An expansion joint is any apparatus containing one or more metal bellows used to absorb dimensional changes such as those caused by thermal expansion or contraction of a pipeline, duct, or vessel and to absorb vibrationscaused by engines, pumps, motors, etc.

Metal bellows and expansion joints are used in power plants to compensate for thermal expansion and vibration in piping and equipment. Medical equipment: Metal bellows are used in medical equipment such as ventilators, anesthesia machines, and surgical robots to provide precise motion control.

Metal bellows movements are normally designed to operate in the plastic range of materials and therefore will take a permanent “set” at the bellows rated movements. When a bellows compresses, extends, or angulates, the movement is absorbed by deformation of the sidewalls of the bellows convolutions.