An expansion joint is a flexible component that effectively compensates for axial deformation. For instance, the expansion joints welded to the shell of a fixed tube sheet heat exchanger have high axial flexibility and are easy to deform, allowing them to compensate for the thermal expansion difference caused by varying wall temperatures in the tubes and shell, thus reducing their axial loads. This minimizes the temperature stress on the tubes, tube plates, and shell, preventing strength failure, instability failure, and tube pull-out failure. There are various types of expansion joints, commonly including bellows, welded ring plates, and cladded types, with bellows expansion joints being the most widely used, while welded ring plate expansion joints are only suitable for atmospheric or low-pressure conditions.