Pressure Vessel Deflection
Pressure Vessel Deflection
(OP)
Hi,
I have observed in many cases that horizontal pressure vessel with saddle support due to the internal pressure gets circumferentially compressed (vertical deflection).
Can anyone explain why it behaves so.
Regards,
smart009
I have observed in many cases that horizontal pressure vessel with saddle support due to the internal pressure gets circumferentially compressed (vertical deflection).
Can anyone explain why it behaves so.
Regards,
smart009





RE: Pressure Vessel Deflection
prognosis: Lead or Lag
RE: Pressure Vessel Deflection
there are other loads acting like thermal and other nozzle loads, but why vessel shows compressive deflection vertically.
Let me know if my question is not clear.
RE: Pressure Vessel Deflection
Draw a cross section through the tank and the saddle, and a free body diagram of the various forces on this cross section. I’m not sure that I understand your question, but I think it is that there might be a slight ovaling or downward deflection of the top of the tank in the region of the saddle. Assuming a cylindrical tank with hemispherical ends, the internal pressures are self equilibrating as normal pressures and hoop stresses and tensile stresses along the length of the tank shell; except for localized secondary stresses. But, in addition, you now have the saddle reaction pushing upwards on the tank shell and you need an equal and opposite downward force system from the top of the tank for equilibrium. These two force systems are a concentration of half of the gravity loads on the tank in the immediate area above the saddle. Unlike the pressure forces, these gravity forces will tend to force/pull the top of the tank down a little bit. The saddle supports the bottom half of the tank and tends to maintain its shape, but the top half is free to move down. This can cause some concentrated secondary stresses in the tank shell right at the top of the saddle, caused by these two different force systems. I assume you’ve run your tank design through some computer software, and that software should show this action and these stresses added to the pressure stresses.
RE: Pressure Vessel Deflection
If you're not familiar with it, look through Zick's paper on the topic, or review the topic in various vessel design handbooks. Zick's paper:
http://lms.i-know.com/pluginfile.php/28927/mod_res...
Note: this paper has been updated a time or two, and this may not be the most recent version.
RE: Pressure Vessel Deflection
here is the image showing how it is behaving.
RE: Pressure Vessel Deflection
RE: Pressure Vessel Deflection
Cheers,
gr2vessels
RE: Pressure Vessel Deflection
The region of the vessel between the two saddle deforms i.e it takes oval shape. to be more clear top side of vessel deforms more than the bottom side of the vessel.
Gravity, thermal loads & nozzle loads might play a role. Let me recollect all your points and think again.
thanks all, if you have any other points to add please, it will help me to understand better.
Thanks,
RE: Pressure Vessel Deflection
You want an intelligent answer but you have not provided any details on which we can determine that answer.
Such as:
- The diameter of the vessel?
- The tangent to tangent length?
- The number of Saddles?
- The tangent to center of each saddle?
- The wall thickness of the vessel shell?
- The type (shape) of the Heads?
- The material of the vessel?
- The age of the vessel?
- The commodity in the vessel?
- The normal operating pressure of the vessel?
"Intelligent questions earn intelligent answers"
prognosis: Lead or Lag
RE: Pressure Vessel Deflection
RE: Pressure Vessel Deflection