1.Introduction of Expansion Joints 

Expansion Joints (they are also called compensators) are compensating elements for thermal expansion and relative movement in pipelines, containers and machines. They consist of one or more metal bellows, connectors at both ends, and tie rods that depend on the application. They are differentiated according to the three basic types of movement: axial, angular and lateral expansion joints.

 

Expansion Joins are elastic vessels that can be compressed when pressure is applied to the outside of the vessel, or extended under vacuum. When the pressure or vacuum is released, the bellows will return to its original shape (provided the material has not been stressed past its yield strength).

2. Product Features:

(1) Economy: Compared with the systems of mechanic stretching and material damping, it has the advantages of little space covering, light weight, easy assembly and disassembly, labor saving and low cost. Its smooth inner wall can reduce flow resistance. It has good water tightness, so there is no need of gasket during the installation. It has wide application, large temperature-resistance scope and long working life. (This product can be used for 20 years if it is used indoors.)

(2) Displacement: Flange is free from pipe decentraction and imbalance. Its good flexibility allows compression, extension, distortion, deflection of vertical displacement, etc. which can prevent the pipeline from damage of deformation and foundation settlement arising from expansion caused by heat and contraction caused by cold.

(3) Shock and noise absorption: The large damping of rubber sphere can effectively buffer and isolate vibration, control and reduce mechanical vibration, and absorb fluid impact noise. The reasonable installation between vibrating machine and metal pipe can decrease structure-borne noise by 15-25 decibels.

(4) Pressure resistance: The multilayered sphere structure can especially endure internal pressure, withstand strong blasting force and impact, and prevent deformation from external pressure. There are many pressure standards on work piece.

(5) Reducibility: After external force compressed, it can recover to original state when this force is removed.

(6) Wide application: Different rubber material and formula can make product possess different resistance to heat, oil, corrosion, age, abrasion and ozone.

3.Manufacture of Expansion Joints 

Welded Expansion Joints can be fabricated from a variety of exotic metals and alloys, whereas formed bellows are limited to alloys with good elongation – brass being a prime example. Welded bellows are not fabricated from brass because of its fundamentally poor weldability. Other advantages to welded bellows include compactness (higher performance in a smaller package), ability to be compressed to solid height with no damage, resistance to nicks and dents, and dramatically greater flexibility.

The welding of metal bellows is a microscopic welding process, typically performed under laboratory conditions at high magnification.

Hydroformed bellows are produced by forcing a metal tube to expand under hydraulic pressure inside a bellows-shaped mold, and assume the convoluted shape of the mold.

Electroformed bellows are produced by plating metal onto a bellows-shaped model (mandrel), and the subsequent mandrel removal by chemical or physical means.

4. Applications of Expansion Joints

Expansion Joints -welded or convoluted (formed), are used in a large number of industrial applications:

Load cells; A load cell deforms if a certain load in the form of a pressure or a strain is imposed on it. This deformation is then detected by a strain gauge through which a low voltage direct current is flowing. The change in voltage is detected and made visible on a control panel. A bellows is mounted over the gauge to protect it from outside influences.

Vacuum interrupters; For the switching of very high voltages in transformer stations sparks should be avoided. To prevent any danger that the surrounding atmosphere will explode, oxygen has to be removed in the area where the sparks occur. This can be done by sealing the spark area completely. Bellows are used to seal such confined volumes and the inside of the bellows is evacuated or filled with an inert gas.

Mechanical Seals; These are mostly used to close the inside of a pump from the outside world to prevent leakage. For that purpose, a mechanical seal is mounted on the pump shaft. As the pump shaft is turning, there has to be a sealing element consisting of a stationary and a rotating ring. To enforce sufficient pressure on the two rings one is fitted with a spring. This spring can also have the form of a diaphragm (welded) bellow.

Pressure gauges: If the pressure of aggressive fluids or gases has to be measured, the gauge has to be isolated from the flow. For critical applications a diaphragm sealing is used instead of abourdon tube in the gauge. This gives more security that the aggressive media will not leak. The diaphragm is a self-contained sensor, transmitting the displacement to the measuring device.

Sensors: In this application diaphragm or convoluted bellows are completely sealed and filled with a certain gas. Two electrical poles are penetrating the inside of the bellows. By varying the current of those two poles the temperature inside the bellows can be regulated. The expansion or contraction of the bellows is used as an actuator to control a certain movement.

Valve Sealing: A bellows is used between the housing and the rising stem to seal the inside completely from the outside world. In Europe this is of particular importance as regulations such as TA Luft prohibit any leakage.

Couplings for stepper motors and servomotors: The flexible part, capable of compensating for misalignment is made by a bellows. It ensures that there is no angular positioning difference between the two coupling halves. This is essential if the positioning accuracy should be extremely precise.

Exhaust Bellows: Running engines cause self vibration. To compensate for those movements and temperature differences resulting in thermal expansion, bellows are used to connect the exhaust gas pipes to the funnel.

Piping expansion joint: In this application, bellows are formed in series to absorb thermal movement and vibration in piping systems that transport high temperature media such as exhaust gases or steam.

Metal bellows are also used in other products and market segments, including medical applications like implantable drug pumps, to industrial actuators, to aerospace applications such as altitudesensors and fluid management devices (accumulators, surge arresters, volume compensators, and fluid storage). Metal bellows are also found in space applications, providing reservoirs with potable water as well as accumulators to collect wastewater.

6.Quality Assurance of Expansion Joints 

Henan Liwei Pipeline Equipment Co. Ltd is committed to maintaining a Total Quality Program throughout all phases of its operation. The existing program represents an ongoing effort by the management and employees to continually reduce the variability in all processes and to produce the highest quality products for their customers.

7.The Protection of bellows

The entire installation and construction process should be to prevent collision from hard objects .Try to avoid the weld spatters, Gas cutting sparks or Grinding wheel sparks splashing to the bellows when welding, gas cutting or wheel grinding near bellows .It was suggested to use asbestos cloth or wet rag without Oxygen ions to cover the surface of bellows .And it was not allowed to line an arc on bellows while welding or put a welding line directly on bellows.
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