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 are 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? The most accessible way is to apply a product to the metal that forms 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 combined under the name “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 rubles/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.
Without reliable anti-corrosion protection it will not last for a long time none metal structure. Rust protection is important unless you plan to replace the fence every few years.
Metal fencing is no exception. The service life of products can be extended by proper processing. Below we will talk about the technology of painting structures made of metal picket fence, profiled sheet and mesh, and we will also analyze the coloring compositions that are optimally suited for metal surfaces.
Rust protection for fences step by step
We start by preparing the metal for painting.
This point is fundamental, as it determines how well it will fit on fences made of Euro picket fences or corrugated sheets. finishing layer. First you need to clean the fence from traces of paint, rust, oil, grease, and dirt. Conservative and radical methods are appropriate here.
- Conservative methods include removing rust using a scraper, a metal brush, special knife. Best result An acetylene torch or blowtorch will do.
- When exposed to metal, the outer layer of paint fades, and rust and scale come off due to temperature differences. If it is not possible to remove traces of corrosion, choose a paint composition that is suitable for application to an unprepared surface.
Padding
The next step is applying a primer, which simultaneously protects the metal from corrosion and ensures the paint adheres to the surface. For ferrous metals, experts recommend choosing anti-corrosion primers.
For people of color, on the contrary, property is more important adhesion (aluminum and copper are not subject to corrosion). The primer coat can be applied using a roller, brush or sprayer.
Applying the finishing coat
Once the primer coat has been applied, you can begin painting. You can apply paintwork using 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 blemishes. It is most convenient to use a sprayer. To do this, you need to treat the surface from a distance of 15-20 cm.
The dwell time between coats is reduced to 20 minutes. Rollers are used for smooth 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 the corners are treated with a brush. Then the entire fence is rolled with a roller in 2-3 layers.
Choosing paint for metal
On the website masterovit.ru ( largest producer metal fences in the Russian Federation based on the results of 2015) there was recently a discussion on how to properly paint inexpensive fence from corrugated sheets and which paint and varnish materials are better to choose.
The company’s specialists recommend water-dispersed and special acrylic paints on 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 to choose anti-corrosion compounds that can be applied to traces of rust and paint residues. The formulations contain a solvent, so they eliminate old layer and protect structures from destruction. There are also enamels on the market with additives: rust converters, anti-corrosion primer. They are applied to cleaned surfaces.
Pre-treatment of the base with a primer is not required, which shortens the process of painting the fence. For ferrous metals, anti-corrosion compounds based on water based. Finish coating It is characterized by a high degree of resistance to ultraviolet radiation, rainfall, and sudden temperature changes.
Do you want to know which is the most effective protection from corrosion of 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 roughly divided into several types.
- 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.
- 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.
- 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 metal surface, between which flow electricity. As a result of electrochemical emission, iron particles are transferred from one area to another, which leads to the destruction of the metal product.
- 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 case of laying 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:
- 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.
- Qualitative indicator of acidity soil, which can cause both chemical oxidation and electrochemical corrosion of the metal.
- 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:
- Laying an underground pipeline at depth exceeding the maximum depth of soil freezing for a given region.
- Thermal insulation air and underground lines with help various materials with low thermal conductivity (mineral wool, foam segments, foam propylene sleeves).
- backfilling pipeline trenches bulk material with low thermal conductivity (expanded clay, coal slag).
- Drainage adjacent layers of soil in order to reduce its thermal conductivity.
- 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 how to protect pipes from freezing is to use a special casing consisting of a shell made of thermal insulation material, inside of 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:
- The most common option protective coating is normal waterproof paint or enamel. For example, protection gas pipe passing through the air is always performed using weatherproof enamel yellow color;
- Underground water and gas communications are assembled from steel pipes, which are pre-coated on the outside with a thick layer bitumen mastic, and then wrapped in thick technical paper:
- Coatings made of composite or polymer materials are also highly effective;
- 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.
- Paintwork after drying it should have a continuous, homogeneous surface with high mechanical strength and absolute resistance to water;
- Protective film waterproofing material, with the specified properties, must be elastic and not collapse under the influence of high or low temperatures;
- Raw material to apply the coating it must have good fluidity, high covering ability, as well as good adhesion to the metal surface;
- Anti-corrosion treatment applied to a dry, clean metal surface;
- 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!
Most effective solutions For waterproofing metal, it is customary to consider 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.
- 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.
- 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 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 insulation with glass wool and mineral wool, however, these options are initially designed 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 preserved it for a long time. 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 is another method of protecting metal pipelines from corrosion, 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 leaves it. 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 pre-buried near the pipeline metal objects, 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.
Under its influence, the metal of the pipes is destroyed, which leads to the formation of corrosive fistulas, cracks in bends, and divergence of seams. Cold water pipes are especially affected. If your immediate plans do not include replacing the pipes in your apartment with stainless steel ones (galvanized, plastic, metal-plastic), then you need to take measures to protect the pipes from corrosion.
The most common (and also the simplest) way to protect metal surfaces from rust is to coat them with anti-corrosion compounds. Cold water pipes can be primed ready-made compounds GF-021, GF-032, KF-OZO, PF-046, FL-053, EP-076 and HS-068. Beautiful protective agent can also be prepared at home. Mix 150 g of red lead, 150 g of red lead and 100 g of drying oil and cover with the resulting composition steel pipes.
A good protection against rust is painting the pipes, the main thing is that paints and varnishes were moisture resistant, and the paints intended for painting hot water pipes were also heat resistant. Before painting, it is recommended to prime the surface with lead-lead or similar primer.
If certain sections of pipelines are laid hidden, then it makes sense to select more reliable means of protection for them.
An effective, but rather labor-intensive way to protect pipelines from corrosion is the following (it is applicable only if the pipes have not previously been coated with any compounds; it is rational to carry out such protection at the stage of laying the pipeline). If there is rust on the pipes, clean it off and coat the pipes with the mixture casein glue with cement. When the casein solution has dried, dry the pipes and coat them with oil paint.
Coating pipes with carbonate not only prevents the formation of condensation, but also protects them from corrosion.
Steel outlet pipes and cast iron siphons can be treated with one of the following compounds to protect against corrosion:
- bakelite-aluminum - combine 1 part by weight of aluminum powder and 9 parts by weight of bakelite varnish and mix well;
- ethinol-aluminum - combine 0.7 parts by weight of aluminum powder and 9.3 parts by weight of ethinol varnish and mix well;
- ethinol-glue - combine 1 part by weight of BF-2 glue and 7 parts by weight of ethinol varnish and mix well.
Not only steel pipes, but also parts made of other metals are susceptible to corrosion, so it is recommended to protect all corroding pipeline elements from rust. Thus, on chrome surfaces under conditions high humidity a rusty rash may appear. Its formation helps prevent unvitaminized and unsalted fish oil. If it's summer hot weather, and in winter the room is well heated, then the chrome surfaces are treated every 10-15 days. Wipe chrome parts swab soaked in fish oil, and after a while wipe them with a dry soft cloth. Before the next treatment, remove any remaining grease from the previous treatment with a soft rag moistened with gasoline. This simple measure allows you to protect chrome surfaces from rust for several years.
If rust has already formed on nickel-plated or chrome-plated surfaces (for example, on faucets), rub the rusty areas with a rag soaked in heated vinegar to remove it. You can also remove rust from nickel-plated parts using fat (animal or fish). Apply a layer of grease to the rusty stain and leave it for several days, after which remove the remaining grease with a soft rag moistened with ammonia.
The following composition will help free chrome coatings from rust: dissolve 200 g in 1 liter of water copper sulfate and 50 g concentrated of hydrochloric acid. Soak a cloth swab in the resulting mixture and rub it rust spots until completely removed. To neutralize acid, wash surfaces, then rinse clean water and wipe dry with a soft cloth.
Yellow “rusty” stains on the surfaces of bathtubs, sinks, sinks and shower trays can be removed with slightly salted, heated vinegar.