Requirements for pipeline insulation. Thermal insulation of equipment and pipelines: SNiP, characteristics, types of thermal insulation and requirements for them. Thermal insulation of external pipelines

It is necessary to take into account not only design features equipment and piping when the appropriate type of insulating material is selected, but also other factors. This is required by SNiP for thermal insulation of equipment and pipelines.

Consider the factors influencing the choice of insulating materials.

1. Purpose of the insulating materials themselves.
2. spatial orientation.
3. Possible atmospheric influences.

What are the requirements for thermal insulation of pipelines and equipment, we will consider below in this article.

What is the function of protection?

One of the purposes of thermal insulation of equipment and pipelines is to reduce the values ​​of heat fluxes inside structures. The materials are covered with protective coating shells, which guarantee the complete safety of the layer, in any operating conditions.

Great attention is paid to the issues of thermal insulation in different directions industry and energy. In buildings and equipment in these industries, it is thermal insulation that becomes one of the most important components.

The result is not only a reduction in heat losses during interactions with the environment. But also the expansion of opportunities for maintaining the optimal thermal regime.

Thermal insulation of pipelines and its essence

The calculation for thermal insulation is artificially adapted to all operating conditions characteristic of a particular pipeline or equipment. The conditions themselves are formed with the participation of:

1. Building materials to prepare for the changing seasons.
2. Humidity, contributing to the acceleration of heat transfer.

Professional companies provide contractors with engineering data for future construction. Which requirements have the greatest influence on the selection of suitable insulating coatings?

• Thermal conductivity.
• Soundproofing.
• The ability to absorb or repel water.
• vapor permeability level.
• Fire resistance.
• Density.
• Compressibility.

About the thickness of the insulation of the pipeline and equipment

Be sure to rely on the regulations to determine the allowable thickness for each specific equipment. In them, manufacturers write about what density is stored in the heat flux. SNiPs provide algorithms for solving various formulas along with the formulas themselves.

To identify the minimum thickness of pipelines in one case or another, a limit is determined by the allowable values ​​of losses in certain sections.

Polyurethane insulation

Pipelines with this type of insulation are used when it is necessary to lay the structure above the ground, channelless type. In manufacturing, they try to introduce as many new technologies as possible.

Of the materials, only those of the highest quality are allowed to the process. They are tested in advance in large numbers, according to the joint venture, the thermal insulation of equipment and pipelines does not allow marriage.

The use of polyurethane foam allows to reduce heat loss. And provides durability for the thermal insulation material itself. The composition of polyurethane foam includes environmentally friendly components. This is Izolan-345, as well as Voratek CD-100. Compared to mineral wool, thermal insulation characteristics polyurethane foam is much higher.

PPM and APB insulation

For more than thirty years, so-called polystyrene foam insulation has been used in pipelines. The main type in this case is polymer concrete. Its characteristics can be described as follows:

• Inclusion in group G1 during tests for flammability in accordance with current GOSTs.
• Temperature mode of operation, allowing you to maintain 150 degrees.
• The presence of an integral type structure, which combines the functions of a waterproofing coating together with a heat insulation layer.

Until recently, some regional manufacturers were engaged in the production of reinforced concrete insulation. This material has a very low density. And thermal conductivity, on the contrary, pleasantly surprises.

APB has the following set of advantages:

1. Durability.
2. Waterproof coating with high vapor permeability.
3. The equipment does not corrode.
4. The ability of the pipeline to withstand high temperatures.
5. Fire resistance.

Such pipes are good in that they can be used for a coolant of almost any temperature. This applies to networks not only with water, but also with steam. The type of gasket does not matter.

It is even possible to combine it with underground channelless and channel varieties. But products with PPU thermal insulation are still considered a more technological solution.

About the coefficient of thermal conductivity

Equipment, while it is in operation, it becomes possible to humidify - this is what most affects the calculated coefficient of thermal conductivity.

Special rules exist for the adoption of a factor that implies an increase in the thermal conductivity of insulating coatings. At the same time, they are based on GOSTs and SNiPs, but other factors cannot be dispensed with:

• soil moisture according to SP.
• Varieties to which the material for thermal insulation belongs.

The coefficient is equal to one if we are talking about pipes with polyurethane foam insulation, sheathed in high density polyethylene. It doesn't matter what the moisture level is in the soil where the equipment is installed. The coefficient for equipment and pipes with APB insulation having an integral structure will be different. And allowing for the possibility that the insulating layer may dry out.

1. 1.1 - the level of the coefficient for structures placed in soils with a large amount of water, according to the SP.
2. 1.05 - for soils where the amount of water is not so large.

In practical calculations, special engineering techniques are used. They usually take into account the resistance to external influences from environment. Two-pipe laying involves taking into account the mutual thermal influence of each of the elements on the others.

One of the determining factors in choosing the right thickness is the cost factor. And these indicators can be determined individually for each specific region.

There are other parameters that matter as well. Like the calculated coolant temperature. It is also important at what level the temperature in the environment is.

What other rules should be followed?

The production of equipment and pipes, together with thermal insulation, is carried out not only by Russian, but also by foreign manufacturers.

Some technological pipe-rolling lines are capable of producing a total volume of up to three kilometers of pipe-roll in one day (with a length of the pipe itself up to 12 meters). The product diameter is in the range of 57-1020 millimeters. The protective wrapper can be polyethylene or metal.

But there are still certain shortcomings that cannot be eliminated at the production stage. They were identified by experts through repeated practical tests.

1. During the transportation of pipes with metal coated deformations may appear in the insulating coating.
2. Polyurethane insulation peels off from the pipe, which is subjected to heat treatment.
3. The protective structure is detached from the outer or inner layers of the pipe.

The main problem is the ability of metal pipelines to expand. Temperature heating leads to the fact that the quality characteristics deteriorate. Because an important factor becomes protection against such types of influence.

The length of the pipe itself has the greatest influence on the stability and stability of the thermal insulation of an object. It doesn't matter what medium it is used to transfer. The longer the length, the higher the probability that the layer will simply collapse.

That's why given parameter must be chosen as carefully as possible. The experts themselves have developed optimal performance lengths and diameters of pipes, which will allow you to save the structure, regardless of what operating conditions it is in.

They rely only on SNiP, because the thermal insulation of equipment and pipelines is especially demanding to comply with the rules.

If you are equipping a water supply system country house with your own hands, then pipe insulation must be used. And this applies not only to pipelines passing on the street, but also to water supply systems inside the house. For water supply communications, several types of insulation are used, which differ in purpose and materials used for its manufacture. Each type of insulation performs its own functions. In our article, we will consider in detail what kind of insulation is required for hot and cold water supply pipelines, how this insulation is performed, and what materials can be used for these purposes.

To begin with, many isolation methods are applicable to different systems: water supply, sewerage, heating and ventilation. But in our article we will consider only those methods that are applicable to water pipes hot and cold water supply.

Piping insulation is divided into two types:

• thermal insulation measures;
• waterproofing.

The purpose of each type of isolation measures is as follows:

1. Thermal insulation of the external cold water supply pipeline is needed to protect the system from freezing during the cold season. If the water in the pipe freezes in frost, then it will not be able to get into the house, and it will be quite difficult to find an ice plug and eliminate it.
2. Thermal insulation of external hot water pipes is needed so that hot water does not cool down during transportation to the consumer. In addition, such protection helps to increase the service life of the system.
3. Pipelines are also thermally insulated. hot water, which will be located in the strobes - channels cut in the wall. In this case, these pipe protection methods are needed for the reason that the water temperature in pipes in contact with cold brick or concrete walls, may decrease.
4. Waterproofing of external pipes for hot and cold water supply is needed to protect them from corrosion. The thing is that the moisture present in the soil can cause rusting of steel pipes. However, this does not apply to plastic products.
5. Various types of waterproofing are used to protect pipeline joints from leakage.
6. As for cold water supply systems inside the house, their waterproofing is carried out in order to protect against condensate, which, collecting on pipes, can cause them to corrode. Again, this does not apply to plastic pipelines that are not subject to corrosion.

Exist different types and methods of hydro- and thermal insulation of pipelines and their joints. Let's consider them in more detail.

Pipe insulation

The following methods of thermal insulation of water supply pipes are commonly used:

• The most effective and reliable way to protect water supply pipelines from freezing in winter is to create high pressure in system. Due to this, the liquid moves through the pipes at high speed and does not have time to freeze. But these methods are not suitable for domestic water supply, because when the tap is closed, the liquid will not move in the pipes.
• Enough effective method thermal insulation of external pipes is the laying of a heating cable in the same trench with communications. Such methods are used if the bottom of the trench cannot be buried below the freezing point of the soil. In this case, a ditch is dug with a depth of no more than 40 cm, and a special heating cable is wound around the pipeline. The disadvantage of the method is energy dependence and the cost of paying for electricity.

Important: for these purposes, it is worth purchasing a cable with a power of 10-20 W / m. It can be used both outside and inside communications.

• The simplest and cheap way thermal insulation - the use of special materials that will protect the pipeline from the cold.

Tip: it is very important to create something like an arch from these materials in the upper part of the pipeline, protecting from the cold coming from the surface. The lower part of the element can be heated by heat coming from the ground.

Classification

The following means of isolation are commonly used:

• pouring;
• roll;
• piece;
• combined;
• casing.

Materials for thermal insulation of hot water pipes

Insulation can be internal and external. The following finished products can be used to perform insulation:

1. PPU. This material increases the service life of the pipeline, increases the waterproofing of the system. The material withstands temperature fluctuations and its marginal indicators. Heat loss is no more than 5%.
2. PPMI is used only for hot water communications. This is a monolithic three-layer structure. The density of the material in the cross section is different on different layers. The composition of the product has an anti-corrosion layer, thermal protection and moisture protection. The product increases the service life of the network, does not allow condensate to collect. The material is resistant to temperature extremes and mechanical damage.
3. VUS is a two-layer coating with anti-corrosion characteristics.

Thermal insulation materials for cold water pipes

Pipe insulation can be made using the following materials:

Waterproofing measures

Waterproofing of pipes and joints is carried out using the following materials:

1. PVC tape. This material is used to protect the surface of steel pipelines from corrosion. It is also suitable for sealing joints, threaded connections and in case of fulfillment repair work on water networks.
2. Rubber sheeting was previously used to isolate only underground engineering networks, but now it is also used to protect elements passing through basements houses. This durable, oil and alkali resistant material has an impressive service life. The product does not change its performance characteristics when high temperatures ah and is easy to install due to good elasticity.
3. Waterproofing of pipelines with the help of gluing materials (isola) is characterized by high strength and temperature stability. This elastic material stretches well during installation. Its only drawback is low resistance to organic compounds and solvents. The material is suitable for corrosion protection of external water supply pipelines.
4. Heat shrinkable tape is used to insulate joints of steel and plastic products. The tape consists of a thermofusible layer and polyethylene film. This material is not suitable for pipelines that will be operated at high temperatures. Special heat-shrinkable sleeves are used to protect joints.
5. Self-adhesive tape made of polymeric material. Its second name is fluoroplastic sealant. This material is used to protect against leaks in threaded joints. The product withstands exposure to high temperatures without changing its performance characteristics.

To reduce the level of heat loss in heating systems that occur during the cold period, pipes are insulated. Warm insulating materials contribute to saving the required temperature in the network, eliminating the occurrence of condensate on the pipeline surface and insulation. The use of these types of products prevents icing of water during stagnation, and slows down the process of corrosion that forms over time on pipeline components that are made of metal, prolonging their service life.

When choosing a heater, it is necessary to initially determine the place where it will be used, outside or inside the house. The choice of thermal insulation material is influenced by:

• pipe diameter;
• heating temperature of the heat carrier;
• conditions under which the heating system is operated.

The types of insulation used differ depending on the diameter of the pipes available. Manufacturing companies offer semi-cylinders, soft roll insulation and cylinders with a certain form of rigid execution.

For pipelines with small diameters, half-cylinders and cylinders with characteristic rigidity are suitable. This type of execution has grooves that greatly simplify installation work. This material has an excellent level of resistance to relatively high temperatures, with minimal water absorption. Rigid heat insulator constantly retains its primary shape, providing additional safety from possible mechanical damage.

When choosing, you need to pay attention to the following characteristics of a heat insulator:

• flammability class, especially should be taken into account for further placement inside residential and industrial buildings;
• the level of water absorption, on which the life of the material directly depends, because at a high level of moisture absorption, the insulation rots, starting to decompose, subsequently not presenting any efficiency;
• the degree of resistance to ultraviolet radiation, because a material with a low index, which is located outside the house, will begin to succumb to destruction by sunlight;
• the level of thermal conductivity should be as low as possible, because at a low rate, the heat insulator saves heat better, allowing the use of a heater with a thinner layer.

Varieties of insulation materials

Thermal insulation of heating pipes is carried out after the acquisition of the material, but until this moment it is necessary to learn about the characteristics and advantages of the insulation, as well as its scope. After these data, it will be possible to choose the most suitable and effective option.

This insulation consists of ribs and walls, which form a solid structure of a solid form. He creates heat-insulating shell, which has high level strength, while effectively retaining heat inside the heating network. Polyurethane foam has the following positive qualities:

• odorless and non-toxic;
• does not rot;
• it is environmentally friendly to the human body;
• has excellent dielectric qualities;
• material is resistant to different kind climatic influences, favorably suited for outdoor use;
• a sufficiently strong insulation that excludes the possibility of pipeline breakdowns under the influence of mechanical loads from the outside.

Its only noticeable drawback is its high cost.

mineral wool

Possessing a significant level of efficiency, it is quite in demand among heat insulators. It consists of mineral wool, and has a number of its features:

• cotton wool has low moisture absorption due to the processing with special compounds during the manufacturing process;
• a high degree of thermal stability, which, when heated, ensures the preservation of thermal insulation and mechanical parameters at the primary level;
• is environmentally friendly, does not contain toxic substances;
• it is not afraid of exposure to acids, solvents and other chemical solutions.

Mineral wool is excellent for use as a heat insulator for heating pipes. It is quite often installed on pipelines that are subjected to continuous heating of great force.

Foamed polyethylene

Does not harm the human body. It is not afraid of significant temperature changes and is resistant to moisture. The heater is quite popular among buyers. It has the shape of a tube with a specific thickness, in which an incision is made. It is used as a heat-insulating material for pipes of the heating network, and also for warming warm and cold water pipes.

It preserves its properties when used in conjunction with other building materials, including concrete, lime and others.

This heater for heating pipes appeared on the market quite recently, being a reflective heat insulator, which consists of aluminum foil and cellular polyethylene. Thanks to the 2 layers, the material has excellent thermal performance, which is why it is quite in demand among buyers. Folgoizol has a number of features:

• relatively easy installation, no special means protection;
• it is environmentally friendly, does not emit toxic substances;
• has a long service life;
• has a wide range of uses, suitable for both indoor and outdoor use.

Penofol is distributed in rolls with a different level of density of the polyethylene layer. When choosing a thickness, one should start from the future conditions for the use of a heat insulator. The double layer contributes to the retention of heat in an enclosed space, achieving the maximum allowable efficiency.

Stages of thermal insulation of heating pipes

mineral wool

Processes for warming the heating pipeline with mineral wool must be carried out with gloves on.

1. First of all, the material is cut in accordance with the desired dimensions.
2. It is wound on the pipe, and it does not need to be tightened strongly.
3. At intervals, one should stop, making fixation with electrical tape, wire or a solid rope.
4. Having finished covering the pipeline with mineral wool, it is necessary to prepare protective lining, which is made from roofing felt or corrugated foil, which is pre-cut into pieces.
5. Having installed a shell of foil or roofing felt, it is fixed with plastic ties or ropes.

polyurethane foam shell

With a small diameter, a cylindrical or semi-cylindrical shell shape can be used.

1. Thermal insulation material is put on the pipeline.
2. It is fixed by means of glue, adhesive tape, wire or self-adhesive tape.

If the pipes have large diameter, then you need to pick up a shell, which consists of several parts. This kind of material is fixed according to the groove-thorn principle.

Having made high-quality insulation of heating networks, it will be possible to save a significant amount of heat indoors. Therefore, the choice of insulation should be approached responsibly, weighing all the advantages of heat-insulating building materials available on the market before making a purchase.

In order to reduce heat losses and protect aboveground pipelines from freezing, the project provides for the laying of pipelines in thermal insulation with electrical heating. See section 6.6.2, table 19 for insulation volumes.

The design of thermal insulation was carried out in accordance with SP 61.13330.2012 (updated version of SNiP 41-03-2003) " Thermal insulation equipment and pipelines. The project uses insulating materials that are characterized as non-combustible according to SNiP 21-01-97*.

Insulation of pipelines is carried out after their testing and elimination of all defects found in this case.

The design, material, thickness of thermal insulation and cover layer are given below (Table 21).

Design of thermal insulation of above-ground pipelines

Thermal insulation of underground pipelines is made by heat-insulating semi-cylinders made of extruded polystyrene foam. Waterproofing is made with protective wrapping Polylen-OB according to TU 2245-004-01297859-99. The thermal insulation design is shown below (Table 22).

Construction of thermal insulation of underground pipelines

Fittings, flange connections, details of pipelines are thermally insulated with the same materials as pipelines. Removable heat-insulating structures are provided for fittings, flange connections, as well as in places for measuring and checking the condition of pipelines.

Anti-corrosion insulation of pipelines

The project provides for external anti-corrosion protection of steel technological pipelines.

Coat non-heat-insulated pipelines of above-ground laying (T11, T21 - diethylene glycol pipeline) with enamel PF-115 GOST 6465-76 * in two layers according to the primer GF-0119 GOST 23343-78 * in one layer.

Coat pipelines laid in thermal insulation with electric heating with KO-811 enamel according to GOST 23122-78* (three layers).

To protect underground pipelines from corrosion, cover the outer surface of the pipes with anti-corrosion insulation in accordance with the requirements of GOST R 51164-98 and RD 39‑132‑94, the insulation thickness is at least 2 mm.

To protect pipelines and fittings from soil corrosion during underground laying, a reinforced type protective film coating is adopted, and ECP agents are also used.

At the transition from aboveground to underground laying, insulating flange connections are installed that provide electrical isolation of a cathodically protected object from a cathodically unprotected one and can significantly reduce the risk of corrosion caused by stray currents.

The project provides for the following design of the film insulating coating:

• primer "NK-50" according to TU 5775-001-01297859-95;
• film "Polylen 40-LI-63" according to TU 2245-003-01297859-99 in two layers;
• protective wrapping "Polylen-0B" according to TU 2245-004-0127859-99 in one layer.

At the transition of pipelines from underground laying to aboveground, overlapping is provided protective coatings overlap of at least 0.5 m in both directions.

The application of insulation should be carried out on a previously prepared surface. Prepare parts and pipelines before applying anti-corrosion coatings according to scheme No. 2 of Table 3 or according to Table B.1 (Appendix B) of GOST 9.402-2004. In the absence of grease and marking paints, degreasing before machining is not performed. mechanical cleaning surface from oxides is produced in accordance with table 9 of GOST 9.402-2004 up to 2 degrees.

Corrosion rate monitoring must be carried out in conjunction with operational monitoring of pipelines and equipment using non-destructive methods (pipeline revision, technical certification equipment).

Thermal insulation is of great importance in the construction of a heat pipe. Not only heat losses depend on the quality of the insulating structure of the heat pipe, but, no less important, its durability. With the appropriate quality of materials and manufacturing technology, thermal insulation can simultaneously play the role of anti-corrosion protection. outer surface steel pipeline. Such materials, in particular, include polyurethane and derivatives based on it - polymer concrete and bion.

Thermal insulation is arranged on pipelines, fittings, flange connections, compensators and supports for the following purposes:

reduction of heat losses during its transportation, which reduces the installed capacity of the heat source and fuel consumption;

reducing the temperature drop of the heat carrier supplied to consumers, which reduces the required heat carrier flow and improves the quality of heat supply;

lowering the temperature on the surface of the heat pipe and air in the places of maintenance (chambers, channels), which eliminates the risk of burns and facilitates the maintenance of heat pipes.

The main requirements for thermal insulation structures are as follows:

1) low thermal conductivity both in the dry state and in the state natural humidity;

2) low water absorption and small height of capillary rise of liquid moisture;

3) low corrosivity;

4) high electrical resistance;

5) alkaline reaction of the medium (pH > 8.5);

6) sufficient mechanical strength!

It is not allowed to use materials subject to combustion and decay, as well as containing substances capable of releasing acids, strong alkalis, harmful gases and sulfur.

The most difficult conditions for the operation of heat pipelines arise during underground channel and especially channelless laying due to the moistening of thermal insulation by ground and surface waters and the presence of stray currents in the soil. In this regard, the most important requirements for heat-insulating materials include low water absorption, high electrical resistance, and with channelless laying, high mechanical strength.

As thermal insulation in heating networks, currently used mainly products made of inorganic materials (mineral and glass wool), lime-silica, sovelite, volcanic, as well as compositions made from asbestos, concrete, asphalt, bitumen, cement, sand or other components for channelless laying: bitumen-perlite, asphaltoizol, armo-foam concrete, asphalt-ceramsite-concrete, etc.

Depending on the type of products used, thermal insulation is divided into wrapping (mats, strips, cords, bundles), piece (slabs, blocks, bricks, cylinders, half-cylinders, segments, shells), pouring (monolithic and cast), mastic and backfill.

Wrapping and piece products are used for all elements of heating networks and can be either removable - For equipment requiring maintenance (gland expansion joints, flange connections), or fixed. They are fastened with bandages, wire, screws, etc., made of galvanized, cadmium or corrosion-resistant materials, and a cover layer. Filling and filling insulation is usually used for elements of heating networks that do not require maintenance. Mastic insulation may be used for shut-off and drainage valves and stuffing box expansion joints, provided that removable structures are made for branch pipes of stuffing box expansion joints and stuffing boxes for sealing fittings.

The heat-insulating structures of steel pipelines for above-ground and underground channel laying, as well as for channel-free laying in a monolithic shell, usually consist of three main layers: anti-corrosion, heat-insulating and cover. The anti-corrosion layer is superimposed on the outer; the surface of a steel pipe and is made of coating and wrapping materials in several layers (isol or brizol on insulating mastic, epoxy or organosilicate enamels and paints, glass enamel, etc.). On top of it, the main heat-insulating layer of wrapping, piece or monolithic products is laid. It is followed by a cover layer that protects the heat-insulating layer from moisture and air and from mechanical damage. It is carried out with underground laying of two or three layers of isol or brizol on insulating mastic, asbestos-cement plaster on a metal mesh, varnished fiberglass with various impregnations, foil isol, and with above-ground laying - from sheets of galvanized steel, aluminum, aluminum alloys, glass cement, glass roofing material, fiberglass and so on.

Channel heat pipes. In channels with an air gap, the insulating layer can be made in the form of a suspended or monolithic structure. On fig. 8.25. an example of a suspended insulating structure is shown. It consists of three main elements:

A) anti-corrosion protective layer 2 in the form of several layers of enamel or isol applied at the factory on the steel pipeline 1, having sufficient mechanical strength and having high electrical resistance and the necessary temperature resistance;

b) thermal insulation layer 3, made of a material with a low thermal conductivity, such as mineral wool or foam glass, in the form of soft mats or hard blocks laid on top of a protective anti-corrosion layer;

V) protective mechanical coating 4 in the form of a metal mesh acting as a supporting structure for the heat-insulating layer.

To increase the durability of the heat pipeline, the supporting structure of the suspension insulation (knitting wire or metal mesh) is covered on top with a sheath of non-corrosive materials or asbestos-cement plaster.

Rice. 8.25. Heat conductor in an impassable channel with an air gap

1 - pipeline; 2 - anti-corrosion coating; 3 - heat-insulating layer; 4 - protective mechanical coating

Channelless heat pipes. They find justified application in the case when, in terms of reliability and durability, they are not inferior to heat pipelines in impassable channels and even surpass them, being more economical compared to the latter in terms of initial cost and labor costs for construction and operation.

The requirements for the insulating structures of channelless heat pipelines are the same as for the insulating structure of heat pipelines in channels, namely, high and stable heat, moisture, air and electrical resistance under operating conditions.

Channelless heat pipelines in monolithic shells. The use of channelless heat pipelines in monolithic shells is one of the main ways to industrialize the construction of heat networks. In these heat pipelines, a shell is applied to the steel pipeline at the factory, combining heat and waterproofing structures. Links of such elements of the heat pipeline up to 12 m long are delivered from the factory to the construction site, where they are laid in a prepared trench, butt welding of individual links between themselves and the application of insulating layers to the butt joint. In principle, heat pipes with monolithic insulation can be used not only without channels, but also in channels.

Modern requirements for reliability and durability are quite fully met by heat pipes with monolithic thermal insulation made of cellular polymeric material such as polyurethane foam with closed pores and an integral structure, made by molding on a steel pipe in a polyethylene sheath (type "pipe in pipe").

At the same time, pre-insulated pipelines are made with a sheath made of high-pressure polyethylene. The space between the shell and the pipe is filled with rigid polyurethane foam. Copper conductors are embedded in polyurethane foam to control the presence of moisture in the thermal insulation of the pipeline.

Due to the good adhesion of the peripheral layers of insulation to the contact surface, i.e. to the outer surface of the steel pipe and inner surface polyethylene sheath, the long-term strength of the insulating structure is significantly increased, since during thermal deformation the steel pipeline moves in the ground together with the insulating structure and there are no end gaps between the pipe and the insulation, through which moisture can penetrate to the surface of the steel pipe.

The average thermal conductivity of polyurethane foam insulation is, depending on the density of the material, 0.03 - 0.05 W / (m ∙ K), which is approximately three times lower than the thermal conductivity of most widely used thermal insulation materials for heating networks ( mineral wool, reinforced concrete, bitumen perlite, etc.).

Due to the high thermal and electrical resistance and low air permeability and moisture absorption of the outer polyethylene sheath, which creates additional waterproofing protection, the thermal waterproofing structure protects the heat pipeline not only from heat losses, but, no less important, from external corrosion. Therefore, when using this insulation design, there is no need for special anti-corrosion protection of the surface of the steel pipeline.

The use of pipelines with polyurethane foam insulation makes it possible to reduce heat energy losses by 3-5 times compared to existing species thermal insulation (bitumperlite, expanded clay bitumen, foam concrete, etc.) and obtain annual savings of about 700.0 Gcal/year per 1 km.

The construction of heat networks with polyurethane foam insulation is carried out several times faster compared to channel ones and the cost is 1.3-2 times lower, and the service life is 30 years, while the durability of commonly used structures is 5-12 years.

Bitumoperlite, bitumen expanded clay and other similar insulating materials based on bituminous binder have significant technological advantages that make it possible to industrialize the production of monolithic shells on pipelines relatively easily. But along with this, the specified technology for manufacturing shells needs to be improved to ensure a uniform density and homogeneity of the bitumen-perlite mass both along the perimeter of the pipe and along its length.

In addition, bitumen-perlite insulation, like many other materials based on a bituminous binder, loses water resistance during prolonged heating at a temperature of 150 ° C due to the loss of light fractions, which leads to a decrease in the corrosion resistance of these heat pipes. To increase the anticorrosion resistance of bitumen-perlite in the process of manufacturing hot molding composition, polymer additives are introduced into Portland cement, which increases the temperature resistance, moisture resistance, strength and durability of the structure.

Channelless heat pipes in bulk powders. These heat pipelines are mainly used for pipelines of small diameter - up to 300 mm.

The advantage of channelless heat pipes in bulk powders compared to heat pipes with monolithic shells lies in the ease of manufacturing the insulating layer. The construction of such heat pipelines does not require the presence of a plant in the construction area of ​​heat networks, which must first receive steel pipes for applying a monolithic insulating shell. Insulating bulk powder in appropriate packaging, such as polyethylene bags, is easily transported over long distances by rail or road.

Self-sintering foam concrete, perlite concrete, asphalt or asphalt concrete are used as such powders.

As is known, in two-pipe heating networks temperature conditions, and consequently, the temperature deformations of the supply and return pipelines are not the same. Under these conditions, adhesion of the thermal insulation layer to the outer surface of steel pipelines is unacceptable. To protect the outer surface of steel pipelines from adhesion with the insulating mass, they are covered on the outside with a layer of anti-corrosion mastic material, such as asphalt mastic, before pouring with a liquid foam-cement mortar.

Cast structures for thermal insulation of channelless pipelines. Of the cast structures of channelless heat pipelines, heat pipelines in a foam concrete mass have received some use; perlite concrete can be used as a material for the construction of such heat pipelines. Steel pipelines installed in trenches are filled with a liquid composition prepared directly on the route or delivered in a container from the production base. After setting, the concrete or perlite concrete array is covered with soil.

Control questions

1. What are the main requirements for the design of modern heat pipelines? Name the assortment of pipelines of the heating network and the types of fittings used.

2. Compare underground heat pipelines in through channels, impassable and channelless. Name the advantages and disadvantages of each type of gasket and the main areas of their appropriate application.

3. Name the designs of modern compensators for thermal deformations of pipelines of heating networks. How is the calculation and selection of U - shaped expansion joints?

4. Describe the construction of supports for pipelines of heating networks. Give the calculation formula for determining the resulting force acting on the fixed support of the heat pipe.

5. What are the main features and requirements for heat-insulating structures of heat pipelines?