The most challenging problem for designing industrial piping is how to protect pipeline from stress generated from various factors, such as expansion and contraction of pipe owing to fluctuating temperature of ambient air and fluid, vibration of equipment, movements or fracture of pipe owing to wind pressure or earthquake. The most typical way to cope with this problem is to fix expansion joints at appropriate points of the pipeline so that the generated stress could be absorbed. Metal bellows expansion joints and flexible joints are most widely used for this purpose.

Metal bellows are generally made of metal sheets through the piping and forming process of the following ways:
     1.Hydraulic Forming :Method that uses hydraulic pressure
     2.Roll Forming :Method that rotates roller alternately to the external and internal side of material to form
       bellows gradually
     3.Elastometic Forming : Method that forms material into bellows by compressing donuts-shaped rubber to
       inside the material
     4.Elastometic Forming : This method that produces bellows by pressing material into a mold is mainly used in
       the making of rectan gular expansion joints.
   Arch Shapes and Features of Bellows
This method that produces bellows by pressing material into a mold is mainly used in the making of rectan gular expansion joints.
- U shape
This is the most widely used type of bellows and has a good elasticity. As this type of bellows, however, has low pressure resistance, it needs to insert control ring into the curved part to use for high pressure.
- S shape
With a relatively good pressure resistance compared to U-type, this type of bellows can be used for relatively high pressures. But the use of this type is limited to cases where the expansion percentage is below 50 percent of the compressibility.
- Multi-layer Type
With two or more layers of bellows, this type of bellows has the same elasticity as the U-type bellows while resisting much higher pressures. This type bellows particularly suppresses spring force and has long lifetime.
- Omega shape
With arches shaped like omega (Ω) and a good pressure resistance, this type of bellows can be used for high pressures, but has elasticity lower than U-type.
  Usage of Expansion Joints