What Is A Bellows Expansion Joint?
A bellows expansion joint (compensator) is an expansion joint made of a metal bellows. It is a flexible, thin-walled, transversely corrugated telescopic device consisting of a metal bellows and components. The working principle of the bellows compensator is mainly to use its own elastic expansion function to compensate the axial, angular, lateral and combined displacement of the pipeline due to thermal deformation, mechanical deformation and various mechanical vibrations. Pressure, sealing, corrosion resistance, temperature resistance, impact resistance, vibration and noise reduction, reduce the deformation of the pipeline and improve the service life of the pipeline. It can stretch in the direction of the axis and also allows a small amount of bending. Corrugated Tube Expansion Joint is a common axial bellows expansion joint used for axial length compensation on pipes. In order to prevent exceeding the allowable compensation amount, a protective pull rod or a guard ring is disposed at both ends of the bellows, and a guide bracket is disposed on the pipe at both ends to which it is coupled. There are also corner and transverse expansion joints that can be used to compensate for corner and lateral deformation of the pipe. The advantages of this type of expansion joint are space saving, material saving, standardization and mass production, and the disadvantage is that the life is short. Bellows expansion joints are generally used on pipes with low temperature and pressure and short length. With the increasing level of corrugated pipe production technology, the application range of such expansion joints is expanding.
- Super austenitic special stainless steel: 254SMO, 904L, AL6XN.
- Duplex stainless steel: 2205 duplex steel (S31803).
- Nickel-based alloy steel: INCOLOY800/800H/800HT/840/825, INCONEL600/601/690/625/X-750, Hastelloy C-276/C-22/X, MONEL400/K500
- Pure nickel: N4, N6 (Ni200, Ni201).
- Titanium plate for stamping: GR1, GR2, TA1, TA2.
- Austenitic stainless steel: SUS304, SUS304L, SUS316, SUS316L, SUS310S, SUS321, SUS316Ti.
Metal expansion joint
1 curved tube expansion joint
The tube is bent into a U shape or other shape, also called a bending force. It is compensated by the elastic deformation ability of the body.
An expansion joint. Its advantages are good strength, long life and can be produced on site. The disadvantages are that it takes up a lot of space, consumes more steel and has large frictional resistance. This type of expansion joint is widely used in various steam pipes and long pipes.
2 bellows expansion joint
The bellows expansion joint is an expansion joint made of a metal bellows. It can stretch along the axis of the pipe and allows a small amount of bending. Figure 1 shows a common axial bellows expansion joint for axial length compensation on the pipe. In order to prevent exceeding the allowable compensation amount, a protective pull rod or a guard ring is disposed at both ends of the bellows, and a guide bracket is disposed on the pipe at both ends connected thereto. There are also corner and transverse expansion joints that can be used to compensate for corner and lateral deformation of the pipe. The advantages of this type of expansion joint are space saving, material saving, standardization and mass production, and the disadvantage is that the life is short. Bellows expansion joints are generally used on pipes with low temperature and pressure and short length. With the increasing level of corrugated pipe production technology, the application range of such expansion joints is expanding. Currently, bellows expansion joints can be used in piping systems with a maximum pressure of 6.0 MPa.
3 sleeve expansion joint
The telescopic joint of the casing consists of inner and outer casings capable of axial relative movement. The inner and outer casings are sealed by a stuffing box. Keep the tubes at both ends moving on one axis when in use. The main products are sleeve (core tube), outer casing, sealing material, etc. It is used to compensate the axial expansion and contraction of the pipeline and the axial rotation at any angle. It has the characteristics of small volume and large compensation for hot water, steam and grease. The medium is compensated for the thermal expansion by the sliding movement of the sliding sleeve to the outer sleeve.
The inner sleeve of the sleeve compensator is connected to the pipeline. The principle and structure of the high-performance self-pressure dynamic seal are adopted. It can slide freely in the outer casing along with the expansion and contraction of the pipeline, and can adapt to the sealing requirements of any pipeline. The inner sleeve is sealed with a new synthetic material, which can withstand high temperature, anti-corrosion and anti-aging. It is suitable for temperature from -40 to 150. In special cases, it can reach 350. It can ensure axial sliding and ensure that the medium in the tube does not leak.
Non-metallic expansion joint
1 rubber duct expansion joint
Air duct rubber compensator is divided into four types: FDZ, FVB, FUB and XB. It consists of rubber and rubber-fiber fabric composite material, steel flange, sleeve and thermal insulation material. It is mainly used for various fans and winds. The flexible connection between the tubes is characterized by shock absorption, noise reduction, sealing, medium resistance, easy displacement and installation. It is an ideal accessory for shock absorption, noise reduction, smoke elimination and dust removal in the field of environmental protection. .
2 fiber fabric expansion joint
The fabric compensator is mainly a high temperature resistant material such as fiber fabric, rubber, and the like. It can compensate the vibration of the fan and air duct and the deformation of the pipeline. The fiber fabric expansion joint can compensate for axial, transverse, angular and other products. It has the characteristics of no thrust, simplified bearing design, corrosion resistance, high temperature resistance, noise reduction and vibration damping, etc. It is especially suitable for power plant hot air pipes and soot pipes. The fiber fabric and the thermal insulation cotton body in the non-metallic compensator have the functions of sound absorption and vibration isolation, and can effectively reduce noise and vibration of boilers, fans and the like. The structure is simple, the body is light, and the maintenance is convenient.
Reasonable design of the support in the pipeline system is a necessary condition to ensure the normal operation of the bellows expansion joint. Different types of bellows expansion joints have different requirements for the support of the piping system.
Main fixed bearing
The main anchor is mounted on a pipe system with one or several unconstrained bellows expansion joints that must withstand the forces and moments exerted on each pipe segment connected thereto. For example, the pressure thrust (blind plate force) generated by the medium pressure in the pipe, the force and moment required for the expansion joint to generate the rated displacement, and the friction generated by the adjustable guide support, the directional guide support, as well as the pipeline and The weight of the medium, the fluid impact force, when the unconstrained bellows expansion joint is used, the main fixed support must be set under the following conditions:
- 1) Blind end of the pipe
- 2) Change in media flow
- 3) Pipe branch
- 4) Pipe diameter reduction
- 5) On the pipe between the two bellows expansion joints, the shut-off valve or the pressure reducing valve.
Secondary fixed bearing
The secondary anchor (I anchor) is used to withstand all loads except the pressure thrust (blind plate force).
For a straight pipe section, the secondary fixed bearing is usually used to divide the longer pipe section between the two fixed supports into a plurality of pipe section units, so that only one bellows expansion joint is provided between each pipe section to ensure that the expansion joint can normal work.
The main elastic component of the corrugated compensator is a stainless steel corrugated pipe, which relies on the bellows to expand and contract and bend to compensate the pipe in axial, lateral and angular directions. Its role can play:
- Compensate for axial, lateral and angular thermal deformation of the absorption pipe.
- Absorb equipment vibration and reduce the impact of equipment vibration on the pipeline.
- Absorb the amount of deformation of the pipeline caused by earthquakes and subsidence.
The compensator can be divided into an unconstrained bellows compensator and a constrained compensator according to whether it can absorb the pressure thrust (blind plate force) generated by the medium pressure in the pipeline; according to the displacement pattern of the bellows, it can be divided into axial directions. Type compensator, lateral type compensator, angular type compensator and pressure balanced type bellows compensator.
- Pipes with large deformation and deformation and limited space.
- Large diameter pipes with large deformation and displacement and low working pressure.
- Need to limit the equipment that takes over the load.
- Pipes that require absorption or isolation of high frequency mechanical vibrations.
- Pipes that require the absorption of earthquakes or foundation settlement.
- Absorb the vibration of the outlet of the pipeline pump.
The design, manufacture, installation and operation management of the metal bellows compensator are composed of multiple links. Therefore, reliability should also be considered in several ways. Choosing the material selected for the bellows in the heating pipe network, in addition to its working efficiency, it should also consider its medium, working temperature and external environment. We must also consider the stress corrosion, water treatment agent, and the possibility of cleaning the pipe. Sexual influence materials, and on this basis, with bellows materials, welding, forming, material costs and performance, pointed out the economic and practical production of materials optimized for bellows.
Under normal circumstances, the bellows material should meet the following conditions:
- (1) High elastic limit, tensile strength and fatigue strength to ensure the operation of the bellows.
- (2) Good plasticity to facilitate bellows forming and pass through subsequent processing (work hardening, heat treatment, etc.) to obtain sufficient hardness and strength.
- (3) Good corrosion resistance to meet the requirements of different corrugated pipes in different environments.
- (4) Good welding performance to meet the bellows during the production process required for the welding process.
For the trench laying heat pipe network, when the low-lying pipe, rain or accidental sewage will be soaked in the bellows compensator, consideration should be given to materials such as iron which are more resistant to corrosion, nickel alloys, high-nickel alloys, etc. Due to the rise in the price of this material for the manufacture of bellows, we can consider an additional corrosion layer surface wear-resistant alloy only in contact with corrosive media. The type of bellows fatigue life and the failure analysis of the design of the design can be seen that the stability of this aircraft bellows, stability and corrosion of the two pairs of displacement is related to the fatigue life. Too low will result in lower stability and corrosion-resistant metal bellows fatigue life.
Application of expansion joints in gas pipelines:
Gas pipelines, especially the gas pipelines of some self-contained gas generator kiln, because the gas itself has a certain amount of heat, the pipeline leading to the kiln at the gas station and the kiln close to the gas burner part of the pipeline vary with the gas temperature. The amount of expansion and contraction of the pipeline is sometimes large, and it is necessary to set the expansion joint to relieve the pipeline stress and push-pull force. In some cold gas station pipelines, pipelines that are far away from the pipeline are often provided with expansion devices and expansion joints to relieve the pushing and pulling force of the pipeline due to heat expansion and contraction.
Installation requirements for bellows expansion joints
- The compensator should first check its model, specifications and piping configuration before installation, and must meet the design requirements.
- For the compensator with the inner sleeve, the direction of the inner sleeve should be consistent with the direction of the medium flow. The hinge rotation plane of the hinge type compensator should be consistent with the displacement rotation plane.
- A “cold tight” compensator is required. The auxiliary components used for pre-deformation should be removed after the pipeline is installed.
- It is strictly forbidden to use the method of deformation of the corrugated compensator to adjust the installation of the pipeline to avoid the normal function of the compensator, reduce the service life and increase the load of the piping, equipment and supporting members.
- During the installation process, the welding slag is not allowed to splash onto the surface of the wave shell, and the wave shell is not allowed to be damaged by other machinery.
- After the piping system is installed, the yellow auxiliary positioning members and fasteners used for installation and transportation on the corrugated compensator should be removed as soon as possible, and the limit device should be adjusted to the specified position according to the design requirements, so that the piping system has environmental conditions. Full compensation capacity.
- All active components of the compensator shall not be stuck or restricted by the external components, and the normal movement of each active part shall be guaranteed.
- During the hydrostatic test, the secondary fixed pipe rack with the end of the compensator pipe should be reinforced so that the pipe does not move or rotate. For the compensator for the gas medium and its connecting pipeline, it is necessary to pay attention to whether it is necessary to add a temporary bracket when filling the water. The 96-chloride ion content of the water test water cleaning solution does not exceed 25 PPM.
- After the hydrostatic test is completed, the water in the shell should be drained as soon as possible, and the inner surface of the shell should be quickly dried.
- The insulation material in contact with the compensator bellows should be free of chlorine.
When the bellow expansion joint is purchased, it must be purchased strictly according to the relevant data provided by the design department. The following data requirements must be provided to the manufacturer at the time of purchase:
- Pipe pressure, diameter (general diameter of pipe).
- Pipeline setting situation (separate overhead pipeline, direct buried pipeline).
- The amount of expansion and contraction of the required pipe expansion joint (also called compensation amount).
- Connection between pipe and expansion joint (divided into flange connection and welding).
- Medium, medium temperature.
If you do not know the amount of compensation, you must provide the pipeline to yaang, and the compensation amount is calculated by the manufacturer.
Source: China Bellow Expansion Joint 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.)
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