How to protect metal products from corrosion? All methods of metal corrosion protection, their pros and cons Types of corrosion protection

These methods can be divided into 2 groups. The first 2 methods are usually implemented before the start of the production operation of a metal product (the choice of structural materials and their combinations at the stage of designing and manufacturing a product, applying protective coatings to it). The last 2 methods, on the contrary, can be carried out only during the operation of the metal product (passing current to achieve a protective potential, introducing special additives-inhibitors into the technological environment) and are not associated with any pre-treatment prior to use.

The second group of methods allows, if necessary, to create new protection modes that provide the least corrosion of the product. For example, in certain sections of the pipeline, depending on the aggressiveness of the soil, it is possible to change the density of the cathode current. Or for different grades of oil pumped through pipes, use different inhibitors.

Q: How are corrosion inhibitors applied?

Answer: To combat the corrosion of metals, corrosion inhibitors are widely used, which are introduced in small amounts into an aggressive environment and create an adsorption film on the metal surface, which slows down electrode processes and changes the electrochemical parameters of metals.

Question: What are the ways to protect metals from corrosion using paints and varnishes?

Answer: Depending on the composition of the pigments and the film-forming base, paint coatings can act as a barrier, passivator or protector.

Barrier protection is the mechanical isolation of a surface. Violation of the integrity of the coating, even at the level of the appearance of microcracks, predetermines the penetration of an aggressive medium to the base and the occurrence of under-film corrosion.

Passivation of the metal surface with the help of LCP is achieved by chemical interaction of the metal and coating components. This group includes primers and enamels containing phosphoric acid (phosphating), as well as compositions with inhibitory pigments that slow down or prevent the corrosion process.

Metal protector protection is achieved by adding powder metals to the coating material, which create donor electron pairs with the protected metal. For steel, these are zinc, magnesium, aluminum. Under the action of an aggressive environment, the additive powder gradually dissolves, and the base material does not corrode.

Question: What determines the durability of metal protection against corrosion by paints and varnishes?

Answer: Firstly, the durability of metal protection against corrosion depends on the type (and kind) of the applied paintwork. Secondly, the decisive role is played by the thoroughness of the preparation of the metal surface for painting. The most time-consuming process in this case is the removal of corrosion products formed earlier. Special compounds are applied that destroy rust, followed by their mechanical removal with metal brushes.

In some cases, rust removal is almost impossible to achieve, which implies the widespread use of materials that can be applied directly to surfaces damaged by corrosion - rust coatings. This group includes some special primers and enamels used in multi-layer or independent coatings.

Question: What are highly filled two-component systems?

Answer: These are anti-corrosion paints and varnishes with a reduced solvent content (the percentage of volatile organic substances in them does not exceed 35%). In the market for home use materials, one-component materials are mainly offered. The main advantage of highly filled systems compared to conventional systems is a significantly better corrosion resistance with a comparable layer thickness, less material consumption and the possibility of applying a thicker layer, which ensures that the necessary anticorrosion protection is obtained in just 1-2 times.

Question: How to protect the surface of galvanized steel from destruction?

Answer: Solvent-based anticorrosive primer based on modified vinyl-acrylic resins "Galvaplast" is used for interior and exterior works on bases made of ferrous metals with scale removed, galvanized steel, galvanized iron. The solvent is white spirit. Application - brush, roller, spray. Consumption 0.10-0.12 kg / sq.m; drying 24 hours.

Q: What is patina?

Answer: The word "patina" refers to a film of various shades that forms on the surface of copper and copper-containing alloys under the influence of atmospheric factors during natural or artificial aging. Patina is sometimes referred to as oxides on the surface of metals, as well as films that cause tarnishing over time on the surface of stones, marble or wooden objects.

The appearance of a patina is not a sign of corrosion, but rather a natural protective layer on the copper surface.

Question: Is it possible to artificially create a patina on the surface of copper products?

Answer: Under natural conditions, a green patina is formed on the surface of copper within 5-25 years, depending on the climate and the chemical composition of the atmosphere and precipitation. At the same time, copper carbonates are formed from copper and its two main alloys - bronze and brass: bright green malachite Cu 2 (CO 3) (OH) 2 and azure blue azurite Cu 2 (CO 3) 2 (OH) 2. For zinc-containing brass, the formation of green-blue rosasite of the composition (Cu,Zn) 2 (CO 3) (OH) 2 is possible. Basic copper carbonates can be easily synthesized at home by adding an aqueous solution of soda ash to an aqueous solution of a copper salt, such as copper sulphate. At the same time, at the beginning of the process, when there is an excess of copper salt, a product is formed that is closer in composition to azurite, and at the end of the process (with an excess of soda) - to malachite.

Saving coloring

Question: How to protect metal or reinforced concrete structures from the influence of an aggressive environment - salts, acids, alkalis, solvents?

Answer: To create chemical-resistant coatings, there are several protective materials, each of which has its own area of ​​protection. The widest range of protection has: XC-759 enamels, ELOKOR SB-022 varnish, FLK-2, primers, XC-010, etc. In each individual case, a specific color scheme is selected, according to the operating conditions. Tikkurilla Coatings Temabond, Temacoat and Temachlor paints.

Question: What compositions can be used for painting the internal surfaces of tanks for kerosene and other petroleum products?

Answer: Temaline LP is a two-component epoxy gloss paint with an amino adduct hardener. Application - brush, spray. Drying 7 hours.

EP-0215 ​​is a primer for corrosion protection of the inner surface of caisson tanks operating in a fuel medium with an admixture of water. It is applied on surfaces made of steel, magnesium, aluminum and titanium alloys, operated in various climatic zones, at elevated temperatures and exposed to polluted environment.

Suitable for use with BEP-0261 primer and BEP-610 enamel.

Question: What compositions can be used for the protective coating of metal surfaces in marine and industrial environments?

Answer: Thick-film type paint based on chlorinated rubber is used for painting metal surfaces in marine and industrial environments subject to moderate chemical attack: bridges, cranes, conveyors, port equipment, tank exteriors.

Temacoat HB is a two-component modified epoxy paint used for priming and painting metal surfaces exposed to atmospheric, mechanical and chemical attack. Application - brush, spray. Drying 4 hours.

Question: What compositions should be used to cover difficult-to-clean metal surfaces, including those immersed in water?

Answer: Temabond ST-200 is a two-component modified epoxy paint with aluminum pigmentation and low solvent content. It is used for painting bridges, tanks, steel structures and equipment. Application - brush, spray. Drying - 6 hours.

Temaline BL is a two-component, solvent-free epoxy coating. It is used for painting steel surfaces subject to wear, chemical and mechanical attack when immersed in water, containers for oil or gasoline, tanks and reservoirs, sewage treatment plants. Application - airless spray.

Temazinc is a one component zinc rich epoxy paint with a polyamide hardener. Used as a primer in epoxy, polyurethane, acrylic, chlorinated rubber paint systems for steel and cast iron surfaces exposed to strong atmospheric and chemical attack. It is used for painting bridges, cranes, steel frames, steel structures and equipment. Drying 1 hour.

Question: How to protect underground pipes from fistula formation?

Answer: There can be two reasons for the breakthrough of any pipes: mechanical damage or corrosion. If the first reason is the result of accident and carelessness - the pipe is hooked on something or the weld is broken, then corrosion cannot be avoided, this is a natural phenomenon caused by soil moisture.

In addition to the use of special coatings, there is a protection widely used throughout the world - cathodic polarization. It is a direct current source that provides a polar potential of min 0.85 V, max - 1.1 V. It consists of just a conventional AC voltage transformer and a diode rectifier.

Q: How much does cathodic polarization cost?

Answer: The cost of cathodic protection devices, depending on their design, ranges from 1000 to 14 thousand rubles. A repair team can easily check the polarization potential. Installation of protection is also not expensive and does not involve labor-intensive earthworks.

Protection of galvanized surfaces

Question: Why can't galvanized metals be shot blasted?

Answer: Such preparation violates the natural corrosion resistance of the metal. Surfaces of this kind are treated with a special abrasive agent - round glass particles that do not destroy the protective layer of zinc on the surface. In most cases, it is sufficient to simply treat with an ammonia solution to remove grease stains and zinc corrosion products from the surface.

Question: How to repair a damaged zinc coating?

Answer: Zinc-filled compositions ZincKOS, TsNK, "Vinikor-zinc", etc., which are applied by cold galvanizing and provide anodic protection of the metal.

Question: How is metal protection performed using CNC (zinc-rich compositions)?

Answer: The technology of cold galvanizing with the use of ZNK guarantees absolute non-toxicity, fire safety, heat resistance up to +800°C. The coating of metal with this composition is carried out by spraying, roller or even just a brush and provides the product, in fact, double protection: both cathodic and film. The term of such protection is 25-50 years.

Question: What are the main advantages of the "cold galvanizing" method over hot galvanizing?

Answer: At this method has the following advantages:

1. Maintainability.
2. Possibility of drawing in the conditions of a construction site.
3. There are no restrictions on the overall dimensions of protected structures.

Question: At what temperature is thermal diffusion coating applied?

Answer: Application of thermal diffusion zinc coating is carried out at temperatures from 400 to 500°C.

Question: Are there any differences in the corrosion resistance of a coating obtained by thermal diffusion zinc plating compared to other types of zinc coatings?

Answer: Corrosion resistance of thermal diffusion zinc coating is 3-5 times higher than that of galvanic coating and 1.5-2 times higher than that of hot zinc coating.

Question: What paintwork materials can be used for protective and decorative painting of galvanized iron?

Answer: To do this, you can use both water-based - G-3 primer, G-4 paint, and solvent-based - EP-140, ELOKOR SB-022, etc. Tikkurila Coatings protective systems can be used: 1 Temacoat GPLS-Primer + Temadur, 2 Temaprime EE + Temalac, Temalac and Temadur are tinted according to RAL and TVT.

Question: What kind of paint can gutter and drainage galvanized pipes be painted with?

Answer: Sockelfarg is a black and white water-based latex paint. Designed for application to both new and previously painted outdoor surfaces. Resistant to weather conditions. The solvent is water. Drying 3 hours.

Question: Why are water-based corrosion protection products rarely used?

Answer: There are 2 main reasons: the increased price compared to conventional materials and the opinion in certain circles that water systems have inferior protective properties. However, as environmental legislation tightens, both in Europe and around the world, the popularity of water systems is growing. Experts who tested high-quality water-based materials were able to make sure that their protective properties are not worse than those of traditional materials containing solvents.

Question: What instrument is used to determine the thickness of the paint film on metal surfaces?

Answer: The most easy-to-use device "Konstanta MK" - it measures the thickness of the paintwork on ferromagnetic metals. Much more functions are performed by the multifunctional thickness gauge "Konstanta K-5", which measures the thickness of conventional paintwork, galvanic and hot-zinc coatings on both ferromagnetic and non-ferromagnetic metals (aluminum, its alloys, etc.), and also measures surface roughness, temperature and air humidity, etc.

Rust recedes

Question: How can you treat objects that are heavily corroded by rust?

Answer: The first recipe: a mixture of 50 g of lactic acid and 100 ml of vaseline oil. The acid converts iron metahydroxide from rust into an oil-soluble salt, iron lactate. The cleaned surface is wiped with a cloth moistened with vaseline oil.

The second recipe: a solution of 5 g of zinc chloride and 0.5 g of potassium hydrotartrate dissolved in 100 ml of water. Zinc chloride in an aqueous solution undergoes hydrolysis and creates an acidic environment. Iron metahydroxide dissolves due to the formation of soluble iron complexes with tartrate ions in an acidic medium.

Question: How to unscrew a rusted nut with improvised means?

Answer: A rusted nut can be moistened with kerosene, turpentine, or oleic acid. After a while, she manages to turn it off. If the nut "persists", you can set fire to the kerosene or turpentine with which it was moistened. This is usually sufficient to separate the nut and bolt. The most radical way: a very hot soldering iron is applied to the nut. The metal of the nut expands and the rust lags behind the threads; now a few drops of kerosene, turpentine or oleic acid can be poured into the gap between the bolt and the nut. This time, the nut will definitely loosen!

There is another way to separate rusty nuts and bolts. A “cup” of wax or plasticine is made around the rusted nut, the rim of which is 3-4 mm higher than the level of the nut. Dilute sulfuric acid is poured into it and a piece of zinc is placed. After a day, the nut will easily turn off with a wrench. The fact is that a cup with acid and metallic zinc on an iron base is a miniature galvanic cell. The acid dissolves the rust and the iron cations formed are reduced on the zinc surface. And the metal of the nut and bolt does not dissolve in acid as long as it has contact with zinc, since zinc is a more chemically active metal than iron.

Question: What compositions applied on rust are produced by our industry?

Answer: Domestic solvent-borne compositions applied “on rust” include well-known materials: primer (some manufacturers produce it under the name Inkor) and Gremirust primer-enamel. These two-component epoxy paints (base + hardener) contain corrosion inhibitors and targeted additives that allow them to be applied to dense rust up to 100 microns thick. The advantages of these primers are: curing at room temperature, the possibility of applying to a partially corroded surface, high adhesion, good physical and mechanical properties and chemical resistance, ensuring long-term operation of the coating.

Question: What can be used to paint old rusty metal?

Answer: For dense rust, it is possible to use several paints and varnishes containing rust converters:

• primer G-1, primer-paint G-2 (water-borne materials) – at temperatures up to +5°;
• primer-enamel ХВ-0278, primer-enamel AS-0332 – up to minus 5°;
• primer-enamel "ELOKOR SB-022" (materials based on organic solvents) - up to minus 15°C.
• Primer-enamel Tikkurila Coatings, Temabond (tinted according to RAL and TVT)

Question: How to stop the process of metal rusting?

Answer: This can be done with the help of "stainless primer". The primer can be used both as an independent coating on steel, cast iron, aluminum, and in a coating system that includes 1 primer layer and 2 enamel layers. It is also used for priming corroded surfaces.

"Nerjamet-primer" works on the metal surface as a rust converter, chemically binding it, and the resulting polymer film reliably isolates the metal surface from atmospheric moisture. When using the composition, the total cost of repair and restoration work on repainting metal structures is reduced by 3-5 times. The soil is produced ready for use. If necessary, it must be diluted to working viscosity with white spirit. The drug is applied to metal surfaces with remnants of tightly adhering rust and scale with a brush, roller, spray gun. Drying time at +20° - 24 hours.

Question: Roofing often fades. What kind of paint can be used for painting galvanized roofs and gutters?

Answer: Stainless steel cyclone. The coating provides long-term protection against weather, humidity, UV radiation, rain, snow, etc.

Possesses high covering ability and light fastness, does not fade. Significantly extends the service life of galvanized roofs. Also Tikkurila Coatings, Temadur and Temalac coatings.

Question: Can chlorinated rubber paints protect metal from rust?

Answer: These paints are made from chlorinated rubber dispersed in organic solvents. According to their composition, they are volatile resin and have high water and chemical resistance. Therefore, it is possible to use them for corrosion protection of metal and concrete surfaces, water pipes and tanks. Temanil MS-Primer + Temachlor system can be used from Tikkuril Coatings materials.

Anticorrosive in the bath, bathroom, pool

Question: What kind of coating can be used to protect bath containers for cold drinking and hot washing water from corrosion?

Answer: For containers for cold drinking and washing water, KO-42 paint is recommended;, Epovin for hot water - ZincKOS and Teplokor PIGMA compositions.

Question: What are enameled pipes?

Answer: In terms of chemical resistance, they are not inferior to copper, titanium and lead, and at cost are several times cheaper. The use of enameled pipes made of carbon steels instead of stainless steels gives a tenfold cost savings. The advantages of such products include greater mechanical strength, including in comparison with other types of coatings - epoxy, polyethylene, plastic, as well as higher abrasion resistance, which makes it possible to reduce the diameter of pipes without reducing their throughput.

Question: What are the features of re-enamelling bathtubs?

Answer: Enameling can be done with a brush or spray with the participation of professionals, as well as with a brush yourself. Preliminary preparation of the surface of the bath is to remove the old enamel and clean the rust. The whole process takes no more than 4-7 hours, another 48 hours the bath dries, and you can use it after 5-7 days.

Re-enamelling bathtubs require special care. Such baths cannot be washed with powders such as Comet and Pemolux, or using products containing acid, such as Silit. It is unacceptable to get varnishes on the surface of the bath, including for hair, the use of bleach when washing. Such baths are usually cleaned with soaps: washing powders or dishwashing detergents applied to a sponge or soft cloth.

Question: What paintwork materials can be used to re-enamel bathtubs?

Answer: Composition "Svetlana" includes enamel, oxalic acid, hardener, tinting pastes. The bath is washed with water, etched with oxalic acid (stains, stone, dirt, rust are removed and a rough surface is created). Washed with washing powder. Chips close up in advance. Then enamel should be applied within 25-30 minutes. When working with enamel and hardener, contact with water is not allowed. The solvent is acetone. Bath consumption - 0.6 kg; drying - 24 hours. Fully gaining properties after 7 days.

You can also use two-component epoxy-based paint Tikkurila "Reaflex-50". When using glossy bath enamel (white, tinted), either washing powders or laundry soap are used for cleaning. Fully gaining properties after 5 days. Consumption per bath - 0.6 kg. The solvent is industrial alcohol.

B-EP-5297V is used to restore the enamel coating of bathtubs. This paint is glossy, white, tinting is possible. The finish is smooth, even and durable. Do not use abrasive powders of the “Sanitary” type for cleaning. Fully gaining properties after 7 days. Solvents - a mixture of alcohol with acetone; R-4, No. 646.

Question: How to protect against breakage of steel reinforcement in the swimming pool bowl?

Answer: If the condition of the ring drainage of the pool is unsatisfactory, softening and suffusion of the soil is possible. The penetration of water under the bottom of the tank can cause subsidence of the soil and the formation of cracks in concrete structures. In these cases, the reinforcement in the cracks can corrode to breakage.

In such complex cases, the reconstruction of damaged reinforced concrete structures tank should include the implementation of a protective sacrificial layer of shotcrete on the surfaces of reinforced concrete structures exposed to the leaching action of water.

Obstacles to biodegradation

Question: What external conditions determine the development of wood-destroying fungi?

Answer: The most favorable conditions for the development of wood-destroying fungi are: the presence of air nutrients, sufficient wood moisture and favorable temperature. The absence of any of these conditions will delay the development of the fungus, even if it is firmly established in the wood. Most fungi develop well only at high relative humidity (80-95%). When wood moisture is below 18%, the development of fungi practically does not occur.

Question: What are the main sources of wood moisture and what is their danger?

Answer: The main sources of wood moisture in the structures of various buildings and structures include ground (underground) and surface (storm and seasonal) water. They are especially dangerous for wooden elements of open structures located in the ground (pillars, piles, power transmission line and communication supports, sleepers, etc.). Atmospheric moisture in the form of rain and snow threatens the ground part of open structures, as well as the outer wooden elements of buildings. Operational moisture in a drop-liquid or vapor form in residential premises is present in the form of household moisture released during cooking, washing, drying clothes, washing floors, etc.

A large amount of moisture is introduced into the building when laying raw wood, applying masonry mortars, concreting, etc. For example, 1 sq.m of laid wood with a moisture content of up to 23%, when dried to 10-12%, releases up to 10 liters of water.

The wood of buildings, which dries out naturally, is in danger of decay for a long time. If chemical protection measures were not provided, it, as a rule, is affected by the house fungus to such an extent that the structures become completely unusable.

Condensation moisture that occurs on the surface or in the thickness of structures is dangerous because, as a rule, it is detected already when irreversible changes have occurred in the enclosing wooden structure or its element, for example, internal decay.

Question: Who are the "biological" enemies of the tree?

Answer: These are mold, algae, bacteria, fungi and antimycetes (this is a cross between fungi and algae). Almost all of them can be dealt with with antiseptics. The exception is fungi (saprophytes), since antiseptics act only on some of their species. But it is fungi that are the cause of such widespread rot, which is the most difficult to deal with. Professionals divide rot by color (red, white, gray, yellow, green and brown). Red rot affects coniferous wood, white and yellow - oak and birch, green - oak barrels, as well as wooden beams and cellar ceilings.

Question: Are there ways to neutralize white house fungus?

Answer: White house fungus is the most dangerous enemy of wooden structures. The rate of destruction of wood by white house fungus is such that in 1 month it completely "eats" a four-centimeter oak floor. Previously, in the villages, if the hut was affected by this fungus, it was immediately burned to save all other buildings from infection. After that, the whole world built a new hut for the affected family in another place. Currently, in order to get rid of white house fungus, the affected area is dismantled and burned, and the rest is impregnated with 5% chromic (5% solution of potassium dichromate in 5% sulfuric acid), while it is recommended to cultivate the land on 0.5 m deep.

Question: What are the ways to protect the wood from rotting in the early stages of this process?

Answer: If the process of decay has already begun, it can only be stopped by thorough drying and ventilation of wooden structures. In the early stages, disinfectant solutions, for example, such as the antiseptic compositions "Wood Doctor", can help. They are available in three different versions.

Grade 1 is intended for the prevention of wooden materials immediately after their purchase or immediately after the construction of the house. The composition protects against fungus and woodworm.

Grade 2 is used if fungus, mold or "blue" has already appeared on the walls of the house. This composition destroys existing diseases and protects against their future manifestations.

Grade 3 is the most powerful antiseptic, it completely stops the process of decay. More recently, a special composition (grade 4) has been developed for insect control - “anti-bug”.

SADOLIN Bio Clean is a disinfectant for surfaces contaminated with mold, moss, algae, based on sodium hypochlorite.

DULUX WEATHERSHIELD FUNGICIDAL WASH is a highly effective mold, lichen and rot killer. These compounds are used both indoors and outdoors, but they are effective only in the early stages of rot control. In case of serious damage to wooden structures, rotting can be stopped by special methods, but this is a rather difficult job, usually performed by professionals with the help of restoration chemicals.

Question: What protective impregnations and preservative compositions, presented on the domestic market, prevent biocorrosion?

Answer: Of the Russian antiseptic preparations, it is necessary to mention metacid (100% dry antiseptic) or polysept (25% solution of the same substance). Such conservation compositions as "BIOSEPT", "KSD" and "KSD" have proven themselves well. They protect the wood from damage by mold, fungi, bacteria, and the last two, in addition, make the wood difficult to ignite. Texture coatings "AQUATEX", "SOTEKS" and "BIOX" eliminate the occurrence of fungus, mold and wood blue. They are breathable and have a durability of over 5 years.

A good domestic material for wood protection is GLIMS-LecSil glazing impregnation. This is a ready-to-use aqueous dispersion based on styrene-acrylate latex and reactive silane with modifying additives. At the same time, the composition does not contain organic solvents and plasticizers. Glazing sharply reduces the water absorption of wood, as a result of which it can even be washed, including with soap and water, prevents fire impregnation from washing out, due to antiseptic properties it destroys fungi and mold and prevents their further formation.

Of the imported antiseptic compounds for protecting wood, antiseptics from TIKKURILA have proven themselves well. Pinjasol Color is an antiseptic that forms a continuous water-repellent and weather-resistant finish.

Question: What are insecticides and how are they used?

Answer: To combat beetles and their larvae, poisonous chemicals are used - contact and intestinal insecticides. Fluoride and silicofluoride sodium are allowed by the Ministry of Health and have been used since the beginning of the last century; when using them, safety measures must be observed. To prevent damage to wood by a bug, preventive treatment with fluorosilicic compounds or a 7-10% solution is used. table salt. During historical periods of widespread wooden construction, all wood was processed at the harvesting stage. Aniline dyes were added to the protective solution, which changed the color of the wood. In old houses, to this day, you can find red beams.

The material was prepared by L. RUDNITSKY, A. ZHUKOV, E. ABISHEV

One of the serious threats to tools and structures made of metal is corrosion. For this reason, the problem of their protection from such an unpleasant process is of great relevance. At the same time, many methods are known today that can quite effectively solve this problem.

Anti-corrosion protection - why is it needed

Corrosion is a process accompanied by the destruction of the surface layers of steel and cast iron structures, resulting from electrochemical and chemical effects. The negative consequence of this is serious metal damage, its corrosion, which does not allow it to be used for its intended purpose.

Experts have provided sufficient evidence that annually about 10% of the total metal production on the planet is spent on eliminating losses associated with the effects of corrosion, due to which metals are melted and the metal products lose their operational properties.

At the first signs of corrosion, iron and steel products become less hermetic and durable. At the same time, such qualities as thermal conductivity, plasticity, reflective potential and some other important characteristics deteriorate. In the future, the designs can not be used for their intended purpose at all.

In addition to this, it is with corrosion that the majority of industrial and domestic accidents are associated, as well as some environmental disasters. Pipelines used to transport oil and gas, which have significant areas covered with rust, can lose their tightness at any time, which can pose a threat to human health and nature as a result of a breakthrough of such highways. This gives an understanding of why it is so important to take measures to protect metal structures from corrosion, using traditional and new tools and methods.

Unfortunately, it has not yet been possible to create such a technology that could completely protect steel alloys and metals from corrosion. At the same time, there are opportunities to delay and reduce the negative consequences of such processes. This problem is solved by using a large number of anti-corrosion agents and technologies.

Offered today corrosion control methods can be presented in the form of the following groups:

• Usage electrochemical methods protection of structures;
• Creation of protective coatings;
• Development and production of the latest structural materials demonstrating high resistance to corrosion processes;
• Adding special compounds to a corrosive environment, thanks to which it is possible to slow down the spread of rust;
• A competent approach to the selection of suitable metal parts and structures for the construction industry.

Protection of metal products from corrosion

It is possible to ensure the ability of the protective coating to fulfill its tasks by a range of special features:

Such coatings should be created in such a way that they are located over the entire area of ​​\u200b\u200bthe structure in the form of the most uniform and continuous layer.

Protective coatings for metal available today can be classified into the following types:

• metallic and non-metallic;
• organic and inorganic.

Such coatings are widely used in many countries. Therefore, they will be given special attention.

Corrosion control with organic coatings

Most often, to protect metals from corrosion, they resort to such effective method, as the use of paints and varnishes. This method has been demonstrating high efficiency and simplicity in terms of implementation for many years.

The use of similar compounds in the fight against rust provides enough benefits, among which simplicity and affordable price are not the only ones:

• The coatings used can give the workpiece a different color, as a result, this allows not only to reliably protect the product from rust, but also to provide structures with a more aesthetic appearance;
• No difficulties with the restoration of the protective layer in case of damage.

Alas, however, paint and varnish compositions also have certain shortcomings, which include the following:

• low coefficient of thermal stability;
• low stability in the aquatic environment;
• low mechanical resistance.

This forces, which does not contradict the requirements of the current SNiP, to resort to their help in a situation where the products are exposed to corrosion at a maximum rate of 0.05 mm per year, while the estimated service life should not exceed 10 years.

The range currently on the market paint and varnish compositions can be represented as the following elements:

When choosing one or another paint and varnish composition, one should pay attention to the operating conditions of the processed metal structures. Apply materials based on epoxy elements it is desirable for those products that will be operated in atmospheres containing vapors of chloroform, divalent chlorine, as well as for processing products that are planned to be used in different types of acids.

High resistance to acids is also demonstrated by paints and varnishes containing polyvinylchloride. In addition, they are resorted to in order to protect the metal that will come into contact with oils and alkalis. If the task arises in providing protection for structures that will interact with gases, then usually the choice is stopped on materials containing polymers.

When deciding on the preferred option for the protective layer, one should pay attention to the requirements of domestic SNiPs provided for a particular industry. Such standards contain a list of such materials and methods of protection against corrosion, which can be resorted to, as well as those that should not be used. Let's say if refer to SNiP 3.04.03-85, then there are recommendations for the protection of building structures for various purposes:

• pipeline systems used to transport gas and oil;
• casing steel pipes;
• heating mains;
• structures made of steel and reinforced concrete.

Treatment with non-metallic inorganic coatings

The method of electrochemical or chemical processing allows you to create special films on metal products that do not allow negative impact on the side of corrosion. Usually used for this purpose phosphate and oxide films, during the creation of which the requirements of SNiP are taken into account, since such connections differ in the protection mechanism for various designs.

Phosphate films

It is recommended to opt for phosphate films if it is necessary to provide corrosion protection for products made of non-ferrous and ferrous metals. If we turn to the technology of such a process, then it boils down to placing products in a solution of zinc, iron or manganese in the form of a mixture with acidic phosphorus salts, which are preheated to 97 degrees. The created film seems to be an excellent base so that in the future it can be coated with a paint and varnish composition.

The important point is that durability of the phosphate layer is at a fairly low level. It also has other disadvantages - low elasticity and strength. Phosphating is used to protect parts exposed to high temperatures or salty water environments.

oxide films

Oxide protective films also have their own scope. They are created when metals are exposed to alkali solutions through the use of current. Quite often, a solution such as caustic soda is used for oxidation. Among specialists, the process of creating an oxide layer is often referred to as burnishing. This is due to the creation of a film on the surface of low and high carbon steels, which has an attractive black color.

Oxidation method is in demand in cases where the task of maintaining the original geometric dimensions arises. Most often, a protective coating of this type is created on precision instruments and small arms. Typically, the film has a thickness of no more than 1.5 microns.

Additional ways

There are other ways to protect against corrosion, which are based on the use inorganic coatings:

Conclusion

Each tool and structure, which is made of steel, has limited service life. At the same time, the product may not always demonstrate it in the form that was originally laid down by the manufacturer. This can be prevented by various negative factors, including corrosion. In order to protect against it, one has to resort to various methods and means.

Given the importance of the corrosion protection procedure, it is necessary to choose the right method, and for this it is important to take into account not only the operating conditions of the products, but also their initial properties. Such an approach will provide reliable protection against rust, as a result, the product will be able to be used much longer for its intended purpose.

The main condition for the anticorrosion protection of metals and alloys is to reduce the corrosion rate. It is possible to reduce the corrosion rate by using various methods of protecting metal structures from corrosion. The main ones are:

1 Protective coatings.

2 Treatment of the corrosive environment to reduce corrosivity (especially with constant volumes of corrosive environments).

3 Electrochemical protection.

4 Development and production of new structural materials of increased corrosion resistance.

5 Transition in a number of designs from metal to chemically resistant materials (plastic high-molecular materials, glass, ceramics, etc.).

6 Rational design and operation of metal structures and parts.

1. Protective coatings

The protective coating must be continuous, evenly distributed over the entire surface, impervious to the environment, have high adhesion (adhesion strength) to the metal, be hard and wear-resistant. The coefficient of thermal expansion should be close to the coefficient of thermal expansion of the metal of the protected product.

The classification of protective coatings is shown in fig. 43

Protective coatings

Non-metallic Metal Coating Coatings

InorganicOrganicCathodeAnode

Figure 43 - Classification scheme for protective coatings

1.1 Metal coatings

The application of protective metal coatings is one of the most common methods of corrosion control. These coatings not only protect against corrosion, but also impart a number of valuable physical and mechanical properties to their surface: hardness, wear resistance, electrical conductivity, solderability, reflectivity, provide products with a decorative finish, etc.

According to the method of protective action, metal coatings are divided into cathodic and anodic.

Cathodic coatings have more positive, and anodic - more electronegative electrode potentials compared to the potential of the metal on which they are deposited. So, for example, copper, nickel, silver, gold, deposited on steel, are cathodic coatings, and zinc and cadmium in relation to the same steel are anode coatings.

It should be noted that the type of coating depends not only on the nature of the metals, but also on the composition of the corrosive medium. Tin in relation to iron in solutions of inorganic acids and salts plays the role of a cathode coating, and in a number of organic acids (food canned food) it serves as an anode. Under normal conditions, cathodic coatings protect the metal of the product mechanically, isolating it from the environment. The main requirement for cathode coatings is porosity. Otherwise, when the product is immersed in the electrolyte or when a thin film of moisture condenses on its surface, the exposed (in pores or cracks) areas of the base metal become anodes, and the coating surface becomes a cathode. In places of discontinuities, corrosion of the base metal will begin, which can spread under the coating (Fig. 44 a).

Figure 11 Scheme of corrosion of iron with a porous cathode (a) and anode (b) coating

Anode coatings protect the metal of the product not only mechanically, but mainly electrochemically. In the resulting galvanic cell, the coating metal becomes an anode and undergoes corrosion, and the exposed (in pores) areas of the base metal act as cathodes and do not collapse as long as the electrical contact of the coating with the protected metal is maintained and sufficient current passes through the system (Fig. 4 b). Therefore, the degree of porosity of anode coatings, in contrast to cathodic coatings, does not play a significant role.

In some cases, electrochemical protection can take place during the application of cathodic coatings. This happens if the coating metal in relation to the product is an effective cathode, and the base metal is prone to passivation. The resulting anodic polarization passivates unprotected (in pores) areas of the base metal and makes it difficult to destroy them. This type of anodic electrochemical protection is manifested for copper coatings on steels 12X13 and 12X18H9T in sulfuric acid solutions.

The main method of applying protective metal coatings is galvanic. Thermal diffusion and mechanothermal methods, metallization by spraying and immersion in the melt are also used. Let us analyze each of the methods in more detail.

1.2 Electroplated coatings.

The galvanic method of deposition of protective metal coatings has become very widespread in industry. Compared with other methods of applying metal coatings, it has a number of serious advantages: high efficiency (metal protection from corrosion is achieved by very thin coatings), the possibility of obtaining coatings of the same metal with different mechanical properties, easy controllability of the process (regulation of the thickness and properties of metal deposits by changing the composition of the electrolyte and the electrolysis mode), the possibility of obtaining alloys of various compositions without the use of high temperatures, good adhesion to the base metal, etc.

The disadvantage of the galvanic method is the uneven thickness of the coating on products with a complex profile.

Electrochemical deposition of metals is carried out in a direct current galvanic bath (Fig. 45). The metal-plated product is hung on the cathode. As anodes, plates made of deposited metal (soluble anodes) or of a material insoluble in the electrolyte (insoluble anodes) are used.

An obligatory component of the electrolyte is a metal ion deposited on the cathode. The composition of the electrolyte may also include substances that increase its electrical conductivity, regulate the course of the anode process, ensure a constant pH, surfactants that increase the polarization of the cathode process, brightening and leveling additives, etc.

Figure 5 Electroplating bath for electrodeposition of metals:

1 - body; 2 - ventilation casing; 3 - coil for heating; 4 - insulators; 5 – anode rods; 6 – cathode rods; 7 - bubbler for mixing with compressed air

Depending on the form in which the discharging metal ion is in solution, all electrolytes are divided into complex and simple. The discharge of complex ions at the cathode occurs at a higher overvoltage than the discharge of simple ions. Therefore, deposits obtained from complex electrolytes are finer-grained and uniform in thickness. However, these electrolytes have a lower metal current efficiency and lower operating current densities, i.e. in terms of performance, they are inferior to simple electrolytes, in which the metal ion is in the form of simple hydrated ions.

The distribution of current over the surface of the product in a galvanic bath is never uniform. This leads to different deposition rates and, consequently, to different coating thicknesses in individual sections of the cathode. A particularly strong variation in thickness is observed on products with a complex profile, which adversely affects the protective properties of the coating. The uniformity of the thickness of the deposited coating improves with an increase in the electrical conductivity of the electrolyte, an increase in polarization with an increase in current density, a decrease in the current efficiency of the metal with an increase in current density, and an increase in the distance between the cathode and anode.

The ability of a galvanic bath to give uniform thickness coatings on a relief surface is called scattering power. Complex electrolytes have the highest scattering power.

To protect products from corrosion, galvanic deposition of many metals is used: zinc, cadmium, nickel, chromium, tin, lead, gold, silver, etc. Electrolytic alloys are also used, such as Cu - Zn, Cu - Sn, Sn - Bi and multilayer coatings.

The most effective (electrochemical and mechanical) protection of ferrous metals from corrosion is anodic coatings with zinc and cadmium.

Zinc coatings are used to protect against corrosion of machine parts, pipelines, steel sheets. Zinc is a cheap and readily available metal. It protects the main product by mechanical and electrochemical methods, since in the presence of pores or bare spots, zinc is destroyed, and the steel base does not corrode.

Zinc coatings dominate. Zinc protects about 20% of all steel parts from corrosion, and about 50% of the zinc produced in the world is used for electroplating.

In recent years, work has been developed on the creation of protective galvanic coatings from zinc-based alloys: Zn - Ni (8 - 12% Ni), Zn - Fe, Zn - Co (0.6 - 0.8% Co). In this case, it is possible to increase the corrosion resistance of the coating by 2-3 times.

The problem of protecting metals from corrosion arose almost at the very beginning of their use. People tried to protect metals from atmospheric action with the help of grease, oils, and later coating with other metals and, above all, low-melting tin. In the writings of the ancient Greek historian Herodotus (5th century BC), there is already a mention of the use of tin to protect iron from corrosion.

The task of chemists has been and remains to elucidate the essence of corrosion phenomena, to develop measures that prevent or slow down its course. Corrosion of metals is carried out in accordance with the laws of nature and therefore it cannot be completely eliminated, but can only be slowed down.

Depending on the nature of corrosion and the conditions of its occurrence, various methods of protection are used. The choice of one or another method is determined by its effectiveness in this particular case, as well as economic feasibility.

alloying

There is a way to reduce the corrosion of metals, which cannot be strictly attributed to protection. This method is to obtain alloys, which is called doping. At present, a large number of stainless steels have been created by adding nickel, chromium, cobalt, etc. to iron. Indeed, such steels do not rust, but their surface corrosion occurs, although at a low rate. It turned out that when using alloying additives, the corrosion resistance changes abruptly. A rule has been established, called Tammann's rule, according to which a sharp increase in the corrosion resistance of iron is observed with the introduction of an alloying additive in the amount of 1/8 atomic fraction, that is, one atom of the alloying additive falls on eight iron atoms. It is believed that with such a ratio of atoms, their ordered arrangement in the crystal lattice of the solid solution occurs, which hinders corrosion.

Protective films

One of the most common ways to protect metals from corrosion is to apply on their surface protective films: varnish, paint, enamel, other metals. Paint coatings are most accessible to a wide range of people. Varnishes and paints have low gas and vapor permeability, water-repellent properties, so they prevent access to the metal surface of water, oxygen and aggressive components contained in the atmosphere. Coating the metal surface with a paint layer does not exclude corrosion, but serves only as a barrier for it, which means it only slows down the corrosion process. That is why the quality of the coating is important - layer thickness, porosity, uniformity, permeability, ability to swell in water, adhesion strength (adhesion). The quality of the coating depends on the thoroughness of surface preparation and the method of applying the protective layer. Scale and rust must be removed from the surface of the coated metal. Otherwise, they will prevent good adhesion of the coating to the metal surface. Poor coating quality is often associated with increased porosity. It often occurs during the formation of a protective layer as a result of solvent evaporation and the removal of curing and degradation products (during film aging). Therefore, it is usually recommended to apply not one thick layer, but several thin layers of the coating. In many cases, an increase in the thickness of the coating leads to a weakening of the adhesion of the protective layer to the metal. Air cavities and bubbles cause great harm. They are formed when the quality of the coating operation is low.

To reduce water wettability, paint coatings are sometimes, in turn, protected with wax compounds or organosilicon compounds. Lacquers and paints are most effective in protecting against atmospheric corrosion. In most cases, they are unsuitable for the protection of underground structures and structures, since it is difficult to prevent mechanical damage to the protective layers upon contact with the ground. Experience shows that the service life of paintwork under these conditions is short. It turned out to be much more practical to use thick coatings of coal tar (bitumen).

In some cases, paint pigments also play the role of corrosion inhibitors (inhibitors will be discussed later). These pigments include chromates of strontium, lead and zinc (SrCrO 4 , PbCrO 4 , ZnCrO 4).

Primers and Phosphating

Primers are often applied under the paint layer. The pigments included in its composition must also have inhibitory properties. As the water passes through the primer layer, it dissolves some of the pigment and becomes less corrosive. Among the pigments recommended for soils, red lead Pb 3 O 4- is recognized as the most effective.

Instead of a primer, phosphate coating of the metal surface is sometimes carried out. To do this, solutions of iron (III), manganese (II) or zinc (II) orthophosphates containing orthophosphoric acid H 3 PO 4 itself are applied to a clean surface with a brush or sprayer. Under factory conditions, phosphating is carried out at 99-97 0 C for 30-90 minutes. The metal dissolving in the phosphated mixture and the oxides remaining on its surface contribute to the formation of the phosphate coating.

Several different preparations have been developed for phosphating the surface of steel products. Most of them consist of a mixture of manganese and iron phosphates. Perhaps the most common drug is majef, a mixture of manganese dihydrophosphates Mn(H 2 PO 4) 2 , iron Fe(H 2 PO 4) 2 and free phosphoric acid. The name of the drug consists of the first letters of the components of the mixture. By appearance mazhef is a finely crystalline powder of white color with a ratio between manganese and iron from 10:1 to 15:1. It consists of 46-52% P 2 O 5 ; not less than 14% Mn; 0.3-3% Fe. When phosphated with mazhef, a steel product is placed in its solution, heated to about one hundred degrees. In the solution, iron dissolves from the surface with the release of hydrogen, and a dense, durable and poorly soluble in water protective layer of gray-black manganese and iron phosphates is formed on the surface. When the layer thickness reaches a certain value, further dissolution of iron stops. A film of phosphates protects the surface of the product from atmospheric precipitation, but is not very effective against salt solutions and even weak acid solutions. Thus, a phosphate film can only serve as a primer for the successive application of organic protective and decorative coatings - varnishes, paints, resins. Phosphating process lasts 40-60 minutes. To accelerate it, 50-70 g/l of zinc nitrate is introduced into the solution. In this case, the time is reduced by 10-12 times.

Electrochemical protection

In production conditions, an electrochemical method is also used - treatment of products with alternating current in a solution of zinc phosphate at a current density of 4 A / dm 2 and a voltage of 20 V and at a temperature of 60-70 0 C. Phosphate coatings are a grid of metal phosphates tightly bonded to the surface. By themselves, phosphate coatings do not provide reliable corrosion protection. They are mainly used as a base for painting, providing good adhesion of paint to metal. In addition, the phosphate layer reduces corrosion damage caused by scratches or other defects.

silicate coatings

To protect metals from corrosion, vitreous and porcelain enamels are used, the thermal expansion coefficient of which should be close to that of the coated metals. Enameling is carried out by applying an aqueous suspension to the surface of the products or by dry powdering. First, a primer layer is applied to the cleaned surface and fired in a kiln. Next, a layer of integumentary enamel is applied and the firing is repeated. The most common vitreous enamels are transparent or quenched. Their components are SiO 2 (basic mass), B 2 O 3 , Na 2 O, PbO. In addition, auxiliary materials are introduced: oxidizers of organic impurities, oxides that promote the adhesion of enamel to the surface to be enameled, silencers, dyes. The enamel material is obtained by fusing the initial components, grinding into powder and adding 6-10% clay. Enamel coatings are mainly applied to steel, but also to cast iron, copper, brass and aluminum.

Enamels have high protective properties, which are due to their impermeability to water and air (gases) even with prolonged contact. Their important quality is high resistance at elevated temperatures. The main disadvantages of enamel coatings include sensitivity to mechanical and thermal shocks. With prolonged use, a network of cracks may appear on the surface of enamel coatings, which provides access to moisture and air to the metal, as a result of which corrosion begins.

Cement Coatings

Cement coatings are used to protect cast iron and steel water pipes from corrosion. Since the coefficients of thermal expansion of Portland cement and have become close, it is quite widely used for these purposes. The disadvantage of Portland cement coatings is the same as enamel coatings - high sensitivity to mechanical shocks.

Metal plating

A common way to protect metals from corrosion is to coat them with a layer of other metals. The coating metals themselves corrode at a low rate, as they are covered with a dense oxide film. The coating layer is applied by various methods:

hot coating - short-term immersion in a bath of molten metal;

galvanic coating - electrodeposition from aqueous solutions of electrolytes;

metallization - spraying;

diffusion coating - powder treatment at elevated temperature in a special drum;

using a gas phase reaction, for example:

3CrCl 2 + 2Fe 1000 ` C 2FeCl 3 + 3Cr (in melt with iron).

There are other methods for applying metal coatings. For example, a kind of diffusion method is the immersion of products in a calcium chloride melt, in which the deposited metals are dissolved.

Chemical deposition of metal coatings on products is widely used in production. The chemical metal plating process is catalytic or autocatalytic, and the surface of the product is the catalyst. The solution used contains the compound of the deposited metal and the reducing agent. Since the catalyst is the surface of the product, the release of metal occurs precisely on it, and not in the volume of the solution. At present, methods have been developed for the chemical coating of metal products with nickel, cobalt, iron, palladium, platinum, copper, gold, silver, rhodium, ruthenium, and some alloys based on these metals. Hypophosphite and sodium borohydride, formaldehyde, hydrazine are used as reducing agents. Naturally, chemical nickel plating can not apply a protective coating on any metal.

Metal coatings are divided into two groups:

corrosion resistant;

tread.

For example, for the coating of iron-based alloys, the first group includes nickel, silver, copper, lead, chromium. They are more electropositive with respect to iron, that is, in the electrochemical series of voltages of metals, they are to the right of iron. The second group includes zinc, cadmium, aluminum. They are more electronegative with respect to iron.

In everyday life, a person most often encounters iron coatings with zinc and tin. Sheet iron plated with zinc is called galvanized iron, and plated with tin is called tinplate. The first goes in large quantities to the roofs of houses, and the second - to the manufacture of cans. For the first time, a method of storing food in cans was proposed by the cook N.F. Upper in 1810. Both irons are obtained mainly by pulling a sheet of iron through a melt of the corresponding metal.

Metal coatings protect iron from corrosion while maintaining continuity. If the coating layer is violated, the corrosion of the product proceeds even more intensively than without coating. This is due to the work of the iron-metal galvanic cell. Cracks and scratches are filled with moisture, as a result of which solutions are formed, in which ionic processes facilitate the electrochemical process (corrosion).

Inhibitors

The use of inhibitors is one of the most effective ways combating corrosion of metals in various aggressive environments. Inhibitors- These are substances capable of slowing down the course of chemical processes or stopping them in small quantities. The name inhibitor comes from the Latin inhibere, which means to restrain, stop. Even according to 1980 data, the number of inhibitors known to science was more than five thousand. Inhibitors give the national economy considerable savings.

The inhibitory effect on metals, primarily steel, is exerted by a number of inorganic and organic substances, which are often added to the corrosive medium. Inhibitors tend to create a very thin film on the metal surface that protects the metal from corrosion.

Inhibitors according to H. Fischer can be grouped as follows.

1) Shielding, that is, covering the surface of the metal with a thin film. The film is formed as a result of surface adsorption. When exposed to physical inhibitors, chemical reactions do not occur

2) Oxidizing agents (passivators) such as chromates, which cause the formation of a tightly fitting protective layer of oxides on the metal surface, which slow down the anodic process. These layers are not very durable and can be restored under certain conditions. The effectiveness of passivators depends on the thickness of the resulting protective layer and its conductivity;

3) Cathodic - increasing the overvoltage of the cathodic process. They slow down corrosion in solutions of non-oxidizing acids. Such inhibitors include salts or oxides of arsenic and bismuth.

The effectiveness of the action of inhibitors depends mainly on environmental conditions, so there are no universal inhibitors. Their selection requires research and testing.

The most commonly used inhibitors are: sodium nitrite added to, for example, refrigeration brine solutions, sodium phosphates and silicates, sodium bichromate, various organic amines, benzyl sulfoxide, starch, tannin, etc. Since inhibitors are used up over time, they must be added in an aggressive environment periodically. The amount of inhibitor added to aggressive media is small. For example, sodium nitrite is added to water in an amount of 0.01-0.05%.

Inhibitors are selected depending on the acidic or alkaline nature of the environment. For example, sodium nitrite, which is often used as an inhibitor, can be used mainly in an alkaline environment and ceases to be effective even in slightly acidic environments.