Nozzle Load on FULL VACUUM Vessel 1

[roca]

How do you check the nozzle loads using WRC 197 / 297 for nozzles on a vessel operating at Full Vacuum?
The worst case would be a radial (axial load) pushing into the vessel.
How is the effect of vacuum taken into account?

 

[arto]

Take a look @ Gilbert & Polani's "Stability Design Criterion for Vessels Subjected to Concurren External Pressure & Longitudinal Compressive Loads" ASME Trans Jnl PVP May 79, Vol. 101 pp178-81.

 

[PVGuy]

The way I understood it was that you can plug in the vacuum pressure as internal pressure but reverse the signs for the pressure stress when superimposing the stresses from the applied local loads with the pressure stress. Any comments on this method?

 

[JStephen]

PV Guy, I see two possibilities for problems. One is, if the method used for checking stresses does not check stresses at every point, but only at the point where the maximum is expected to be, then you could miss the maximum stress. And secondly, if in some way, the load was limited by buckling rather than by yielding, you could miss that. Otherwise, the stresses should be workable as you suggest.

 

[JoeTank]

JStephen get a star for that one.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[PVGuy]

Thanks JStephen, forunately I use the original which checks stresses at all the points. Also if the total stress is negative I use the allowable compressive stress by the code (UG-23). Is that what you meant when talking about buckling?

 

[JStephen]

If you have a pressurized vessel, and apply an outward nozzle load to it, you'd just check allowable stresses.

If you have a vessel with vacuum, designed for that vacuum, and you apply an inward nozzle load to it, the nozzle load could act with the vacuum load to buckle the vessel. And that type of failure is not anticipated in the usual nozzle stress calculations.