Bellows-type expansion joints do not have packing. This allows this type of joint to be used where zero leakage is mandatory. Likewise, they do not require the periodic maintenance (lubrication and re-packing) that is associated with slip joints.
Bellows joints absorb expansion and contraction by means of a flexible bellows that is compressed or extended. They can also accommodate direction changes by various combinations of compression on one side and extension on an opposing side. Thus, they can adjust to lateral offset and angular rotation of the connected piping. However, they are not capable of absorbing torsional movement. Typically, the bellows is corrugated metal and is welded to the end pieces.
To provide the requisite flexibility, the metal bellows is considerably thinner than the associated piping. Thus, these expansion joints are especially susceptible to rupture by overpressure. This type of expansion joint is also particularly susceptible to cyclic stress, and the bellows can fail due to metal fatigue if the accumulated flexing cycles exceed the designed fatigue life.
