Metal pipes have not yet completely left our everyday life, giving way to plastic ones. Because metal, in comparison with plastic, is more resistant to high pressure, withstands significantly greater mechanical loads, is resistant to temperature changes, and has a much lower coefficient of thermal expansion.

The main enemy of metal is corrosion. This is especially true for underground metal pipelines.

In the soil, the metal pipeline acts as an electrode, and the wet earth acts as an electrolyte. Hence the very rapid development of corrosion on unprotected pipes, leading to their complete destruction. In addition, such pipes are subjected to direct and very strong mechanical action of the soil, which only activates corrosion processes. Painting pipes with any enamels will not help here, since such protection cannot withstand mechanical stress. And in the conditions of the electrolyte of the soil is very short-lived.

How to protect metal pipes in the ground from corrosion?

Bitumen-based elastic coatings are used to protect underground pipes. These are special mastics in which bitumen is mixed with polymers to give strength. There are types of bituminous mastics specifically designed to protect metal (painted and unpainted) in very difficult operating conditions.

You can also protect the pipes with insulating materials, such as waterproofing. It is asbestos paper treated with bitumen with the addition of polymers or cellulose. By wrapping the pipes in such paper, you create a strong barrier between them and the ground.

Another insulating material is geotextile. This is a polymer canvas with excellent waterproofing and strength properties. It does not decompose in the ground, which means that the protection will be very long-term. In addition, it is a very cheap material, comparable in price to both mastics and hydroisolone.


One of the modern methods of protecting metal pipes is cold galvanizing, which can be performed without any difficulties in any conditions. It is enough to have a roller or brush. At the same time, the result is comparable to factory galvanized or hot-dip galvanized. True, this method of protecting pipes is no longer cheap. The composition for cold galvanizing is made on an epoxy or polystyrene base, to which zinc dust is added, with a particle size of not more than 10 microns. This composition is applied by analogy with staining. But now the pipes will be covered with a strong protective film, elastic enough not to crack, and at the same time very durable and stable in terms of mechanical properties. And zinc in the composition will perform its usual role of electrochemical protection.

Without reliable anti-corrosion protection, not a single metal structure will last for a long time. Rust protection is important unless you plan on replacing your fence every few years.

Metal fences are no exception. You can extend the life of products by properly processing them. Below we will talk about the technology of painting structures made of metal picket fence, profiled sheet and mesh, as well as analyze the coloring compositions that are best suited for metal surfaces.

Rust protection for the fence in stages

We start by preparing the metal for painting

This moment is fundamental, since it determines how well the finishing layer will lie on the fences from the eurostudent or profiled sheet. First you need to clean the fence from traces of paint, rust, oil, grease, dirt. Conservative and radical methods are appropriate here.

• Conservative ones include cleaning rust with a scraper, a metal brush, a special knife. The best result will give an acetylene torch or a blowtorch.
• When exposed to metal, the outer layer of paint burns out, and rust and scale move away due to temperature differences. If it is not possible to remove traces of corrosion, choose a coloring composition that is suitable for application to an unprepared surface.

Padding

The next stage is the application of a primer, which simultaneously protects the metal from corrosion and ensures that the paint adheres to the surface. For ferrous metals, experts recommend choosing anti-corrosion primers.

For non-ferrous, on the contrary, the property of adhesion is more important (aluminum and copper are not subject to corrosion). The primer coat can be applied with a roller, brush or sprayer.

Applying the finish coat

After the primer layer is applied, you can start painting. It can be applied with a sprayer, brush or roller.

It is better to paint in 2-3 layers with drying intervals. This will give a more uniform surface without flaws. The sprayer is the easiest to use. To do this, you need to process the surface from a distance of 15-20 cm.

The exposure time between layers is reduced to 20 minutes. Rollers are used for flat surfaces. Before painting, it is recommended to dilute the mixture with a solvent in a ratio of 9 to 1. Hard-to-reach places and corners are treated with a brush. Then all the fences are rolled in 2-3 layers.

The choice of paint for metal

On the website masterovit.ru (the largest manufacturer of metal fences in the Russian Federation in 2015) there was a recent discussion on how to properly paint an inexpensive corrugated fence and what paintwork materials are best to choose.

The company's specialists recommend water-dispersion and special acrylic paints for metal. The latter option is preferable, since it allows you to reliably protect the surface from corrosion and negative external factors (precipitation, UV radiation).

A good solution is the choice of anti-corrosion compounds that are allowed to be applied to traces of rust and paint residue. The compositions contain a solvent, so they remove the old layer and protect structures from destruction. There are also enamels with additives on the market: rust converters, anti-corrosion primers. They are applied to clean surfaces.

Pre-treatment of the base with a primer is not required, which reduces the process of painting the fence. For ferrous metals, water-based anti-corrosion compounds are optimal. The topcoat is highly resistant to ultraviolet radiation, rainfall, sudden changes in temperature.

The weak point of metal pipes is susceptibility to corrosion. Over time, cast iron and steel pipes inevitably rust, and this affects the performance of the pipeline in a bad way. In order for the pipeline to serve longer and its condition not adversely affect water quality, rust should be removed in a timely manner.

Rust affects not only the fact that in places of formed plaque, the pipe can simply leak, but also the quality of the transported liquid. Water in rusty pipes has an unpleasant odor and becomes suitable only for technical use.

Corrosion in heating pipes reduces heating efficiency, which inevitably increases operating costs.

Methods for cleaning rusty pipes

The appearance of corrosion can occur both on the outside and on the inside of the pipe. Cleaning methods depend on the localization of plaque and the degree of damage.

It is not necessary to clean heavily corroded pipes from rust - this can damage them, and as a result, the pipe will become unusable. Therefore, in the case of severe corrosion damage, it is much more expedient to simply replace the damaged section of the pipeline or the entire line.

Only if the pipe is slightly damaged by rust, cleaning will be effective and increase the life of the pipe for some time.

Cleaning the pipe from the outside

If the pipe is rusted on the outside, you can use:

Note! Special rust removers should be used strictly following the instructions and dosage. They contain strong alkalis, which, if the instructions are violated, can damage the pipes.

Cleaning the pipe from the inside

In addition to corrosion, scale and various deposits accumulate on the inner walls of pipes. To maintain the throughput of the pipe, it is necessary to regularly clean and flush it from the inside for preventive purposes.

Description:

Pipeline protection against corrosion is not only a task for manufacturers or builders, but also for the network designer and the end user. The phenomenon of corrosion may be due to an insufficiently balanced composition of the liquid flowing through the pipes, an incorrect combination of different metals, or, finally, insufficient attention to the protection of the pipeline.

HOW TO PROTECT PIPELINE FROM CORROSION

Pipeline protection against corrosion is not only a task for manufacturers or builders, but also for the network designer and the end user. The phenomenon of corrosion may be due to an insufficiently balanced composition of the liquid flowing through the pipes, an incorrect combination of different metals, or, finally, insufficient attention to the protection of the pipeline.

Corrosion of pipelines is a phenomenon caused mainly by electrochemical reactions of metal oxidation when interacting with moisture. The metal gradually changes at the ionic level and, disintegrating, disappears from the surface of the pipe. Oxidation, which characterizes the phenomenon of corrosion of metal pipelines, can occur for various reasons and, therefore, arises on the basis of various mechanisms. The oxidation process may depend on the nature of the liquid flowing through the pipeline, or on the properties of the environment in which the pipeline is laid. In this regard, when choosing the most appropriate methods of counteracting corrosion mechanisms, it is necessary to take into account the specifics of the situation in which it is observed. In some cases, the fight against corrosion is carried out by taking enhanced measures for the chemical treatment of the flowing liquid in order to correct its corrosive properties, in other cases, by using protective coatings for pipelines (internal or external) or by using special methods of so-called "cathodic protection". First of all, careful selection of material for the pipeline is necessary. It is advisable to use materials that are less susceptible to corrosion (for example, copper or stainless steel).

When they are used, a continuous thin surface oxide film (“inert film”) is formed at the initial stage of corrosion, which then protects the underlying metal from the effects of corrosion. However, corrosion pockets can also form on such materials for various reasons. The reason is the uneven formation of the film or its breakthrough. The use of more valuable materials is not always justified due to their high cost.

Chemical treatment of aggressive water

Water flowing through the pipeline may have aggressive properties. Often this is due to the treatment of such water with chlorine or the processes of coagulation and flocculation occurring in the water directly at the water treatment plant. Aggressiveness may be due to the content of oxygen, chlorine, carbonates and bicarbonates in the water. Aggressiveness decreases with increasing levels of acidity and hardness and increases with increasing temperature and the content of dissolved air and carbon dioxide.

The main purpose of chemical water treatment is to convert potentially aggressive water into slightly calcifying water. Moderate hardness is, in fact, desirable, since it contributes to the formation of deposits of calcium salts on the inner surface of the pipe, which protect the metal. By adding appropriate inhibitory substances to water, it is possible to slow down the corrosion process, reducing it to less dangerous manifestations (uniform corrosion instead of deep localized), and also to promote - through a chemical reaction - the formation of lime deposits, which, adhering tightly to the metal, form a coating that protects it from corrosive attack. In public water networks, water treatment is mainly reduced to the addition of calcium, or soda (NaOH), or sodium carbonate (Na 2 CO 3). In sections of the water supply system that ensure the distribution of water to individual points of water intake, water treatment with special “sequestering” additives (mainly polyphosphates) is considered an effective method of anti-corrosion protection. The main task of additives of this kind is to correct excessive water hardness, which otherwise can lead to the formation of undesirable pockets of lime deposits. In galvanized steel pipelines, when polyphosphates, phosphates or silicates are added to water, a film of polyphosphate, phosphate or zinc or iron silicate is formed on the inner surface of the pipeline, protecting the metal from corrosion. It is allowed to use such reagents in water supply networks for drinking purposes, subject to compliance with the requirements established by the current sanitary and epidemiological regulations.

Protective coatings

Coatings can be applied to both internal and external surfaces of the pipeline. The protective coating forms the protection of the pipeline, which is of the active or passive type. In some cases, both types of protection may be combined. In the case of active protection, the coating creates conditions that prevent the spread of metal corrosion. The surface of steel pipes is covered with a more or less dense layer of an electrochemically less noble metal (usually zinc), which, while protecting the base metal, takes on the effects of corrosion. Active protection protects the inner surface of the pipe to a greater extent from the corrosive effects of the flowing liquid. From the outside, this protection forms a base coat reinforced with passive protection.

The task of passive protection is to protect metal pipes from the damaging effects of the environment. In buried areas of water pipes, it is very important to reliably protect the metal from direct contact with the ground. A similar protection is used to achieve - by means of an internal coating - in pipelines intended for the delivery of water of a particularly aggressive type. The application of protective layers made of lacquers, paints or enamels creates a continuous impermeable barrier that protects the underlying metal from the corrosive effects of the environment.

For this purpose, bituminous products obtained from the distillation of coal or oil or from synthetic resins, thermoplastic (polyethylene, polypropylene, polyamides) and thermosetting (epoxy, polyurethane, polyesters) are most often used.

Before coating, it is necessary to properly prepare the treated pipe surface and thoroughly clean it of everything that may be harmful in terms of corrosion (moisture, varnish residues, grease or oil stains, dirt or dust, rust). For external protection of open-laying pipelines, paint and varnish coatings or powder plastic materials can be resorted to. Coating is carried out in various ways depending on the material of the pipeline. Liquid formulations are applied with a brush, immersion in a solution or spraying from a pistol.

Powder substances (predominantly plastic materials) are applied to a pipe preheated to a temperature above the melting point of the powder. The powder is applied to the surface of the pipe by electrostatic or air spraying. Thermoplastic materials can also be applied by extrusion. The application of surface layers of metal (eg zinc) is carried out by immersing the pipe in molten metal or by electrolytic deposition. Another method often used to cover buried pipelines is to evenly apply a continuous film of a protective material with good adhesion properties to a previously cleaned pipe, and then apply a protective layer of a bituminous mixture and two layers of glass wool (or fabric) impregnated bituminous mixture, to give resistance to external influences.

It is better if the protective treatment of cut pipes is carried out at the factory.

At the object, when laying with a protective coating, only seams and couplings are sealed, as well as possible places of damage to the factory coating.

Pre-coated pipes should be protected during stacking, transportation and installation from impacts, scratches and other mechanical impacts that could damage the bitumen layer. It should be borne in mind that protective treatment loses its original properties after a certain time. Hence the need for periodic inspection of the network, current and preventive maintenance.

Buried pipelines are susceptible to corrosion due to the aggressiveness of the soil. Depending on the properties of the soil (more precisely, the parameters of its resistance) and the metal from which the pipeline is made, corrosive batteries are formed. The metal, which acts as an anode with respect to the soil, which in this case acts as a cathode, tends to decompose and go into solution.

One of the types of protective measures is passive protection. For laying the pipeline, pipes with a protective moisture-proof coating with insulating couplings are used. In this case, the electrical length of the pipeline is broken, the exchange of electric current between the pipes and the soil is inhibited. It should be recognized that this approach does not always give a 100% result, since in places where the protective coating of pipes is broken during the laying of the pipeline, corrosion centers may form. Corrosion can be combated by the method of "cathodic protection": if the potential of the metal is artificially lowered, the anodic reaction is suppressed. To do this, it is necessary to carry out an electrical connection of the pipeline to the network, which has an anode in its composition. The so-called "sacrificial anode" is made of a metal that has a higher electronegativity, i.e., less noble than iron. As a rule, magnesium alloy is used for this purpose. With this connection, corrosion is localized on magnesium, which slowly decomposes itself and protects the pipeline. In the case of practical application of this technology, first of all, the degree of soil aggressiveness should be measured.

Then, in areas where it is necessary to organize the protection of the pipeline, a certain amount of consumable anodes is dug in at the calculated points. The weight and number of anodes are determined in such a way as to provide anti-corrosion protection of the pipeline for a period of 10–15 years.

Another way that protects the metal from the aggressiveness of the soil is the protection of the "induced current". For this, an external DC source is used, which comes from a power supply device consisting of a transformer and a rectifier. The positive pole of the power supply is connected to the anode diffuser (grounding, consisting of a graphite or iron-containing anode), the negative pole is connected to the pipeline representing the object of protection. The transmitted protective current is determined by the parameters of the pipeline (length, diameter, existing degree of insulation) and the degree of aggressiveness of the soil. The current dissipated by grounding creates an electric field that envelops the pipe and lowers its potential, which gives a protective effect. The reliability and efficiency of cathodic protection are ensured, among other things, by periodic inspection of the network, checking the operability of the equipment used and timely troubleshooting.

stray current

Stray current is an electric current that appears in some soils from the dispersion of electrified, for example, railway (tram) tracks, where the rails act as return conductors of supply substations. Another source of stray current can be the grounding of electrical industrial equipment. As a rule, this is a high current, and it primarily affects the pipeline, which is characterized by good conductivity (in particular, with welded joints). Such a current enters the pipe at a certain point, which plays the role of a cathode, and, having overcome a more or less long section of the pipeline, exits at another point, which acts as an anode. The electrolysis that occurs at the same time gives corrosion of the metal. The passage of current in the section from the cathode to the anode causes the transition of iron-containing particles into solution and over time can lead to thinning and ultimately perforation of the pipe. The damage is more significant, the higher the strength of the passing current. The corrosive action of the stray current is certainly more destructive than the action of corrosive batteries formed due to the aggressiveness of the soil.

Against it, measures of "electric drainage" are effective. The essence of the technique is as follows: at a certain point, the pipeline is connected directly to a stray current source (for example, to a substation or railway track) using a special cable with low electrical resistance. The connection must be suitably polarized (using unidirectional adapters) so that the current always flows in the direction from the pipeline to the dispersion source. Electrical drainage requires strict adherence to the terms of routine inspections, careful adjustment and regular checks. Most often, this technique is combined with other methods of protection.

Reprinted with abridgements from RCI Magazine #8. 2003.

Translation from Italian S.N. Bulekova.

Sacrificial anode

The embedded magnesium block, by virtue of the position occupied by magnesium on the electrochemical potential scale relative to iron, behaves like an anode in the corrosive battery formed between it and the steel pipeline.

The current generated by the electromotive force of the corrosive battery moves in the direction "anode - soil - pipe - connecting cable - anode". The slow decomposition of magnesium protects the pipeline from corrosion.

This system is mainly used to protect steel tanks and pipelines of limited length (from several hundred meters to several kilometers).

Usually the anode is placed in a cotton (or jute) bag in a clay mixture, the task of which is to ensure the uniform consumption of the anode and the required level of humidity, as well as to prevent the formation of a film that hinders its decomposition.

Access to the electrical cable and checking the condition of the protective coating by measuring the battery current is provided through a special well.

Cathodic protection "induced current"

To organize such protection, a DC generator is required, to the negative pole of which the protected pipeline is connected. The positive pole is connected to a system of anode diffusers buried in the same area of ​​soil.

The connecting cable must have low electrical resistance and good insulation. The electric current produced by the generator is transmitted through the anodes to the soil and enters the pipeline. The pipeline acts as a cathode and thus protected from corrosion. The current goes along the following route: electric generator - connecting cable - dissipative electrode - soil - protected metal structure - connecting cable - electric generator. The anodes used are of a low-consumption type (usually graphite or iron-containing) and are buried 1.5 m at a distance of 50–100 m from the pipeline. A DC generator (125-500 W) usually consists of a rectifier fed from the mains through a transformer.

Do you want to know what is the most effective corrosion protection for steel pipes? Metal pipes during operation are constantly exposed to various adverse factors. To solve this problem, a comprehensive protection of pipelines against corrosion according to SNiP 2.03.11-85 "Protection of building structures against corrosion" has been specially developed.

External polymer coating - reliable protection against corrosion of steel pipes

Corrosion Control Methods

In this article, the reader is offered a detailed instruction, which describes in detail the basic principles for the implementation 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 conditionally divided into several types.

1. atmospheric corrosion occurs when iron interacts with water vapor, which is contained in the surrounding air, as well as as a result of direct contact with water during precipitation. During the course of a 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.

1. Chemical corrosion arises as a result of the interaction of iron with various active chemical compounds (acids, alkalis, etc.). In this case, the ongoing chemical reactions lead to the formation of other compounds (salts, oxides, etc.), which, like rust, gradually destroy the metal.
2. Electrochemical corrosion occurs when the iron product is in the electrolyte environment for a long time (an aqueous solution of salts of various concentrations). In this case, anode and cathode sections are formed on the metal surface, 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 a metal product.
3. Impact of negative temperatures in cases where pipes are used to transport water, it leads to its freezing. Upon transition to a solid state of aggregation, a crystal lattice is formed in water, as a result of which its volume increases by 9%. Being in a closed 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 linear thermal expansion of the material. In order to prevent rupture of pipes and damage to supporting 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 of 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 on the basis of the average annual climatic 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 of the soil, therefore, before digging a trench with your own hands, it is necessary to submit soil samples for analysis to a specialized laboratory.

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

1. Chemical composition and the concentration of salts of various metals in groundwater. The density of the electrolyte and the electrical permeability of the soil largely depend on this indicator.
2. Quality indicator of acidity soil, which can cause both chemical oxidation and electrochemical corrosion of the metal.
3. Earth electrical resistance. The lower the electrical resistance value, the more susceptible the metal is to damage caused by electrochemical emission.

Note!

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

Low temperature protection

In the case of underground or air laying of water and sewer networks, the most important condition for their uninterrupted operation is the protection of pipes from freezing and maintaining 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. Underground pipeline laying at depth exceeding the maximum depth of soil freezing for a given region.
2. thermal insulation air and underground lines using various materials with low thermal conductivity (mineral wool, foam plastic segments, foam sleeves).

1. backfilling pipeline trenches with loose 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 utilities in rigid closed boxes made of reinforced concrete, which provide an air gap between the pipe and the ground.

The most advanced method of how to protect 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 laid.

Note!

The depth of soil freezing for each specific region, as well as the method of its calculation, is regulated by the regulatory documents SNiP 2.02.01-83 * "Foundations of buildings and structures" and SNiP 23-01-99 * "Construction 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 ordinary waterproof paint or enamel. For example, the protection of a gas pipe passing through the air is always done with yellow weather-resistant enamel;
2. Underground water and gas pipelines are assembled from steel pipes, which are pre-coated on the outside with a thick layer of bituminous mastic, and then wrapped with thick technical paper:
3. Coatings made of composite or polymeric materials also have high efficiency;
4. Cast iron elements of sewer communications are covered from the inside and outside with a thick layer of cement-sand mortar, which, after solidification, forms a uniform monolithic surface. Thus, you can protect the support.

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

1. Paintwork after drying, it should have a continuous, uniform 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 for coating, it must have good fluidity, high covering power, as well as good adhesion to the metal surface;
4. Anti-corrosion treatment applied to a dry, cleaned metal surface;
5. Electrical conductivity. Another indicator of a quality insulating material is that it must be an absolute dielectric. This property provides reliable protection of pipelines from stray currents, which increase the adverse effects of electrochemical corrosion.

Note!

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

Active and passive electrochemical protection

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

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

1. Active cathodic method consists in the directed movement of electrons in a direct current circuit:

• To do this, a pipeline is connected to the negative pole of the DC source, and an anode ground rod is connected to the positive pole, which is buried in the ground nearby;
• After the voltage is applied, 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 ground electrode is gradually destroyed, and the released electrons, instead of the pipeline, react with the electrolyte.

1. Passive tread protection piping is as follows:

• An electrode made of a more electronegative metal, such as zinc or magnesium, is placed next to 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:

• 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 good example of passive tread protection is the well-known zinc coating of iron products, or, more simply, galvanization.

Conclusion

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