Expansion joints can also be called pipeline expansion joints, expansion joints, compensators, and expansion joints. Expansion joints are new products for connecting pumps, valves, pipelines and other equipment with pipelines. They are connected by full bolts to make them a whole and have a certain amount of displacement, which is convenient for installation. Can withstand the axial pressure of the pipeline. In this way, during installation and maintenance, it can be adjusted according to the size of the on-site installation. During work, it not only improves work efficiency but also protects the pipeline equipment such as pumps and valves.

The connection form of the expansion joint is a flange connection, one side is flanged and the other side is welded.


Expansion joint action

1. Compensate the expansion and contraction deformation caused by the axial, lateral and angular heat of the absorption pipeline.

2. Absorb equipment vibration and reduce the impact of equipment vibration on the pipeline.

3. Absorb the deformation of the pipeline caused by earthquakes and subsidence.


Because of the thermal expansion and contraction of the pipeline, for the pipeline, it is necessary to generate the stress and push-pull force of the pipe wall; the size of the pipe wall stress affects the strength of the pipeline, the push-pull force increases, and the fixed bracket of the pipeline needs to be done. , to withstand the push-pull force generated by the expansion and contraction of the pipeline; therefore, the variable opening method of the expansion joint compensation is used to reduce the stress and thrust of the pipe wall.

Expansion joints are classified by structure expansion joint (expansion joint) is mainly used to compensate the expansion and contraction deformation of the pipeline due to temperature changes, and is also used for the length compensation of the pipeline due to installation and adjustment. There are 3 types of casing expansion joints.

Elbow expansion joint

An expansion joint that bends the pipe into a U-shape or other shape (the following figure [Bend-tube expansion joint]), and compensates by the elastic deformation ability of the shape. Its advantages are good strength, long life, and it can be made on-site. The disadvantages are that it takes up a lot of space, consumes a lot of steel and has large frictional resistance. This kind of expansion joint is widely used in various steam pipelines and long pipelines.

Bellows expansion joint

An expansion joint made of metal bellows. It can expand and contract along the axis, and also allows a small amount of bending. The following figure [bellows expansion joint] is a common axial bellow expansion joint, which is used for axial length compensation on the pipeline. In order to prevent exceeding the allowable compensation amount, protective rods or protective rings are arranged at both ends of the bellows, and guide brackets are arranged on the pipes at both ends connected with it. In addition, there are corner and lateral expansion joints, which can be used to compensate the corner deformation and lateral deformation of the pipeline. The advantages of this type of expansion joint are space-saving, material saving (public number: pump housekeeper), easy standardization and mass production, but the disadvantage is that the service life is short. Bellows expansion joints are generally used on pipelines with low temperatures and pressure and short lengths. With the improvement of the production technology level of bellows, the application scope of such expansion joints is expanding. It consists of bellows (a kind of elastic element) that constitute the main body of its work, and accessories such as end pipes, brackets, flanges, and conduits. Mainly used in various pipelines, it can compensate the thermal displacement of the pipeline, and mechanical deformation and absorb various mechanical vibrations, playing the role of reducing the deformation stress of the pipeline and improving the service life of the pipeline. The connection method of the corrugated compensator is divided into flange connection and welding. The directly buried pipeline compensator is generally welded.


Casing expansion joint

It consists of inner and outer casings that can perform the relative axial movement (the following figure [casing expansion joint]). A stuffing box is used to seal between the inner and outer casings. When in use, keep both ends of the tube moving on an axis. Guide brackets are installed at both ends of the expansion joint. Its advantages are small frictional resistance to fluid flow and compact structure; its disadvantages are poor sealing and large thrust to the fixed bracket. Casing expansion joints are mainly used for water pipelines and low-pressure steam pipelines.



Extenders are classified by material

According to the material, it is mainly divided into rubber pipe expansion joints and metal pipeline expansion joints.

Features of rubber pipe expansion joints

1. Small size, light weight, good elasticity, easy installation and maintenance.

2. During installation, axial, lateral, meridional and angular displacements can be generated, and it is not limited by the user’s non-concentric pipeline and non-parallel flanges.

3. It can reduce vibration and noise during work.

4. The special synthetic rubber can be resistant to high temperatures, acids and alkalis, and oil. It is an ideal product for chemical corrosion-resistant pipelines.

Features of metal pipe expansion joints

The amount of expansion and contraction compensation is large, and it can withstand high temperatures and pressure.

Non-metallic expansion joints

The air duct rubber compensator is composed of rubber and rubber-fiber fabric composite materials, steel flanges, sleeves, and thermal insulation materials. It is mainly used for flexible connections between various fans and air ducts. Its functions are shock absorption, Noise reduction, sealing, medium resistance, easy displacement and installation, it is an ideal accessory for shock absorption, noise reduction, smoke and dust removal in the field of environmental protection.


Fiber Fabric Expansion Joint

The fabric compensator is mainly made of fiber fabric, rubber, and other high-temperature-resistant materials. It can compensate the vibration of fans and air ducts and the deformation of pipes. Fiber fabric expansion joints can compensate axial, lateral, angular and other products, and have the characteristics of no thrust, simplified bearing design, corrosion resistance, high-temperature resistance, noise reduction and vibration reduction, etc., especially suitable for hot air ducts and smoke and dust ducts in power plants. The fiber fabric and thermal insulation cotton body in the non-metallic compensator have the functions of sound absorption and vibration isolation, which can effectively reduce the noise and vibration of boilers, fans and other systems. Simple structure, light body and easy maintenance.

Characteristics and application scope of various pipe expansion joints

Non-metallic expansion joints

Non-metallic flexible compensator: also known as a non-metallic expansion joint, non-metallic fabric compensator, can compensate axial, lateral, angular, with no thrust, simplified bearing design, corrosion resistance, high-temperature resistance, noise reduction and vibration reduction, etc., especially suitable for hot air ducts and smoke ducts.


1. Compensation for thermal expansion: It can compensate for multiple directions, which is much better than the metal compensator which can only compensate in one way.

2. Compensation for installation error: Since the system error is unavoidable in the process of pipeline connection, the fiber compensator can better compensate for the installation error.

3. Noise reduction and vibration reduction: The fiber fabric and thermal insulation cotton body have the functions of sound absorption and vibration isolation transmission, which can effectively reduce the noise and vibration of boilers, fans and other systems.

4. No reverse thrust: Because the main material is fiber fabric, it can be transmitted weakly. Using fiber compensators simplifies the design, avoids the use of large supports, and saves a lot of material and labor.

5. Good high-temperature resistance and corrosion resistance: The selected fluoroplastics and silicone materials have good high-temperature resistance and corrosion resistance.

6. Good sealing performance: There is a relatively complete production and assembly system, and the fiber compensator can ensure no leakage.

7. Lightweight, simple structure, convenient installation and maintenance.

8. The price is lower than the metal compensator, and the quality is better than imported products.

Stainless steel: There are four types: straight, double, angular and square.

The stainless steel compensator can compensate axial, lateral and angular directions, and has the characteristics of no thrust, simplified bearing design, corrosion resistance, high-temperature resistance, noise reduction and vibration reduction, etc. It is especially suitable for hot air ducts and smoke and dust ducts.

Metal: The reliability of the metal corrugated compensator is composed of multiple links such as design, manufacture, installation and operation management. Reliability should also be considered from these aspects. Material selection For the selection of corrugated pipes used in the heating pipe network, in addition to the working medium, working temperature and external environment, the possibility of stress corrosion, the influence of water treatment agents and pipe cleaning agents on materials, etc. should also be considered. On this basis, combined with the welding and forming of the bellows material and the performance-price ratio of the material, an economical and practical material for making the bellows is selected.

In general, the material used for the bellows should meet the following conditions:

(1) High elastic limit, tensile strength and fatigue strength to ensure the normal operation of the bellows.

(2) Good plasticity is convenient for the processing and forming of bellows, and sufficient hardness and strength can be obtained through subsequent processing processes (cold work hardening, heat treatment, etc.).

(3) Good corrosion resistance to meet the working requirements of bellows in different environments.

(4) Good welding performance, meeting the welding process requirements of bellows in the production process.

For the thermal pipe network laid in the trench, when the compensator is located in a low terrain, the bellows will be soaked by rainwater or accidental sewage, and materials with stronger corrosion resistance should be considered, such as iron-nickel alloys, high-nickel alloys, etc. Due to the high price of such materials, when manufacturing bellows, it can be considered to only add a layer of corrosion-resistant alloy to the surface in contact with the corrosive medium. Fatigue life design From the failure type and cause analysis of the bellows compensator, it can be seen that the plane stability, circumferential stability and corrosion resistance of the bellows are related to its displacement, that is, the fatigue life. Too low a fatigue life will lead to a decrease in the stability and corrosion resistance of metal bellows.

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