This section describes what types of deflections that the metallic bellows expansion joints can accept. In order to properly apply expansion joints to piping systems, it is necessary that both the piping specialist and the metallic bellows expansion joint designer each understand how the piping flexes and how the various expansion joint types function and what they are capable of doing.

Axial Deflection

Axial deflection refers to movement being parallel to the centerline of the expansion joint. Compression is the axial deflection which will shorten the bellows length, while extension is the axial deflection which stretches the expansion joint. Often confusion occurs because thermal expansion in the piping will cause the expansion joint to be compressed. 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 stretch or experience extension.