Pipe expansion joints are necessary in systems that convey high temperature commodities such as steam or exhaust gases, or to absorb movement and vibration. A typical type of expansion joint for pipe systems is a bellows which can be manufactured from metal (most commonly stainless steel), plastic (such as PTFE), fabric (such as glass fibre) or an elastomer such as rubber. A bellow is made up of a series of one or more convolutions, with the shape of the convolution designed to withstand the internal pressures of the pipe, but flexible enough to accept the axial, lateral, and/or angular deflections. Expansion joints are also designed for other criteria, such as noise absorption, anti-vibration, earthquakemovement, and building settlement. Metal expansion joints have to be designed according to rules laid out by EJMA, while for fabric expansion joints only guidelines and a state-of-the-art description exists by the Quality Association for Fabric Expansion Joints.
Pipe expansion joints are also known as compensators, as they 'compensate' for the thermal movement.