Overground and underground laying of heating mains. Constructions of overhead laying of heating networks. Underground laying of heating networks

Heat pipelines are laid underground or overground. The underground method is the main one in residential areas, since it does not clutter up the territory and does not deteriorate the architectural appearance of the city. The above-ground method is usually used on the territories of industrial enterprises with the joint laying of energy and technological pipelines. In residential areas, the above-ground method is used only in especially difficult conditions: permafrost and subsiding soils during thawing, swampy areas, a large density of existing underground structures, terrain heavily indented by ravines, the intersection of natural and artificial obstacles.

Underground heat pipelines are currently being laid in through and non-through channels (previously used semi-through channels are not used now) or in a channelless way. In addition, in residential neighborhoods, distribution networks are sometimes laid in technical undergrounds (corridors, tunnels) of buildings, which makes construction and operation cheaper and easier.

When laid in canals and technical undergrounds of buildings, heat pipes are protected from all sides from mechanical influences and loads and, to some extent, from ground and surface waters. For the perception of the own weight of the heat conductor, special movable supports are installed. With channelless laying, heat pipes are in direct contact with the ground and external mechanical loads are taken up by the pipe and the heat-insulating structure. In this case, no movable supports are installed, and the heat pipes are laid directly on the ground or a layer of sand and gravel. The cost of ductless laying is 25-30% less than in ducts, however, the working conditions of heat pipelines are more difficult.

The depth of laying heat pipelines from the upper level of channels or an insulating structure (with channelless laying) to the ground surface is 0.5-0.7 m. At a high level groundwater it is artificially reduced by the device of associated drainage from gravel, sand and drainage pipes under the channel or insulating structure.

Channels are currently made, as a rule, from unified precast concrete parts. To protect against ground and surface water, the outer surface of the canals is covered with bitumen with waterproofing roll material... To collect moisture that gets inside the channels, their bottom should be given a transverse slope of at least 0.002 in one direction, where sometimes closed (plates, gratings) trays are made, through which water flows into collection pits, from where it is discharged into drains.

It should be noted that, despite the waterproofing of the channels, the natural moisture contained in the soil penetrates into them through their outer walls, evaporates and saturates the air. When moist air is cooled, moisture accumulates on the ceilings and walls of the duct, which flows down and can cause moisture to the insulation.

In through channels are provided best conditions for the operation, operation and repair of heat pipelines, however, in terms of capital costs, they are the most expensive. In this regard, it is advisable to construct them only in the most critical areas, as well as when laying heat pipelines together with other utilities. With the joint laying of various communications, the through channels are called collectors. In cities, they are now widespread. In fig. 6.4 shows a cross-section of a typical one-section collector.

Passage ducts (collectors) are equipped with natural or forced ventilation, ensuring the air temperature in the duct is not higher than 40 ° С during repair periods and not higher than 50 ° С during operation, electric lighting with voltage up to 30 V, telephone communication. To collect moisture at low points of the route, pits are arranged that communicate with drains or are equipped with automatic or remote-controlled evacuation pumps.

Rice. 6.4. Section of a typical urban collector

1 and 2 - supply and return pipelines; 3 - condensate pipeline; 4 - telephone cables; 5 - power cables; 6 - steam line; 7 - water supply

The overall dimensions of the passage channels (collectors) are selected on the basis of the condition of free access to all elements of the heat pipelines, which makes it possible to carry out a complete overhaul them without opening and destroying road surfaces. The width of the passage in the channel is taken at least 700 mm, and the height - at least 2 m (it is allowed to take a height up to the beam of 1.8 m). Every 200-250 m along the route, hatches are made, equipped for descending into the channel with ladders or brackets. In places where a large number of equipment is located, special widening (cameras) can be arranged or pavilions can be built.

Non-passable channels are usually used for heat pipelines with a diameter of up to 500-700 mm. They are made rectangular, vaulted and cylindrical from reinforced concrete slabs and vaults, asbestos-cement and metal pipes, etc. In this case, an air gap is usually left between the surface of the heat pipes and the channel walls, through which the thermal insulation dries out and moisture is removed from the channels. As an example, Fig. 6.5 shows a section of a rectangular no-passage channel made of unified precast reinforced concrete parts.

Rice. 6.5. Cross-sections of the no-passage channel

1 and 2 - tray blocks, respectively, lower and upper; 3 - connecting element with cement whitening; 4 - base plate; 5 - sand preparation

The overall dimensions of the no-pass channels are chosen mainly depending on the distance between the heat pipes and between the surfaces of the insulating structure and the channels, as well as on the condition of providing convenient access to the equipment in the chambers. To reduce the distance between heat pipelines, equipment is sometimes installed on them at random.

Channelless laying is usually used for pipes of small diameters (up to 200-300 mm), since when laying such pipes in non-passable channels, their operating conditions are practically more difficult (due to the drift of the air gap in the channels by dirt and the difficulty of removing moisture from them at the same time ). In recent years, in connection with the increase in the reliability of channelless laying of heat pipes (through the introduction of welding, more advanced heat-insulating structures, etc.), it is also being used for pipes of large diameters (500 mm and more).

Heat pipelines laid by a channelless method are subdivided depending on the type of thermal insulation structure: in monolithic shells, cast (prefabricated-cast) and backfill (Figure 6.6) and, depending on the nature of the perception of weight loads: unloaded and unloaded.

Rice. 6.6. Types of channelless heat pipelines

a - in a prefabricated and monolithic shell; b-cast and prefabricated cast; c - filling

Constructions in monolithic shells are usually performed at the factory. On the route, only butt welding of individual elements and insulation of butt joints is carried out. Cast structures can be manufactured both in the factory and on the route by pouring pipelines (and butt joints after pressure testing) with liquid initial heat-insulating materials, followed by their setting (solidification). Backfill insulation is performed on pipelines mounted in trenches and compressed from loose thermal insulation materials.

Unloaded structures include structures in which the thermal insulation coating has sufficient mechanical strength and relieves pipelines from external loads (weight of soil, weight of vehicles passing on the surface, etc.). These include cast (precast-cast) and monolithic shells.

In unbalanced structures, external mechanical loads are transmitted through thermal insulation directly to the pipeline. These include backfill heat pipelines.

On underground heat pipelines, equipment requiring maintenance (valves, stuffing box expansion joints, drainage devices, drains, air vents, etc.) are placed in special chambers, and flexible expansion joints - in niches. Chambers and niches, like canals, are constructed from precast concrete elements. Structurally, the chambers are performed underground or with aboveground pavilions. Underground chambers are arranged with pipelines of small diameters and the use of valves with manual drive... Chambers with aboveground pavilions provide better maintenance of large-sized equipment, in particular, valves with electric and hydraulic drives, which are usually installed with pipeline diameters of 500 mm or more. In fig. 6.8 shows the construction of an underground chamber.

The overall dimensions of the chambers are selected based on the condition of ensuring the convenience and safety of equipment maintenance. To enter the underground chambers in the corners, hatches are arranged diagonally - at least two with an internal area of ​​up to 6 m 2 and at least four with a larger area. The diameter of the hatch is taken to be at least 0.63 m. Under each hatch, ladders or brackets are installed with a step of no more than 0.4 m to descend into the chambers. The bottom of the chambers is made with a slope of> 0.02 to one of the corners (under the hatch), where they arrange pits covered from above with a grate for collecting water with a depth of at least 0.3 m and dimensions in terms of 0.4x0.4 m. Water is drained from the pits by gravity or by means of pumps into drains or receiving wells.

Rice. 6.8. Underground chamber

Overhead heat pipelines are laid on free-standing supports (low and high) and masts, on overpasses with a continuous superstructure in the form of trusses or beams and on rods attached to the tops of the masts (cable-stayed structures). At industrial enterprises, sometimes simplified gaskets are used: on consoles (brackets) along the structures of buildings and supports (cushions) along the roofs of buildings.

Supports and masts are usually made of reinforced concrete or metal. Spans of overpasses and anchor posts (non-movable supports) are usually made of metal. At the same time, building structures can be built with one-, two- and many-tiered ..

Laying heat pipes on free-standing supports and masts is the simplest and is usually used with a small number of pipes (two to four). At present, in the USSR, standard designs of free-standing low and high reinforced concrete supports have been developed, performed with one rack in the form of a T-shaped support and with two separate columns or frames in the form of U-shaped supports. To reduce the number of racks, pipelines large diameter can be used as load-bearing structures for laying or suspending small-diameter pipelines to them, requiring more frequent installation of supports. When laying heat pipes on low supports, the distance between their lower generatrix and the ground surface should be at least 0.35 m with a group of pipes up to 1.5 m wide and at least 0.5 m with a width of more than 1.5 m.

Laying heat pipelines on racks is the most expensive and requires the highest metal consumption. In this regard, it is advisable to use it with a large number of pipes (at least five to six), as well as when it is necessary to regularly monitor them. In this case, pipelines of large diameters are usually supported directly on the racks of overpasses, and small ones - on supports laid in the superstructure.

The laying of heat pipes on suspended (cable-stayed) structures is the most economical, since it can significantly increase the distance between the masts and thereby reduce the consumption of building materials. When jointly laying pipelines of various diameters between the masts, runs are made from channels suspended on rods. Such purlins allow the installation of additional supports for pipelines of small diameters.

To service equipment (valves, stuffing box expansion joints), platforms with fences and ladders are arranged: stationary at a distance of 2.5 m or more from the bottom of the insulating structure to the earth's surface, or mobile - at a shorter distance, and hard-to-reach places and on flyovers - walk-through bridges. When laying heat pipes on low supports, in the places where equipment is installed, it is necessary to cover the surface of the earth with concrete, and on the equipment - the device of metal casings.

Pipes and fittings... For the construction of heating networks, steel pipes are used, connected by electric or gas welding. Steel pipes are subject to internal and external corrosion, which reduces the service life and reliability of heating networks. In this regard, galvanized steel pipes are used for local hot water supply systems that are subject to increased corrosion. In the near future, the use of enameled pipes is planned.

Of steel pipes for heating networks, they are currently mainly used electric-welded with a longitudinal straight and spiral seam and seamless, hot-deformed and cold-deformed, made from steels of grades St. 3, 4, 5, 10, 20 and low alloyed. Electric-welded pipes are produced up to a nominal diameter of 1400 mm, seamless - 400 mm. For hot water supply networks, water and gas steel pipes can also be used.

In recent years, work has been carried out on the use of non-metallic pipes (asbestos-cement; polymer, glass, etc.) for heat supply. Their advantages include high corrosion resistance, while polymer and glass pipes have lower roughness compared to steel pipes. Asbestos-cement and glass pipes are connected using special structures, and polymer pipes are welded, which greatly simplifies installation and increases the reliability and tightness of the joints. The main disadvantage of these non-metallic pipes is the low permissible temperatures and pressures of the coolant, about 100 ° C and 0.6 MPa. In this regard, they can only be used in networks operating with low water parameters, for example, in hot water supply systems, condensate pipelines, etc.

The fittings used in heating networks, according to their purpose, are divided into shut-off, control, safety (protective), throttling, condensate drainage and control and measuring.

The main valves of general purpose are usually shut-off valves, since they are most widely used directly on the route of heating networks. Other types of fittings are installed, as a rule, in heating points, pumping and throttling substations, etc.

The main types of shut-off valves in heating networks are gate valves and valves. Gate valves are usually used in water networks, valves - in steam. They are made of steel and cast iron with flanged and coupling connecting ends, as well as with ends for welding pipes of various nominal diameters.

Shut-off valves in heating networks are installed on all pipelines leaving the heat source, in branch nodes with dy> 100 mm, in branch nodes to individual buildings with dy 50 mm and branch length l> 30 m or to a group of buildings with a total load of up to 600 kW (0.5 Gcal / h), as well as on fittings for water discharge, air release and starting drains. In addition, sectional valves are installed in water networks: at d y> 100 mm through l ce kts<1000 м; при d y =350...500 мм через l секц <1500 м при условии спуска воды из секции и ее заполнения водой не более чем за 4 ч, и при d y >600 mm through l c ekts<3000 м при условии спуска воды из секции и ее заполнения водой не более чем за 5 ч.

In the places where the sectional valves are installed, jumpers are made between the supply and return pipelines with a diameter equal to 0.3 of the diameter of the main pipelines, to create circulation of the coolant in case of accidents. On the lintel, two valves are sequentially installed and a control valve between them at d y = 25 mm to check the tightness of the valves closing.

To facilitate the opening of valves with d y> 350 mm on water networks and with d y> 200 mm and p y> 1.6 MPa on steam networks requiring a large torque, bypass lines (unloading bypasses) are made with a shut-off valve. In this case, the valve is relieved of pressure forces when the valves are opened and the sealing surfaces are protected from wear. In steam networks, bypass lines are also used to start up steam lines. Gate valves with d y> 500 mm, which require more than 500 Nm torque for their opening or closing, must be used with an electric actuator. All valves with remote control are also provided with an electric drive.

Pipes and fittings are selected from the produced assortment depending on the conditional pressure, operating (design) parameters of the coolant and environment.

The nominal pressure determines the maximum allowable pressure that pipes and fittings of a certain type can withstand for a long time at a normal temperature of the medium + 20 ° C. As the temperature of the medium rises, the permissible pressure decreases.

Working pressures and temperatures of the coolant for the selection of pipes, fittings and equipment of heating networks, as well as for calculating pipelines for strength and when determining the loads on building structures should be taken equal, as a rule, to the nominal (maximum) values ​​in the supply pipelines or at the discharge of pumps, taking into account terrain. The values ​​of operating parameters for various cases, as well as restrictions on the choice of materials for pipes and fittings, depending on the operating parameters of the coolant and the environment, are specified in SNiP II-36-73.

Duct laying satisfies most requirements, however, its cost, depending on the diameter, is 10-50% higher for channelless. Channels protect pipelines from the effects of ground, atmospheric and flood waters. The pipelines in them are laid on movable and fixed supports, while an organized thermal elongation is provided.

The technological dimensions of the channel are taken on the basis of the minimum clear distance between the pipes and the structural elements, which, depending on the pipe diameter 25-1400 mm, is accordingly taken equal to: 70-120 mm to the wall; to overlap 50-100 mm; to the surface of the insulation of the adjacent pipeline 100-250 mm. Channel depth

taken on the basis of the minimum volume earthworks and uniform distribution of concentrated loads from vehicles on the floor. In most cases, the thickness of the soil layer above the floor is 0.8-1.2 m, but not less than 0.5 m.

With centralized heat supply, non-through, semi-through or through channels are used for laying heating networks. If the depth of the laying exceeds 3 m, then for the possibility of replacing the pipes, semi-through or through channels are constructed.

Non-passable channels used for laying pipelines with a diameter of up to 700 mm, regardless of the number of pipes. The design of the channel depends on the moisture content of the soil. In dry soils, block canals with concrete or brick walls or reinforced concrete single and multi-cell canals are more often arranged. In soft soils, a concrete base is first made, on which a reinforced concrete slab is installed. At a high level of groundwater, a drainage pipeline is laid at the base of the channel to drain them. The heating network in non-passable channels, if possible, is placed along the lawns.

Currently, predominantly channels are arranged from prefabricated reinforced concrete trough elements (regardless of the diameter of the pipelines to be laid) of types KL, KLs, or wall panels of types KS, etc. The channels are covered with flat reinforced concrete slabs. All types of canal bases are made of concrete slabs, lean concrete or sand preparation.

If it is necessary to replace pipes that have failed, or when repairing a heating network in non-passable channels, it is necessary to break the ground and disassemble the channel. In some cases, this is accompanied by the opening of the pavement or asphalt pavement.

Semi-bore channels. In difficult conditions of intersection of existing underground utilities by pipelines of the heating network, under the carriageway, with a high level of groundwater standing, semi-through channels are arranged instead of impassable ones. They are also used when laying a small number of pipes in those places where, according to the operating conditions, the opening of the roadway is excluded, as well as when laying pipelines of large diameters (800-1400 mm). The height of the semi-bore is taken at least 1400 mm. The channels are made of prefabricated reinforced concrete elements - bottom slabs, wall blocks and floor slabs.

Passage channels. Otherwise they are called collectors; they are constructed with a large number of pipelines. They are located under the bridges of large highways, on the territory of large industrial enterprises, in areas adjacent to the buildings of combined heat and power plants. Together with heat pipelines, other underground utilities are also placed in these channels: electric and telephone cables, water supply, low pressure gas pipeline, etc. For inspection and repair in the collectors, free access of service personnel to pipelines and equipment is provided.

Collectors are made of reinforced concrete ribbed slabs, frame structure links, large blocks and volumetric elements. They are equipped with lighting and natural supply and exhaust ventilation with three-fold air exchange, providing an air temperature of no more than 30 ° C, and a device for removing water. The entrances to the collectors are provided every 100-300 m. For the installation of compensating and locking devices on the heating network, special niches and additional manholes must be made.

Channelless laying. To protect pipelines from mechanical influences with this method of laying, reinforced thermal insulation is arranged - a shell. The advantages of channelless laying of heat pipelines are the relatively low cost of construction and installation work, a small amount of earthwork and a reduction in construction time. Its disadvantages include an increased susceptibility of steel pipes to external soil, chemical and electrochemical corrosion.

With this type of gasket, movable supports are not used; pipes with thermal insulation are laid directly on a sand cushion, poured onto the pre-leveled bottom of the trench. Fixed supports for channelless pipe laying, as well as for channel pipe laying, are reinforced concrete shield walls installed perpendicular to the heat pipelines. With small diameters of heat pipes, these supports, as a rule, are used outside the chambers or in chambers with a large diameter with high axial forces. To compensate for thermal elongation of pipes, bent or stuffing box expansion joints are used, located in special niches or chambers. In order to avoid trapping the pipes in the ground and to ensure their possible movement, at the turns of the track, no-pass channels are constructed.

For channelless laying, filling, prefabricated and monolithic types of insulation are used. A monolithic casing made of autoclaved reinforced foam concrete has become widespread.

Above ground laying. This type of gasket is the most convenient in operation and repair and is characterized by minimal heat loss and ease of locating accident sites. The supporting structures for the pipes are free-standing supports or masts that ensure that the pipes are located at the desired distance from the ground. With low supports, the clear distance (between the insulation surface and the ground) with a pipe group width of up to 1.5 m is taken as 0.35 m and at least 0.5 m for a larger width. Supports are usually made of reinforced concrete blocks, masts and overpasses are made of steel and reinforced concrete. The distance between supports or masts for overground laying of pipes with a diameter of 25-800 mm is taken equal to 2-20 m. Sometimes one or two intermediate suspended supports are arranged with the help of guy ropes in order to reduce the number of masts and reduce capital investments in the heating network.

To service fittings and other equipment installed on pipelines of the heating network, special platforms with fences and ladders are arranged: stationary at a height of 2.5 m or more and mobile at a lower height. In places where main valves, drainage, drainage and air devices are installed, insulated boxes are provided, as well as devices for lifting people and fittings.

5.2. Drainage of heating networks

In case of underground laying of heat pipelines, in order to avoid the penetration of water to the thermal insulation, an artificial lowering of the groundwater level is envisaged. For this purpose, together with heat pipelines, drain pipelines are laid 200 mm below the base of the channel. The drainage device consists of a drainage pipe and a sand and gravel backfill filtration material. Depending on the working conditions, various drainage pipes are used: for free-flow drainages - socket ceramic, concrete and asbestos-cement, for pressure - steel and cast iron with a diameter of at least 150 mm.

When cornering and when there are differences in the laying of pipes, inspection wells are arranged according to the sewer type. On straight sections, such wells are provided for at least 50 m.If drainage water cannot be drained into reservoirs, ravines or into the sewer by gravity, pumping stations are built, which are placed near the wells at a depth depending on the mark of the drainage pipes. Pumping stations They are built, as a rule, from reinforced concrete rings with a diameter of 3 m. The station has two compartments - a turbine room and a reservoir for receiving drainage water.

5.3. Facilities on heating networks

Heating chambers are intended for servicing equipment installed on heating networks during underground laying. The dimensions of the chamber are determined by the diameter of the pipelines of the heating network and the dimensions of the equipment. In the chambers, shut-off valves, stuffing boxes and drainage devices, etc. are installed. The width of the passages is taken at least 600 mm, and the height - at least 2 m.

Heating chambers are complex and expensive underground structures, therefore, they are provided only at the places of installation of valves and stuffing box expansion joints. The minimum distance from the ground surface to the top of the chamber overlap is assumed to be 300 mm.

Currently, precast concrete heating chambers are widely used. In some places, the chambers are made of brick or monolithic reinforced concrete.

On heat pipelines with a diameter of 500 mm and above, electric gate valves with a high spindle are used, therefore, an overhead pavilion with a height of about 3 m is erected above the recessed part of the chamber.

Supports. To ensure an organized joint movement of the pipe and insulation during thermal elongations, movable and fixed supports are used.

Fixed supports, intended for fixing pipelines of heating networks at characteristic points, are used with all methods of laying. Typical points on the route of the heating network are considered to be the places of branches, places of installation of valves, stuffing box expansion joints, mud collectors and places of installation of fixed supports. The most widespread are panel supports, which are used both for channelless laying and for laying pipelines of heating networks in non-passable channels.

The distances between the fixed supports are usually determined by calculating the strength of the pipes at the fixed support and depending on the value of the compensating capacity of the adopted expansion joints.

Movable supports installed at channel and channelless laying of pipelines of a heating network. There are the following types of different designs of movable supports: sliding, roller and suspended. Sliding supports are used for all laying methods, except for channelless ones. Rollers are used for overhead laying along the walls of buildings, as well as in collectors, on brackets. Suspended supports are installed when laying above ground. In places of possible vertical displacements of the pipeline, spring supports are used.

The distance between the movable supports is taken on the basis of the deflection of the pipelines, which depends on the diameter and thickness of the pipe wall: the smaller the pipe diameter, the smaller the distance between the supports. When laying pipelines with a diameter of 25-900 mm in channels, the distance between the movable supports is taken, respectively, 1.7-15 m. When laying above the ground, where a slightly greater deflection of pipes is allowed, the distance between the supports for the same pipe diameters is increased to 2-20 m.

Compensators used to relieve temperature stresses arising in pipelines during elongation. They can be flexible U-shaped or omega-shaped, hinged or stuffing box (axial). In addition, pipelines' bends at an angle of 90-120 ° are used on the route, which work as expansion joints (self-compensation). Installation of expansion joints is associated with additional capital and operating costs. The minimum costs are obtained with the presence of self-compensation sections and the use of flexible expansion joints. When developing projects for heating networks, the minimum number of axial expansion joints is taken, making the most of the natural compensation of heat pipelines. The choice of the type of compensator is determined by the specific conditions for laying pipelines of heating networks, their diameter and parameters of the coolant.

Anticorrosive coating of pipelines. To protect heat pipelines from external corrosion caused by electrochemical and chemical processes under the influence of the environment, anti-corrosion coatings are used. Factory made coatings are of high quality. The type of anti-corrosive coating depends on the temperature of the heating medium: bituminous primer, several layers of insulating mastic, wrapping paper or putty and epoxy enamel.

Thermal insulation. For thermal insulation of pipelines of heating networks use various materials: mineral wool, foam concrete, reinforced foam concrete, aerated concrete, perlite, asbestos cement, sovelite, expanded clay concrete, etc. Suspended insulation from mineral wool is widely used for duct laying, from autoclaved reinforced foam concrete, sometimes asphalt-toizol, bitumen perlite, and foam glass and backfill insulation.

Thermal insulation consists, as a rule, of three layers: heat-insulating, cover and finishing. The cover layer is designed to protect the insulation from mechanical damage and moisture ingress, i.e. to preserve the thermal properties. For the device of the covering layer, materials are used that have the necessary strength and moisture-permeability: roofing paper, glassine, fiberglass, foil-insol, sheet steel and duralumin.

As a cover layer for channelless laying of heat pipes in moderately humid sandy soils use reinforced waterproofing and asbestos-cement plaster on a wire mesh frame; for duct laying - asbestos-cement plaster on a wire mesh frame; for overhead laying - asbestos-cement half-cylinders, a sheet steel casing, galvanized or painted aluminum paint.

Suspended insulation is a cylindrical shell on the pipe surface made of mineral wool, molded products (slabs, shells and segments) and autoclaved aerated concrete.

The thickness of the thermal insulation layer is taken according to the calculation. The maximum temperature is taken as the design temperature of the coolant if it does not change during the operating period of the network (for example, in steam and condensate networks and hot water pipes), and the average for the year if the temperature of the coolant changes (for example, in water networks). The ambient temperature in the collectors is taken to be + 40 ° C, the average temperature of the soil on the pipe axis is the average for the year, the temperature of the outside air during the overhead laying is the average for the year. In accordance with the design standards for heating networks, the maximum thickness of thermal insulation is taken based on the installation method:

When laying above ground and in collectors with a pipe diameter of 25-1400
mm insulation thickness 70-200 mm;

In ducts for steam networks - 70-200 mm;

For water networks - 60-120 mm.

Armature, flange connections and other fittings of heating networks, as well as pipelines, are covered with a layer of insulation equal to 80% of the thickness of the pipe insulation.

With channelless laying of heat pipes in soils with increased corrosive activity, there is a risk of pipe corrosion from stray currents. To protect against electrocorrosion, measures are provided to exclude the penetration of stray currents to metal pipes, or arrange so-called electrical drainage or cathodic protection (cathodic protection stations).

The information technology plant "LIT" in Pereslavl-Zalessky produces flexible heat-insulating products made of foamed polyethylene with a closed pore structure "Energoflex". They are environmentally friendly, as they are made without the use of chlorofluorocarbons (freon). During operation and processing, the material does not emit toxic substances into the environment and does not have harmful effects on the human body through direct contact. Working with it does not require special tools and increased security measures.

"Energoflex" is intended for thermal insulation of engineering communications with a coolant temperature from minus 40 to plus 100 ° С.

Energoflex products are manufactured in the following form:

Tubing 73 sizes with inner diameters from 6 to 160 mm and
wall thickness from 6 to 20 mm;

Rolls 1 m wide and 10, 13 and 20 mm thick.

The thermal conductivity of the material at 0 ° C is 0.032W / (m- ° C).

Mineral wool heat-insulating products are manufactured by the enterprises of JSC Termosteps (Tver, Omsk, Perm, Samara, Salavat, Yaroslavl), AKSI (Chelyabinsk), JSC Tizol, Nazarovsky ZTI, Komat plant (Rostov -on-Don), Mineralnaya Vata CJSC (Zheleznodorozhny, Moscow Region), etc.

Also imported materials from ROCKWOLL, Ragos, Izomat and others are used.

The operational properties of fibrous thermal insulation materials depend on the composition of the raw materials and technological equipment used by various manufacturers and vary in a fairly wide range.

Mineral wool technical thermal insulation is divided into two types: high temperature and low temperature. ZAO Mineralnaya Vata produces ROCKWOLL thermal insulation in the form of fiberglass mineral wool slabs and mats. More than 27% of all fibrous heat-insulating materials produced in Russia is accounted for by URSA heat-insulating materials produced by JSC "Flyderer-Chudovo". These products are made of staple glass fiber and have high thermal and acoustic characteristics. Depending on the brand of the product, the thermal conductivity coefficient

such insulation ranges from 0.035 to 0.041 W / (m- ° C), at a temperature of 10 ° C. Products are characterized by high environmental performance; they can be used if the temperature of the coolant is in the range from minus 60 to plus 180 ° С.

ZAO Izolyatsionny Zavod (St. Petersburg) produces insulated pipes for heating systems. As insulation, ar-foam concrete is used here, the advantages of which include:

High limiting application temperature (up to 300 ° С);

High compressive strength (not less than 0.5 MPa);

Can be used for channelless installation at any depth
bin of laying of heat pipelines and in all soil conditions;

The presence on the insulated surface of a passivating protective
the film that occurs when the foam concrete comes into contact with the pipe metal;

The insulation is non-flammable, which allows it to be used for all
types of laying (aboveground, underground, channel or channelless).

The thermal conductivity coefficient of such insulation is 0.05-0.06 W / (m- ° C).

One of the most promising methods today is the use of pre-insulated ductless pipelines with polyurethane foam (PPU) insulation in a polyethylene sheath. The use of pipe-in-pipe pipelines is the most progressive way of energy saving in the construction of heating networks. In the USA and Western Europe, especially in the northern regions, these designs have been used since the mid-60s. In Russia - only since the 90s.

The main advantages of such designs:

Increasing the durability of structures up to 25-30 years and more, i.e. in
2-3 times;

Reduction of heat losses up to 2-3% in comparison with the existing ones
20 ^ 40% (or more) depending on the region;

Reduction of operating costs by 9-10 times;

Reducing the cost of repairing heating mains by at least 3 times;

Reducing capital costs during the construction of new heating mains in
1.2-1.3 times and a significant (2-3 times) reduction in construction time;

Significant increase in the reliability of heating mains constructed by
new technology;

The possibility of using the system of operational remote
control over the moisture content of the insulation, which makes it possible to timely react
for violation of the integrity of a steel pipe or polyethylene guide
insulating cover and prevent leaks and accidents in advance.

On the initiative of the Moscow Government, Gosstroy of Russia, RAO UES of Russia, CJSC MosFlowline, TVEL Corporation (St. Petersburg) and a number of other organizations, the Association of Producers and Consumers of Industrial Polymer Insulated Pipelines was established in 1999.

CHAPTER 6. CRITERIA FOR SELECTING THE OPTIMAL OPTION

The following types of overhead gaskets are currently in use:

On free-standing masts and supports (Fig. 4.1);

Rice. 4.1. Laying pipelines on free-standing masts

Fig.4.2 - on overpasses with a continuous superstructure in the form of trusses or beams (Fig. 4.2);

Rice. 4.2. Overpass with a superstructure for laying pipelines

Fig.4.3 - on rods attached to the tops of the masts (cable-stayed structure, Fig. 4.3);

Rice. 4.3. Piping with suspension rods (cable-stayed structure)

On brackets.

Layers of the first type are most rational for pipelines with a diameter of 500 mm and more. In this case, pipelines of larger diameter can be used as load-bearing structures for laying or suspending several small-diameter pipelines to them, requiring more frequent installation of supports.

It is advisable to use gaskets on an overpass with a continuous deck for passage only with a large number of pipes (at least 5 - 6 pcs.), And also if it is necessary to regularly monitor them. In terms of construction cost, the overpass is the most expensive and requires the highest metal consumption, since trusses or beam decking are usually made of rolled steel.

The laying of the third type with a suspended (cable-stayed) superstructure is more economical, since it can significantly increase the distance between the masts and thereby reduce the consumption of building materials. The most simple constructive forms of the suspension gasket are obtained with pipelines of equal or similar diameters.

When laying pipelines of large and small diameters together, a slightly modified cable-stayed structure with girders from channels suspended on rods is used. The girders allow the installation of pipe supports between the masts. However, the possibility of laying pipelines on racks and with a suspension on rods in urban conditions is limited and is applicable only in industrial areas. The most widely used is the laying of water pipelines on free-standing masts and supports or on brackets. Masts and supports are usually made of reinforced concrete. Metal masts are used in exceptional cases with a small amount of work and reconstruction of existing heating networks.

According to their purpose, masts are divided into the following types:

§ for movable supports of pipelines (so-called intermediate);

§ for fixed supports of pipelines (anchor), as well as those installed at the beginning and at the end of the route section;

§ tracks installed at bends;

§ serving to support the expansion joints of pipelines.

Depending on the number, diameter and purpose of the pipelines to be laid, the masts are made of three different design forms: single-column, two-column and four-column spatial structures.

When designing air gaskets, one should strive to increase the distance between the masts as much as possible.

However, for unimpeded water flow when pipelines are turned off, the maximum deflection should not exceed

f = 0,25∙i∙l,

where f- pipeline deflection in the middle of the span, mm; i - the slope of the pipeline axis; l- distance between supports, mm.

Precast concrete masts are usually assembled from the following elements: posts (columns), girders and foundations. The dimensions of the prefabricated parts are determined by the number and diameter of the pipelines to be laid.

When laying from one to three pipelines, depending on the diameter, single-column freestanding masts with consoles are used; they are also suitable for cable-stayed suspension of pipes on rods; then a top device is provided for attaching the rods.

Solid rectangular masts are acceptable if the maximum cross-sectional dimensions do not exceed 600 x 400 mm. For large dimensions, to facilitate the structure, it is recommended to provide cutouts along the neutral axis or to use prefabricated centrifuged reinforced concrete pipes as racks.

For multi-tube mast gaskets intermediate supports most often they are designed with two-rack structures, single-tier or two-tier.

Prefabricated two-post masts consist of the following elements: two posts with one or two consoles, one or two crossbars and two glass-type foundations.

The masts, on which the pipelines are fixed motionlessly, experience the load from the horizontally directed forces transmitted by the pipelines, which are laid at a height of 5 - 6 m from the ground surface. To increase stability, such masts are designed in the form of a four-post spatial structure, which consists of four posts and four or eight crossbars (with a two-tiered pipeline arrangement). The masts are installed on four separate glass-type foundations.

When laying large-diameter pipelines above ground, the bearing capacity of the pipes is used, and therefore no superstructure is required between the masts. The suspension of large-diameter pipelines on rods should also not be used, since such a structure will practically not work.

Fig.4.4 As an example, the laying of pipelines on reinforced concrete masts is shown (Fig.4.4).

Two pipelines (direct and return) with a diameter of 1200 mm are laid on roller supports on reinforced concrete masts installed every 20 m. The height of the masts from the ground surface is 5.5 - 6 m. Prefabricated reinforced concrete masts consist of two foundations connected by a monolithic joint, two columns of rectangular cross-section 400 x 600 mm and a crossbar.

Rice. 4.4. Laying of pipelines on reinforced concrete masts:

1 - column; 2 - crossbar; 3 - communication; 4 - foundation; 5 - connecting joint; 6 - concrete preparation.

The columns are connected by metal diagonal ties made of angle steel. The connection of the ties with the columns is made with gussets welded to the embedded parts, which are embedded in the columns. The crossbar, which serves as a support for the pipelines, is made in the form of a rectangular beam with a cross section of 600 x 370 mm and is attached to the columns by welding embedded steel sheets.

The mast is designed for the weight of the pipe span, horizontal axial and lateral forces arising from the friction of the pipelines on the roller bearings, as well as for the wind load.

Rice. 4.5. Fixed support:

1 - column; 2 - transverse crossbar; 3 - longitudinal transom; 4 - transverse connection; 5 - longitudinal connection; 6 - foundation

The fixed support (Fig. 4.5), designed for a horizontal force from two pipes of 300 kN, is made of prefabricated reinforced concrete parts: four columns, two longitudinal girders, one transverse support girder and four foundations connected in pairs.

In the longitudinal and transverse directions, the columns are connected by metal diagonal ties made of angle steel. On the supports, the pipelines are fixed with clamps covering the pipes and gussets in the lower part of the pipes, which abut against a metal frame made of channels. This frame is attached to the reinforced concrete girders by welding to the embedded parts.

The laying of pipelines on low supports found wide application during the construction of heating networks on the unplanned territory of the areas of new urban development. It is more expedient to cross rugged or swampy areas, as well as small rivers in this way, using the bearing capacity of the pipes.

However, when designing heating networks with laying pipelines on low supports, it is necessary to take into account the time frame for the planned development of the territory occupied by the route for urban development. If in 10-15 years it is necessary to conclude pipelines in underground channels or to reconstruct a heating network, then the use of air laying is impractical. To substantiate the application of the method of laying pipelines on low supports, technical and economic calculations must be performed.

When laying pipelines of large diameters (800-1400 mm) above ground, it is advisable to lay them on free-standing masts and supports using special prefabricated reinforced concrete structures of factory production that meet the specific hydrogeological conditions of the heating main line.

Design experience shows the cost-effectiveness of using pile foundations for foundations of both anchor and intermediate masts and low supports.

Large-diameter elevated heating mains (1200-1400 mm) of considerable length (5-10 km) were built according to individual projects using high and low supports on a pile foundation.

There is experience in the construction of a heating main with pipe diameters D y= 1000 mm from the thermal power plant with the use of rack piles on swampy sections of the route, where rocky soils lie at a depth of 4-6 m.

Calculation of supports on a pile foundation for the combined action of vertical and horizontal loads is carried out in accordance with SNiP II-17-77 "Pile foundations".

When designing low and high supports for laying pipelines, the structures of unified prefabricated reinforced concrete free-standing supports designed for technological pipelines can be used [3].

The project of low supports of the "swinging" type of foundations, consisting of a reinforced concrete vertical shield installed on a flat foundation slab, was developed by AtomTEP. These supports can be used in various soil conditions (with the exception of heavily watered and subsiding soils).

One of the most common types of air-laying pipelines is laying the latter on brackets that are reinforced in the walls of buildings. The use of this method can be recommended when laying heating networks on the territory of industrial enterprises.

When designing pipelines located on the outer or inner surface of the walls, you should choose such an arrangement of pipes so that they do not cover window openings, do not interfere with the placement of other pipelines, equipment, etc. The most important thing is to ensure that the brackets are securely fastened to the walls of existing buildings. The design of pipelines on the walls of existing buildings should include a survey of the walls in nature and a study of the projects on which they were built. With significant loads transmitted by pipelines to the brackets, it is necessary to calculate the overall stability of the building structures.

The pipelines are laid on brackets with welded sliding support bodies. The use of roller movable supports for external laying of pipelines is not recommended due to the difficulty of their periodic lubrication and cleaning during operation (without which they will work as sliding ones).

In the case of insufficient reliability of the walls of the building, constructive measures should be taken to disperse the forces transmitted by the brackets by reducing spans, installing struts, vertical struts, etc. Brackets installed in places where fixed supports of pipelines are installed should be performed according to the calculation of the forces acting on them. Usually they require additional fastening by means of struts in the horizontal and vertical planes. In fig. 4.6 is given typical design brackets for laying one or two pipelines with a diameter of 50 to 300 mm.

Rice. 4.6. Laying of pipelines on brackets.

Pipelines heating networks can be laid on the ground, in the ground and above the ground. With any method of installing pipelines, it is necessary to ensure the greatest reliability of the heat supply system at the lowest capital and operating costs.

Capital expenditures are determined by the cost of construction and installation work and the cost of equipment and materials for laying the pipeline. V operational include the costs of servicing and maintaining pipelines, as well as costs associated with heat loss in pipelines and electricity consumption along the entire route. Capital costs are mainly determined by the cost of equipment and materials, while operating costs are determined by the cost of heat, electricity and repairs.

The main types of pipeline laying are underground and aboveground. Underground laying pipelines are the most common. It is subdivided into laying pipelines directly in the ground (channelless) and in channels. When laid on the ground, the pipelines can be on the ground or above the ground at such a level that they do not obstruct the movement of vehicles. Above ground pads are used on suburban highways at the intersection of ravines, rivers, railways and other structures.

Overhead gaskets pipelines in channels or trays located on the surface of the earth or partially buried, are used, as a rule, in areas with permafrost soils.

The method of installing pipelines depends on the local conditions of the object - purpose, aesthetic requirements, the presence of complex intersections with structures and communications, soil category - and should be taken on the basis of technical and economic calculations possible options... The minimum capital costs are required for the installation of a heating main using underground pipe laying without insulation and channels. But significant losses of thermal energy, especially in wet soils, lead to significant additional costs and to premature failure of pipelines. In order to ensure the reliability of the operation of heat pipelines, it is necessary to use their mechanical and thermal protection.

Mechanical protection pipes when installing pipes underground can be ensured by arranging channels, and thermal protection - by confusing the use of thermal insulation applied directly to the outer surface of the pipelines. Insulating pipes and laying them in channels increase the initial cost of the heating main, but quickly pay off during operation by increasing operational reliability and reducing heat losses.

Underground pipelines.

When installing pipelines of heating networks underground, two methods can be used:

1. Direct laying of pipes in the ground (channelless).
2. Laying of pipes in channels (duct).

Laying of pipelines in channels.

In order to protect the heat conductor from external influences, and to ensure free thermal elongation of the pipes, channels are intended. Depending on the number of heat pipelines laid in one direction, non-passable, semi-passable or pass-through channels are used.

To secure the pipeline, as well as to ensure free movement at temperature extensions, the pipes are laid on supports. To ensure the outflow of water, the trays are stacked with a slope of at least 0.002. Water from the lower points of the trays is removed by gravity into the drainage system or from special pits using a pump is pumped into the sewer.

In addition to the longitudinal slope of the trays, the floors should also have a transverse slope of the order of 1-2% to remove flood and atmospheric moisture. At a high level of groundwater, the outer surface of the walls, ceilings and the bottom of the channel is covered with waterproofing.

The depth of laying the trays is taken from the condition of the minimum volume of earthworks and the uniform distribution of concentrated loads on the overlap during the movement of vehicles. The soil layer above the canal should be about 0.8-1.2 m and no less. 0.6 m in places where traffic is prohibited.

Non-passable channels they are used for a large number of pipes of small diameter, as well as for two-pipe laying for all diameters. Their design depends on the moisture content of the soil. In dry soils, the most widespread are block channels with concrete or brick walls or reinforced concrete single or multi-cell.

The channel walls can be 1/2 brick (120 mm) thick for small-diameter pipelines and 1 brick (250 mm) for large-diameter pipelines.

The walls are erected only from ordinary bricks of a grade not lower than 75. Due to its low frost resistance, silicate bricks are not recommended to be used. The channels are covered with a reinforced concrete slab. Brick channels, depending on the category of soil, have several varieties. In dense and dry soils, the bottom of the canal does not require concrete preparation; it is enough to compact the crushed stone directly into the ground. In soft soils, an additional reinforced concrete slab is laid on the concrete base. At a high level of standing groundwater, drainage is provided for their removal. The walls are erected after the installation and insulation of pipelines.

For pipelines of large diameters, channels are used that are assembled from standard reinforced concrete elements of the trough type KL and KLs, as well as from prefabricated reinforced concrete slabs KS.

KL type ducts consist of standard trough elements covered with flat reinforced concrete slabs.

KLs type channels consist of two trough elements, stacked on top of each other and connected on a cement mortar using an I-beam.

In channels of the KS type Wall panels They are installed in the grooves of the bottom plate and poured with concrete. These channels are covered with flat reinforced concrete slabs.

The foundations of all types of canals are made of concrete slabs or sand-preparation, depending on the type of soil.

Along with the channels discussed above, their other types are also used.

Vaulted channels consist of reinforced concrete vaults or shells of a semicircular shape, which cover the pipeline. At the bottom of the trench, only the base of the channel is made.

For large-diameter pipelines, a vaulted two-cell channel with a dividing wall is used, while the arch of the channel is formed from two semi-vaults.

When installing a no-pass channel, intended for laying in wet and soft soils, the walls and bottom of the channel are made in the form of a reinforced concrete trough-shaped tray, and the overlap consists of prefabricated reinforced concrete slabs. The outer surface of the tray (walls and bottom) is covered with waterproofing from two layers of roofing material on bitumen mastic, the surface of the base is also covered with waterproofing, then the tray is installed or concreted. Before backfilling the trench, the waterproofing is protected with a special wall made of brick.

Replacing pipes that have failed, or repairing thermal insulation in such channels is possible only when developing groups, and sometimes disassembling the pavement. Therefore, the heating network in non-passable canals is routed along lawns or on the territory of green plantations.

Semi-bore channels. In difficult conditions of intersection of existing underground devices by heat pipelines (under the carriageway, with a high level of groundwater standing), semi-through channels are arranged instead of impassable ones. Semi-bore ducts are also used with a small number of pipes in those places where, according to the operating conditions, the opening of the passable part is excluded. The height of the semi-passage channel is taken equal to 1400 mm. The channels are made of prefabricated reinforced concrete elements. The designs of semi-through and through channels are practically the same.

Pass-through channels used in the presence of a large number of pipes. They are laid under the bridges of large highways, in the territories of large industrial enterprises, in areas adjacent to the buildings of thermal power plants. Along with heat pipelines, other underground communications are also located in the passage channels - electric cables, telephone cables, water supply, gas pipeline, etc. The collectors provide free access for service personnel to the pipelines for inspection and elimination of the accident.

Passage ducts must have natural ventilation with a threefold air exchange, providing an air temperature of no more than 40 ° C, and lighting. The entrances to the passage channels are arranged every 200 - 300 m. In the places where the stuffing box expansion joints are located, designed for the perception of thermal elongations, locking devices and other equipment, special niches and additional hatches are arranged. The height of the passage ducts must be at least 1800 mm.

Their designs are of three types - from ribbed slabs, from frame structure links and from blocks.

Passage channels made of ribbed slabs, are made of four reinforced concrete panels: a bottom, two walls and a floor slab, pre-fabricated on rolling mills. The panels are bolted together and the outer surface of the channel ceiling is covered with insulation. Channel sections are installed on a concrete slab. The weight of one section of such a channel with a section of 1.46x1.87 m and a length of 3.2 m is 5 tons, the entrances are arranged every 50 m.

Passage channel made of reinforced concrete links of the frame structure, the top is covered with insulation. Channel elements have a length of 1.8 and 2.4 m and are of normal and increased strength when deepened, respectively, up to 2 and 4 m above the ceiling. The reinforced concrete slab is placed only under the joints of the links.

The next view is collector made of reinforced concrete blocks three types: L-shaped wall, two floor slabs and a bottom. The blocks at the joints are connected with monolithic reinforced concrete. These collectors are also made normal and reinforced.

Channelless laying.

In case of channelless laying, reinforced thermal insulation - a shell - protects pipelines from mechanical influences.

Merits channelless pipelines are: a relatively low cost of construction and installation work, a decrease in the volume of earthworks and a reduction in construction time. To her disadvantages include: the complication of repair work and the difficulty of moving pipelines, clamped by soil. Channelless pipelines are widely used in dry sandy soils. It finds application in wet soils, but with an obligatory device in the zone of the location of drainage pipes.

Movable supports are not used for channelless pipelines. Pipes with thermal insulation are laid directly on a sand cushion located on the pre-leveled bottom of the trench. A sand pillow, which is a bed for pipes, has the best elastic properties and allows the greatest uniformity of temperature movements. In soft and clayey soils, the layer of sand at the bottom of the trench should be at least 100-150 mm thick. Fixed supports for channelless pipe laying are reinforced concrete walls installed perpendicular to the heat conductors.

Compensation of thermal displacements of pipes in any way of their channelless laying is provided with the help of bent or stuffing box expansion joints installed in special niches or chambers.

At the turns of the track, in order to avoid trapping the pipes in the ground and ensuring possible movements, impassable channels are arranged. At the points of intersection of the wall dripping with the pipeline, as a result of uneven settlement of the soil and the base of the channel, the greatest bending of the pipelines occurs. To avoid pipe bending, it is necessary to leave a gap in the wall hole, filling it with an elastic material (for example, asbestos cord). Thermal insulation of the pipe includes an insulating layer of autoclaved concrete with a bulk density of 400 kg / m3, with steel reinforcement, a waterproofing coating consisting of three layers of brizol on a bitumen-rubber mastic, which contains 5-7% crumb rubber and a protective layer made of asbestos-cement plaster on a steel mesh.

The return lines of pipelines are insulated in the same way as the supply lines. However, the presence of isolation of the return lines depends on the diameter of the pipes. With a pipe diameter of up to 300 mm, an insulation device is mandatory; with a pipe diameter of 300-500 mm, the insulation device should be determined by the technique by an economic calculation based on local conditions; with a pipe diameter of 500 mm or more, an insulation device is not provided. With such insulation, pipelines are laid directly on the leveled compacted soil of the trench base.

To lower the groundwater level, special drainage pipelines are provided, which are laid at a depth of 400 mm from the bottom of the channel. Depending on the operating conditions, drainage devices can be made of various pipes: for gravity drainages, ceramic concrete and asbestos-cement are used, and for pressure - steel and cast iron.

Drainage pipes are laid with a slope of 0.002-0.003. When cornering and when there are differences in the level of pipes, special inspection wells are arranged according to the sewer type.

Aboveground laying of pipelines.

If we proceed from the convenience of installation and maintenance, laying pipes above the ground is more profitable than laying underground. It also requires less material costs. However, this will impair appearance environment and therefore this type of pipe laying can not be used everywhere.

Supporting structures with overhead laying of pipelines serve: for small and medium diameters - overhead supports and masts, ensuring the location of pipes at the required distance from the surface; for pipelines of large diameters, as a rule, trestle supports. Supports are usually made of reinforced concrete blocks. Masts and ramps can be either steel or reinforced concrete. The distance between the supports and the masts for overhead laying should be equal to the distance between the supports in the channels and depends on the diameters of the pipelines. In order to reduce the number of masts, intermediate supports are arranged using guy wires.

When laying above ground, thermal elongations of pipelines are compensated by using bent expansion joints, which require minimal maintenance time. The valves are serviced from specially arranged sites. Roller supports should be used as movable ones, creating minimal horizontal forces.

Also, when laying above-ground pipelines, low supports can be used, which can be made of metal or low concrete blocks. At the intersection of such a route with footpaths, special bridges are installed. And at the intersection with highways - either they perform a compensator of the required height or a channel is laid under the road for the passage of pipes.

Section Contents

Heat networks are divided into underground and aboveground (air) by the way they are laid. Underground laying of pipelines of heating networks is carried out: in channels of non-through and semi-through cross-sections, in tunnels (through channels) with a height of 2 m or more, in common collectors for joint laying of pipelines and cables for various purposes, in intra-quarter collectors and technical undergrounds and corridors, without channels.

Above-ground laying of pipelines is carried out on free-standing masts or low supports, on overpasses with a solid span, on masts with pipes suspended on rods (cable-stayed structure) and on brackets.

A special group of structures includes special structures: bridge crossings, underwater crossings, tunnel crossings and crossings in cases. These structures, as a rule, are designed and built according to separate projects with the involvement of specialized organizations.

The choice of the method and structures for laying pipelines is determined by many factors, the main of which are: the diameter of the pipelines, the requirements for the operational reliability of heat pipelines, the efficiency of structures and the method of construction.

When placing the route of heating networks in areas of existing or prospective urban development, for architectural reasons, underground pipelines are usually taken. In the construction of underground heating networks, the most widely used is the laying of pipelines in non-through and semi-through channels.

The duct design has a number of positive properties that meet the specific operating conditions of hot pipelines. Channels are a building structure that encloses pipelines and thermal insulation from direct contact with the ground, which exerts both mechanical and electrochemical effects on them. The design of the channel completely relieves the pipelines from the action of the soil mass and temporary transport loads, therefore, when calculating their strength, only stresses arising from the internal pressure of the coolant, its own weight and temperature elongations of the pipeline are taken into account, which can be determined with a sufficient degree of accuracy.

Laying in the channels provides free temperature movement of pipelines both in the longitudinal (axial) and transverse directions, which allows using their self-compensating ability in the corner sections of the heating network route.

The use of the natural flexibility of pipelines for self-compensation during duct laying makes it possible to reduce the number or completely abandon the installation of axial (stuffing box) expansion joints that require the construction and maintenance of chambers, as well as bent expansion joints, the use of which is undesirable in urban conditions and leads to an increase in pipe costs by 8 15%.

The design of the channel laying is universal, since it can be applied under various hydrogeological soil conditions.

With sufficient tightness of the building structure of the canal and properly working drainage devices, conditions are created that prevent the penetration of surface and ground water into the canal, which ensures that the thermal insulation is not humidified and protects the outer surface of steel pipes from corrosion. The route of heating networks laid in canals (as opposed to channelless ones) can be chosen without significant difficulties along the road and impassable territory of the city together with other communications, bypassing or with a slight approximation to existing structures, as well as taking into account various planning requirements (perspective changes in the terrain, the purpose of the territory, etc.).

One of the positive properties of duct laying is the possibility of using lightweight materials (products made of mineral wool, fiberglass, etc.) with a low coefficient of thermal conductivity as suspended thermal insulation of pipelines, which makes it possible to reduce heat losses in networks.

In terms of performance, the laying of heating networks in non-through and semi-through channels has significant differences. Impassable channels, inaccessible for inspection without opening the pavement, excavating the soil and disassembling the building structure, do not allow detecting damage to the thermal insulation and pipelines, as well as prophylactically eliminating them, which leads to the need for repair work at the time of emergency damage.

Despite the disadvantages, laying in non-passable channels is a common type of underground laying of heating networks.

In semi-bore ducts, accessible for the passage of operating personnel (with disconnected heat pipelines), inspection and detection of damage to thermal insulation, pipes and building structures, as well as their current repairs, can in most cases be performed without breaking and disassembling the duct, which significantly increases the reliability and service life heating networks. However, the internal dimensions of semi-passable channels exceed the dimensions of non-passable channels, which naturally increases their construction cost and material consumption. Therefore, semi-through channels are mainly used when laying pipelines of large diameters or in certain sections of heating networks when the route passes through an area that does not allow for the production of openings, as well as at a great depth of channeling, when the backfill over the overlap exceeds 2.5 m.

As operating experience shows, large-diameter pipelines laid in non-passable channels, inaccessible for inspection and maintenance, are most susceptible to accidental damage due to external corrosion. These damages lead to a prolonged cessation of heat supply to entire residential areas and industrial enterprises, the production of emergency recovery work, disruption of traffic, disruption of landscaping, which is associated with high material costs and danger for operating personnel and the population. The damage caused by damage to large pipelines is not comparable to damage to medium and small pipelines.

Considering that the rise in the cost of construction of single-cell semi-passable ducts in comparison with non-passable ducts with a heating network diameter of 800 - 1200 mm is insignificant, their use should be recommended in all cases and along the entire length of heating mains of the indicated diameters. When recommending the laying of large-diameter pipelines in semi-bore ducts, one cannot fail to note their advantages over non-bore ducts in terms of maintainability, namely the ability to replace worn out pipelines in them over a considerable length without breaking and disassembling the building structure using closed way installation work.

The essence of the closed method for replacing worn-out pipelines is to remove them from the channel by horizontal movement simultaneously with the installation of new insulated pipelines using a jack.

The need for the construction of tunnels (passage channels) arises, as a rule, at the head sections of the main heating networks departing from large CHP plants, when it is necessary to lay a large number of pipelines hot water and a couple. In such heating tunnels, the laying of cables of high and low currents is not recommended due to the practical impossibility of creating the required constant temperature regime in it.

Heating tunnels are mainly constructed on transit sections of large-diameter pipelines from CHP plants located on the outskirts of the city, when above-ground pipelines cannot be allowed for architectural and planning reasons.

Tunnels should be located in the most favorable hydrogeological conditions in order to avoid the installation of deeply located associated drainage and drainage pumping stations.

Common collectors, as a rule, should be provided in the following cases: if it is necessary to simultaneously place two-pipe heating networks with a diameter of 500 to 900 mm, a water supply system with a diameter of up to 500 mm, communication cables 10 pcs. and more, electric cables with voltage up to 10 kV in the amount of 10 pcs. and more; during the reconstruction of city highways with a developed underground economy; with a lack of free space in the cross-section of the streets for placing networks in trenches; at intersections with main streets.

In exceptional cases, as agreed with the customer and operating organizations, it is allowed to lay pipelines with a diameter of 1000 mm and water lines up to 900 mm, air ducts, refrigeration lines, circulating water supply pipelines and others in the collector. engineering networks... The laying of gas pipelines of all types in common urban collectors is prohibited [1].

Common collectors should be laid along city streets and roads in a straight line, parallel to the axis of the carriageway or the red line. It is advisable to place collectors on technical strips and under strips of green spaces. The longitudinal profile of the collector must ensure the gravity drainage of emergency and ground water. The slope of the collector tray should be taken at least 0.005. The collector depth must be assigned taking into account the depth of the intersected communications and other structures, the bearing capacity of the structures and temperature regime inside the manifold.

When deciding on the laying of pipelines in a tunnel or collector, one should take into account the possibility of ensuring the drainage and emergency waters from the collector to existing storm water and natural water bodies. The placement of the collector in the plan and profile in relation to buildings, structures and parallel lines of communications should ensure the possibility of carrying out construction work without violating the strength, stability and working condition of these structures and communications.

Tunnels and collectors located along city streets and roads, as a rule, are constructed in an open way using standard precast concrete structures, the reliability of which must be checked taking into account the specific local conditions of the route (characteristics of hydrogeological conditions, traffic loads, etc.).

Depending on the number and type of engineering networks laid together with pipelines, a common collector can be one- or two-section. The choice of the design and internal dimensions of the collector should also be made depending on the availability of the communications to be laid.

The design of common collectors should be carried out in accordance with the scheme of their construction for the future, drawn up taking into account the main provisions of the master plan for the development of the city for the estimated period. When building new areas with green streets and free planning of residential buildings heating network together with other underground networks, they are placed outside the carriageway - under technical strips, strips of green spaces, and in exceptional cases - under sidewalks. It is recommended to place engineering underground networks in undeveloped areas near the right-of-way of streets and roads.

The laying of heating networks on the territory of newly built areas can be carried out in collectors constructed in residential quarters and microdistricts for the placement of utilities serving this development [2], as well as in technical undergrounds and technical corridors of buildings.

Laying of distribution heating networks with a diameter of up to D y 300 mm in technical corridors or basements of buildings with a clear height of at least 2 m is allowed, provided that their normal operation is possible (ease of maintenance and repair of equipment). The pipelines must be laid on concrete supports or brackets, and the compensation for thermal expansion is carried out by means of U-shaped bent expansion joints and corner pipe sections. Technical undergrounds should have two entrances that are not connected to the entrances to the living quarters. Electrical wiring should be carried out in steel pipes, and the design of the luminaires should exclude access to lamps without special devices. It is forbidden to arrange storage or other premises in the places where the pipeline passes. The laying of heating networks in microdistricts along routes coinciding with other engineering communications should be combined in common trenches with the placement of pipelines in channels or without channels.

The method of overhead (aerial) laying of heating networks has limited application in the conditions of the existing and future development of the city due to the architectural and planning requirements for structures of this type.

Above-ground pipelines are widely used on the territory of industrial zones and individual enterprises, where they are placed on racks and masts together with industrial steam pipelines and technological pipelines, as well as on brackets fixed on the walls of buildings.

The above-ground method of laying has a significant advantage over the underground method during the construction of heating networks in areas with a high level of groundwater standing, as well as in collapsing soils and in permafrost regions.

It should be taken into account that the design of thermal insulation and the actual pipelines during air laying are not subjected to the destructive action of soil moisture, and therefore their durability is significantly increased and heat losses are reduced. The cost-effectiveness of the above-ground laying of heating networks is also essential. Even with favorable soil conditions, in terms of the cost of capital costs and the consumption of building materials, air laying of pipelines of medium diameters is more economical than underground laying in channels by 20 - 30%, and with large diameters - by 30 - 40%.

In connection with the increased design and construction of suburban CHP and nuclear heating plants (AST) for centralized heat supply in large cities, the issues of increasing the operational reliability and durability of transit heating mains of large diameter (1000-1400 mm) and the length, while reducing their metal consumption and the consumption of material resources. The existing experience in the design, construction and operation of overground heating mains of large diameter (1200-1400 mm) with a length of 5-10 km gave positive results, which indicates the need for their further construction. It is especially advisable to lay aboveground heating mains under unfavorable hydrogeological conditions, as well as on sections of the route located on undeveloped territory, along highways and at the intersection of small water barriers and ravines.

When choosing methods and structures for laying heating networks, special construction conditions in areas should be taken into account: with seismicity of 8 points or more, the spread of permafrost and subsidence from soaking of soils, as well as in the presence of peat and silty soils. Additional requirements for heating networks in special construction conditions are set out in SNiP 2.04.07-86 *.