Methods for laying pipelines for heating networks. Designs for overhead installation of heating networks. Aboveground installation of pipelines

Pipelines Heating networks can be laid on the ground, in the ground and above the ground. With any method of pipeline installation, 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 costs of equipment and materials for laying the pipeline. IN 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 determined mainly by the cost of equipment and materials, and operating costs are determined mainly by the cost of heat, electricity and repairs.

The main types of pipeline laying are underground And aboveground. Underground pipeline installation is the most common. It is divided into laying pipelines directly in the ground (channelless) and in channels. When laid above ground, pipelines can be located on the ground or above the ground at such a level that they do not interfere with the movement of traffic. Overhead gaskets are used on suburban highways when crossing ravines, rivers, railway tracks 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 facility - 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. Minimum capital costs are required for the installation of a heating main using underground laying pipes without insulation and channels. But significant losses of thermal energy, especially in wet soils, lead to significant additional costs and premature failure of pipelines. In order to ensure reliable operation of heat pipelines, it is necessary to apply mechanical and thermal protection.

Mechanical protection pipes when installing pipes underground can be provided by installing channels, and thermal protection can be achieved by using thermal insulation applied directly to the outer surface of the pipelines. Insulating pipes and laying them in channels increases the initial cost of the heating main, but quickly pays off during operation by increasing operational reliability and reducing heat losses.

Underground laying of pipelines.

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

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

Laying pipelines in channels.

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

To secure the pipeline, as well as ensure free movement during thermal expansion, the pipes are laid on supports. To ensure the outflow of water, the trays are laid 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 it is pumped into the sewer system.

In addition to the longitudinal slope of the trays, the floors must also have a transverse slope of about 1-2% to remove flood and atmospheric moisture. When the groundwater level is high, the outer surface of the walls, ceiling and bottom of the canal is covered with waterproofing.

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

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

The channel walls can have a thickness of 1/2 brick (120 mm) with pipelines not large diameter and 1 brick (250 mm) for pipelines of large diameters.

The walls are erected only from ordinary brick of a grade not lower than 75. Sand-lime brick Due to its low frost resistance, it is not recommended to use. 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 weak soils, additional iron is placed on the concrete base concrete slab. When groundwater levels are high, drainage is provided to drain them. The walls are erected after installation and insulation of the pipelines.

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

KL type channels consist of standard tray elements covered with flat reinforced concrete slabs.

KLS type channels consist of two tray elements stacked on top of each other and connected at cement mortar using an I-beam.

In KS-type channels, wall panels are installed in the grooves of the bottom slab and filled with concrete. These channels are covered with flat reinforced concrete slabs.

The bases 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, other types are also used.

Vaulted channels consist of reinforced concrete arches or semicircular shells that 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 channel arch is formed from two half-vaults.

When installing a non-passable 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 ceiling consists of prefabricated reinforced concrete slabs. The outer surface of the tray (walls and bottom) is covered with waterproofing from two layers of roofing felt on bitumen mastic, the surface of the base is also covered with waterproofing, then the tray is installed or concreted. Before filling the trench, the waterproofing is protected with a special wall made of brick.

Replacement of failed pipes or repair of thermal insulation in such channels is possible only by developing groups, and sometimes by dismantling the pavement. Therefore, the heating network in non-passable channels is routed along lawns or in green areas.

Semi-bore channels. In difficult conditions where heat pipes cross existing underground devices (under the roadway, with a high level of groundwater), semi-passable channels are installed instead of impassable ones. Semi-through channels are also used for a small number of pipes in places where, due to operating conditions, opening of the roadway is excluded. The height of the semi-bore 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 almost similar.

Passage channels used when there are a large number of pipes. They are laid under the pavements 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 located in the passage channels - electrical cables, telephone cables, water supply, gas pipelines, etc. The collectors provide free access for service personnel to the pipelines for inspection and emergency response.

Passage channels must have natural ventilation with a threefold air exchange, ensuring an air temperature of no more than 40 ° C, and lighting. Entrances to passage channels are arranged every 200 - 300 m. In places where gland expansion joints designed to absorb thermal expansion, locking devices and other equipment are located, special niches and additional hatches are installed. The height of the passage channels 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, manufactured in a factory method on rolling mills. The panels are connected with bolts, and the outer surface of the channel overlap is covered with insulation. Channel sections are installed on a concrete slab. The weight of one section of such a channel with a cross-section of 1.46x1.87 m and a length of 3.2 m is 5 tons, entrances are arranged every 50 m.

Passage channel made of reinforced concrete frame links, the top is covered with insulation. The channel elements have a length of 1.8 and 2.4 m and are of normal and increased strength when buried, 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 bottom. The blocks at the joints are connected with monolithic reinforced concrete. These collectors are also made normal and reinforced.

Channelless installation.

When laying without a channel, pipelines are protected from mechanical influences by reinforced thermal insulation - a shell.

Advantages advantages of channelless pipeline laying are: relatively low cost of construction and installation work, reduction in the volume of excavation work and reduction in construction time. To her shortcomings include: the complication of repair work and the difficulty of moving pipelines clamped by soil. Channelless pipeline laying is widely used in dry sandy soils. It is used in wet soils, but with mandatory device in the area where drainage pipes are located.

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

Compensation for thermal movements of pipes for any method of their ductless installation is ensured using bent or stuffing box compensators installed in special niches or chambers.

At the turns of the route, in order to avoid pinching the pipes in the ground and to ensure possible movements, impassable channels are installed. In places where the pipeline intersects the wall of the drip, as a result of uneven settlement of the soil and the base of the channel, the greatest bending of the pipelines occurs. To avoid bending the pipe, it is necessary to leave a gap in the hole in the wall, filling it with elastic material (for example, asbestos cord). Thermal insulation of the pipe includes an insulating layer of autoclaved concrete with a volumetric weight of 400 kg/m3, having steel reinforcement, waterproofing coating, consisting of three layers of brizol on bitumen-rubber mastic, which includes 5-7% rubber crumbs and a protective layer made of asbestos-cement plaster on a steel mesh.

Return pipelines are insulated in the same way as supply lines. However, the presence of return line insulation depends on the diameter of the pipes. For pipe diameters up to 300 mm, insulation is required; with a pipe diameter of 300-500 mm, the insulation device must be determined by the technique using an economic calculation based on local conditions; for pipes with a diameter of 500 mm or more, insulation is not provided. Pipelines with such insulation are laid directly on the leveled compacted soil of the base of the trench.

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

Drainage pipes are laid with a slope of 0.002-0.003. At turns and when there are differences in pipe levels, special inspection wells are installed, similar to sewer wells.

Overhead laying of pipelines.

Based on the ease of installation and maintenance, laying pipes above the ground is more profitable than laying them underground. It also requires less material costs. However, this will spoil the appearance environment and therefore this type of pipe laying cannot be used everywhere.

Load-bearing structures 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. The supports are usually made of reinforced concrete blocks. Masts and overpasses can be either steel or reinforced concrete. The distance between supports and masts during overhead installation should be equal to the distance between 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 using bent expansion joints, which require minimum costs time for service. Maintenance of fittings is carried out from specially arranged sites. Roller bearings should be used as moving ones, creating minimal horizontal forces.

Also, when laying pipelines above ground, low supports can be used, which can be made of metal or low concrete blocks. At the intersection of such a route with pedestrian paths install special bridges. And when crossing roads, either a compensator of the required height is installed or a channel is laid under the road for the passage of pipes.

Heat pipes are laid underground or above ground. The underground method is the main one in residential areas, since it does not clutter the area and does not deteriorate the architectural appearance of the city. The above-ground method is usually used in the territories of industrial enterprises for the joint laying of energy and process pipelines. In residential areas, the above-ground method is used only in particularly difficult conditions: permafrost soils and soils that subside during thawing, wetlands, a high density of existing underground structures, terrain heavily indented by ravines, the intersection of natural and artificial obstacles.

Underground heat pipelines are currently laid in through and non-through channels (previously used semi-through channels are no longer used) or in a channelless manner. In addition, in residential neighborhoods, distribution networks are sometimes laid in technical underground areas (corridors, tunnels) of buildings, which makes construction and operation cheaper and easier.

When laid in ducts and technical undergrounds of buildings, heat pipes are protected on all sides from mechanical influences and loads and, to some extent, from ground and surface waters. To support the heat pipe's own weight, special movable supports are installed. With ductless installation, heat pipes are in direct contact with the ground and external mechanical loads are absorbed by the pipe and the heat-insulating structure. In this case, movable supports are not installed, and the heat pipes are laid directly on the ground or a layer of sand and gravel. The cost of channelless installation is 25-30% less than in channels, but the operating conditions of heat pipelines are more difficult.

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

Channels are currently made, as a rule, from standardized prefabricated reinforced concrete parts. To protect against ground and surface water, the outer surface of the channels is covered with bitumen and covered with waterproof 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 covered trays (with slabs, gratings) are made, through which the 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 them through their outer walls, evaporates and saturates the air. When humid air cools, moisture accumulates on the ceilings and duct walls, which flows down and can cause the insulation to become moist.

The passage channels provide best conditions for operation, operation and repair of heating 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 engineering communications. When various communications are laid together, the passage channels are called collectors. They are now widespread in cities. In Fig. Figure 6.4 shows a cross-section of a typical single-section collector.

Passage channels (collectors) are equipped with natural or forced ventilation, ensuring the air temperature in the channel is not higher than 40°C during repair periods and not higher than 50°C during operation, electric lighting with a voltage of up to 30 V, and a telephone connection. To collect moisture, pits are installed at low points along the route, connected to drains or equipped with pump-out pumps with automatic or remote control.

Rice. 6.4. Cross section of a typical city sewer

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

dimensions passage channels (collectors) are selected from the condition of free access to all elements of heat pipelines, allowing for complete major renovation them without opening or destroying road surfaces. The width of the passage in the channel is taken to be at least 700 mm, and the height is at least 2 m (the height to the beam is allowed to be 1.8 m). Every 200-250 m along the route, hatches are made, equipped with ladders or brackets for descending into the canal. In areas where a large amount of equipment is located, special expansions (chambers) can be installed or pavilions can be built.

Non-pass channels are usually used for heat pipes with a diameter of up to 500-700 mm. They are made in rectangular, vaulted and cylindrical shapes from reinforced concrete slabs and vaults, asbestos-cement and metal pipes etc. In this case, as a rule, an air gap is left between the surface of the heat pipes and the walls of the channel, through which the thermal insulation dries and moisture is removed from the channels. As an example in Fig. Figure 6.5 shows a cross-section of a rectangular non-passable channel made from standardized prefabricated reinforced concrete parts.

Rice. 6.5. Sections of a non-passable channel

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

The overall dimensions of non-pass channels are selected mainly depending on the distance between the heat pipes and between the surfaces of the heat-insulating structure and channels, as well as on the condition of ensuring convenient access to the equipment in the chambers. To reduce the distance between heat pipes, equipment is sometimes installed staggered on them.

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 inclusion of dirt in the air gap in the channels and the difficulty of removing moisture from them in this case ). IN last years In connection with the increased reliability of ductless installation of heat pipelines (through the introduction of welding, more advanced thermal insulation structures, etc.), it is also beginning to be used for pipes of large diameters (500 mm or more).

Heat pipelines laid in a ductless manner are divided depending on the type of thermal insulation structure: in monolithic shells, cast (precast) and backfill (Fig. 6.6) and depending on the nature of the perception of weight loads: unloaded and unloaded.

Rice. 6.6. Types of ductless heat pipes

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

Structures in monolithic shells are usually made in factory conditions. On the route, only butt welding of individual elements and insulation of butt joints is carried out. Cast structures can be manufactured both in a factory and on the road by pouring pipes (and butt joints after crimping) with liquid initial thermal insulation materials, followed by their setting (hardening). Backfill insulation is performed on pipelines mounted in trenches and pressed from bulk materials. thermal insulation materials.

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

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

On underground heat pipelines, equipment that requires maintenance (valves, stuffing box expansion joints, drainage devices, vents, vents, etc.) is placed in special chambers, and flexible expansion joints- in niches. Chambers and niches, like channels, are constructed from prefabricated reinforced concrete elements. Structurally, the chambers are made underground or with above-ground pavilions. Underground chambers are used for pipelines of small diameters and the use of manually operated valves. Chambers with above-ground pavilions provide better service for large equipment, in particular, valves with electric and hydraulic drives, which are usually installed with pipeline diameters of 500 mm or more. In Fig. Figure 6.8 shows the design of an underground chamber.

The overall dimensions of the chambers are chosen to ensure the convenience and safety of equipment maintenance. To enter underground chambers, hatches are installed in diagonal corners - at least two for an internal area of ​​up to 6 m2 and at least four for 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 in increments of no more than 0.4 m for descending into the chambers. The bottom of the chambers is made with a slope > 0.02 to one of the corners (under the hatch), where pits for collecting water with a depth of at least 0.3 m and a plan size of 0.4x0.4 m are installed, covered with a grating on top. Water from the pits is drained by gravity or using pumps into drains or receiving wells.

Rice. 6.8. underground chamber

Aboveground heating pipes laid on free-standing supports (low and high) and masts, on overpasses with a continuous span in the form of trusses or beams and on rods attached to the tops of the masts (cable-stayed structures). In industrial enterprises, simplified gaskets are sometimes used: on consoles (brackets) on building structures and on supports (pillows) on the roofs of buildings.

Supports and masts are usually made of reinforced concrete or metal. Overpass spans and anchor posts (non-moving supports) are usually made of metal. In this case, building structures can be constructed as one-, two-, or multi-tiered.

Laying heat pipes on separate supports and masts is the simplest and is usually used with a small number of pipes (two to four). Currently, the USSR has developed standard designs free-standing low and high reinforced concrete supports, made with one post in the form of a T-shaped support and with two separate posts or frames in the form of U-shaped supports. To reduce the number of racks, large-diameter pipelines can be used as load-bearing structures for laying or hanging small-diameter pipelines from them, which require more frequent installation of supports. When laying heat pipelines on low supports, the distance between their lower generatrix and the ground surface must be at least 0.35 m for a group of pipes up to 1.5 m wide and at least 0.5 m for a group of pipes more than 1.5 m wide.

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

Laying heat pipes on suspended (cable-stayed) structures is the most economical, as it allows you to significantly increase the distance between masts and thereby reduce consumption building materials. When laying pipelines of different diameters together between masts, runs are made from channels suspended on rods. Such purlins allow the installation of additional supports for small diameter pipelines.

To service equipment (valves, stuffing box expansion joints), platforms with fences and ladders are installed: stationary at a distance from the bottom of the heat-insulating structure to the ground surface of 2.5 m or more, or mobile at a shorter distance, and in hard-to-reach places and on overpasses - walkthrough bridges. When laying heat pipelines on low supports, the ground surface should be covered with concrete at the equipment installation sites, and metal casings should be installed on the equipment.

Pipes and fittings. For the construction of heating networks, steel pipes are used, connected using 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, for local hot water supply systems, which are subject to increased corrosion, galvanized steel pipes are used. In the near future, it is planned to use enameled pipes.

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

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, and polymer and glass pipes have lower roughness compared to steel pipes. Asbestos-cement and glass pipes are connected using special designs, and polymer pipes are welded, which greatly simplifies installation and increases the reliability and tightness of connections. The main disadvantage of these non-metallic pipes is the low permissible temperatures and pressures of the coolant - approximately 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 valves used in heating networks are divided according to their intended purpose into shut-off, control, safety (protective), throttling, condensate drainage and control and measuring valves.

To the main fittings general purpose usually include 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 for heating networks are gate valves and gate valves. Valves are usually used in water networks, valves - in steam networks. 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 d y >100 mm, in branch nodes to individual buildings with d y 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 draining water, releasing air and starting drains. In addition, sectional valves are installed in water networks: for d y >100 mm through l ce kc<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.

At the installation sites of sectional valves, 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 coolant circulation in case of accidents. Two valves and a control valve between them at d y = 25 mm are installed in series on the jumper to check the tightness of the valves.

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 high torque, bypass lines (unloading bypasses) are made with shut-off valve. In this case, the valve is relieved from pressure forces when the valves open and the sealing surfaces are protected from wear. In steam networks, bypass lines are also used to start steam pipelines. Valves with d y > 500 mm, requiring a torque of more than 500 Nm to open or close, must be used with an electric drive. All valves are also equipped with an electric drive for remote control.

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

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

Operating 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 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 selection of pipe materials and fittings depending on the operating parameters of the coolant and the environment, are specified in SNiP II-36-73.

Section Contents

Based on the method of installation, heating networks are divided into underground and above-ground (air). Underground installation of heating network pipelines is carried out: in channels of non-passing and semi-through cross-section, in tunnels (passing channels) with a height of 2 m or more, in common collectors for the joint installation of pipelines and cables for various purposes, in intra-block collectors and technical undergrounds and corridors, without ducts.

Overhead installation pipelines are carried out on free-standing masts or low supports, on trestles with a continuous 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 transitions in cases. These structures, as a rule, are designed and built according to separate projects with the involvement of specialized organizations.

The choice of method and design 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 cost-effectiveness of structures and the method of construction.

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

The channel design has a number of positive properties that meet the specific operating conditions of hot pipelines. Channels are a building structure that protects pipelines and thermal insulation from direct contact with the soil, which has 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 the stresses arising from the internal pressure of the coolant, its own weight and temperature elongations of the pipeline, which can be determined with a sufficient degree of accuracy, are taken into account.

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

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

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

With sufficient tightness of the building structure of the channel and properly working drainage devices conditions are created that prevent surface and ground water from penetrating into the channel, which ensures that the thermal insulation does not get wet and protects the outer surface of steel pipes from corrosion. The route of heating networks laid in channels (as opposed to channelless) can be selected without significant difficulties along the road and non-road areas of the city together with other communications, bypassing or with a slight approach to existing structures, and also taking into account various planning requirements (prospective changes in the terrain, purpose of the territory, etc.).

One of the positive properties of channel laying is the possibility of using lightweight materials (products made of mineral wool, fiberglass, etc.) with a low thermal conductivity coefficient, which allows reducing heat losses in networks.

By performance qualities The laying of heating networks in non-through and semi-through channels has significant differences. Impassable channels that are inaccessible for inspection without opening the road surface, excavating the soil and dismantling it building structure, do not allow detection of damage to thermal insulation and pipelines, as well as preventive elimination of them, which leads to the need for repair work at the time of emergency damage.

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

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

As operating experience shows, large-diameter pipelines laid in non-passable channels inaccessible for inspection and current repairs, are most susceptible to accidental damage due to external corrosion. These damages lead to a long-term cessation of heat supply to entire residential areas and industrial enterprises, emergency restoration work, disruption of traffic, disruption of amenities, which is associated with high material costs and danger for operating personnel and the population. The damage caused by damage to large diameter pipelines cannot be compared with damage to medium and small diameter pipelines.

Considering that the increase in the cost of construction of single-cell semi-through channels compared to non-through channels with a heating network diameter of 800 - 1200 mm is insignificant, their use should be recommended in all cases and throughout the entire length of heating mains of the indicated diameters. Recommending the laying of large-diameter pipelines in semi-through channels, one cannot fail to note their advantages over non-through channels in terms of the degree of maintainability, namely the ability to replace worn out pipelines in them over a considerable distance without digging up and dismantling the building structure using closed method production of 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 jacking installation.

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

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

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

General 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, electrical cables voltage up to 10 kV in quantity of 10 pcs. and more; during the reconstruction of city highways with developed underground infrastructure; when there is insufficient free space in the cross-section of streets for placing networks in trenches; at intersections with main streets.

In exceptional cases, in agreement with the customer and operating organizations, it is allowed to lay pipelines with a diameter of 1000 mm and water pipelines up to 900 mm, air ducts, cold pipelines, recycling water supply pipelines and other utility networks in the collector. The laying of gas pipelines of all types in public city sewers is prohibited [1].

Common sewers should be laid along city streets and roads in a straight line, parallel to the axis of the roadway or red line. It is advisable to place collectors on technical strips and under green belts. The longitudinal profile of the collector must ensure gravity drainage of emergency and groundwater. The slope of the collector tray should be at least 0.005. The depth of the collector must be determined taking into account the depth of intersecting communications and other structures, the load-bearing capacity of structures and temperature regime inside the collector.

When deciding whether to lay pipelines in a tunnel or sewer, consideration should be given to the possibility of ensuring the drainage of drainage and emergency water from the sewer into existing storm drains and natural bodies of water. The placement of the collector in plan and profile in relation to buildings, structures and parallel communications should ensure the possibility of carrying out construction work without compromising the strength, stability and working condition of these structures and communications.

Tunnels and sewers located along city streets and roads are usually constructed open method using standard prefabricated reinforced concrete structures, the reliability of which must be checked taking into account the specific local conditions of the route (characteristics of hydrogeological conditions, transport loads, etc.).

Depending on the number and type of utility networks laid together with pipelines, the 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 presence of laid communications.

The design of general sewers must be carried out in accordance with the scheme for 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 constructing new areas with green streets and free-plan residential development, heating networks, together with other underground networks, are placed outside the roadway - under technical lanes, stripes of green spaces, and in exceptional cases - under sidewalks. It is recommended to place underground utility networks in undeveloped areas near the right-of-way of streets and roads.

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

Laying heating distribution networks with a diameter of up to D 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). Pipelines must be laid on concrete supports or brackets, and compensation for thermal expansions must be carried out using U-shaped bent expansion joints and corner sections of pipes. Technical underground must have two entrances that do not communicate with the entrances to residential premises. Electrical wiring must be carried out in steel pipes, and the design of the lamps must exclude access to the lamps without special devices. It is prohibited to arrange storage or other premises in the areas 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) installation of heating networks has limited application in the conditions of existing and future city development due to the architectural and planning requirements for structures of this type.

Aboveground installation of pipelines is widely used in industrial zones and individual enterprises, where they are placed on overpasses and masts together with production steam pipelines and process pipelines, as well as on brackets mounted on the walls of buildings.

The above-ground installation method has a significant advantage over the underground method when constructing heating networks in areas with high groundwater levels, as well as in subsidence soils and in permafrost areas.

It should be taken into account that the design of thermal insulation and the pipelines themselves, when laid by air, are not subject to the destructive action of ground moisture, and therefore their durability is significantly increased and heat losses are reduced. The cost-effectiveness of overhead installation of heating networks is also significant. Even under favorable soil conditions, in terms of the cost of capital costs and consumption of building materials, aerial laying of medium-diameter pipelines is 20 - 30% more economical than underground laying in channels, and for large diameters - by 30 - 40%.

In connection with the increased design and construction of suburban thermal power plants and nuclear heat supply stations (HPPs) for district heating major cities great importance issues of increasing the operational reliability and durability of transit heating mains of large diameter (1000 - 1400 mm) and length while simultaneously reducing their metal consumption and consumption of material resources are emerging. The existing experience in the design, construction and operation of large-diameter overhead heating mains (1200-1400 mm) with a length of 5-10 km has given positive results, which indicates the need for their further construction. It is especially advisable to lay heating pipelines above ground under unfavorable hydrogeological conditions, as well as on sections of the route located in undeveloped areas along highways and at the intersection of small water obstacles and ravines.

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

It is produced in non-through, through, and semi-through channels, as well as in general collectors along with other communications. Using the example of Leningrad, in recent years, channelless installation has begun to be used, which is considered the most effective. But even in this option, individual sections are laid into channels - compensation niches, turning angles, etc.

If the underground laying of heating networks is carried out in an unplanned area, local planning of the earth's surface is carried out. This is done for the purpose of draining surface water. Elements of heating networks (external surfaces of ceilings and walls of channels, chambers, etc.) are finished with coating bitumen insulation. If the installation takes place under green areas, the structures are covered with adhesive waterproofing, which is made from bitumen roll materials. Networks installed below the maximum groundwater level are equipped with associated drainage. Its diameter must be more than 150 mm.

Installation of expansion joints

Underground pipeline laying involves the installation of compensators. Installation of compensators in the design position is permitted after preliminary testing of heating networks for tightness and strength, their backfilling and underground laying of chambers, channels and panel supports.

If the heating networks being laid are installed to service shut-off brick or reinforced concrete fittings, underground chambers are installed. The main heating networks pass through the chambers. They are equipped with inserts with shut-off valves for installing branches to consumers. The height of the chamber must correspond to the safety of maintenance.

IN major cities underground pipeline laying carried out in conjunction with other engineering networks. City and intra-block tunnels are combined with water pipelines with a diameter of up to 300 mm, power cables voltage up to 10 kV and communication cables. City tunnels with pipelines compressed air with pressure up to 16 MPa are combined with pressure sewerage. Intra-block tunnels are laid together with water networks with a diameter of up to 250 mm and a gas pipeline natural gas with pressure up to 0 005 MPa and diameter no more than 150 mm. Heating networks are laid in cases or tunnels under city passages, at the intersection of large highways and under areas with modern pavement.

Underground pipeline installation can be carried out in non-passable channels.

Channelless underground installation is carried out throughout the territory of populated areas. Installation is carried out in non-passable channels together with other utility networks in city-wide or intra-block sewers. Aboveground pipeline installation is carried out at enterprise sites. Heating networks are installed on separate racks and supports. Sometimes underground installation is also allowed.

More information about underground installation of expansion joints

For channelless installation and in non-passable channels, it is carried out underground installation of bellows expansion joints in the cells. Special pavilions are not constructed when heating networks are laid on separate supports or overpasses. They are installed at fixed supports. Only one compensator is mounted between two fixed supports. Guide supports are installed before and after expansion joints. One of the guide supports must be stationary.

For aesthetic and architectural reasons, it is provided in residential areas.

When laying heating networks underground and for air installation, a crane is used. It is also used on masts, trestles, for the construction of office premises 3 floors high and above-ground pavilions of pumping stations.

In special collectors and together with other utility networks, underground pipeline laying within a populated area (city or town). Installation is carried out in semi-through, non-through and through channels directly in the ground.

All pipelines laid underground must be inspected periodically. The condition of thermal insulation, building insulation structures and the pipelines themselves are monitored. Preventative planned excavations are carried out in accordance with the schedule, at least once a year. The number of pits is determined depending on the condition of the underground gaskets and the length of the heating networks.

Laying pipes in a trench is carried out using the same mechanisms as for underground laying of heating networks. These are truck cranes, pipe layers and cranes crawler. If these mechanisms are not available or it is not possible to use them due to cramped production conditions, then the pipes can be lowered into the trench using mounting tripods, which are equipped manual winches or hoists. For pipes with a small diameter, 2 ropes are used and they are lowered into the trench manually.

The method of laying heating networks during reconstruction is chosen in accordance with the instructions of SNiP 2.04.07-86 “Heating networks”. Currently, in our country, about 84% of heating networks are laid in ducts, about 6% - ductless, the remaining 10% - above ground. The choice of one method or another is determined by local conditions, such as the nature of the soil, the presence and level of groundwater, the required reliability, cost-effectiveness of construction, as well as operating costs of maintenance. Laying methods are divided into above-ground and underground.

Aboveground laying of heating networks

Aboveground installation of heating networks is rarely used, since it disrupts the architectural ensemble of the area, has, all other things being equal, higher heat losses compared to underground installation, does not guarantee against freezing of the coolant in the event of malfunctions and accidents, and restricts passages. When reconstructing networks, it is recommended to use it at high groundwater levels, in permafrost conditions, with unfavorable terrain, in the territories of industrial enterprises, in areas free of buildings, outside the city or in places where it does not affect the architectural design and does not interferes with traffic.

Advantages of above-ground installation: accessibility of inspection and ease of operation; the ability to quickly detect and eliminate an accident in heating pipelines; absence of electrocorrosion from stray currents and corrosion from aggressive groundwater; lower cost of construction compared to the cost of underground installation of heating networks. Aboveground installation of heating networks is carried out: on separate supports (masts); on overpasses with a span in the form of purlins, trusses or suspended (cable-stayed) structures; along the walls of buildings. Free-standing masts or supports can be made of steel or reinforced concrete. For small volumes of construction of above-ground heating networks, steel masts made of profiled steel are used, but they are expensive and labor-intensive and therefore are being replaced by reinforced concrete ones. Reinforced concrete masts are especially advisable for mass construction on industrial sites, when it is cost-effective to organize their production in a factory.

For joint laying of heating networks with other pipelines for various purposes, overpasses made of metal or reinforced concrete are used. Depending on the number of simultaneously laid pipelines, the spans of overpasses can be single-tiered or multi-tiered. Heat pipelines are usually laid on the lower tier of the overpass, while pipelines with a higher coolant temperature are placed closer to the edge, thereby providing a better location U-shaped expansion joints having different sizes. When laying heating mains on the territory of industrial enterprises, the method of above-ground installation on brackets fixed in the walls of buildings is also used. The span of heat pipes, i.e. the distances between the brackets are chosen taking into account the load-bearing capacity of the building structures.

Underground laying of heating networks

In cities and towns, heating mains are mainly laid underground, which does not spoil the architectural appearance, does not interfere with traffic and reduces heat loss by using the heat-shielding properties of the soil. Soil freezing is not dangerous for heating pipelines, so they can be laid in the zone of seasonal soil freezing. The shallower the depth of the heating network, the smaller the volume of excavation work and the lower the cost of construction. Underground networks most often laid at a depth of 0.5 to 2 m and below the surface of the earth.

The disadvantages of underground heating pipes are: the danger of moisture and destruction of insulation due to exposure to ground or surface water, which leads to a sharp increase in heat losses, as well as the danger of external corrosion of pipes due to the influence of stray electric currents, moisture and aggressive substances contained in the soil. Underground installation of heat pipelines involves the need to open up streets, driveways and courtyards.

Structurally, underground heating networks are divided into two fundamentally various types: ducted and ductless.

The design of the channel completely unloads heat pipelines from the mechanical impact of the soil mass and temporary transport loads and protects pipelines and thermal insulation from the corrosive influence of the soil. Laying in channels ensures free movement of pipelines during temperature deformations in both the longitudinal (axial) and transverse directions, which allows the use of their self-compensating ability in corner sections of the route.

Laying in passage channels (tunnels) is the most advanced method, since this ensures constant access for service personnel to pipelines to monitor their operation and carry out repairs, which in the best possible way ensures their reliability and durability. However, the cost of laying in passage channels is very high, and the channels themselves have large dimensions (clear height - at least 1.8 m and passage - 0.7 m). Pass-through channels are usually installed when laying a large number of pipes laid in one direction, for example, at the outlets from a thermal power plant.

Along with installation in non-passable channels, channelless installation of heat pipes is becoming increasingly popular. Refusal to use channels when laying heating networks is very promising and is one of the ways to reduce their cost. However, in channelless laying, the thermally insulated pipeline, due to direct contact with the ground, is subject to more active physical and mechanical influences (soil moisture, soil pressure and external loads, etc.) than in channel laying. Channelless installation is possible using a mechanically strong thermal and waterproofing shell that can protect pipelines from heat loss and withstand loads transmitted by the soil. Heating networks with pipe diameters up to 400 mm inclusive are recommended to be laid primarily using a ductless method.

Among channelless gaskets, progressive gaskets using reinforced foam concrete, bitumen perlite, asphalt expanded clay concrete, phenolic foam, polyurethane foam, polyurethane foam and other thermal insulation materials as monolithic thermal insulation have become most widespread in recent years. Ductless installations of heating networks continue to improve and are becoming increasingly widespread in construction and reconstruction practice. When reconstructing intra-block heating mains, there are more ample opportunities laying networks along basements than with new construction, since the construction of new sites often precedes the construction of buildings.

Installation of heating networks, laying pipes

Installation of pipelines and installation of thermal insulation on them is carried out using pre-insulated polyurethane foam pipes, shaped products in polyurethane foam insulation (fixed supports, tees and tee branches, transitions, end elements and intermediate elements, etc.), as well as polyurethane foam shells. Thermal insulation of straight sections, branches, pipeline elements, sliding supports, ball valves is being installed, as well as butt joints are being installed using heat-shrinkable sleeves, heat-shrinkable tape, polyurethane foam components, galvanized casings and heat-insulating polyurethane foam shells.

Laying heating networks and installing polyurethane foam insulation is carried out in several stages - preparatory stage (excavation, delivery of polyurethane foam pipes and elements to the route, inspection of products), laying of pipelines (installation of pipes and elements), installation of UEC system devices and installation of butt joints.

The depth of laying polyurethane foam pipes when laying heating networks should be taken into account the difference in density between the polyurethane foam steel pipe and the thermal insulation layer of polyurethane foam, as well as heat transfer standards and normatively permissible heat losses.

The development of trenches for channelless installation should be carried out mechanically in compliance with the requirements of SNiP 3.02.01 - 87 "Earth structures".

The minimum depth for laying polyurethane foam pipes in a polyethylene shell when laying heating mains in the ground should be at least 0.5 m outside the roadway and 0.7 m within the roadway, counting to the top of the thermal insulation.

The maximum depth of laying thermally insulated pipes when installing pipelines in polyurethane foam insulation when laying heating networks should be determined by calculation taking into account the stability of the polyurethane foam layer under static load.

Installation of polyurethane foam pipes is usually carried out at the bottom of the trench. It is allowed to weld straight sections in the section at the edge of the trench. Installation of polyurethane foam pipes in a polyethylene sheath is carried out at outdoor temperatures down to -15 ... -18°C.

Steel pipes are cut (if necessary) using a gas cutting machine, and the thermal insulation is removed using a mechanized machine. hand tools on a section 300 mm long, and the ends of the thermal insulation during cutting of steel pipes are covered with a moistened cloth or a rigid screen to protect the thermal insulation layer of polyurethane foam.

Welding of pipe joints and inspection of welded connections of pipelines during the installation of polyurethane foam pipes should be carried out in accordance with the requirements of SNiP 3.05.03-85 "Heat networks", VSN 29-95 and VSN 11-94.

When performing welding work, it is necessary to protect the polyurethane foam insulation and polyethylene sheath, as well as the ends of the wires coming out of the insulation, from sparks.

When using a heat-shrinkable sleeve as protection for a welded joint, it is put on the pipeline before the start of welding work. When sealing a joint using a fill joint or a polyurethane foam shell joint, where a galvanized casing and heat-shrink tape are used as a protective layer, pipe welding is carried out regardless of the availability of materials for sealing the joints.

Before the construction of a heating main during ductless pipe laying, polyurethane foam pipes, fittings in polyurethane foam insulation, thermally insulated with polyurethane foam Ball Valves and elements of the pipeline system are subjected to a thorough inspection in order to detect cracks, chips, deep cuts, punctures and other mechanical damage to the polyethylene thermal insulation shell. If cracks, deep cuts and other damage to the coating of polyurethane foam pipes in a polyethylene or galvanized shell are detected, they are repaired by extrusion welding, by applying heat-shrinkable cuffs (couplings) or galvanized bandages.

Before installing a ductless heating main, pipelines in polyurethane foam insulation and fittings in polyurethane foam are laid out on the edge or bottom of the trench using a crane or pipe layer, soft “towels” or flexible slings.

Lowering insulated polyurethane foam pipes into a trench should be done smoothly, without jerking or hitting the walls and bottom of channels and trenches. Before installing polyurethane foam pipes in trenches or channels, it is imperative to check the integrity of the signal wires of the operational remote control system (SODC system) and their isolation from the steel pipe.

In order to prevent damage to the shell, polyurethane foam pipes laid on a sandy base during channelless installation should not rest on stones, bricks and other solid inclusions, which should be removed, and the resulting depressions should be filled with sand.

If it is necessary to control calculations of the laying depths of heat pipelines with polyurethane foam insulation in a polyethylene shell for specific installation conditions, the design resistance of polyurethane foam should be taken as 0.1 MPa, for a polyethylene shell - 1.6 MPa.

If it is necessary to lay underground heating networks with thermal insulation of polyurethane foam in a polyethylene shell at a depth more than permissible, they should be laid in channels (tunnels). When laying routes under the roadway, railway tracks and other objects located above the PPU pipe, the pipes in PPU insulation are made with reinforcement (polyethylene overlay rings along the entire length of the shell) and are laid in a steel case that protects from external mechanical influences.