Under what operating conditions are expansion joints required in fixed-tube-sheet heat exchangers?

When there is a large difference between the temperature of the tube side and that of the shell side, expansion joints may be necessary; the result can be determined through SW6 calculations

Do I need to enter the parameters of the expansion joint when performing the calculation? Or should I enter the previous conditions first, and only after the calculation is completed will it be suggested that an expansion joint be added? I haven’t done this before; please ask a friend to give me more guidance.

When using SW6 to calculate the tube sheet, the program will give a warning if expansion joints are required. Generally, based on experience, if the materials of the tube side and shell side are different – with the tube side made of stainless steel and the shell side made of low-alloy carbon steel – even a temperature difference of just a few degrees may require the use of expansion joints. Since the temperatures on the tube side and shell side differ, as well as the types of materials used for the heat exchange tubes and the shell cylinder, the amounts of expansion vary; therefore, an expansion joint is needed to accommodate these differences, otherwise problems may occur with the tube sheet. If the expansion joint data is entered first when entering the data, the tube sheet calculation will be done as if an expansion joint is present, and the design will also have to be carried out according to the design with an expansion joint. If it is not certain whether an expansion joint is needed, it can be left unentered; it can be entered later if necessary.

During the training in Shanghai this time, the instructor mentioned briefly that the example given was similar to yours.

The posts are about to sink; let’s keep discussing them. By how much should the linear expansion coefficients of the shell and the heat exchange tubes differ before it’s necessary to use expansion joints?

In the case of dissimilar steels in the tube and shell sides, especially carbon steel and stainless steel, empirical values indicate that thermal stress must be given special consideration when the temperature difference exceeds 50 degrees. When either the axial force on the shell, the axial force on the heat exchange tubes, or the pulling force between the heat exchange tubes and the tube sheet is not within the specified limits, it is necessary to consider adding expansion joints.

Your insights and experience are extremely valuable; I’ve learned a lot of new things. Thank you so much. I’m grateful to wangjinbo66 for initiating this discussion. I’m familiar with the performance, operating conditions, and installation of expansion joints, but I’m not as familiar with the choices made during the initial design phase

The original requirement was that when the temperature difference between the tube side and the shell side exceeded 50°, it was necessary to consider installing expansion joints. Now, after calculation using software, those exceeding that temperature are also not required; the software can perform accurate calculations, and it is sufficient to ensure that the thermal stress is below the allowable stress value for use.

The axial stress of the shell, the axial stress of the heat exchange tubes, and the pulling force between the heat exchange tubes and the tube sheet are calculated under various conditions based on temperature differences; if any of these values do not meet the required standards, it is necessary to consider installing expansion joints.

The materials of the tube side and shell side are the same or have similar coefficients of thermal expansion. If the wall temperature difference is around 50 degrees, it is advisable to consider installing expansion joints. Whether such joints are necessary should be determined based on the calculation results, as well as by considering the impact of adjusting the tube sheet thickness on the pulling stress and axial stress acting on the heat exchange tubes. When the coefficients of thermal expansion differ significantly, it is necessary to take account of this factor when the wall temperatures are close to each other; however, when the temperature difference is large, this may not be necessary. (Because typically, due to the material used, the thermal expansion coefficient of the heat exchange tubes is relatively low, resulting in relatively high wall temperatures.) 1. The software may suggest adding an expansion joint, but it isn’t always necessary; if the thickness of the tube sheet can be adjusted slightly to avoid this issue, then there is no need to install an expansion joint. 2. If the software does not give a recommendation to add it, one can also make a judgment by examining the calculation sheet to determine the stress. Consider adding expansion joints to significantly reduce the thickness of the tube sheet.