Stretching value of n-shaped expansion joints. Calculation of pre-stretching of the compensator during installation

Compensators of thermal networks. In this article we will talk on the selection and calculation of compensators for thermal networks.

What are compensators for? Let's start with the fact that when heated, any material expands, which means that the pipelines of heating networks lengthen with an increase in the temperature of the coolant passing through them. For trouble-free operation of the heating network, compensators are used that compensate for the elongation of pipelines during their compression and tension, in order to avoid pinching of pipelines and their subsequent depressurization.

It should be noted that for the possibility of expansion and contraction of pipelines, not only compensators are designed, but also a system of supports, which, in turn, can be both "sliding" and "dead". As a rule, in Russia the regulation of the heat load is of high quality - that is, when the temperature changes environment, the temperature at the outlet of the heat supply source changes. Due to the qualitative regulation of the heat supply, the number of expansion-compression cycles of pipelines increases. The resource of pipelines is reduced, the risk of pinching is increasing. Quantitative load regulation is as follows - the temperature at the outlet of the heat supply source is constant. If it is necessary to change the heat load, the coolant flow rate changes. In this case, the metal of the heating network pipelines works in lighter conditions, the minimum number of expansion-compression cycles, thereby increasing the resource of the heating network pipelines. Therefore, before choosing expansion joints, their characteristics and quantity must be determined with the amount of expansion of the pipeline.

Formula 1:

δL=L1*a*(T2-T1)where

δL - pipeline elongation,

mL1 - length of the straight section of the pipeline (distance between fixed supports),

ma - coefficient of linear expansion (for iron it is equal to 0.000012), m/deg.

T1 - maximum temperature of the pipeline (the maximum temperature of the coolant is taken),

T2 - minimum temperature pipeline (you can take the minimum ambient temperature), ° С

For example, consider the solution of an elementary problem of determining the magnitude of the elongation of the pipeline.

Task 1. Determine how much the length of a straight section of a pipeline 150 meters long will increase, provided that the coolant temperature is 150 ° C, and the ambient temperature during the heating period is -40 ° C.

δL=L1*a*(T2-T1)=150*0.000012*(150-(-40))=150*0.000012*190=150*0.00228=0.342 meters

Answer: the length of the pipeline will increase by 0.342 meters.

After determining the amount of elongation, it should be clearly understood when a compensator is needed and when it is not needed. For an unambiguous answer to this question, you need to have a clear pipeline diagram, with its linear dimensions and supports applied to it. It should be clearly understood that a change in the direction of the pipeline is able to compensate for extensions, in other words, rotation with overall dimensions not less than the dimensions of the compensator, with correct arrangement of supports, is able to compensate for the same elongation as the compensator.

And so, after we determine the amount of elongation of the pipeline, we can proceed to the selection of compensators, you need to know that each compensator has a main characteristic - this is the amount of compensation. In fact, the choice of the number of compensators comes down to the choice of the type and design features compensators. To select the type of compensator, it is necessary to determine the diameter of the heat network pipe based on bandwidth pipe the required power of the heat consumer.

Table 1. The ratio of U-shaped compensators made from bends.

Table 2. Selection of the number of U-shaped compensators based on their compensating capacity.

Task 2 Determining the number and size of compensators.

For a pipeline with a diameter of DN 100 with a length of a straight section of 150 meters, provided that the carrier temperature is 150 ° C, and the ambient temperature during the heating period is -40 ° C, determine the number of compensators. bL = 0.342 m (see Task 1). According to the Table 1 and Table 2, we determine the dimensions of n-shaped expansion joints (with dimensions of 2x2 m it can compensate for 0.134 meters of pipeline extension), we need to compensate for 0.342 meters, therefore Ncomp \u003d bL / ∂x \u003d 0.342 / 0.134 \u003d 2.55, rounded up to the nearest whole number in the direction of increase and that - 3 compensators with dimensions of 2x4 meters are required.

Currently, lens compensators are becoming more widespread, they are much more compact than U-shaped, however, a number of restrictions do not always allow their use. The resource of the U-shaped compensator is much higher than the lens one, due to the poor quality of the coolant. The lower part of the lens compensator is usually "clogged" with sludge, which contributes to the development of parking corrosion of the metal of the compensator.

The displacement value (compensating capacity) of compensators is usually expressed as a combination of positive and negative numerical values ​​(±). A negative (-) value indicates the allowable compression of the compensator, a positive (+) value indicates its allowable expansion. The sum of the absolute values ​​of these values ​​is the total displacement of the compensator. In most cases, compensators work in compression, compensating for the thermal expansion of pipelines, less often (cooled media and cryogenic products) - in tension.

Pre-stretching during installation is necessary for rational use full displacement of the compensator, depending on the nature of the pipeline, installation conditions and the prevention of stress conditions.

The peak values ​​of pipeline expansion depend on the minimum and maximum temperature its operation. For example, the minimum temperature of the pipeline Tmin = 0°C and the maximum T max = 100°C. Those. temperature difference At = 100°C. With a pipeline length L equal to 90 m, the maximum value of its pipeline extension AL will be 100 mm. Imagine that expansion joints with an offset of ±50 mm are used for installation on such a pipeline, i.e. with a total offset of 100 mm. Let's also imagine that the ambient temperature at the stage of their installation T y is 20°C. The nature of the work of the compensator under such conditions will be as follows:

• at 0°C - the compensator will be stretched by 50 mm
• at 100°C - the compensator will be compressed by 50 mm
• at 50°C - the compensator will be in a free state
• at 20°C - the compensator will be stretched by 30 mm

Therefore, a preliminary stretching of 30 mm during installation (T y = 20°C) will ensure its efficient operation. When the temperature rises from 20°C to 50°C during commissioning of the pipeline, the compensator will return to the free (non-stressed) state. When the temperature of the pipeline rises from 50°С to 100°С, the offset of the compensator relative to the free state in the direction of compression will be calculated 50 mm.

Definitionvaluespreliminarysprains

Let's take the length of the pipeline equal to 33 meters, maximum / minimum operating temperature+150°С /-20°С respectively. With such a temperature difference, the linear expansion coefficient a will be 0.012 mm/m*°C.

The maximum pipe extension can be calculated as follows:

∆L = α*L*Δ t = 0.012 x 33 x 170 = 67 mm

The prestretch value PS is determined by the formula:

PS = (ΔL/2) - ΔL(Ty-Tmin): (Tmax-Tmin)

Thus, during the installation of the compensator, it must be installed with a pre-stretch PS equal to 18 mm.

On fig. 1 shows the distance required to mount the compensator in the pipeline line, defined as the sum of the free length lq of the compensator and the pre-stretch PS.

On fig. 2 shows that during installation, on one side, the compensator is fixed with a flange or welded.

Installation of heat networks, which must be carried out by the in-line method, includes earthwork, assembly and welding, stone, concrete, reinforced concrete, insulating, pressure testing, carpentry and other works.

With a properly organized flow method of construction, work is carried out in a certain technological sequence. The flow is organized in such a way as to most economically dispose of forces and means, to perform a large amount of work in a short time, at low cost and with high quality construction.

Heating networks in cities and other settlements are laid in lanes specially designated for the construction of engineering structures, parallel to the red lines of streets, roads and driveways outside the carriageway and green spaces. When justified, it is possible to lay networks under the carriageway and sidewalks.

For heating networks, underground laying is mainly provided, less often - aboveground(in the territories of enterprises, outside the city, with a high level of groundwater, in areas permafrost and other cases where underground laying is impossible or impractical).

When laying underground, pipelines of heating networks (heat pipelines) are laid in channels - special building structures, protecting pipelines, or channelless. Channels can be through and non-through. Depending on the accepted design of underground laying (in impassable or through channels, collectors), it is allowed to lay heat networks together with other engineering networks(water supply, communication cables, power cables, pressure sewerage).

With above-ground (open) laying, heat pipes are laid on brackets along the walls of buildings, on concrete, reinforced concrete and metal supports. When passing heat pipes through railways and water barriers use bridge structures. Heat pipelines laid under the bed of a river or canal, along the slopes and bottom of the ravine, are bent in accordance with the terrain. Such structures are called siphons. When laying under the riverbed, heat pipelines are enclosed in steel pipes (cases). Against the ascent, the pipes are held by weights. In this way, other types of underground networks (water supply, gas pipeline and sewerage) are also built when they cross rivers, ravines and other similar obstacles.

Assembly steel pipes large diameters into links using a pipe-laying crane. Prior to the start of pipe assembly, pipes are brought into the links and laid out along a pre-marked axis; clean the ends of the pipes from contamination and straighten the deformed edges.

Steel pipes are assembled into links in the following sequence: the beds are laid and aligned, the pipes are laid on the beds using a pipe-laying crane; clean and prepare pipe edges for welding; center the joints with a centralizer, supporting the pipes with a pipe-laying crane during the tacking of the joint by electric welding; pipe joints are welded with the pipe link turning; the beds are removed and the assembled link is installed on the inventory linings.

Laying and alignment of beds. Pipelayers, pulling the tape measure along the axis of the layout of the links, mark on it the places for laying the beds. Then they bring the beds and lay them out according to the markings, while the middle of the beds should coincide with the axis of the layout. At the ends of the extreme beds, four metal pins are hammered and a twine is pulled between the extreme beds at the level of the top of the beds. Focusing on this level, intermediate beds are installed, cutting off or knocking out the soil under them with shovels.

Laying pipes on the bed. Having marked the middle of the pipe with a tape measure, the pipe-laying crane is installed so that its boom is above the center of gravity of the pipe. The pipe is slinged, and the crane operator lifts it by 20-30 cm. After making sure that the slinging is reliable and correct, the crane operator lifts the pipe to a height of 1 m and, at the command of the pipelayer, lays the pipe on the bed. Pipelayers, standing at both ends of the pipe, keep it from turning.

Cleaning and preparation of pipe edges for welding. When loading, transporting or unloading, ellipticity, dents, etc. may form at the ends of the pipes. If necessary, the ends of the pipes should be straightened. The curvature of the ends is straightened with the help of screw jacks or manually by hitting a sledgehammer with preheating of the pipe at the place of straightening.

In the event that the deformed ends cannot be straightened, they are cut off by gas cutting, followed by cleaning the edges.

Using chisels and hammers, pipelayers clean the edges of pipes from dirt and ice. Electric grinders, files, reversible angular pneumatic brushes clean the edges to a metallic sheen for a length of at least 10 mm from the outside and from the inside.

Centering the joint and supporting pipes when tacking the joint. The driver sets the pipe-laying crane opposite the middle of the pipe and lowers the towel sling. The pipelayer slings the pipe and gives the command to lift it by 0.5 m and move it to the docking point. After moving the pipe, the workers lay it on the beds, visually center the joint, straighten and fix the pipe on the beds with wooden stakes. Then a centralizer is installed on the joint and the joint is fixed by turning the handle.

The electric welder, having checked the size of the gap between the ends of the pipes to be joined along the entire circumference with a universal template and making sure that the size of the gap corresponds to the norm, welds the joint.

If, when checking with a template, the gap between the ends of the pipes does not meet the regulatory requirements, the pipelayers loosen the centralizer, the crane operator changes the gap with the movement of the boom, while the pipelayers help him with crowbars. After obtaining the required gap, the position of the pipe is finally fixed with wooden wedges, the centralizer lever is tightened to failure, and then the joint is seized by welding. After tacking the joint, the pipelayers remove the centralizer.

Turning the link when welding pipes. After applying a seam to a quarter of the circumference of the pipe on each side, the pipelayers turn the link, fixing it with wooden wedges on the beds at the joint.

Installation and welding of mobile supports. Movable supports perceive the load from the weight of the heat pipe, in addition, ensure the movement of the pipeline in the axial direction, which occurs due to a change in its length with a change in temperature. Factory-made movable supports are sliding, skid, roller, suspended. Of the listed designs of movable bearings, sliding bearings are the most widely used.

Sliding supports can be low and high, normal length and shortened. The type of support is chosen depending on the thickness of the thermal insulation and the distance between the supports. Low (linings) and high supports protect pipes from abrasion when moving heat pipes. In addition, high supports protect the thermal insulation from contact with the base of the channel.

Sliding supports are installed on the support stones with some displacement towards the fixed support. At start hot water the pipeline will heat up and lengthen somewhat; the sliding support welded to the pipeline will shift towards the compensator and take up a working position on the support stone. If the sliding support is installed on the support stone without mounting offset, then it can come off the support stone during the operation of the heat pipeline. The sliding support moves along a metal lining, concreted into the support stone and protruding above its upper plane.

The distance between the sliding supports depends on the distance between the supporting stones, which in turn is taken depending on the nominal diameter of the pipes.

It is not allowed to weld sliding supports in places of welded joints. The support must be welded without lateral displacements in relation to the vertical axis of the pipeline.

Having marked the installation sites of the supports on the pipes, they are adjusted in place, grabbed and welded. Sliding supports are welded before pressure testing of the pipeline, since it is not allowed to perform welding work on a pipeline that has passed a hydraulic or pneumatic test for density and strength.

Installation of stuffing box compensators. Gland compensators perceive axial temperature deformations of pipelines of heating networks and thereby protect the pipeline and fittings from destructive stresses.

Gland compensators are made one-sided and two-sided. The compensating capacity of a double-sided compensator is twice that of a single-sided compensator.

The compensator is connected to the main pipeline by welding.

The compensator is installed in the extended position to the full length of the stroke, which depends on the compensating capacity, with a gap between the body thrust ring and the safety ring on the sleeve. The gap compensates for the change in the length of the pipeline when the temperature of the pipes drops after the compensator is installed (due to a decrease in the outside air temperature).

When installing the compensator, the stuffing box seals (gland) should be carefully stuffed, since the replacement of the stuffing during operation leads to a shutdown of the heating networks. The joints of the stuffing box rings must be displaced relative to each other, the seams of the stuffing box compensators must be even, and the craters must be welded.

Flange installation. Pipe fittings and linear equipment are connected to the pipeline by welding or by flanges tightened with bolts, studs and nuts. With a conditional internal pressure in the pipeline up to 40 kgf / cm2 (4 MPa), bolts are used, at 40 kgf / cm2 or more, studs are used. The density of the flange connection depends on the accuracy of the surface treatment of the flanges, the quality of the bolts and the uniformity of their tightening. The flanges must be parallel to one another.

Flanges are welded perpendicular to the axes of the nozzles. The misalignment should not exceed 1 mm per 100 mm of the outer diameter of the flange (but not more than 3 mm). After fitting the flanges, two or three bolts are installed in place to align the gasket, then the remaining bolts are mounted, nuts are screwed onto them and the flange connection is tightened. To avoid distortion, the nuts are tightened gradually in a crosswise manner.

The diameter of the bolts must match the diameter of the holes of the flanges to be connected.. The bolt heads are located on one side of the connection. Flanged bolts may protrude above the nut by at least three threads and by no more than half the bolt diameter. It is necessary that the inner diameter of the gasket correspond to the inner diameter of the pipe with a tolerance of 3 mm, and its outer diameter must be not less than the diameter of the connecting ledge and not more than the diameter of the circle tangent to the bolts.

For a tighter fixing of the gasket, sometimes a protrusion is made on one of the flanges to be connected, and a depression on the other. The protrusion enters the cavity, and thus the gasket is securely fastened between the flanges. For the same purpose, concentrically located recesses - risks are applied to the mirror of the flanges.

When installing pipe fittings , for example gate valves, excessive tightening of the flanges with bolts should not be allowed, since the density and strength of the flange connection is reduced.

Stretching U-shaped compensators. To increase the compensating ability, U-shaped expansion joints are stretched. The stretching value specified in the project should be equal to half the elongation of the compensated section. The compensator is stretched only after fixed supports are installed on its two sides; thus, when the expansion joint is stretched, the pipeline remains motionless at the points of its welding to the supports. Only one joint remains unwelded - in the place of expansion joint stretching.

The compensator is stretched with the help of corner ties, jacks, hoists, etc.. At an equal distance along the circumference of the pipe of the U-shaped compensator, four plates are welded, and four plates are welded to the previously laid pipe. The distance between the plates must not exceed the length of the tie bolts. Coupling bolts are inserted into the hole of the plates and, by screwing the nuts, the compensator is stretched, bringing the edges of the pipes together to the gap required for welding. The joints are seized by electric welding, the plates are cut off cutting torch and the joint is welded.

Installation of heating network nodes. The pipelayer cleans the ends of pipes and pipes from rust and dirt with a steel brush or file. Then, using a crane, the unit is fed into the heating network chamber, where it is installed in the design position. After that, the edges are adjusted and trimmed and the joints are centered with an external centralizer. The joints are welded, the centralizer is transferred to the next work.

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1.1. Products are allowed to be used in construction areas with a design outdoor temperature for designing heating systems not lower than minus 40°С. The seismicity of construction areas is not more than nine points on the Richter scale.

1.2. Products are allowed to be used when the content of chlorides in the network water is not more than 250 mg/kg.

1.3. Products must be installed on straight sections of pipelines, limited by fixed supports. Only one product is allowed between fixed supports.

A deviation from straightness in plan and profile is allowed with the obligatory installation of guide supports in the same places at least two in front of each compensating device.

1.4. Way of accession to the pipeline - welding.

1.5. For any method of laying pipelines, except for underground channelless, the installation of compensating devices should be provided, as a rule, at one of the fixed supports.

1.6. On channelless underground heating networks, the product should be placed in the middle of the pipeline section, limited by fixed supports.

1.7. Before and after the compensating device, it is necessary to install guide supports, which exclude the movement of pipelines in the radial direction.

When channelless laying of the pipeline, the installation of guide supports is not required.

Examples of layouts for the bellows compensating device, guides and fixed supports are shown in the figure:

6.8. On sections of pipelines with bellows compensating devices, the use of suspended supports is not allowed.

6.9. When choosing fixed supports, the following factors should be considered:

Spacer force of the compensator;

Compensator stiffness force;

Friction in guides and sliding bearings;

Value centrifugal force that occurs when the pipeline is bent.

Calculation of loads on end and intermediate fixed supports at various ways installation of bellows compensating devices is carried out at the stage of designing a heat network and is given in special literature.

6.10. The maximum distance between the fixed supports of the pipeline is determined by the formula:

where 0.9 is the safety factor, taking into account calculation inaccuracies and errors

installation features;

Compensating capacity of the compensator, mm

a - average coefficient of linear expansion of pipe steel at

heating from 0°С to t°С, mm/m°С;

t - design temperature of network water in the supply pipeline, °С;

t RO - calculated outdoor temperature for system design

heating, taken equal to average temperature air most-

colder than the five-day period according to the chapter SNiP "Construction climatology

and geophysics”, °C.

1.8. Products do not require maintenance during operation and belong to the class of non-repairable products, they do not require the construction of special chambers, and when laying on the ground - platforms for maintenance.

Installation instructions.

2.1. Installation of products is carried out in accordance with the design of the pipeline, executed by the design organization.

2.2. Before installation, products must be checked for compliance with their specifications the design of the heating network, as well as the absence of mechanical damage.

2.3. When moving compensating devices during the installation period, measures must be taken to protect the product from shocks, shocks and exclude pollution or flooding. groundwater its internal cavity.

2.4. While doing welding work The ends of the insulation of the compensating device should be protected with detachable tin screens 0.8 ... 1 mm thick to prevent its ignition.

Installation of products is allowed to be carried out at an air temperature of at least minus 30 ° C.

2.5. Before welding the product to the pipeline, the deviations of the product connections with the pipeline are checked, which should not exceed the following values: nozzle alignment tolerance - 2 mm;

the tolerance of parallelism of the ends of the connecting pipes and connected pipes is 3 mm.

The maximum welding gap between the branch pipe and the pipeline is 2 mm.

2.6. The product should be installed on heat pipelines so that the direction of the arrow (if any) on the body of the compensating device coincides with the direction of movement of the coolant.

2.7. Products are mounted on the pipeline with preliminary stretching.

The length of the compensator during installation Lmount., mm is determined by the formula:

L builds.- building length of the compensator in the state of delivery, mm;

Compensating capacity of the compensator, mm;

A- coefficient of linear expansion of pipe steel,

removable 0.012 mm/m °С;

t hire. - the lowest air temperature during operation, °C;

L- the length of the compensator section between the fixed supports,

on which the compensator is mounted, m.

The mounting length of the compensating device is set by the installer.

The sections of the pipeline before and after the compensating device must be mounted and fixed in fixed supports so that the distance between the ends of the pipes at the installation site of the product corresponds to the installation length L mont. at ambient temperature at the moment of fixing the pipeline in the second fixed support; the ambient air temperature and the distance between the ends of the fixed pipes must be recorded in an act;

The compensating device is welded to one of the sections of the pipeline;

A universal mounting device is installed on the free connecting pipe of the product and the free end of the pipeline, with the help of which the compensator of the product is stretched to the junction with the pipeline, and the joint is welded;

Remove the mounting fixture from the product.

When expanding the compensator, it is necessary to ensure the same movement of the connecting pipes relative to the ends of the product.

If it is impossible to install the product in the middle of the straight section of the heat pipeline between the fixed supports, it is allowed to install it anywhere in the straight section of the heat pipeline. To do this, when the expansion joint is stretched, it is necessary to ensure the movement of the connecting pipes relative to the ends of the compensating device by inversely proportional lengths of the sections of the heat pipe between the product and the fixed supports.

2.9. The connection of the conductors-indicators of the product with a common signal system must be made after the completion of welding work, before insulating the joints of the connecting pipes with the heat conductor. Indicator conductors should not touch the metal of the pipes anywhere.

The displacement value (compensating capacity) of compensators is usually expressed as a combination of positive and negative numerical values ​​(±). A negative (-) value indicates the allowable compression of the compensator, a positive (+) value indicates its allowable expansion. The sum of the absolute values ​​of these values ​​is the total displacement of the compensator. In most cases, compensators work in compression, compensating for the thermal expansion of pipelines, less often (cooled media and cryogenic products) - in tension.

Pre-stretching during installation is necessary for the rational use of the full displacement of the compensator, depending on the nature of the pipeline, installation conditions and the prevention of stress conditions.

Peak values ​​of pipeline expansion depend on the minimum and maximum temperatures of its operation. For example, the minimum temperature of the pipeline Tmin = 0°C and the maximum T max = 100°C. Those. temperature difference At = 100°C. With a pipeline length L equal to 90 m, the maximum value of its pipeline extension AL will be 100 mm. Imagine that expansion joints with an offset of ±50 mm are used for installation on such a pipeline, i.e. with a total offset of 100 mm. Also, imagine that the ambient temperature at the stage of their installation T y is 20°C. The nature of the compensator under such conditions will be as follows:

• at 0°C - the compensator will be stretched by 50 mm
• at 100°C - the compensator will be compressed by 50 mm
• at 50°C - the compensator will be in a free state
• at 20°C - the compensator will be stretched by 30 mm

Therefore, a preliminary stretching of 30 mm during installation (T y = 20°C) will ensure its efficient operation. When the temperature rises from 20°C to 50°C during commissioning of the pipeline, the compensator will return to the free (non-stressed) state. When the temperature of the pipeline rises from 50°С to 100°С, the offset of the compensator relative to the free state in the direction of compression will be calculated 50 mm.

Definitionvaluespreliminarysprains

We will take the length of the pipeline equal to 33 meters, the maximum / minimum operating temperature is +150 ° C / -20 ° C, respectively. With such a temperature difference, the coefficient of linear expansion a will be 0.012 mm/m*°C.

The maximum pipe extension can be calculated as follows:

∆L = αxLxΔ t = 0.012 x 33 x 170 = 67 mm

The prestretch value PS is determined by the formula:

PS = (ΔL/2) - ΔL (Ty-Tmin): (Tmax-Tmin)

Thus, during the installation of the compensator, it must be installed with a pre-stretch PS equal to 18 mm.

On fig. 1 shows the distance required to mount the compensator in the pipeline line, defined as the sum of the free length lq of the compensator and the pre-stretch PS.

On fig. 2 shows that during installation, on one side, the compensator is fixed with a flange or welded.