Regarding the value of FG in flange calculations
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In flange calculations, the flange torque under operating conditions is given by Mp = FdLd + FtLt + FgLg. What value should be used for FG in this formula? The screenshot is as follows: Clause 7.3.2 of GB150.3 states in the symbols that the compressive force of FG narrow-face flange gaskets includes three scenarios: Fa, Fp, and W (pre-tightening). Does this refer to the maximum value among these three? Or is the FG here directly taken as the pre-tension force Fp in the operating state? In the calculations for the reverse flange, this FG provides a formula; in fact, this formula is nothing other than Fp. In the SW6 calculation manual, it is given that FG = Fp. So what is the purpose of specifying this FG in the standards? You can just use Fp directly, everyone. What do you think?
This post was last edited by wanlirn on 2018-1-12 at 17:39. All three operating conditions need to be verified; as for the reverse flange, it’s just a matter of notation – it actually has no relevance at all
Pre-tensioning condition, FG=W； Operating condition, FG=FP. Refer to Table 7-5 in GB150.3:
Yes, I’ve seen this watch. The flange torque under the pre-tensioning condition is Ma, while the flange torque under the operating condition is Mp. Since FG is derived in the calculation of the flange torque Mp under the operating condition, there is no need to distinguish between three different conditions anymore; at this point it is simply Fp.
Regarding the calculation conditions for flanges, there should be only two conditions: pre-tensioning and operation. The “three cases” in §7.3.2 are unclear; should they be understood as merely a review? §7.6.3 In the formula for calculating the reverse flange torque, FG is also based on the operating conditions. The pre-tightening torque is given by Equation 7-11; in fact, this also means that FG = W.
Five years later, this issue finally found an answer in the draft 150; the new draft simply changed “FG” to “Fp”"