Channel laying satisfies most of the requirements, however, its cost, depending on the diameter, is 10-50% higher than channelless. Channels protect pipelines from the impact of ground, atmospheric and flood waters. Pipelines in them are laid on movable and fixed supports, while organized thermal elongation is ensured.
The technological dimensions of the channel are taken based on the minimum clear distance between the pipes and structural elements, which, depending on the diameter of the pipes 25-1400 mm, respectively, is taken equal to: to the wall 70-120 mm; to overlap 50-100 mm; to the surface of the insulation of the adjacent pipeline 100-250 mm. Channel depth
are taken based on the minimum volume of earthworks and the uniform distribution of concentrated loads from vehicles on the floor. In most cases, the thickness of the soil layer above the ceiling is 0.8-1.2 m, but not less than 0.5 m.
With district heating, impassable, semi-through or through channels are used for laying heating networks. If the laying depth exceeds 3 m, then in order to be able to replace pipes, semi-through or through channels are constructed.
impassable 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 channels with concrete or brick walls or reinforced concrete single- and multi-cell channels are more often arranged. In weak 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 canal to drain it. The heating network in impassable channels, if possible, is placed along the lawns.
At present, channels are predominantly made of prefabricated reinforced concrete tray elements (regardless of the diameter of the pipelines being laid) of types KL, KLs, or wall panels of types KS, etc. The channels are covered with flat reinforced concrete slabs. The bases of channels of all types 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 impassable channels, it is necessary to break the soil and disassemble the channel. In some cases, this is accompanied by the opening of the bridge or asphalt pavement.
semi-through channels. In difficult conditions where pipelines of the heating network intersect existing underground utilities, under the roadway, with a high level of standing groundwater, semi-passage channels are arranged instead of impassable ones. They are also used when laying a small number of pipes in places where, according to 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-through channel is assumed to be at least 1400 mm. Channels are made of prefabricated reinforced concrete elements - bottom slabs, wall blocks and floor slabs.
through channels. Otherwise they are called collectors; they are built in the presence of a large number of pipelines. They are located under bridges of large highways, on the territory of large industrial enterprises, in areas adjacent to the buildings of thermal power plants. Together with heat pipelines, other underground communications 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 for maintenance personnel to pipelines and equipment is provided.
Collectors are made of reinforced concrete ribbed slabs, frame structure links, large blocks and bulk elements. They are equipped with lighting and natural supply and exhaust ventilation with triple air exchange, providing an air temperature of no more than 30 ° C, and a device for removing water. Entrances to the collectors are provided every 100-300 m. To install 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, the gaskets arrange reinforced thermal insulation - 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 the increased susceptibility of steel pipes to external soil, chemical and electrochemical corrosion.
With this type of laying, movable supports are not used; pipes with thermal insulation are laid directly on a sand cushion, poured onto a previously leveled bottom of the trench. Fixed supports for channelless pipe laying, as well as for channel laying, are reinforced concrete shield walls installed perpendicular to the heat pipes. These supports, with small diameters of heat pipes, are usually used outside the chambers or in chambers with a large diameter at high axial forces. To compensate for thermal elongation of pipes, bent or stuffing box compensators are used, located in special niches or chambers. At the turns of the route, in order to avoid clamping the pipes in the ground and to ensure their possible movement, impassable channels are constructed.
For channelless laying, backfill, prefabricated and monolithic types of insulation are used. A monolithic shell made of autoclaved reinforced foam concrete has become widespread.
Above ground lining. This type of gasket is the most convenient in operation and repair and is characterized by minimal heat loss and ease of detection of accident sites. Supporting structures for pipes are free-standing supports or masts that ensure that the pipes are located at the right distance from the ground. With low supports, the clear distance (between the surface of the insulation and the ground) with a group of pipes up to 1.5 m wide is assumed to be 0.35 m and not less than 0.5 m for a larger width. The supports are usually made of reinforced concrete blocks, the masts and flyovers are made of steel and reinforced concrete. The distance between the supports or masts for above-ground laying of pipes with a diameter of 25-800 mm is assumed to be 2-20 m. Sometimes one or two intermediate suspension supports are arranged using stretch marks to reduce the number of masts and reduce capital investments in the heating network.
For maintenance of fittings and other equipment installed on the pipelines of the heating network, special platforms with fences and stairs are arranged: stationary at a height of 2.5 m or more and mobile - at a lower height. In places of installation of main valves, drain, drainage and air devices, insulated boxes are provided, as well as devices for lifting people and fittings.
5.2. Drainage of thermal networks
When laying underground heat pipes, in order to avoid water penetration to thermal insulation, an artificial lowering of the groundwater level is provided. For this purpose, together with heat pipelines, drainage pipelines are laid below the base of the channel by 200 mm. The drainage device consists of a drainage pipe and a filtration material of sand and gravel. Depending on the working conditions, various drainage pipes are used: for non-pressure drainage - socketed ceramic, concrete and asbestos-cement pipes, for pressure pipes - steel and cast iron pipes with a diameter of at least 150 mm.
At bends and with differences in pipe laying, manholes are arranged like sewer wells. In straight sections, such wells are provided for at least 50 m. If the drainage of drainage water into reservoirs, ravines or sewers by gravity is not possible, pumping stations are built, which are placed near the wells at a depth depending on the mark of the drainage pipes. Pumping stations are built, as a rule, from reinforced concrete rings with a diameter of 3 m. The station has two compartments - a machine room and a reservoir for receiving drainage water.
5.3. Buildings on thermal networks
Heating chambers designed to service equipment installed on heating networks with 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. Stop valves, gland and drainage devices, etc. are installed in the chambers. The width of the passages is taken at least 600 mm, and the height is at least 2 m.
Heating chambers are complex and expensive underground structures, therefore they are provided only in places where shut-off valves and stuffing box expansion joints are installed. The minimum distance from the ground surface to the top of the chamber ceiling is assumed to be 300 mm.
At present, heat-extraction chambers made of prefabricated reinforced concrete 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 above-ground pavilion with a height of about 3 m is built above the recessed part of the chamber.
Supports. To ensure organized joint movement of the pipe and insulation during thermal elongation, movable and fixed supports are used.
fixed supports, designed to fix pipelines of heating networks at characteristic points, they are used for all laying methods. Characteristic points on the route of the heating network are considered to be the places of branches, the installation sites of valves, stuffing box compensators, mud collectors and the installation sites of fixed supports. The most widespread are shield supports, which are used both for channelless laying and for laying pipelines of heating networks in impassable 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 magnitude of the compensating capacity of the accepted expansion joints.
Movable supports installed with channel and channelless laying of pipelines of the 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 channelless. Rollers are used for above-ground laying along the walls of buildings, as well as in collectors, on brackets. Suspension supports are installed with above-ground laying. In places of possible vertical movements of the pipeline, spring supports are used.
The distance between the movable supports is taken based on the deflection of the pipelines, which depends on the diameter and wall thickness of the pipes: the smaller the pipe diameter, the smaller the distance between the supports. When laying pipelines with a diameter of 25-900 mm in the channels, the distance between the movable supports is assumed to be 1.7-15 m, respectively. When laying above ground, where a slightly larger pipe deflection is allowed, the distance between the supports for the same pipe diameters is increased to 2-20 m.
Compensators used to relieve thermal stresses that occur in pipelines during elongation. They can be flexible U-shaped or omega-shaped, articulated or stuffing box (axial). In addition, the existing pipeline turns at an angle of 90-120 ° are used, which work as compensators (self-compensation). The installation of expansion joints is associated with additional capital and operating costs. The minimum costs are obtained in the presence of self-compensation sections and the use of flexible compensators. When developing projects for heating networks, a minimum number of axial expansion joints is adopted, making maximum use of the natural compensation of heat pipes. 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.
Anti-corrosion 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. Coatings made in the factory are of high quality. The type of anti-corrosion coating depends on the temperature of the coolant: bituminous primer, several layers of isol on insulating mastic, wrapping paper or putty and epoxy enamel.
Thermal insulation. For thermal insulation of pipelines of heating networks, various materials are used: mineral wool, foam concrete, armored foam concrete, aerated concrete, perlite, asbestos cement, sovelite, expanded clay concrete, etc. For channel laying, suspension insulation from mineral wool is widely used, for channelless - from autoclaved armored foam concrete, asphalt -toisol, bitumen perlite and foam glass, and sometimes backfill insulation.
Thermal insulation consists, as a rule, of three layers: heat-insulating, integumentary 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 cover layer, materials are used that have the necessary strength and moisture permeability: roofing felt, glassine, fiberglass, foil insulation, sheet steel and duralumin.
As a cover layer for channelless laying of heat pipelines in moderately moist sandy soils, reinforced waterproofing and asbestos-cement plaster over a wire mesh frame are used; for channel laying - asbestos-cement plaster on a wire mesh frame; for above-ground laying - asbestos-cement semi-cylinders, sheet steel casing, galvanized or painted aluminum paint.
Suspension insulation is a cylindrical shell on the surface of the pipe, made of mineral wool, molded products (plates, shells and segments) and autoclaved foam concrete.
The thickness of the thermal insulation layer is taken according to the calculation. As the design temperature of the coolant, the maximum is taken if it does not change during the working 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 assumed to be +40°C, the soil on the axis of the pipes is the average for the year, the outside air temperature for above-ground laying is the average for the year. In accordance with the norms for designing heat networks, the maximum thickness of thermal insulation is taken based on the laying method:
For above-ground laying and in collectors with a pipe diameter of 25-1400
mm insulation thickness 70-200 mm;
In channels for steam networks - 70-200 mm;
For water networks - 60-120 mm.
Fittings, flange connections and other fittings of heating networks, as well as pipelines, are covered with a layer of insulation with a thickness equal to 80% of the thickness of the pipe insulation.
With channelless laying of heat pipelines in soils with increased corrosive activity, there is a danger of corrosion of pipes from stray currents. To protect against electrical corrosion, measures are taken to prevent the penetration of stray currents to metal pipes, or arrange the so-called electrical drainage or cathodic protection (cathodic protection stations).
The plant of information technologies "LIT" in the city of Pereslavl-Zalessky produces flexible heat-insulating products made of polyethylene foam 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 release toxic substances into the environment and does not have harmful effects on the human body upon direct contact. Working with it does not require special tools and increased security measures.
"Energoflex" is designed for thermal insulation of engineering communications with a coolant temperature from minus 40 to plus 100 °C.
Energoflex products are produced in the following form:
Tubes 73 standard sizes with an internal diameter 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 coefficient of thermal conductivity of the material at 0°C is 0.032W/(m-°C).
Mineral wool heat-insulating products are produced by the enterprises of JSC "Termosteps" (Tver, Omsk, Perm, Samara, Salavat, Yaroslavl), AKSI (Chelyabinsk), JSC "Tizol", Nazarovsky ZTI, plant "Komat" (Rostov -on-Don), CJSC Mineralnaya Vata (Zheleznodorozhny, Moscow Region), etc.
Imported materials from ROCKWOLL, Ragos, Izomat, etc. are also used.
The performance properties of fibrous heat-insulating materials depend on the composition of the feedstock and process equipment used by various manufacturers and vary over a fairly wide range.
Technical thermal insulation made of mineral wool is divided into two types: high-temperature and low-temperature. CJSC "Mineralnaya vata" produces thermal insulation "ROCKWOLL" in the form of fiberglass mineral wool boards and mats. More than 27% of all fibrous heat-insulating materials produced in Russia fall on the share of URSA heat-insulation produced by Fleiderer-Chudovo OJSC. These products are made of staple glass fiber and are characterized by high thermal and acoustic characteristics. Depending on the brand of the product, the coefficient of thermal conductivity
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°C.
CJSC Izolyatsionny Zavod (St. Petersburg) produces insulated pipes for heating systems. Here, reinforced concrete is used as insulation, the advantages of which include:
High limiting temperature of application (up to 300°С);
High compressive strength (not less than 0.5 MPa);
Can be used for channelless laying at any depth
bin laying of heat pipelines and in all soil conditions;
The presence of a passivating protective layer on the insulated surface
a film that occurs when foam concrete comes into contact with pipe metal;
The insulation is non-combustible, which allows it to be used in 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 channelless pipelines with polyurethane foam (PPU) insulation in a polyethylene sheath. The use of pipelines of the "pipe in pipe" type is the most progressive way of energy saving in the construction of heat networks. In the USA and Western Europe, especially in the northern regions, these designs have been used since the mid-60s. In Russia - only from the 90s.
The main advantages of such structures:
Increasing the durability of structures up to 25-30 years or more, i.e. in
2-3 times;
Reduction of heat losses up to 2-3% compared to existing ones
20^40% (and more) depending on the region;
Reducing operating costs by 9-10 times;
Reducing the cost of repairing heating mains by at least 3 times;
Decreased capital costs in the construction of new heating pipelines in
1.2-1.3 times and a significant (2-3 times) reduction in construction time;
A significant increase in the reliability of heating mains constructed according to
new technology;
The possibility of using a system of operational remote control
control over the moisture content of the insulation, which allows timely response
check for violation of the integrity of the steel pipe or polyethylene guide
insulation coating and prevent leaks and accidents in advance.
On the initiative of the Government of Moscow, Gosstroy of Russia, RAO UES of Russia, CJSC MosFlowline, TVEL Corporation (St. Petersburg) and a number of other organizations, the Association of Manufacturers and Consumers of Industrial Polymer Insulation Pipelines was established in 1999.
CHAPTER 6. CRITERIA FOR SELECTING THE BEST OPTION
It is produced in impassable, continuous, and semi-through channels, as well as in common collectors along with other communications. On the example of Leningrad, in recent years, channelless laying has been used, which is considered the most effective. But even in this version, individual sections fit into the channels - compensatory niches, angles of rotation, etc.
If the underground laying of heating networks is carried out on an unplanned territory, local planning of the earth's surface is carried out. This is done in order to divert surface water. Elements of heat networks (outer surfaces of ceilings and walls of channels, chambers, etc.) are finished with coated bitumen insulation. If the laying takes place under green areas, the structures are covered with pasted waterproofing, which is made from bituminous roll materials. Networks installed below the maximum standing groundwater level are equipped with associated drainage. Its diameter should be more than 150 mm.
Installation of compensators
Underground piping involves the installation of compensators. Installation of compensators in the design position is allowed after preliminary testing of heat networks for tightness and strength, their backfilling and underground laying of chambers, channels and shield supports.
If the heat networks being laid are installed to service shut-off brick or reinforced concrete fittings, underground chambers are arranged. The main heating networks pass through the chambers. Inserts with shutoff valves are installed in them for mounting branches to consumers. The height of the chamber must meet the safety of the service.
In major cities underground pipelines carried out in conjunction with other engineering networks. City and intra-quarter tunnels are combined with water pipes up to 300 mm in diameter, power cables up to 10 kV and communication cables. City tunnels with compressed air pipelines with a pressure of up to 16 MPa are combined with a pressure sewer. Intra-quarter tunnels are laid together with water networks up to 250 mm in diameter and a natural gas pipeline with a pressure of up to 0,005 MPa and a diameter of not more than 150 mm. In cases or tunnels, heating systems are laid under city driveways, at the intersection of major highways and under areas with modern coverage.
Underground laying of the pipeline can be carried out in impassable channels.
Channelless underground laying is carried out on the territory of settlements. Installation is carried out in impassable channels together with other engineering networks in citywide or intra-quarter collectors. Above-ground laying of the pipeline is carried out at the sites of enterprises. In this case, heating networks are installed on separate overpasses and supports. Sometimes underground laying is also allowed.
More about underground laying of expansion joints
With channelless laying and in impassable channels, underground installation of bellows expansion joints in the chambers. Special pavilions for are not built when laying heating systems 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 fixed.
For aesthetic and architectural reasons, it is envisaged in residential areas.
When laying underground heating networks and for air installation, a crane is used. It is also used on masts, trestle bridges, 3-story office buildings and elevated pavilions of pumping stations.
In special collectors and together with other engineering networks, underground pipeline within a locality (city or town). Installation is carried out in semi-through, impassable and through channels directly in the ground.
All pipelines laid underground should be checked periodically. The state of thermal insulation, building and insulation structures and the pipelines themselves are monitored. Preventive planned drillings 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 laying and the length of the heating networks.
Laying pipes in a trench is carried out with the participation of the same mechanisms as in the underground laying of heating networks. These are truck cranes, pipelayers and caterpillar cranes. 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 by means of mounting tripods, which are equipped with manual winches or hoists. For pipes with a small diameter, 2 ropes are used and they are lowered into the trench manually.
Heat pipelines are laid underground or above ground. The underground method is the main one in residential areas, since it does not clutter up the territory and does not worsen the architectural appearance of the city. The above-ground method is usually used in the territories of industrial enterprises during the joint laying of energy and technological pipelines. In residential areas, the above-ground method is used only in especially difficult conditions: permafrost and soils that subside during thawing, wetlands, a high density of existing underground structures, terrain heavily indented by ravines, crossing 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 way. In addition, in residential areas, distribution networks are sometimes laid in technical undergrounds (corridors, tunnels) of buildings, which reduces the cost and simplifies construction and operation.
When laying in channels and technical undergrounds of buildings, heat pipelines are protected from all sides from mechanical influences and loads and, to some extent, from ground and surface waters. To perceive the own weight of the heat pipe, special movable supports are installed. With channelless laying, heat pipes are in direct contact with the ground and external mechanical loads are perceived by the pipe and the heat-insulating structure. At the same time, movable supports are not installed, and heat pipes are laid directly on the ground or a layer of sand and gravel. The cost of channelless laying is 25-30% less than in channels, however, the operating conditions of heat pipelines are more difficult.
The depth of the heat pipelines from the upper level of the channels or the insulating structure (with channelless laying) to the surface of the earth is 0.5--0.7 m. At a high level of 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 prefabricated reinforced concrete parts. To protect against ground and surface waters, the outer surface of the channels is covered with bitumen with pasting 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 trays are sometimes closed (by slabs, gratings), through which water flows into prefabricated 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 cools, moisture accumulates on the ceilings and walls of the channel, which flows down and can cause dampening of the insulation.
Passing channels provide the 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 build them only in the most critical areas, as well as when laying heat pipelines together with other utilities. When laying various communications together, the passage channels are called collectors. In cities, they are now widely used. On fig. 6.4 shows a 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 periods of repairs and not higher than 50 ° C during operation, electric lighting with a voltage of up to 30 V, telephone communication. To collect moisture at low points on the route, pits are arranged that communicate with drains or are equipped with automatic or remote-controlled pumping pumps.
Rice. 6.4. Cross section of a typical city collector
1 and 2 - supply and return pipelines; 3 - condensate pipeline; 4 - telephone cables; 5 - power cables; 6 - steam pipeline; 7 - plumbing
The overall dimensions of the passage channels (collectors) are selected from the condition of free access to all elements of the heat pipelines, which allows them to be completely overhauled without opening and destroying the road surfaces. The width of the passage in the channel is taken at least 700 mm, and the height is 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 with ladders or brackets for descending into the canal. In places where a large amount of equipment is located, special widenings (chambers) can be arranged or pavilions can be built.
Impassable channels are usually used for heat pipes with a diameter of up to 500-700 mm. They are made of rectangular, vaulted and cylindrical shapes from reinforced concrete slabs and vaults, asbestos-cement and metal pipes, etc. At the same time, as a rule, an air gap is left between the surface of the heat pipes and the channel walls, through which the thermal insulation dries and moisture is removed from the channels. As an example, in fig. 6.5 shows a section of a rectangular impassable channel made from unified prefabricated reinforced concrete parts.
Rice. 6.5. Cross-sections of impassable 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 impassable channels are chosen mainly depending on the distance between the heat conductors and between the surfaces of the heat-insulating structure and channels, as well as on the condition of providing convenient access to the equipment in the chambers. To reduce the distance between the heat pipes, the equipment on them is sometimes installed apart.
Channelless laying is usually used for pipes of small diameters (up to 200-300 mm), since when laying such pipes in impassable channels, their working conditions turn out to be almost more difficult (due to the entry of the air gap in the channels with dirt and the difficulty of removing moisture from them at the same time ). In recent years, due to the increase in the reliability of channelless laying of heat pipelines (through the introduction of welding, more advanced heat-insulating structures, etc.), it is also being used for pipes of large diameters (500 mm or more).
Heat pipes laid in a channelless way are divided depending on the type of heat-insulating structure: in monolithic shells, cast (prefabricated cast) and backfill (Fig. 6.6) and depending on the nature of the perception of weight loads: unloaded and unloaded.
Rice. 6.6. Types of channelless heat pipes
a - in a combined and monolithic shell; b-cast and prefabricated cast; c - backfilling
Structures in monolithic shells are usually performed in the factory. On the route, only butt welding of individual elements and isolation of butt joints are 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 (hardening). Backfill insulation is performed on pipelines mounted in trenches and compressed from loose heat-insulating materials.
Unloaded structures include structures in which the heat-insulating coating has sufficient mechanical strength and unloads pipelines from external loads (soil weight, weight of vehicles passing on the surface, etc.). These include cast (prefabricated cast) and monolithic shells.
In unloaded structures, external mechanical loads are transferred through thermal insulation directly to the pipeline. These include backfill heat pipes.
On underground heat pipelines, equipment that requires maintenance (gate valves, stuffing box expansion joints, drainage devices, vents, air vents, etc.) is placed in special chambers, and flexible expansion joints are placed in niches. Chambers and niches, like channels, are constructed from precast concrete elements. Structurally, the chambers are made underground or with above-ground pavilions. Underground chambers are arranged with pipelines of small diameters and the use of manually operated valves. Chambers with elevated 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. On fig. 6.8 shows the construction of an underground chamber.
The overall dimensions of the chambers are chosen from the condition of ensuring the convenience and safety of equipment maintenance. To enter the underground chambers, hatches are arranged diagonally in the corners - at least two with an internal area of \u200b\u200bup to 6 m 2 and at least four with a larger area. The diameter of the hatch is taken at least 0.63 m. Under each hatch, ladders or brackets are installed with a step of no more than 0.4 m for descending 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 pits are arranged, covered from above with a grate, to collect water with a depth of at least 0.3 m and dimensions in terms of 0.4x0.4 m. Water from the pits is discharged by gravity or with the help of pumps into drains or receiving wells.
Rice. 6.8. underground chamber
Aboveground heat pipelines they are laid on free-standing supports (low and high) and masts, on flyovers with a continuous span structure in the form of trusses or beams and on rods attached to the tops of masts (cable structures). At industrial enterprises, sometimes simplified gaskets are used: on consoles (brackets) along building structures and stands (pillows) along building roofs.
Supports and masts are usually made of reinforced concrete or metal. Overpass spans and anchor posts (non-movable supports) are usually made of metal. At the same time, building structures can be built one-, two- and many-tiered.
The laying of heat pipelines on free-standing supports and masts is the simplest and is usually used with a small number of pipes (two to four). At present, standard designs of free-standing low and high reinforced concrete supports have been developed in the USSR, made with one column 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, large diameter pipelines can be used as load-bearing structures for laying or hanging small diameter pipelines to them, requiring 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 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 overpasses 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 or six), as well as, if necessary, regular supervision of them. In this case, pipelines of large diameters usually rest directly on racks of overpasses, and small ones - on supports laid in the superstructure.
Laying heat pipelines on suspended (cable-stayed) structures is the most economical, as it allows you to 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 runs allow you to install additional supports for pipelines of small diameters.
To service equipment (gate valves, stuffing box compensators), platforms with fences and ladders are arranged: 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 flyovers - through bridges. When laying heat pipelines on low supports at the equipment installation sites, the ground surface should be covered with concrete, and the equipment should be covered with metal casings.
Pipes and fittings. For the construction of heating networks, steel pipes are used, connected by electric or gas welding. Steel pipes are exposed to internal and external corrosion, which reduces the service life and reliability of heating networks. In this regard, for local hot water systems that are subject to increased corrosion, galvanized steel pipes are used. In the near future, the use of enameled pipes is planned.
From steel pipes for heating networks, currently, they mainly use electric-welded pipes with a longitudinal straight and spiral seam and seamless, hot-worked and cold-worked, made from steel grades St. 3, 4, 5, 10, 20 and low alloy. 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 for heat supply (asbestos-cement; polymer, glass, etc.). Their advantages include high corrosion resistance, and for polymer and glass pipes and 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 are the low allowable 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 systems, condensate pipelines, etc.
The valves used in heating networks are divided into shut-off, control, safety (protective), throttling, condensate drain and control and measuring valves.
Shut-off valves are usually referred to the main general-purpose fittings, 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 valves. Gate valves are usually used in water networks, valves - in steam. They are made of steel and cast iron with flanged and coupling ends, as well as ends for welding pipes of various nominal diameters.
Shut-off valves in heat networks are installed on all pipelines extending from the heat source, at branch nodes with d y > 100 mm, at 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 fittings for draining water, venting air and starting drains. In addition, sectional valves are installed in water networks: with 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.
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. On the jumper, two valves are installed in series and a control valve between them at d y \u003d 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 that require high torque, bypass lines (discharge bypasses) are made with a shut-off valve. In this case, the valve is relieved from 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 steam pipelines. Gate valves with d y > 500 mm, requiring more than 500 Nm of torque to open or close, must be used with an electric drive. With electric drive, all gate valves are also provided for remote control.
Pipes and fittings are selected from the manufactured assortment depending on the conditional pressure, operating (calculated) parameters of the coolant and the environment.
Conditional pressure determines the maximum allowable 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 medium temperature rises, the allowable pressure decreases.
The operating pressures and temperatures of the coolant for the selection of pipes, fittings and equipment for 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 on 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 indicated in SNiP II-36-73.
§ 2. Methods of underground, ground and above-ground laying and their technical and economic indicators
The installation of sanitary and technical communications in areas of permafrost can cause soil thawing from the release of heat from pipelines. As a result, the stability of both the pipelines themselves and buildings may be impaired. Methods for laying sanitary and technical communications should be linked to the construction methods of buildings and structures and depend on the properties of the foundation soils and other factors, the most important of which is the location of the network route in relation to the built-up area and its architectural and planning solution.
There are the following types of laying of sanitary communications: underground, ground and above ground. These types of gaskets, in turn, can be single and combined.
Ground and overground laying due to the absence of contact between pipes and the ground and limited heat release into the soil, the bases disturb the natural thermal regime of permafrost soils to the least extent. Such gaskets clutter up the territory of populated areas, make it difficult to arrange driveways, organize snow protection and snow removal.
underground laying it is advisable to carry out within the boundaries of the development of the settlement in order to achieve maximum improvement of the territory. Water and sewer networks can be laid directly in the ground, and heating networks and steam pipelines can be laid in special channels. In the presence of such channels, it is advisable to lay water supply, sewerage and electrical cables in them.
Underground laying of heating networks is very expensive and requires special measures to preserve the thermal regime of permafrost soils at the base of the networks. So, for example, the cost 1 line m channel for heating in Norilsk is on average 300 rubles. The cost of a two-tier channel for the combined installation of a heating network, water supply, sewerage and electrical cables under the same conditions averages about 450 rubles. behind 1 line m. Therefore, the underground laying of heating networks is advisable only for compact development of multi-storey (4-5 floors) buildings and in conjunction with other communications.
If the development is carried out by two- and three-story buildings with gaps, then the underground laying of heating networks is usually not economically feasible. In such cases, above-ground laying is most often used along the facades and attics of buildings, and between buildings - along flyovers, fences and fences. At the same time, water supply and sewerage can be laid in the ground without channels. If the soils of the pipe base are subsiding, then to ensure their stability, it is necessary to replace the soils with non-subsiding soils to a depth determined by thermal engineering calculations.
For small settlements, if it is possible to trace the network within blocks without crossing streets or with a minimum number of intersections, it is most economical to lay heating networks on the ground in ring insulation or in insulated boxes together with water supply. Sewerage should be laid in the ground channelless.
In subsiding soils during thawing, especially in those that turn into a fluid-plastic or fluid state during thawing, when laying pipelines underground, an artificial foundation is required. The cost of such a foundation is directly dependent on the depth of thawing of the soil under the pipes.
When laying pipelines in soils that do not subside and do not lose their bearing capacity during thawing, the decisive condition is to protect them from freezing by reducing heat losses. In this case, the depth of laying is increased to 1.5-2.0 m; a large depth is undesirable, since it is difficult to detect pipeline accident sites and repair them both in summer and especially in winter.
In order to reduce heat loss and the size of taliks under pipes, underground laying of water supply and sewerage in thermal insulation is used: in boxes made of wood or reinforced concrete with sawdust or mineral wool backfill, in annular - made of foam concrete, mineral wool, felt impregnated with resin. All these types of thermal insulation do not achieve the goal when wetting the insulation material. Local malfunctions of waterproofing (and therefore thermal insulation) lead to thawing of the base and uneven precipitation of pipelines, the most undesirable. Restoration of heat and waterproofing during repairs is a complex and time-consuming process. The use of boxes creates additional difficulties in detecting and eliminating leaks. Any leakage entails a violation of thermal insulation. The cost of thermal insulation usually exceeds the cost of an artificial foundation for water supply and sewerage. Therefore, the widespread use of thermal insulation for water and sewer pipelines when laying them in the ground is impractical.
Consider some designs of pipeline foundations laid in the ground.
Ground base(Fig. IV-1). Ice-saturated local soils at the base of the heat-generating pipeline to the estimated thawing depth are replaced by non-sagging soils with a low filtration coefficient. Sandy, gravel-sandy soils in some cases are compacted by preliminary thawing. For replacement, light sandy loams and fine-grained silty sands in the thawed state are used; at the same time, an admixture of pebbles, gravel, crushed stone up to 40 ..... -45% or local dehydrated and compacted soil is desirable. A waterproofing layer of clay concrete or clay is laid under the pipe on an artificial soil base. 25-30 cm.
The width of the artificial base is taken equal to the width of the trench, and the height is determined by calculation.
In the absence of leakage, the radius of thawing from heat generation from water or sewer pipelines does not, on average, usually exceed 1.2 m. If we take into account the increased intensity of soil thawing, which replaces ice-saturated soils, then the replacement depth will not exceed 1.5 m. It must be assumed that in many cases a soil foundation will be economically viable and technically feasible.
Leg base is used to reduce the unevenness of subsidence during thawing of subsiding soils and is carried out in the form of longitudinal beds in two logs. To prevent warping of beds during subsidence, as a result of which the pipeline is destroyed, their reliable fastening is necessary.
floating base used in ice-saturated soils and is a continuous flooring of plates laid across the trench; this type of foundation is quite reliable, but cannot be widely recommended due to the high cost and consumption of a large amount of timber.
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Rice. IV-2. Pipeline on a pile foundation. 1 - pipeline; 2 - log (beam) ∅30 cm on dowels (joints apart); 3 - piles ∅30 cm through 3m with recess for 3m below the active layer; 4 - gaskets through 10 cm; 5 - backfilling with local soil
pile foundation(fig. IV-2) is applied in strongly subsidence soils. Driving piles into permafrost requires time-consuming and expensive work to steam the soil or drill wells. Piles often have to be placed, because in pipes bearing a large load from the soil, significant bending moments occur on the supports. Such bases are characterized by high cost.
underground overpasses(Fig. IV-3) due to the high cost, they are used in exceptional cases, for example, for sewerage with subsiding soils that thaw to a great depth, when passing the route near a building with large heat emissions, built according to methods I or IV and located higher in relief.
The question of the use of one or another type of foundation is decided by comparing technical and economic indicators.
To eliminate the possibility of intensive movement of the flow of supra-permafrost waters along underground pipelines, clay-concrete bridges are used across the trenches. The lintels cut into the frozen base and trench walls on 0.6-1.0 m. The distance between the jumpers is assigned depending on the longitudinal slope in such a way that the pressure at the jumper does not exceed 0.4-0.5 m; Usually this distance ranges from 50 to 200 m.
In pebbly, gravel and other well-filtering soils, the installation of jumpers is not advisable, since the flow of supra-permafrost waters easily bypasses them.
Laying in earth embankments
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Rice. IV-4. Laying pipes in earthen ridges. 1 - pipeline; 2 - a layer of clay concrete with a thickness 20 cm; 3 - local soil; 4 - sand and gravel layer; 5 - local dehydrated and compacted soil
This method of laying (Fig. IV-4) is used under fairly favorable permafrost and ground conditions, in the absence of heat-insulating materials on site, and the pipeline route must pass through an undeveloped area. This type of gasket has several advantages:
- it is not required to carry out labor-intensive earthworks for digging trenches;
- pipe leaks are easier to detect and repair;
- filtration of supra-permafrost waters along pipes is excluded;
- the presence of a talik around the pipes allows longer interruptions in the movement of water through them than with ground and above-ground laying;
- there is no need for heat and waterproofing of pipes.
The main disadvantages of this method are the excessive clutter of the territory and the complexity of the arrangement of crossings. In addition, this creates conditions for greater snow coverage of the territory.
Underground laying of pipelines in channels
Laying pipelines in underground channels is a relatively expensive type of network construction; nevertheless, in some cases, channel laying is expedient, given not only one-time capital investments, but also operating costs. The feasibility of combined laying of communications in underground channels in comparison with a single underground one should be confirmed by the cost of construction attributed to 1 m 2 living space, and reliability in the operation of engineering networks. Combined laying is usually justified in adverse climatic and permafrost-soil conditions.
Channels can be through (semi-through) and non-through, single-tier and two-tier. In two-tier channels, the lower tier of which is a passage, the upper tier can be either semi-passage or impassable. The design of the channel with a semi-passage upper tier is cumbersome and high cost. The single-tier design of channels is the most economical and convenient in operation.
In the case of the installation of different types of channels in a populated area (which must be justified), it should be, based on the conditions of industrialization of construction, to achieve the minimum number of standard sizes of elements.
Impassable up to 0.9 m channels (Fig. IV-5) can be used in short sections (house outlets and inputs, intersections with roads, etc.) while ensuring stability conditions and operating requirements. Impassable channels should be arranged with a minimum penetration into the ground (no more than 0.5-0.7 m from floor to ground level). They must have a removable cover for cleaning channels, inspection and repair of pipelines. The longitudinal slope of impassable channels to ensure the drainage of water along the bottom must be at least 0.007.
Passage channels with a height of at least 1.8 m(Fig. IV-6) must have dimensions that provide free passage through them for inspection and repair of pipes, fittings and electrical cables.
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Rice. IV-7. Reinforced concrete two-tier passage channel. 1 - sewerage; 2 - heating system: 3 - water supply; 4 - shelves for electrical cables and communication cables; 5 - sand, δ = 10 cm; 6 - clay concrete, δ = 20 cm; 7 - replaced soil (calculated thickness)
With significant deepening of the channels and high heat generation of communications, the taliks formed under the channels can reach significant sizes. In such cases, in order to reduce the penetration of heat into the base, on the basis of a technical and economic comparison with other options, the expediency of installing two-tier channels is revealed (Fig. IV-7). In the lower passage tier of such a channel, a sewer pipeline and electrical cables are placed, in the upper - impassable or semi-passage - pipes of the heating system and water supply are laid.
When laying the sewerage and water pipes together, the water valves must be placed in special chambers or sections isolated from the sewer pipeline.
In order to prevent the destruction of both the channels themselves and closely located buildings and structures from thawing soils in the base, it is necessary:
- thermally insulate pipelines, minimizing their heat release;
- ventilate the channels in winter to remove heat so that the soils thawed over the summer at their base (completely froze;
- arrange waterproofing along the bottom of the channel, preventing water from penetrating into the base soils. The foundations under the channels should be made of non-subsidence or low subsidence soils.
In addition to replacing subsiding soils, it is possible to use preliminary thawing and compaction of base soils. Channels should be made of reinforced concrete, reinforced cement or other effective material. The arrangement of channels made of wood or concrete can be allowed with special justification, since concrete channels are expensive and do not meet the strength requirements for uneven subsidence of the base, and wooden ones are prone to decay, require extensive waterproofing work, and are silted up with the smallest particles of soil; in the presence of sewerage, they create unsanitary conditions for the water supply.
Channel ventilation is arranged natural and artificial (forced). Natural is carried out by arranging ventilation holes along the top of the channel at a distance 20-25 m depending on the dimensions of the channel and communications laid in it (Fig. IV-8). The efficiency of natural ventilation can be improved by installing exhaust shafts in buildings located near the canal; while the distance between the holes on the channel for air inflow can be increased up to 100-150 m.
Drainage from the canal of emergency or waste water should be carried out from its end part, using a longitudinal slope, or from intermediate water collectors (waterproofed pits) by pumping out water with pumps.
Heat pipelines and steam pipelines placed in channels should be removed as far as possible from the bottom of the channel; they must be in annular thermal insulation (for example, from foam concrete with asbestos-cement plaster and waterproofing). The use of plastics for this purpose, which have enhanced heat and waterproofing properties (polystyrene, polyethylene, etc.), has great prospects.
The technical and economic feasibility of laying sewer networks in channels together with networks for various purposes in comparison with a single underground laying is revealed based on a comparison of the cost of construction and operation, referred to 1 m 2 living space, as well as assessing the stability of networks, their durability and thermal impact on nearby buildings and structures.
Ground laying of pipelines
The ground type of laying usually includes pipelines laid on low supports. In this case, between the pipe and the ground surface there must be a blown space of at least 30 cm, which is necessary to reduce heat release into the base soils and prevent snow drifts.
Ground laying of pipelines should be used outside the construction of populated areas (as the cheapest), on low and swampy sections of the route, in places with heavily ice-saturated permafrost soils.
On the built-up area, ground laying is allowed with a small number of intersections of the pipeline with driveways and sidewalks. Pipelines are thermally and waterproofed. The use of combustible materials both for the manufacture of ducts and heat-insulating backfills for steam pipelines and heating networks at a heat carrier temperature of 90 °C and above is not recommended by fire regulations. Slag filling should also not be widely used due to the possible destruction of metal pipes by corrosion when the slag is moistened.
Wooden boxes, being in conditions of variable humidity, are deformed, the backfill is blown out, poured out and easily moistened. Waterproofing boxes with roll materials does not achieve the goal, since roll coatings are easily damaged. Therefore, reinforced concrete boxes are more reliable, but their cost with backfill is higher than the cost of ring heat and waterproofing of pipes.
In the case of combined laying, mainly for the sake of ease of use, thermal insulation is performed independently for pipelines for various purposes.
Ground pipelines can be based on bulk sand and gravel or any other non-subsidence or low subsidence soil laid without disturbing the natural moss-vegetation cover during the work. With subsiding soils of natural foundation, it is necessary to replace them with non-sagging soils to a depth determined by the calculation.
Special supports are arranged on an artificial soil base under the pipelines.
Lying supports of the transverse beds have an insignificant height, as a result of which, when the supports subside, the thermal insulation of the pipes falls on the ground, is easily moistened and deteriorates. The arrangement of common supports for several pipelines is not recommended, since under an uneven load, the beds give an uneven settlement.
City supports(Fig. IV-9) are a more advanced type of wooden supports; they make it easy to straighten the profile of pipelines in case of small subsidence of the base by wedging elements of the towns.
Reinforced concrete intermediate supports sliding and roller types (Fig. IV-10) are more economical and more durable than wooden ones. Their disadvantage is the difficulty of straightening pipelines during the settlement of embankments; to level the base, the pipeline has to be raised and the supports removed.
motionless(anchor) supports(Fig. IV-11) are made of wood, concrete and reinforced concrete. With wooden supports, the pipes are fixed to the support bars with bolts or pins.
Frame fixed supports require the performance of large volumes of work on the development and excavation of soils from pits. Therefore, they can be recommended in cases where the use of pile supports is impractical (active layer of high thickness, high-temperature frozen soils, characterized by low freezing forces, boulder gravelly soils, etc.).
Massive concrete supports are arranged for pipelines of large diameters and during the construction of pipelines in 2 stages. For fastening metal parts, nests are left in the concrete mass, which, for the time being before the construction of the pipeline of the second stage, must be filled with concrete of the lowest grades. Otherwise, water accumulates in them, which, when frozen, can break the concrete mass. In order to avoid thawing of the foundation soils due to exothermy during concrete hardening, as well as from heat inflow through the support body, a sand cushion with a thickness of 20-30 cm.
In general, ground laying in the conditions of the Far North is the most economical type of laying sanitary and technical communications (excluding sewers).
Above ground piping
Above-ground laying of pipelines is carried out on overpasses, on pile supports, towering above the terrain (Fig. IV-12), along the walls of buildings, attics and fences. The elevated type of pipeline laying is used when crossing roads, hollows, ravines and streams, in factory areas, in places with heavily ice-saturated soils of permafrost.
Similarly to ground laying, pipes are laid in annular thermal insulation or in insulated boxes.
Overpasses can be made of wood, reinforced concrete and metal. Metal overpasses are used in flammable places. The production of reinforced concrete overpasses is difficult, and their cost is high. Therefore, pile and frame wooden overpasses have received the main application.
Advantages of above-ground laying:
- pipes and boxes do not cause snow deposits and do not interfere with snow removal;
- the issue of intersections with passages and passages is successfully solved;
- pipes and their insulation are not exposed to mechanical damage from vehicles and pedestrians;
- pipelines are not subject to snow drifts, are easily accessible for inspection and repair.
Disadvantages of above-ground laying:
- high cost compared to ground laying;
- the inconvenience of installing fittings, especially fire hydrants;
- more significant than with ground laying, heat losses due to high wind speeds and the absence of snow deposits on pipes;
- pipes laid on the facades of buildings, overpasses and fences spoil the appearance of the inhabited place;
- when laying pipes along the walls of buildings, the principle of priority in the construction of sanitary communications is violated.
Technical and economic indicators for some types of gaskets are given in appendices 1 and 2.
Pipelines thermal 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 works and the cost of equipment and materials for laying the pipeline. AT operational include the costs of servicing and maintaining pipelines, as well as the costs associated with heat loss in pipelines and electricity consumption throughout the route. Capital costs are determined mainly 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 elevated. Underground piping is the most common. It is divided into laying pipelines directly in the ground (channelless) and in channels. When laying on the ground, pipelines can be on the ground or above the ground at such a level that they do not interfere with the movement of vehicles. Above-ground laying is used on suburban highways when crossing ravines, rivers, railways and other structures.
Above ground laying 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 of possible options. 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 premature failure of pipelines. In order to ensure the reliability of the heat pipelines, it is necessary to apply their mechanical and thermal protection.
Mechanical protection pipes when installing pipes underground can be provided by arranging channels, and thermal protection can be confused with the use of thermal insulation applied directly to the outer surface of pipelines. Insulation of pipes and their laying 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 laying of pipelines.
When installing pipelines of heating networks underground, two methods can be used:
- Direct laying of pipes in the ground (channelless).
- Pipe laying in channels (channel).
Laying pipelines in channels.
In order to protect the heat conduit from external influences, and to ensure free thermal elongation of the pipes, channels are intended. Depending on the number of heat pipes laid in one direction, impassable, semi-through or through channels are used.
To fix the pipeline, as well as to ensure free movement during temperature elongations, 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 with the help of a pump it 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, ceiling and bottom of the channel is covered with waterproofing.
The depth of laying the trays is taken from the condition of a minimum amount of excavation and a uniform distribution of concentrated loads on the floor during the movement of vehicles. The soil layer above the channel should be about 0.8-1.2 m and not less. 0.6 m in places where vehicular traffic is prohibited.
impassable channels are used for a large number of pipes of small diameter, as well as a two-pipe gasket 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 channels are most widely used.
The channel walls can have a thickness of 1/2 brick (120 mm) for small diameter pipelines and 1 brick (250 mm) for large diameter pipelines.
The walls are erected only from ordinary brick of a grade of at least 75. Silicate brick is not recommended for use due to its low frost resistance. 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 channel does not require concrete preparation, it is enough to compact the crushed stone directly into the soil. In weak soils, an additional reinforced concrete slab is laid on a concrete base. With a high level of standing groundwater, drainage is provided for their removal. The walls are erected after installation and insulation of pipelines.
For pipelines of large diameters, channels are used, assembled from standard reinforced concrete elements of the KL and KLs tray type, as well as from prefabricated reinforced concrete slabs KS.
Channels of the KL type consist of standard tray elements covered with flat reinforced concrete slabs.
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Channels of the KLS type consist of two tray elements stacked on top of each other and connected on a cement mortar using an I-beam.
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In channels of the KS type, wall panels are installed in the grooves of the bottom plate and poured with concrete. These channels are covered with flat reinforced concrete slabs.
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The bases of channels of all types are made of concrete slabs or sand preparation, depending on the type of soil.
Along with the channels discussed above, other types of them are also used.
Vaulted channels consist of reinforced concrete vaults or semicircular shells that cover the pipeline. At the bottom of the trench, only the base of the channel is made.
For pipelines of large diameter, a vaulted two-cell channel with a dividing wall is used, while the arch of the channel is formed from two semi-arches.
When installing an impassable 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 precast concrete slabs. The outer surface of the tray (walls and bottom) is covered with waterproofing from two layers of roofing material on bituminous mastic, the base surface is also covered with waterproofing, then the tray is installed or concreted. Before backfilling the trench, the waterproofing is protected by a special wall made of bricks.
Replacement of pipes that have failed, or repair of thermal insulation in such channels is possible only during the development of groups, and sometimes the dismantling of the pavement. Therefore, the heating network in impassable channels is routed along lawns or in the territory of green spaces.
semi-through channels. In difficult conditions for the intersection of existing underground devices by heat pipelines (under the roadway, with a high level of standing groundwater), semi-passage channels are arranged instead of impassable ones. Semi-through channels are also used with a small number of pipes in those places where, according to the operating conditions, opening the carriageway is excluded. The height of the semi-through channel is taken equal to 1400 mm. Channels are made of precast concrete elements. The designs of semi-through and through channels are almost the same.
through channels used in the presence of a large number of pipes. They are laid under 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 also located in the passage channels - electrical cables, telephone cables, water supply, gas pipelines, etc. The collectors provide free access for maintenance personnel to pipelines for inspection and elimination of an accident.
Passage channels must have natural ventilation with three air exchanges, providing an air temperature of no more than 40 ° C, and lighting. Entrances to the passage channels are arranged every 200 - 300 m. In places where stuffing box expansion joints are located, designed to perceive thermal elongations, locking devices and other equipment, special niches and additional hatches are arranged. The height of the passage channels must be at least 1800 mm.
Their structures are of three types − from ribbed slabs, from links of a frame structure and from blocks.
Grommets made of ribbed plates, are made of four reinforced concrete panels: the bottom, two walls and the floor slab, manufactured in the factory on rolling mills. The panels are connected with bolts, and the outer surface of the channel overlap is covered with insulation. Sections of the channel 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, the entrances are arranged every 50 m.
Passage channel from reinforced concrete links of a frame structure, covered with insulation on top. Channel elements have a length of 1.8 and 2.4 m and are of normal and increased strength with a depth of up to 2 and 4 m above the ceiling, respectively. A 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. Blocks at the joints are connected by monolithic reinforced concrete. These collectors are also made in normal and reinforced.
Channelless laying.
With channelless laying, the protection of pipelines from mechanical influences is performed by reinforced thermal insulation - a shell.
Virtues channelless laying of 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 shortcomings include: the complication of repair work and the difficulty of moving pipelines clamped by the ground. Channelless laying of pipelines is widely used in dry sandy soils. It finds application in wet soils, but with a mandatory device in the area where the 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 a previously leveled bottom of the trench. The sand cushion, which is a bed for pipes, has the best elastic properties and allows the greatest uniformity of temperature movements. In weak and clayey soils, the sand layer 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 pipes.
Compensation for thermal movements of pipes in any way of their channelless laying is provided with the help of bent or stuffing box compensators installed in special niches or chambers.
At the turns of the route, in order to avoid clamping the pipes in the ground and to ensure possible movements, impassable channels are arranged. As a result of uneven settlement of the soil and the base of the channel, the greatest bending of the pipelines occurs at the intersections of the drip wall with the pipeline. To avoid pipe bending, it is necessary to leave a gap in the wall hole, filling it with elastic material (for example, asbestos cord). The thermal insulation of the pipe includes an insulating layer of autoclaved concrete with a bulk weight of 400 kg/m3, having steel reinforcement, a waterproofing coating consisting of three layers of brizol on bitumen-rubber mastic, which includes 5-7% rubber crumb and a protective layer , made of asbestos-cement plaster on a steel mesh.
The return lines of the pipelines are insulated in the same way as the supply lines. However, the presence of insulation 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 must be determined by the technique of economic calculation based on local conditions; with a pipe diameter of 500 mm or more, the insulation device is not provided. Pipelines with such insulation 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: ceramic concrete and asbestos-cement pipes are used for non-pressure drainage, and steel and cast iron pipes are used for pressure ones.
Drainage pipes are laid with a slope of 0.002-0.003. At bends and at differences in pipe levels, special manholes are arranged like sewer wells.
Above ground piping.
Based on the ease of installation and maintenance, laying pipes above the ground is more profitable than laying underground. It also requires less material costs. However, this spoils the appearance of the environment and therefore this type of pipe laying cannot be applied everywhere.
load-bearing structures for above-ground laying of pipelines serve: for small and medium diameters - above-ground supports and masts, ensuring the location of pipes at the right distance from the surface; for pipelines of large diameters, as a rule, trestle supports. Supports are usually made of reinforced concrete blocks. Masts and flyovers can be either steel or reinforced concrete. The distance between the supports and masts during above-ground 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 with braces.
When laying above ground, thermal elongations of pipelines are compensated with the help of bent compensators, which require minimal maintenance time. Maintenance of fittings is carried out from specially arranged sites. Roller bearings should be used as movable bearings, 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 footpaths, special bridges are installed. And at the intersection with highways, either a compensator of the required height is made or a channel is laid under the road for the passage of pipes.
