The method of laying heat networks during reconstruction is chosen in accordance with the instructions of SNiP 2.04.07-86 "Heat networks". Currently, in our country, about 84% of heating networks are laid in channels, about 6% - without channels, the remaining 10% - above ground. The choice of one or another method is determined by local conditions, such as the nature of the soil, the presence and level of groundwater, the required reliability, the economy of construction, as well as the operating costs of maintenance. Ways of laying are divided into above-ground and underground.
Above-ground laying of heating networks
The above-ground laying of heating networks is rarely used, since it violates the architectural ensemble of the area, has, other things being equal, higher heat losses compared to the underground laying, does not guarantee against freezing of the coolant in case of malfunctions and accidents, and hampers driveways. When reconstructing networks, it is recommended to use it at a high level of groundwater, in permafrost conditions, with unfavorable terrain, on the territories of industrial enterprises, on sites free from buildings, outside the city or in places where it does not affect the architectural design and does not hinders traffic.
Advantages of above-ground laying: accessibility of inspection and ease of use; the ability to detect and eliminate an accident in heat pipelines as soon as possible; lack of electrocorrosion from stray currents and corrosion from aggressive groundwater; lower cost of construction compared to the cost of underground laying of heating networks. Above-ground laying of heating networks is carried out: on separate supports (masts); on flyovers with a span structure in the form of girders, trusses or suspended (cable-stayed) structures; along the walls of buildings. Freestanding masts or poles can be made of steel or reinforced concrete. With small volumes of construction of above-ground heating networks, steel masts made of profile steel are used, but they are expensive and labor-intensive and therefore are being replaced by reinforced concrete ones. It is especially advisable to use reinforced concrete masts in mass construction at industrial sites, when it is cost-effective to organize their manufacture in the factory.
For the joint laying of heating networks with other pipelines for various purposes, flyovers made of metal or reinforced concrete are used. Depending on the number of pipelines being laid at the same time, span structures of overpasses can be single-tier and multi-tier. 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 for U-shaped expansion joints of various sizes. When laying heating mains on the territory of industrial enterprises, the method of above-ground laying on brackets fixed in the walls of buildings is also used. Span of heat pipelines, i.e. the distances between the brackets are chosen taking into account the bearing capacity of the building structures.
Underground laying of heating networks
In cities and towns, for heating mains, underground laying is mainly used, which does not spoil the architectural appearance, does not interfere with traffic and reduces heat loss through the use of the heat-shielding properties of the soil. Soil freezing is not dangerous for heat pipelines, so they can be laid in the zone of seasonal soil freezing. The smaller the depth of the heating network, the smaller the volume of earthworks and the lower the cost of construction. Underground networks are most often laid at a depth of 0.5 to 2 m and below the surface of the earth.
The disadvantages of underground laying of heat pipelines 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 action of stray electric currents, moisture and aggressive substances contained in the soil. Underground laying of heat pipelines is associated with the need to open streets, driveways and yards.
Structurally, underground heating networks are divided into two fundamentally different types: channel and channelless.
The design of the channel completely unloads the heat pipelines from the mechanical impact of the soil mass and temporary transport loads and protects the pipelines and thermal insulation from the corrosive effect of the soil. Laying in channels ensures free movement of pipelines under temperature deformations both in the longitudinal (axial) and transverse directions, which allows using their self-compensating ability at the corner sections of the route.
Laying in passage channels (tunnels) is the most advanced method, since it provides constant access for maintenance personnel to pipelines to monitor their operation and repair, which in the best way ensures their reliability and durability. However, the cost of laying in through channels is very high, and the channels themselves have large dimensions (clear height - at least 1.8 m and passage - 0.7 m). Through channels are usually arranged when laying a large number of pipes laid in one direction, for example, at outlets from a thermal power plant.
Along with laying in impassable channels, channelless laying of heat pipelines is gaining more and more development. 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 heat-insulated pipeline, due to direct contact with the soil, is under conditions of more active physical and mechanical influences (soil moisture, soil pressure and external loads, etc.) than in channel laying. Channelless laying is possible when using a mechanically strong thermal and waterproofing shell that can protect pipelines from heat loss and withstand loads transmitted by soil. Heating networks with pipe diameters up to 400 mm inclusive are recommended to be laid mainly in a channelless way.
Among channelless gaskets, the most widespread in recent years have been progressive gaskets using reinforced foam concrete, bitumen perlite, expanded clay asphalt concrete, phenolic foam plastic, foam polymer concrete, polyurethane foam and other thermal insulation materials as monolithic thermal insulation. Channelless laying of heating networks continue to improve and are becoming more widespread in the practice of construction and reconstruction. During the reconstruction of intra-quarter heating mains, there are more opportunities for laying networks through basements than with new construction, since the construction of new sections often outstrips the construction of buildings.
Installation of heating networks, pipe laying
Installation of pipelines and installation of thermal insulation on them is carried out using pre-insulated PPU pipes, fittings in PPU insulation (fixed supports, tees and tee branches, transitions, end elements and intermediate elements, etc.), as well as PPU shells. Thermal insulation of straight sections, branches, pipeline elements, sliding supports, ball valves are being installed, as well as butt joints are being installed using a heat-shrink sleeve, heat-shrink tape, PPU components, galvanized casings and heat-insulating shells made of polyurethane foam.
The laying of heating networks and the installation of PPU thermal insulation is carried out in several stages - the preparatory stage (earthworks, delivery of PPU 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 laying depth of PPU pipes when laying heating networks should be carried out taking into account the difference in density between the PPU steel pipe and the heat-insulating layer of polyurethane foam, as well as heat transfer rates and normatively permissible heat losses.
The development of trenches for channelless laying should be carried out mechanically in compliance with the requirements of SNiP 3.02.01 - 87 "Earthworks".
The minimum depth of laying PPU pipes in a polyethylene sheath when laying heating mains in the ground should be taken at least 0.5 m outside the carriageway and 0.7 m within the carriageway, counting to the top of the thermal insulation.
The maximum laying depth of heat-insulated pipes during installation of pipelines in polyurethane foam insulation when laying heat networks should be determined by calculation, taking into account the stability of the polyurethane foam layer to the action of a static load.
PPU pipes are usually installed at the bottom of the trench. It is allowed to weld straight sections in the section on the edge of the trench. Installation of PPU pipes in a polyethylene sheath is carried out at an outdoor temperature of up to -15 ... -18 ° С.
Cutting of steel pipes (if necessary) is carried out with a gas cutter, while the thermal insulation is removed with a mechanized hand tool in 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 hard screen to protect the thermal insulation layer of polyurethane foam.
Welding of pipe joints and control of welded joints of pipelines during the installation of PPU 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 emerging from the insulation, from sparks.
When using a heat-shrink sleeve as a protection for a welded joint, it is put on the pipeline before the start of welding. When sealing a joint using a pouring joint or a joint from a PPU shell, where a galvanized casing and heat-shrinkable tape are used as a protective layer, pipes are welded regardless of the availability of materials for sealing joints.
Before starting the construction of a heating main with channelless pipe laying, PPU pipes, fittings in PPU insulation, ball valves thermally insulated with polyurethane foam 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 sheath of thermal insulation. If cracks, deep cuts and other damages are found in the coating of PPU pipes in a polyethylene or galvanized sheath, they are repaired by extrusion welding, by applying heat-shrinkable cuffs (couplings) or galvanized bandages.
Before installation of the heating main of channelless laying, pipelines in PPU insulation and fittings in PPU are laid out on the crest or the bottom of the trench using a crane or pipelayer, soft "towels" or flexible slings.
The lowering of the insulated PPU pipes into the trench should be carried out smoothly, without jerking and hitting the walls and bottom of the channels and trenches. Before installing PPU pipes in trenches or channels, it is imperative to check the integrity of the signal wires of the operational-remote control system (SOODK system) and their isolation from the steel pipe.
PPU pipes laid on a sandy base during channelless laying, in order to prevent damage to the shell, should not be supported by stones, bricks and other solid inclusions that should be removed, and the resulting depressions should be covered with sand.
If it is necessary to perform control calculations of the laying depths of heat pipelines with polyurethane foam insulation in a polyethylene sheath for specific laying conditions, the design resistance of polyurethane foam should be taken as 0.1 MPa, polyethylene sheath - 1.6 MPa.
If it is necessary to lay underground heating networks with PPU thermal insulation in a polyethylene sheath 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, pipes in PPU insulation are made with reinforcement (polyethylene overlays along the entire length of the shell) and are laid in a steel case that protects against external mechanical influences.
§ 2. Methods of underground, ground and above-ground laying and their technical and economic indicators
The arrangement of sanitary and technical communications in areas of permafrost can cause soil thawing due to the release of heat by 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. per 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 overpasses, 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, an artificial foundation is required when laying pipelines underground. 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 device 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.
One of the main features of heat pipelines is the relatively high temperature of the product transported through them - water or steam, in most cases exceeding 100 ° C, which largely determines the nature of the designs of heat networks, since it requires thermal insulation and ensuring freedom of movement of pipes when they are heated. or cooling.
The presence of thermal insulation and the requirement for free movement of pipes greatly complicates the design of heat pipelines - the latter are laid in channels, tunnels or protective shells.
Periodic heating of the walls of heat pipelines to a temperature of 130-150°C makes unsuitable anti-corrosion coatings, usually used to protect unheated steel pipelines laid in the ground. To protect heat pipelines from external corrosion, it is necessary to use such building and insulating structures that prevent the penetration of ground moisture to pipelines.
The currently used designs of heat pipelines are distinguished by a significant variety. According to the method of laying, heating networks are divided into underground and aboveground (air).
Underground laying of pipelines of heating networks is carried out:
a) in impassable and semi-passage channels;
b) in tunnels or collectors together with other communications;
c) in shells of various shapes and in the form of filling pads.
When laying underground along the route, chambers, niches for compensators, fixed supports, etc. are constructed.
Above-ground laying of pipelines of heating networks is carried out:
a) on overpasses with a continuous span;
b) on separate masts (supports);
c) on suspended superstructures (cable-stayed).
A special group of structures includes special structures: underwater, elevated and underground passages and a number of others.
The main disadvantages of heat pipelines used in the construction of underground structures are: fragility, large heat losses, laboriousness of manufacture, significant consumption of building materials and high construction cost.
The greatest application was received by prefabricated structures of impassable channels with concrete walls. The use of impassable channels is justified in the case of laying heating networks in wet soils, subject to associated drainage . It is necessary to focus on the use of impassable channels made of unified prefabricated reinforced concrete parts. These reinforced concrete channels can be used for heating networks with a diameter of up to 600 mm. It is possible to use impassable channels assembled from vibro-rolled plates.
Impenetrable channels with suspended thermal insulation that forms an air gap around the pipes are indispensable in sections of the route with self-compensation of thermal elongations of heat pipes. A characteristic feature of the channel laying of heating networks, in contrast to the channelless one, is the provision of movement of heat pipelines in the longitudinal and transverse directions.
When laying heat pipelines under driveways with heavy traffic and improved road surface, semi-through channels made of prefabricated reinforced concrete parts are used. When laying a large number of heat pipes of significant diameters, tunnels are used.
For heating mains of large diameters, there are also typical channel designs that have proven themselves both in construction and in operation. For example, heating mains with a diameter of 700-1200 mm are being built in Moscow. However, channel designs must be improved until more rational solutions are obtained. For laying heat pipelines, prefabricated reinforced concrete channels of single-cell and double-cell sections are used. Basically, these channels are designed as a semi-through type for the possibility of inspection by maintenance personnel, as well as to ensure maximum reliability of heating mains in operation.
In Moscow and some other cities, channelless laying of heat pipelines with a two-layer cylindrical shell consisting of a reinforced concrete pipe and a heat-insulating layer (mineral wool) has been used.
Reinforced concrete pipes have sufficient mechanical strength, high resistance to shock and vibration loads, good moisture resistance. Therefore, they reliably protect the heat pipeline from the effects of moisture and the loads transmitted by the soil. Thus, more favorable conditions for the operation of heat pipelines are achieved: stresses in the pipe walls are reduced and the durability of thermal insulation is ensured.
The outer reinforced concrete shell remains motionless when the heat pipe moves in the axial direction due to temperature deformations, which distinguishes this design from the structure with an armored concrete shell moving along the ground along with the heat pipe.
A similar design is also carried out using asbestos-cement pipes and reinforced concrete half-cylinders as the outer shell.
The use of channelless structures can be recommended when laying in dry soils with the protection of the outer surface of heat pipelines with two layers of insulating material. The channelless laying of heat pipelines with backfill thermal insulation with peat, diatomaceous earth, etc. turned out to be unsuccessful. Currently, experimental work is underway to create a backfill material.
The designs of chambers used in the construction of heating networks are very diverse. Prefabricated chambers made of reinforced concrete parts are designed for heat pipes of small and medium diameters. Large chambers are made of concrete blocks and monolithic reinforced concrete. The structures of fixed supports in the channels are made of monolithic, as well as prefabricated reinforced concrete. In Moscow, Novosibirsk and other cities, the so-called common collectors, in which heat pipes are laid together with electric and telephone cables, water supply and other underground networks, have become widespread.
Passing channels and common collectors are equipped with electric lighting, telephone communication, ventilation, various automatic control devices and drainage facilities.
In ventilated walk-through tunnels, a favorable temperature and humidity regime of the air environment is provided, which contributes to the good preservation of heat pipes.
During the construction of common collectors in Moscow by an open method, the construction of large ribbed reinforced concrete blocks, proposed by engineers N. M. Davidyants and A. A. Lyamin, has proven itself well.
The method of joint laying of underground networks in common collectors has a number of advantages, of which the most significant are : increasing the durability of the material part of the networks and ensuring the best operating conditions. When operating heat networks in collectors, as well as when it is necessary to build new underground networks, it is not required to open urban areas for repairs. The placement of networks for various purposes in collectors makes it possible to organize their integrated and planned design, construction and operation and makes it possible to streamline the entire system of placing underground networks more compactly both in plan and in cross-section of city passages. Underground city collectors are modern engineering structures.
a - separate;
b - joint;
T K - telephone sewerage;
E - electrical cables;
T - heat pipes 2d = 400 mm;
Г - gas pipeline d=300 mm
B - water supply d \u003d 300 mm;
C - drain d = 600 mm;
K - sewerage d \u003d 200 mm;
T KAB - telephone cables
Internal view of the common manifold
The number of pipelines and cables placed in collectors of various sections
The design of underground, above-ground and underwater transitions of heat pipelines through natural and artificial obstacles is included in the general complex of designing heat networks and is only rarely carried out by specialized organizations.
Underwater river crossings are carried out in the form of through tunnels and siphons; air crossings over rivers to railways - in the form of bridge crossings. It is possible to lay heat pipelines on existing bridges and overpasses.
When the route crosses the heating networks of railways and roads, as well as city passages, underground passages are most often built, carried out in a closed way to ensure the smooth operation of roads.
Underpasses are carried out mainly in the form of tunnels, constructed with the help of metal shields of circular cross section. These tunnels require significant deepening, and therefore often fall into the groundwater zone, which complicates the work and requires the organization of drainage from the tunnel during operation.
Another type of underpass is the laying of steel cases, inside which heat pipes are placed. Cases are laid by forcing or puncturing steel pipes with hydraulic jacks. The implementation of this type of crossing is advisable where it is possible to pass above the groundwater level without disturbing existing underground communications.
Underpasses made of steel cases are widely used in the construction of heating networks.
The correct choice of one or another type of transition is the main task in the design, since the cost of these structures is very high and significantly increases the total cost of heating networks.
At industrial enterprises, elevated laying of heat pipelines along overpasses, often made of rolled metal, has become widespread.
The design of overpasses using precast concrete is now greatly facilitated in connection with the release of the standard project "Unified prefabricated reinforced concrete free-standing supports for technological pipelines" (IS-01-06 series).
In urban heating networks, above-ground laying of heat pipelines was carried out mainly along metal lattice masts. Reinforced concrete masts began to be manufactured only at the present time. So, for example, reinforced concrete masts made of prefabricated parts for heating mains with a diameter of 1200 mm have found application in Moscow. Structural parts of these masts are manufactured at the factory and assembled on the track.
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.
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 networks. 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
