Vertical tank design 2

[401laurent]

Hi,
I have to design an atm. vertical S.S tank ( 8'(dia., 30' H),
supported on skirt or legs. for milk , insulated .
for heads, I want to use fabricated conical with knuckle .
could some one response to theses questions please:
1- witch standards can I use.( I know API650, but this consider only vertical tank with flat bottom )
2- How can I calculate the thickness of the bottom heads.
3- I have used Compress program for ASME tank, and I consider that my design pressure is only atm. (=0), and a btm conical head with knuckle =6%, and the thk calculated is 5/8 po. witch is in my opignion very heigh, because ,in ASME code the safety factor (S.F) is about 3.5, and in other standards may be it less.
to confirm this statement?
4- How to design the legs if I want to welds them to Btm Head.

Thanks you.

 

[JStephen]

1- Which standards can I use: There are not any that specifically apply to your geometry. You can use any of the tank standards (or PV standards) "to the extent applicable". API-650 will be useful mainly as a source of allowable stresses. API-620 also includes design of suspended bottoms, but it may be the source of the 5/8" thickness you're coming up with- it is poorly written for small-radius knuckles. I assume the Compress method would be based on ASME, so it may not be any better. Perhaps consider a conventional F&D head, which should be readily available and calculate out fairly thin.

2- How can I calculate the thickness of the bottom heads.
See above.

3- I have used Compress program for ASME tank...and the thk calculated is 5/8: I would guess that this is due to the methods used rather than to the factor of safety. Try a larger knuckle radius or switch to an F&D head, or perhaps increase the cone slope.

4- How to design the legs if I want to welds them to Btm Head: See the various Pressure Vessel Handbooks for some information on designing supports. See ASCE 7 for applicable loads.

 

[JoeTank]

API-620 would be a good standard for your case. It addresses vessel of the shape you describe. I too think that the 5/8" knuckle seems too thick. Increase your knuckle radius to 10% or 20% or more to thin it out.

Joe Tank

 

[401laurent]

Hi,
thanks for your help, so you propose to use API 620 as Standards for this design, I think that API 620 is used specially for Large diameter Tank.
second ,in my case I can't increase my Knuckle radius, in my shop I'm limited regarding my forming machine to only
1 po.radius .so can I suppose that it's aproximatly the head have a conical shape. and calculate as then.

I haven't the API 620, could you give me only the formulas for calculating the bottom head with this shape.
Thank you again.

 

[LSThill]

401laurent (Mechanical)

Question: 3- I have used Compress program for ASME tank and 4-How to design the legs if I want to welds them to Btm Head.

Use Compress program to help you design the legs using 8 inch Dia. Pipe Sch 80 for the legs.

Reference ARCHITECTURAL INSTITUTE OF JAPAN
DESING RECOMMENDATION FOR STORAGE TANKS AND THEIR SUPROTS 1996 EDITION – Earthquake Resistant Design of Storage Tanks and Their Supports -

Dennis Moss Pressure Vessel Design Manual

 

[SnTMan]

401laurent, you may be able to "spoof" your software by entering whatever allowable stress you decide is appropriate, or creating in its database a new material(s) with the allowables you want.

Regards,

Mike

 

[JStephen]

Note that API-620 addresses the design of suspended bottoms, but does assumes the structure in question is axisymmetric- so it doesn't address legs, or the stresses in the shell due to the legs.

Can you just delete the knuckle all together? You may need a small compression ring then, but it would probably be easier to do than a knuckle.

 

[LSThill]

401laurent (Mechanical)
Dennis Moss Pressure Vessel Design Manual 3rd Edition.

Reference Page 109
Chapter 3
Design of Vessel Support
Section 109