In order to properly specify expansion joints for piping systems, the piping specialist and must be aware of the various types of deflections that can be taken by an expansion joint bellows. Piping flexibility programs can determine where stresses are excessive, and if an expansion joint is necessary or not. Expansion joint placement and proper selection still depends on understanding the different types of bellows deflections.
Axial Deflection (View Axial Movements)
Axial deflection refers to movement of the bellows along the longitudinal axis of the bellows. Compression is the axial deflection which will shorten the bellows length, while extension is the axial deflection which extends the expansion joint. Often confusion occurs because thermal expansion in the piping will cause the expansion joint to compress. The specification for an expansion joint should always state the movements as they affect the expansion joint, and not as they are produced by the system. Piping which is operating at temperatures lower than ambient, such as in cryogenic systems, will contract, causing the expansion joint to extend.