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What is a pipe expansion joint

What is a pipe expansion joint?

Expansion joint is also called pipe expansion joint, compensator expansion joint. The expansion joint is a new product for the connection of pumps, valves, pipelines and other equipment with pipelines. It is connected by full bolts to make it a whole, and has a certain displacement, which is convenient for installation. It can bear the axial pressure of pipeline. In this way, the installation and maintenance can be adjusted according to the on-site installation size. When working, it not only improves the work efficiency, but also plays a certain role in protecting the pumps, valves and other pipeline equipment.
The connection form of the expansion joint is flange connection, with one side flange and one side welding.

Classification of pipe expansion joint

Classification by structural form

Bend expansion joint is a kind of expansion joint that bends the pipe into U shape or other shape (Fig. 1 [elbow expansion joint]) and compensates by using the elastic deformation ability of the shape. It has the advantages of good strength, long service life and can be made on site, but it has the disadvantages of large space occupation, large steel consumption and large friction resistance. This kind of expansion joint is widely used in all kinds of steam pipes and long pipes.

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Fig. 1 bend expansion joint
Bellows expansion joint is a kind of expansion joint made of metal bellows. It can stretch along the axis and allow a small amount of bending. Figure 2 [bellows expansion joint] is a common axial bellows expansion joint, which is used for axial length compensation on the pipeline. In order to avoid exceeding the allowable compensation amount, a protective pull rod or a protective ring is set at both ends of the bellows, and a guide bracket is set on the pipes at both ends connected with the bellows. In addition, there are corner type and transverse type expansion joints, which can be used to compensate the corner deformation and transverse deformation of the pipeline. This kind of expansion joint has the advantages of saving space, saving materials, being convenient for standardization and mass production, but has the disadvantages of short service life. Bellows expansion joints are generally used in pipes with low temperature and pressure and short length. With the improvement of bellows production technology, the application scope of this kind of expansion joint is expanding.

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Figure 2 bellows expansion joint
The casing expansion joint is composed of inner and outer casings which can make relative axial movement (Fig. 3 [casing expansion joint]). Stuffing box is used to seal the inner and outer casing. When in use, keep the pipes at both ends moving on the same axis. A guide bracket is arranged at both ends of the expansion joint. It has the advantages of small frictional resistance to fluid flow and compact structure; The disadvantage is that the sealing performance is poor and the thrust on the fixed support is large. Casing expansion joint is mainly used for water pipeline and low pressure steam pipeline.

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Fig. 3 casing expansion joint
Expansion joint (expansion joint) is mainly used to compensate the expansion deformation of pipeline due to temperature change, and also for the length compensation of pipeline due to installation and adjustment. It is mainly divided into elbow expansion joint, bellows expansion joint and casing expansion joint.

Classification by material

According to the material mainly divided into rubber pipe expansion and metal pipe expansion.
Characteristics of rubber pipe expansion device:

  • 1. Small size, light weight, good elasticity, easy installation and maintenance.
  • 2Axial, transverse, meridional and angular displacement can be produced during installation, which is not limited by the user’s pipe not concentric and flange not parallel.
  • 3It can reduce vibration and noise when working.
  • 4The special synthetic rubber can resist high temperature, acid and alkali, and oil. It is an ideal product for chemical corrosion-resistant pipeline.

Characteristics of metal pipe expansion joint

Large expansion compensation, high temperature and pressure.

Nonmetal expansion joint

The air duct rubber compensator is composed of rubber and rubber fiber fabric composite material, steel flange, sleeve and thermal insulation material. It is mainly used for flexible connection between various fans and air pipes. Its functions are shock absorption, noise reduction, sealing, medium resistance, easy displacement and installation. It is an ideal best matching set for shock absorption, noise reduction, smoke elimination and dust removal in the field of environmental protection.
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Fabric expansion joint

Fabric compensator is mainly made of high temperature resistant materials such as fiber fabric, rubber and so on. It can compensate the vibration of fan and duct and the deformation of duct. Fiber fabric expansion joint can compensate axial, transverse, angular and other products. It has the characteristics of no thrust, simplified support design, corrosion resistance, high temperature resistance, noise elimination and vibration reduction. It is especially suitable for hot air pipe and smoke pipe in power plant. The fiber fabric and insulation cotton in the non-metal compensator have the functions of sound absorption and vibration isolation, which can effectively reduce the noise and vibration of the boiler, fan and other systems. Simple structure, light weight and convenient maintenance.

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Structure of the expansion joint

Reasonable design of the support in the piping system is the necessary condition to ensure the normal function of bellows expansion joint. Different types of bellows expansion joint have different requirements for the support of the pipeline system.

Main Anchor 

The main anchor is installed on the pipe system with one or several unconstrained bellows expansion joints. It must bear the force and moment exerted on it by each pipe section connected with it. For example, the pressure thrust (blind plate force) generated by the medium pressure in the pipeline, the force and moment required for the expansion joint to produce the rated positioning displacement, the friction force generated by the adjustable guide support and the directional guide support, the weight of pipeline and medium, and the fluid impact force, when the corrugated pipe expansion joint without restraint is selected, the main fixed support must be set under the following conditions:

  • 1) Blind end of pipeline;
  • 2) Change of medium flow direction;
  • 3) Pipeline branch;
  • 4) Pipe diameter change;
  • 5) The pipe between two bellows expansion joints is located at the stop valve or pressure reducing valve.

I anchor 

I anchor is used to bear all loads except pressure thrust (blind plate force).
For the straight pipe section, the secondary fixed support is usually used to divide the long pipe section between two fixed supports into several pipe section units, so that only one bellows expansion joint is set between each pipe section to ensure the normal operation of the expansion joint.

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Characteristics and application scope of various pipe expansion joints

Nonmetal expansion joint
Non metal flexible compensator: also known as non-metal expansion joint and non-metal fabric compensator, it can compensate axial, transverse and angular directions. It has the characteristics of no thrust, simplified support design, corrosion resistance, high temperature resistance, noise elimination and vibration reduction. It is especially suitable for hot air pipe and smoke pipe.

  • 1. Thermal expansion compensation: it can compensate for multi direction, which is much better than the metal compensator which can only compensate single mode.
  • 2. Compensation installation error: due to the pipeline connection process, system error is inevitable, fiber compensator better compensates the installation error.
  • 3. Noise elimination and vibration reduction: fiber fabric and thermal insulation cotton have the functions of sound absorption, vibration isolation and transmission, which can effectively reduce the noise and vibration of boiler, fan and other systems.
  • 4. No thrust: because the main material is fiber fabric, it can’t transfer. Using fiber compensator can simplify the design, avoid using large supports and save a lot of materials 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: a relatively complete production and assembly system, fiber compensator can ensure no leakage.
  • 7. Light weight, simple structure, easy installation and maintenance.
  • 8. The price is lower than that of metal compensator and the quality is better than that of imported products.

Stainless steel expansion joint

There are four types: straight cylinder type, compound type, angular type and square type.
Stainless steel compensator can compensate axial, transverse, angular, with no thrust, simplified support design, corrosion resistance, high temperature resistance, noise reduction and other characteristics, especially suitable for hot air pipe and smoke pipe.
Metal expansion joint

The reliability of metal corrugated compensator is composed of design, manufacture, installation and operation management. Reliability should also be considered from these aspects. In addition to the working medium, working temperature and external environment, the possibility of stress corrosion, the influence of water treatment agent and pipeline cleaning agent on the material selection of bellows used in heat supply network should also be considered. On this basis, combined with the welding and forming of bellows material and the performance price ratio of the material, the economical and practical bellows material should be selected.
Generally, the material of bellows should meet the following conditions:

  • (1) High elastic limit, tensile strength and fatigue strength to ensure normal operation of bellows.
  • (2) Good plasticity, easy to form the bellows, and can obtain enough hardness and strength through the subsequent treatment process (cold work hardening, heat treatment, etc.).
  • (3) Good corrosion resistance, to meet the requirements of bellows in different environments.
  • (4) Good welding performance, to meet the welding process requirements of bellows in the production process.

For the heat supply piping system laid in trench, when the pipeline where the compensator is located is low, rainwater or accidental sewage will soak the bellows. Therefore, the materials with stronger corrosion resistance, such as iron nickel alloy and high nickel alloy, should be considered. Because of the high price of this kind of material, it can be considered to add a layer of corrosion-resistant alloy only on the surface contacting with corrosive medium when manufacturing bellows. Fatigue life design from 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, i.e. fatigue life. Too low fatigue life will lead to the degradation of the stability and corrosion resistance of metal bellows.

Source: China Expansion Joints Manufacturer – Yaang Pipe Industry (

(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.)

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