Calculation of sw6 tower shell flange
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SW6 was used to calculate a vacuum tower unit; for the cylinder flanges, type B with a pressure rating of 2.5 MPA was selected. The calculated axial stress was not within acceptable limits. By using bolts one size smaller or reducing the number of bolts, the requirement could be met. I don’t quite understand why? The following are the instructions in SW6: This module can perform design and verification calculations for loose-type, integral-type, arbitrary-type, reverse flange, and wide-face flanges. If a verification calculation is performed, regardless of whether the verification is successful or not, the screen display of the calculation results will indicate the minimum acceptable thickness of the flange that meets the design requirements. However, this thickness value is derived under the current design conditions and may not necessarily be a reasonable one. In particular, when the calculated bending moment of the flange is determined by the pre-tensioning moment, reducing the number of bolts or their nominal diameter may yield more reasonable results.
When calculating the flanges of a tower, it is necessary to input the two parameters for flange calculation – additional bending moment and axial tensile load – to carry out the verification calculations. Since these two parameters of the tower are quite important, the container flange cannot be selected solely based on the design pressure; other loads must also be taken into account, and an equivalent design pressure must be determined to select the appropriate flange.
This clearly indicates that the stress condition of the flange at this point is determined by the pre-tightening moment; the pre-tightening moment is greater than the operating moment. At this stage, it is sufficient to adjust the parameters of the bolts (their diameter, quantity, and material) as well as the type of gaskets (i.e., the values of m and y), provided that the gaskets meet the operational requirements. Given that the tower operates in a vacuum environment, non-metallic soft gaskets can be used, which results in relatively lower values for m and y； For details on flange calculations, refer to the relevant sections on flange calculation in GB150
It might be that the bolt spacing is too small, making it impossible to arrange them properly.