Expansion joints are flexible elements that effectively compensate for axial deformation. For instance, those welded to the shell of a fixed tube sheet heat exchanger have a high degree of axial flexibility and are easily deformed, allowing them to compensate for the thermal expansion differences caused by varying wall temperatures in the tubes and shell, thereby reducing their axial loads. This minimizes the temperature difference stress on the tubes, tube plates, and shell, avoiding strength failure, instability failure, and tube pull-out failure. There are various types of expansion joints, commonly including bellows, welded ring plates, and clamped shell structures. The bellows type is widely used, while the welded ring plate type is only suitable for atmospheric or low-pressure conditions.