API 650 - Appendix V

[DSB123]

Hi Members,
Just a question about the "Design of Storage Tanks for External Pressure" - Appendix V in the latest edition of API 650.
The equation for the unstiffened height of the shell (Hsafe)(Eqn V.8.2.1.2) yeilds very small figures for the unstiffened height which results in a large number of stiffeners when compared with the previous editions of API 650. Is the equation correct? or is their some error there as there are "typos" in other equations?

 

[JStephen]

I don't think it's a typo as they do have an example problem using that equation, and it's printed the same way there.

Per V.8.1, you can adjust the safety factor from 3.0 to 2.0 which will help some.

Per 5.2.5, if external pressure is only 1" of water, you don't need to comply with App. V.

Using the equation, plugging in 36 psf for the pressure and 29,000,000 psi for E, gives you a constant of 161,111. Adjusting for safety factor gives 241,667. This compares to the 600,000 factor in the base code.

One of the technical inquiries, Inquiry 650-1-10/07, says, "It is my opinion that the equation for H1 in Par. 3.9.7.1 does not provide a factor of safety against buckling...." The response to this inquiry is "Yes". I don't know if that means "Yes, you're right, there's no safety factor" or if that means "Yes, there is too a safety factor".