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Flange loads are forces and moments that act on a flanged joint in addition to internal pressure and can affect its strength or tightness.
The rating of a flange states which internal pressure it withstands at which temperature. In a pipe, however, more arrives: weight, thermal expansion and occasional loads produce forces and moments at every point of the line – including where a flange sits.
A flanged joint is the weakest link at that point. Not because it breaks, but because it leaks long before the pipe next to it reaches its limit.
The four load components act very differently. An axial tensile force unloads the gasket evenly around the circumference. A bending moment unloads it on one side and compresses it more on the other – on the tension side the joint can open. Torsion and shear are transmitted only by friction at the gasket and can displace it.
In most piping the bending moment is the governing component.
The most widespread estimate converts axial force F and bending moment M into a notional additional pressure: p_eq = 16 · M / (π · G³) + 4 · F / (π · G²), where G is the effective gasket diameter. This equivalent pressure is added to the design pressure and the sum compared with the allowable pressure of the flange at operating temperature.
The method is simple and conservative – often very much so. If it shows an exceedance, that is first of all a reason for a more exact calculation, not necessarily for a heavier flange.
A calculation to EN 1591-1 treats flange, bolts and gasket as a preloaded system and includes axial force and bending moment as external loads. It verifies not only strength but also that the gasket remains sufficiently compressed in every condition. For highly utilised joints and fluids with a tightness requirement this is the more meaningful route.
The best flanged joint is the one that sits at a quiet spot.
What Entracon offers here is on the matching page.
See what we offer| Load component | Effect | Significance |
|---|---|---|
| Internal pressure | Unloads the gasket, loads bolts and flange | Covered by the rating |
| Axial tension | Unloads the gasket evenly | Mostly small |
| Bending moment | Unloads the gasket on one side | Mostly governing |
| Torsion, shear | Transmitted by friction at the gasket | Rarely governing; watch with smooth gaskets |
The pressure-temperature rating is established for internal pressure. If a flange is not used up to its pressure limit, the margin is available for external loads – that is the idea of the equivalent pressure method. With the rating fully used, nothing is left by calculation.
It increases capacity but makes the joint heavier and stiffer and usually affects the valves too. First check whether the routing or a support can reduce the moment at the flange location.
The pipe stress analysis. It reports forces and moments per load case for each flange location; the governing combinations for the check are selected from these.
One short conversation usually settles more than three quotations. Call or write — you will reach an engineer directly.
Start typing – for example “balancer”, “SAP” or “pipe stress”.
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