API 650 One foot Method

No - according to API 650 3.6.3.1 - the one foot method may not be used on tanks over 60m in diameter.

Accordingly - you must make sure, when designing with the variable point method that you meet the 3.6.4.1 criteria of

L/H ≤ 1000/6

Just out of curiosity what is a one 'foot method'?

It's the method of calculating shell thickness at design points 1 foot above the bottom of each shell course. The variable-design-point method gives shell thicknesses at design points that result in the calculated stresses being relatively close to the actual circumferential shell stresses.

what if L/H ≥ 1000/6.

That's a big tank.

If you can't adjust the diameter/thickness to height criteria - build two tanks.

Actually - thinking a little more ..................

(whoops it is actually 5.6.4.1 in the 11th Ed of API 650 - I originally looked at an older addition)

That is not that big of a tank - I don't see that you should have a problem, without knowing your design conditions and running the numbers - just a quick look at Table K-1 in Appendix K reveals that you should be fine.

Digging even more - according to 5.6.5:

For tanks where L/H is greater than 1000/6 (2 in US customary units), the selection of shell thicknesses shall be based on an elastic analysis that shows the calculated shell stresses to be below the allowable stresses given in Table 5.2. The boundary conditions for the analysis shall assume a fully plastic moment caused by yielding of the plate beneath the shall and zero radial growth.

(Please don't ask me how to perform this analysis - I have never done it)

Thank you all for your reply.