Problems encountered in the external pressure calculation of SW6 heat exchange tubes
Thread Content
In the new version of SW6, the calculation of the external pressure on the straight sections of the heat exchange tubes is included when calculating the tube sheets. However, an issue arises during this external pressure calculation. There is a U-tube heat exchanger with the following design parameters: shell side design pressure: 2.9 MPa, design temperature: -45/115°C; tube side design pressure: 2.9 MPa, design temperature: -45/175°C. Therefore, low-temperature material 09MnD is used for the heat exchange tubes. When calculating the external pressure on these tubes, the conditions of 2.9 MPa and 175°C are used. But when using SW6 for this calculation, it becomes impossible to proceed with the calculation. It was found that the reason for this is that for 09MnD, there are no B-value curves for external pressure stress at design temperatures above 150°C (according to GB150). The applicable temperature range for external pressure calculations using 09MnD is up to 150°C only; beyond that temperature, no B-value curves are available. As long as the design temperature exceeds 150°C, SW6 cannot perform the calculation. Although it is possible to carry out additional calculations for the heat exchange tubes, once the design temperature exceeds 150°C, it becomes impossible to calculate the tube sheet aspects, and thus no calculation report can be generated. In reality, such design conditions that involve both low-temperature and high-temperature operations are quite common (that is, using low-temperature heat exchange tubes while the design temperature still exceeds 150°C). This results in SW6 being unable to perform calculations in such situations. I’m not sure how this problem can be solved
Hasn’t anyone encountered this problem? Why isn’t there anyone answering?
I have encountered this situation too. When calculating the negative pressure, if the design temperature exceeds the range specified by the curve, either the material needs to be changed or communication should be held with the process engineering team to reduce the design temperature; there is no other solution.
Is there a condition of low temperature and low stress in low-temperature operating conditions? High temperature: if 09MnD cannot be used, stainless steel can be used
Modify design parameters or change materials
Software is just a tool; it can’t be used for that purpose, so you just have to do the calculations by hand and add them in. You can also try using PVELite.
Changing the material means that the entire equipment has to be redesigned. When communicating with the engineering team, it makes sense to specify a design temperature. In fact, this is an equipment unit that was already built previously; it wasn’t a problem back then when SW6 wasn’t used. The thickness calculations for the external pressure on the heat exchange tubes were quite small in those cases. Now, with the new version, external pressure calculations have been added, which has led to some situations where calculations cannot be performed. Personally, I think there’s no issue with the external pressure calculations; I could even carry out these calculations manually. But the key problem is that it’s not possible to generate calculation reports for the tube sheet area
With the change in material, the entire device is essentially redesigned
In your case, you can discuss this with your review and approval personnel; bring GB150.1-2011, go to page P9, clause 4.1.6b, and follow the design outlined in Appendix D.
Lower the temperature. What is the operating temperature? With a design temperature drop of 25 degrees, there should be no problem, right? Otherwise, since you won’t change the materials, the design of this heat exchanger does not comply with GB/T151!