An expansion joint is a flexible element that effectively compensates for axial deformation. For example, the expansion joint with high axial flexibility and ease of deformation, welded to the shell of a fixed tube plate heat exchanger, can compensate for the thermal expansion difference between the tube and shell due to different wall temperatures, reducing their axial loads. This, in turn, minimizes the temperature difference stress on the tubes, tube plates, and shell, thus preventing strength failure, instability failure, and tube pull-out failure. There are various types of expansion joints, commonly including bellows, plate welding, and cladded structures. Among them, bellows expansion joints are suitable only for atmospheric or low-pressure conditions.