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Construction of a pipeline from polyethylene pipes

Most of all pipelines laid in cities date back to the Soviet era. The deterioration of heating mains, sewerage, gas and water communications reaches 70%, which is due to the material from which the pipes are made. This is a steel that is subjected to intense corrosive attack. The construction of gas pipelines from polyethylene pipes is becoming more popular today. As the service life expires, many accidents occur on various pipelines: pipes burst under high pressure, numerous leaks form, which lead to significant water losses. Performance indicators are deteriorating: due to a decrease in the cross-section of pipes, their throughput is reduced, water is polluted, and its biological indicators are reduced.

Advantages of polyethylene pipes

Pipes made of polyethylene (PE) are modern alternative to their obsolete physically and morally metal predecessors. They have a number of indisputable advantages in comparison with products made of steel or cast iron.

1. The absence of corrosion damage, which minimizes the cost of installation, maintenance and repair.
2. Ease of use: polyethylene products are easy to cut, so they can be easily adjusted to size as in construction site, and in the field when laying pipelines.
3. High throughput due to the fact that the inner walls of PE products are smooth.
4. Pipes made of polyethylene have an elastic structure of the inner walls, on which scale does not form as a result and they are not clogged from the inside with various suspensions contained in the liquid.
5. Polyethylene is chemically inert, successfully resists aggressive effects, therefore, it does not need additional special protection.
6. Polyethylene is not electrically conductive, so it is not afraid of stray currents that destroy metal pipes.
7. The bending radius of a polyethylene pipe can be up to 10 of its outer diameters, depending on temperature, which reduces the cost of connecting parts and facilitates the design and construction of pipelines.
8. Polyethylene pipe has high flexibility: the minimum bending radius is 25 pipe diameters at 200°C.
9. Significantly less weight compared to metal pipes, which facilitates installation and installation.
10. PE pipes are resistant to temperature changes and have high sanitary and hygienic characteristics.

Scheme of deformation of polyethylene pipes depending on the type of soil.

Important note. Freezing of the soil leads to the movement of pipelines in a vertical plane. These movements are uneven, resulting in deformations (bends). Prediction of these states should determine how much the bending radius of a polyethylene pipe depends on the level of temperature decrease. In order to determine the bending radius, it is necessary to make special calculations. Or refer to special tables, which indicate the minimum bending radius for a particular type of pipe.

The minimum bending radius of a polyethylene pipe is recommended by the manufacturer for each type and grade of pipes. If it is not possible to obtain the desired bending radius, then bends, tees, etc. should be used.

Thanks to its technological and performance characteristics polyethylene pipes received wide application: they are used in the construction of new pipelines and in the repair of old communications that have served their time.

Scope of polyethylene pipes

Polyethylene products are widely used in modern construction.

They are used in the construction of water pipes, sewerage, gas pipelines. PE pipes are used in pressure and gravity sewerage, serve as protective cases for electrical and telephone wires.

With the help of polyethylene pipes, the reconstruction of old networks is carried out. Replacement can be carried out with the destruction of worn-out communications, but it is possible to lay new ones in parallel with the old ones, which does not require stopping the water supply to the population and blocking the sewerage system. Reconstruction of wells and other communication and plumbing structures depends on the degree of their deterioration. Individual parts may be subject to partial replacement (necks, shut-off valves etc.), if necessary overhaul with a complete replacement of pipelines.

Installation of polyethylene pipes for sewerage

Sewer networks are internal and external. Their purpose is to collect and transport sanitary and storm sewage, which has a different chemical composition. Any sewer problems dramatically affect the quality of life.

Elements and assembly for polyethylene pipes internal sewerage

Polyethylene pipes for sewerage began to be produced not so long ago, and today they fully meet the high requirements due to their inertness to the effects of mineral acids, alkalis and other aggressive substances. PE sewer pipes have a large throughput due to the absence of internal roughness. When arranging external systems sewers use frost-resistant PE pipes. Installation of internal sewerage does not require pipes with such high performance characteristics.

Sewer pipes are attractive to specialists working on the arrangement of such systems in that their installation is much easier in comparison with traditional sewer networks. Installation of internal sewer communications using polyethylene pipes does not require complex special equipment. Small-diameter polyethylene pipes are mounted using compression fittings.

Equipment outdoor sewerage produced by butt welding: special welding equipment allows installation, reducing the number of joints up to five times in comparison with metal sewer pipes

Connection of water polyethylene pipes

PE products are connected in three main ways:

1. butt welding,
2. socket welding with embedded electric heaters
3. installation with compression fittings.

A detachable connection is also possible, which is carried out by steel clamping flanges. Installation of bends and branches of pipelines is carried out using welded or cast fittings.

Different connection methods are used depending on the working conditions. If there are conditions for the placement of welding equipment, then butt welding is necessary. Butt welding is used when working with pipes of large diameters (from 630 mm).

The limited working space (wells, chambers, trenches) requires electrofusion welding using embedded heaters.

If it is necessary to connect pipes with a diameter of up to 63 mm, compression fittings are used, which creates detachable structures. This connection is easy to use, has high performance, does not require complex special equipment. Compound internal systems pipelines are most often carried out in this way. Their installation is available even to non-professionals.

Laying pipelines

Laying polyethylene pipelines carried out in two main ways. These are the traditional laying of pipes in an open trench and trenchless laying - a method of deep directional drilling.

Polyethylene pipelines for open method fit into a trench, the width of which is determined by the need to create conditions for work. Water supply and sewerage equipment requires a trench width of 40 cm more than the outer diameter of the pipeline. These parameters are most often specified in the project. Long-length polyethylene pipes are often laid in a trench dug with a narrow-reach chain excavator. In this case, the width of the trench decreases.

The trench must be properly prepared. Its arrangement depends on the condition of the soil. If the bottom of the trench is hard and dense, then a pillow device is necessary. The bottom is covered with a layer (about 10-15 cm) of sand or other granular material and leveled. At a distance of 2 meters from the manhole, the pillow is rammed. There should be no stones, lumps at the bottom frozen ground. When working with loose soil, which has a risk of displacement, it is necessary to strengthen the bottom. In such cases, the bottom of the trench is reinforced with geotextiles.

With a flat trench bottom with optimal performance soil cushion is not needed. You can get by with a small excavation of the earth at the base of the pipe to its width and replace it with a softer one.

Trench backfilling

The soil excavated during the trenching, in which there are no stones of 20 mm in size, is used for the initial backfill. It is made for the entire length of the pipe, about 15 cm high from its top. If it is necessary to compact the backfill, the soil must meet certain requirements. Fine gravel (20-20 mm) or crushed stone (4-44 mm) can be used. Soil must not be dumped directly onto the pipeline. Laid to the bottom of the trench and sprinkled pipeline needs to be sealed. The backfilled soil is compacted in layers of 20 cm on both sides of the pipe so that it does not move. The soil is not compacted directly above the pipe.

Backfilling is carried out after compaction and obtaining a compacted layer of about 30 cm on top of the pipe. Backfilling of the trench can be done with excavated soil, the size of the largest stones is allowed no more than 300 mm. Even if there is a layer of protective backfilling with a thickness of about 30 cm, the size of the stones in the soil, which is used for backfilling, cannot be more than 60 mm.

Trenchless pipeline laying

In some cases, when pipeline lines intersect with a railway, a busy highway, a river, and other obstacles, laying an open trench is not possible. The reason may also be the need to minimize the cost of digging a trench. This is the basis for applying the method of trenchless laying of polyethylene pipelines. The method of trenchless laying of horizontally directional drilling (HDD method) has become widespread.

Horizontal drilling is in a special way communication devices without opening the ground. Work begins at the point where the pipe is brought to the surface. Technology guarantees high precision the output of the drill in the proposed place of exit to the surface. The method allows laying underground pipes with a length of more than 100 m and a diameter of up to 630 mm or more. There are two main ways horizontal drilling: managed and unmanaged.

Controlled horizontal drilling is carried out by tunneling machines, through flushing and pilot drilling.

Unguided horizontal drilling is carried out by two methods: 1) without casing (ramming, displacement drilling, auger drilling) and 2) with casing pipes(drilling injection, puncture drilling, impact drilling, ram drilling).

Horizontal drilling methods and trenchless laying of polyethylene pipes are considered the most modern technology. To expand the well, a special drilling extension is used. To improve the wiring, the well is treated with drilling mud, which forms and lubricates the channel itself.

Thus, the characteristics of polyethylene products make it possible to carry out their installation and laying using any currently known method, taking into account the limitations imposed by the minimum allowable radius of their bending.

A pulled or pushed polyethylene pipe is able to repeat the configuration of the old route, which has a radius of curvature of more than 120 diameters of the pipe itself. Metal products practically do not have such a bending radius.

Organization of installation work

Welding is carried out either according to the basic scheme, or by the route method. The basic method is used in cases where the object is located near the welding site, where the pipes are pre-connected, and then they are brought to the pipeline route in finished sections. The length of the section can reach more than 30 m. On site, they are welded into a single thread, which then carefully, so as not to violate the bending radius, must be laid in a trench.

Route welding starts along the trench. Then the installation and welding is carried out by mobile welding units. Pipes of small diameter can be laid manually in the trench. However, pipelayers or cranes are most often used. The finished thread should be lowered without jerks, evenly, having previously secured it with hemp ropes or soft slings, which should be located at a distance of 5-10 meters from each other. The solid welded string must be lowered into the trench carefully so that the critical bending radius is not exceeded during the laying process. Beforehand, you should wait at least 2 hours after welding the last link.

Disadvantages of polyethylene pipes

Problems with polyethylene products are associated with the characteristics of all viscoelastic thermoplastics. Their strength largely depends on the degree of bending and compression, and in general it is relatively small. Polyethylene is sensitive to ultraviolet light, which has to be compensated for with coloring additives (usually soot) and the use of a protective color. The thermal expansion of polyethylene is quite high and it has to be compensated with the help of a constructive L- or U-shaped bend of the pipe.

Today, domestic underground pipelines have a length of about 2 million km. Basically, these are steel pipelines. The share of polyethylene pipes accounts for, for example, about 10% of the entire length of gas pipelines. Other networks also have not very high performance for this parameter. However, there is a strong trend towards the fact that modern pipelines are changing in percentage terms in favor of polyethylene pipes.

In this article we will tell you how to install polyethylene pipes with your own hands. This will save several times when laying most communications. Exist different kinds the products mentioned, as well as how to install them. This article will cover all these aspects.

Application area

Polyethylene is widely used in the production of various products. It is a polymer that has a number of very useful properties. For example, it is immune to the action of most acids, gasoline, various oils and other solvents. This means that when in aggressive environment the service life of such material can be very long. In industry, this raw material is used in the manufacture of packaging for various food products. The material does not have a detrimental effect on the human body, although it is a product of the oil industry.

In addition to all of the above, this polymer can be easily processed. In order to make a planned product from it, no special unique conditions of temperature or pressure are required. Pipes are easily obtained from it, which are used for various purposes:

• gas pipelines;
• pipelines for transportation of chemically aggressive substances in industry;
• irrigation systems;
• for transportation of liquids containing abrasive inclusions;
• systems designed to lower the water level.

This widespread use is due to the ease of installation and the high flexibility of the final product.

Types of polyethylene pipes

All polyethylene pipes are divided according to the pressure they can withstand. There are three main types:

• PVD. Such products withstand high pressure. They are used on high-pressure highways and sections. Their diameter can exceed 1 m. They are relevant for the organization of water supply to microdistricts or even cities.
• HDPE. The most common and most common type. Plastic pipes low pressure are used for plumbing, in which case they most often have a blue stripe along their entire length, or they can be completely painted blue. For laying gas lines, material with a yellow stripe is used.
• The third type is made from recycled materials. Typically, such pipes are used for laying various communication lines. Products serve as sleeves that prevent harmful effects on the cable.

The advantages of such products are:

• resistance to corrosion;
• high flexibility and plasticity during installation;
• ease of connection;
• high mechanical strength;
• the impossibility of the formation of growths and blockages due to the smoothness of the walls;
• resistance to water hammer (short-term excess of the permissible pressure by several times is allowed);
• good dielectric;
• the possibility of installation in a limited space;
• the value of hydrolosses is lower than that of other materials;
• higher density than steel - 8 times;
• welded seams are stronger than the strength of the pipes themselves;
• relatively small weight;
• 50 years of service without the need for maintenance.

Note! Polyethylene is not suitable for organizing hot water and heating systems. This is due to the fact that some of its types lose their strength already at 60 °, and at 100 ° they begin to melt and spread.

Mounting methods

Even a novice can handle the installation, provided they have the necessary tools and basic knowledge. All types of pipe joints of this type are divided into two main categories:

• Detachable. Special fittings have been developed for them. The assembly of the entire structure is possible with the presence of elementary tools that any owner possesses.
• Monolithic. In this case, there are two options that can be applied. One of them involves gluing with a special composition that does not adversely affect the body. The second is soldering. She has her subspecies. It is carried out using a special apparatus that heats the ends, after which docking occurs. Special couplings have also been developed in which spirals are built in (they are also called elements with a mortgage heater) that carry out welding.

Practical guide

The first connection method, discussed above, is often used at home. The tool that will be needed when assembling the entire structure:

• pipe scissors or hacksaw;
• special key with chain;
• fitting;
• roulette.

Note! Often the chain wrench is replaced with a conventional gas wrench or simply tightened by hand. To ensure the highest reliability, it is better to use products designed for this purpose.

The whole installation process will be as follows:

• All pipe is produced in bays, so it will need to be conveniently placed to simplify the task. The required length is measured and cut off from the bay with a hacksaw or scissors.
• The edge that will go into the fitting is well aligned. This must be done so that subsequently there is no skew, and so that the grip is uniform.
• The chamfer is removed under the cone, this will make it easier to pass the sealing gum.
• The coupling is unscrewed from the fitting.
• The sealing ring is removed.
• First, the coupling, and then the sealing ring, is put on the pipe.
• The ring must be turned so that its conical part abuts against the coupling, and the flange against the fitting.
• The pipe is wetted with water or soapy water. This will make it easier to fix it.
• The fitting is put on the pipe until it stops. In this case, you need to make sure that the sealing gum that is in it does not wrap inside the hole. If this happens, then you need to remove the fitting and repeat everything from the very beginning.
• Before filling the pipe with earth, it is advisable to check it by applying working pressure.

Review compression fitting for PE pipes see below:

Note! To switch from metal pipe fittings with metal threads are perfect for polyethylene. This will be the key to a high-quality connection that will not fail during a pressure surge.

Butt joint is somewhat more complicated and requires specialized tool. The main one is the welding machine. It consists of the following blocks:

• Centralizer. A special fixing clip that allows you to position two parts clearly opposite each other. Also, with the help of this element, fixation and clamping are carried out in order to form quality seam.
• Trimmer. small tool with electric motor, which has two cutting heads. Its purpose is to process the edges so that they have a flat plane.
• Hydraulic block. Designed to carry out the movement of two parts of the centralizer. It has a pressure gauge, which makes it possible to select the required value in bars.
• Heater. This is a kind of soldering iron that melts the edge for subsequent joining.

If you plan to do the installation professionally, then it makes sense to purchase such a device, otherwise it is enough just to rent it. The sequence of actions will be as follows:

• One of the parts to be welded must be movable. If this condition is not met, then the centralizer will not fulfill its role.
• Using a caliper, the ovality of the pipe is checked. The diameter must be the same at any point where the gauge is applied.
• The compliance of the actual wall thickness with the declared one is checked. It must be the same for both elements. If they are unequal, then the soldering will not reach the required strength.
• The elements are installed in the centralizer. Between them, it is necessary to maintain such a distance that in the open position it is possible to safely install the trimmer and the heating element.
• The clamp is carried out in pairs. The rear latches can be tightened slightly more than the front ones. It is better not to overdo it with the latter, so as not to violate the correctness of the butt circle.
• Movement pressure is set. In order to do this, you must first unscrew the valve to bleed the air. Further, twisting it, the value at which the movement begins is determined.
• The compression pressure on the solder is calculated. This is done according to the table, which is usually located on the unit. If it is not there, then you can use the following formula: divide the area of ​​\u200b\u200bthe end of the pipe by total area section of the cylinders, multiply the result by 0.15 and add the resistance pressure.
• The parts to be welded are cleaned of sand and other dirt with a damp cloth.
• Edge processing is in progress. To do this, a trimmer is installed close to one pipe. It turns on and with the help of a hydraulic unit, two workpieces are shifted. The process continues until 3-4 turns of solid chips are formed on each side.
• The pressure is released and the parts move apart.
• The cutting tool retracts into place.
• A test docking is being done to make sure the process went as it should.
• Ends are cleaned again. But this time it is necessary to use alcohol or a special solvent.
• The soldering iron turns on and heats up to the required temperature.
• The time of the planned soldering is set on the timer. It is usually also indicated in the table.
• The sting is installed between the pipes.
• The pipes are brought to the soldering iron. It is necessary to wait until an influx of 1 mm thick forms. After that, the pressure is released and the time for welding is recorded.
• After the welding time has elapsed, the soldering iron is removed. There will be 5 seconds to bring the details together.
• After docking, you will need to wait about 5 seconds more under pressure, after which it is reset and a timer is started to cool down.

The cooling process should not be accelerated in any way. Also, during this time, you should not tilt the pipe or try to remove the centralizer. Otherwise, the joint will be broken, and depressurization will subsequently occur.

The video shows the process of butt welding in detail:

Electrofusion welding is an achievement that allows you to join seams in places where other methods are simply not applicable. The advantages of this solution are:

• high speed of ongoing processes;
• minimum probability of errors;
• high safety of the whole process;
• the possibility of articulation of fixed workpieces;
• the inner diameter of the pipes remains practically unchanged;
• simplifies the process when performing tasks with large pipe diameters;
• the advantage of working with workpieces of various diameters and wall thicknesses;
• minimum consumption of electrical energy when performing tasks.

Of the tools you will need:

• Special cleaning fluid. It can come in a kit with fittings or be purchased separately. The use of acetone or other solvents not intended for these purposes is not recommended.
• Oxide remover. An ordinary scraper or an apparatus that is installed directly on the pipe can act as its role. On the large diameters using the second one is preferable. The fact is that it is necessary not only to create a rough surface, but to remove about 0.1 mm of material so that soldering can occur.
• Welding machine. In this case, a special development is used. Its task is to apply a specific voltage to the clutch for a certain period of time. It is assembled on semiconductors, which explains its economy and high performance. On the front panel, as a rule, there is a digital display, which makes it possible to check the correctness of the entered data. The design provides a port for connecting a scanner, it is necessary to automatically enter the required parameters through a barcode that is printed on the fitting. Information about the work done is stored in the internal memory and can later be transferred to a USB flash drive if there is a USB port.
• Retainer or positioner. For this type of connection, it has a slightly different structure than in the previous case. Its main purpose is to compensate for ovality that may be present due to pipe storage in a coil or under load.
• Pipe cutter. In order for the edges to be flat and without jagged, it is desirable to use this particular tool. A hacksaw and a knife will be poor helpers in this case.
• Permanent marker. It should be white or yellow so that the marks made are clearly visible on the pipe.
• Roulette.

To achieve the ideal result, you will need to follow the following steps:

• Ends are being prepared. To do this, they are cut with a pipe cutter.
• Using a tape measure, the total length of the coupling is measured.
• A label is applied to each pipe. It should be from the edge at a distance of half the size of the fitting plus 2 cm of margin.
• Filmed upper layer in which the reaction with oxygen has taken place. In order to make it easier to maintain uniformity, it is necessary to apply several longitudinal lines from the mark to the end. As the tool progresses, it will be seen which part is not covered enough.
• The end will be chamfered under the cone to facilitate the entry of the pipe into the fitting.
• A positioner is installed on each of the pipes. It is clamped until the nozzle is perfectly round.
• Both the pipe itself and the inner walls of the fitting are treated with a degreasing composition.
• The coupling is put on the pipe up to half the depth of its size. Usually there is a limiter inside that will not let you go further.
• A second pipe is brought in and inserted.
• The evenness of the entire plane is checked.
• The terminals from the welding machine are connected to special connectors.
• The barcode is read using a scanner.
• The whole process is started. It is important to wait not only for the welding time, but also for the total cooling time, which is also shown on the display. During this period, do not touch or try to change the configuration of the equipment. This may result in a poor quality joint.
• At the end of the procedure, data on the operator, time, temperature and date are applied to the joint.

There are basic mistakes that are very important to avoid. For example, it is necessary that the pipe and fitting are not at an angle. This will cause the molten mass to simply flow out. If the ovality is not compensated, then the coupling will simply be impossible to put on, or a monolithic adhesion will not form. If the pipe is not immersed enough, the spiral will simply melt the material inside, but the articulation will not occur.

Installation of XLPE pipes

This type of pipe is rather an exception to the rule. It withstands temperatures up to 120° and can be safely used for heating and hot water systems. Such material is produced by ion bombardment, which leads to the formation of a unique structural lattice. It is she who is the key to strength. Interestingly, when exposed to temperatures above 400°C, the material decomposes into carbon dioxide and water. Others interesting characteristics are:

• Resistance to low temperatures. The pipe feels good even at -50°. In this case, the physical impact does not have a detrimental effect.
• High elasticity. The pipe can be bent in half without breaking.
• Resistant to cracking during operation.
• High smoothness of the inner surface. This allows you to reduce noise during the circulation of water.
• The product shrinks. When exposed enough high pressure the material tends to expand and after a while take its original shape.
• Abrasion resistance. This means that the pipe can be walled up in a screed and not worry that something will happen to it.

Installation can be carried out using two types of fittings:

• Threaded. In this case, it is not required special tool, and the overall process resembles the installation of metal-plastic pipes.
• Crimping. For this option, you will need a special expander and a special hand vise.

The process for the first option boils down to the following steps:

• Using scissors, the pipe of the required size is cut.
• The nut is unscrewed from the fitting and the sealing ring is removed.
• A nut is first put on the pipe and then an o-ring.
• The part of the pipe that will be put on the fitting is flared.
• The sealing ring is moved as close as possible to the fitting.
• With the help of one wrench the connector is held, the nut is tightened second. It advances the seal to the designated position and presses the pipe walls even more.

With the crimping method, everything happens as follows:

• A ring is put on the pipe. It moves from the edge by the distance that it will go inner part fitting.
• A head of the required diameter is installed on the expander. It is inserted into the pipe and the handles are compressed. Then they quickly open up, the tool turns a little, sinks a little deeper and again the handles come together. Such actions are carried out until the butt rests against the limiter.
• The fitting is inserted.
• Using a hand vise, the ring is pressed onto upper part connections.

Note! There is one more progressive method. Instead of a metal ring, a special polymer is used. It is put on the pipe so that part of it protrudes by 1 mm. Further, the pipe expands with it. When the fitting is inserted, an automatic seating occurs. Within an hour, the stiffness of the joint reaches such a level that it can withstand a pressure of 15 atmospheres.

Perhaps you also had experience when a water supply system was installed from polyethylene pipes or other communications. Share your best practices and tricks acquired in the process. Leave comments on the article.