced protection against mechanical damage. If we are talking about communications that actively interact with oxygen and gases, you should use a tool that minimizes the effects of water and oxygen. Accordingly, increased attention on the part of the manufacturer will be given to insulation from moisture, steam and low temperatures. In this case, additives and special plasticizers should be added, because the causes of metal corrosion are different and all types should be protected.

Mix "Urizol"

The Urizol mixture should be considered separately, as it is used to coat the pipeline. It is also suitable for fittings, fittings, valve assemblies and those products that are constantly in contact with oil or gases. This composition is needed in order to get rid of the influence of underground and atmospheric influences. Often this mixture is also used for the insulation of concrete materials. This substance is applied very simply, without any difficulty. In order to treat the surface, it is necessary to use a sprayer. This is the only way to avoid corrosion of metals and alloys of similar products. As soon as the components are combined, the reaction begins. This results in polyurea. After that, the mixture passes into a gel-like and non-fluid state, and after some time becomes solid. If the polymerization rate is slow, smudges will begin to form. They are harmful, because they make it difficult to increase the thickness of the coating. It should be noted that this mixture retains a sticky state for a long time. Due to this, all layers will be as uniform as possible, and intermediate thickness measurements will be equal to each other. If the polymerization process is too fast, then the adhesion of the composition will decrease. In this case, the thickness of the resulting layer for insulation will be uneven. By the way, the spray gun will quickly clog if the coating speed is too fast. Metal corrosion factors will not appear if everything is done correctly. In order to prevent such situations, it is necessary to carefully select the components and follow the manufacturing rules.

Paints and enamels

Protection of metal-plastic structures can be carried out using three methods.

Coatings have already been described. They are simple, have a variety of colors, and with the help of them you can easily process huge surfaces. Since the process of metal corrosion is quite fast, then you should immediately think about coating with materials.

The second type is plastic coatings. As a rule, they are made of nylon, PVC. This coating will provide maximum protection against water, acids and alkalis.

The third type is rubber coating. Often it is used to protect tanks and other structures from the inside.

Phosphating and chromating

The metal surface must be properly prepared for the protection process. Which methods will be used depends entirely on the type of surface. For example, black metals protected by phosphating. Non-ferrous metals can be processed by both methods. In general, if we talk about chemical preparation, it is necessary to clarify that it takes place in several stages. To begin with, the surface is degreased. Then it is washed with water. Next, a conversion layer is applied. After that, it is washed again with two types of water: drinking and demineralized, respectively. The next thing to do is passivation. Chemical treatment should be carried out by spraying, immersion, steam jet and water jet methods. The first two methods must be applied using special units that will fully prepare the surface for work. Which method to choose, it is necessary to decide depending on the size, configuration of the product, and so on. In order to better understand this issue, one should know the equations for the reactions of corrosion of metals.

Conclusion

The article described what corrosion is and what types it has. Now any person after reading this article will be able to understand how to protect any material from aging. By and large, this is quite easy to do, knowing all the necessary instructions. The main thing is to understand all the characteristics of the environment in which the material is used. If the products are located in a place where constant vibrations occur, as well as there are strong loads, then cracks will occur in the paintwork. Because of this, moisture will begin to get on the metal, respectively, the corrosion process begins immediately. In such cases, it is better to additionally use rubber sealants and gaskets, then the coating will last a little longer.

In addition, it must be said that the design, with premature deformation, will quickly deteriorate and age. Accordingly, this can lead to unforeseen circumstances. This will bring material damage and may result in the death of a person. Accordingly, special attention should be paid to corrosion protection.

Chemical and physico-chemical reactions that occur at the time of the interaction of the environment with metals and alloys, in most cases lead to their spontaneous destruction. The process of self-destruction has its own term - "corrosion". The result of corrosion is a significant deterioration in the properties of the metal, as a result of which products from it quickly fail. Every metal has properties that allow it to resist destruction. Corrosion resistance or, as it is also called, the chemical resistance of a material, is one of the main criteria by which metals and alloys are selected for the manufacture of certain products.

Depending on the intensity and duration of the corrosion process, the metal can be subjected to both partial and complete destruction. The interaction of a corrosive environment and metal leads to the formation of such phenomena as scale, oxide film and rust on the metal surface. These phenomena differ from each other not only in appearance, but also in the degree of adhesion to the surface of metals. So, for example, in the process of oxidation of a metal such as aluminum, its surface is covered with a film of oxides, which is characterized by high strength. Thanks to this film, destructive processes are stopped and do not penetrate inside. If we talk about rust, then the result of its impact is the formation of a loose layer. The corrosion process in this case very quickly penetrates into the internal structure of the metal, which contributes to its early destruction.

Indicators by which the classification of corrosion processes is carried out:

• type of corrosive environment;
• conditions and mechanism of flow;
• the nature of corrosion damage;
• type of additional impact on the metal.

According to the mechanism of the corrosion process, both chemical and electrochemical corrosion of metals and alloys are distinguished.

Chemical corrosion- this is the interaction of metals with a corrosive environment, during which a one-time implementation of the oxidation of the metal and the restoration of the oxidizing component of the environment are observed. Interacting products are not spatially separated.

Electrochemical corrosion- this is the interaction of metals with a corrosive medium, which is an electrolyte solution. The process of ionization of metal atoms, as well as the process of reduction of the oxidizing component of a given corrosive environment, proceed in different acts. The electrode potential of the electrolyte solution has a significant effect on the rate of these processes.

Depending on the type of aggressive environment, there are several types of corrosion.

atmospheric corrosion represents the self-destruction of metals in an air atmosphere, or in a gas atmosphere characterized by high humidity.

Gas corrosion- this is the corrosion of metals that occurs in a gaseous environment, the moisture content of which is minimal. The absence of moisture in the gas medium is not the only condition that contributes to the self-destruction of the metal. Corrosion is also possible at high temperatures. This type of corrosion is most common in the petrochemical and chemical industries.

radiation corrosion It is the self-destruction of a metal under the influence of radioactive radiation of varying degrees of intensity on it.

underground corrosion- this is corrosion that occurs in soils and various soils.

contact corrosion represents a type of corrosion, the formation of which is facilitated by the contact of several metals that differ from each other in stationary potentials in a particular electrolyte.

Biocorrosion- this is the corrosion of metals, occurring under the influence of various microorganisms and their vital activity.

Corrosion by current (external and stray)- another type of corrosion of metals. If the metal is affected by a current from an external source, then this is corrosion by an external current. If the impact is carried out by means of a stray current, then this is corrosion of the stray current.

Corrosive cavitation is a process of self-destruction of metals, the occurrence of which is facilitated by both shock and corrosion effects of the external environment.

stress corrosion is a metal corrosion, the cause of which is the interaction of a corrosive medium and mechanical stresses. This type of corrosion is a significant danger for metal structures that are subjected to severe mechanical stress.

Fretting corrosion- a type of corrosion of metals, which leads to a combination of vibration and exposure to a corrosive environment. To minimize the possibility of friction and vibration corrosion, care must be taken in the choice of construction material. It is also necessary to apply special coatings and, if possible, reduce the coefficient of friction.

According to the nature of destruction, corrosion is divided into continuous and selective.

continuous corrosion completely covers the surface of the metal. If the rate of destruction on the entire surface is the same, then this is uniform corrosion. If the destruction of the metal in its various parts occurs at different rates, then corrosion is called uneven.

Selective corrosion implies the destruction of one of the components of the alloy or one structural component.

localized corrosion, which manifests itself in the form of spots separately scattered over the surface of the metal, is a recess of different thicknesses. Destructions can be sinks or dots.

Subsurface corrosion It is formed directly on the surface of the metal, after which it actively penetrates deep into. This type of corrosion is accompanied by delamination of metal products.

Intergranular corrosion manifests itself in the destruction of the metal along the grain boundaries. It is rather difficult to determine it by the appearance of the metal. However, the strength and ductility of the metal change very quickly. Products from it become fragile. This type of corrosion is most dangerous for chromium and chromium-nickel steels, as well as for aluminum and nickel alloys.

crevice corrosion It is formed on those parts of metals and alloys that are in threaded fasteners, various gaps and under all kinds of gaskets.