Nozzle Pressure Thrust in WRC-107 Calculations
Nozzle Pressure Thrust in WRC-107 Calculations
(OP)
When evaluating piping loads and moments on a pressure vessel nozzle using WRC-107, should the nozzle pressure thrust be included as a radial load?





RE: Nozzle Pressure Thrust in WRC-107 Calculations
BT
RE: Nozzle Pressure Thrust in WRC-107 Calculations
Thanks for your response. Yes, we are talking the same direction. Forces along the axis of the nozzle are termed radial loads in WRC-107 since they act on the shell toward the center or axis of the vessel.
RE: Nozzle Pressure Thrust in WRC-107 Calculations
What do others think?
RE: Nozzle Pressure Thrust in WRC-107 Calculations
In my opinion these are the facts:
- most client specifications do not explicitly state whether pressure end loads are included in their standard nozzle loads; I suspect they are normally (but silently) included
- as far as primary stresses are concerned, the verification of nozzle reinforcement takes care of nozzle end loads; so, if pressure is the only source of stress and design is per Div.1 (no check of secondary stresses required) there is no need of WRC calculations
- when other loads on the nozzle exist (here a difference should be made for loads of thermal origin, but this is a completely different discussion) or secondary stresses need be evaluated (Div.2), then the pressure end effects should be included in WRC calcs, as this will be a source of bending in the vessel wall near the nozzle; for this calculation the actual geometry of nozzle (including any reinforcement) should of course be used, but also the longitudinal and circumferential stresses in vessel wall should be included with no intensification (plainly PD/2t or PD/4t, t being the design thickness at the nozzle location)
- if I remember correctly, BS5500 had a different approach on this point: pressure stresses are intensified by a suitable coefficient, and I suppose this was to include the effect of local bending: in that case the end load should be excluded from nozzle loads.
prex
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RE: Nozzle Pressure Thrust in WRC-107 Calculations
RE: Nozzle Pressure Thrust in WRC-107 Calculations
Just curious: If you take a free body diagram at a section cut through the nozzle, say just before the flange, I would argue that at that cut the nozzle neck has a longitudinal stress which equals P*R/2*t. This longitudinal stress, in units of force per unit area could be multiplied by the cross sectional area of the cut to develop a load which is longitudinal in the nozzle... or radial to the vessel shell.
If you state that these radial loads due to pressure do not exist, how do you explain the presence of longitudinal stress in the nozzle neck, or does the longitudinal stress also not exist?
jt
RE: Nozzle Pressure Thrust in WRC-107 Calculations
RE: Nozzle Pressure Thrust in WRC-107 Calculations
RE: Nozzle Pressure Thrust in WRC-107 Calculations
For most machinery, I have found that the pressure thrust load is not included, as the major concern is overall distortion and misalignment, not nozzle stress. There are exceptions.
RE: Nozzle Pressure Thrust in WRC-107 Calculations
Thanks very much for your valuable input. For the benefit of others COADE has published on their website a few informative articles on this subject in their Mechanical Engineering News. See July 2001 page 9 and June 1997 page 10. From their articles it can be seen that pressure thrust should generally be included in WRC-107 calculations unless the piping system has restraints in place to counter the force.
RE: Nozzle Pressure Thrust in WRC-107 Calculations
RE: Nozzle Pressure Thrust in WRC-107 Calculations
RE: Nozzle Pressure Thrust in WRC-107 Calculations
bvi is correct.
To help you better understand the subject of nozzle thrust and how it may or may not be influenced by attached piping and why it exists around openings in general, I would suggest that you view the information COADE has published on their website. See their Mechanical Engineering News, July 2001 page 9 and June 1997 page 10.