Regardless of the material from which they are made, they are subject to thermal expansion 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 you neglect it and do not install the necessary compensators, then, when the route is laid open, the pipes may sag or even cause the entire system to fail. Therefore, the calculation of temperature expansion 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 do you need to take into account thermal expansion of pipelines?
• How to calculate the deflection of a pipeline during thermal elongation.
• How to calculate and install the arm of a thermal expansion compensator.
• How to compensate for temperature deformations of polymer pipelines.
• Which polymer pipelines are best used for open plumbing and heating distribution.

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

Temperature extensions or shortenings 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 the pipelines, and also to 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 of cold and hot water supply pipes into the floor screed without the use of insulation or protective corrugation.
• Open pipe laying, for example, when installing heating system radiators, without the use of special compensators.

Sergei Bulkin Head of the technical department of the “Internal engineering systems” direction at REHAU

Accounting for temperature extensions of pipelines from polymer materials, in particular, from PE-Xa, should be made only with their laying open. When laying hidden, compensation for 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, compensation of elongations occurs due to stresses in the screed or plaster.

The technology for concealed laying of pipelines in grooves or in screeds should provide the ability to compensate for the resulting deformations without mechanical damage to pipes and connecting elements.

Note that the screed can withstand stress without destruction, because the resulting forces are very small and constitute an insignificant percentage of its available safety margin. You just need to make sure that when pouring screed or plastering walls, the solution does not get inside the corrugated pipe or under the thermal insulation. The pipes are connected to the water fittings through wall elbows, which are firmly fixed to the 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 collectors a 90° turn is performed at the exit from the screed or from under the plaster.

Thus, forces from very short sections that can be neglected will be transferred to the nodes connecting the pipelines to the collector.

When laid open, the thermal expansion of polymer pipelines, in particular pipelines made of PE-Xa, will be very noticeable, because these pipelines have a high thermal expansion coefficient.

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

This 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 pipeline will be shortened.

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

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

Temperature extensions or shortenings of pipelines occur due to changes in the operating temperature of the water circulating through them, as well as the ambient temperature. When laid open, the pipeline must be free to lengthen or shorten without overstressing the material of the pipes, fittings and connections of the pipeline. This is achieved due to the compensating ability of the pipeline elements. For example:

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

The installation of compensators is necessary only for significant linear extensions of pipelines. Since the system must be rational, the thermal elongation of the pipeline is first calculated. Let's take pipelines made of cross-linked polyethylene RE-Xa. To calculate we need:

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

Sergei Bulkin

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

ΔL = L α ΔТ (t max. operating – t installation). Where:

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

Substitute the values ​​into the formula:

ΔL = L α (t max. work. – t installation) = 10 0.15 (70 – 20) = 75 mm.

Those. In this case, the 10-meter section will lengthen 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 significant 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 capable of perceiving pipeline deflection (ΔН) starting from 5 mm.

Pipe deflection as a result of thermal expansion.

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

Calculation of pipeline deflection and methods for compensating for temperature deformations of polymer pipelines

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

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

Sergei Bulkin

There are different ways to combat temperature deformations of polymer pipelines:

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

Let's look at each of these methods.

Methods for compensating for temperature deformations of polymer pipelines

1. Installation of additional fastening clamps.

By installing additional fastening clamps, sagging or deflection of pipelines is prevented. The recommended maximum distance between clamps for polymer pipes made of PE-Xa is 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 polymer pipes made of PE-Xa, because These pipes are highly elastic. At the same time, places where pipelines turn at 90° can be used as L-shaped compensators. It is necessary to use the formula, as described above, to determine the temperature 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 allow the pipe to bend freely. To do this, the first fastening clamp, after turning, should be installed at a certain distance from the turn.

Construction of an L-shaped compensator on polymer pipes.

• LBS – compensator arm length;
• x – minimum distance from the wall;
• ΔL – temperature elongation;
• FP – fixed support;
• L – pipe length;
• GS – sliding clamp.

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 compensators so as not to disturb the bend of the pipe.

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

• C – pipe material constant;
• d – outer diameter of the pipeline in mm;
• ΔL – thermal elongation of the pipeline section.

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

Sergei Bulkin

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

3. U-shaped compensator device.

U-shaped compensators are installed in cases where compensation of thermal expansion at the edges of the site is undesirable. It is installed, as a rule, in the middle of the pipeline section, and compensation for temperature expansion is directed towards the center of the section. The bases of the U-shaped compensator are shifted towards 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.

Construction of a U-shaped compensator on polymer pipes.

4. Fixing groove as a compensator for thermal expansion.

The fixing gutter is a three-meter-long galvanized steel tray with flanging along the edges. Fixing gutters are produced for the corresponding diameters of pipelines. The pipelines are snapped into the fixing grooves. In this case, the fixing groove covers the pipe approximately 60°.

The frictional forces of the pipeline against the walls of the gutter exceed the force of thermal expansion of the pipeline.

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

When installing a fixing trench at the bottom of the pipeline, its mechanical protection is ensured.

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

5. Using fixed supports

If it is necessary to compensate for temperature elongations on a long section of a pipeline on which there are many branches, for example, a water riser in a 20-story building, on each floor of which tees for apartment wiring are installed, then compensation for temperature elongations can be done by installing fixed supports. To do this, conventional sliding clamps are installed on both sides of the tee behind the sliding sleeves.

Formation of a fixed support as a compensator for thermal expansion of the pipeline.

The clamps will not allow the shaped part to move either up or down. Thus, the long section is divided into many short sections equal to the floor height, approximately 3 m. As we remember from the calculation formula, thermal elongation is directly proportional to the length of the section, and we have 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, a “idle” riser, which does not have side branches along its entire length, then you can artificially install, for example, equal 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 installations

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

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

ΔL = L α (t max. work. – t installation) = 10 0.026 (70 – 20) = 13 mm.

For comparison: we previously calculated the thermal elongation of a conventional PE-Xa pipeline 10 m long, which amounted to 75 mm.

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

Z conclusion

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

A modern way to extend the life of pipeline systems is the use of expansion joints. They help prevent various changes that occur in pipes due to constant changes in temperature, pressure and various types of vibrations. The absence of compensators on pipes can lead to such undesirable consequences as a change in the length of the pipe, its expansion or compression, which subsequently leads to a pipeline breakthrough. In this regard, the problem of reliability of pipelines and compensators is given the closest attention and a search is carried out optimal solutions to ensure the technical safety of compensation systems.

There are pipe, stuffing box, lens and bellows compensators. Most in a simple way is the use of natural compensation due to the flexibility of the pipeline itself using elbows U-shaped. U-shaped expansion joints are used for overhead and channel laying of pipelines. For them, when laying above ground, additional supports are required, and when laying in channels, special chambers are required. All this leads to a significant increase in the cost of the pipeline and the forced alienation of areas of expensive land.

Stuffing box compensators, which until recently were most often used in Russian heating networks, also have a number of serious disadvantages. On the one hand, the stuffing box compensator can provide compensation for axial movements of any magnitude. On the other hand, there are currently no gland seals capable of ensuring the tightness of pipelines with hot water and ferry for a long time. In this regard, regular maintenance of the stuffing box expansion joints is required, but even this does not prevent coolant leaks. And since when laying heat pipelines underground, special service chambers are required to install stuffing box expansion joints, this significantly complicates and makes the construction and operation of heating pipelines with expansion joints of this type more complicated and more expensive.

Lens compensators are used mainly on heat and gas mains, water and oil pipelines. The rigidity of these expansion joints is such that significant effort is required to deform them. However, lens compensators have a very low compensating ability compared to other types of compensators; moreover, the labor intensity of their manufacture is quite high, and a large number of welds (which is caused by manufacturing technology) reduces the reliability of these devices.

Considering this circumstance, the use of bellows-type expansion joints, which do not leak and do not require maintenance, is currently becoming relevant. Bellows expansion joints are small in size, can be installed anywhere in the pipeline using any method of laying it, and do not require the construction of special chambers or maintenance during the entire service life. Their service life, as a rule, corresponds to the service life of pipelines. The use of bellows expansion joints ensures reliable and effective protection pipelines from static and dynamic loads arising from deformations, vibration and water hammer. Thanks to the use of high-quality stainless steels in the manufacture of bellows, bellows expansion joints are capable of operating in the most severe conditions with temperatures of working media from “absolute zero” to 1000 ° C and withstand operating pressures from vacuum to 100 atm, depending on the design and operating conditions.

The main part of the bellows expansion joint is the bellows - an elastic corrugated metal shell that has the ability to stretch, bend or shift under the influence of temperature changes, pressure and other types of changes. They differ from each other in such parameters as dimensions, pressure and types of displacements in the pipe (axial, shear and angular).

Based on this criterion, compensators are divided into axial, shear, angular (rotary) and universal.

The bellows of modern expansion joints consist of several thin layers of stainless steel, which are formed using hydraulic or conventional pressing. Multi-layer expansion joints neutralize the impact high pressure And various kinds vibrations without causing reaction forces, which in turn are provoked by deformation.

The Kronstadt company (St. Petersburg), the official representative of the Danish manufacturer Belman Production A/S, supplies Russian market bellows expansion joints specially designed for heating networks. This type of compensator is widely used in the construction of heating networks in Germany and Scandinavia.

The design of this compensator has a number of distinctive features.

Firstly, all layers of the bellows are made of high-quality stainless steel AISI 321 (analogue 08Х18Н10Т) or AISI 316 TI (analog 10Х17Н13М2Т). Currently, in the construction of heating networks, expansion joints are often used in which the inner layers of the bellows are made of a material of lower quality than the outer ones. This can lead to the fact that with any, even minor damage to the outer layer, or with a small defect weld, water, which contains chlorine, oxygen and various salts, will get inside the bellows and after some time it will collapse. Of course, the cost of a bellows in which only the outer layers are made of high-quality steel is somewhat lower. But this difference in price cannot be compared with the cost of work in the event of an emergency replacement of a failed compensator.

Secondly, Belman expansion joints are equipped with both an external protective casing that protects the bellows from mechanical damage, and an internal pipe that protects the internal layers of the bellows from the effects of abrasive particles contained in the coolant. In addition, the presence of internal bellows protection prevents sand from depositing on the bellows lenses and reduces flow resistance, which is also important when designing a heating main.

Ease of installation is another distinctive feature Belman compensators. This compensator, unlike its analogues, is supplied completely ready for installation in the heating network: the presence of a special fixing device allows the compensator to be mounted without resorting to any preliminary stretching and does not require additional heating of the heating network section before installation. The compensator is equipped with a safety device that protects the bellows from twisting during installation and prevents excessive compression of the bellows during operation.

In cases where the water flowing through the pipeline contains a lot of chlorine or may enter the groundwater compensator, Belman offers a bellows in which the outer and inner layers are made of a special alloy that is particularly resistant to aggressive substances. For ductless laying of heating mains, these expansion joints are produced in polyurethane foam insulation and are equipped with an operational remote control system.

All of the above advantages of compensators for heating networks produced by Belman, coupled with high quality manufacturing, allow us to guarantee trouble-free operation of the bellows for at least 30 years.

Literature:

1. Antonov P.N. “On the peculiarities of using compensators”, magazine “ Pipeline accessories", No. 1, 2007.
2. Polyakov V. “Localization of pipe deformation using bellows expansion joints”, “Industrial Vedomosti” No. 5-6, May-June 2007
3. Logunov V.V., Polyakov V.L., Slepchenok V.S. “Experience in using axial bellows expansion joints in heating networks,” Heat Supply News magazine, No. 7, 2007.

Any material: solid, liquid, gas, 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, a pipe, the main indicator is the longitudinal expansion along the axis - thermal (temperature) elongation. This phenomenon must be taken into account during the implementation of certain engineering works.

For example, during a train ride, a characteristic tapping sound is heard due to 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 thermal expansion, when using inappropriate materials 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 fixed supports and on installation elements increase, which reduces the durability of the system as a whole, and, in In extreme cases, it can lead to an accident.

The increase in pipeline length is calculated using the formula:

ΔL - increase in element length [m]

α - coefficient thermal expansion material

lo - initial element length [m]

T2 - final temperature [K]

T1 - initial temperature [K]

Thermal expansion compensation for pipelines engineering systems 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 absorb linear expansion of pipes (compensators);
• pre-tensioning of pipes (this method is quite dangerous and should be used with extreme caution).

Fig.5

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

This installation 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 specified 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 hidden : in the floor (in a corrugated pipe)…

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

When performing this type of compensation, you should pay attention to the serviceability of the fittings. Excessive stress due to bending of pipes can lead to cracks in the tee (Figure 6). To ensure this is avoided, changes in the direction of the pipeline route must occur at a distance of at least 10 outer diameters from the fitting nozzle, and the pipe next to the fitting must be rigidly fixed, this, in turn, minimizes the impact of bending loads on the fitting nozzles.

Fig.6

Another type of natural temperature compensation is the so-called “rigid” fastening of pipelines. It represents the division of the pipeline into limited sections of temperature compensation in such a way that the minimum increase in the pipe does not significantly affect the linearity of its laying, and excess stress goes into efforts to fasten points of fixed supports (Fig. 7).

Fig.7

This type of compensation works for longitudinal bending. To protect pipelines from damage, it is necessary to divide the pipeline with points of fixed supports into compensation sections of no more than 5 m. It should be noted that with such installation, pipeline fastenings are affected not only by the weight of the equipment, but also by stresses from thermal expansion. This leads to the need to calculate the maximum permissible load on each of the supports each time.

The forces arising from thermal elongations and acting on the 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 - elastic modulus (Young's) of the pipe material [N/mm]

ΔT - change (increase) in temperature [K]

In addition, the point of fixed support is also affected by the own weight of the pipeline section filled with coolant. In practice, the main problem is that not a single fastener manufacturer provides data on the maximum permissible loads on their fastening elements.

Natural compensators for thermal expansion are G, P, Z-shaped compensators. 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 compensation arm for compensators of type “G”, “P” and “Z” is determined depending on the resulting thermal elongations, type of material and pipeline diameter. The calculation is performed using the formula:

[m]

K - pipe material constant

Dz - outer diameter of the pipeline [m]

ΔL - thermal elongation of a pipeline section [m]

The material constant K is related to the stresses that a given type of pipeline material can withstand. For individual KAN-therm Systems, the material constant K values ​​are presented below:

Push PlatinumK = 33

Compensation arm of compensator type “G”:

A - length of compensation arm

L - initial length of the pipeline section

ΔL - lengthening of the pipeline section

PP - movable support

A - length of compensation arm

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

S - expansion joint width

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

A - length of compensation arm

L1, L2 - initial length of segments

ΔLx - lengthening of the pipeline section

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

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

Fig.9

In addition to geometric temperature compensators, there are a large number of design solutions for this type of element:

• bellows expansion joints,
• elastomeric compensators,
• fabric expansion joints,
• loop-shaped compensators.

Due to the relatively high price of some options, such expansion joints are most often used in places where space is limited or technical capabilities geometric compensators or natural compensation. These expansion joints have a limited service life, calculated in operating cycles - from full expansion to full compression. For this reason, for equipment that operates 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 expansion. Bellows are often made of stainless steel. This design determines the service life of the element - approximately 1000 cycles.

The service life of bellows-type axial expansion joints is significantly reduced if the expansion joint is installed out of alignment. This feature requires high precision of their installation, as well as their correct fastening:

• it is possible to install no more than one compensator in the temperature compensation area between 2 adjacent points of fixed supports;
• the movable supports must completely enclose the pipes and not create much resistance to compensation. Maximum size backlashes no more than 1 mm;
• axial compensator It is recommended, for greater stability, to be installed 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 .

09.04.2011

Introduction

In recent years, ductless laying of heat pipelines using pre-insulated steel pipes has become widely used in Russia; starting bellows compensators (SC) and pre-insulated bellows compensating devices (SCU) are used to compensate for temperature deformations.

As described earlier, the use of starting compensators for ductless installation is advisable on heating networks in those heat supply systems, where quantitative regulation of thermal loads is applied. In addition, starting bellows expansion joints can be used in regions with mild climatic conditions, when the temperature differences of the coolant relative to the average temperature are insignificant and stable. At quality regulation thermal loads during peak heating modes, as well as when the coolant cools down and is drained, which quite often happens in many regions of Russia, the temperature stresses on the pipeline and fixed supports increase sharply, which often leads to accidents at the starting compensators.

Taking into account also the difficulties in “launching” the starting compensator and pipeline repairs, axial SCs are used in most regions of Russia. Sometimes, when laying a pre-insulated heat pipe without ducts, an axial bellows compensator is placed in the chamber. But in most cases, thermally waterproofed I&C systems are used, manufactured at insulation factories from axial SKUs. The designs of these I&C systems are varied (each plant has its own design), but they all have common features:

• waterproofing of the moving part of the control system does not provide long-term protection from groundwater under repeated cyclic exposure, which leads to wet thermal insulation, increased electrochemical corrosion of compensator parts and pipelines, chloride corrosion of the bellows, which cannot be allowed, and the operational-remote control system (ORC) in this case doesn't work because the signal conductors inside the compensation device were laid in an insulating cambric along its entire length (up to 4.5 m);
• Due to the insufficient bending rigidity of the design of such an I&C system, the bellows are not protected from bending moments, therefore the requirements for pipeline alignment during installation increase.

On the creation of a reliable design of a thermally waterproofed axial control system

Having analyzed the features of existing I&C structures, NPP Kompensator OJSC, together with VNIPIenergoprom Association OJSC, since 2005, has been closely engaged in developing its own design of a fully thermally waterproofed axial I&C system for ductless installation of heat pipelines, providing reliable waterproofing from groundwater and protection of the bellows from possible deflection of the pipeline throughout the entire service life.

During the development process we tested various options unit for waterproofing the moving part of the control system against groundwater for cyclic operation: sealing rings made of rubber of various grades; sealing cuffs of various profile configurations; gland packing. Cyclic tests of I&C prototypes with various designs of waterproofing units were carried out in a bathtub filled with a water-sand suspension, simulating worst conditions their operation. Tests have shown that different kinds seals operating under friction conditions do not provide reliable waterproofing for several reasons: the possibility of grains of sand getting between the seal and the polyethylene shell, which will eventually lead to a breakdown of the waterproofing; as well as the inability to ensure the stability of the quality of installation of sealing rings or cuffs of a fixed size due to the large spread (up to 14 mm) of the permissible maximum deviations of the diameter of the polyethylene shell and its ovality. The waterproofing unit using gland packing performed best. But it is not possible to control the quality of waterproofing with gland packing during the manufacture of control and equipment systems.

Then it was decided to use an additional protective bellows in combination with a stuffing box as a waterproofing unit ( detailed description designs, see work). The I&C prototypes successfully passed cyclic tests, and in 2007 they began mass production. The main consumer of this I&C design is the heating network enterprises of the Republic of Belarus, where the requirements for the quality and reliability of the construction of heating networks are somewhat higher than in Russia. Only a few dozen such I&C systems have been installed in Russian heating networks due to their relatively high cost compared to the cost of compensation devices used previously.

At the same time, serial deliveries of a simplified design of thermally and water-insulated control and equipment systems began without an additional protective bellows, but with the use of an anti-corrosion coating for the working bellows. This design meets all the requirements, the waterproofing unit is made using stuffing box packing. Over the past 3.5 years, such thermally waterproofed I&C systems have found widespread use in many regions of the Russian Federation.

Taking into account the wishes of installation and operating organizations, as well as taking into account the high cost of thermally waterproofed I&C systems with an additional protective bellows, the team of NPP Kompensator OJSC was tasked with creating a less labor-intensive design of a thermally waterproofed I&C system that provides reliable waterproofing from groundwater and is “indifferent” to possible misalignment of the pipeline.

The additional protective bellows, which significantly increased the cost of the control and equipment system, had to be abandoned, and then the question of ensuring reliable waterproofing arose again. Again, various design solutions for the waterproofing unit were considered. The friction seal was abandoned immediately. The stability of the quality of waterproofing with gland packing depends on the “human factor”. It was tempting to use a rubber coupling, as is done at some insulation factories, but tests of the rubber coupling for axial movements showed that when compressed, the coupling does not take the shape of a corrugation, and at the junction it breaks, in which a rupture of the coupling forms over time. And it is very difficult to select sheet rubber material and glue for it that retain their physical and mechanical properties for 30 years, since rubber sheets mass-produced by our industry do not meet these requirements.

At the beginning of 2009, a new design of a thermally waterproofed I&C system was developed, which took into account all the wishes of installation and operating organizations: less labor-intensive in manufacturing and in which a fundamentally new waterproofing unit was used. The design is based on the proven design of the I&C system for ground and duct laying of heat pipelines, which have been successfully in operation since 1998. It also provides cylindrical guide supports installed on both sides of the bellows, which telescopically move along with the branch pipes of the compensation device along the inner surface of the thick-walled casing and protect bellows against loss of stability in case of pipeline misalignment.

Waterproofing of the moving part of the control system is carried out using an elastic, one-piece cast membrane. The membrane is hermetically fixed to the structure of the compensation device. This allows us to guarantee complete protection of the bellows and thermal insulation from the penetration of groundwater throughout the entire service life of the I&C system. The membrane itself is protected from soil and sand by a tightly packed stuffing box. Thus, the new waterproofed design of the compensation device provides two-level protection of the outer surface of the bellows and the structure of the control system as a whole.

Signal conductors UEC systems inside the compensation device are laid in an electrically insulating heat-resistant cambric, perforated to allow the UEC system to operate in the event of a breach of the tightness of the bellows or waterproofing membrane, which is unlikely, since the breach of tightness in this design is minimized.

The entire outer surface of the I&C casing is protected from the effects of the external environment by a specially designed heat-shrinkable polyethylene cuff. The new design also provides for thermal insulation of the bellows, which eliminates the possibility of condensation forming inside the control system.

So, in the new design of the SKU, a fundamentally new solution is used as a waterproofing unit - a waterproof elastic membrane. What is it?

The waterproof elastic membrane is made by casting in molds from a mixture based on specially developed rubber and is designed for a service life of the I&C system of up to 50 years when installed without ducts.

The membrane used for waterproofing in the design of the control and equipment system makes it possible to avoid using a friction unit as the main sealing element. The specially designed shape of the membrane allows for its unhindered movement during thermal deformations of the heat pipe relative to the stationary casing of the control system.

Temperature tests of the membrane conducted by VNIPIenergoprom Association showed that at a temperature of 150 °C the membrane does not lose its physical and mechanical properties and is in working condition throughout the entire service life of the I&C system.

Qualification tests of a new design of a thermally waterproofed axial I&C system with a membrane were carried out in the summer of 2009 together with representatives of VNIPIenergoprom Association OJSC and NP RT.

When testing the control system to confirm the probability of failure-free operation during cyclic operation, the worst operating conditions were simulated: a prototype of the compensation device was placed in a barrel of water and subjected to cyclic axial compression-tension tests. After every 1000 cycles, control measurements of the electrical resistance were carried out between the pipes of the control system and the signal conductors of the UEC system at a test voltage of 500 V.

After completing the assigned operating time, taking into account the probability of failure-free operation (a total of about 30,000 cycles), the cyclic tests were stopped. The prototype SKU was tested for strength and tightness, after which the casing was removed from it. No destruction of the bellows, membrane, or traces of water penetration into the inside of the control system were found.

The Interdepartmental Testing Commission gave the go-ahead for serial production of thermally and water-insulated I&C systems of a new design at NPP Kompensator OJSC, which began in 2010.

Based on the results of deliveries of the first batches of I&C systems of a new design to heating network enterprises, wishes and proposals from design and installation organizations were collected, based on the analysis of which changes were made to the design of the thermally waterproofed I&C system regarding ease of installation and thermal insulation of the junction of the I&C system with the pipeline, optimization of weight and size characteristics, unification of parts SKU. The waterproofing unit of the SKU has also been improved in terms of increasing its reliability and protection from mechanical damage.

VNIPIenergoprom conducts constant monitoring, production and laboratory tests of thermally and water-insulated I&C systems and other products of JSC NPP Kompensator to confirm their technical characteristics.

Literature

1. Logunov V.V., Polyakov V.L., Slepchenok V.S. Experience in using axial bellows expansion joints in heating networks // Heat supply news. 2007. No. 7. pp. 47-52.
2. Maksimov Yu.I. Some aspects of the design and construction of channelless thermally stressed pre-insulated pipelines using starting compensators // Heat supply news. 2008. No. 1. P. 24-34.
3. Ignatov A.A., Shirinyan V.T., Burganov A.D. Upgraded bellows compensation device in polyurethane foam insulation for heating networks // Heat supply news. 2008. No. 3. P. 52-53.
4. GOST 30732-2006 Steel pipes and fittings with thermal insulation made of polyurethane foam with a protective sheath. Technical conditions.
5. Events and plans of NP “Russian Heat Supply” // Heat supply news. 2009. No. 9. P. 10. Heat supply news No. 4 (April), 2011

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DECISION of the State Mining and Technical Supervision of the Russian Federation dated 10-06-2003 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 provides for steam or hot water purging, the compensating capacity of the 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 corrugated compensators 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 (with limited space), they can be placed vertically with a loop up or down with the 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. The connection pipe for the drainage pipe is made of 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 compensators should be made in accordance with the requirements of regulatory and technical documentation.





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