There are a number of options for temperature compensation extensions in heating networks. Flexible expansion joints are made from pipes; they most often have G- or U-shape. Typically, flexible compensators, regardless of the method of heat-conducting laying, are laid in channels of a non-passable section (niches), which repeat the shaped appearance of the compensator in plan.

In underground heating networks, mainly on large-diameter pipelines, axial expansion joints of the sliding type (stuffing box expansion joints) are most often used. In areas of installation, gland expansion joints have the property of sectioning pipelines into sections that are not metallic connected to each other. IN in this case in the presence of a potential difference between the compensator glass and the body, the electrical circuit will close through the water, which can cause an electrochemical process to occur, and corrosion processes on the internal surfaces of the stuffing box compensator. But as practice shows, in frequent cases a metal connection occurs between two parts of the compensator due to contact of the glass with the ground axle. During the use of the stuffing box compensator, metallic contact between its individual parts can sometimes occur and be interrupted.

Stuffing box compensators, shut-off valves, as well as other equipment that requires maintenance, are placed in chambers located no more than 150-200 meters from each other. The chambers are made of brick masonry, monolithic concrete or reinforced concrete. Due to the significant dimensions of the equipment, cameras are usually quite large. Due to the fact that there is a sharp difference between the enclosing structures and the temperatures of the equipment, constant convection of moist air occurs in the chambers and, as a result, condensation on surfaces that have a temperature below the dew point.

As a result, concentrated moistening of the thermal insulation of the pipes in the chamber and the areas adjacent to it, the channel, occurs in certain areas, with drops from the ceilings from the walls through which the pipes are introduced into the chambers, using a film of moisture that flows from the shield planes of the supports, that are placed in the cells. The pipes are introduced into the chambers through special windows in the chamber walls. The structure of the input unit is important, mainly for ductless thermal conductors due to the possibility of pipe subsidence and, as a result, deformation of the insulation structure. The structure of the unit’s pipes entering the chambers also determines the level of protection of thermal insulation from aeration and moisture in this area.

In order to ensure compensation for temperature elongations in fairly short sections of the point, individual thermal wires are fixed with fixed supports, and another part of the thermal wires moves freely in relation to these supports. In this way, the fixed supports divide the heat pipeline into sections that are independent with respect to temperature expansion. At the same time, the supports absorb the forces that arise in pipelines using various methods and schemes for compensating for temperature elongations. The installation of fixed supports is provided for when in various ways thermally conductive gasket.

The installation areas for fixed supports are combined, as usual, with the nodes of pipe branches, the locations of shut-off equipment on pipelines, stuffing box compensators, mud traps and other equipment. The distance between the fixed supports depends mainly on the pipeline diameter, the temperature of the coolant, and the compensation ability of the installed compensators. At a maximum water temperature of 150 degrees, for pipelines with a diameter of 50 to 1000 millimeters, the distance between supports can be from 60 to 200 meters.

Steel channels, reinforced concrete beams (frontal supports) or reinforced concrete panels (panel supports) can be used in the form of a supporting structure in fixed supports. Frontal supports are usually installed in chambers, panel supports in at the moment more widely consumed ones are installed in channels and chambers. A gap is assumed in the section of the pipe passage through the panel support. Pipes in these areas must have a protective coating, as in other areas. pipe parts. The gap between the supports and pipes must be filled with elastic padding, which prevents moisture from entering the gap. In the case of consumption of moisture-absorbing packings, as practice has shown, a dangerous focus of corrosion processes may form in this area. The panel supports must have holes in the lower part to allow water to pass through and prevent the soil from sinking into the channels.

The load-bearing structures of fixed supports have direct contact with the ground or through the enclosing structure of chambers and channels. Therefore, in the absence of dielectric gaskets between the stop (frontal supports) or support rings (panel supports) and the structure of the load-bearing support, the fixed support is the grounding of the heat pipe concentrated, that is, the elements, which causes the possibility of stray currents entering the heating network, and in cases of consuming electrochemical protection - an element , which reduces its effectiveness.

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 at alternating thermal mode;

· constancy of mechanical properties;

· resistance to external and internal corrosion;

· low roughness internal surfaces;

· no erosion of internal surfaces;

· low coefficient temperature deformations;

· high heat-insulating properties of pipe walls;

· simplicity, reliability and tightness of the connection individual elements;

· ease of storage, transportation and installation.

All types of pipes known to date do not simultaneously satisfy all of the listed requirements. In particular, these requirements are not fully satisfied by 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 connections (welding) ensured almost one hundred percent use of these pipes in district heating systems.

The main types of steel pipes used for heating networks:

With a 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.

Heat network pipelines are connected to each other using electric or gas welding. For water heating networks, preference is given to steel grades St2sp and St3sp.

The pipeline layout, placement of supports and compensating devices must be selected in such a way that the total stress from all simultaneously acting loads in any section of the pipeline does not exceed the permissible one. The weakest point steel pipelines The areas that should be used for stress testing are welds.

Supports.

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

Free supports take 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 that arise at the fixation points under the influence of temperature deformations and internal pressure.

When installing ductless installations, they usually avoid installing free supports under pipelines in order to avoid uneven fits and additional bending stresses. In these heat pipelines, the 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, you should not only be guided by the value of the design forces, but also take into account the operation of the supports under operating conditions. As pipeline diameters increase, 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 Suspended support.

In some cases, when, according to the conditions of pipeline placement, relatively 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 distances from a fixed support, due to different angles turn. As you move away from the fixed support, the temperature deformation of the pipeline and the angle of rotation of the hangers increase.

Compensation for temperature deformations.

Temperature deformations are compensated special devices– compensators.

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

Radial expansion joints allow pipeline movement in both axial and radial directions. With radial compensation, the thermal deformation of the pipeline is absorbed due to the bending of 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, unloading of fixed supports from internal pressure forces. Disadvantage: lateral movement of deformed areas. This requires an increase in the cross-section of non-passable channels and complicates the use of backfill insulation and channelless installation.

Axial expansion joints allow the pipeline to move only in the direction of the axis. They are made of 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 stuffing box: b) three-wave lens compensator

1 – glass; 2 – body; 3 – packing; 4 – thrust ring; 5 – ground book.

• 3. Basic design parameters. Temperature, pressure, permissible voltage.
• 4. Basic requirements for the designs of welded apparatus (give regulatory documents). Testing devices for strength and tightness.
• 5. Shell plates. Basic concepts and definitions. Stressed state of shells of revolution under the influence of internal pressure.
• 10. Mechanical vibrations of shafts. Critical speed of a shaft with one load (analysis of the dynamic deflection formula). Vibration resistance condition. The phenomenon of self-centering.
• 11.Features of calculation of shafts with several masses. The concept of an accurate method for calculating critical speeds. Approximate methods.
• 12. Shaft vibrations. Gyroscopic effect. Influence of various factors on critical speed
• 15. Calculation of column apparatus for wind loads. Design scheme, design states. Determination of axial load.
• 16. Determination of wind load and bending moment. Checking the strength of the column apparatus body.
• 17. Calculation of column apparatus for wind loads. Types and design of supports for vertical devices. Selecting the type of support.
• 18. Calculation of column apparatus for wind loads. Checking the strength and stability of the support shell and its components.
• 19. Heat exchangers. Determination of temperature forces and stresses in the body and tubes of the type Tn (Give a calculation diagram, formulas without derivation. Analysis of formulas).
• 20. Heat exchangers. Determination of temperature forces and stresses in the body and tubes of the type tk (Give a calculation diagram, formulas without derivation. Analysis of formulas).
• 21) Purpose and role of machines and devices. Main trends in the development of instrumentation for oil and gas refining processes
• 24. The role and place of column devices in the technological process. Contents of the device passport.
• 25. Internal devices of column apparatuses. Types of plates, their classification and requirements for them. Design of fastening internal devices. Fender devices.
• 26. Attachment contact devices. Types and classification of nozzles. Principles for choosing nozzles.
• 27. Vacuum columns. Features of design and operation. Vacuum-creating systems, structures.
• 28. Tubular furnaces. Purpose, their place and role in the technological system and scope. Classification of tube furnaces and their types.
• 30. Tubular coil, its design, methods of fastening. Selection of size and materials of pipes and bends, technical requirements.
• 31. Burner devices used in tube furnaces. Classification, device and principle of operation.
• 32. Methods of creating draft in furnaces. Methods for recycling heat from flue 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. Hard type heat exchangers. Advantages and disadvantages. Methods of attaching the tube sheet to the body. Heat exchangers with compensator.
• 35. Heat exchangers of non-rigid design. U-tube heat exchanger design.
• 36. Heat exchangers with floating head. Features of the device and design of floating heads. Heat exchanger of the “pipe in pipe” type.
• 37. Air coolers. Classification and scope. The design of the avo.
• 38. Classification of technological pipelines. Pipeline categories. Purpose and application.
• 39. Temperature deformations of pipelines and methods for 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. Number of transfer units. Transfer unit height. Differential equation of convective diffusion.
• 45 Calculation of the height of mass transfer devices. The number of theoretical steps of concentration change and the height equivalent to the theoretical step. Graphical method for calculating the number of theoretical plates.
• 48. Distillation processes. Physico-chemical fundamentals. Raoult's law. Equilibrium line equation, relative volatility. Representation of distillation processes on y- 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 plate column devices, types of packings and plates. Hollow spray columns 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. Design of settling tanks. Determination of 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. Designs of flotation plants.
• 59. Physical principles and methods of gas purification. Types of gas purification devices.
• 1. Gravity purification of gases.
• 2. Under the influence of inertial forces and centrifugal forces.
• 4. Wet gas cleaning
• 60. The concept of a boundary layer. Laminar boundary layer. Turbulent boundary layer. Velocity profile and friction in pipes.
• 61. General requirements for flaw detection means
• 63. Classification of non-destructive testing methods.
• 64. Classification of optical instruments for visual optical inspection.
• 65 Essence and classification of capillary flaw detection methods.
• 66. Scope and classification of magnetic testing methods.
• 67. Fluxgate 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- pipeline length;

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

  If the pipeline cannot freely lengthen or shorten (and technological pipelines are exactly like that), then temperature deformations cause compressive stresses in the pipeline (during elongation) or tensile stresses (during shortening), which are determined by the formula:

  δ=E ξ=E ∆l/l

  where E is the elastic modulus 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 will reach 2.5 MN/m2, at = 300 ° C the value = 750 MN/m2. From the above it follows that pipelines operating at temperatures varying over a wide range, in order to avoid destruction, must be equipped with compensating devices that can easily perceive temperature stresses

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

  To compensate for temperature deformations in process pipelines, U-shaped, lens, wavy and gland compensators are used.

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

  are bulky and require the installation of special supports. They are usually placed horizontally and equipped with drainage devices.

  Lens compensators are used for gas pipelines at operating pressures up to 1.6 MPa. They are similar in design to compensators for shell-and-tube heat exchangers.

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

  On pipelines made of cast iron and non-metallic materials, stuffing box compensators are installed (Fig. 5.3), which consist of a housing 3 mounted on a support 1, a packing 2 and a core 4. Compensation for temperature deformations occurs due to the mutual movement of the housing 3 and inner tube 5. Stuffing box expansion joints have a high compensating ability, however, due to the difficulty of ensuring sealing when transporting flammable, 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 secure pipelines. Pipelines made of fragile materials (glass, graphite compositions, etc.) are laid in solid trays and solid bases.

  

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DECISION of the Gosgortekhnadzor of the Russian Federation dated 06/10/2003 80 ON APPROVAL OF RULES FOR THE DESIGN AND SAFE OPERATION OF TECHNOLOGICAL... Relevant in 2018

5.6. Compensation for temperature deformations of pipelines

5.6.1. Temperature deformations should be compensated by turns and bends of the pipeline route. If it is impossible to limit yourself to self-compensation (for example, on completely straight sections of considerable length), U-shaped, lens, wavy and other compensators are installed on pipelines.

In cases where the design involves steam purging or hot water, the compensating capacity of pipelines must be designed for these conditions.

5.6.2. It is not allowed to use stuffing box compensators on process pipelines transporting media of groups A and B.

Installation of lens, stuffing box and wavy expansion joints on pipelines with a nominal pressure of more than 10 MPa (100 kgf/cm2) is not allowed.

5.6.3. U-shaped expansion joints should be used for process pipelines of all categories. They are made either bent from solid pipes, or using bent, steeply curved or welded elbows.

5.6.4. For U-shaped expansion joints, bent bends should be used only from seamless pipes, and welded bends should be used from seamless and welded straight-seam pipes. The use of welded bends for the manufacture of U-shaped expansion joints is permitted in accordance with the instructions of clause 2.2.37 of these Rules.

5.6.5. It is not allowed to use water and gas pipes for the manufacture of U-shaped expansion joints, and electric welded pipes with a spiral seam are recommended only for straight sections of expansion joints.

5.6.6. U-shaped expansion joints must be installed horizontally, maintaining the required overall slope. As an exception (if limited area) they can be placed vertically with a loop up or down with appropriate drainage device at the lowest point and air vents.

5.6.7. Before installation, U-shaped compensators must be installed on pipelines together with spacer devices, which are removed after securing the pipelines to fixed supports.

5.6.8. Lens expansion joints, axial, as well as hinged lens expansion joints, are used for process pipelines in accordance with the regulatory and technical documentation.

5.6.9. When installing lens compensators on horizontal gas pipelines with condensing gases, condensate drainage must be provided for each lens. Connection for drainage pipe made from seamless pipe. When installing lens compensators with an internal sleeve on horizontal pipelines, guide supports must be provided on each side of the compensator at a distance of no more than 1.5 DN of the compensator.

5.6.10. When installing pipelines, compensating devices must be pre-stretched or compressed. The amount of preliminary stretching (compression) of the compensating device is indicated in project documentation and in the passport for the pipeline. The amount of stretch can be changed by the amount of correction taking into account the temperature during installation.

5.6.11. The quality of expansion joints to be installed on process pipelines must be confirmed by passports or certificates.

5.6.12. When installing a compensator, the following data is entered into the pipeline passport:

technical characteristics, manufacturer and year of manufacture of the compensator;

distance between fixed supports, necessary compensation, amount of pre-stretch;

ambient air temperature when installing the compensator and date.

5.6.13. Calculation of U-shaped, L-shaped and Z-shaped expansion joints should be produced in accordance with the requirements of regulatory and technical documentation.

Thermal elongation of pipelines at a coolant temperature of 50 °C and above must be absorbed 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 through the use of route turns (self-compensation) can be used for all methods of laying heating networks, regardless of pipeline diameters and coolant parameters at an angle of up to 120°. When the angle is more than 120°, and also in the case when, according to strength calculations, the rotation of the pipelines cannot be used for self-compensation, the pipelines at the turning point are secured with fixed supports.

To ensure proper operation of compensators and self-compensations, pipelines are divided by fixed supports into sections that are independent of one another with respect to thermal elongation. On each section of the pipeline, limited by two adjacent fixed supports, installation of a compensator or self-compensation is provided.

When calculating pipes to compensate for thermal expansion, 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, and therefore is widely used in practice. Natural compensation for thermal expansion is achieved at turns and bends of the route due to the flexibility of the pipes themselves. Its advantages over other types of compensation are: simplicity of design, reliability, lack of need for supervision and maintenance, and unloading of fixed supports from internal pressure forces. The installation of natural compensation does not require additional consumption of pipes and special building structures. The disadvantage of natural compensation is the lateral movement of deformed sections of the pipeline.

Let us determine the total thermal elongation of the pipeline section

For trouble-free operation of heating networks, it is necessary that compensating devices be designed for maximum pipeline extensions. Therefore, when calculating elongations, the coolant temperature is taken to be maximum and the ambient temperature to be 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 – distance between fixed supports, m;

t – design temperature difference, taken as the difference between the operating temperature of the coolant and the design temperature of the outside air for heating design.

l= 1.23*10 -2 *20*149 = 36.65 mm.

l= 1.23* 10 -2 * 16* 149 = 29.32 mm.

l= 1.23*10 -2 *25*149 = 45.81 mm.

Similarly we find  l for other areas.

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

Kgs; , N; Page 28 (35)

where E is the elastic modulus of pipe steel, kgf/cm2;

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

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

t – calculated temperature difference, °C;

A, B - auxiliary dimensionless coefficients.

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

Table 11

Pipe outer diameter d H, mm

Pipe wall thickness s, mm

During the operation of the heating network, voltages 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 expansion joints (stuffing, U- and S-shaped, and others) are used. Wide Application found U-shaped compensators. To increase the compensating capacity of U-shaped expansion joints and reduce the bending compensation stress in the operating state of the pipeline, for sections of pipelines with flexible expansion joints, the pipeline is pre-stretched in a cold state during installation.

Pre-stretching is done:

at coolant temperatures 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.

Estimated thermal expansion of the pipeline

Mm Page 37 (36)

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

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

1 section x = 119 mm

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

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

Figure 3 – U-shaped compensator

7 section х = 0.5*270 = 135 mm,

N = 2.5, V = 9.7, R k – 0.57 tf = 57 kgf = 5700 N.

We calculate the remaining sections in the same way.