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There are two standards that deal with bending moments on flanged connections and give a simplified calculation method:
  • ASME III div.1 par. 3658. Here the equivalent pressure is calculated from the axial force and bending moments.
  • ASME B31.8 Appendix E Note 14 of table E1. Here the bending moment to produce leakage of a flanged joint is calculated.

Both equations are used for an estimation only. On this web-page both methods are combined in a calculator. In this way one can manipulate with different figures.
The equivalent pressure method is based on the stresses in the flange. The ASME B31.8 approach is based on leakage. It is now possible to determine the maximum bending moment fulfilling both criteria.
Thus making a quick estimate for different conditions. The final result can than be calculated with a more detailed analysis.
If the calculated equivalent pressure remains below the allowable limits than no detailed analysis is necessary. 

Example of use:

  • Fill out pressure
  • Choose bolts and number of bolts
  • Fill out Bolt circle
  • Fill out average gasket diameter
  • 'Fill out the horizontal bending moment
  • Press '+ Equivalent Pressure' button. This will add-up the equivalent pressure to the original pressure
  • Reduce the elevated pressure back to its original value
  • Press 'Allow. Bending' button

The calculated allowable bending moment will be higher than the original Horz. bending moment. The newly calculated boltforce fulfils both the ASME III criteria and the ASME B31.8 criteria.

Equivalent Pressure Calculator
Bending Moment to produce Flange Leakage
Pressure Bar MPa Stress
Number of Bolts
mm Bolt circle
mm Gasket diam.
Nmm Horiz. Bending
Nmm Vert. Bending
N Tension Force

This calculator proofs that simple calculations can be easily performed with web-pages like this one.