§ 2. Methods of underground, above-ground and above-ground laying and their technical and economic indicators

The installation of sanitary and technical communications in areas of permafrost can cause the soil to thaw due to the heat generated by the pipelines. As a result, the stability of both the pipelines themselves and buildings may be compromised. Methods for laying sanitary and technical communications must be linked to the methods of construction 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, above-ground and above-ground. These types of gaskets, in turn, can be single or combined.

Ground and overhead laying Due to the absence of contact of pipes with the ground and limited heat release into the soil, the foundations disturb to the least extent the natural thermal regime of permafrost soils. Such gaskets clutter the territory of populated areas, complicate the construction of passages, the organization of snow protection and snow removal.

Underground laying It is advisable to carry out within the boundaries of the settlement in order to achieve maximum improvement of the territory. Water supply and sewerage networks can be laid directly in the ground, and heating networks and steam pipelines can be laid in special channels. If there are such channels, it is advisable to lay water supply, sewerage and electrical cables in them.

Underground installation of heating networks is very expensive and requires special measures to preserve the thermal regime of permafrost soils at the base of networks. So, for example, the cost 1 linear m channel for district heating in the conditions of Norilsk averages 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 linear m. Therefore, underground installation of heating networks is advisable only in compact buildings with multi-story (4-5 floors) buildings and in conjunction with other communications.

If the development is carried out with two- and three-story buildings with gaps, then the underground installation of heating networks usually turns out to be economically infeasible. 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. In this case, water supply and sewerage can be laid in the ground without channels. If the soils of the base of the pipes are subsidence, then to ensure their stability it is necessary to replace the soils with non-subsidence ones to a depth determined by thermal engineering calculations.

For small villages, if it is possible to route the network within blocks without crossing streets or with a minimum number of intersections, the most economical option is to lay heating networks above ground in ring insulation or in insulated ducts together with a water supply system. In this case, the sewerage system must be laid in the ground without channels.

In soils that subsidence during thawing, especially in soils that transform during thawing into a fluid-plastic or fluid state, when laying underground pipelines, an artificial foundation is necessary. The cost of such a foundation is directly dependent on the depth of thawing of the soil under the pipes.

When laying pipelines in non-sagging and non-losing areas during thawing bearing capacity In soils, the decisive condition is to protect them from freezing by reducing heat loss. In this case, the depth of placement is increased to 1.5-2.0 m; greater depth is undesirable, as it makes it difficult to detect pipeline failure sites and repair them, both in summer and especially in winter.

In order to reduce heat loss and the size of the taliks under the pipes, underground laying of water supply and sewerage systems is used in thermal insulation: in boxes made of wood or reinforced concrete filled with sawdust or mineral wool, in a ring box made of foam concrete, mineral wool, felt impregnated with resin. All of these types of thermal insulation fail to achieve their goal when the insulating material is wet. Local faults in waterproofing (and therefore thermal insulation) lead to thawing of the base and uneven settlement of pipelines, which is the most undesirable. Restoring thermal and waterproofing during repairs is a complex and labor-intensive process. The use of boxes creates additional difficulties in detecting and eliminating leaks. Any leak 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 supply and sewer pipelines when laying them in the ground is impractical.

Let's consider some designs of pipeline foundations laid in the ground.

Soil foundation(Figure IV-1). Ice-saturated local soils at the base of the fuel pipeline are replaced by non-subsidence soils with a low filtration coefficient to the calculated thawing depth. Sandy, gravel-sandy soils in some cases are compacted by preliminary thawing. For replacement, light sandy loams and fine-grained silty sands in a thawed state are used; in this case, an admixture of pebbles, gravel, crushed stone up to 40.....-45% or local dehydrated and compacted soil is desirable. A waterproofing layer of adobe concrete or clay with a thickness of 25-30 cm.

The width of the artificial foundation is assumed to be equal to the width of the trench, and the height is determined by calculation.

In the absence of a leak, the radius of thawing from heat releases from water supply or sewer pipelines on average does not exceed 1.2 m. If we take into account the increased intensity of thawing of soils that replace ice-saturated soils, then the depth of replacement will not exceed 1.5 m. It must be assumed that in many cases the soil foundation will be economically beneficial and technically feasible.

Flat base It is used to reduce the unevenness of subsidence during thawing of subsidence soils and is made in the form of longitudinal logs in two logs. To prevent the tracks from warping during subsidence, as a result of which the pipeline is destroyed, they must be securely fastened.

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 (timber) ∅30 cm on dowels (staggered joints); 3 - piles ∅30 cm through 3m with recess on 3m below the active layer; 4 - gaskets through 10 cm; 5 - backfilling with local soil

Pile foundation(Fig. IV-2) is used in highly subsidence soils. Driving piles into permafrost soil requires labor-intensive and expensive work for steaming soil or drilling wells. Piles have to be placed frequently, because in pipes that carry 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 their high cost, they are used in exceptional cases, for example, for sewerage in subsidence soils that thaw to great depths, when the route passes near a building with large heat releases, built according to methods I or IV and located higher in the relief.

The issue of using one or another type of basis is resolved by comparing technical and economic indicators.

To eliminate the possibility of intense movement of supra-permafrost water flow along underground pipelines, clay concrete bridges are used across the trenches. The lintels cut into the frozen base and walls of the trenches on 0.6-1.0 m. The distance between the lintels is determined depending on the longitudinal slope so that the pressure at the lintel does not exceed 0.4-0.5 m; Typically this distance ranges from 50 to 200 m.

In pebble, gravel and other well-filtering soils, the installation of dams is not advisable, since the flow of supra-permafrost water easily bypasses them.

Laying in earthen beads

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Rice. IV-4. Laying pipes in earthen beads. 1 - pipeline; 2 - thick clay concrete layer 20 cm; 3 - local soil; 4 - sand and gravel layer; 5 - local dewatered and compacted soil

This installation method (Fig. IV-4) is used under fairly favorable permafrost-soil conditions, in the absence of thermal insulation materials on site, and the pipeline route must pass through an undeveloped area. This type of gasket has several advantages:

• there is no need to carry out labor-intensive earthworks of digging trenches;
• pipe leaks are easier to detect and fix;
• filtering of supra-permafrost water along the pipes is eliminated;
• the presence of a talik around the pipes allows longer interruptions in the movement of water through them than with ground and above-ground installations;
• there is no need for thermal and waterproofing of pipes.

Main disadvantages this method is excessive cluttering of the territory and complexity of crossings. In addition, this creates conditions for greater snow cover in the area.

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 advisable, taking into account 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 m2 living space, and reliability in the operation of utility networks. Combined laying is usually justified in unfavorable climatic and frozen soil conditions.

Channels can be pass-through (semi-pass-through) and non-pass-through, single-tier and two-tier. In two-tier channels, the lower tier of which is passable, the upper tier can be either semi-passable or non-passable. The design of the channel with a semi-through upper tier is cumbersome and high cost. The single-tier channel design is the most economical and convenient to use.

In the case of installing different types of channels in a populated area (which must be justified), it is necessary, based on the conditions of industrialization of construction, to achieve a 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 inlets, road intersections, etc.) while ensuring stability conditions and operating requirements. Non-passable channels should be constructed with minimal penetration into the ground (no more than 0.5-0.7 m from the floor to the ground surface). They must have a removable cover for cleaning channels, inspecting and repairing pipelines. The longitudinal slope of non-passable channels to ensure water drainage 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 network: 3 - water supply; 4 - shelves for electrical and communication cables; 5 - sand, δ = 10 cm; 6 - clay concrete, δ = 20 cm; 7 - replaced soil (calculated thickness)

With significant channel depths and large heat releases from communications, taliks formed under the channels can reach significant sizes. In such cases, to reduce the penetration of heat into the base, based on a technical and economic comparison with other options, the feasibility 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 - non-passable or semi-passable - heating network and water supply pipes are laid.

When laying a combined sewer and water supply system, water valves must be placed in special chambers or sections isolated from the sewer pipeline.

In order to prevent destruction of both the canals themselves and nearby buildings and structures from thawing of the soil at the base, it is necessary:

• thermally insulate pipelines, minimizing their heat generation as much as possible;
• ventilate the channels in winter to remove heat so that the soils at their base that have thawed over the summer are completely frozen;
• arrange waterproofing along the bottom of the canal, preventing water from penetrating into the foundation soils. The foundations under the canals should be made of non-subsidence or low-subsidence soils.

In addition to replacing subsidence soils, it is possible to use preliminary thawing and compaction of foundation soils. Channels must be made of reinforced concrete, reinforced cement or other effective material. The construction 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 foundation settlements, and wooden ones are susceptible to rotting, require big works for waterproofing, they are silted with the smallest particles of soil; If they have sewerage, they create unsanitary conditions for the water supply.

Ventilation of channels is arranged natural and artificial (forced). Natural is carried out by device 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 increased by installing exhaust shafts in buildings located near the canal; in this case, the distance between the holes on the channel for air flow can be increased to 100-150 m.

Discharge of emergency or waste water from the canal should be carried out from its end part, using a longitudinal slope, or from intermediate water collectors (waterproof pits) by pumping water out with pumps.

Heat and steam pipelines placed in channels should be moved as far as possible from the bottom of the channel; they must be in ring thermal insulation (for example, foam concrete with asbestos-cement plaster and waterproofing). The use of plastics with increased heat and waterproofing properties (foam plastic, polyethylene, etc.) for these purposes has great prospects.

The technical and economic feasibility of laying sewer networks in canals 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, attributed to 1 m2 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 above-ground type of installation usually includes pipelines laid on low supports. In this case, between the pipe and the ground surface there must be a ventilated space of at least 30 cm, which is necessary to reduce heat release into the foundation soils and prevent snow drifts.

Ground laying of pipelines should be used outside the built-up areas of populated areas (as it is the cheapest), in low-lying and swampy sections of the route, in places with heavily ice-saturated permafrost soils.

In the built-up area, ground installation is allowed if there are a small number of pipeline intersections 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 coolant temperature of 90 °C and above is not recommended by fire regulations. Slag backfill 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 filling is blown out, spills out and is easily moistened. Waterproofing boxes with rolled materials does not achieve the goal, since roll coverings are easily damaged. Therefore, boxes made of reinforced concrete 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 installation, mainly for ease of use, thermal insulation is carried out independently for pipelines for various purposes.

The base for above-ground pipelines can be bulk sand-gravel or any other non-subsidence or low-subsidence soil, laid without disturbing the natural moss and vegetation cover during the work. In case of subsidence of natural foundation soils, it is necessary to replace them with non-subsidence ones to a depth determined by calculation.

Special supports are installed on an artificial soil foundation under the pipelines.

Leg supports of the transverse beams have a small height, as a result of which, when the supports settle, the thermal insulation of the pipes falls on the ground, easily becomes moistened and deteriorates. The installation of common supports for several pipelines is not recommended, since with uneven load the tracks give uneven settlement.

Town supports(Fig. IV-9) are a more advanced type of wooden supports; they make it easy to straighten the profile of pipelines in the event of small subsidence of the foundation by wedging the elements of the towns.

Reinforced concrete intermediate supports sliding and roller type (Fig. IV-10) are more economical and durable than wooden ones. Their disadvantage is the difficulty of straightening pipelines when embankments settle; To level the base, the pipeline must be lifted and the supports removed.

Fixed(anchor) supports(Fig. IV-11) are made of wood, concrete and reinforced concrete. At wooden supports the pipes are secured to the support beams with bolts or pins.

Frame fixed supports require large volumes of work to develop and excavate soil 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 crushed 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 must be filled with concrete of the lowest grades until the construction of the second stage pipeline. Otherwise, water accumulates in them, which, when frozen, can tear the concrete mass. To avoid thawing of the foundation soil due to exotherm during concrete hardening, as well as from heat flow through the support body, a sand cushion of thickness is laid on the bottom of the pit 20-30 cm.

In general, ground installation in the Far North is the most economical view laying sanitary and technical communications (excluding sewerage).

Aboveground pipeline laying

Aboveground laying of pipelines is carried out on overpasses, on pile supports rising above the terrain (Fig. IV-12), along the walls of buildings, attics and fences. The above-ground type of pipeline laying is used when crossing roads, hollows, ravines and streams, in factory areas, and in places with heavily ice-saturated permafrost soils.

Similar to above-ground installation, pipes are laid in ring thermal insulation or in insulated boxes.

Overpasses can be made of wood, reinforced concrete and metal. Metal trestles are used in flammable areas. The production of reinforced concrete overpasses is difficult and their cost is high. Therefore, pile and frame wooden trestles are mainly used.

Advantages of above-ground installation:

• pipes and ducts do not cause snow deposits and do not interfere with snow removal;
• the issue of intersections with driveways and walkways is successfully resolved;
• pipes and their insulation are not subject to mechanical damage from vehicles and pedestrians;
• pipelines are not subject to snow drifts and are easily accessible for inspection and repair.

Disadvantages of above-ground installation:

• high cost compared to land installation;
• inconvenience of installing fittings, especially fire hydrants;
• more significant heat losses than during ground installation due to high wind speeds and the absence of snow deposits on the pipes;
• pipes laid along building facades, overpasses and fences spoil appearance populated place;
• When laying pipes along the walls of buildings, the principle of priority for the construction of sanitary communications is violated.

Technical and economic indicators for some types of gaskets are given in Appendices 1 and 2.

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

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

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

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

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

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

Pass-through channels provide the best conditions for work, operation and repair of heat pipelines, but in terms of capital costs they are the most expensive. In this regard, it is advisable to construct them only in the most critical areas, as well as when laying heat pipelines together with other utilities. When various communications are laid together, the passage channels are called collectors. They are now widespread in cities. In Fig. Figure 6.4 shows a cross-section of a typical single-section collector.

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

Rice. 6.4. Cross section of a typical city sewer

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

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

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

Rice. 6.5. Sections of a non-passable channel

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

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

Channelless laying is usually used for pipes of small diameters (up to 200-300 mm), since when laying such pipes in non-passable channels, their operating conditions are practically more difficult (due to the inclusion of dirt in the air gap in the channels and the difficulty of removing moisture from them in this case ). In recent years, due to the increase in the reliability of ductless installation of heat pipelines (through the introduction of welding, more advanced thermal insulation structures, etc.), they are beginning to use it for pipes of large diameters (500 mm or more).

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

Rice. 6.6. Types of ductless heat pipes

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

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

Unloaded structures include those in which the thermal insulation coating has sufficient mechanical strength and relieves the pipelines from external loads (the weight of the soil, the weight of transport passing on the surface, etc.). These include cast (precast) 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 (valves, stuffing box expansion joints, drainage devices, vents, vents, etc.) is placed in special chambers, and flexible expansion joints are placed in niches. Chambers and niches, like channels, are constructed from prefabricated reinforced concrete elements. Structurally, the chambers are made underground or with above-ground pavilions. Underground chambers are used for pipelines of small diameters and the use of valves with manual drive. Chambers with above-ground pavilions provide best service large-sized equipment, in particular, valves with electric and hydraulic drives, which are usually installed with pipeline diameters of 500 mm or more. In Fig. Figure 6.8 shows the design of an underground chamber.

The overall dimensions of the chambers are chosen to ensure the convenience and safety of equipment maintenance. To enter underground chambers, hatches are installed in diagonal corners - at least two for an internal area of ​​up to 6 m2 and at least four for a larger area. The diameter of the hatch is taken to be at least 0.63 m. Under each hatch, ladders or brackets are installed in increments of no more than 0.4 m for descending into the chambers. The bottom of the chambers is made with a slope > 0.02 to one of the corners (under the hatch), where pits for collecting water with a depth of at least 0.3 m and a plan size of 0.4x0.4 m are installed, covered with a grating on top. Water from the pits is drained by gravity or using pumps into drains or receiving wells.

Rice. 6.8. underground chamber

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

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

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

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

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

To service equipment (valves, stuffing box 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 overpasses there are walkway bridges. When laying heat pipelines on low supports, the ground surface should be covered with concrete at the equipment installation sites, and metal casings should be installed on the equipment.

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

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

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

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

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

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

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

At the installation sites of sectional valves, jumpers are made between the supply and return pipelines with a diameter equal to 0.3 of the diameter of the main pipelines to create coolant circulation in case of accidents. Two valves and a control valve between them at d y = 25 mm are installed in series on the jumper to check the tightness of the valves.

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

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

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

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

Heated water from a thermal power plant or a district boiler house is supplied to consumers via external heating networks by pumps for the centralized supply of heat to industrial enterprises, residential buildings and public buildings.

The route of heating networks in cities and other populated areas laid in technical lanes designated for utility networks parallel to the red lines of streets, roads and driveways. The route of heating networks runs between the roadway and a strip of green space. Inside microdistricts and blocks, the route of heating networks must also pass outside the roadway.

For heating networks in cities and other populated areas, underground installation is provided: in non-passable and through channels; in city and intra-block collectors together with other engineering networks and without installing channels (heating networks with a diameter of up to 500 mm).

In the territories of industrial enterprises, heating networks are laid on separate low and high supports or overpasses. Joint overhead installation of heating networks with process pipelines is allowed, regardless of the parameters of the coolant and the parameters of the environment in the process pipelines,

Most often, heating networks are laid in non-passable channels made of precast reinforced concrete (), which are single-cell, double-cell and multi-cell.

Rice. 142. Non-passable CL channels: a - single-cell, b - double-cell; 1 - tray element, 2 - sand preparation, 3 - floor slab, 4 - cement dowel, 5 - sand

Rice. 143. Laying of heating networks: a - in a non-passage channel with bitumen-perlite insulation, b - channelless, C - circulation pipeline, D - hot water pipeline, X - cold water pipeline, T - return pipeline of the heating system, GP - leading pipeline of the heating system

On, and shows one of the options for intra-block installation of heating networks in non-passable channels. The heating system pipelines are laid in one channel, the hot water supply system pipelines in the other, and cold water supply pipelines run between the channels directly in the ground.

When laying heating networks in the groundwater zone, the outer surfaces of the walls and ceilings of the heating channels should be covered with bitumen insulation, and drainage should be installed to lower the groundwater level along the route.

Thermal insulation is provided for heating network pipelines, fittings, flange connections, compensators and pipe supports, regardless of the coolant temperature and installation methods. The temperature on the surface of the thermal insulation structure of the pipeline in technical undergrounds and basements of residential and public buildings should be no more than 45 ° C, and in tunnels, collectors, chambers and other places accessible to maintenance, no more than 60 ° C.

Currently, the industry produces industrial bitumen perlite thermal insulation for heating pipes, which is applied to pipes by pressing at the factory. Such insulation is produced in two types: for laying heat pipelines and water supply networks in a channelless manner directly in the ground and in non-passable channels (see a); for laying heating pipes and water supply networks in technical undergrounds of buildings, passage channels, as well as indoors.

Bitumen-perlite insulation is a mixture of expanded perlite sand, petroleum bitumen and a passivating additive that reliably protects pipelines from corrosion. A covering layer of two layers of fiberglass glued to bitumen mastic or SKS-65 latex is applied on top of the bitumen-perlite insulation.

To weld heat pipes on the route, the ends of the pipes, 200 mm on each side, must not be insulated.

Channelless combined installation of pipelines for heating networks, hot and cold water supply with bitumen-perlite insulation (b) is allowed in all soils, except subsidence. When laying pipelines without channels in dry soils with a filtration coefficient Kf equal to 5 m/day or more, drainage is not required. In all other cases, it is necessary to arrange associated drainage. Channelless installation of pipelines for heating networks and hot water supply is used on routes. Chambers or channels should be provided in places where turns and expansion joints are installed.

The depth of installation of pipelines with bitumen-perlite insulation in areas of channelless installation must be at least 0.8 m from the planned surface of the earth to the top of the insulation in order to ensure strength and protection of the cold water supply from freezing.

The passage channel for a large number of pipes is shown in Fig. 144.

Rice. 144. Laying heating networks in the passage channel:

1 - supply pipelines, 2 - sliding support, 3 - steel beam, 4 - return pipeline, 5 - pipeline insulation, 6 - side walls of the channel, 7 - drainage tray

Such channels have large cross sections, which allows maintenance personnel to monitor and repair pipelines. Passage channels are installed mainly in the territories of large industrial enterprises and at the outlets of heat pipelines from powerful thermal power plants. The walls of the 6 passage channels are made of reinforced concrete, concrete or brick; The covering of passage channels is usually made of prefabricated reinforced concrete.

In the passage channels it is necessary to install a tray 7 for water drainage. The slope of the canal bottom towards the water drainage site must be at least 0.002. Support structures for pipes located in the passage channels are made of steel beams 3, cantilevered

straight sections in walls or mounted on racks. The height of the passage channel should be about 2000 mm, the width of the channel should be at least 1800 mm.

Pipelines in channels are laid on movable or fixed supports.

Movable supports serve to transfer the weight of the heat pipes to the supporting structures. In addition, they provide movement of pipes that occurs due to changes in their length with changes in coolant temperature. Movable supports can be sliding or roller.

Rice. 145. Supports: c - sliding, b - roller, c - fixed

Sliding supports (, a) are used in cases where the base for the supports can be made strong enough to withstand large horizontal loads. Otherwise, they resort to roller supports (, b), which create smaller horizontal loads. Therefore, when laying pipes of large diameters in tunnels, roller supports should be installed on frames or on masts.

Fixed supports ( ,c) serve to distribute pipeline extensions between expansion joints and to ensure uniform operation of the latter. In the chambers of underground channels and during above-ground installations, fixed supports are made in the form of metal structures, welded or bolted to pipes. These structures are embedded in foundations, walls and channel ceilings.

To absorb thermal elongations and relieve pipes from temperature stresses, bent and stuffing box compensators are installed on the heating network.

Rice. 146. Bent expansion joints

Bent expansion joints () U- and S-shaped are made from pipes and bends (bent, steeply curved and welded) for pipelines with a diameter of 50 to 1000 mm. These compensators are installed in non-passable channels, when inspection of laid pipelines is impossible, as well as in buildings with channelless installation. The permissible bending radius of pipes in the manufacture of expansion joints is 3.5-4.5 times the outer diameter of the pipe.

Bent U-shaped expansion joints are placed in niches. The dimensions of the niche in height coincide with the dimensions of the channel, and in plan they are determined by the dimensions of the compensator and the gaps necessary for the free movement of the compensator during temperature deformation. The niches where compensators are installed are covered with reinforced concrete slabs.

Rice. 147. Stuffing box compensators: a - one-sided, b - two-sided; 1 - body. 2 - glass, 3 - flanges

Stuffing box expansion joints are manufactured single-sided ( , a) and double-sided ( , b) for pressures up to 1.6 MPa for pipes with a diameter of 100 to 1000 mm. Stuffing box compensators are small in size, have a large compensating capacity and offer little resistance to the flowing fluid.

Stuffing box expansion joints consist of a housing 1 with a flange 3 on the widened front part. A movable glass 2 with a flange is inserted into the compensator body for installing the compensator on the pipeline. To prevent the stuffing box compensator from leaking coolant between the rings, stuffing box packing is placed in the gap between the body and the glass. The stuffing box is compressed by a flange liner using studs screwed into the compensator body. Compensators are attached to fixed supports.

The chamber for installing valves on heating networks is shown in Fig. 148.

Rice. 148. Chamber for installing valves on heating networks:

1 - branch of the supply main pipeline, 2 - branch of the return main pipeline, 3 - chamber, 4 - parallel valves, 5 - pipeline supports, 6 - return main pipeline, 7 - supply main pipeline

When laying heating networks underground, underground chambers 3 are installed to service shut-off valves rectangular shape. Branches 1 and 2 of the network to consumers are laid in the chambers. Hot water is supplied to the building through a pipeline laid on the right side of the channel. The supply 7 and return 6 pipelines are installed on supports 5 and covered with insulation.

The walls of the cells are made of bricks, blocks or panels, the ceilings are prefabricated from reinforced concrete in the form of ribbed or flat slabs, the bottom of the chamber is made of concrete. The entrance to the cells is through cast-iron hatches. To descend into the chamber, staples are sealed under the hatches in the wall. The height of the chamber must be at least 1800 mm. The width is chosen so that the passages between the walls and pipes are at least 500 mm.

Channel gasket satisfies most requirements, but its cost, depending on the diameter, is 10-50% higher than channelless. Channels protect pipelines from the effects of ground, atmospheric and flood waters. The pipelines in them are laid on movable and fixed supports, while ensuring organized thermal elongation.

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, is respectively taken equal to: to the wall 70-120 mm; to overlap 50-100 mm; to the insulation surface of the adjacent pipeline 100-250 mm. Channel depth

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

At centralized heating For laying heating networks, non-through, semi-through or through channels are used. If the laying depth exceeds 3 m, then semi-through or through channels are constructed to make it possible to replace pipes.

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 soil moisture. In dry soils, block channels with concrete or brick walls, or reinforced concrete single- and multi-cell ones are more often installed. IN weak soils perform first concrete base, on which a reinforced concrete slab is installed. When the groundwater level is high, a drainage pipeline is laid at the base of the canal to drain it. If possible, the heating network in non-passable channels is placed along the lawns.

Currently, channels are mainly constructed from 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 all types of channels are made of concrete slabs, lean concrete or sand preparation.

If it is necessary to replace failed pipes, or when repairing a heating network in non-passable channels, it is necessary to tear up the soil and dismantle the channel. In some cases, this is accompanied by opening of the bridge or asphalt surface.

Semi-bore channels. In difficult conditions when pipelines of the heating network cross existing underground communications, under the roadway, and at a high level of groundwater, semi-passable channels are installed instead of impassable ones. They are also used when laying a small number of pipes in places where, due to operating conditions, opening of the roadway is excluded, as well as when laying large diameter pipelines (800-1400 mm). The height of the semi-bore channel is taken to be at least 1400 mm. The channels are made from prefabricated reinforced concrete elements - a bottom slab, a wall block and a floor slab.

Passage channels. Otherwise they are called collectors; they are constructed in the presence of a large number of pipelines. They are located under the pavements 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: electrical and telephone cables, water supply, gas pipelines low pressure etc. For inspection and repair in collectors, free access of maintenance personnel to pipelines and equipment is provided.

Collectors are made of reinforced concrete ribbed slabs, frame structure links, large blocks and volumetric elements. They are equipped with lighting and natural supply and exhaust ventilation with threefold air exchange, ensuring 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. For installation of compensating and locking devices Special niches and additional manholes must be made on the heating network.

Channelless installation. To protect pipelines from mechanical influences with this installation method, reinforced thermal insulation - a shell - is installed. The advantages of ductless installation of heat pipelines are the relatively low cost of construction and installation work, a small amount of excavation work 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 gasket, movable supports are not used; pipes with thermal insulation are laid directly on sand cushion, poured onto the pre-leveled bottom of the trench. Fixed supports for ductless pipe laying, as well as for channel pipes, are reinforced concrete shield walls installed perpendicular to the heat pipes. For small diameter heat pipes, these supports are usually used outside the chambers or in chambers with a large diameter under large axial forces. To compensate for thermal elongation of pipes, bent or stuffing box expansion joints are used, located in special niches or chambers. At the turns of the route, in order to avoid pinching the pipes in the ground and to ensure their possible movement, impassable channels are constructed.

For channelless installation, backfill, prefabricated and monolithic types of insulation are used. Monolithic shells made of autoclaved reinforced foam concrete have become widespread.

Overhead laying. This type of gasket is the most convenient to operate and repair and is characterized by minimal heat losses and ease of detection of accident sites. Supporting structures for pipes are free-standing supports or masts that ensure the pipes are located at the required distance from the ground. For low supports, the clear distance (between the insulation surface and the ground) for a group of pipes up to 1.5 m wide is taken to be 0.35 m and at least 0.5 m for larger widths. Supports are usually made of reinforced concrete blocks, masts and overpasses are made of steel and reinforced concrete. The distance between supports or masts when laying pipes with a diameter of 25-800 mm above ground is taken to be 2-20 m. Sometimes one or two intermediate suspended supports are installed using guy wires in order to reduce the number of masts and reduce capital investments in the heating network.

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

5.2. Drainage of heating networks

When laying heat pipes underground, in order to avoid water penetration into the thermal insulation, an artificial lowering of the groundwater level is provided. For this purpose, together with the heat pipes, drainage pipelines are laid 200 mm below the base of the channel. The drainage device consists of a drainage pipe and a filter material of sand and gravel. Depending on the working conditions, various drainage pipes are used: for non-pressure drainage - socket ceramic, concrete and asbestos-cement, for pressure drainage - steel and cast iron diameter not less than 150 mm.

At turns and when there are differences in pipe laying, inspection wells are installed like sewer wells. On straight sections, such wells are provided at least 50 m apart. If the drain drainage water into reservoirs, ravines or sewers by gravity is impossible, pumping stations are built, which are placed near wells at a depth depending on the elevation of the drainage pipes. Pumping stations are usually built 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. Structures on heating networks

Heating chambers are intended for servicing equipment installed on heating networks with underground installation. The dimensions of the chamber are determined by the diameter of the heating network pipelines and the dimensions of the equipment. Shut-off valves, stuffing box and drainage devices, etc. are installed in the chambers. The width of the passages is 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 compensators are installed. Minimum distance from the ground surface to the top of the chamber ceiling is taken equal to 300 mm.

Currently, heating chambers made of precast 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, electrically driven valves with a high spindle are used, so an above-ground pavilion about 3 m high is built above the recessed part of the chamber.

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

Fixed supports, intended for securing pipelines of heating networks at characteristic points, they are used for all installation 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 traps and the installation sites of fixed supports. The most widespread are panel supports, which are used both for ductless installation and for laying heating network pipelines in non-passable channels.

The distances between fixed supports are usually determined by calculating the strength of pipes at a fixed support and depending on the magnitude of the compensating capacity of the adopted compensators.

Movable supports installed for ducted and ductless installation of heating network pipelines. 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 overhead laying along the walls of buildings, as well as in collectors and on brackets. Suspended supports are installed when laying above ground. In places where there is possible vertical movement 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 diameter of the pipe, the smaller the distance between the supports. When laying pipelines with a diameter of 25-900 mm in channels, the distance between movable supports is taken to be 1.7-15 m. When laying above ground, where a slightly larger deflection of pipes is allowed, the distance between supports for the same pipe diameters is increased to 2-20 m.

Compensators used to relieve temperature stresses that arise in pipelines during elongation. They can be flexible U-shaped or omega-shaped, hinged or stuffing box (axial). In addition, pipeline turns at an angle of 90-120° available on the route are used, which work as compensators (self-compensation). Installation of expansion joints involves additional capital and operating costs. Minimum costs are obtained in the presence of self-compensation areas and the use of flexible compensators. When developing heat network projects, a minimum number of axial expansion joints is used, making maximum use of the natural compensation of heat pipes. The choice of compensator type is determined by the specific conditions for laying pipelines of heating networks, their diameter and coolant parameters.

Anti-corrosion coating of pipelines. To protect heat pipes from external corrosion caused by electrochemical and chemical processes under the influence of the environment, anti-corrosion coatings are used. High quality have coatings made in the factory. The type of anti-corrosion coating depends on the temperature of the coolant: bitumen primer, several layers of insulation over 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, reinforced foam concrete, aerated concrete, perlite, asbestos cement, sovelite, expanded clay concrete, etc. For duct installation, suspended insulation made from mineral wool is widely used, for non-channel installation - from autoclaved reinforced foam concrete, asphalt -toizol, bitumen perlite and foam glass, and sometimes backfill insulation.

Thermal insulation usually consists of three layers: thermal insulation, cover and finishing. The covering layer is designed to protect the insulation from mechanical damage and moisture, i.e. to preserve thermal properties. To construct the covering layer, materials are used that have the necessary strength and moisture permeability: roofing felt, glassine, fiberglass, foil insulation, sheet steel and duralumin.

As a covering layer for ductless installation of heat pipes in moderately humid conditions sandy soils use reinforced waterproofing and asbestos-cement plaster over a wire mesh frame; for channel installation - asbestos-cement plaster over a wire mesh frame; for above-ground installation - asbestos-cement half-cylinders, sheet steel casing, galvanized or painted aluminum paint.

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

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

For overhead installation and in collectors with pipe diameter 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 shaped parts 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.

When laying heat pipes without ducts in soils with increased corrosive activity, there is a danger of pipe corrosion from stray currents. To protect against electrical corrosion, measures are taken to prevent penetration stray currents to metal pipes, or arrange so-called electrical drainage or cathodic protection (cathodic protection stations).

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

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

Energoflex products are produced in the following forms:

Tubes in 73 standard sizes with internal diameters from 6 to 160 mm and
wall thickness from 6 to 20 mm;

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

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

Mineral wool thermal insulation products are produced by the enterprises of Termosteps JSC (Tver, Omsk, Perm, Samara, Salavat, Yaroslavl), AKSI (Chelyabinsk), Tizol JSC, Nazarovsky ZTI, Komat plant (Rostov -on-Don), CJSC "Mineral Wool" (Zheleznodorozhny, Moscow region), etc.

Imported materials from ROCKWOLL, Ragos, Izomat and others are also used.

The performance properties of fibrous thermal insulation materials depend on the composition of the raw materials and technological 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. The company JSC "Mineral Wool" produces thermal insulation "ROCKWOLL" in the form of fiberglass mineral wool boards and mats. More than 27% of all fibrous thermal insulation materials produced in Russia are URSA thermal insulation produced by JSC Flyderer-Chudovo. These products are made from staple glass fiber and are characterized by high thermal and acoustic characteristics. Depending on the brand of the product, the thermal conductivity coefficient

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

CJSC "Isolation Plant" (St. Petersburg) produces insulated pipes for heating networks. Reinforced foam concrete is used as insulation here, the advantages of which include:

High maximum application temperature (up to 300°C);

High compressive strength (not less than 0.5 MPa);

Can be used for channelless installation on any depth
without laying heat pipelines and in all soil conditions;

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

The insulation is non-flammable, which allows it to be used in all
types of installation (overground, underground, channel or non-channel).

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 pipelines channelless laying with polyurethane foam (PPU) insulation in a polyethylene shell. The use of “pipe-in-pipe” type pipelines is the most progressive way of energy saving in the construction of heating networks. In the USA and Western Europe, especially in the northern regions, these designs have been used since the mid-60s. In Russia - only since the 90s.

The main advantages of such designs:

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

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

Reducing operating costs by 9-10 times;

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

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

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

Possibility of using an operational remote control system
control of insulation moisture, which allows timely response
to damage the integrity of a steel pipe or polyethylene guide
insulation coating and prevent leaks and accidents in advance.

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

CHAPTER 6. CRITERIA FOR SELECTION OF THE OPTIMAL OPTION

Aboveground pipeline laying

Overhead laying of pipelines through in-plant car roads and railway access roads are maintained in compliance with the following basic requirements. The intersection of roads by pipeline networks is accepted at an angle of 90° to the axis of the road, and in cases where it is impossible to meet this requirement, it is allowed to reduce the intersection angle to 45°C.

Heating networks are laid by above-ground or underground (extremely rare) methods. When laying above ground, pipelines are laid on overpasses or on free-standing supports. At underground method pipelines are laid in non-passable channels.

Simple suspended supports are used for overhead laying of pipelines on overpasses with guy wires in self-compensation areas or when installing U-shaped compensators. The maximum spans between suspended supports are additionally checked by calculating the maximum permissible load on the support.

In industrial buildings and structures, overhead installation of pipelines should be provided (along walls, columns and other building structures), and if such placement is not possible, it is allowed to provide for the laying of pipelines in underground channels. overhead pipeline laying

When laying pipelines above ground, in order to avoid freezing of the transported medium at subzero outside temperatures, a continuous supply of steam and condensate must be provided (especially for small-diameter pipelines) or associated heating of the condensate pipelines must be provided.

Exhaust and secondary steam lines and condensate lines are, whenever possible, laid together with existing fresh steam lines, water lines and process pipelines. When the groundwater level is high, above-ground installation of steam and condensate pipelines should be preferably used.

Aboveground pipeline laying was carried out mainly on overpasses and high supports. Some domestic factories also used lowered laying (2-2.5 m from the ground level).

As a rule, above-ground installation of pipelines should be provided on overpasses or free-standing supports.

Aboveground laying of pipelines for transporting heated products should be provided on free-standing supports and overpasses with a height that eliminates the thermal impact of pipelines on permafrost foundation soils.

When laying pipelines above ground, depending on their characteristics and operating conditions, the following types of supports are used: fixed and movable (sliding, roller and suspended). Movable supports allow the pipeline to move during temperature deformations.

Aboveground laying of pipelines along racks is convenient to use, since the pipelines are accessible for repair and monitoring; however, this method is expensive and therefore has not been widely used.

For turbulent mode (pipe diameter 200-- 300 mm, g 80 ° C) Besh recommends taking the following values ​​for k in W/m deg dry soil, sand -- 5.8 moist damp soil -- 5.8 + 11.6 soil , containing groundwater, quicksand, -- 17.4 87.0. For overhead laying of pipelines in still air = 12--14 W/m deg, and in rain and wind A = 14--23 W/m deg.

Note The mass of snow and ice should be taken into account in calculations only when laying pipelines above ground outdoors.

When laying pipelines above ground through roadways and streets, the height of the pipelines (clear) from ground level to the outer surface of the insulation must be at least 4.5 m, except for laying through the railway track, when the distance from the rail head to the outer surface of the insulation should not be less than 6 m (for normal gauge). When the distance from the bottom point of the pipeline insulation to the ground level is less than 2 m, then transition stairs must be installed for the passage of people. When installing pipelines on an overpass, the edges of the latter must be at least 5 m from combustible buildings and explosive production premises from the ammonia storage warehouse - 10 m from the axis of the railway track - 3 m and from travel and pedestrian roads.

Foreign practice in the operation of chemical and oil refineries also confirms the feasibility of above-ground installation of pipelines.

Each of the three types of above-ground pipeline laying (high, low and low) has its own technical and economic indicators, which serve as a criterion for selection in specific conditions optimal type gaskets, including combined high with low, low with low, etc.

When laying a pipeline above ground, in order to maintain the brine temperature at least 2-3 °C, depending on local climatic conditions, the pipeline should be thermally insulated or also heated. When laying the brine pipeline above ground in the southern regions, its thermal insulation is not provided.

Overhead laying of pipelines is carried out on overpasses, pile supports, along the walls of buildings and when crossing roads and ravines, in factory territories. Pipes are laid in ring thermal insulation or in insulated boxes. The above-ground laying of the pipeline is carried out on a bedding with embankment. When laying above ground, heat and waterproofing of pipelines is provided.

The disadvantage of above-ground pipeline installation is the need to allocate a strip of irrigated or arable land at least 4 m wide for permanent use.

At the intersections of overpasses on which pipelines with flammable gases are laid, railways and internal plant tracks, valves, water collectors, stuffing box compensators, flange connections and other mounting components in which leaks may occur during operation should not be installed on pipelines. In these cases, pipelines are installed only by welding. The underground or above-ground installation of pipelines with flammable gases together with telephone, power and lighting cables is not allowed.

When laying pipelines above ground on overpasses or free-standing supports, joint laying of pipelines of all categories with process pipelines for various purposes is allowed, with the exception of laying in overpass-type galleries, as well as cases where such laying contradicts the requirements of other safety rules.

Defects are eliminated by reducing overpressure to zero and turning off the compressor. During pneumatic strength tests, a protected (safe) area must be established both indoors and outdoors. The minimum zone distance must be at least 25 m for overhead pipeline installation and at least 10 m for underground installation. The boundaries of the zone are fenced off.

Deviations from the design position of the supports when laying pipelines above ground should not exceed 5 mm for the displacement of the foundations relative to the alignment axes, 10 mm for the deviation of the support axes from the vertical, and +5 mm for the elevation of the top of the supports.

Overhead laying of pipelines on high supports is dangerous look work, therefore it is necessary to strictly comply with all safety rules and requirements of the work project.

When laying pipelines above ground through passages, the height of the pipelines (in clear) from the ground level to the outer surface of the insulation must be at least 5 m, except for cases of laying through the railway track, when the distance (in clear) from the rail head to the outer surface of the pipeline insulation must be at least 6 m (for normal gauge).

When laying together overhead pipelines of large and small diameters in order to increase the distances between supporting structures (overpass masts), it is recommended to a) use large-diameter pipes Vu = 500 mn or more) as load-bearing structures to create support or hang small-diameter pipes from them b) apply local stiffening of pipes of small and medium diameters by welding stiffeners.

Fittings and instruments for ground and above-ground pipeline laying are placed in chambers-wells, chambers-booths, chambers-thermal centers.

When laying pipelines above ground, they use paint coatings, in which the most common are the following.

Aboveground laying of pipelines on low supports is provided only in cases where traffic, lifting mechanisms and equipment are not expected to move in the area of ​​the territory through which pipelines are laid.

The above-ground pipeline laying scheme is carried out in such a way as to make maximum use of the plant territory intended for creating fire-prevention gaps between objects.

U-shaped expansion joints have a large compensation capacity (up to 700 mm) and are used primarily for above-ground laying of pipelines, regardless of their diameter.

Aboveground laying of pipelines is carried out on overpasses, pile supports, along the walls of buildings and is used when crossing roads and ravines, in factory territories. Pipes are laid in ring thermal insulation or in insulated boxes.

The assignment for the development of drawings of canals and overpasses is drawn up on the basis of the routing of the main technological lines and regulatory guidelines for underground and above-ground laying of pipelines. As a rule, water conduits and sewer lines are laid in intra-shop channels. The cross-sectional dimensions of the channel should ensure ease of installation and repair of pipes, placement of separate outlets to technological equipment, placement of primary elements of instrumentation and instrumentation (diaphragms, water meters, etc.) and installation of shut-off valves.

The laying of pipelines can be underground (in through-channels - tunnels, non-through-through channels and cable-free - directly in the ground), above-ground on supports and above-ground - on overpasses. Ground and above-ground laying of pipelines is preferable, since it provides the possibility of visual monitoring of the condition of pipelines and facilitates their installation and repair. Laying pipelines in the ground, especially gas pipelines, is dangerous because leaks can travel significant distances from the point of damage to the pipeline, and determining the location of the leak is difficult and common.

Before filling the pipelines with coolant, they are thoroughly washed and the tightness of the bolts on the flange connections is checked, the operation of shut-off valves, air bleed valves, drainage devices, packing of seals for compensators, valves and valves, the presence of sleeves for thermometers and fittings for pressure gauges in the required places, accessibility and uncluttered premises of subscriber inputs. When laying pipelines above ground, the condition of the supporting structures and the correct installation of movable supports are also checked.

Underground or above-ground laying of pipelines with flammable gases together with telephone, power and lighting cables is prohibited.

Fire hydrants are installed on main sections of networks. Overhead pipelines It is advisable to lay it in earthen ridges, buried channels using continuous backfill, as well as in semi-buried channels. Aboveground laying of pipelines is carried out on low supports, masts, overpasses or in ventilated undergrounds of buildings, in heated rooms and insulated ducts.