Is it necessary to use expansion joints in the strength calculation of fixed-tube-sheet heat exchangers?

Since the design temperatures are the same, there’s no need for them; expansion joints are only necessary when there is a large temperature difference in the shell and tube design

It’s an interesting topic; although the conclusion is acceptable, I still want to shed some doubt on it: 1. Leaving aside the fact that the temperature difference between the tube side and the shell side is indeed small, there is actually a temperature difference – it’s just a matter of the magnitude of the stress resulting from that difference. 2. After reviewing the calculation process, I noticed that the author set the design temperatures for both the tube side and the shell side to be equal, which means there is no temperature difference at all in the calculation. The only potential risk factor is pressure; the results obtained with and without considering the temperature difference are identical. This calculation approach isn’t logically sound, and using it as a basis for not installing expansion joints lacks sufficient justification. Of course, I also understand that the original poster simplified things when the temperature difference was small. 3. The heat transfer calculation for heat exchangers involves an average temperature difference, but it requires complex calculations. It is recommended to input the average temperature of the tube side and the average temperature of the shell side and perform further calculations; only if the resulting temperature difference stress is within acceptable limits can it be considered to have a solid basis.

If the temperature difference between the average inlet and outlet temperatures of the tube side or shell side is 34°C, the corrected average temperature difference for heat transfer calculations is 27.74°C. The original poster might as well calculate by varying the design temperature to create an average temperature difference, and see what the results regarding stress due to temperature differences are.

1 According to the calculation, both the average metal temperature of the heat exchange tubes and the average metal temperature of the shell are set to 0; as a result, under a series of identical conditions such as equal length, equal metal temperature, and equal material, the values of axial stress remain the same. 2 A heat exchanger with a diameter of 1700 was just analyzed using SW-6; the tube sheet thickness was 116 mm. The shell and tubes were made of the same material. The average metal temperature of the shell was set at 160, and that of the tubes at 130. The axial stress exceeded the allowable limit, resulting in a failure in the verification process. The verification was successful after thickening the tube sheet. 3 It is recommended that the poster adjust the parameters for calculation