Nozzle local stress due to axial force induced by internal pressure on blind flange

[abehong]

Hello

I encountered a question from client which never think about before . There is a 24 in manway on a pressure vessel with fairly high design pressure. One of mechanical engineer ask me whether or not I checked the local stress for this mayway due to axial force induced by internal pressure on manway blind flange in my design. To be honest, I generally do not have this design consideration in the nozzle design & local stress analysis. Nozzle local stress analysis normally only applies for process nozzle. But it seems to have really large axial induced force due to internal pressure, especially for large opening nozzle. Just want to get some comments from some pressure vessel experts.

Thanks

 

[TGS4]

Those local stresses are already included in the nozzle reinforcement considerations. There's a reason that you didn't consider it additionally before - because it doesn't need additional consideration.

 

[gr2vessels]

Just a small addition;- you have calculated and selected the manway nozzle neck thickness for the mentioned internal pressure and welded to it a suitable class of standard flange for the pressure/temperature of your vessel (if not standard, then a suitable designed Appx. 2 flange + cover). You only need to check the reinforcement for those nozzles affected by external additional loads, like piping loads.

 

[racookpe1978]

See above.

Another way of looking at it: You have a 24 in dia manway in the PV wall, right?

Well, that stress from the internal pressure is pushing "out" on the same 3.14 x 12^2 area that is the internal area of the manway cover. That is also the same area that was "removed" from the PV wall to make the manway hole. So, there is no "extra" force imposed on the PV wall from the manway due to internal pressure. (Weight of the manway cover, manway walls, bolts, and reinforcement are extra. Piping loads weights, and reactions, if one were connected to a pipe nozzle would also be extra.) So, if the manway wall were the same thickness as the PV wall (given the difference in hoop stress due to a smaller diameter) then there is no additional load due to the manway.)

Reinforcement is needed to take into account the change in direction of the PV wall into the manway wall.

 

[innovation2]

Do a search for "Pressure Thrust", basically it is what the engineer is asking about. Worth a read at least.