What is a compensator?

2019-05-25

Compensator is also known as expansion joint, or bellows expansion joint. The utility model is composed of a bellows (an elastic element) constituting the main body of the bellows and accessories such as an end pipe, a bracket, a flange, a conduit, etc. The utility model belongs to a compensation element. The effective expansion deformation of bellows is used to absorb the size changes of pipelines, conduits and containers caused by thermal expansion and cold contraction, or to compensate the axial, transverse and angular displacements of pipelines, conduits and containers. It can also be used for noise reduction and vibration reduction. It is widely used in modern industry. In heating, in order to prevent pipeline deformation or damage caused by thermal elongation or thermal stress during heating, compensators need to be installed on the pipeline to compensate the thermal elongation of the pipeline, thereby reducing the stress of the pipe wall and the force acting on the valve or support structure.

Types of Compensators

Effect of compensator

Selection techniques

Material classification

Main production

Installation pressure test

Reliable research

Fatigue test

Types of Compensators

(1) Corrugated compensator

1. The meaning of the corrugated compensator:
The corrugated compensator is a compensating device that utilizes the effective telescopic deformation of the elastic member of the bellows to absorb the dimensional change caused by the expansion, contraction or the like of the pipeline, the duct or the container, and belongs to a compensating element.
2. Classification of corrugated compensators:
The corrugated compensator (bellows bexpansion joint) is classified according to the displacement form and can be basically divided into an axial type, a transverse type, an angular type and a pressure balanced type bellows expansion joint (corrugated pipe).
According to whether it can absorb the pressure thrust (blind plate force) generated by the pressure of the medium in the pipeline, it can be divided into unconstrained corrugated expansion joints (bellows bexpansion joints) and constrained corrugated expansion joints (bellows bexpansion joints).
According to the waveform structure parameters of the corrugated compensator, it can be divided into U-shaped, Ω-shaped, S-shaped, V-shaped corrugated expansion joints (corrugated pipes). At present, the expansion joints (corrugated pipe) products at home and abroad adopt U-shaped waveform structure. Mostly.
3. Advantages of the corrugated compensator:
The utility model has the advantages of compact structure, less space occupation and direct burying; the disadvantage is that the manufacturing is difficult, the pressure resistance is low, and the compensation ability is small. The compensation capacity is related to the outer dimensions, wall thickness and diameter of the corrugated tube: the higher the pressure, the thicker the wall, the smaller the diameter, the greater the rigidity, and the smaller the compensation capacity. Waveform compensator is generally used for applications where the nominal pressure is ≤1.0MPa and the nominal diameter is ≥150mm. It can also be used for large diameter pipes with normal pressure and low pressure. It can be used in boiler flue gas ducts up to DN4000mm.
4. The disadvantages of the corrugated compensator:
The corrugated compensator has a thin wall that cannot withstand torque and vibration, and has poor safety; high equipment investment, strict design requirements, high construction and installation accuracy, and often fail to reach the expected life; axial corrugated compensator generates pressure thrust on the fixed bracket, resulting in The fixed bracket has a large thrust and is therefore expensive.
5. Application conditions of corrugated compensator:
The corrugated compensator cannot bear the weight and should be hoisted separately. Unless the corrugated compensator is used for reinforcement, the corrugated compensator should not be hoisted together with the pipe after welding. In the installation, the degree of the corrugated compensator should be correctly designed according to the data recommended by the manufacturer. Under any circumstances, the bellows cannot be stretched or compressed or twisted to compensate for the installation deviation, so as not to affect the normal function of the corrugated compensator, reduce the service life and increase The piping, equipment, and support members are loaded. There should be enough space around the expansion joint to ensure that the expansion joint can move freely within the design range.
(2) Rotary compensator

1. The advantages of the rotary compensator

(1) High product safety performance: The product structure is reasonable, and the rotary compensator adopts a double seal form, one end is end seal and one side is ring seal;
(2) Convenient design: When designing the heating network, the conditions for compensation of the bellows compensator are harsh. The five golden principles must be followed. The sleeve compensator should be “strictly found” and consider the bellows compensator and sleeve. The stress of the compensator, the blind plate force, and the like. The types of rotary compensators are various, and the compensation problem of the pipeline can be solved by selecting the appropriate type of rotary compensator according to the direction of the pipeline;
(3) Long product life: the life of the product can reach more than 20 years;
(4) Large compensation amount: the compensation amount can reach 1800 mm (other compensators, such as the compensation amount of the bellows compensator, the maximum compensation amount is 300-400 mm). For pipelines above DN 200, the unilateral compensation amount can be reached. 130~200 m, for pipelines with ≤ DN 200, the unilateral compensation amount can reach 100-130 m, which can be used for long-distance transmission steam pipeline compensation;
(5) High economical operation of the pipeline: using the rotary compensator compensation, because the compensator compensates for the distance increase, the elbow is reduced compared with the natural compensation and the sleeve compensation, thereby reducing the pressure drop and reducing the tube loss of the heating network as a long distance conveying. One of the main compensation methods for the heat network;
(6) Installation method and type diversification: According to the direction of the pipeline, combined with the topography of the site, the type of compensation of the rotary compensator is selected to solve the compensation problem of the steam pipeline. The installation is convenient, no need for cold drawing, pre-tightening and other construction processes. Welding can be;
(7) Investment province: Due to the long compensation distance of the rotary compensator, the number of compensators used is reduced, and the thrust of the fixed pier for civil construction is small, the number of fixed piers is relatively small, and the scale of the fixed pier is relatively small, which greatly saves the civil works. Compared with other compensators, the total investment of the project should be saved by 20% to 40%, and the economic benefits are considerable.

2. Application conditions of the rotary compensator:
The rotary compensator is generally installed on the pipeline in groups of 200 to 500 m (determined according to natural terrain), and there are more than 10 installation forms, which can be determined according to the direction of the pipeline. After adopting this type of compensator, the distance between the fixed brackets is increased, and the guide brackets should be appropriately added to avoid the deflection of the pipe sections; in order to reduce the frictional resistance of the pipe sections, a rolling bearing should be installed on the sliding brackets.
(3) Square compensator

1. The meaning of the square compensator
The square compensator is also called a square expansion force or a expansion force bend, and the elastic deformation bent by the tube absorbs the thermal expansion of the pipe. To make a square compensator, a seamless quality steel pipe must be used. The whole compensator is preferably made of a single pipe.
2. The advantages of the square compensator:

(1) It is convenient to manufacture and install. Compared with the sleeve compensator and the corrugated compensator, the axial thrust acting on the fixed bracket is small, and the thermal compensation amount is large, which is suitable for various pressure and temperature conditions;
(2) High safety, no maintenance in normal operation, no need to set up inspection wells.

3. Application conditions of square compensator:
When installing the square compensator, in order to reduce the deformation elastic force and improve the compensating ability of the compensator, the outer arm must be pre-pulled for a certain length and then installed on the pipeline.

Effect of compensator

In the design of piping compensation, the most economical way is natural compensation. Natural compensation is to compensate the thermal displacement by the flexibility of the natural bending shape of the pipeline. Obviously, the ability of natural compensation is limited. When natural compensation can not meet the requirements, it is usually necessary to consider installing metal bellows expansion joints and other compensation devices.
The main loads of the piping system are external loads (self weight of pipes and flowing medium, internal pressure, wind load, earthquake load, etc.) and displacement load. The purpose of setting up the pipe compensator is to eliminate the force acting on the equipment or pipe, and separate the complex pipe into a relatively simple and independent expansion section to ensure the best use effect of the expansion joint. The pipeline compensator can compensate the axial, transverse and angular thermal deformation of the absorption pipeline, absorb the vibration of the equipment, reduce the influence of the vibration of the equipment on the pipeline, and absorb the deformation amount of the earthquake and ground subsidence on the pipeline. The compensator is applied to the inlet and outlet of the hot and cold piping system, iron and steel plant, thermal power plant, flue gas desulphurization, dust removal equipment, air heating, auxiliary air blower and so on. Therefore, various compensators are widely applied.

Compensation to absorb the axial, lateral and angular thermal deformation.
Corrugated compensator is convenient for installation and disassembly of valve piping.
Absorb the equipment vibration, reduce the impact of equipment vibration on the pipeline.
Absorb earthquake and subsidence to the deformation of pipeline.

Selection techniques

The compensator adopts a rectangular section with rounded waveforms, and a single expansion joint in the pipeline is subjected to two-dimensional displacement. The elbow joint consisting of two expansion joints can withstand displacement in three dimensions. Rectangular rounded metal corrugated expansion joints have full height and half height type. According to the flue size, the stress and strain requirements can be selected by users.

After selecting suitable compensator according to the thermal displacement of piping system, users should at least provide the flow medium in the pipe, the design pressure of the flue duct, the maximum temperature at operation, the wave shape selected by the shape dimension (long and wide) of the cross section of the flue duct (full height 216mm, half high 108mm) and wave number (a single corrugation number of no more than 6 waves), so as to carry out the structural design and manufacture of the compensator.
Maximum permissible expansion per wave: full high delta alpha = + 24mm half high type delta = = 12mm.
Ash tray: the air duct or dust less pipe can not be used, for the dusty flue should be used ash board.
In order to reduce the waviness of bellows, cold drawing 50% should be considered.
The compensator is suitable for occasions where the sectional area is less than 4.6 square meters and the size of the flue duct is less than 1.5m but larger than 0.6mm. The standard full height corrugated compensator is suitable for all smoke channels.

Model selection

Due to various constraints, it is quite complicated, but any complex pipe system can choose several fixed brackets to choose different settings in different parts, and divide it into several separate pipe segments with relatively simple shapes, “Z” pipe segments and “∏” type pipe sections, etc., and determine the deformation and compensation amount of each pipe section separately. Due to the variety of compensators, it is very important to select the correct type. Therefore, in the overall design of the pipe system, the pipeline should be fully considered. The design of the strike and support system (including fixed pipe racks, guided slide pipe racks, etc.) and the comprehensive consideration of the shape and configuration of the compensator to achieve the best combination of safety, rationality, application and economy. The bellows compensator is a flexible element with a bellows as the core, and is compensated in three directions of axial, lateral and angular directions on the pipeline. The axial type compensator reduces the self-excitation of the medium. There is no inner casing inside the product, which limits the radial compensation ability to a large extent. Therefore, it is generally only used to absorb or compensate the axial displacement of the pipeline. (If a small amount of radial displacement is required in the piping system, it can be ordered. Explain the maximum displacement of the diameter): The lateral displacement compensator (large rod) mainly absorbs the lateral displacement perpendicular to the axis of the compensator. The small rod lateral displacement compensator is suitable for absorbing lateral displacement, and can also absorb axial, angular and arbitrary three. Combination of directional displacements: hinge compensator (also called angular compensator). It is used with two or three compensators (single hinge compensator has no compensating ability) to absorb lateral deformation in a unidirectional plane, and the universal hinge (angular) compensator is supported by two or three It can absorb the amount of deformation in the three-dimensional direction.

Material classification

Metal

The metal corrugated compensator is made of austenitic stainless steel or according to the user’s requirements. It has excellent softness, corrosion resistance and high temperature resistance (-235°C to +450°C), high pressure resistance (up to 32 MPa), can be connected in any direction in the pipeline to compensate and absorb vibration, reduce noise, change the direction of media transport, eliminate pipes or pipes and equipment The mechanical flange displacement, etc., double flange metal corrugated hose is especially suitable for flexible joints of various pumps and valves with displacement and vibration.

Nonmetallic fabric

The elastic elements which constitute the main body of the work are non-metallic materials. Usually, the fabric is made of rubber material. In addition to the high temperature (above 400), the material can not satisfy the operating conditions. All other working conditions can replace fiber fabrics.

Main production

Structure and properties of non-metallic fabric compensator

The product mainly uses the unique properties of rubber. Such as high elasticity and high Air tightness Resistance to dielectric and weatherability and radiation resistance. The polyester cord with high strength, heat stability and stability is diagonally checked and checked by high pressure and high temperature molding. The internal density is high and can withstand higher pressure. elastic deformation Excellent results. Product structure design The section has high arc length and long curve, and has a large multidirectional function. It is especially suitable for complex geological conditions and settlement amplitude. Big sum The location of pipeline damage caused by frequent cold and heat changes in pipeline operation. The physical displacement of pump, valve and pipeline displacement is effectively eliminated by the elastic sliding transfer of rubber and the heat dissipation function of deformation mechanical force. Because rubber is a poor conductive material, it is also an ideal environmental protection product for reducing vibration and noise transmission. The product is designed with smooth inner wall. After actual testing, it has no effect on the flow rate and flow rate of the medium, and it will never rust. Basically, it can avoid maintenance during effective campaign period.

Product characteristics

Its products are hydraulically formed and mechanically formed, and are assisted by computer optimization design and manufacture. They have the advantages of accurate size, clean surface, no trauma, compact product structure, large amount of compensation, no leakage, corrosion resistance, long life, easy installation and reliable product quality. At the same time, we can develop other types and uses for users according to the user’s working environment, conditions and fatigue damage times. Corrugated compensator 。 This product is widely used in steel, petroleum, chemical industry, metallurgy, electricity and so on. Water supply and drainage Construction and other industries.

Installation pressure test

Before installation, check the type and specification of expansion joint of corrugated compensator and the bearing configuration of piping must have compound design requirements.

For the expansion joint with inner liner, attention should be paid to the direction of the inner liner and the direction of the medium flow (marked by the direction of the expansion joint). The hinge rotation screen of the plane angular expansion joint should be consistent with the displacement plane.

The expansion joints needed to be “cold and tight” should be used. The auxiliary components used for pre deformation should be removed after expansion joints are pre deformed.

After installation of the piping system, the auxiliary positioning mechanism and fastener for the installation of the transport protection should be removed immediately, and the limit device should be transferred to the specified position according to the design requirements, so that the piping system can be fully compensated for the environmental conditions.

In addition to the pre deformation of pre tension or “cold tightening”, it is strictly prohibited to use the method of deformation of bellows to adjust the installation deviation of pipelines, so as not to affect the normal function of expansion joints, otherwise it will reduce its service life and increase the load of piping, equipment and supporting members.

All movable elements of expansion joint shall not be jammed by external components or restrict normal movement parts.

During the installation process, slag is not allowed to splash onto the surface of the corrugated pipe and other mechanical damage to the bellows.

When hydraulic pressure tests are carried out for expansion joints and connecting pipes for gas medium, it is necessary to consider whether it is necessary to add temporary supports to the joints of the expansion joints for water bearing.

Water test must be pure and non corrosive, and the content of chloride in water should not exceed 25ppm. After the water pressure test is finished, the water in the bellows should be drained as soon as possible and the inner surface of the corrugated shell will be dried quickly.

The pipeline is better for the neutral. If there is no other way to guarantee, the straight pipe should be used to cut the equal length pipeline and then install the expansion joint.

It should be noted that expansion joints do not absorb torque. Therefore, expansion joints are not allowed to be twisted when installing expansion joints.

All movable elements of expansion joints shall not be jammed by external components or restrict the normal operation of their active parts.

The insulation layer should be on the expansion joint outside the protective sleeve, not directly on the bellows.Chlorine containing thermal insulation materials shall not be used.

During installation, slag is not allowed to splash to the surface of bellows and other mechanical damage to bellows.

The bracket must meet the design requirements. It is strictly prohibited to test the pressure in the pipeline before the bracket is installed, so as not to pull the expansion joint out.

Expansion joint allowed no more than 1.5 times the nominal system pressure test.

In the operation of the pipeline with expansion joints, the valve should be opened and closed gradually to avoid rapid changes in temperature and pressure in the pipeline, resulting in damage to the support or expansion joints.

Reliable research

The reliability of the compensator consists of multiple steps in design, manufacturing, installation and operation management. Reliability should also be considered from these aspects. Material selection For the selection of corrugated pipes used for heating pipe networks, in addition to the working medium, working temperature and external environment, the possibility of stress corrosion, the effect of water treatment agents and pipe cleaning agents on materials, etc., should also be considered. On the basis of this, combined with the welding, forming of the bellows material and the performance and price ratio of the material, an economical and practical corrugated pipe making material is preferred.

In general, the materials for selecting bellows should meet the following requirements:

(1) High elastic limit, tensile strength and fatigue strength to ensure normal operation of bellows.
(2) Good plasticity, which is convenient for forming the bellows and can be obtained through the subsequent treatment process (cold hardening, heat treatment, etc.) hardness and strength.
(3) Better corrosion resistance to meet the requirements of bellows in different environments.
(4) Good welding performance to meet the welding requirements of bellows in the manufacturing process.
For the heat pipe network laid out by the trench, rainwater or accidental sewage will be immersed in the bellows when the pipeline of the compensator is low. The materials with stronger corrosion resistance, such as iron nickel alloy and high nickel alloy, should be chosen. Because of the high price of such materials, it is possible to add only one layer of corrosion resistant alloy to the surface of the bellows when making bellows.

Fatigue test

The fatigue life design is based on the failure type and cause analysis of bellows compensator. It can be seen that the plane stability, circumferential stability and corrosion resistance of bellows are related to their displacement, namely fatigue life. Low fatigue life will lead to a decrease in stability and corrosion resistance of bellows. According to the test and application experience, the fatigue life of bellows for heating engineering should not be less than 1000 times.

Bellows should not be weighed and should be hoisted separately. In addition to the pre deformation required for pre stretching or cold tightening, it is strictly prohibited to adjust the installation deviation of the pipe by using the method of deforming the bellows; the welding slag is not allowed to splash onto the surface of the bellows and subjected to other mechanical damage during installation; all activities of the bellows are carried out. element It shall not be jammed or restricted by external components.

The failure of most bellows is caused by external environmental corrosion. Therefore, in the design of the compensator, the contact between the external corrosive medium and bellows can be considered. For example, the external pressure axial compensator can be increased between the outlet ring and the outlet pipe. Packing seal The function of the device is equivalent to that of the device. Sleeve compensator It not only resists the invasion of the external corrosive medium, but also adds a safety barrier to the bellows compensator. Even if the bellows are damaged, the compensator can also play a compensatory role and avoid the bellows failure.

There are metal compensators and compensators. Non-metallic Compensator According to the different uses of the medium, it can also be divided into professional anticorrosion compensator and high temperature compensator.

Source: China Compensator Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

Please notice that you might be interested in the other technical articles we’ve published: