Whether to set the expansion joint needs to be determined according to the specific design parameters of the heat exchanger and the stress level obtained through calculation. Some data in history, restricted by calculation method, through a simple cylinder or rough calculations obtained the axial stress of heat exchange tube is more than a specified value to judge whether setting expansion joint, it is not reasonable, they assume that it is absolutely rigid tube plate, each heat exchange tube bundle of all in the same pull, pressure, with the actual situation of the tube sheet and tube bundle force. In addition, some designers even more rough through the tube, the operation of the shell side temperature difference, or the design temperature difference is more than a specified value (e.g., more than 50 ℃), to determine whether to need to set expansion joint, which is not correct, because the operation temperature difference and temperature difference design is not the same as the metal temperature difference, more can't instead of heat exchange tube and shell side differential thermal expansion between the cylinder. In particular, when the two materials are different (for example, the heat exchange tube is stainless steel and the shell side cylinder is carbon steel), the linear expansion coefficient of the two materials is very different, which may occur in extreme cases: the metal temperature difference between the shell side is very large, but the thermal expansion difference is zero; The temperature difference between tube and shell is very small or zero, and the thermal expansion difference is very large. Therefore, in the calculation of the tube plate, in accordance with the temperature difference of various working conditions to calculate the shell of the axial stress sigma c, the heat exchange pipe of the axial stress sigma t, between the heat exchange pipe and the tube plate of the pulling force q, one can not meet the strength (or stability) conditions, it is necessary to set up the expansion joint. When expansion joints are set in fixed tube-plate heat exchanger, the axial stiffness of the shell is greatly reduced, thus the transverse shear force and bending moment around the tube-plate are greatly reduced, and the tube-plate stress is greatly relieved. The smaller thickness can meet the design requirements. This method is also very effective in reducing the pulling force between the tube plate and the tube.

 

 

 

Therefore, it is necessary and economical to set expansion joint when the thermal expansion difference of the shell is large. In the calculation of tube plate strength check, when the tube plate thickness is determined, without expansion joint, sometimes the tube plate strength is not enough, after the expansion joint, the tube plate thickness may meet the requirements, at this time, can be set up expansion joint to reduce the tube plate, but from the material consumption, manufacturing difficulty, safety and economic effects and other comprehensive evaluation.