Uplift Load Cases formula(Table 5.20) in API 650 13th edition different from 12th edition ???

[TheEverest]

I found out that the formula for Uplift Load Cases in Table 5.20b is different in the 13th edition from that of the 12th edition. Also, W1, W2, and W3 are defined differently in the 13th edition. Will it make a huge difference if we follow the 12th edition rather than the 13th edition in this case?

Can anybody please reply asap?

 

[JStephen]

Sorry, no "ASAP" due to having to look up two or three different things to compare.
First off, the last addendum of the 12th edition appears to be the same as the 13th. Per the margin markings, these were updated in both the 2014 and 2015
The prior addendum includes a t-h term in the pressure component and excludes it in the weight definitions. Basically, that 8t-h is the roof weight, converted to inches of water and rounded off.
It seems the last several editions have continuously revised the overturn and uplift criteria. Some of this seems to be updates, some is just corrections in previous updates. I think some of this is trying to align the code with newer ASCE 7 provisions. Some of it is trying to reconcile wind uplift on the roof, which physics says is there, with the fact that the tanks generally don't blow over, either.
Most of these terms, if you work through the units, are just P/A and Mc/I type calculations.
A more specific question may get you a better answer.