Magazine "News of heat supply", No. 3, (19), March, 2002, P.25 - 31, www.ntsn.ru

Ph.D. V.E. Bukhin, Senior Research Fellow, NPO Stroypolimer

Russia is a country with a high level of district heating (up to 80%). The country is pierced by about 280 thousand km of heating networks (in two-pipe terms) with pipe diameters from 57 to 1400 mm, a tenth of which are mains, the rest are distribution heating networks.

The predominant method of laying heating networks in the Russian Federation is laying in impassable channels with mineral wool insulation (80%). Channelless laying, made from prefabricated structures using insulation from armored concrete and bitumen-containing masses (bitumen perlite, bitumen vermiculite, bitumen expanded clay), makes up 10% of the total length of heating networks.

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

The total heat loss in district heating systems is about 20% of the supplied heat (78 million tons of reference fuel per year), which is 2 times higher than in the advanced countries of Western Europe.

District heating systems in the Russian Federation currently provide 2,171 million Gcal per year of heat consumption, which is approximately the same as 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 district heating and possessing the world's largest system of heat networks, Russia is significantly behind the advanced foreign countries in the technical level - in the use of modern materials and technologies for laying heat pipelines.

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

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

The most effective solution to the above problems is the widespread introduction into the practice of building heating networks of pipelines with polyurethane foam thermal insulation of the "pipe in pipe" type.

This idea is not new. The Vechernyaya Moskva newspaper dated December 10, 1963 reported that the Mosinzhproekt Institute carried out experimental work on the use of polyethylene pipes and foamed polymeric materials for insulating underground heating networks. However, in those years this direction was not widely used.

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

The heat-insulating materials used must have high heat-insulating properties (the thermal conductivity 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. e. be safe for the life and health of people and the natural 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 sheath made of a polyethylene pipe is shown in fig. one.

For example, in Western Europe, such designs have been successfully used since the mid-60s and are normalized 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:

· increase in durability (resource of pipelines) by 2-3 times;

reduction of heat losses by 2-3 times;

· decrease in operating costs by 9 times (specific damage is reduced by 10 times);

· reduction of capital expenditures in construction by 1.3 times;

· Availability of a system of operational remote monitoring of the dampening of thermal insulation.

Pre-insulated pipes are successfully used for the construction of:

· networks of heat supply;

systems of hot water supply;

· technological pipelines;

oil pipelines.

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

Table 1. The main physical and mechanical indicators of pipeline steel

For the manufacture of insulated pipes, steel pipes are used with outer diameters of 57 - 1020 mm, up to 12 m long, corresponding to GOST 550, GOST 8731, GOST 8733, GOST 10705, GOST 20295, the requirements of current regulatory documents for heating networks and the Rules for the Design and Safe Operation of Pipelines steam and hot water.

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

Treated water must be used to avoid pipe corrosion. Water treatment depends on local conditions, but the following requirements are recommended:

lack of free oxygen

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

In Russia, pre-insulated steel pipes with thermal insulation made of polyurethane foam and a polyethylene waterproofing sheath have been used since 1993. Their release is organized at several enterprises (CJSC MosFlowline, Moscow; CJSC TVEL Corporation, St. Petersburg; OJSC NPO Stroypolymer, Moscow; CJSC "Teploizolstroy", Mytishchi; 000 Heat-insulated pipes plant "Alexandra", Nizhny Novgorod; CJSC "Sibpromkomplekt", Tyumen, etc.), united in the Association of manufacturers and consumers of pipelines with industrial polymer insulation.

The technical requirements for insulated pipes and pipeline parts are standardized in GOST 30732-2001 "Steel pipes and fittings with thermal insulation made of polyurethane foam in a polyethylene sheath", put into effect on July 1, 2001 by the Decree of the Gosstroy 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 sheath is drawn up 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 systems - Piping system consisting of a steel main pipeline with polyurethane thermal insulation and an outer shell of polyethylene;

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

In the new standard, which combines the technical conditions of 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 also comply with the requirements of European standards: hazard class, explosive category of production, 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 fittings with thermal insulation made of polyurethane foam in a polyethylene sheath (hereinafter referred to as insulated pipes and products) intended for underground channelless laying of heat 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).

Very often, when creating water supply systems or transporting various kinds 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 the effects of cold. Be that as it may, it is the too low temperature on the street 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 thermal insulation of pipelines, the developers decided to go further and created the so-called pre-insulated samples.

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

Article content

What is the difference between simple pipes?

An ordinary pipe for transporting a certain kind of substance, what is it? Most likely, a steel or plastic elongated segment of a hollow cylinder is called a pipe.

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

In the latter case, we are talking about high-pressure lines installed at industrial enterprises, where it is necessary to be able to distill carriers under enormous pressure and temperature through communication systems.

No matter how thick the wall of the pipe 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. The carrier 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 the winter. An exception will not be the system of warm water supply or heating.

Even if the heating pipe does not freeze due to the conflict of 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 rather impressive part of the thermal energy free of charge, which is also not very good. After all, the efficiency decreases, and resources for its artificial increase will have to be spent many times more.

Alternative option

Protecting heating or water pipes is easy enough. You just need to think over the system of their thermal insulation. The materials are used from the same line as the raw materials for insulating the load-bearing structures of the house.

Most often used:

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

Each option is good in its own way. But all of them, one way or another, involve additional processing of the pipe, which takes time and money. This process can be simplified.

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

After all, all samples are unified, manufacturers know which models to focus on and what exactly the buyer needs, and therefore they 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 due to the fact that household pipelines are laid mainly inside buildings or underground.

That is, they do not have access to air, which means that there is no danger of freezing. If, however, some section is nevertheless laid on the surface, then due to the small 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 in order to have access to any of their sections if necessary.

This, in turn, creates the need for high-quality protection of pipes from low temperatures, which automatically increases the demand for industrial pre-insulated pipes.

Their design is very simple. In fact, we have an ordinary pipe with a coaxial sheath. That is, the outer shell is mounted 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 sheath is filled with a heat insulator. At the very beginning, they used different materials, but now they give preference to penoizol.

So it turns out that heat-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.

As an outer shell use:

• tin steel;
• plastic (including corrugated).

Penoizol properties

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 useful 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 that are necessary for high-quality insulation. The problem here is only that penoizol is applied in the form of finished foam.

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

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

For independent 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 the factory, where all stages are automated and calculated to the second. Here, pipes pre-insulated with penoizol have become a real breakthrough.

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

At the exit, pipes are obtained with perhaps the best, additional mechanical protection and good cost.

Note that pipes insulated without penoizol can also be found on the market. For example, foamed, flexible models with a shell filled with foamed polyethylene, etc.

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

Types of pre-insulated pipes

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

• rigid;
• flexible.

Rigid pipes are standard. There is an inner section of a pipe of a certain diameter, treated with a layer of penoizol. The thickness of the layer depends on the tasks that are set for a particular system.

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

The outer protective layer is made of tin steel, in rare cases, stainless steel. Such products are perfect for assembling main water supply systems, pressure industrial pipelines, central wiring, etc.

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

The segment 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 feel any significant consequences on the functioning of the water supply system.

Connection of pre-insulated pipes (video)

Additional Variations

Pre-insulated pipes are produced mainly single and monolithic. But this is not always the case. 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 of such a structure does not threaten.

The option with several small pipes is interesting in that it is possible to lay entire clusters of communications in this way, while forming a compact, aesthetic and extremely convenient system.

Its only drawback is the need to open the casing in the event of a breakthrough in one of the pipes. Moreover, it is not so easy to understand what exactly broke through and where.

Also, any self-respecting manufacturer of pre-insulated pipes is engaged in the manufacture of protected fittings that would fit their products. The most common options are quadruple wiring, corner fittings, locking elements, etc.

Magazine "News of heat supply" No. 5, 2005, www.ntsn.ru

IN AND. Manyuk, President; Ph.D. I.L. Meisel, Executive Director, Association of Manufacturers and Consumers of Industrial Polymer Insulated Pipelines, Moscow

On February 28, 2005, a conference was held in Moscow dedicated to the experience of production, design, construction and operation of pipelines for thermal networks with polyurethane foam insulation, organized by the Association of Manufacturers and Consumers of Pipelines with Industrial Polymer Insulation. More than 60 organizations from various regions of Russia took part in the conference. These are, first of all, manufacturers of pre-insulated pipes, construction organizations that actively use them when laying heating networks, manufacturers of raw materials, equipment, as well as the largest research and design institutes, incl. and foreign partners. At the conference, an interested exchange of views took place on the problems that have existed in this area for the last decade, when this direction in heat supply has been massively developing.

The general opinion of the conference participants was the following - to ensure the reliability, durability and energy efficiency of heat network structures, pipelines with polyurethane foam insulation should be used as widely as possible for both underground channelless laying and above-ground laying. Today, there are practically no alternatives to this direction in heat supply.

In his report “Experience of mass production and application of pipelines with polyurethane foam insulation in Russia”, the Executive Director of the Association, Ph.D. I.L. Meisel, summed up more than a decade of experience in the production and use of such pipelines in construction. If in 1994 in Russia there were only a few enterprises producing pipes pre-insulated with polyurethane foam, then by the beginning of 2005 there were about 70 of them. Thus, there are about 30 such enterprises in the Central Federal District (including in Moscow and Moscow region - 21 enterprises), in the North-West - 8, in the Volga region - 9, in the Urals - 9, in the Siberian - 9, in the South - 4. The total capacity of enterprises is about 10 thousand km per year, both main and distributing pipelines (from 57 mm and below, up to 1200 mm). However, due to the lack of financing, the capacities of enterprises are used on average by 30-60%.

It was emphasized that the Association and its members have developed regulatory documentation for the successful use of pipelines with polyurethane foam insulation. The main documents are the following:

Interstate standard GOST 30732-2001 "Steel pipes and fittings with thermal insulation made of polyurethane foam in a polyethylene sheath";

ST 4937-001-18929664-04 "Steel pipes and fittings with thermal insulation made of polyurethane foam with steel protective coating";

SP 41-105-2002 "Design and construction of thermal networks of channelless laying from steel pipes with industrial thermal insulation from polyurethane foam in a polyethylene sheath";

RD 10-400-01 "Standards for calculating the strength of heating network pipelines";

Computer programs "START";

SNiP 41-02-2003 "Heat networks";

SNiP 41-03-2003 "Thermal insulation of equipment and pipelines";

SP 41-107-2004 "Design and installation of underground pipelines for hot water supply from PE pipes with thermal insulation from polyurethane foam in a polyethylene sheath", etc.

In order for the application of new products to be successful, it is necessary to pay close attention to the quality of manufactured products, to increase the level of design and installation with the obligatory use of operational remote control systems (ODC) during operation.

I.L. Meisel stressed that in order to improve the level of design and construction of heating mains, the Association has created training centers through which hundreds of specialists in designers and builders have passed (every year, about 700-800 people study at the training centers of NPO Stroypolimer and CJSC MosFlowline).

New approaches in the development of SNiP 41-02-2003 "Heat Networks" were reported by the head of the department of JSC "Association VNIPIEnergoprom", Doctor of Technical Sciences. G.H. Umerkin. Particular attention was paid to such concepts as the probability of failure-free operation of the system, the coefficient of availability (quality) of the system, the survivability of the system, etc.

The report of the director of thermal networks of JSC "Lenenergo" E.G. Khachaturov. He noted that in the heating networks of JSC "Lenenergo" the use of pipes in polyurethane foam insulation began in 1993 and 123 km have already been laid.

Previously, pipes without operational remote control systems (ODC) were used. And only since 2003, the company made an unambiguous decision - not a single meter of the pipeline in polyurethane foam insulation should be laid without a control system. A real tool has appeared that allows you to control the quality of products at all stages, starting from the input control of the delivered products. Installers now know that they will be able to hand over the object only if the insulation resistance meets the standard.

During storage and laying of pipelines, the insulation can be damaged, therefore, after installing the pipe in the trench, before insulating the joint, its resistance must be measured again. If it is normal, then the metal of the joint is treated with an anti-corrosion coating, the joint is insulated with foam, and the resistance is measured again. Since 2004, all joints must be treated with an anti-corrosion coating. For this, mastic produced by CJSC NPK Vector is used. The ends of thermal insulation are also covered with mastic of the same company to protect against moisture in adverse weather conditions and even when the pits are flooded.

Head of the operation service of the Teplosetservis enterprise V.I. Kashinsky dwelled on the experience of operating steel pipelines with polyurethane foam insulation in the heating networks of OAO Mosenergo for the period from May 1996 to March 2004. During this period, the following malfunctions were noted during the operation of 218.4 km of pipelines with polyurethane foam insulation:

Damage to steel pipes from internal corrosion - 4%;

Weld defects - 5%;

Defects in sealing butt coupling joints - 23%;

Errors in the installation of operational remote control systems (SODK) - 5%;

Destruction of elements for connecting SODK (terminals, terminal boxes, connecting cables, etc.) - 26%;

Mechanical damage during earthworks - 3%;

Failure of SODK devices - 1%.

Thus, there is no damage from external corrosion (for old traditional designs of heating networks in impassable channels with thermal insulation made of mineral wool materials, damage from this type of corrosion was about 75%), from internal corrosion - no more than 4%. The main type of damage is vandalism and lack of coordination between the various earthmoving organizations.

After training and accumulation of experience by specialists of installation organizations, defects in the sealing of coupling joints are gradually reduced. Specific damage rate of steel pipelines (number of damages per year related to one km) for the period from 1999 to 2003 for channelless gaskets in polyurethane foam insulation was 0.0107, and for other types of gaskets - 1.244, i.e. differs by two orders of magnitude. (The speaker agreed with the remark that the comparison is not entirely correct, because the damage was assessed with respect to new channelless pipelines in polyurethane foam insulation and "old" heating mains of traditional types, which, moreover, have a much longer length - approx. ed.).

Director of OAO "Association VNIPIEnergoprom" and President of NP "Russian Heat Supply" V.G. Semenov stressed the need to improve the quality of products. Having dwelled on the unconditional advantages of laying heat networks with polyurethane-insulated pipes, especially in significant heat savings, the speaker recommended strengthening control at all stages of design, production and construction of heat networks.

A.V. Fisher, Chief Specialist of OAO Mosproekt, made a report on the experience of designing heat networks. He noted that in Moscow, flexible pipes made of cross-linked polyethylene with polyurethane foam insulation are widely used in the reconstruction and new construction of heat networks after central heating in hot water and heating systems, which significantly (up to 50 years or more) increases the service life and reliability of heat networks and the entire heating system as a whole. In order to be able to use such pipes more widely, it is necessary to develop a “Code of Rules for the Design of Heat Networks Using Pipes Made of Polymer Materials”, which will legalize the abolition of the use of shut-off and drain valves on branches to individual buildings and a number of other issues that greatly facilitate and reduce the cost of installation and further operation of heat networks based on cross-linked polyethylene.

The issues of strength calculation of pipelines of heat networks with polyurethane foam insulation were discussed in the report of V.Ya. Magalif. He touched upon the use of START computer programs in these calculations. A heated discussion was caused by the corrected method for calculating the wall thickness of tee branches, which leads to their significant increase. According to V.Ya. Magalifa, the methodology is based on the strength calculation standards set out in RD 10-400-01, approved by the State Technical Supervision Authority. However, these thicknesses do not correspond to GOST 30732-2001 “Steel pipes and fittings with thermal insulation made of polyurethane foam in a polyethylene sheath”.

Achievements in the production and use of steel pipes with polyurethane foam insulation were reported in the reports of the chief engineer of CJSC Mos-Flowline V.G. Kukhtin and director of ZAO Sibpromkomplekt (Tyumen) G.A. Razmazin. The need for a complete set of heating networks (production of shaped elements, valves, materials for insulating joints, SODK, etc.) was noted. For example, CJSC MosFlowline, in addition to pipes and fittings, manufactures and supplies for installation ball valves and, since 2005, compensators (starter and bellows).

A number of speakers presented products manufactured by their organizations for the production and installation of heat networks with PPU-insulated pipes.

Director of PC "Polymer-Complex" V.I. Timokhin and head of the representative office "Cannon" (Italy) A.Yu. Bobkov was told about filling machines, the general director of NPP Izolan LLC (Vladimir) M.Ya. Tsarfin and a representative of VIKORD LLC A.V. Shapovalov (Togliatti) about raw material systems for PPU, the president of ENEKOS (St. Petersburg) - about ball valves D y 300-800 mm, a representative of LLC Olmaks" - about manual extruders for welding polyethylene casings.

V.A.Polyakov (CJSC MosFlowline) stressed in his report the need to install systems for operational remote monitoring of the state of moisture in polyurethane foam and spoke about new multilevel detectors for fixing moisture.

In conclusion, the president of the Association, V.I. Manyuk, recommended that the participants of the conference make wider use of the experience gained by the members of the Association in the production and use of pipes with polyurethane foam insulation in heating networks.

Pipes ISOPROFLEX 0.6 MPa
CASAFLEX
Pipes ISOPROFLEX 75A 1.0 MPa
Steel pipes in polyurethane foam insulation
Steel pipes in VUS insulation
Pipes ISOPROFLEX Quadriga and Tandem
Convectors
Steel panel radiators
Movable supports according to GOST 14911-82, OST 36-94-83
Movable supports of heating networks series 5.903-10-13 issue 8-95
Fixed supports of heating networks series 5.903-10-13 issue 7-95
Movable supports series 4.903-10 issue 5
Fixed supports series 4.903-10 issue 4

The economic component of the use of pipes for district heating in our cities is determined by the quality and durability of pipelines and thermal insulation. In Russia, all pre-insulated pipes that are produced can be divided into two types - polymer pipes and steel pipes. Heat-insulating layer - polyurethane foam PPU. It has a fine-mesh structure with closed pores. The advantages of polyurethane foam are low thermal conductivity and low moisture absorption. The weak side is flammability.

The main types of pre-insulated pipes that are used for heating networks:

1. Steel pipes in PPU insulation . Thermally insulated pipes are produced in accordance with GOST 30732-2006 "Steel pipes and fittings with thermal insulation made of polyurethane foam with a protective sheath". Steel pipes in PPU are operated at a pressure of up to 1.6 MPa and a coolant temperature of up to 1400 degrees (it is possible to increase the temperature to no more than 1500 degrees). Diameter of steel pipes - up to 1420 mm. The protective sheath of heat-insulated pipes is made of PE (for channelless laying), as well as galvanized steel (for above-ground laying). The quality of manufactured products is determined not only by the quality of steel pipes and their casing, but also by the technology of manufacturing polyurethane foam insulation.

The priority in the use of steel pre-insulated pipes is due to a large range of sizes, high thermal stability, the possibility of using at high pressure, and the presence of highly qualified personnel in construction and maintenance companies. The main disadvantage of steel pipes is low corrosion resistance. The use of conductors-indicators in the operational remote control system (RTCS) is necessary in the fight against corrosion. They are located in the PPU. The use of SODK makes it possible to detect an area with excessive moisture content of the insulation, which contributes to the prompt execution of work on the repair of heat-insulated pipes. The service life (according to GOST 30732-2006) of a pre-insulated pipeline made of steel (at least 30 years) is possible only with a very high-quality installation of this pipeline, which meets all standards for water treatment and with the mandatory presence of SODK. One of the main reasons for the early wear of steel pipes in PPU is the wetting of the heat insulator, due to poor tightness of the external insulation, with poor-quality work on the insulation of the joints. Another reason for wear is a technological defect during welding of pipes in PE sheaths.

2. Polymer pipes "Isoproflex" - these are pipes made of cross-linked polyethylene (PEX) in polyurethane foam insulation. These thermally insulated pipes have good flexibility (bending radius approx. 1 m) and heat resistance up to 95°C. The maximum working pressure is up to 1.0 MPa. The possibility of using long lengths allows for quick installation. The main positive features of Isoproflex pipes are flexibility, high chemical resistance. This makes it possible to exclude SODK. But there are also disadvantages - this is a large thickness of the pipe wall and, therefore, a high cost. It is cheaper to operate plastic pipelines than steel ones. There is no need for repair work caused by corrosion, as with steel pipes. There are no costs for maintaining the UEC systems.

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Pre-insulated heating mains: what are the advantages?

Pre-insulated pipes are a special type of product that is used when laying large heating mains and heating systems. Unique features of such products are given not only by materials, but also by the presence of a technical control system, which is not used for pipes of other types.

Pipe scheme
1 - pressure corrugated pipe made of stainless steel; 2 - conductors-indicators (when producing pipes with the ODK system); 3 - thermal insulation made of polyurethane foam;
4 - corrugated protective sheath made of polyethylene.

When laying such routes, heat losses are reduced significantly, they amount to a value of up to 2%, which was previously considered impossible even when using heaters. Pre-insulated pipes are already fully finished products that do not require additional work during installation, which significantly reduces all costs for installation and further maintenance.

Feature of pre-insulated pipelines

The pre-insulated pipeline is a special system that is designed for laying heating mains. Such pipes have numerous advantages and features, the main thing being that the pipe consists of several layers, each of which has its own characteristics.

So, part of the pipes, which is intended for underground laying, is made of steel and a polyurethane sheath, between which a heat-insulating layer is laid, but for pipes of the above-ground system, the outer sheath is made of galvanization, which effectively protects the route from corrosion, adverse weather conditions, and other influences. .

Production specifics

Steel pre-insulated products are intended for laying heating mains, while pipelines in a steel or polyethylene sheath are laid in a channelless underground way, and in galvanized - in through channels or tunnels above the ground.

The pipes themselves are a “sandwich” structure, consisting of the following layers: a pressure steel inner pipe, a special signal wire SODK (technical control), a heat-insulating layer (usually made of foamed polyurethane), a protective sheath. It turns out a special pipe, consisting of two separate pipes with thermal insulation, which is located between them.

It is the features of production that ensure the resistance of pipes to corrosion, which is very important for the constituent elements of any heating main.

Before the start of insulation, the pipe undergoes special treatment in a shot blasting machine. This gives the surface a slight roughness, which improves the adhesion of the thermal insulation layer to the core of the inner tube.

The polyethylene sheath is also subjected to a corona treatment on its inside, which guarantees excellent adhesion between the insulation and the pipe. All pipes pre-treated in this way acquire their own unique properties, allowing them to be used in the most adverse conditions.

Technical quality control

Today, insulated pipes are offered, which can have sheaths made of various materials. Most often, these are shells made of polyethylene and galvanized steel, which may be suitable for laying underground and aboveground routes.

A casing made of such materials provides protection against any mechanical damage, moisture, and corrosion. In addition, the diffusion of polyurethane, which is the main material for the production of the pipe itself, is prevented.

Solder pipe connections.

Most often, high-density polyethylene is used for the manufacture of an insulating sheath, which is considered the most effective for underground laying. Polyethylene itself is thermally and light-stabilized, its color is black, it is produced strictly in accordance with GOST 16330, but in some cases GOST 18599 can be used.

It is used for insulation and polyurethane foam, which is excellent for steel pipes.

All pre-insulated pipes are subject to mandatory technical control, which allows us to guarantee the quality of the product. During laboratory tests, such characteristics of the pipe are determined as:

• density;
• compressive strength at 10 percent strain;
• volume fraction of all closed pores;
• water absorption during boiling;
• shear strength;
• thermal conductivity.

Welded joints are 100% checked using the modern ultrasonic testing method, which is a mandatory requirement before implementation.

Benefits of using

Scheme of assembly of parts of a pre-insulated flexible piping system.

All pre-insulated steel products differ from others for laying heating mains by the following advantages:

1. The on-line remote control system makes it possible to significantly increase the strength and reliability of such pipes, and to reduce all the costs of repairing the laid heating mains.
2. The service life is about 30 years, while simple uninsulated pipelines last only 10-15 years. This reduces the cost of replacing unusable pipes, maintenance of the route, and repairs.
3. Such a pipe reduces heat loss during use to 2%, although when laying uninsulated pipelines, such losses are quite significant - from 25%.
4. Steel insulated tracks are laid much easier and faster than usual, construction time is reduced by about two to three times, since there is no need to arrange channels and wells, and this causes a reduction in all costs.
5. All steel pipes do not require additional anti-corrosion coating, as they already have all the necessary properties. This allows you to reduce the cost of laying many times over.
6. The heat resistance of pipes is up to 150 degrees.

We can draw the following conclusions: all pre-insulated pipelines are much more profitable for the installation of heating mains, since they are more modern and less expensive. Their durability is twice as long, and maintenance and repair costs are reduced by the same amount. In a word, this is a profitable and promising option.