Device for compensating thermal elongation of pipelines of heating networks. On the application of modern engineering solutions for compensation of temperature deformations of pipelines of heating networks

Pipes and their connections.

Heat transport technology imposes the following basic requirements on pipes used for heat pipelines:

sufficient mechanical strength and tightness at existing coolant pressures;

elasticity and resistance to thermal stresses under alternating thermal mode;

the constancy of mechanical properties;

resistance to external and internal corrosion;

small roughness internal surfaces;

absence of erosion of internal surfaces;

· small coefficient of temperature deformations;

high thermal insulation properties pipe walls;

Simplicity, reliability and tightness of connection individual elements;

Ease of storage, transportation and installation.

All types of pipes known so far do not simultaneously satisfy all the listed requirements. In particular, steel pipes used for transporting steam and hot water. However, high mechanical properties and elasticity steel pipes, as well as the simplicity, reliability and tightness of the joints (welding) ensured the almost one hundred percent use of these pipes in district heating systems.

The main types of steel pipes used for heating networks:

Diameter up to 400 mm inclusive - seamless, hot-rolled;

With a diameter above 400 mm - electric welded with a longitudinal seam and electric welded with a spiral seam.

Pipelines of heating networks are interconnected by means of electric or gas welding. For water heating networks, preference is given to steel grades St2sp and St3sp.

The piping scheme, the placement of supports and compensating devices must be chosen so that the total stress from all at the same time acting loads in no section of the pipeline did not exceed the permissible. Most weak point steel pipelines, along which stress testing should be carried out, are welds.

Supports.

Supports are critical parts of the heat pipeline. They perceive forces from pipelines and transfer them to load-bearing structures or soil. When constructing heat pipelines, two types of supports are used: free and fixed.

Free supports perceive the weight of the pipeline and ensure its free movement during temperature deformations. Fixed supports they fix the position of the pipeline at certain points and perceive the forces arising in the places of fixation under the influence of temperature deformations and internal pressure.

With channelless laying, they usually refuse to install free supports under pipelines in order to avoid uneven landings and additional bending stresses. In these heat pipelines, pipes are laid on untouched soil or a carefully compacted layer of sand. When calculating bending stresses and deformations, a pipeline lying on free supports is considered as a multi-span beam.

According to the principle of operation, free supports are divided into sliding, roller, roller and suspended.

When choosing the type of supports, one should not only be guided by the value of the calculated forces, but also take into account the operation of the supports under operating conditions. With an increase in the diameters of pipelines, the friction forces on the supports increase sharply.

Rice. A Sliding support: 1 - thermal insulation; 2 - supporting semi-cylinder; 3 - steel bracket; 4 - concrete stone; 5 – cement-sand mortar

Fig. B Roller support. Fig. B Roller support. Fig. D Suspension support.

In some cases, when, according to the conditions for the placement of pipelines, relative load-bearing structures sliding and rolling supports cannot be installed, suspended supports are used. The disadvantage of simple suspension supports is the deformation of the pipes due to the different amplitudes of the suspensions located on different distance from a fixed support, due to different angles turn. As the distance from the fixed support increases, the temperature deformation of the pipeline and the angle of rotation of the hangers increase.

Compensation for temperature deformations.

Compensation for temperature deformations is carried out by special devices - compensators.

According to the principle of operation, compensators are divided into radial and axial.

Radial expansion joints allow movement of the pipeline in both axial and radial directions. With radial compensation, the thermal deformation of the pipeline is perceived due to the bending of the elastic inserts or individual sections of the pipeline itself.

Fig. Compensators. a) U-shaped; b) Ω-shaped; c) S-shaped.

Advantages - simplicity of the device, reliability, offload fixed supports from internal pressure. The disadvantage is the transverse movement of the deformable sections. This requires an increase in the cross section of impassable channels and complicates the use of backfill insulation and channelless laying.

Axial expansion joints allow movement of the pipeline only in the direction of the axis. They are of a sliding type - stuffing box and elastic - lens (bellows).

Lens compensators are installed on pipelines low pressure- up to 0.5 MPa.

Rice. Compensator. a) one-sided gland: b) three-wave lens compensator

1 - glass; 2 - body; 3 - stuffing; 4 - thrust ring; 5 - grundbuksa.

Regardless of the material from which they are made, they are subject to thermal elongation and contraction. To find the magnitude of the linear change in the length of pipelines during their expansion and contraction, a calculation is performed. If they are neglected and the necessary expansion joints are not installed, then, when the route is laid open, the pipes can sag or even cause the entire system to fail. Therefore, the calculation of thermal elongation of pipelines is mandatory and requires professional knowledge.

In this part training course"", with the participation of a specialist from REHAU, we will tell you:

• Why is it necessary to take into account the temperature elongation of pipelines.
• How to calculate the deflection of the pipeline with thermal elongation.
• How to calculate and mount the shoulder of the expansion compensator.
• How to compensate for thermal deformations of polymer pipelines.
• What polymer pipelines are best used for open plumbing and heating wiring.

The need to calculate the temperature elongation of pipelines made of polymeric materials

Temperature elongation or contraction of pipelines occur under the influence of changes in the operating temperature, the water moving through them, as well as the temperature environment. Accordingly, during installation, it is necessary to ensure a sufficient degree of freedom of pipelines, as well as calculate the necessary tolerances for increasing their length. Often, novice developers do not take these changes into account when installing plumbing and heating wiring. Typical mistakes:

• Embedding pipes of cold and hot water supply into the floor screed without the use of insulation or protective corrugation.
• Open pipe laying, for example, when installing heating radiators, without the use of special compensators.

Sergey Bulkin Head of the technical department of the direction "Internal engineering systems" of the company REHAU

Accounting for temperature elongations of pipelines from polymer materials, in particular, from PE-Xa, should be made only with their open laying. With hidden laying, compensation of temperature elongations occurs due to bends of pipelines laid in a protective corrugated pipe or in thermal insulation, when the direction of the route changes. In this case, the elongation is compensated for by stresses in the screed or plaster.

The technology of hidden laying of pipelines in strobes or in a screed should provide the ability to compensate for the resulting deformations without mechanical damage to pipes and connecting elements.

Note that the screed withstands stress without damage, because. the resulting forces are very small and make up an insignificant percentage of the available safety margin. It is only necessary to ensure that when pouring the screed or plastering the walls, the solution does not get inside the corrugated pipe or under the thermal insulation. Connection of pipes to water fittings is carried out through wall brackets, which are firmly fixed to building structure or on a special bracket. As a result, axial movements of pipes in thermal insulation or a protective corrugated pipe, due to temperature elongations, do not exert any force on the connection unit. When connecting pipelines to distribution manifolds, a 90° turn is made at the exit from the screed or from under the plaster.

Thus, forces from very short sections, which can be neglected, will be transmitted to the nodes of the connection of pipelines to the collector.

With open laying, thermal elongations of polymer pipelines, in particular, pipelines made of PE-Xa, will be very noticeable, because. these pipelines are large ratio temperature elongation.

The physical meaning of the thermal elongation coefficient is that it shows how many millimeters 1 m of pipe will lengthen when it is heated by 1 degree.

The same value also has the opposite meaning, i.e. if the pipeline is cooled by 1 degree, then the coefficient of thermal elongation will show how many millimeters 1 m of the pipeline will be shortened.

The coefficient of thermal elongation is physical characteristic the material from which the pipeline is made.

Calculation of thermal expansion of pipelines made of cross-linked polyethylene PE-Xa

Thermal elongation or contraction of pipelines occurs due to changes in the operating temperature of the water circulating through them, as well as the ambient temperature. With open laying, the pipeline must be free to lengthen or shorten without overstressing the material of pipes, fittings and pipeline connections. This is achieved due to the compensating ability of the pipeline elements. For example:

• Correct placement of supports (fasteners).
• The presence of bends in the pipeline at the points of rotation, other bent elements and the installation of temperature compensators.

The device of compensators is necessary only with significant linear extensions of pipelines. Since the system must be rational, the thermal expansion of the pipeline is first calculated. Let's take pipelines made of cross-linked polyethylene RE-Xa. For the calculation we need:

Tab. 1. Thermal elongation coefficient and material constant for water pipes.

Sergey Bulkin

The thermal elongation of a pipeline section is proportional to its length and the difference between the installation temperatures and the maximum operating temperature. If, for example, we install a 10 m long section of a hot water pipeline, and the ambient temperature, i.e. installation temperature is 20°C, and the maximum operating temperature is 70°C, then the thermal expansion can be calculated by the formula

ΔL \u003d L α ΔТ (t max. working - t installation). Where:

• ΔL - temperature elongation in mm;
• L - pipeline length in m;
• α - coefficient of thermal elongation in mm/m·K;
• ΔT is the temperature difference in K.

Substitute the values ​​in the formula:

ΔL \u003d L α (t max. working - t installation) \u003d 10 0.15 (70 - 20) \u003d 75 mm.

Those. This will lengthen the 10-meter section by 75 mm or 7.5 cm. This will lead to deformation of the system and sagging of the pipeline. These deformations, first of all, violate appearance systems. But over a considerable length, they can destroy, first of all, fastening devices or lead to breakage of shut-off and control valves or fittings. The human eye is able to perceive the deflection of the pipeline (ΔH), starting from 5 mm.

Pipe deflection due to thermal expansion.

The next step is to calculate the amount of deflection (sagging) of the pipeline.

Calculation of the pipeline deflection and methods for compensating for thermal deformations of polymer pipelines

Knowing the length of the section between the clamps (L) and its length at maximum operating temperature(L 1), the pipeline deflection is determined using the relationship:

In total, with a temperature elongation of the pipeline by 75 mm on a 10-meter section, the deflection will be:

Sergey Bulkin

There are many ways to deal with thermal deformations of polymer pipelines.:

• Installation of additional fastening clamps.
• device L-shaped compensator.
• The device of the U-shaped compensator.
• The use of a fixing chute as a compensator.
• The device of additional fixed supports.
• The use of metal-polymer pipelines, in which the aluminum layer is firmly glued to the inner self-supporting layer of PE-Xa.

Let's consider each of these methods.

Ways to compensate for thermal deformations of polymer pipelines

1. Device for additional fastening clamps.

Due to the device of additional fastening clamps, sagging or deflection of pipelines is prevented. Recommended maximum distance between clamps for polymer pipes from PE-Xa are given in table 2.

2. L-shaped compensator device.

L-shaped compensators are arranged in the same way as when laying steel pipelines. It is much more efficient to install L-shaped expansion joints on PE-Xa polymer pipes, because these pipes are highly flexible. At the same time, 90° pipe bends can be used as L-shaped compensators. It is necessary, according to the formula, as described above, to determine the thermal elongation ΔL from the straight section before the turn. This value affects the distance from the pipeline to the building structure. The distance to the building structure must be at least ΔL. In addition, it is necessary to give the pipe the ability to bend freely. To do this, the first fastening clamp, after turning, should be installed at a certain distance from the turn.

The device of the L-shaped compensator on polymer pipes.

• LBS is the length of the compensator arm;
• X - minimum distance from the wall;
• ΔL is thermal elongation;
• FP - fixed support;
• L is the length of the pipe;
• GS - sliding collar.

The length of the compensator arm mainly depends on the material (material constant C). Compensators are usually installed in places where the direction of the pipeline changes.

Fixing gutters are not installed on expansion joints so as not to disturb the bend of the pipe.

The length of the compensator arm is determined by the formula:

• C is the pipe material constant;
• d- outside diameter pipeline in mm;
• ΔL - temperature elongation of the pipeline section.

If the thermal elongation was 75 mm, the material constant C = 12, and the pipeline diameter is 25 mm, then the length of the compensator arm will be:

Sergey Bulkin

The L-shaped compensator is the most economical device for compensating for thermal expansion. Its device does not require any additional devices and elements.

3. The device of the U-shaped compensator.

U-shaped compensators arranged in cases where compensation of temperature elongations at the edges of the section is undesirable. It is arranged, as a rule, in the middle of the pipeline section, and the temperature elongation compensation is directed towards the center of the section. The bases of the U-shaped compensator are displaced to the center evenly on both sides, so each side compensates for half of the thermal expansion ΔL/2. The arms of the U-shaped compensator are the LBS compensation arms.

The length of the compensator arm is calculated using the above formula, and the width of the base of the U-shaped compensator must be at least half the length of the compensator arm.

The device of the U-shaped compensator on polymer pipes.

4. Fixing chute as a compensator for thermal elongations.

The fixing chute is a three-meter long galvanized steel lodgement with a beaded edge. Fixing gutters are available for the corresponding diameters of pipelines. Pipelines snap into fixing grooves. In this case, the fixing chute surrounds the pipe by approximately 60°.

The forces of friction of the pipeline against the walls of the gutter exceed the force of thermal elongation of the pipeline.

When installing the fixing gutter, it is necessary to maintain a distance of 2 mm from the polymersliding sleeves.

When installing a fixing chute from the bottom of the pipeline, its mechanical protection is provided.

When using a fixing gutter, the minimum distance between the fastening clamps when using pipelines of all diameters can be 2 m.

5. Use of fixed supports

If thermal expansion needs to be compensated for a long pipe section with many branches, such as a water riser in a 20-story building with apartment tees installed on each floor, then thermal expansion can be compensated by installing fixed supports. To do this, conventional sliding clamps are installed on both sides of the tee behind the compression sleeves.

Formation of a fixed support as a compensator for temperature elongations of the pipeline.

The clamps will not allow the shaped part to move either up or down. Thus, a long section is divided into many short sections, equal height floors, approximately 3 m. As we remember from the calculation formula, the temperature elongation is directly proportional to the length of the section, and we reduced it. When installing fixed supports on each floor on the riser, no other compensators for thermal expansion of the pipeline will be required. If there is, for example, an “idle” riser, which does not have side outlets along its entire length, then it is possible to artificially install, for example, equal bore couplings on this riser and form fixed supports on them, as described above. To reduce costs, you can install L or U-shaped expansion joints on the riser or install a bellows expansion joint.

Polymer pipelines for modern open plumbing and heating distribution

Modern metal-polymer pipelines are a cross-linked polyethylene pipe in which an aluminum layer is firmly glued to an inner self-supporting PE-Xa layer. Such pipelines have the lowest coefficient of thermal elongation, because the aluminum layer compensates for thermal elongations and keeps the inner polymer layer from thermal deformations.

The coefficient of thermal elongation of metal-polymer pipelines is only 0.026 mm/m·K, which is 5.76 times less than that of conventional pipelines made of cross-linked polyethylene.

The temperature elongation of a section of a metal-polymer pipeline 10 m long at an ambient temperature (i.e., an installation temperature of 20 ° C and a maximum operating temperature of 70 ° C) will be only:

ΔL \u003d L α (t max. working - t installation) \u003d 10 0.026 (70 - 20) \u003d 13 mm.

For comparison: earlier we calculated the thermal expansion of a conventional PE-Xa pipeline 10 m long, which was 75 mm.

Therefore, metal-polymer pipelines are positioned as pipelines for open laying. But the option with metal-polymer pipes will be more expensive, because. these pipes cost more than conventional PE-Xa pipes.

W conclusion

It is impossible to ignore the temperature elongation of pipelines made of cross-linked polyethylene PE-Xa during open laying of plumbing and installation heating system. To compensate for elongations, one of the methods listed above should be used, strictly following the manufacturer's recommendations.

Thermal elongation of pipelines at a coolant temperature of 50 ° C and above should be taken up by special compensating devices that protect the pipeline from the occurrence of unacceptable deformations and stresses. The choice of compensation method depends on the parameters of the coolant, the method of laying heating networks and other local conditions.

Compensation for thermal elongation of pipelines due to the use of turns in the route (self-compensation) can be used for all methods of laying heating networks, regardless of the diameters of the pipelines and the parameters of the coolant at an angle of up to 120 °. If the angle is more than 120°, and also in the case when, according to the strength calculation, the rotation of the pipelines cannot be used for self-compensation, the pipelines at the turning point are fixed with fixed supports.

To ensure the correct operation of compensators and self-compensation, pipelines are divided by fixed supports into sections that do not depend on each other in terms of thermal elongation. Each section of the pipeline, limited by two adjacent fixed supports, provides for the installation of a compensator or self-compensation.

When calculating pipes for thermal elongation compensation, the following assumptions were made:

fixed supports are considered absolutely rigid;

the resistance of the friction forces of the movable supports during thermal elongation of the pipeline is not taken into account.

Natural compensation, or self-compensation, is the most reliable in operation, therefore it is widely used in practice. Natural compensation of temperature elongations is achieved at the turns and bends of the route due to the flexibility of the pipes themselves. Its advantages over other types of compensation are: simplicity of device, reliability, lack of need for supervision and maintenance, unloading of fixed supports from the forces of internal pressure. The natural compensation device does not require additional consumption of pipes and special building structures. The disadvantage of natural compensation is the transverse movement of the deformable sections of the pipeline.

Determine the total thermal elongation of the pipeline section

For trouble-free operation of heating networks, it is necessary that compensating devices are designed for maximum elongation of pipelines. Therefore, when calculating elongations, the coolant temperature is assumed to be maximum, and the ambient temperature - minimum. Complete thermal elongation pipeline section

l= αLt, mm, Page 28 (34)

where α is the coefficient of linear expansion of steel, mm/(m-deg);

L is the distance between fixed supports, m;

t is the calculated temperature difference, taken as the difference between the operating temperature of the coolant and the calculated outdoor temperature for heating design.

l\u003d 1.23 * 10 -2 * 20 * 149 \u003d 36.65 mm.

l\u003d 1.23 * 10 -2 * 16 * 149 \u003d 29.32 mm.

l\u003d 1.23 * 10 -2 * 25 * 149 \u003d 45.81 mm.

Similarly, we find  l for other areas.

The forces of elastic deformation arising in the pipeline when compensating for thermal elongation are determined by the formulas:

kgs; , N; Page 28 (35)

where E - the modulus of elasticity of pipe steel, kgf / cm 2;

I- moment of inertia of the cross section of the pipe wall, cm;

l- the length of the smaller and larger section of the pipeline, m;

t – calculated temperature difference, °C;

A, B are auxiliary dimensionless coefficients.

To simplify the determination of the elastic deformation force (P x, P v) table 8 gives an auxiliary value for various pipeline diameters.

Table 11

During the operation of the heating network, stresses appear in the pipeline, which create inconvenience for the enterprise. To reduce the stresses that arise when the pipeline is heated, axial and radial steel compensators (gland, U- and S-shaped, and others) are used. U-shaped compensators have found wide application. To increase the compensating capacity of the U-shaped compensators and reduce the bending compensation stress in the working condition of the pipeline for sections of pipelines with flexible compensators, the pipeline is pre-stretched in a cold state during installation.

Pre-stretching is done:

at a coolant temperature up to 400 °C inclusive by 50% of the total thermal elongation of the compensated section of the pipeline;

at a coolant temperature above 400 °C by 100% of the total thermal elongation of the compensated section of the pipeline.

Calculated thermal elongation of the pipeline

mm Page 37 (36)

where ε is a coefficient that takes into account the pre-stretching of expansion joints, possible inaccuracy in the calculation and relaxation of compensation stresses;

l- total thermal elongation of the pipeline section, mm.

1 section х = 119 mm

According to the application, at x = 119 mm, we select the expansion of the compensator H = 3.8 m, then the shoulder of the compensator B = 6 m.

To find the force of elastic deformation, we draw a horizontal line H \u003d 3.8 m, its intersection with B \u003d 5 (P k) will give a point, lowering the perpendicular from which to digital values ​​\u200b\u200bP k, we get the result P k - 0.98 tf = 98 kgf = 9800 N.

Picture 3 - U-shaped compensator

7 plot x = 0.5 * 270 = 135 mm,

H \u003d 2.5, B \u003d 9.7, P k - 0.57 tf \u003d 57 kgf \u003d 5700 N.

The rest of the sections are calculated in the same way.

• 3. Main design parameters. Temperature, pressure, allowable stress.
• 4. Basic requirements for the design of welded machines (give regulatory documents). Testing devices for strength and tightness.
• 5. Shell plates. Basic concepts and definitions. Stress state of shells of revolution under the influence of internal pressure.
• 10. Mechanical oscillations of the shafts. Critical shaft speed with one load (dynamic deflection formula analysis). Vibration condition. The phenomenon of self-centering.
• 11. Features of the calculation of shafts with several masses. The concept of the exact method for calculating critical speeds. Approximate methods.
• 12. Shaft vibrations. Gyroscopic effect. The influence of various factors on the critical speed
• 15. Calculation of column apparatus for the action of wind loads. Design scheme, design states. Determination of axial load.
• 16. Determination of wind load and bending moment. Checking the strength of the casing of the column apparatus.
• 17. Calculation of column apparatus for the action of wind loads. Types and design of supports for vertical apparatus. Support type selection.
• 18. Calculation of column apparatus for the action of wind loads. Checking the strength and stability of the support shell and its nodes.
• 19. Heat exchangers. Determination of thermal forces and stresses in the body and tubes of the type TN (Give a design scheme, formulas without derivation. Analysis of formulas).
• 20. Heat exchangers. Determination of thermal forces and stresses in the body and tubes of the type TK (Give a calculation scheme, formulas without derivation. Analysis of the formulas).
• 21) The purpose and role of machines and devices. The main trends in the development of instrumentation for oil and gas processing processes
• 24. The role and place of column apparatus in the technological process. The content of the passport for the device.
• 25. Internal devices of column apparatuses. Types of plates, their classification and requirements for them. The design of the fastening of internal devices. Breakers.
• 26. Attached contact devices. Types and classification of nozzles. Nozzle selection principles.
• 27. Vacuum columns. Design and operation features. Vacuum generating systems, structures.
• 28. Tube furnaces. Purpose, their place and role in the technological system and scope. Classification of tube furnaces and their types.
• 30. Tubular coil, its design, mounting methods. Selection of the size and materials of pipes and bends, technical requirements.
• 31. Burner devices used in tube furnaces. Classification, device and principle of operation.
• 32. Ways to create traction in furnaces. Methods for utilizing the heat of exhaust gases.
• 33. Heat exchangers. General information about the heat transfer process. Requirements for devices. Classification of heat exchange equipment.
• 34. Shell and tube heat exchangers. Rigid type heat exchangers. Advantages and disadvantages. Ways of attaching the tube sheet to the body. Heat exchangers with compensator.
• 35. Non-rigid heat exchangers. U-tube heat exchanger design.
• 36. Floating head heat exchangers. Features of the device and design of floating heads. Heat exchanger type "pipe in pipe".
• 37. Air coolers. Classification and scope. The design of the aircraft.
• 38. Classification of technological pipelines. Categories of pipelines. Appointment and application.
• 39. Temperature deformations of pipelines and ways of their compensation.
• 40. Pipe fittings. Classification. Features of constructive and material execution.
• 41. Fundamentals of mass transfer. Classification of mass transfer processes. Mass transfer, mass transfer, mass transfer. Diffusion and convective mechanisms of mass transfer. Equilibrium and driving force of mass transfer.
• 42. Mass transfer equation, mass transfer coefficient. Mass transfer equation, mass transfer coefficient. Material balance of mass transfer. Working line equation.
• 43 Average driving force of mass transfer. Calculation of the average driving force of mass transfer. The number of transfer units. The height of the transfer unit. Differential equation of convective diffusion.
• 45 Calculation of the height of the mass transfer apparatus. The number of theoretical concentration steps and the height equivalent to the theoretical step. Graphical method for calculating the number of theoretical plates.
• 48. Distillation processes. Physical and chemical bases. Raul's Law. Equilibrium line equation, relative volatility. Image of distillation processes on y-x and t-X-y diagrams.
• 49 Simple distillation, material balance of simple distillation. Schemes of fractional and stepwise distillation, distillation with partial reflux.
• 51. Packed and tray columns, types of packings and trays. Hollow spray towers used for absorption and extraction. film absorbers.
• 54 Purpose and basic principles of the Crystallization process. Technical methods of the crystallization process in industry. What types of apparatus are used to carry out the crystallization process.
• 56. General information about the settling process. Sump design. Determination of the deposition surface.
• 57. Separation of inhomogeneous systems in the field of centrifugal forces. Description of the centrifugation process. Centrifuge device. Separation in a cyclone.
• 58. Wastewater treatment by flotation. Types and methods of flotation. Structures of flotation plants.
• 59. Physical bases and methods of gas purification. Types of gas cleaning devices.
• 1. Gravitational gas cleaning.
• 2. Under the influence of inertial forces and centrifugal forces.
• 4. Wet cleaning of gases
• 60. The concept of a boundary layer. laminar boundary layer. Turbulent boundary layer. Velocity profile and friction in pipes.
• 61. General requirements for the means of flaw detection
• 63. Classification of non-destructive testing methods.
• 64. Classification of optical instruments for visual-optical control.
• 65 Essence and classification of methods of capillary flaw detection.
• 66. Scope and classification of magnetic control methods.
• 67. Ferroprobe control method

• ∆l=α l ∆t

  where α is the coefficient of linear expansion of the pipe metal; for steel a=12-10-6 m/(m °C);

  l is the length of the pipeline;

  ∆t is the absolute temperature difference of the pipeline before and after heating (cooling);

  If the pipeline cannot freely lengthen or contract (and technological pipelines are exactly like that), then thermal deformations cause compressive stresses (during elongation) or tension (during contraction) in the pipeline, which are determined by the formula:

  δ=E ξ=E ∆l/l

  where E is the modulus of elasticity of the pipe material

  ∆l - relative elongation (shortening) of the pipe

  If we take E = 2.1 * 105 MN / m2 for steel, then according to formula (13) it turns out that when heated (cooled) by 1 ° C, the temperature stress reaches 2.5 MN / m2, at = 300 ° C value = 750 MN/m2. It follows from the foregoing that pipelines operating at temperatures that vary over a wide range, in order to avoid destruction, must be equipped with compensating devices that easily perceive thermal stresses.

  Due to the temperature difference between the transported products and the environment, pipelines are subject to temperature deformations. Typically, pipelines are of considerable length, so their overall thermal deformation can be large enough to cause a rupture or bulging of the pipeline. In this regard, it is necessary to ensure the ability of the pipeline to compensate for these deformations.

  To compensate for temperature deformations on technological pipelines, U-shaped, lens, wavy and stuffing box compensators are used.

  U-shaped expansion joints (Fig. 5.1) are widely used for ground process pipelines, regardless of their diameter. Such compensators have a large compensating capacity, they can be used at any pressure, however, they

  bulky and require the installation of special supports. Usually they are placed horizontally and provided with drainage devices.

  Lens expansion joints are used for gas pipelines at operating pressures up to 1.6 MPa. By design, they are similar to expansion joints of shell-and-tube heat exchangers.

  Wavy expansion joints (Fig. 5.2) are used for pipelines with non-aggressive and medium-aggressive media at pressures up to 6.4 MPa. Such a compensator consists of a corrugated flexible element 4, the ends of which are welded to the nozzles 1. Restrictive rings 3 prevent the element from buckling and limit the bending of its wall. Outside, the flexible element is protected by a casing 2, inside it has a cup 5 to reduce the hydraulic resistance of the compensator.

  On pipelines made of cast iron and non-metallic materials, gland compensators are installed (Fig. 5.3), which consist of a body 3 fixed on a support 1, packing 2 and a bottom box 4. Compensation for temperature deformations occurs due to the mutual movement of the body 3 and inner pipe 5. Stuffing box compensators have a high compensating ability, however, due to the difficulty of ensuring sealing when transporting combustible, toxic and liquefied gases, they are not used.

  Pipelines are laid on supports, the distance between which is determined by the diameter and material of the pipes. For steel pipes with a diameter of up to 250 mm, this distance is usually 3-6 m. Hangers, clamps and brackets are used to fasten pipelines. Pipelines made of fragile materials (glass, graphite compositions, etc.) are laid in solid trays and solid bases.

  

Any material: solid, liquid, gaseous, in accordance with the laws of physics, changes its volume in proportion to the change in temperature. For objects whose length significantly exceeds the width and depth, for example, pipes, the main indicator is the longitudinal expansion along the axis - thermal (temperature) elongation. Such a phenomenon must necessarily be taken into account in the course of the implementation of certain engineering works.

For example, during a train ride, a characteristic tapping is heard due to the thermal joints of the rails (Fig. 1), or when laying power lines, the wires are mounted so that they sag between the supports (Fig. 2).

fig.4

The same thing happens in engineering plumbing. Under the influence of temperature elongation, with the use of materials that do not correspond to the case and the absence of measures for thermal compensation in the system, the pipes sag (Fig. 4 on the right), the forces on the fastening elements of the fixed supports and on the installation elements increase, which reduces the durability of the system as a whole, and, in extreme cases, it can lead to an accident.

The increase in the length of the pipeline is calculated by the formula:

ΔL - element length increase [m]

α - coefficient thermal expansion material

lo - initial element length [m]

T2 - final temperature [K]

T1 - initial temperature [K]

Compensation of thermal expansions for pipelines engineering systems It is carried out mainly in three ways:

• natural compensation by changing the direction of the pipeline route;
• the use of compensation elements that are able to extinguish the linear expansion of pipes (compensators);
• pipe pretensioning ( this way quite dangerous and should be used with extreme caution).

fig.5

Natural compensation is used mainly for the “hidden” installation method and is the laying of pipes with arbitrary arcs (Fig. 5). This method is suitable for plastic pipes of low rigidity, such as pipelines of the KAN-therm Push System: PE-X or PE-RT. This requirement is stated in SP 41-09-2005(Design and installation internal systems water supply and heating of buildings using pipes made of “cross-linked” polyethylene) in paragraph 4.1.11 In the case of laying PE-S pipes in the floor structure, stretching in a straight line is not allowed, but they should be laid in arcs of small curvature (snake) (...)

Such laying makes sense when installing pipelines according to the “pipe in pipe” principle, i.e. in a corrugated pipe or in pipe thermal insulation, which is indicated not only in SP 41-09-2005, but also in SP 60.13330-2012 (Heating, ventilation and air conditioning) in clause 6.3.3 ... The laying of pipelines from polymer pipes should be provided for hidden : in the floor (in the corrugated pipe) ...

Thermal elongation of pipelines is compensated by voids in protective corrugated pipes or thermal insulation.

When performing compensation of this type, attention should be paid to the serviceability of the fittings. Excessive stress due to pipe bending can lead to cracking of the tee (fig. 6). To ensure that this is avoided, the change in the direction of the pipeline route should occur at a distance of at least 10 outer diameters from the fitting nozzle, and the pipe next to the fitting should be rigidly fixed, this, in turn, minimizes the effect of bending loads on the fitting nozzles.

fig.6

Another type of natural temperature compensation is the so-called “hard” fastening of pipelines. It is a breakdown of the pipeline into limited sections of temperature compensation in such a way that the minimum increase in the pipe in a meaningful way did not affect the linearity of its laying, and excessive stresses went into efforts on fixing points of fixed supports (Fig. 7).

fig.7

This type of compensation works on buckling. To protect pipelines from damage, it is necessary to divide the pipeline by fixed support points into compensation sections of no more than 5 m. It should be noted that with such laying, not only the weight of the equipment, but also stresses from thermal elongation affect the pipeline fastenings. This leads to the need to calculate the maximum allowable load on each of the supports each time.

The forces arising from thermal elongations and acting on fixed support points are calculated using the following formula:

DZ - outer diameter of the pipeline [mm]

s - pipeline wall thickness [mm]

α - coefficient of thermal elongation of the pipe

E - modulus of elasticity (Young's) of the pipe material [N/mm]

ΔT - change (increase) in temperature [K]

In addition, the self-weight of the pipeline segment filled with coolant also acts on the fixed support point. In practice, the main problem is that no manufacturer of fasteners provides data on the limit permissible loads on their fasteners.

Natural compensators for thermal elongation are G, P, Z-shaped expansion joints. This solution is used in places where it is possible to redirect free thermal extensions of pipelines to another plane (Fig. 8).

fig.8

The size of the expansion arm for compensators type "G", "P" and "Z" is determined depending on the thermal elongation obtained, the type of material and the diameter of the pipeline. The calculation is performed according to the formula:

[m]

K - pipe material constant

Dz - outer diameter of the pipeline [m]

ΔL - thermal elongation of the pipeline section [m]

The material constant K is related to the stresses that the given type pipeline material. For individual Systems KAN-therm values ​​for material constant K are given below:

Push PlatinumK = 33

Compensation arm of the "G" type compensator:

A - length of the compensation arm

L - initial length of the pipeline section

ΔL - elongation of the pipeline section

PP - mobile support

A - length of the compensation arm

PS - point of fixed support (fixed fixation) of the pipeline

S - compensator width

To calculate the compensation shoulder A, it is necessary to take the greater of the values ​​of L1 and L2 as the equivalent length Le. Width S must be S = A/2, but not less than 150 mm.

A - length of the compensation arm

L1, L2 - initial length of segments

ΔLx - elongation of the pipeline section

PS - point of fixed support (fixed fixation) of the pipeline

To calculate the compensation shoulder, it is necessary to take the sum of the lengths of the segments L1 and L2 as the equivalent length Le: Le = L1 + L2.

fig.9

In addition to geometric temperature compensators, there are a large number of constructive solutions this kind of elements:

• bellows expansion joints,
• elastomeric expansion joints,
• tissue compensators,
• loop compensators.

Considering relatively high price some options, such expansion joints are most often used in places where space is limited or technical capabilities geometric expansion joints or natural compensation. These expansion joints have a limited service life calculated in operating cycles from full expansion to full contraction. For this reason, for equipment operating cyclically or with variable parameters, it is difficult to determine the final operating time of the device.

Bellows expansion joints use the elasticity of the bellows material to compensate for thermal elongations. Bellows are often made from of stainless steel. This design determines the life of the element - approximately 1000 cycles.

The service life of axial expansion joints of the bellows type is significantly reduced in case of misalignment of the expansion joint. This feature requires high precision of their installation, as well as their correct fastening:

• it is possible to mount no more than one compensator in the temperature compensation area between 2 adjacent points of fixed supports;
• movable supports must completely encircle the pipes and not create a large compensation resistance. Maximum size backlash no more than 1 mm;
• axial compensator it is recommended, for greater stability, to install at a distance of 4Dn from one of the fixed supports;

If you have any questions about temperature compensation of pipelines of the KAN-therm System, you can contact .