large tanks and API650: caesar example and questions

See attached .zip file containing:

-a word document with model desxcription and the final questions
-the caesar model

thank you

Problem 1 - This isn't an API 650 tank. API 650 starts a diameters much larger than this. While I've never attempted API 650 calcs on a small tank such as this, I guess now we know what happens.

Problem 2 - Even if this were an API 650 tank, the assumption that thermal growth of the perimeter directly translates into increase in radius is not reflective of reality. Thus, there shouldn't be a rigid element going to the center. To the bottom of the tank? Sure.

Observation - Rigid elements in CAESAR are not true rigid elements. They are as stiff as the pipe you specify them as, with the thickness multiplied by... 10? If I recall correctly. Check the help file.

Is there guidance for a tank such as this? Run FEA to obtain deflections.

FEA is becoming common now, so better request the deflections from tank vendor if they happen to use FEA to check nozzle loads. You can request this to be used for your boundary condition. Just take note that FEA software will just give the translational displacements and no rotational displacements. It needs some manual post processing to get the rotational displacements (I think one FEA software have developed a procedure how to get this). Not sure if there are other FEA software which automatically produce rotational displacements.

In my case, since the tank dia. is greater than 120 ft., I use the API 650 formula for getting the rotation of nozzle due to tank bulging.

Normally, I don't model a rigid element to the center of tank. I just model it at nozzle/shell junctions and impose the boundary conditions there (maximum tank settlement from Geotech report at the edge of tank ,displacement and rotations from FEA software or using API 650) and model the nozzle flex at the shell/nozzle junction (some FEA software can generate this nozzle flexibility). Then I submit the generated nozzle loads to tank vendor for verification. I normally do a verification myself (since there is available tool inhouse) to avoid iterations with tank Vendor. API 650 Appendix P can also be used for tanks 120 ft and above.

Just correct me fellow Stressers if any wrong statement I've made.

Cheers!!

thank you.
let's take a 40m diameter tank.
here attached the caesar file according to Borzki.

why do i have an huge 5639.18mm radial deflection and and incredible -107.42 longitudinal rotation?

do you have a caesar example about tank modeling and API650 settings?

Hi,

Please check specific gravity. It's very high (900). Water SG=1.

Warm Regards,

don't worry :P
fluid density units are Kg/m3 so for water is 1000. Here we have a fluid a bit lighter than water.

ehm... i understood what was the problem. inside the "Nozzle flax", "Fluid SG" i put 900 as i did in "fluid density". so the Fluid SG is:

water=1 (and fluid density 1000kg/m3)
hot oil=0.9 (and fluid density 900kg/m3)

is it right?

caesar help reports:
<>

i thought it was the same of fluid density

got it.

warm regards,

In US notation, it shows up as Fluid SG, not density. The helpfile calls it out as unitless, thus, I would not expect it to change based on SI units.