Externally pressurized expansion joints are suited for piping systems that require large amounts of axial compression or extension. In externally pressurized expansion joints, the bellows elements are arranged so that the media flow is on the external surface of the bellows. Externally pressurizing the bellows eliminates pressure instability as a limitation to the design and permits the absorption of large amounts of axial expansion.
Typical movement conditions that occur in a piping system:
- Installation: allow one cycle for installation misalignment
- Start-up / Shut down: movements produced between the minimum ambient temperature and the maximum start-up temperature. This is normally a very low number of cycles.
- Operating: movements produced due to temperature fluctuations during system operation. This is typically a very small movement for a very large number of cycles.
- Excursion: movement resulting from a worst case / upset scenario, occurring during system operation. This is normally a very low number of cycles.
U.S. Bellows externally pressurized expansion joints are designed for 1000 cycles for any one tabulated movement shown. Movement may be increased, decreasing the cycle life, by using the graph below. This graph may also be used for superimposing more than one movement condition on the bellows at one time.
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