API650 v11 - Appendix E - extra thickness of the shell
API650 v11 - Appendix E - extra thickness of the shell
(OP)
Hi gentlemen,
Please excuse me in advance for these beginner's questions, but I need to understand the API650 (version 11) code which is used by our customers.
I think of having succeeds in understanding the formulas and the typo mistakes but there remain to me these questions:
- When we calculated the values of compressive stress at shell bottom and maximum allowable compressive stress, how can we determine the extra thickness of the shell to apply for seismic risk? And this, for each shell course.
- How, in the current version of the code (v11), can we use the old value of Z (Zone coefficient) used in the previous version?
Thanks a lot for your help.
Please excuse me in advance for these beginner's questions, but I need to understand the API650 (version 11) code which is used by our customers.
I think of having succeeds in understanding the formulas and the typo mistakes but there remain to me these questions:
- When we calculated the values of compressive stress at shell bottom and maximum allowable compressive stress, how can we determine the extra thickness of the shell to apply for seismic risk? And this, for each shell course.
- How, in the current version of the code (v11), can we use the old value of Z (Zone coefficient) used in the previous version?
Thanks a lot for your help.





RE: API650 v11 - Appendix E - extra thickness of the shell
You can't really use the Z factor in the current standard. You can check in prior versions, and see what the equivalent acceleration was, and apply that acceleration to your tank. But it won't be an exact match. The ratio of convective to impulsive acceleration may be different between the older and newer standards. The older standards used direct sum for calculating moment, while the newer one uses the square root of the sum of the squares, which will change the moment as well.
RE: API650 v11 - Appendix E - extra thickness of the shell
The use of Z factor is now clear for me ^^
But on the thickness of the shell, I'm not really sure to understand. If the better method is to thicken the annular bottom ring, why my customer apply an extra thickness on each shell course? For example I have calculate the thickness of a little tank with the classical method (section 5 of the code) and the result is five courses with thickness from 6 (bottom) to 5mm (up). Our customer, with seismic risk, find five courses from 13 to 6mm...
I thought the seismic risk generate an (virtual) extra load which be use in the calculation of thickness of each shell course. Isn't it?
Thanks in advance
RE: API650 v11 - Appendix E - extra thickness of the shell
The issue with the annular plate comes from Eq. E.6.2.2.1-2(a) and (b). When J is near 1.54, the denominator is small, and stresses are large. If wa is not limited by the 1.96HDG limitation, then thickening the annular ring (or adding an annular ring if there's not one) will help. If the tank is anchored anyway, or J is not near 1.54, or the wa is limited by the 1.96HDG factor, then thickening the annular ring won't help.
RE: API650 v11 - Appendix E - extra thickness of the shell
I will try to obtain more informations from the customer and work on your ideas...
Have a nice day