An expansion joint is a flexible element that effectively compensates for axial deformation. For instance, an expansion joint welded to the shell of a fixed tube sheet heat exchanger has a high degree of axial flexibility and is prone to deformation, which can compensate for the thermal expansion difference between the tubes and the shell due to varying wall temperatures, thereby reducing their axial loads. This minimizes the temperature stress between the tubes, tube sheets, and shell, preventing strength failure, instability failure, and tube pull-out failure. There are various types of expansion joints, commonly including bellows, ring-plate welding, and cladded designs, among which bellows-type expansion joints are widely used, while ring-plate welding expansion joints are only suitable for atmospheric or low-pressure conditions.