Dear Users ,
When I design a low pressurized storage tank ( as per API 650- Appendix F) . I have come across with a differences between 10 th edition , Addendum 4 ( December 5 ) and all others.

According to the 10 th edition , Addendum 4 ( December 5 )
F.5 Required Compression Area at the Roof-to-shell junction.
the total required compression area at the roof-to-shell
junction is the greater of those calculated from the following
equations:
A= (D^2)*(Pi-0,08*th)/(1,1*tan@) @:Roof Degree
A = (D^2)*(0,4*Pi-0,08*th+0,72*((V/120)^2))/(1,1*tan@)

First formula is similar to me. Cause this formula is mostly same in all editions.
But did you realize that, the second formula is only used in 10 th edition , Addendum 4 .
Why this formula is cancelled in latest editions. ?
This formula is reasonable . Cause it takes into consider both internal pressure and uplift wind load. ? Am I wrong. ?

Dear users ,when I calculate compression ring area , which formula should I use ? and why ?
Could you please explain me as quick as possible ? I would be so so appreciate.
Thanks in advance
Best Regards
Caner F.

In fact it was the same formula applied twice - for "design" and "operational" conditions.
In the first form, area is calculated based on internal design pressure.
In the second form, it was a try to guess a reasonable "equivalent operating internal pressure" i.e. the operating internal pressure plus reasonable wind uplift likely to be coincident with operational conditions.

The operational internal pressure was presumed as 40% of design pressure (however if the ratio of operating pressure to design pressure exceeds 0.4, the actual ratio has to be considered in formula).

The internal pressure equivalent to wind uplift was taken as 50% of the design wind uplift specified in 3.2.1 in 10th edn (and 5.2.1 in 11th edition) as 1.44 kPa *((V/190)^2) or 30 lbf/ft2 *((V/120)^2) on horizontal projected areas of conical or doubly curved surfaces.
BTW, you can see that the second SI formula is wrong in 10th edition, since considers V/120 instead V/190.

Now you have all elements to say it is reasonable or not.
IMH, if you consider the second formula gives you a conservative result in your calculation, you still can use it despite it is not longer considered by 11th edition.

Best regards.

Dear Mariog,

Your explanation is so useful.Thank you.
I have considered first formula.

Best Regards.
Caner