The flange loading calculation method outlined below involves determining the effective pressure in the flange due to:

  • External Moment.
  • External Force.

The sum of operating/design pressure and effective pressure is then compared with the allowable pressure specified in ASME B16.5 or ASME B16.47.

This calculation is based on the methodology used in ASME III Subsection NC-3658. The following equation is used to determine the equivalent or effective pressure (Pe) due to external loads.

Pe = 16M/πG3 + 4F/πG2


  • Pe = Equivalent pressure N/mm2
  • F = Axial external force in tension N
  • M = External bending moment Nmm
  • G = Diameter at location of gasket load reaction mm

Acceptance Criteria

The external load on the flange is acceptable if the following criteria is satisfied.

Pd + Pe <= PR Where

  • Pd = Design pressure N/mm2
  • Pe = Equivalent pressure N/mm2
  • PR = Rated flange pressure N/mm2