How to protect metal pipes from corrosion. How to paint metal fence posts

Do you want to know which is the most effective protection from corrosion steel pipes? During operation, metal pipes are constantly exposed to various unfavorable factors. To solve this problem it was specially developed comprehensive protection pipelines against corrosion according to SNiP 2.03.11-85 “Protection building structures from corrosion."

External polymer coating — reliable protection against corrosion of steel pipes

Corrosion control methods

This article invites the reader detailed instructions, which describes in detail the basic principles of anti-corrosion protection for metal products. I will tell you how to protect any metal surface from corrosion.

Classification of harmful factors

According to the mechanism of occurrence and the degree of destructive impact, all harmful factors can be divided into several types.

1. Atmospheric corrosion occurs when iron interacts with water vapor contained in the surrounding air, as well as as a result of direct contact with water during precipitation. During the chemical reaction, iron oxide is formed, or, more simply, ordinary rust, which significantly reduces the strength of metal products, and over time can lead to their complete destruction.

Electrochemical corrosion underground destroys even thick-walled pipes

1. Chemical corrosion arises as a result of the interaction of iron with various active chemical compounds(acids, alkalis, etc.). At the same time, leaking chemical reactions lead to the formation of other compounds (salts, oxides, etc.), which, like rust, gradually destroy the metal.
2. Electrochemical corrosion occurs when an iron product long time is in an electrolyte environment (an aqueous solution of salts of varying concentrations). In this case, anodic and cathodic areas are formed on the surface of the metal, between which an electric current flows. As a result of electrochemical emission, iron particles are transferred from one area to another, which leads to the destruction of the metal product.
3. Impact negative temperatures in cases where pipes are used to transport water, it leads to freezing. Upon transition to solid state of aggregation, a crystal lattice is formed in water, as a result of which its volume increases by 9%. Being in a confined space, water begins to put pressure on the walls of the pipe, which ultimately leads to their rupture.

Note!

A significant difference in average annual and average daily temperatures leads to significant fluctuations in the total length of the pipeline, which are caused by the linear thermal expansion of the material. To prevent pipe rupture and damage load-bearing structures, after a certain distance on the line it is necessary to install thermal compensators.

Soil analysis

In order to choose the most effective method protection, it is necessary to have accurate information about the nature of the environment and the specific operating conditions of the steel pipeline. In the case of laying an internal or overhead line, this information can be obtained on the basis of subjective observations, as well as based on the average annual climate regime for a given region.

In the case of laying an underground pipeline, the corrosion resistance and durability of the metal largely depend on the physical parameters and chemical composition soil, so before digging a trench with your own hands, you need to submit soil samples for analysis to a specialized laboratory.

The most important indicators that need to be clarified during the analysis process are the following soil qualities:

1. Chemical composition and salt concentration various metals V groundwater. The density of the electrolyte and the electrical permeability of the soil largely depend on this indicator.
2. Qualitative indicator of acidity soil, which can cause both chemical oxidation and electrochemical corrosion of the metal.
3. Electrical resistance of the earth. The lower the electrical resistance value, the more susceptible the metal is to the destructive effects caused by electrochemical emission.

Note!

To obtain objective analysis results, soil samples must be removed from the soil layers in which the pipeline will pass.

Low temperature protection

In the case of underground or overhead installation of water supply and sewerage networks, the most important condition their uninterrupted operation is to protect pipes from freezing and maintain the water temperature at a level not lower than 0°C during the cold season. To reduce the negative impact of the environmental temperature factor, the following technical solutions are used:

1. Laying an underground pipeline at depth exceeding the maximum depth of soil freezing for a given region.
2. Thermal insulation air and underground lines with help various materials with low thermal conductivity (mineral wool, foam segments, foam propylene sleeves).

Foil sleeves made of mineral wool for pipe insulation

1. backfilling pipeline trenches bulk material with low thermal conductivity (expanded clay, coal slag).
2. Drainage adjacent layers of soil in order to reduce its thermal conductivity.
3. Pad underground communications in rigid closed boxes made of reinforced concrete, which ensure the availability air gap between the pipe and the ground.

The most progressive method of protecting pipes from freezing is to use a special casing consisting of a shell made of heat-insulating material, inside which an electric heating element is placed.

Note!

The depth of soil freezing for each specific region, as well as the methodology for its calculation, is regulated regulatory documents SNiP 2.02.01-83* “Foundations of buildings and structures” and SNiP 23-01-99* “Building climatology”.

External waterproofing coating

The most common way to combat metal corrosion is to apply a thin layer of durable, waterproof protective material to its surface.

I will give simple examples:

1. The most common protective coating option is conventional waterproof paint or enamel. For example, protection gas pipe passing through the air is always performed using weatherproof enamel yellow color;
2. Underground water and gas pipelines are assembled from steel pipes, which are pre-coated on the outside with a thick layer of bitumen mastic and then wrapped in thick technical paper:
3. Coatings made of composite or polymer materials are also highly effective;
4. Cast iron elements of sewer lines are covered inside and out with a thick layer of cement-sand mortar, which, after hardening, forms a homogeneous monolithic surface. This way you can protect the support.

To choose the right suitable material for external coating, you need to know that anti-corrosion protection of metal must simultaneously have several qualities.

1. Paintwork after drying it should have a continuous, homogeneous surface with high mechanical strength and absolute resistance to water;
2. Protective film waterproofing material, with the specified properties, must be elastic and not collapse under the influence of high or low temperatures;
3. Raw material to apply the coating it must have good fluidity, high covering ability, as well as good adhesion to the metal surface;
4. Anti-corrosion treatment applied to a dry, clean metal surface;
5. Electrical conductivity. Another indicator of a high-quality insulating material is that it must be an absolute dielectric. Thanks to this property, reliable protection of pipelines from stray currents is provided, which increases adverse effect electrochemical corrosion.

Note!

The most effective solutions for waterproofing metal are considered to be compositions based on bitumen resins, two-component polymer compositions, as well as roll polymer materials on a self-adhesive basis.

Active and passive electrochemical protection

Underground engineering Communication are more susceptible to the occurrence of corrosion centers than air and internal pipelines, because they are constantly in an electrolyte environment, which is a solution of salts contained in groundwater.

In order to minimize the destructive effects caused by the reaction of iron with a water-salt electrolyte solution, active and passive methods of electrochemical protection are used.

1. Active cathode method consists in the directional movement of electrons in a direct electric current circuit:

• To do this, to the negative pole of the source direct current a pipeline is connected, and an anode grounding rod is connected to the positive one, which is buried in the ground nearby;
• After applying voltage, the electrical circuit is completed through the soil electrolyte, as a result of which free electrons begin to move from the ground rod to the pipeline;
• Thus, the grounding electrode is gradually destroyed, and the released electrons react with the electrolyte instead of the pipeline.

1. Passive tread protection pipelines is as follows:

• An electrode made of a more electronegative metal, such as zinc or magnesium, is placed near the iron in the ground;
• The steel pipe and the electrode are connected electrically through a controlled load;
• In the electrolyte environment they form a galvanic couple, which during the reaction causes the movement of electrons from the zinc protector to the protected pipeline.

3.Electrical drainage protection is also a passive method, which is performed by connecting the pipeline to the ground loop:

• The connection is made in accordance with the requirements of the PUE;
• This method helps to get rid of the occurrence of stray currents and is used if the pipeline is located near the contact electrical network of ground or rail transport.

Note!

A clear example of passive protective protection is the well-known zinc coating of iron products, or, more simply, galvanization.

Conclusion

Each of the above methods has its own advantages and disadvantages, so they must be used depending on specific conditions. In conclusion, I can only say that regardless of the chosen method, the cost of repairing and replacing the pipeline will cost much more than the cost of the most complex and time-consuming protection.

Metal pipes have many advantages, but during their operation everyone can face one problem - corrosion. Corrosion of pipes leads to a reduction in their service life and waste of a huge amount of metal, especially when it comes to steel pipes. In connection with it, accidents and water leaks occur on water supply lines; because of it, the roughness of the inner surface of the pipes increases, which is accompanied by the appearance of additional resistance, a drop in water pressure and, ultimately, an increase in the cost of its supply.
In other words, metal corrosion creates the need for additional construction and operating costs in water supply systems. That is why special attention is paid to the fight against corrosion in plumbing practice.

Causes of corrosion from outside and inside pipes

Both the internal and external surfaces of pipe walls suffer from metal corrosion. Corrosion from outside pipes occurs due to metal contact with soil, which is why it is sometimes called soil corrosion. Solutions of salts contained in the soil are liquid electrolytes, and therefore they destroy the structure of the metal during prolonged interaction with it. As a special characteristic of soil, its corrosive activity is distinguished, which is inversely proportional to the electrical resistance of the soil, that is, the higher electrical resistance, the less corrosive activity of the soil, and vice versa - the lower the electrical resistance of the soil, the higher its corrosive activity. Thanks to the fact that this dependence is known, specialists can determine the corrosive activity of soils by measuring only the level of their electrical resistance.
Corrosion inside pipes occurs from the corrosive properties of the water itself. Water with a low pH value and a high content of oxygen, sulfates, chlorides and dissolved carbon dioxide quickly leads to corrosion of the inner surface of the walls of metal pipes.

Methods for protecting metal pipes from corrosion

External insulation

The first and most important way is external insulation. In addition to anti-corrosion functions, it reduces heat loss and provides mechanical protection. Can be used to create insulation different materials, let's briefly consider the possible options.
1. Bitumen insulation. It consists of a layer of polyethylene, which is protected by a bitumen coating. Sometimes there may be fiberglass wrapped around the pipes. Can be used for pipelines located in clay, sandy and rocky soils.
2. Polyethylene anti-corrosion insulation. It consists of a multi-layer coating, specially designed to protect pipelines from corrosion.
3. Polyurethane foam insulation. There are two types. The first is the use of polyurethane foam shells, used for above-ground and underground pipelines for channel and non-channel pipe installation. The second is the creation of a polyurethane foam shell by injecting liquid polyurethane foam between the pipe and pre-created polyethylene insulation, after which the polyurethane foam hardens and turns into a complete shell.

There is also glass wool insulation and mineral wool, however, these options are initially intended to reduce heat loss and prevent the creation of condensation, and not to protect against corrosion, which is why they are used primarily for insulating pipelines of heating networks.
The thickness of the insulating layer can vary. In each specific case, the thickness is calculated depending on the functional load on the pipeline, the importance of the water line and the corrosive activity of the soil in which it is located - the higher this activity, the thicker the insulating layer should be.

Internal insulation

It is advisable to insulate pipes not only from the outside, but also from the inside. For example, in the USA, an internal cement coating with a thickness of 3–6 millimeters was previously successfully used for steel and cast iron pipes, and this for a long time kept throughput pipelines to high level. Can be applied cement-sand mortars, varnishes. In addition, it is possible that the water itself through special treatment deprive it of its corrosive properties.

Cathodic protection

Cathodic protection - another method of protection metal pipelines from corrosion, which is fundamentally different from those discussed above. It is based on the electrochemical theory of corrosion, according to which corrosion is associated with galvanic vapors that are formed in the area of ​​contact of metals with the soil environment, and the destruction of metals occurs in places where current flows out of it into the environment. Consequently, if you connect an external source of direct current and direct the current into the ground through old iron pipes, rails and other metal objects previously buried near the pipeline, then the surface of the pipeline will turn into a cathode, which will protect it from the destructive influence of galvanic couples. And the current must be diverted from the pipeline through a special wire to the negative pole of an external source. The disadvantage of this method is that it requires energy, so it is often used as an additional, but not the main method.

Removing water pipes from electric transport routes

Corrosion of metal pipes can be facilitated by the influence of stray currents, which are especially exposed to pipes laid near the tracks of intra-factory or urban electric transport. This can be avoided in two ways - by removing water pipes from electric transport tracks and adhering to the well-known rules for constructing rail roads for electric transport.

Listed protection methods water pipes against corrosion are usually used in combination. These methods summarize the experience of many years of practice and various technical studies, so their effectiveness is not only proven, but also tested by life.

Painting heating pipes is a typical task that arises where the system has not been replaced with options made of plastic, stainless steel, or copper. How to put a conventional system in order so that it has best view? Reliability of protection is also important; the paint must be resistant to temperatures and external influences, do not bring harmful substances into the house. Therefore, its selection and application must be approached carefully...

Everything is serious with pipes...

It is better to paint and protect heating pipes according to the rules, otherwise there will be increased costs.

If you do not provide high-quality protection for steel pipes from the very beginning, then the metal will rust under a layer of paint. This will manifest itself as swelling, peeling of the layer, and rust in places. Then it will be necessary to mechanically strip off the rust and the old paint, after which... do it according to the rules - triple labor costs and financial frustration will occur.

The intensity of corrosion will depend on the environment and humidity. Externally, steel parts that are exposed to precipitation oxidize intensively. In contact with the ground this process is even faster.

In a room, especially in a dry and heated room, this process is slow. But many people have probably seen rust on radiators and pipes, even painted ones. How to process these parts reliably, especially when it comes to operation in adverse conditions?

Painting of steel parts

Steel and cast iron are painted according to the following scheme.

• 1. Mechanical removal rust, old paint, cleaning contaminants down to metal, degreasing with a solvent.
• 2. Treatment of the entire surface and internal cavities with a rust inhibitor. Phosphoric acid is most often used. This is an important point. When acid reacts with iron oxides, stable substances are formed in the form of a film on the part.
• 3. Metal primer. Primer is a special composition that firmly binds to the surface of the part and penetrates into the smallest irregularities. Forms a strong protective film. It is recommended to use only high-quality compounds.
• 4. Painting. The paint layer must be resistant to external influences. Preferably from the same manufacturer as the primer for the best combination.

Additional information - the sequence of work when painting and protecting heating system elements is shown in the figure.

What is special about heating protection?

Heating pipes and radiators become hot. At the same time, they are located in residential premises. Therefore, compositions that can be used for painting heating system, must be:

• elastic, does not crack with constant temperature expansions. Do not lose adhesion to metal.
• do not release any components, including when heated.

But not only that, for outdoor work, the compositions must also be resistant to freezing if the pipes are overwintered without heating in open form. And also to precipitation with aggressive acid-base water, and to exposure to ultraviolet radiation, if there is no external additional protection.

For outdoor use, the protection must be particularly resistant to electrochemical reactions, and for soil - also to significant mechanical impacts.

What is used for pipes

To the delight of the consumer, some modern paint products meet the above requirements. On sale you can find special compositions for heating heating systems.

As a rule, water-based surface paints are used for pipes and radiators inside the house. They are considered the most harmless and do not smell. But fillers can be different.

For outdoor work, weatherproof compositions can be oil based. They take longer to dry, but what is more important is the resistance of the film they create to aggressive water. They can be applied to various pipes. True, the protection of heating mains outside buildings and in the ground is carried out in slightly different ways.

Heating mains outside and underground

Heating pipelines outside the building are usually thermally insulated. In addition to the usual protection against corrosion, they are equipped with a shell of insulation. Thin pipes, which are used in private homes, are often encased in a shell made of dense polyurethane foam or extruded polystyrene. These thermal insulation materials water-repellent, even if leakage occurs outer covering, they will likely prevent further spread of moisture.

The shell is placed on the pipes in a checkerboard pattern, and the joints are taped with construction tape.

A roofing felt casing is glued on top of the thermal insulation using a composition that is not aggressive to polystyrenes, which acts as a long-term protection against moisture.

But large diameters are often thermally insulated with rolled glass wool. This method is cheaper. A bitumen-roofing felt cover is installed on top.

The pipes themselves under thermal insulation are usually treated with a rust inhibitor and a high-quality primer.

New silver for pipes

One of the reliable methods of protecting heating pipes, which can be used at home, is coating with a zinc-polymer composition. The so-called “cold galvanizing”. This is not at all what is called galvanizing in a factory, but nevertheless, the protection is advertised as something else. Zinc dust is added to the polymer-epoxy composition, with a chip size of less than 10 microns. Suitable as a replacement for the usual “silver”, as an option, although not cheap, but as an interesting experiment….

What compositions are used - what to paint with?

Currently, the following series of paints are widely used for painting pipes:

These and other coatings for heating pipes and radiators can be found on store shelves. True, they are only part necessary protection metal from corrosion. Full painting also includes the processes listed above.

Corrosion is the scourge of all metal structures, and leaking pipes are horrible dream any home owner. The appearance of rust is inevitable, like the change of seasons, it is caused by physical and chemical environmental factors. But it is possible to slow down the development of corrosion and reduce its destructive effects.

Metal and plastic: pros and cons

The common opinion of experts in the field of repair is that there is only one radical way to combat corrosion - replacing all pipes with plastic ones. But metal pipes don’t give up so easily, because it’s not always possible to make major renovation throughout the apartment. In addition, steel and cast iron pipes much stronger and more reliable than plastic and metal-plastic ones. They are more resistant to high blood pressure and temperature (especially to their differences), have a low coefficient thermal expansion(do not deform) and high thermal conductivity.

Plastic is theoretically very durable, but this has not yet been tested by time. The safety of this material during long-term use has not been sufficiently studied, but it is already known that it is afraid of chlorinated water. So metal pipes still have a place in our homes, which means that the problem of protecting them from corrosion is still relevant.

There is aggression all around!

How to deal with rust in living conditions? Most affordable way- applying a product to the metal that forms a protective film on its surface: paint, varnish, enamel. Paint and varnish coatings have low vapor and gas permeability and high water-repellent properties. Thus, they do not allow moisture, oxygen and other aggressive substances, which cause corrosion, to reach the metal surface. Paintwork materials are relatively inexpensive and can be easily applied with a regular brush or spray. They save protective properties for several years. Their important quality is resistance to high temperatures, the main disadvantage is sensitivity to mechanical damage and temperature changes, which causes small cracks to form on the surface, allowing moisture and air access to the metal. Therefore, staining should be done regularly.

Main quality!

A barrier in the form of paintwork materials does not stop corrosion completely, but only slows it down. Therefore, the quality of the coating comes to the fore - high strength of adhesion of the composition to the base (adhesion), uniformity of application, lack of porosity and air bubbles. And the quality of the coating is directly related to how the base is prepared. Old, flaking paint must be carefully removed. If the pipe is rusty, then you need to clean off the loose layers, and then use a special rust converter (150-200 rubles / kg). These products are based on acid (usually phosphoric acid). It chemically interacts with rust and turns it into iron salts - a neutral substance that forms a uniform and durable additional protective film.

Next, apply an anti-corrosion primer and only then apply a paint compatible with the primer. The thicker the layer of the latter, the worse grip with base. Therefore, the main rule is that several are better thin layers coatings than one thick.

The range of anti-corrosion coatings is quite extensive. The simplest ones are GF-021 primer (the cost of this product from the Khimservice company is 50 rubles/kg) and PF-115 enamel (for example, the price for this material from the RegionSnab company is 48 rubles/kg). More expensive, but also effective - polyurethane, alkyd, epoxy coatings, which not only protect the metal well, but also have excellent decorative properties(in particular, enamel “liquid plastic”). It’s good if the paint contains corrosion inhibitors - substances that slow down oxidation. The most convenient to use products are those that are called “rust paint 3 in 1” (about 200 rubles/kg) - they simultaneously contain a rust converter, an anti-corrosion primer and wear-resistant enamel.

What's underground?

Pipes running underground are especially susceptible to corrosion. suburban area There is no way to do without them. A different corrosion mechanism occurs in the soil than in the atmosphere. The main cause of soil corrosion is electrochemical factors: a metal pipe in the ground becomes an electrode, and wet soil becomes an electrolyte.

Paintwork materials are not suitable for isolating a pipeline from this aggressive environment, since protective layer mechanically damaged upon contact with the ground. Much more practical are elastic coatings based on coal tar (bitumen) with various additives, mineral or polymer, that increase its strength. This mixture is called bitumen mastic(from 25 rub./kg). Another option is to wrap the pipes with any insulating material, for example, waterproofing (from 40 rubles/sq. m), which is asbestos paper coated with bitumen with the addition of cellulose.

What's new?

A relatively new effective and inexpensive method of protection against soil corrosion is the use of geotextiles (from 20 rubles/sq. m). This non-woven polymer fabric has excellent water and breathability, is durable, wear-resistant and can withstand high mechanical loads and exposure to aggressive environments. Geotextiles create a reliable separation layer between the pipe and the soil. The best effect will be achieved by simultaneously wrapping the pipe, lining the trench and good drainage. In this case, the water entering the ground is not retained, which means it does not have time to affect the protective coating of the pipe. Synthetics practically do not decompose in the soil, which allows drainage based on them to function for a long time. Working with geotextiles is simple and does not require special qualifications.

A truly unique method of protection is cold galvanizing. Metal-polymer compositions (200-350 rubles/kg) have a protective effect that is comparable to galvanizing performed traditional way- hot or galvanic. Such compositions provide protection in water, soil, and atmosphere for many years; they are used both to obtain independent protective coatings, and as primers before applying paintwork materials. The cold galvanizing system contains a binder - polystyrene, epoxy, alkyd and other bases and zinc powder (“zinc dust”), in which approximately 95% of metallic zinc is present with a particle size of less than 10 microns. Apply the composition as regular paint- with a brush or roller. After drying, a polymer-zinc film is formed on the surface, combining all the advantages of polymer and zinc coatings: the first forms a mechanical barrier protection, and the second - electrochemical. In addition, this coating is quite elastic and does not give microcracks, and it is also easy to repair.

Proper anti-corrosion protection will help maintain its original appearance. various designs and metal pipes. Subject to choice quality materials, correct application, thorough surface preparation will save you from extra costs, will save time and effort.

Corrosion is one of the main problems of all metal structures. Many experts believe that the appearance of rust is an inevitable process, and their only recommendation is to replace metal pipes with plastic ones. However, given the fragility of plastic, such perturbations cannot be carried out everywhere. In addition, the development of corrosion can be slowed down, significantly reducing its destructive effect.

There are several ways to combat corrosion of profile pipes in Moscow, and the simplest of them is to apply special means, forming a protective film on its surface. This medium can be paint, varnish or enamel. For paint coatings characterized by low gas permeability and gas permeability, as well as water repellency. Such coatings do not allow the metal to come into contact with moisture, oxygen and other aggressive substances that cause corrosion. Paintwork materials are relatively inexpensive and very easy to apply. To do this, use an ordinary brush. A spray option is also available.

Protective qualities paint and varnish materials remain for several years, after which the layer must be renewed. They have several disadvantages:

1. Cannot withstand significant mechanical damage.
2. Not resistant to temperature changes.

As a result, over time, cracks form on the surface of painted pipes, so this type of protection should be carried out regularly.

How to properly prepare a pipe for painting

In order to reliably protect a pipe from corrosion, it is necessary not only to use high-quality protective substances, but also to take care of their correct application. First of all, here it is necessary to achieve high adhesion, that is, the quality of adhesion of the applied composition to the metal. This method anti-corrosion profile pipes in Moscow assumes a uniform application layer, absence of air bubbles and porosity. Therefore, the quality of the coating will directly depend on the preparation of the base.

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