Calculation of forces in the fixed supports of the heat pipeline. Loads on fixed supports

The supports serve to absorb the force from the pipelines and transfer them to the supporting structures or the ground, as well as to ensure the organized joint movement of pipes and insulation during thermal deformations. In the construction of heat pipelines, two types of supports are used: movable and fixed.

Movable supports perceive the weight of the heat pipe and ensure its free movement on building structures during temperature deformations. When the pipeline is moved, the movable supports move with it. Movable supports are used for all laying methods, except channelless. With channelless laying, the heat pipeline is laid on untouched soil or a carefully compacted layer of sand. At the same time, movable supports are provided only in the places where the route turns and the installation of U-shaped compensators, i.e., in areas where pipelines are laid in channels. Movable supports experience mainly vertical loads from the mass of pipelines

According to the principle of free movement, sliding, rolling and suspended bearings are distinguished. sliding supports are used regardless of the direction of horizontal movements of pipelines for all laying methods and for all pipe diameters. These supports are simple in design and reliable in operation.

Roller supports used for pipes with a diameter of 175 mm or more with axial movement of pipes, when laying in tunnels, collectors, on brackets and on free-standing supports. The use of roller bearings in impassable channels is impractical, since without supervision and lubrication, they quickly corrode, stop rotating and begin to actually work as sliding bearings. Roller bearings have less friction than sliding bearings, however, if poorly maintained, the rollers warp and may jam. So they need to be given the right direction. For this, annular grooves are provided in the rollers, and guide bars are provided on the base plate.

Roller bearings(rarely used, since it is difficult to ensure the rotation of the rollers. Roller and roller bearings work reliably on straight sections of the network. At the turns of the route, pipelines move not only in the longitudinal, but also in the transverse direction. Therefore, the installation of roller and roller bearings on curved sections is not recommended. in this case use ball bearings. In these supports, the balls move freely along with the shoes along the backing sheet, and are kept from rolling out of the support by the protrusions of the base sheet and shoe.

If, according to local conditions for laying heat pipelines relative to the supporting structures, sliding and roller supports cannot be installed, suspension supports are used. The non-rigid suspension design allows the support to easily rotate and move with the pipeline. As a result, as the distance from the fixed support increases, the angles of rotation of the hangers increase, respectively, the skew of the pipeline and the tension in the rods under the action of the vertical load of the pipeline increase.

Suspension supports, compared to sliding supports, create much lower forces along the pipe axis in horizontal sections.

motionless pipelines are divided by supports into independent sections. With the help of fixed supports, the pipes are rigidly fixed at certain points along the routes between expansion joints or sections with natural compensation for temperature deformations, which, in addition to vertical loads, perceive significant horizontal forces directed along the axis of the pipeline and consisting of unbalanced forces of internal pressure, resistance forces of free supports and the reaction of compensators . The forces of internal pressure are of the greatest importance. Therefore, to facilitate the design of the support, they try to place it on the route in such a way that the internal pressures in the pipeline are balanced and not transferred to the support. Those supports to which the reactions of internal pressure are not transmitted are called unloaded fixed supports; the same supports that must perceive unbalanced forces of internal pressure are called unloaded supports.

Exist intermediate and end supports. Forces act on the intermediate support from both sides, on the end support from one side. Fixed pipe supports are designed for the greatest horizontal load under various operating modes of heat pipelines, including with open and closed valves

Fixed supports are provided on pipelines for all methods of laying heating networks. The magnitude of temperature deformations and stresses in pipes largely depends on the correct placement of fixed supports along the length of the heating network route. Fixed supports are installed on the branches of pipelines, at the locations of shut-off valves, stuffing box compensators. On pipelines with U-shaped compensators, fixed supports are placed between the compensators. For channelless laying of heating networks, when self-compensation of pipelines is not used, fixed supports are recommended to be installed at the turns of the route.

The distance between the fixed supports is determined based on the given configuration of the pipelines, the temperature elongation of the sections and the compensating ability of the installed compensators. The fixed fastenings of pipelines are performed by various structures, which must be strong enough and rigidly hold the pipes, preventing them from moving relative to the supporting structures.

The structures of fixed supports consist of two main elements: load-bearing structures (beams, reinforced concrete slabs), to which forces are transferred from pipelines, and the supports themselves, with the help of which the pipes are fixed (welded scarves, clamps). Depending on the laying method and installation location, fixed supports are used: thrust, shield and clamp. Supports with vertical double-sided stops and frontal ones are used when they are installed on frames in chambers and tunnels and when laying pipelines in through, semi-through and impassable channels. Shield supports are used both for channelless laying and for laying heat pipes in impassable channels when the supports are placed outside the chambers.

Shield fixed supports are vertical reinforced concrete shields with holes for the passage of pipes. Axial forces are transferred to the reinforced concrete shield by rings welded to the pipeline on both sides, reinforced with stiffeners. Until recently, asbestos was laid between the pipe and concrete. At present, the use of asbestos packings is not allowed. The load from pipelines of heating networks through shield supports is transferred to the bottom and walls of the channel, and in case of channelless laying - to the vertical ground plane. Shield supports are made with double symmetrical reinforcement, since the acting forces from the pipes can be directed in opposite directions. In the lower part of the shield, holes are made for the passage of water (in case it enters the channel).

Calculation of fixed supports.

Fixed supports fix the position of the pipeline at certain points and perceive the forces that occur at the fixation points under the influence of temperature deformations and internal pressure.

Supports have a very important effect on the operation of the heat pipeline. Serious accidents are not uncommon due to incorrect placement of supports, poor choice of structures or careless installation. It is very important that all supports are loaded, for which it is necessary during installation to verify their placement along the route and their position in height. With channelless laying, they usually refuse to install free supports under pipelines in order to avoid uneven subsidence, as well as additional bending stresses. In these gaskets, pipes are laid on undisturbed soil or a carefully compacted layer of sand.

The span (distance) between the supports determines the bending stress that occurs in the pipeline and the deflection arrow.

When calculating bending stresses and deformations, a pipeline lying on free supports is considered as a multi-span beam. On fig. T.c.19 shows a diagram of the bending moments of a multi-span pipeline.

Consider the forces and stresses acting in pipelines.

We accept the following notation:

M- force moment, N*m; Q B , Q g - vertical and horizontal force, N; q in , q G- specific load per unit length, vertical and horizontal, H / m; ..N - horizontal reaction on the support, N.

The maximum bending moment in a multi-span pipeline occurs at the support. The magnitude of this moment (9.11)

where q - specific load per unit length of the pipeline, N/m; - span length between supports, m. Specific load q is determined by the formula
(9-12)

where q B - vertical specific load, taking into account the weight of the pipeline with the coolant and thermal insulation; q G - horizontal specific load, taking into account the wind force,

(9-13)

where w - wind speed, m/s; - air density, kg / m 3; d And - outer diameter of pipeline insulation, m; k - aerodynamic coefficient equal to an average of 1.4-1.6.

Wind force should be taken into account only in overhead open laying heat pipes.

The bending moment at the middle of the span

(9.14)

At a distance of 0.2 from the support, the bending moment is zero.

The maximum deflection occurs in the middle of the span.

Pipe deflection boom
, (9.15)

Based on the expression (9-11), the span between the free supports is determined

(9-16) from where
,m(9-17)

When choosing a span between supports for real piping schemes, it is assumed that under the most unfavorable operating conditions, for example, at the highest temperatures and pressures of the coolant, the total stress from all acting forces in the weakest section (usually a weld) does not exceed the allowable value [].

A preliminary estimate of the distance between the supports can be made based on equation (9-17), assuming the bending stress 4 equal to 0.4-0.5 allowable stress:

Fixed supports perceive the reaction of internal pressure, free supports and

compensator.

The resulting force acting on a fixed support can be represented as

but - coefficient depending on the direction of action of the axial forces of the internal pressure on both sides of the support. If the support is unloaded from the force of internal pressure, then but=0 otherwise but=1; R- internal pressure in the pipeline; - the area of ​​the internal section of the pipeline; - coefficient of friction on free supports;
- the difference in the lengths of pipeline sections on both sides of the fixed support;
- the difference between the friction forces of axial sliding compensators or the elastic forces of flexible compensators on both sides of the fixed support.

26. Compensation for thermal elongation of pipelines of heat supply systems. Fundamentals of calculation of flexible compensators.

In heat networks, gland, U-shaped, and, more recently, bellows (wavy) expansion joints are most widely used. In addition to special compensators, the natural angles of rotation of the heating main are also used for compensation - self-compensation. Compensators must have sufficient compensating capacity
to perceive the thermal elongation of the pipeline section between the fixed supports, while the maximum stresses in the radial compensators should not exceed the allowable ones (usually 110 MPa). It is also necessary to determine the reaction of the compensator used in the calculation of loads on fixed supports. Thermal elongation of the design section of the pipeline
, mm, determined by the formula

, (2.81)

where

\u003d 1.2 10ˉ² mm / (m o C),

- estimated temperature difference, determined by the formula
, (2.82)

where

L

Flexible expansion joints unlike stuffing boxes, they are characterized by lower maintenance costs. They are used for all laying methods and for any coolant parameters. The use of stuffing box expansion joints is limited to a pressure of not more than 2.5 MPa and a coolant temperature of not more than 300°C. They are installed during underground laying of pipelines with a diameter of more than. 100 mm, when laying above ground on low pipe supports with a diameter of more than 300 mm, as well as in cramped places where it is impossible to place flexible expansion joints.

Flexible expansion joints are made from bends and straight sections of pipes using electric arc welding. The diameter, wall thickness and steel grade of the compensators are the same as those of the pipelines of the main sections. During installation, flexible expansion joints are placed horizontally; vertical or inclined installations require air or drainage devices that make maintenance difficult.

To create maximum expansion capacity, flexible expansion joints are stretched in a cold state before installation and fixed with spacers in this position. the value

extensions of the compensator are recorded in a special act. Stretched compensators are attached to the heat pipe by welding, after which the spacers are removed. Due to pre-stretching, the compensatory capacity is almost doubled. To install flexible compensators, compensatory niches are arranged. A niche is an impassable channel of the same design, corresponding in configuration to the shape of the compensator.

Gland (axial) compensators are made from pipes and from sheet steel of two types: one-sided and two-sided. The placement of double-sided expansion joints is well combined with the installation of fixed supports. Gland compensators are installed strictly along the axis of the pipeline, without distortions. The stuffing of the stuffing box compensator is a ring made of asbestos graphic cord and heat-resistant rubber. Axial compensators should be used for channelless pipelines.

The expansion capacity of stuffing box expansion joints increases with increasing diameter.

Flexible compensator calculation.

Thermal elongation of the design section of the pipeline
, mm, determined by the formula

, (2.81)

where
- average coefficient of linear expansion of steel, mm / (m o C), (for typical calculations, you can take
\u003d 1.2 10ˉ² mm / (m o C),

- estimated temperature difference, determined by the formula

, (2.82)

where - design temperature of the coolant, o C;

- estimated outdoor air temperature for heating design, o C;

L- distance between fixed supports, m.

The compensating capacity of stuffing box expansion joints is reduced by a margin of 50 mm.

Stuffing Box Reaction - Friction Force in Stuffing Box Packing is determined by the formula, (2.83)

where - operating pressure of the coolant, MPa;

- length of the packing layer along the axis of the gland compensator, mm;

- outer diameter of the branch pipe of the stuffing box compensator, m;

- coefficient of friction of the packing against the metal, is taken equal to 0.15.

Technical characteristics of bellows expansion joints are given in Table. 4.14 - 4.15. Axial reaction of bellows expansion joints is made up of two parts

(2.84)

where - axial reaction caused by wave deformation, determined by the formula

, (2.85)

where  l- temperature elongation of the pipeline section, m;  - wave stiffness, N/m, taken according to the compensator passport; n- the number of waves (lenses). - axial reaction from internal pressure, determined by the formula

, (2.86)

where - coefficient depending on the geometric dimensions and wall thickness of the wave, equal to an average of 0.5 - 0.6;

D And d are the outer and inner diameters of the waves, respectively, m;

- excess pressure of the coolant, Pa.

When calculating self-compensation, the main task is to determine the maximum stress  at the base of the short arm of the track turn angle, which is determined for turn angles of 90 ° along formula
; (2.87)

for angles greater than 90 o, i.e. 90+  , according to the formula
(2.88)

where  l- elongation of the short arm, m; l- length of the short arm, m; E- the modulus of longitudinal elasticity, equal to the average for steel 2 10 5 MPa; d- outer diameter of the pipe, m;

- the ratio of the length of the long arm to the length of the short arm.

Loads on fixed supports are divided into vertical and horizontal.

1. Vertical loads are determined by the formula:

where - the weight of 1 meter of the pipeline (the weight of the pipe with water and insulation).

span between movable supports.

We reduce the table value by 2 times, because installed compensator.

When placing a support in a thermal chamber, additionally take into account the weight of the reinforcement, compensators and the weight of the branches, falling on this support with a factor of 0.5, because weight is distributed between two supports. Those.:

2. Horizontal loads are divided into lateral and axial.

Horizontal axial loads on fixed supports arise under the action of forces:

Friction in supports during thermal elongation of pipelines;

Friction in compensators during thermal elongation of pipelines;

Elastic deformation of flexible expansion joints or self-compensation during stretching in a cold state or thermal elongation of pipelines.

Only the horizontal axial load acts on the support, because the branch is fixed with a support. The horizontal axial load on the support at is determined by the formula in Table 18:

where is the friction force in the compensators.

- area of ​​the outer diameter of the sleeve of the stuffing box compensator.

18. Calculation of forces acting on movable supports

Loads on movable supports are divided into horizontal and vertical. They depend on the weight of the pipeline section per support and the type of support.

where - the weight of 1 meter of the pipeline (the weight of the pipe with water and insulation). Accept for .

The span between the movable supports..

Horizontal loads arise due to the friction reaction of the support during its movement due to the thermal expansion of the pipeline. The horizontal load on the movable support is determined by the formula:

where is the coefficient of friction of the movable supports. For sliding bearings

Bibliographic list

1. Sokolov E.Ya. Heat supply and heat networks: a textbook for universities. – 5th ed., revised. - M .: Energoizdat, 1982. - 360s., Ill.

2. Water heating networks: A reference guide for design / I.V. Belyaikina, V.P. Vitaliev, N.K. Gromov and others; Ed. N.K. Gromova, E.P. Shubin. - M.: Energoatomizdat, 1988. - 376 p.

3. Handbook on adjustment and operation of water heating networks / V.I. Manyuk, Ya.I. Kallinsky, E.B. Hizh et al. 2nd ed., revised. And add. - M .: Stroyizdat, 1982. - 215s.

4. Rivkin S.L., Alexandrov A.A. Thermodynamic properties of water and steam. Directory. Moscow: Energoatomizdat, 1984.

5. Heat supply: Proc. manual for universities / V.E. Kozin, T.A. Levina, A.P. Markov and others - M .: Higher School, 1980. - 408s.

6. Designer's Handbook. Design of thermal networks. Ed. A.A. Nikolaev. M .: Publishing house of literature on construction, 1965. - 360s. ill.

7. Handbook of the designer of industrial, residential and public buildings. Part 1. Ed. Staroverov. M .: Publishing house of literature on construction, 1967.

Determine Horizontal Thrust H on a fixed support B. Determine the vertical standard load F v on a mobile support.

The scheme of the calculated section is shown in Fig. 6

Pipeline with d n xS= 200x6 mm. Weight of one running meter of pipeline with water and insulation G h = 513 N. Distance between movable supports L= 9 m. Friction coefficient in movable bearings m= 0.4. Compensator response P k = 9.56 kN. Force of elastic deformation of the angle of rotation P x = 0.12 kN.

Calculation of horizontal forces H th on support B for various thermal operating modes of the pipeline will be performed according to the formulas:

H th = P to + m× G h × L 1 - 0.7 × m× G h × L 2 \u003d 9560 + 0.4 × 513 × 55 - 0.7 × 0.4 × 513 × 35 \u003d 15818 (N)

H th = P to + m×G h × L 2 - 0.7 × m×G h × L 1 \u003d 9560 + 0.4 × 513 × 35 - 0.7 × 0.4 × 513 × 55 \u003d 8842 (N)

H th = P x + m× G h × L 2 – 0.7×( P to + m×G h × L 1) \u003d 120 + 0.4 × 513 × 35 -

-0.7 × (9560 + 0.4 × 513 × 55) = -7290 (N)

H th = P x + m×G h × L 1 – 0.7×( P to + m×G h × L 2) = 120 + 0.4 × 513 × 55–

-0.7 × (9560 + 0.4 × 513 × 35) = 6378 (N)

As the calculated effort, we take the largest value H th = 15818 N = 15.818 kN. Vertical normative load on the movable support F v is determined by the formula:

F v= G h × L= 513 × 7 = 3591 N = 3.591 (kN)

Calculation of descenders.

Drainage device (valve) - a device that allows you to prevent the pressure that has arisen in the heating network.

Determine the diameters of the downcomers (air vents and drains) for the pipeline section, the diagram of which is shown in Fig. 7.

Let's do the calculations for the left side. Determine the reduced diameter d red by the formula:

Assuming a flow coefficient for the valve m= 0.0144, coefficient

n= 0.72 with an emptying time of no more than 2 hours, we determine the diameter of the descender for the left side d 1

Let's perform similar calculations for the right side. RH descender diameter d 2

Determine the diameter of the fitting and valves d for both sides

Since the calculated diameter of the descender d=18 mm less than recommended d y \u003d 50 mm (see recommendations in the manual), for installation we accept a fitting with the largest diameter from the compared d y = 50 mm.

Elevator selection

An elevator (water jet pump) is a device for mixing high-temperature water from a heating network with water from the return line of the heating system and creating circulation pressure in the latter.

For a heating system with an estimated consumption of network water for heating G = 4.7 t / h and an estimated mixing ratio u p = 2.2, determine the diameter of the elevator neck and the diameter of the nozzle based on the condition of damping the entire available pressure.

Head loss in the heating system at a calculated flow rate of mixed water h = 1.5 m.

Estimated throat diameter d g is determined by the formula:

The calculated value of the diameter of the neck is rounded down to the standard diameter. d d = 30 mm. Available pressure in front of the elevator H for calculating the nozzle is determined as the difference in the available pressure in front of the heating system H TP and pressure loss in the heating system h.

H = H tp - h= 25–1.5 = 23.5 m

The calculated nozzle diameter is determined by the formula:

(mm)

Selected elevator 40s10bk, capacity 3.0 - 5.0 t/h

Specifications:

1) The maximum temperature of the water coming from the heating system is 150 °C;

2) Maximum return water temperature - 70 °C;

3) Maximum working pressure - 10 kgf/cm 2 ;

4) The minimum pressure required for the operation of the elevator is 1 ... 1.5 kgf / cm 2;

5) Material of body, fitting, flanges - steel;

6) Nozzle material - brass (steel).

Conclusion

In this course work, the calculation of heat flows for heating, ventilation and hot water supply of houses in the microdistrict of the city is carried out.

Calculations of thermal loads for heating, ventilation and hot water supply are made. Dependences of these loads on the outside air temperature are constructed. It can be seen from the heat load graphs that heating loads are highly dependent on the outdoor temperature; load on hot water supply (DHW), and practically do not change throughout the year.

Estimated coolant flow rates were determined, pipelines were selected for each section of the network based on coolant flow rates and allowable pressure losses in the section. A piezometric graph is plotted and thermal insulation is selected.

Literature and websites:

1.SNiP 2.01.01-82. Construction climatology and geophysics / Gosstroy of the USSR M .: Stroyizdat, -1997. -140s.

2. SNiP 2.04.07-86*. Thermal networks -M.: Gosstroy, -2001. -48 s.

3. Heat supply / Kozin V. E. and others - M .: Higher school, -1980. -408 p.

4. Sokolov E. Ya. Heating and heating networks. -M.: MPEI Publishing House, -1999. -472 p.

5.Heat engineering handbook / Ed. Yureneva V. N. and Lebedeva P. D. in 2 vols. M .: Energy. -1995. T. 1. -744 p.

6.Designer's Handbook. Design of thermal networks / Ed. Nikolaeva A. A. -M.: Stroyizdat. -1965. -360 s.

7. Handbook of heat supply and ventilation / Shchekin R. V. and others. In 2 books. Kyiv: Budivelnik, -1996, Book. 1. -416 p.

8.Safonov A.P. Collection of tasks for district heating and heating networks. -M.: Energy, -1994. -240 s.

9. Gromov N. K. Subscriber devices of water heating networks. -M.: Energy, -1989. -248 s

10. Heat supply: a textbook for students.: Higher school, 1980 - 408 pages. V.E. Kozin, T.A. Levina, A.P. Markov, I.B. Pronina, V.A. Slemzin

11.B. M. Borovkov, A. A. Kalyutik, V. V. Sergeev. Repair of heat engineering equipment and heating networks.

12. Shiraks Z. E. Heat supply. -M.: Energy, -1999. -256 p.

13. http://www.twirpx.com/files/tek/warming/

14. http://www.bestreferat.ru/referat-category-92-1.html

15.http://ru.wikipedia.org/wiki/%D2%E5%EF%EB%EE%F2%E5%F5%ED%E8%EA%E0

16. http://dic.academic.ru/dic.nsf/bse/139128/Heat engineering

17.http://www.politerm.com.ru/zuluhydro/help/piezografic_construction

Applications:

Appendix No. 1 Equivalent length values ​​for pipes with åx = 1

Appendix №2 The value of the coefficient k2.

Annex No. 3 Technical characteristics of the main network pumps.

Determination of vertical and horizontal load on a fixed support.

Definition of vertical load

Loads acting on fixed supports are divided into vertical and horizontal. Vertical loads include weight ( R in ) and compensation (P k), if the pipeline is located in a vertical plane).

R in - ql, H, P.37 (37)

where q - weight of 1 m of the pipeline (weight of the pipe, insulating structure and water);

q = q tr + q out + q in N/m;

l- span between the movable supports, m.

1 section: P in \u003d 1217 * 13.0 \u003d 15821 N

7 section: R in = 843 * 11.6 \u003d 9778.8 N

Similarly, we calculate other sections of pipelines.

If the fixed support is located in the pipeline node, then it is necessary to take into account the additional load from the fittings and stuffing box expansion joints.

In the graduation project, it is necessary to determine the loads on 2-3 fixed supports (according to the task of the head). Determine the vertical load for given supports.

Horizontal loads on fixed supports are more diverse. They arise under the influence of the following forces:

forces of elastic deformation of flexible compensators or self-compensation during their stretching in a cold state or during thermal elongation of pipelines;

forces of internal pressure when using unbalanced stuffing box compensators;

friction forces in stuffing box expansion joints during thermal elongation of the pipeline;

friction forces in movable supports during thermal elongation of pipelines laid in channels and on the ground;

forces of friction of the pipeline against the ground during channelless laying.

Friction force in movable bearings.

N Page 38 (38)

where μ is the coefficient of sliding friction; accept for sliding supports μ = 0.3 - steel on steel; μ = 0.6 - steel on concrete; for roller, roller, ball and suspension bearings μ = 0,1;

q - weight of 1 m pipeline, N/m;

L 1 - the length of the pipeline from the fixed support to the compensator or from the fixed support to the turn (with self-compensation), m.

1 section: \u003d 0.3 * 1217 * 130 \u003d 47463 N

7 plot: = 0.3 * 843 * 120 \u003d 30348 N

Internal pressure force

N Page 38 (39)

where P slave is the working pressure of the coolant, Pa;

f 1 and f 2 - larger and smaller section of the pipe, m.

At pipe bends of 90 ° and with closed valves f 2 = 0.

1 section: P vd \u003d 1.6 * (58 - 0) \u003d 92.8 N

7 section: R vd \u003d 1.6 * (40 - 0) \u003d 64 N

Table 12

Axial forces act on each fixed support from the left and right. Depending on the direction of the reactions, the forces are partially balanced or summed up.

Fixed supports that perceive partially balanced horizontal axial forces are called unloaded (intermediate). They are located between adjacent straight sections of pipelines. Unloaded (end) supports are placed at pipeline bends or in front of the plug and perceive horizontal forces acting from one side.

When calculating loads, it is necessary to consider all possible operating modes of the pipeline from cold to working state.

When determining the horizontal axial load on the support for each operating mode of the pipeline, the forces acting on the fixed support in one direction are added up, and then the smaller one is subtracted from the greater sum of forces, while taking into account possible deviations from the calculated values, the friction forces and the forces of elastic deformation are subtracted with a coefficient of 0.7, which provides some margin in the design load on the fixed support. If the sum of the forces acting on the support from both sides is equal, one of the sums with a coefficient of 0.3 is taken as the calculated one.

V.V. Logunov, General Director;
V.L. Polyakov, chief designer of projects for thermal networks;
M.Yu. Yudin, head of the technical support department,
PJSC NPP Compensator, St. Petersburg;

E.V. Kuzin, Director, ATEX-ENGINEERING LLC, Irkutsk

Introduction

The issue of energy efficiency of heat networks is closely related to the technologies and materials used in the construction and reconstruction of heat networks. At the same time, modern energy-saving technologies are becoming increasingly important. Despite the fact that bellows expansion joints are considered a novelty in Russia, a change in approach is already clearly visible, from when they were resorted to from the impossibility of solving the problem of thermal expansion by classical methods, to the moment when in many regions bellows expansion joints became a prerequisite for technical specifications for the development of pipeline projects. And today the question of using bellows expansion joints remains open only in the absence of sufficient information to determine the appropriateness of their use in comparison with classical types of expansion joints. In this article, we will consider the technical aspects of using bellows expansion joints instead of stuffing boxes.

Load comparison of stuffing box and bellows expansion joints

One of the topical issues when making a decision to abandon gland expansion joints is the possibility of maintaining existing fixed supports. The solution of this issue is complicated due to significant differences in the regulatory documentation for stuffing box and bellows expansion joints. In this article, we will establish for which type of expansion joints, other things being equal, the axial load on the fixed supports is greater. The axial load from the bellows compensator on the end fixed support is defined as:

P kno \u003d P p + P W + P tr

where R p - expansion force of the bellows compensator, R W - force from the axial rigidity of the bellows compensator, R tr - forces from the friction of the pipeline in movable supports (sliding supports in the sections of channel and above-ground laying, or friction of the heat pipe against the ground in areas of channelless laying).

The axial load from the gland compensator is determined by a similar formula:

P kno \u003d P C p + P C tr + P tr

where P C p is the expansion force of the stuffing box compensator, P c tr is the force from friction of the stuffing box of the stuffing box compensator, P tr is the force from friction of the pipeline in movable supports (sliding supports in the sections of channel and above-ground gaskets, or friction of the heat pipe against the soil in areas of channelless laying ).

Any axial expansion joints, whether stuffing box, bellows or lens, due to the absence of a rigid axial connection, transmit a spacer force (from the internal pressure of the medium) acting on the pipeline wall and perceived by the end fixed supports (Fig. 1).

The expansion force is defined as the product of the pressure and the area of ​​application of the force. In the case of a bellows expansion joint, the effective area of ​​the bellows is taken under the force application area, and in the case of a stuffing box compensator, the force application area is determined by the outer diameter of the compensator nozzle (Fig. 2).

Accordingly, they can be subjected to hydraulic tests with a test pressure of 1.25РN. The expansion force from any axial expansion joint increases in proportion to the increase in pressure. In RD-3-VEP-2011, the maximum expansion force for bellows expansion joints is given at test pressure. Whereas for stuffing box expansion joints, as well as for all others, in GOST R 55596-2013, when calculating the expansion force, the nominal pressure value is used. It is this difference in the approach to the calculation of axial forces that is decisive when making a decision to replace the stuffing box compensator with a bellows compensator.

Let's compare the loads from the stuffing box and bellows compensator for several diameters (DN), for PN = 16 kgf / cm 2, provided that the spacer force will be calculated in two versions: taking into account the test pressure (P pr), and nominal (PN) (table . one). The stiffness of bellows expansion joints will be determined according to RD-3-VEP-2011 (Table 2). The values ​​of the friction force of the seals of stuffing box compensators are given from the albums of drawings of stuffing box compensators (passport value of the friction force) (Table 3). The friction of the pipeline in the movable supports in this calculation is neglected.

Table 1. Spacer force of stuffing box and bellows compensators at РN=16 kgf/cm2.

Table 2. Force of rigidity of the bellows compensator.

Table 3. Friction forces of stuffing box compensator (series 5.903-13 issue 4).

Table 4. The total value of the loads on the end fixed supports.

As can be seen from Table. 4, in most of the cases considered, when calculating the force using a similar method, the load on the end fixed supports from the bellows compensator turned out to be less than the similar load from the stuffing box compensator. Exceeding the load by 1% for DN1000 is also not critical when deciding whether to replace the stuffing box expansion joint with a bellows expansion joint.

Thus, if you change the existing stuffing box expansion joint to a bellows expansion joint, then in most cases there will be no need to strengthen the existing end fixed supports (all calculations for bellows expansion joints are correct only for bellows expansion joints according to YANSH.300260.029TU. - Approx. Aut.).