Expansion joint refers to a flexible element that can effectively compensate for axial deformation. For example, the expansion joint welded to the shell of the fixed tube-plate heat exchanger has large axial flexibility and is easy to deform, which can compensate for the difference in thermal expansion between the tube and the shell due to the difference in wall temperature, reduce their axial load, and reduce the tube , The temperature difference stress between the tube sheet and the shell avoids strength damage, instability damage and pipe pull-off damage. There are many types of expansion joints, commonly used structures such as wave, ring plate welding and sandwich shell type. Among them, wave expansion joints are the most widely used, and ring plate welded expansion joints are only suitable for normal pressure or low pressure occasions.

Expansion joints are also called compensators, or expansion joints. It is composed of bellows (a kind of elastic element) and accessories such as end pipes, brackets, flanges, and conduits that constitute the main body of the work. Expansion joint is a flexible structure set on the container shell or pipeline in order to compensate for the additional stress caused by temperature difference and mechanical vibration. The effective expansion and contraction of the bellows of its working body can absorb the dimensional changes caused by thermal expansion and contraction of pipelines, ducts, containers, etc., or to compensate the axial, lateral and angular displacement of pipelines, ducts, and containers. It can also be used for noise reduction, vibration reduction, and heating. In order to prevent the pipe from being deformed or damaged due to thermal elongation or temperature stress when the heating pipe is heating up, a compensator must be installed on the pipe to compensate for the thermal elongation of the pipe. Thereby reducing the stress of the pipe wall and the force acting on the valve or the support structure.

As an elastic compensating element that can expand and contract freely, the expansion joint has the advantages of reliable work, good performance, and compact structure. It has been widely used in chemical, metallurgical and nuclear energy sectors.