To help installers. Calculation of thermal expansion of pipelines Formula for stretching a U-shaped compensator of a heating network

Installation of heating networks, which must be carried out using the in-line method, includes earthworks, installation and welding, stone, concrete, reinforced concrete, insulation, crimping, carpentry and other works.

With a properly organized flow construction method, work is performed in a certain technological sequence. The flow is organized in such a way as to use forces and resources most economically, to complete a large volume of work in a short time, at low cost and with high quality construction.

Heating networks in cities and other populated areas are laid in strips specially designated for the construction of engineering structures, parallel to the red lines of streets, roads and driveways outside the roadway and green belts. Once justified, it is possible to lay networks under the roadway and sidewalks.

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

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

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

Assembling large-diameter steel pipes into links using a pipe-laying crane. Before the start of pipe assembly work, pipes are delivered into sections and laid out along a pre-marked axis; clean the ends of pipes from dirt and straighten deformed edges.

Steel pipes are assembled into links in the following sequence: the tracks are laid and aligned, the pipes are laid on the tracks 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 while tack welding the joint; weld pipe joints by rotating the pipe section; remove the beds and install the assembled link on inventory pads.

Laying and alignment of beds. Pipelayers, pulling a tape measure along the axis of the links, mark on it the places where the beds will be laid. 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. Four metal pins are driven into the ends of the outer beds and twine is pulled between the outer beds at the level of the top of the bed. Focusing on this level, intermediate beds are installed, cutting off or tamping down the soil under them with shovels.

Laying pipes on flats. Having marked the middle of the pipe using 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 slung, and the crane operator lifts it by 20-30 cm. After making sure that the sling 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. Pipe layers, standing at both ends of the pipe, keep it from turning around.

Cleaning and preparing pipe edges for welding. During loading, transportation or unloading, ellipse, dents, etc. may form at the ends of the pipes. If necessary, the ends of the pipes should be straightened. Curved ends are straightened using screw jacks or manually using a sledgehammer with pre-heating of the pipe at the straightening site.

If the deformed ends cannot be straightened, they are cut with gas cutting and then the edges are cleaned.

Using chisels and hammers, pipe layers clear the edges of pipes from dirt and ice. Using electric grinders, files, and reversible angled pneumatic brushes, the edges are cleaned to a metallic shine for a length of at least 10 mm from the outside and inside.

Centering the joint and supporting the pipes when the joint is tacked. The operator places the pipe-laying crane opposite the middle of the pipe and lowers the sling-towel. The pipe layer rigs the pipe and gives the command to lift it 0.5 m and move it to the joining point. After moving the pipe, workers lay it on the beds, visually center the joint, straighten and secure the pipe on the beds with wooden stakes. Then a centralizer is installed on the joint and the joint is secured by turning the handle.

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

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

Rotating the link when welding pipes. After applying a seam to a quarter of the pipe's circumference on each side, pipelayers rotate the link, securing it with wooden wedges on the beds at the joint.

Installation and welding of moving supports. Movable supports take up the load from the weight of the heat pipeline; in addition, they ensure the movement of the pipeline in the axial direction, which occurs due to a change in its length when the temperature changes. Factory-made movable supports can be sliding, skid, roller, or suspended. Of the listed designs of movable supports, sliding supports are the most widely used.

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

Sliding supports are installed on supporting stones with some displacement towards the fixed support. When starting hot water the pipeline will heat up and lengthen somewhat; the sliding support welded to the pipeline will move towards the compensator and take a working position on the support stone. If the sliding support is installed on the support stone without mounting displacement, it may come off the support stone during the operation of the heat pipeline. The sliding support moves on a metal pad concreted into the supporting 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 at welded joints. The support must be welded without lateral displacements in relation to the vertical axis of the pipeline.

Having marked the installation locations of the supports on the pipes, they are adjusted in place, grabbed and welded. Weld the sliding supports before crimping the pipeline, since welding work is not allowed on a pipeline that has passed a hydraulic or pneumatic test for density and strength.

Installation of stuffing box expansion joints. Stuffing box expansion joints perceive axial temperature deformations of heating network pipelines and thereby protect the pipeline and fittings from destructive stresses.

Stuffing box expansion joints are manufactured as single-sided or double-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 stroke length, which depends on the compensating capacity, with a gap between the housing thrust ring and the safety ring on the cup. The gap compensates for the change in pipeline length when the temperature of the pipes decreases after installing the compensator (due to a decrease in the outside air temperature).

When installing the compensator, the stuffing box seals (oil seal) should be carefully filled, since replacing the packing during operation leads to a stop in the operation of the heating networks. The joints of the oil seal rings must be offset from one another, the seams of the oil seal expansion joints must be smooth, and the craters must be welded.

Installation of flanges. Pipeline fittings and linear equipment are connected to the pipeline by welding or on flanges tightened with bolts, studs and nuts. At a nominal internal pressure in the pipeline of 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 processing of the flanges, the quality of the bolts and the uniformity of their tightening. The flanges must be parallel to one another.

The flanges are welded perpendicular to the axes of the pipes. 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 in place, install two or three bolts to align the gasket, then mount the remaining bolts, screw the nuts onto them and tighten the flange connection. To avoid distortion, the nuts are tightened gradually in a cross pattern.

The diameter of the bolts must correspond to the diameter of the holes of the flanges being connected. The bolt heads are located on one side of the connection. Flange connection bolts may protrude above the nut by at least three threads and by no more than half the diameter of the bolt. It is necessary that the inner diameter of the gasket corresponds to the inner diameter of the pipe with a tolerance of 3 mm, and its outer diameter must be no less than the diameter of the connecting protrusion and no more than the diameter of the circle tangent to the bolts.

To secure the gasket more tightly, sometimes a protrusion is made on one of the flanges being connected, and a depression on the other. The protrusion fits into the recess, and thus the gasket is securely fastened between the flanges. For the same purpose, concentrically located recesses - marks - are applied to the flange mirror.

When installing pipeline fittings , for example, valves, the flanges must not be excessively tightened with bolts, as the density and strength of the flange connection is reduced.

Stretching U-shaped expansion joints. To increase the compensating capacity, U-shaped compensators are stretched. The amount of stretch indicated in the project must be equal to half the elongation of the compensated section. The compensator is stretched only after fixed supports are installed on both sides; Thus, when the compensator is stretched, the pipeline remains motionless in the places where it is welded to the supports. Only one joint remains unwelded - at the expansion joint.

The compensator is stretched using corner ties, jacks, hoists, etc.. Four plates are welded at an equal distance around the circumference of the U-shaped compensator pipe, as well as four plates to the previously laid pipe. The distance between the plates should not exceed the length of the tie bolts. Pinch bolts are inserted into the hole of the plates and, by screwing in the nuts, the compensator is stretched, bringing the edges of the pipes together to the gap required for welding. The joints are caught by electric welding, the plates are cut off with a gas cutter and the joint is welded.

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

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Compensators for heating networks. This article will discuss the selection and calculation of compensators for heating networks.

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

It is worth noting that to allow expansion and contraction of pipelines, not only compensators are designed, but also a system of supports, which, in turn, can be either “sliding” or “dead”. How usually in Russia regulation of the thermal load is qualitative - that is, with temperature changes environment, the temperature at the outlet of the heat supply source changes. Due to quality regulation heat supply - the number of expansion-compression cycles of pipelines increases. The service life of pipelines is reduced, and the risk of pinching increases. 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 changes. In this case, the metal of the heating network pipelines operates under easier conditions, expansion-compression cycles minimum quantity, thereby increasing the service life of the heating network pipelines. Therefore, before choosing compensators, their characteristics and quantity, you need to determine the amount of expansion of the pipeline.

Formula 1:

δL=L1*a*(T2-T1)where

δL is the amount of pipeline extension,

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

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

T1 - maximum pipeline temperature (the maximum coolant temperature is assumed),

T2 - minimum temperature pipeline (minimum ambient temperature can be accepted), °C

As an example, let’s consider solving an elementary problem of determining the amount of pipeline extension.

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, you should clearly understand when an expansion joint is needed and when it is not needed. To answer this question unambiguously, you need to have a clear diagram of the pipeline, with its linear dimensions and supports marked on it. It should be clearly understood that changing the direction of the pipeline can compensate for elongations, in other words, turning 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 have determined the amount of pipeline elongation, 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 type and design features compensators. To select the type of compensator, it is necessary to determine the diameter of the heating network pipe based on the pipe capacity of the required power of the heat consumer.

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

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

Task 2 Determining the number and dimensions of compensators.

For a pipeline with a diameter of DN 100 with a straight section length 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 Problem 1). From the Table. 1 and Table 2 we determine the dimensions of n-shaped compensators (with dimensions of 2x2 m it can compensate for 0.134 meters of pipeline extension), we need to compensate 0.342 meters, therefore Ncomp = bL/∂x = 0.342/0.134 = 2.55, round to the nearest integer In the direction of increasing this, 3 compensators measuring 2x4 meters are required.

Currently, lens compensators are becoming more widespread; they are much more compact than U-shaped ones, however, a number of restrictions do not always allow their use. The service life of a U-shaped compensator is significantly higher than that of a lens compensator, 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 compensator metal.

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

Preliminary 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 pipeline expansion values depend on the minimum and maximum temperature its operation. For example, the minimum operating temperature of the pipeline is Tmin = 0°C and the maximum Tmax = 100°C. Those. temperature difference At = 100°C. With a pipeline length L equal to 90 m, the maximum value of its extension to the pipeline AL will be 100 mm. Let’s imagine that for installation on such a pipeline, compensators with an offset of ±50 mm are used, 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's operation 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

Consequently, preliminary stretching by 30 mm during installation (T y = 20°C) will ensure its effective operation. When the temperature rises from 20°C to 50°C during commissioning of the pipeline, the compensator will return to the free (unstressed) state. When the pipeline temperature increases from 50°C to 100°C, the displacement of the compensator from the relatively free state towards compression will be the calculated 50 mm.

Definitionvaluespreliminarysprains

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

The maximum extension of the pipeline can be calculated as follows:

ΔL = αxLxΔ t = 0.012 x 33 x 170 = 67 mm

The pre-stretch 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.

In Fig. Figure 1 shows the distance required for installing the compensator in the pipeline line, defined as the sum of the values of the compensator length lq in the free state and pre-stretch PS.

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

Calculation of a U-shaped compensator consists in determining the minimum dimensions of the compensator sufficient to compensate for temperature deformations of the pipeline. By filling out the form above, you can calculate the compensating capacity of a U-shaped compensator of given dimensions.

The algorithm of this online program is based on the method for calculating a U-shaped compensator given in the Designer’s Handbook “Design of Heat Networks” edited by A. A. Nikolaev.

Maximum voltage in the back of the compensator it is recommended to take in the range from 80 to 110 MPa.

The optimal ratio of the expansion joint overhang to the outer diameter of the pipe is recommended to be taken in the range H/Dн = (10 - 40), while the expansion joint overhang of 10DN corresponds to a DN350 pipeline, and an overhang of 40DN corresponds to a DN15 pipeline.

The optimal ratio of the width of the compensator to its reach is recommended to be taken in the range L/H = (1 - 1.5), although other values can be accepted.

If a compensator is needed to compensate for the calculated thermal expansions, it is too large sizes, it can be replaced with two smaller compensators.

When calculating the thermal elongation of a pipeline, the temperature of the coolant should be taken as maximum, and the temperature of the environment surrounding the pipeline as minimum.

The following restrictions were adopted in the calculation:

The pipeline is filled with water or steam
The pipeline is made of steel pipe
The maximum temperature of the working environment does not exceed 200 °C
The maximum pressure in the pipeline does not exceed 1.6 MPa (16 bar)
The compensator is installed on horizontal pipeline
The compensator is symmetrical, and its arms are the same length
Fixed supports are considered absolutely rigid
The pipeline does not experience wind pressure or other loads
The resistance of frictional forces of movable supports during thermal elongation is not taken into account
Smooth bends

It is not recommended to place fixed supports at a distance of less than 10DN from the U-shaped compensator, since transferring the pinching moment of the support to it reduces flexibility.

It is recommended that the pipeline sections from the fixed supports to the U-shaped compensator be of the same length. If the compensator is not located in the middle of the site, but is shifted towards one of the fixed supports, then the forces of elastic deformation and stress increase by approximately 20-40%, in relation to the values obtained for the compensator located in the middle.

To increase the compensating ability, preliminary stretching of the compensator is used. During installation, the compensator experiences a bending load, when heated it assumes a non-stressed state, and at maximum temperature it comes into tension. Pre-stretching the compensator by an amount equal to half the thermal elongation of the pipeline allows you to double its compensating capacity.

Scope of application

U-shaped compensators are used to compensate for thermal expansion of pipes on long straight sections, if there is no possibility of self-compensation of the pipeline due to turns of the heating network. The absence of compensators on rigidly fixed pipelines with a variable temperature of the working environment will lead to an increase in stress that can deform and destroy the pipeline.

Flexible expansion joints are used

At overhead installation for all pipe diameters, regardless of coolant parameters.
When laid in tunnels and general manifolds on pipelines from DN25 to DN200 at a coolant pressure of up to 16 bar.
For ductless installation for pipes with diameters from DN25 to DN100.
If the maximum operating temperature exceeds 50°C

Advantages

High compensation capacity
Maintenance free
Easy to make
Low forces transmitted to fixed supports

Flaws

High pipe flow
Large footprint
High hydraulic resistance

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

The peak expansion values of the pipeline depend on the minimum and maximum temperatures of its operation. For example, the minimum operating temperature of the pipeline is Tmin = 0°C and the maximum Tmax = 100°C. Those. temperature difference At = 100°C. With a pipeline length L equal to 90 m, the maximum value of its extension to the pipeline AL will be 100 mm. Let’s imagine that for installation on such a pipeline, compensators with an offset of ±50 mm are used, i.e. with a total offset of 100 mm. Let’s also imagine that the ambient temperature at the stage of their installation Ty is 20°C. The nature of the compensator's operation 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

Definitionvaluespreliminarysprains

Let's assume the pipeline length is 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 extension of the pipeline can be calculated as follows:

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

The pre-stretch 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.

In Fig. Figure 1 shows the distance required for installing the compensator in the pipeline line, defined as the sum of the values of the compensator length lq in the free state and pre-stretch PS.

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