Stress analysis for large diamater storage tanks
Stress analysis for large diamater storage tanks
(OP)
I am trying to do a stress analysis on a 42" nozzle in a 200' diameter storage tank. Talking with another engineer, I have found that because of the large diameter, WRC-297 does not apply, and API-650 APP-P is limited to the bottom two shell rings. This nozzle is near the top of the shell. I have been provided nozzle loadings (forces and moments in all axis). My method of apporach was first to use several formulas from Roarks flat plate analysis to develop stress for input into 2D mohr's circle formula to find principle stresses, but was left with an axial load that was not accounted for. I have tried to work through the 3D analysis but have had trouble understanding the procedure. Any help would be appreciated. I can provide my calcs through email for review.





RE: Stress analysis for large diamater storage tanks
RE: Stress analysis for large diamater storage tanks
RE: Stress analysis for large diamater storage tanks
Will this nozzle see any hydrostatic pressure?
RE: Stress analysis for large diamater storage tanks
RE: Stress analysis for large diamater storage tanks
Your pad is 23" wide. We have a common practice that intermediate weld is required if pad width > 16 x pad thickness to ensure no separation of pad to shell, and to ensure loads will be well distributed. This is for typical vessels, not knowing if it is suitable for tank or not. Check it out.
RE: Stress analysis for large diamater storage tanks
1) If no one has performed an analysis of the nozzle, then presumably no one knows what the stiffness of the nozzle is (nor the deflections of the nozzle due to hydrostatic load in the tank), in which case, the proposed loads are likely to very wrong. Check back for the sources of those loads before spending too much time trying to confirm the stresses. Garbage in = garbage out.
2) Consider detailing the nozzle and/or the piping to minimize the loads transferred into the nozzle.
3) Generally, with the WRC-297 or related analysis, you'll run into issues with the t/R ratios, not the absolute diameter of the nozzle or the tank, check specifically into the limits.
4) If the nozzle is near a fixed roof, the stress situation, so far as applied loads go, should not be drastically different from a nozzle near the bottom- you still have a nozzle in a cylinder near a fixed end.
5) Typically, cylindrical shells will be very strong axially, and very flexible radially. If the primary loading is vertical, it likely doesn't merit a stress analysis.
RE: Stress analysis for large diamater storage tanks
JStephen -
1. the loads provided are the loads from the piping that will be connected to the flange. How would you go about giving an educated guess to the deflections? Assumptions have to be made, but I don't have any experience dealing with nozzle loading on tanks this large.
3. I was unclear with my diameter comment, but was trying to say the same thing...at a diameter of 200', the shell thickness would need to be on the order of feet, not fractions of an inch. In this case, the shell thickness is 3/8" thk
4. This is an open top tank so that would not apply, but assuming it would be a fixed roof, would I be able to use the head pressure of the fluid above and still apply API 650 app P Calcs(run the calcs as if the tank was up side down)? That is a very creative idea and if it would be applicable, that would be of great use to me in the future!
RE: Stress analysis for large diamater storage tanks
RE: Stress analysis for large diamater storage tanks
Purpose developed FEA sofware is available just for your analysis
http://www.paulin.com/Products.html
Regards