BASIC PRINCIPLES: Metal Bellows Expansion Joints

1. The temperature of the system when installed (or not in operation) is different from the operating temperature.
2. The temperature cycles during the system's normal operation.
3. The system is exposed to variations in ambient temperature.

If these thermal movements (expansion when incresasing temperature and contraction with decreasing temperature) are not compensated for in the system design, they may cause high stress, and possibly result in the failure of the piping or connected equipment. There are three basic methods of compensation for thermal movements in a piping system:

1. Design a flexible piping system which utilizes changes of direction to absorb movement.
2. Use pipe loops or bends to absorb the movement.
3. Use expansion devices such as metal bellows expansion joints, packed expansion joints, ball joints and flexible metal hose.

Flexible piping systems and pipe loops are seldom feasible or economical where space is limited. Even if space limitation are not a factor, the cost of extra pipe, insulation and supports for a flexible piping system or loops often exceeds the cost of expansion joints to do the same job. Further, the extra heat loss and pressure drop resulting from increased length for the pipe loops may increase operating costs.

Hyspan Precision Products manufactures a complete range of metal bellows expansion joints. A bellows is a flexible seal. This convoluted part of the joint is designed to flex when thermal movement in the piping system occurs. Thus, by determining the thermal movement that will occur in the piping system, expansion joints may be specified, manufactured and installed in the system to accommodate these movements.

A bellows can be designed and fabricated to absorb axial, lateral and angular movements. Expansion applications can require one, two or three motions in a single expansion joint design.

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