We study the features of pre-insulated pipes. Basic principles for the design of pre-insulated pipelines

DI. Dashkevich, engineer for thermal automation and operational systems remote control, RUE "Vitebskenergo", Vitebsk, Republic of Belarus

Introduction

Problems of operation and repair insulated pipes pipelines, a group of specialists from the Vitebsk Heat Networks branch of RUE Vitebskenergo began to work on the simplest thing - monitoring the condition of the thermal insulation layer (TIS) of pre-insulated pipes. The approach to monitoring was carried out comprehensively; monitoring of the condition of TIS was organized at all stages of pipeline construction:

■ 100% input control pre-insulated pipes and fittings with the rejection of products that have deviations from existing standards and norms of insulation resistance according to the manufacturer’s instructions;

■ monitoring the condition of the heat-insulating layer during the laying of heating mains from pre-insulated pipes with mandatory 100% control of the tightness of butt joints after shrinkage of heat-shrinkable couplings;

■ checking the condition of the thermal insulation layer of a pre-insulated pipeline before commissioning and during operation.

This approach allowed us to achieve certain results after just one year of monitoring:

■ the receipt of defective pre-insulated products into the enterprise warehouse was excluded;

■ the condition of the thermal insulation layer of previously constructed pipelines was analyzed.

Reasons for reducing the resistance of the thermal insulation layer

The analysis showed that the vast majority insulated pipelines, built earlier, require repairs, because operational remote control systems (ODC) determined a decrease in the resistance of the insulating layer below the established norm. Determining the reasons for this decrease began with checking the condition of the input cables at the intermediate and end elements. It was determined that in more than 50% of cases the reason for the decrease in insulation resistance is the installation of couplings to extend the input cable in violation of the installation technology or the use low-quality materials for these purposes. In particular, the application open flame for shrinkage of the couplings, which led to burnout of the coupling, the insulating layer of the signal wires, and, ultimately, during periodic checks with a voltage of 500 V - to an electrical breakdown at the junction. Currently, it has been repeatedly verified that to shrink cable joints it is necessary to use an electric hair dryer on which to install operating temperature no more than 240 °C, and also use cable couplings appropriate diameter for NYM 3x1.5 and NYM 5x1.5 cables. In addition, dismountable cable glands on end and intermediate elements, which are manufactured at almost all enterprises of the Republic of Belarus that produce pre-insulated pipes, were questionable. Operating experience has shown that the most reliable cable entries are those when the cable is welded into the shell pipe, which ensures complete tightness at the point where the cable enters the pre-insulated pipe.

In the remaining 50% of cases, the reason for the decrease in insulation resistance was the lack of end elements, damage to the metal plugs of the insulation of the end elements by corrosion and moistening of the heat-insulating layer at the butt joints due to poor-quality installation of heat-shrinkable couplings.

The main reason for the penetration of moisture into the internal space of the metal insulation plugs was the absence of a sealing adhesive composition at the point of contact between the plug and the shell pipe, and the absence of polyurethane foam insulation in the cavity formed when installing the plug between its cover and the shell pipe.

In the first case, the manufacturers tried to ensure the tightness of the structure with one layer of heat-shrinkable tape, which, as practice has shown, does not provide any tightness, but only prevents the entry of dirt and sand, while water penetrates freely into the space between the shell pipe and the metal plug.

In the second case, moisture did not get inside the shell, but the lack of polyurethane foam insulation in the above cavity contributed to the formation of condensation due to the temperature difference between steel pipe and from the outside of the shell pipe, and as a result, moisture accumulated in the cavity, and a decrease in the insulation resistance of the pre-insulated pipeline as a whole.

Manufacturers have been repeatedly asked to:

■ the cover of the metal insulation plug should be made of metal with a thickness no less than the wall thickness of the steel pipe for which the end element is made;

■ make the cylindrical part of the plug from a sheet of steel no less than 3 mm thick;

■ seal the place where the plug comes into contact with the shell pipe with an adhesive compound and install a full-fledged heat-shrinkable sleeve at the same place with a lining under its edges of an adhesive compound with high adhesion to the shell pipe and metal and final strengthening of the edges of the heat-shrinkable coupling with heat-shrinkable tape, with the obligatory coating of the unprotected surface of the plug with an anti-corrosion coating.

Unfortunately, these proposals went unnoticed by the manufacturers. Moreover, one of the factories in the Republic of Belarus began to produce metal plugs from galvanized iron with a thickness of less than 1 mm. The question arises: how long will such an end element lie in the ground during channelless installation?

Solving problems of the UEC system

The issue of protecting pre-insulated pipelines, on which end elements were not initially installed, was resolved by installing split metal insulation plugs with the installation of cable entries on them, if necessary. Moreover, the installation of such plugs was carried out without shutting down the heating network. Repair work of UEC systems, if appropriate technical conditions were available, was carried out without excavation, because access to cables of the ODK system with end elements is mainly located in basements and thermal chambers.

The next stage in organizing repairs of pre-insulated pipelines with an insulation resistance below the established standard was the problem of finding places to moisten the PU foam insulation at the butt joints.

Work in this direction began with studying the principle of measurement with a Reis-105R pulse reflectometer, and then continued with the recording of reflectograms with this device on heating mains that were put into operation, and in parallel on heating mains that were just beginning to be laid. It quickly became obvious that with the same physical length of a pre-insulated pipe, the electrical length of the pipe, or rather the signal conductor, could be different, and the electrical length could be different for both the signal conductor and the transit one on a straight section of the pre-insulated pipe. This meant only one thing - the conductors in the thermal insulation do not run exactly at the same distance from the steel pipe.

This assumption was confirmed practically during the installation of the pipeline. When cutting pipes into pieces, there have been cases and occur during each repair season when signal conductors are located in the polyurethane foam insulation in an arbitrary place (almost coming together), i.e. their location does not comply with the manufacturers' instructions: they should be located at a distance of 20-25 mm from the steel pipe and be oriented at 3 and 9 o'clock or at 2 and 10 o'clock.

They learned to compensate for such geometric deviations of signal conductors using reflectometer settings by adjusting the so-called shortening coefficient so that the physical length of the pipe corresponds to the electrical one. But the problems didn't end there. If the problems were resolved when taking reflectograms from the pipe, then after connecting the input cable the question arose at what shortening factor to take the reflectogram, because The cable shortening coefficient is very different from the pipe coefficient. Today, regulatory documents describe the method of taking reflectograms when using NYM 3x1.5 and NYM 5x1.5 cables in the UEC system, but there is no description of what the reflectogram should look like before connecting the cable, after connecting the cable, within what limits the signal shortening coefficient should be conductors on pre-insulated pipe and NYM 3x1.5 and NYM 5x1.5 cables. Experience in the operation and repair of pipelines at the Vitebsk Heating Networks branch has shown that the shortening coefficient of a pre-insulated pipe and the cable shortening coefficient must be standardized either by the current one or by some other regulatory document.

This message is due for the following reasons:

■ during the input control of the UEC system, only the insulation resistance of the signal conductors and their integrity are checked;

■ during commissioning, there are cases when a contractor, in order to hand over to the customer a heating main with a low resistance of polyurethane foam insulation, goes to all sorts of tricks (soldering the resistance of the established or higher standard into the chain of signal conductors or laying a cable on top of the shell pipe to ensure upon delivery required value of polyurethane foam insulation resistance).

Practice has proven that it is possible to exclude the supply of pre-insulated pipes with internal defects at the incoming inspection stage, if at the same time the normalized shortening coefficient of each pipe is checked. Technically this is possible. The length of the supplied pipes ranges from 11.2 to 11.6 m, respectively, and the length of the signal conductors is within these limits. The technical characteristics of the Reis-105R (Reis-105M) indicate that the minimum value of the measured distances is 12.5 m, while the measurement error will be 0.8%, i.e. the physical length of the pipe will have to differ from the electrical length of the signal conductors ±0.09 m with a standardized shortening factor.

Technically, manufacturing plants can decide to ensure that the signal wires of the UEC system run in the annulus strictly parallel to the axis of the steel pipe in accordance with the requirements mentioned above. Depending on the manufacturing technology, this requires changing the design of centralizers and increasing their number by linear meter pipes to prevent sagging of the signal conductor during foaming of the interpipe space.

When accepting a heating network for operation, the standardized shortening coefficient will allow you to be absolutely confident in the integrity of the contractor’s specialists.

Repairing damage to pipelines put into operation

When taking reflectograms on pre-insulated pipelines that had already been put into operation, we also encountered other problems, when from one control point the reflectogram shows, for example, two moistening points, and in the opposite direction - three or one humidifying place, or the end of the signal wire is not visible at all. After taking more than 100 reflectograms and analyzing them, we came to the conclusion that there is also such a thing as the degree of moisture. The number of identified wet spots indicates that one of the places is the most wet and excavation to eliminate the defect must be done there first.

But the most big problems began when excavations began at suspected sites of pipeline damage. Many questions arose: how and how to perform reverse thermal and waterproofing of dismantled butt joints and where to get equipment for welding cut heat-shrinkable couplings?

Even the construction organizations that installed pre-insulated pipelines were not prepared for such a turn of events. There were no materials or equipment in the warehouses, because it was initially believed that pre-insulated pipes would not be repaired throughout the entire period of their operation. Then the question logically arises: why is the UEC system needed, to identify moisture spots and eliminate them in a timely manner, or just for statistics?

During the opening of the “damaged” butt joints, it was discovered that the moistening of the PU foam insulation, as already mentioned above, occurred due to leakage of the heat-shrinkable couplings, or more precisely due to the lack of adhesion to the heat-shrinkable coupling and the shell pipe of the adhesive tape, which is placed under the edges of the coupling as seal. Currently, specialists of the Vitebsk Heating Networks branch have come to the conclusion that it is permissible to use mastic couplings up to a shell pipe diameter of 315 mm inclusive, i.e. mastic heat-shrinkable couplings of small diameters, when using high-quality adhesive tape, can provide tightness for the entire period of operation of a pre-insulated pipeline. Starting from a diameter of 400 mm and above, it is necessary to use heat-shrinkable couplings with welded elements, but one more technical requirement must be met - it is necessary that the grade of the coupling material (low-density polyethylene (HDPE)) corresponds to the grade of HDPE of the shell pipe, then welding will be performed qualitatively.

The next problem was the circumstances when excavations are carried out in the supposed place where the heat-insulating layer is moistened, but no signs of moistening are found in this place. In such a situation, two solutions emerged. The first is to continue point excavations with a preliminary measurement of the insulation resistance at the place where the cable breaks in the direction of lower insulation resistance and, thus, localize the place of moisture. With this approach, it was necessary to carry out up to five spot excavations, which were not planned before the start of repair work. The second path logically followed by itself - in order to relatively accurately determine the location of moisture in the PU insulation, it is necessary to compare reflectograms taken after the drop in insulation resistance with reflectograms that were obtained before the drop in insulation resistance, but we did not have such information. The database had to be created on repaired heating mains, and on newly built ones, sample reflectograms had to be taken even before they were put into operation. Thus, another reason has been identified why it is necessary to normalize the shortening factor for pre-insulated pipes and output cables.

On the regulations for the removal of pipelines for repairs

The need to take exemplary reflectograms during the construction of pre-insulated pipelines revealed several more technical and organizational problems - this is the absence of the majority construction organizations necessary instruments due to their high price and the absence in the project estimates for the construction of a heating main of items on the preparation of as-built documentation and the taking of reflectograms, which in the Republic of Belarus must be carried out by the contractor in accordance with the provisions.

Employees of the Vitebsk Heat Networks branch tried to correct this omission by introducing the necessary items into the project estimates at the approval stage, but encountered opposition from Gosstroyekspertiza, which demanded that these items be deleted, citing the fact that this type of work relates to commissioning, and not to the editing room.

The lack of as-built documentation for UEC systems and standard reflectograms has also become relevant because heating mains, including pre-insulated pipelines, are currently being transferred from the balance of housing and communal services to the balance of power engineers. The question arises: how to accept pipelines in the absence of as-built documentation and reflectograms? In addition, there is another difficulty: what method should be used to repair them? The solution seems quite obvious: it is necessary to excavate the entire route along the canal, identify defects, eliminate them, draw up documentation, and take reflectograms. But where to get the money for this?

All of the above applies to a greater extent to preparatory activities, preceding the repair, which in turn is aimed at identifying and eliminating the causes of moisture in the PU foam insulation. Experience of the Vitebsk Heating Networks branch in the field of repair of pre-insulated pipelines (from 2007 to the present, more than 25 sections of pre-insulated pipelines have been repaired various diameters) shows that replacement of such pipes with new ones was required only in two cases, when corrosion at the butt joints reached critical values. But we must take into account that these areas were in close proximity to the tram tracks. In other areas, despite the fact that the butt joints that began to leak various reasons, were in a humid environment for a long time (5-8 years), no traces of progressive corrosion were found. The insulation resistance here fluctuated throughout the year from 20 to 800 kOhm, which is below the established norm. According to the indications, these areas required repairs.

At the same time, a number of questions arise. Was it necessary to make repairs in these areas? What needs to be dealt with - corrosion or heat losses that occur at wet butt joints? When and at what values ​​of insulation resistance is it necessary to take prompt action and, accordingly, under what conditions should claims be made to contractors if the heating main is under warranty? Thus, in the Republic of Belarus there is a need to create some kind of regulatory document that would regulate the actions of maintenance personnel in removing pre-insulated pipelines for repairs. RUE “Vitebskenergo” has currently prepared a manual “On carrying out repair work to eliminate moisture in polyurethane foam insulation and damage to the polyethylene shell of pre-insulated pipes and fittings.” But a number of questions still remain open. In particular, what should a contractor who installed a pre-insulated pipeline and delivered it with good insulation resistance readings do, if a few months after commissioning the readings fell below the normalized ones, but were in the range from 100 to 900 kOhm (using Reis-105 and Reis-205, with such values ​​of insulation resistance, it is impossible to determine the location of moisture): wait until the insulation resistance drops, and if it does not drop, should such readings be considered grounds for suspension? warranty period until the readings are restored to the normalized value by the contractor? These and other questions arise only because in more than 50% of newly built heating mains, the insulation resistance over time becomes below the established norm.

conclusions

In order to ensure that after the construction of pre-insulated heating mains there is no need to take them out for repairs, in our opinion, it is necessary to approach technological process complex pipeline laying.

1. It is necessary to organize the strictest incoming inspection of pre-insulated pipes and fittings. In this case, pay special attention to:

■ absence of peeling of polyurethane foam insulation from the steel pipe and from the shell pipe;

■ compliance of the insulation resistance of pipes and fittings with the standard, integrity of the loop in each product;

■ product compliance geometric dimensions provided by the project specification;

■ lack of ovality on the steel pipe and shell pipe.

2. During the installation of a pre-insulated pipeline, it is necessary to organize strict technical supervision, paying special attention to:

■ tightness of the interpipe space at the butt joints after shrinking the heat-shrinkable coupling (its welding, if welded elements are used) by creating overpressure 0.03 MPa and washed the edges of the coupling to control and identify the location of air leakage from the interpipe space. The tightness test using this method should be carried out with all butt joints, without exception, in the presence of a representative of the customer’s technical supervision;

■ correct backfilling, creating a sand cushion for pre-insulated pipes or laying pipes in the channel on sandbags with a step of no more than 2 m between bags to avoid sagging;

■ correct backfilling after pipeline installation;

■ preventing channel flooding during pipeline installation before thermal and waterproofing of butt joints.

3. After installation is completed, receive from the contractor executive documentation to the extent specified in regulatory documents, and with information content, agreed with the customer, as well as sample reflectograms in graphic and electronic form.

4. After the heating network is put into operation, carry out continuous monitoring of the condition of the thermal insulation layer at least twice a month.

In conclusion, here are a few wishes aimed at eliminating these shortcomings.

First of all, it is necessary to establish factory production of sealed cable terminals on end and intermediate elements (two factories (one in the Russian Federation, one in the Republic of Belarus) already produce such products - author's note), as well as reliable metal plugs for the insulation of the structure, which described above. The jacket pipe and heat-shrinkable couplings must be made from weld-compatible low-density polyethylene. In addition, in the manufacture of pre-insulated pipelines and fittings, it is necessary to eliminate the prerequisites for the peeling of polyurethane foam insulation from the steel pipe and shell pipe, which may occur during transportation, installation and operation, for which, during production, it is advisable to carry out coronal treatment of the inner surface of the shell pipe before foaming and producing machining the outer surface of the steel pipe by shot blasting machine. It is also necessary to resolve the issue of normalizing the shortening coefficient for a pre-insulated pipe.

Literature

1. STB 1295-2001 “Steel pipes pre-thermo-insulated with polyurethane foam. Technical conditions".

2. TKP 45-4.02-89-2007 “Ductless heating networks made of steel pipes, pre-thermo-insulated with polyurethane foam in a polyethylene shell.”

Pre-insulated pipelines for district heating systems

Ph.D. V.E. Bukhin, senior researcher,

NPO "Stroypolymer"

Russia is a country with a high level of centralized heat supply (up to 80%). The country is penetrated by about 280 thousand km of heating networks (in two-pipe calculation) with pipe diameters from 57 to 1400 mm, a tenth of which are main lines, the rest are distribution heating networks.

The predominant method of laying heating networks in Russian Federation is laying in non-passable channels with mineral wool thermal insulation (80%). Channelless installation, carried out from factory-made structures using reinforced foam concrete insulation and bitumen-containing masses (bitumen-perlite, bitumen-overmiculite, bitumen-ceramsite), accounts for 10% of the total length of heating networks.

Due to the moistening of the materials used during operation, the heat-protective properties of thermal insulation structures are sharply reduced, which leads to heat losses that are 2-3 times higher than the standard ones.

Total heat losses in district heating systems amount to about 20% of the supplied heat (78 million tons standard fuel per year), which is 2 times higher than that of advanced countries in Western Europe.

District heating systems in the Russian Federation currently provide heat consumption of 2171 million Gcal per year, which approximately corresponds to the annual heat consumption of all Western European countries and is almost 10 times higher than the heat consumption provided by district heating systems in these countries. Being a pioneer in the field of centralized heating and possessing the world's largest system of heating networks, Russia is significantly behind advanced foreign countries in the technical level - in use modern materials and technologies for laying heat pipelines.

About 90% of fuel savings achieved through combined heat generation methods are “lost” in heating networks. The durability of heating networks is 1.5-2 times lower than abroad and does not exceed 12-15 years. The situation in the hot water supply system is no better.

The volume of planned repairs and reconstruction of heating networks in the Russian Federation currently amounts to 10-15% of the total demand, but due to economic problems, no more than 4-6% is actually carried out.

Most effective solution problems posed above is the widespread introduction into practice of construction of thermal networks of pipelines with foam polyurethane thermal insulation"pipe in pipe" type.

This idea is not new. The newspaper "Evening Moscow" dated December 10, 1963 reported that the Mosinzhproekt Institute had conducted experimental work by use polyethylene pipes and foamed polymer materials for insulation of underground heating networks. However, in those years this direction was not widespread.

Taking into account the expanding use in Russia of pre-insulated pipes in district heating systems and the great interest shown in this problem by specialists in design, construction and operating organizations, this article discusses the main provisions of the new technology.

Applicable thermal insulation materials must have high thermal insulation properties(the thermal conductivity coefficient of the material should not exceed 0.06 W/(m°C)) durability (resistance to water, chemical and biological aggression), frost resistance, mechanical strength and environmental safety, i.e. be safe for the life and health of people and the environment. Polyurethane foam most fully meets these requirements.

Polyurethane foam thermal insulation is usually applied to pipes at the factory, and the joints are thermally insulated at the construction site, after welding and testing of the pipeline. A diagram of a pipe with thermal insulation made of polyurethane foam and a protective shell made of polyethylene pipe is shown in Fig. 1.

For example, in Western Europe, such designs have been successfully used since the mid-60s and are standardized by the European standard EN 253:1994, as well as EN 448, EN 488 and EN 489. They provide the following advantages over existing designs:

• · increased durability (pipeline service life) by 2-3 times;
• · reduction of heat losses by 2-3 times;
• · reduction operating costs 9 times (specific damage rate decreases 10 times);
• · reduction of capital costs in construction by 1.3 times;
• · availability of a system for operational remote monitoring of thermal insulation moisture.

Pre-insulated pipes have been successfully used for construction:

• · heating networks;
• · hot water supply systems;
• · process pipelines;
• · oil pipelines.

The pipes themselves are made of various materials depending on operating conditions. Currently, steel pipes are most widely used for the construction of heating mains, the main physical and chemical indicators of which are given in Table 1.

Table 1. Basic physical and mechanical parameters of steel pipelines

For the manufacture of insulated pipes, steel pipes with outer diameters of 57 - 1020 mm, length up to 12 m are used, corresponding to GOST 550, GOST 8731, GOST 8733, GOST 10705, GOST 20295, current requirements regulatory documents on heating networks and "Rules for design and safe operation steam pipelines and hot water".

Steel bends, tees, transitions and other parts must comply with the requirements of GOST 17375, GOST 17376 and GOST 17378.

To avoid pipe corrosion, it is necessary to use treated water. Water treatment depends on local conditions, but it is recommended that the following requirements:

• · pH=9.5-10;
• · lack of free oxygen;
• · total salt content not more than 3000 mg/l.

The standard length of pipes is 6.0-12.0 m, but the technology makes it possible to apply thermal insulation to pipes of any length and made from other materials (see, for example, the magazine "Pipelines and Ecology" 1997, No. 1, p. 5 about polypropylene pipes PPR with thermal insulation for hot water supply).

In Russia, pre-insulated steel pipes with thermal insulation made of polyurethane foam and a polyethylene waterproofing shell have been used since 1993. Their production is organized at several enterprises (JSC MosFlowline, Moscow; JSC TVEL Corporation, St. Petersburg; JSC NPO Stroypolymer, JSC Moscow; CJSC "Teploizolstroy", Mytishchi; 000 Plant of thermally insulated pipes "Alexandra", Nizhny Novgorod; CJSC "Sibpromkomplekt", Tyumen, etc.), united in the Association of Manufacturers and Consumers of Pipelines with Industrial Polymer Insulation.

Technical requirements to insulated pipes and pipeline parts are normalized in GOST 30732-2001 “Steel pipes and fittings with thermal insulation made of polyurethane foam in a polyethylene shell”, put into effect on July 1, 2001 by Decree of the State Construction Committee of Russia dated March 12, 2001 No. 19.

The standard for steel pipes and fittings with thermal insulation made of polyurethane foam in a polyethylene shell is compiled taking into account the following European standards developed by the European Committee for Standardization (CEN):

EN 253-1994. Welded pipelines, pre-insulated for underground hot water supply systems - A pipeline system consisting of a steel main pipeline with polyurethane thermal insulation and an outer sheath of polyethylene;

EN 448-1994. Welded pipelines, pre-insulated for underground hot water supply systems - Prefabricated fittings made of steel distribution pipes with polyurethane thermal insulation and an outer sheath of polyethylene.

In the new standard, which united technical specifications Russian manufacturers, the values ​​of indicators relating to apparent density, compressive strength at 10% deformation, thermal conductivity, water absorption, volume fraction of closed pores correspond to those specified in European standards. In addition, the requirements for polyurethane foam in terms of safety and environmental protection requirements also comply with the requirements of European standards: hazard class, explosive production category, flammability group of polyurethane foam, requirements for the disposal of waste generated during the production of pipes, their removal and disposal.

The standard applies to steel pipes and shaped products with thermal insulation made of polyurethane foam in a polyethylene shell (hereinafter referred to as insulated pipes and products) intended for underground ductless installation of heating networks with design coolant parameters: operating pressure up to 1.6 MPa and temperature up to 130 °C (a short-term increase in temperature up to 150 °C is allowed).

In order to ensure maximum efficiency (insulation cost/heat loss), a certain thickness of polyurethane foam thermal insulation is established for different climatic zones. Therefore, pipes and fittings can be of two types in terms of insulation thickness: type 1 - standard, type 2 - reinforced. The dimensions of insulated pipes are shown in table. 2, design - in Fig. 1.

Table 2. Dimensions of thermally insulated pipes, mm.

Protective covers usually made in the form of thin-walled pipes (shells) made of polyethylene high density. They are intended for pipelines directly located in the ground, ensuring their waterproofness and mechanical protection (Table 3). For pipelines located above the ground, a protective shell made of galvanized steel with a zinc coating thickness of at least 70 microns is used.

Table 3. Dimensions of polyethylene shell pipes, mm.

The dimensions of shaped products (except for the diameters of steel pipes and polyethylene shell pipes) are recommended and are determined by the design solution. Design solutions usually based on manufacturers' recommendations. For example, NPO "Stroypolymer" accompanies its products with a guide to the design and construction of "Steel pipelines with factory thermal insulation."

The wall thickness of the pipe and fittings is determined by calculation and rounded to the recommended thicknesses, which are given in the appendix to the standard.

Insulation of pipeline connecting parts (bends, tees) is carried out by cutting the polyethylene shell, followed by contact or extrusion welding.

For the manufacture of waterproofing shell pipes, high-density polyethylene of grades 273-79, 273-80 and 273-81, classified as PE 63, is used. European companies also use PE 80 polyethylene, which has higher minimum long-term strength and resistance to crack propagation. The main characteristics of polyethylene shell pipes are given in table. 4.

Table 4. Main characteristics of waterproofing polyethylene shell pipes

Rigid polyurethane foam used for thermal insulation is made from high molecular weight alcohol - polyol and isocyanate. The foam is a homogeneous mass with an average pore size of 0.5 mm and has the physical and mechanical characteristics given in table. 5.

Table 5. Properties of rigid polyurethane foam in thermal insulation construction

Thermal insulation is applied along the entire length of steel pipes and fittings, with the exception of the end sections, equal to 150 mm for pipe diameters up to 219 mm, and 210 mm for pipes with a diameter of 273 mm or more.

The service life of thermal insulation of pipes and fittings must be at least 25 years. Polyurethane foam does not have a harmful effect on environment and ensures high-quality insulation operation at temperatures up to 130 °C.

Insulation of pipe sections with welded joints or repair of insulation can be carried out according to one of the following schemes:

• 1. Installation of insulating linings (shells) made of rigid polyurethane foam with further application of waterproofing material.
• 2. Installation of polyethylene couplings with polyurethane foam poured into the cavity of the coupling.

For waterproofing joints wide application received heat-shrinkable polyethylene shells, characterized by low cost and ease of installation.

To insulate the joints of heat-insulated pipes with a protective shell made of galvanized steel, special steel couplings are used. They are used on straight sections of pipelines, on bends and branches for pipes with outer shell diameters of 63-450 mm, as well as during hot tapping, when a branch is installed without shutting off the heat supply.

The technology for installing couplings is simple and requires a minimum of tools. The joint consists of two parts, which are fastened together using special cones or screws. The sealant located between the outer shell of the pipe and the coupling makes the joint waterproof. Thermal insulation is carried out using foam packages, which are easy to handle and, when pouring, provide an accurate dosage and uniformity of polyurethane foam throughout the entire volume.

To insulate and repair joints of pipes with diameters of 90-1300 mm, bandage couplings made of polyethylene with embedded electric spiral are used. Bandage couplings are available in three types and differ in the method of fixation on the outer shell during the welding process.

Small bandage couplings are used for pipes with outer shell diameters of 90-200 mm. Medium-sized bandage couplings are used for diameters of 225-800 mm. For outer shells with diameters of 800-1200 mm, bandage couplings consisting of two parts are used. All couplings are supplied with all necessary components. During welding, small couplings are pressed against the polyethylene shell of the pipe using mechanical clamps, and medium and large size couplings - using pneumatic ones. In all cases, the welding process is performed automatically and controlled using a special welding computer.

Bandage couplings meet the highest requirements for strength and reliability. The pipe was tested in 1993 central heating length 2.5 m, diameter 200 mm. The joint with the bandage coupling successfully passed tests, including 1000 axial vibrations in a box of sand and 600 hours in a container of water at elevated pressure. This test corresponds to 30 years of operation. Currently, more than 350,000 bandage couplings are installed in world practice. Special tools and computer controlled welding guarantee fast and reliable installation insulation of joints. The equipment required for welding is mounted on vehicle trailers and includes a generator, compressor and computerized welding unit.

The described system of heating networks with polymer thermal insulation is intended for direct installation in the ground. The system is "connected", i.e. The steel pipe, thermal insulation and outer shell are firmly connected to each other. The joints are insulated using connecting parts that ensure 100% tightness.

Such systems meet all SNiP requirements for the design and construction of heating networks. To ensure optimal adhesion between the steel pipe and the foam insulation, all steel pipes are pre-treated sandblasting. The outer shell is made of high density polyethylene, and its inner surface treated with corona discharge to obtain optimal adhesion between polyethylene and foam insulation.

What is the expected service life of pre-insulated pipelines? This issue is significant for all district heating (DH) enterprises.

The article "Tests to determine the service life of pre-insulated pipes in district heating systems", published in the journal "Pipelines and Ecology", 2000, No. 1, examines the results of studies and observations carried out in Denmark on a network of main pipelines, including supply and return pipelines 100 km long with diameters 100-800 mm. Tests have been carried out since 1987.

The service life of pre-insulated pipes in district heating systems depends on the aging process of the pre-insulated pipe, including possible corrosion of the steel pipe, the temperature resistance of the polyurethane foam insulating material, as well as a polyethylene shell. Other critical factors include changes in the strength properties of the above materials over time. long period, the influence of temperature and pressure, as well as deformation conditions in the pipeline system.

Corrosion of a steel pipe depends primarily on how hermetically the system is sealed against the penetration of water from the outside, since internal corrosion of a working steel pipe can hardly be observed in systems operated with treated water. Therefore, an indispensable condition is to maintain the tightness of the pipe-shell joints. pipe thermal insulation polyurethane foam polyethylene

The polymer materials used in pre-insulated pipes impose restrictions on the temperature of the supplied water and thus affect the service life of the pipes. Technical impacts on the system throughout its entire service life are increased requirements to the insulating material (polyurethane foam), its compressive strength and adhesion (cohesion) between the steel pipe and the waterproofing shell.

Stresses and deformations depend on operating conditions, temperature conditions and pressure, as well as from pipe laying technology and the condition of the surrounding soil. Due to the fact that it is the properties of the material (polyurethane foam insulation and polyethylene sheath) that have a decisive influence on the service life of pre-insulated pipes in district heating systems, the characteristics of two properties of polyurethane foam were considered, namely: temperature resistance and compressive strength.

Temperature resistance. In accordance with the requirements of the European standard EN 253, the service life of pre-insulated pipes must be at least 30 years, provided that the system is continuously operated at a temperature of 120 °C. In a system where the temperature is less than 95 °C, the service life can be practically unlimited. Throughout the tests, the temperature of the supplied water varied in the range of 100-115 °C, and the temperature of 115 °C was maintained during the three coldest periods. winter months. Assuming that Maximum temperature supplied water will be 110 °C for the remaining period until the end of the year, then the system will have total term service life is 75 years, and this complies with the EN 253 standard. A service life of 75 years does not mean that the pre-insulated pipes in a certain section of the pipeline do not need repair at all. This only means that the polyurethane foam insulation material is expected to maintain its strength characteristics over the specified period. When designing a central heating system, a certain number of load cycles are calculated - temperature fluctuations from operating temperatures to soil temperatures and back to operating temperatures over 30 years, which should be used in calculating fatigue characteristics. (In Russia, the service life of thermal insulation made of polyurethane foam is determined according to GOST R 30732, Appendix D - Methodology integral assessment service life of polyurethane foam insulation of heating networks at variable temperature chart coolant). The specified number of load cycles remains, although the polyurethane foam insulation material retains its properties over a longer period. Thus, it is very important to ensure that pipes for district heating systems, in constant daily use, are subjected to fewer load cycles than allowed in accordance with the calculations, so that more high term services of polyurethane foam insulation material.

The compressive strength of polyurethane foam insulating material is limited and determines the conditions for maximum depth of pipes being laid and the technology for laying pipes for district heating systems. It was found that when exposed to a temperature of 140 °C for a long period, the compressive strength of polyurethane foam with a density of 75 kg/m3 drops to zero over a period of approximately 15 months. At temperatures above 125°C, the compressive strength will remain the same as new polyurethane foam after approximately two years of service. The limited compressive strength of the insulating material dictates restrictions on the maximum depth of laid pipes in central heating systems, especially in cases where a change in the direction of the pipeline route is required. To reduce earth pressure when moving pipes horizontally, other precautions should be used as an alternative.

The tables below 6 and 7 give a clear idea of ​​the economic efficiency of using various types of thermal insulation.

Table 6. Cost of laying 1 km of a two-pipe heating main

Table 7. Estimation of economic efficiency of 1 km of two-pipe heating main in USD

From the tables above, you can see the advantages of polyurethane foam insulation, which are confirmed by many years of experience in operating heating networks in Russia and foreign countries.

The design of heating networks is carried out on the basis current standards using " Standard solutions laying pipelines in polyurethane foam insulation", " Technological maps for builders", developed at the VNIPIENERGOPROM Institute, and methodological recommendations manufacturing plants. Design and calculation methods are practically no different from traditional channelless installation. Maximum use of existing standard building construction. There is also the possibility of abandoning drainage or switching to lighter types.

Very often, when creating water supply systems or transporting various types of industrial liquids, the question of protecting pipelines arises.

They need to be protected from mechanical damage, atmospheric influences, but first of all, protection is needed from exposure to cold. Be that as it may, it is precisely the too low temperature outside that most seriously affects the condition of the pipes, as well as their carrier.

Thermally insulated pipes perform their functions at any air temperature, which distinguishes them from ordinary ones. Realizing the popularity of pipeline thermal insulation, the developers decided to go further and created so-called pre-insulated samples.

What is it and what are they? We will enlighten you on this issue.

Contents of the article

What are the differences between simple pipes?

An ordinary pipe for transporting certain types of substances, what is it? Most likely, a pipe is a steel or plastic oblong section of a hollow cylinder.

The pipe may have walls different thicknesses, a certain diameter, can even bend. The walls can be very thin, for domestic use, or quite thick, up to 10-15 mm or even more.

In the latter case we're talking about about lines high pressure, mounted on industrial enterprises, where it is necessary to be able to transport media under enormous pressure and temperature through communications systems.

No matter how thick the pipe wall is, it still cannot protect its insides from freezing. Metal conducts heat very well, as does plastic, although the latter has a slightly lower thermal conductivity.

At zero temperature, a pipe without protection can still function properly, but at -10 it can no longer function. The media will either freeze completely or begin to slowly deposit on the walls. Sooner or later, all this will affect the functioning of the system, completely blocking it.

That's why it's so necessary. Without it, any pipeline laid along the street will simply freeze during winter. Warm water supply or heating systems will not be an exception.

Even if the heating pipe does not freeze due to the conflict between high and low temperatures There will be a discrepancy in the temperature of the carrier at the inlet and outlet of the line.

The carrier will lose a fairly impressive part of the thermal energy free of charge, which is also not very good. After all, efficiency decreases, and resources will have to be spent many times more to artificially increase it.

Alternative option

It is quite easy to protect heating or water supply pipes. You just need to think about their thermal insulation system. Materials are used from the same line as the raw materials for insulation load-bearing structures Houses.

Most often used:

• mineral wool;
• expanded polystyrene;
• penoizol;
• foamed polyethylene.

Each option is good in its own way. But they all, one way or another, assume additional processing pipes, which takes time and money. This process can be simplified.

Unlike the load-bearing structures of a house, which, by the way, have also recently begun to be produced pre-insulated, pipes are very easy to pre-treat.

After all, all samples are unified, manufacturers know which models to focus on and what exactly the buyer needs, and therefore act in key areas.

This is how pre-insulated pipes appeared - that is, those that were treated with thermal insulation at the production stage at the factory.

Technology and design

Most often, pre-insulated pipes are produced in large sizes. This is explained by the fact that household pipelines are laid mainly inside buildings or underground.

That is, they have no access to air, which means there is no danger of freezing. If some section is nevertheless laid on the surface, then due to its short length, it will not be difficult for the owner to isolate it.

While in industry they try to keep all pipeline lines on the surface so that, if necessary, they have access to any section of them.

This, in turn, creates the need to properly protect pipes from the effects of low temperatures, and therefore automatically increases the demand for industrial pre-insulated pipes.

Their design is very simple. In essence, we have a regular pipe with a coaxial shell. That is, the outer shell is placed on the inner, solid body of the pipe. They are mounted when the axes coincide, that is, the axes do not intersect and are kept parallel to each other.

The gap between the pipe body and its protective shell is filled with a heat insulator. At the very beginning we used different materials, now preference is given to penoizol.

So it turns out that thermally insulated products are analogues of conventional ones, only in a two-layer protective casing. Its first layer functions directly as thermal insulation, and the second as additional mechanical protection.

The outer shell is used:

• tin steel;
• plastic (including corrugated).

Properties of penoizol

Manufacturers of pre-insulated pipes chose Penoizol for a reason. It has a lot of useful properties, but at the same time it also has disadvantages.

Among the beneficial properties are:

1. Low thermal conductivity.
2. High strength.
3. Efficiency.
4. Low weight.
5. Vapor permeability.
6. Zero reaction to moisture.
7. No corrosion.
8. Durability.

Great stuff, isn't it? It has all the properties necessary for high-quality insulation. The only problem here is that penoizol is applied in the form of ready-made foam.

The process is in many ways similar to applying polyurethane foam, only on a much larger scale.

And this, frankly speaking, is not always convenient. For normal interaction, you will need expensive equipment, ingredients for mixing the composition, as well as some experience, since penoizol tends to shrink, unevenly, depending on many factors.

For self-use, and even on pipes, this option is unacceptable. The result will be shapeless, unaesthetic, and the process itself will take a lot of time.

Another thing is processing at a factory, where all stages are automated and calculated down to the second. Here, pipes pre-insulated with foam insulation became a real breakthrough.

They are easy to produce (you just need to assemble the coaxial base and fill the gap between the shell and the protective casing), they are extremely effective and quite cheap (the price is falling due to unification and faster production).

The end result is pipes with perhaps better protection, additional mechanical protection and good cost.

Note that on the market you can also find pipes insulated without penoizol. For example, processed with foam plastic, flexible models with a shell filled with foamed polyethylene, etc.

But they are almost always inferior to the samples described above in all respects, including economic ones, and therefore have not found such popularity.

Types of pre-insulated pipes

There are two main types of pre-insulated pipes. There are pipes:

• hard;
• flexible.

Rigid pipes – standard option. There is an internal section of pipe of a certain diameter, treated with a layer of penoizol. The thickness of the layer depends on the tasks assigned to a particular system.

In cold regions it can be 10 centimeters or more, while in warmer regions insulation with a thickness of about 5 cm is sufficient.

Outer protective layer made of tin steel, in rare cases stainless steel. Such products are perfect for assembling main water supply systems, pressure industrial pipelines, central distribution lines, etc.

Flexible variations are produced using a similar technology, only instead of an outer metal shell, a corrugated one is made plastic frame. It cannot be called extremely flexible, and it is not so easy to bend penoizol inside, but still a certain degree of freedom is allowed.

The section can be laid along a small radius, if desired, bent and twisted the way you want. Even if the insulation inside is damaged, you will not experience any significant consequences on the functioning of the water supply system.

Connecting pre-insulated pipes (video)

Additional Variations

Pre-insulated pipes are produced mainly in single and monolithic forms. But this doesn't always happen. For narrower tasks, models with combined wiring are also produced.

That is, they may have not one large segment inside the casing, but several. Of course, they are much thinner and not as effective, but they are well insulated and reinforced. Any damage or freezing similar design not a threat.

The option with several small pipes is interesting because entire clusters of communications can be laid this way, while forming a compact, aesthetic and extremely convenient system.

Its only drawback is the need to open the casing if one of the pipes breaks. Moreover, it is also not so easy to understand what exactly broke through and where.

Also, any self-respecting manufacturer of pre-insulated pipes produces protected fittings that would fit their products. The most common options are - quadruple connections, corner fittings, locking elements, etc.

In Russia the most high level centralized heating (about 80%). The total length of heating networks in two-pipe terms with pipe diameters from 57 to 1400 mm is about 260 thousand km. The predominant method of laying heating networks is in non-passable channels with mineral wool thermal insulation.

Channelless installation, carried out from factory-made structures using reinforced foam concrete insulation and bitumen-containing masses (bitumen perlite, bitumen-overmiculite, bitumen-ceramsite), makes up 10% of the total length of heating networks. About 90% of fuel savings achieved through combined heat generation methods are lost in heating networks.

The service life of heating networks is one and a half to two times lower than abroad, and does not exceed 12-15 years. The most effective solution to the problems is the widespread introduction into practice of constructing heating networks of pipelines with polyurethane foam thermal insulation of the “pipe-in-pipe” type. The idea is not new. Back in the 1960s, experimental work was carried out in the USSR on the use of polyethylene pipes and foamed polymer materials for insulating underground heating networks. But then this direction was not widespread due to the limited production and high cost of the polymer materials used.

Technical requirements for thermal insulation

The materials used must have high thermal insulation properties (the thermal conductivity coefficient of the material should not exceed 0.06 W/(m⋅°C), durability (resistance to water, chemical and biological aggression), frost resistance and mechanical strength, fire and environmental safety. The most Polyurethane foam fully meets these requirements.

Polyurethane foam thermal insulation is usually applied to pipes at the factory, and the joints are thermally insulated at the construction site after welding and testing of the pipeline. In Western Europe, such designs have been used since the mid-1960s and meet European standards EN 253:1994, as well as EN 448, EN 488 and EN 489.

They provide the following advantages over existing structures: increasing the durability (resource) of pipelines by two to three times; reduction of heat losses by two to three times; reduction in operating costs by half (specific damage rate is reduced by 10 times); reduction of capital costs in construction by two to three times; Availability of a system for operational remote monitoring of thermal insulation moisture.

Pre-insulated pipes are made from a variety of materials depending on the operating conditions. Steel pipes are most widely used for the construction of heating mains.

Compliance of pre-insulated pipes with state standards

For the manufacture of insulated pipes, steel pipes with outer diameters of 57-1020 mm, up to 12 m long, complying with GOST 550, 8731, 8733, 10705, 20295, the requirements of current regulatory documents for heating networks and the Rules for the design and safe operation of steam and hot water pipelines are used. Steel bends, tees, transitions and other parts must comply with the requirements of GOST 17375, 17376 and 17378.

The main reason for the widespread use of steel pipes is due to their relatively low cost, ease of processing combined with high strength and the ability to use traditional welding as a pipe joining method. To avoid pipe corrosion, it is necessary to use treated water. Water treatment depends on local conditions, but the following are generally recommended:

• pH = 9.5-10;
• lack of free oxygen;
• total salt content 3000 mg/l.

The standard length of pipes is 6-12 m, but the technology makes it possible to apply thermal insulation to pipes of any length and made of other materials. Technical requirements for insulated pipes and pipeline parts are set out in GOST 30732-2001 “Steel pipes and fittings with thermal insulation made of polyurethane foam in a polyethylene shell”, put into effect on 07/01/01.

The standard applies to steel pipes and shaped products with thermal insulation made of polyurethane foam in a polyethylene shell, intended for underground ductless installation of heating networks with the following design parameters of the coolant: operating pressure up to 1.6 MPa and temperature up to 130 °C (short-term temperature increases up to 150 are allowed °C). GOST 30732-2001 is compiled taking into account European standards:

• EN 253-1994 “Welded, pre-insulated pipelines for underground hot water supply systems. A pipeline system consisting of a steel main pipeline with polyurethane thermal insulation and an outer sheath of polyethylene";
• EN 448-1994 “Welded pipelines, pre-insulated, for underground hot water supply systems. Prefabricated fittings made of steel distribution pipes with polyurethane thermal insulation and an outer shell of polyethylene.”

Type and size

To ensure maximum efficiency (insulation cost/heat loss), certain diameters of external insulation of polyurethane foam pipelines are established for different climatic zones. Pipes and fittings can have two types of insulation thickness: type 1 - standard, type 2 - reinforced. Protective casings are made in the form of thin-walled pipes made of high-density polyethylene.

They are designed for pipelines located directly in the ground, ensuring their waterproofness and mechanical protection (Table 2). For pipelines located above the ground, a protective shell made of galvanized steel with a zinc coating thickness of at least 70 microns is used. The dimensions of shaped products (except for the diameters of steel pipes and polyethylene pipe shells) are recommended and are determined by the design solution.

Design decisions are usually based on manufacturer recommendations. For example, some companies accompany their products with a design and construction manual, “Factory Insulated Steel Pipelines.” The wall thickness of the pipe and fittings is determined by calculation and rounded to the recommended thicknesses, which are given in the appendix to the standard.

For the manufacture of waterproofing pipe shells, high-density polyethylene of grades 273-79, 273-80 and 273-81, classified as PE63, is used. European companies also use PE80 polyethylene, which has higher minimum long-term strength and resistance to crack propagation. Rigid polyurethane foam used for thermal insulation is made from high molecular weight alcohols - polyol and isocyanate.

Polystyrene foam is a homogeneous mass with an average pore size of 0.5 mm. The service life of thermal insulation of pipes and fittings must be at least 25 years. Polyurethane foam does not have a harmful effect on the environment and provides high-quality insulation at temperatures up to 130 ° C.

Installation practice

Insulation of pipe sections with welded joints or repair of insulation can be carried out according to one of the following schemes:

1. Installation of insulating linings made of rigid polyurethane foam with further application of waterproofing material.
2. Installation of polyethylene couplings with polyurethane foam poured into the cavity of the coupling.

For waterproofing joints, heat-shrinkable polyethylene shells, which are characterized by low cost and ease of installation, are widely used. To insulate the joints of heat-insulated pipes with a protective shell made of galvanized steel, special steel couplings are used. They are used on straight sections of pipelines, on bends and branches for pipes with outer shell diameters of 63-450 mm, as well as during hot tapping, when a branch is installed without shutting off the supply.

The technology for installing couplings is simple and requires a minimum of tools. The joint consists of two parts, fastened using special cones or screws. The sealant located between the outer shell of the pipe and the coupling makes the joint waterproof. Thermal insulation is carried out using foam packages; they are easy to handle and provide precise dosage and uniformity of polyurethane foam when pouring.

To insulate and repair joints of pipes with diameters of 90-1300 mm, bandage couplings made of polyethylene with embedded electric spiral are used. Bandage couplings are available in three types and differ in the method of fixation on the outer shell during the welding process. Small bandage couplings are used for pipes with outer shell diameters of 90-200 mm. Medium-sized bandage couplings are used for diameters of 225-800 mm.

For outer shells with diameters of 800-1200 mm, bandage couplings consisting of two parts are used. All couplings are supplied with all necessary components. During welding, small couplings are pressed against the polyethylene shell of the pipe using mechanical clamps, and medium and large couplings are pressed using pneumatic clamps. In all cases, the welding process is performed automatically and controlled using a special welding computer.

To ensure optimal adhesion between the steel pipe and the foam insulation, all steel pipes are pre-sandblasted. The outer shell is made of high-density polyethylene, and its inner surface is treated with corona discharge to obtain optimal adhesion between polyethylene and foam insulation.

The service life of pre-insulated pipes in DH systems depends on the aging process of the pipe itself, including possible corrosion of the steel pipe, the temperature resistance of the polyurethane foam insulation material, and the polyethylene sheath. Other critical factors include changes in the strength characteristics of the above materials over a long period, the effects of temperature and pressure, and deformation conditions in the piping system. Corrosion of a steel pipe depends on how tightly the system is sealed against the penetration of water from the outside, since internal corrosion of a working steel pipe can hardly be observed in systems operated with treated water.

Therefore, an indispensable condition is to maintain the tightness of the pipe-shell joints. Stresses and deformations depend on operating conditions, temperature conditions and pressure, as well as on pipe laying technology and the condition of the surrounding soil. Due to the fact that it is the properties of the material (polyurethane foam insulation and polyethylene sheath) that have a decisive influence on the service life of pre-insulated pipes in district heating systems, the characteristics of two properties of polyurethane foam were considered, namely: temperature resistance and compressive strength.

Temperature resistance

In accordance with the requirements of the European standard EN 253, the service life of pre-insulated pipes must be at least 30 years, provided that the system is continuously operated with a coolant temperature of 120 °C. In a system where the temperature is less than 95 °C, the service life can be virtually unlimited. During testing, the supply water temperature varied between 100-115°C and was maintained at 115°C throughout the three coldest winter months.

Assuming a maximum supply water temperature of 110°C for the remainder of the year, the system will have a total service life of 75 years, which is in accordance with EN 253. A service life of 75 years does not mean that the pipes do not need repairs at all . This means that the polyurethane foam insulation material is expected to maintain its strength characteristics over the specified period.

When designing a central heating system, a certain number of load cycles are calculated - temperature fluctuations from operating temperatures to soil temperatures and back to operating temperatures over a period of 30 years, which is used in calculating fatigue characteristics. In Russia, the service life of thermal insulation made of polyurethane foam is determined according to GOST R 30732, Appendix D - a method for integral assessment of the service life of polyurethane foam insulation of heating networks with a variable temperature schedule of the coolant.

The number of load cycles remains the same, although the polyurethane foam insulating material retains its properties further.

Compressive strength

The compressive strength of polyurethane foam insulating material is limited and determines the conditions for maximum depth of pipes being laid and the technology for laying pipes for district heating systems. It has been established that when exposed to a temperature of 140 °C over a long period, the compressive strength of polyurethane foam with a density of 75 kg/m3 drops to zero within 15 months.

At temperatures above 125°C, the compressive strength will remain the same as new polyurethane foam after approximately two years of service. The limited compressive strength of the insulating material dictates restrictions on the maximum depth of laid pipes in central heating systems, especially in cases where a change in the direction of the pipeline route is required. To reduce earth pressure when moving pipes horizontally, other precautions should be used as an alternative.

Economic justification

Data in table. 5 and 6 give an idea of ​​the economic efficiency of using various types of thermal insulation. The advantages of PPU insulation are visible, which are confirmed by many years of experience in operating heating networks in Russia and foreign countries. The design of heating networks is carried out on the basis of current standards using “Standard solutions for laying pipelines in polyurethane foam insulation”, “Technological maps for builders” developed by VNIPI-Energoprom, and methodological recommendations from manufacturers.

Design and calculation methods do not differ from traditional channelless installation. Existing standard building structures were used to the maximum extent possible. It is possible to abandon drainage or switch to its lighter types.

Insulated pipelines of the Flexalen system

For our country, due to the rather harsh climate, the thermal insulation of pipes is a separate, serious issue. The pipeline can be heated different ways, the best of which is to lay pre-insulated pipelines. Such flexible pipes, being laid in the route, do not require further insulation - the pipes have already been insulated.

Flexalen is a system of universal pre-insulated pipes. The flexalen system is based on polybutene pipes. The pipes are made of polybutene, enclosed in thermal insulation made of foamed polyethylene or polyurethane and closed in a plastic corrugated casing.

Thermaflex has taken a serious step towards developing the market of external engineering systems by releasing New Product– flexible pre-insulated polymer pipelines Flexalen. The Flexalen system made it possible to combine the advantages of polymer pipelines and highly effective thermal insulation into a single whole. Flexalen pipelines are designed for ductless installation of heating, cold, hot and water supply systems. They are based on pipes made of polybutene, a material whose main characteristics are superior to polymers widely represented on the Russian market (PEX cross-linked polyethylene and PP polypropylene). The Flexalen system uses a unique patented system of pre-insulation of flexible polymer pipelines. Polybutene pipelines are enclosed in a homogeneous thermal insulation layer of Thermaflex polyethylene foam. The outer corrugated plastic casing is extruded directly onto the thermal insulation, welding to it. This ensures reliable waterproof connection casing and thermal insulation. Currently, Flexalen pre-insulated pipelines are widely used not only in Europe, but also on the Russian market. This includes cottage construction, laying heating mains in cities, and use at industrial facilities, i.e. at sites where the heating point is located outside the main building and where it is necessary to lay communications between several objects. First of all, these are external network engineering cold and hot water supply and heating.

Thermaflex holding has factories and representative offices around the world, including in Russia. The production of thermal insulation at Thermaflex factories is characterized by high technological processes and the presence of the most modern equipment. Thermaflex factories have certificates of full compliance with international standards. The production of thermal insulation and pre-insulated pipelines at Thermaflex factories has reached a level where the products produced are the standard of all requirements set by the European Union for thermal insulation of pipelines as a whole. Calculation of thermal insulation is carried out according to installed program Thermaflex and Flexalen calculations in accordance with technical parameters a separate project. Based on the calculation, the price for thermal insulation is formed.

Thus, with the help of Thermaflex products, one of the serious problems when laying pipes - thermal insulation of pipelines.