Appendix C. Metal structures. Corrosion protection requirements

• Causes of corrosion
• Types of corrosion
• Solid
• Local

The word corrosion comes from the Latin corrodere. It literally means “to corrode.” The most common type of corrosion is metal. However, there are cases when products made from other materials also suffer from corrosion. Stones, plastic and even wood are susceptible to it. Today, more and more often, people are faced with the problem of corrosion of architectural monuments made of marble and other materials. From this we can conclude that a process such as corrosion means destruction under the influence of the environment

Causes of metal corrosion

Most metals are susceptible to corrosion. This process is their oxidation. It leads to their decomposition into oxides. In common parlance, corrosion is called rust. It is a finely ground light brown powder. On many types of metals, during the oxidation process, a special composition appears in the form of an oxide film bonded to them. It has a dense structure, due to which oxygen from the air and water cannot penetrate into the deep layers of metals for their further destruction.

Aluminum belongs to the category of very active metals. From a theoretical point of view, when it comes into contact with air or water, it should easily split. However, during corrosion, a special film is formed on it, which compacts its structure and makes the process of rust formation almost impossible.

Chemical coatings

Refers to methods of temporary anti-corrosion protection of steel, for example, during plastic deformation at elevated temperatures. The most widely used technologies are phosphating and oxalation.

When phosphating, the surface is covered with a continuous layer of phosphate salts of iron and manganese, and when oxalating, it is covered with water-soluble salts of oxalic acid. Phosphating is used for processing unalloyed steels, oxalation – for alloyed ones. The coating adheres firmly to the surface, helping to reduce friction and reduce tool wear. After stamping is completed, the coating is removed.

Table 1. Metal compatibility

Appendix C. Metal structures. Corrosion protection requirements

Printable version Table C.1. Groups of paint and varnish coatings for the protection of metal structures

Table C.2 - Methods of protecting steel chimneys

Table C.3 - Coating materials for corrosion protection of internal surfaces of steel tanks for liquid media

Table T.4 - Protection of steel ropes used outdoors

Table C.5 - Materials for welding steel structures in aggressive environments, corresponding to low-alloy steel grades

Table C.6 - Methods of protection against corrosion of metal structures

Table C.7 - Groups of paint and varnish coatings for protecting steel and aluminum structures from corrosion

Table C.7 (Changed edition, Amendment No. 1).

Table C.8 - Paint and varnish coatings for corrosion protection of thin galvanized sheet metal, applied on lines for continuous painting of coiled metal

Table C.8 (Changed edition, Amendment No. 1).

Table C.9. Options for protective coatings for steel tanks for acids, alkalis and liquid mineral fertilizers

Table T.10 - Methods of corrosion protection of load-bearing and enclosing structures made of thin-sheet cold-rolled steel

Table C.11 - Reference data on the rate of corrosion penetration of carbon steel and zinc coatings under various operating conditions

Tables Ts.10, Ts.11 (Introduced additionally, Amendment No. 1).

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Table 2. Compatibility of steel with metals

Methods of applying anti-corrosion protection to metal structures

Application by brush

The most popular application method is to use a synthetic fiber brush.

Roller application

Use any fine-pile construction roller

Types of metal corrosion

Complete corrosion

The least dangerous thing for various metal objects is complete corrosion. It is especially not dangerous for those situations where damage to devices and equipment does not violate the technical standards for their further use. The consequences of this type of corrosion can be easily predicted and equipment adjusted accordingly.

Local corrosion

The greatest danger is local corrosion. In this case, the loss of metal is not large, but through damage to the metal is formed, which leads to failure of the product or equipment. This type of corrosion occurs in products that come into contact with sea water or salts. This appearance of rust causes the surface of the metal base to partially corrode and the structure loses its reliability.

A large number of problems arise in places where sodium chloride is used. This substance is used to remove snow and ice on roads in urban areas. This type of salt causes them to turn into liquid, which, already diluted with salts, ends up in city pipelines. In this case, protecting metals from corrosion will not hurt. All underground communications begin to collapse when water and salts enter. In the United States of America, it is estimated that approximately two billion dollars are spent annually on road repairs. However, utility companies are not yet ready to abandon this type of salt for treating road surfaces due to its low cost.

Types and causes of corrosion on metal products

When taking measures to protect metal products from corrosion, you need to know what exactly it is. The following types of corrosion exist:

• Liquid. Forms on metal surfaces in contact with a damp environment. As for seawater, the oxidation process occurs much faster in it due to the increased concentration of salt in the liquid.
• Soil. This type is typical for metal structures that interact with the ground for a long time. When exposed to chemical elements contained in groundwater, soil or various leaks, irreversible chemical processes are triggered.
• Atmospheric. The main cause of oxidation is the interaction of the metal with water vapor and oxygen contained in the air. If the air is saturated with contaminants of chemically active substances, then rust appears faster.

The manifestation of corrosion on metal structures can be expressed as:

• the formation of a continuous layer of rust or individual areas of surfaces;
• the appearance of deep cracks;
• small affected areas directed towards the inside of the product;
• oxidation of one of the alloy components;
• deep distribution throughout the entire volume;
• several signs at once.

One of two reasons for the development of such a process may be:

• Chemical interaction - when a metal begins to deteriorate due to a chemical reaction with active components.
• Electrochemical nature, due to the fact that upon contact with electrolytic solutions, electric currents are generated, under the influence of which electrons are replaced in the metal. This leads to destruction of the crystal lattice and the formation of rust.

Methods for protecting metals from corrosion

Since ancient times, people have tried to protect metals from corrosion. Constant precipitation rendered metal products unusable. That is why people lubricated them with various fatty oils. Then they began to use coatings of other metals that do not rust for this purpose.

Modern chemists carefully study all possible methods of combating metal corrosion. They create special solutions. Methods are being developed to reduce the risk of corrosion on metals. An example would be a material such as stainless steel. For its production, iron was used, supplemented with cobalt, nickel, chromium and other elements. With the help of elements added to it, it was possible to create a metal on which rust does not form for a longer period of time.

To protect various metals from corrosion, various substances have been developed that are actively used in modern industry. Varnishes and paints are actively used today. They are the most affordable means of protecting metal products from rust. They create a barrier for water or air to reach the metal itself. This allows you to temporarily delay the appearance of corrosion. When applying paint or varnish, you should take into account the thickness of the layer and the surface of the material. To achieve the best result, the coating of metals against corrosion should be done in an even and dense layer.

Definition of corrosion

Corrosion is the gradual destruction of objects, usually metals, caused by an active electrolyte environment and a chemical oxidation reaction.

The essence of the corrosion process is the presence of a constantly operating anodic reaction. It is caused by the dissolution of a metal, which generates electrons. Part of the activation energy is additionally spent on another process called the cathodic reaction. These two processes balance the charges produced. The zones causing these processes can be located close or far from each other, depending on the situation.

The electrons generated in the process must be consumed through a cathodic reaction. Hydrogen ions and electrons react to form atomic and then hydrogen gas. However, hydrogen is a powerful reducing agent, so further corrosion can be prevented by creating a thin film of gas on the metal surface. It serves as a polarizer, reducing metal contact with water and reducing corrosion. Thus, anything that destroys the barrier film increases the rate of corrosion.

The main factors determining the intensity of the process are:

• Speed;
• Temperature;
• The level of mechanical and thermal stresses that arise;
• The nature of the ongoing chemical reactions.

Corrosion hinders the introduction of new metal materials into production and causes significant damage to the economy.

Chemical corrosion of metals

Essentially, corrosion can be of two types:

• chemical,
• electrochemical.

Chemical corrosion is the formation of rust under certain conditions. In industrial environments, it is not uncommon to encounter this type of corrosion. Indeed, in numerous modern enterprises, metals are heated before creating products from them, which leads to the formation of such a process as accelerated chemical corrosion of the metal. This produces scale, which is a product of its reaction to the appearance of rust during heating.

Scientists have proven that modern iron is much more susceptible to rust. It contains a large amount of sulfur. It appears in the metal due to the fact that coal is used during the extraction of iron ores. The sulfur from it gets into the iron. Modern people are surprised that ancient objects made from this metal, which archaeologists find at excavations, retain their external qualities. This is due to the fact that in ancient times charcoal was used to extract iron, which contains virtually no sulfur that could get into the metal.

Anti-corrosion paint as protection for metal structures

Anti-corrosion paint is a liquid material applied to metal using traditional paint methods, protecting it from corrosion, that is, it is a corrosion inhibitor. In the vast majority of cases, anti-corrosion paint is given the desired color by adding color pigments. The AKTERM company recommends using 3 in 1 enamel primer AKTERM Plast as an anti-corrosion protection for metal structures

AKTERM Primer-enamel Plast

A one-component, quick-drying decorative coating, used as anti-corrosion protection for metal structures, bridges, cell phone towers, ship hulls, vehicle bodies and rolling stock operating under the influence of external climatic factors. Weather resistance up to 10 years. Colored in RAL. Universal anti-corrosion protection of metal
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Anti-corrosion paints can have heat-reflecting (heat-insulating) properties, in addition to anti-corrosion - the AKTERM Anticor material has such properties

AKTERM Anticor

Heat-reflecting coating to protect metal surfaces from corrosion, operating temperature from -50ºС to +150ºС Thermal insulation + anti-corrosion properties of metal
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Anti-corrosion paint can also have electro-chemical protective properties, in which case zinc is applied (cold galvanizing) as a metal coating - in fact, zinc paint is used, which is called a cold galvanizing composition.

AKTERM Zinc

The composition of cold galvanizing, which is based on 96% zinc, has electrochemical protection of the metal, as well as a protective effect - comparable in protective properties to hot and galvanic methods of galvanizing. The composition is suitable for outdoor and indoor ventilated areas. Electro-chemical protection of metal + anti-corrosion of metal
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Polyurethane compounds are also used to give the anti-corrosion material increased abrasion resistance properties and prevent metal destruction - AKTERM Anticor PU - this composition can be classified as a “metal corrosion protector”.

AKTERM Anticor PU

Two-component coating, used as an independent protective and decorative anti-corrosion protector for external surfaces, tanks, tanks, cars, bodies and components of vehicles and rolling stock, structures made of steel, cast iron, aluminum and titanium alloys, operated in all types of atmosphere and load categories C2 -C4. Protection up to 20 years. Colored in RAL. Abrasion resistance + fracture prevention + anti-corrosion
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These metals are susceptible to corrosion.

There are various types of metals. Most often, iron is used to create any items or objects. It is from it that twenty times more products and objects are made than from other metals combined. This metal began to be used most actively in industry in the late 18th and early 19th centuries. It was during this period that the first cast iron bridge was built. The first sea vessel appeared, for the manufacture of which steel was used.

In nature, iron nuggets are found in rare cases. Many people believe that this metal is not terrestrial, it is classified as cosmic or meteorite. It is this that is most susceptible to corrosion.

There are also other metals that are susceptible to corrosion. Among them, copper, silver, and bronze stand out.

Paints for coating metal products

Paints intended for treating metal surfaces are standard and heat-resistant. In most cases, three types of compounds are used: epoxy, acrylic and alkyd. There are also special anti-corrosion paints that have the following advantages:

• effectively protect the coating from atmospheric influences and temperature changes;
• can be easily applied with a roller, brush or spray;
• many of them are quick-drying;
• have a wide selection of colors;
• are durable.

As for the most inexpensive and accessible means, then you should pay attention to ordinary silver. This coating contains aluminum powder, which forms a protective film on the product treated with it.