Required thickness according to API 620

[Andres Romero]

Hello everyone, I need to calculate the required thickness for a cylindrical-conical-cylindrical stainless steel tank, and I'm having trouble selecting the formulas.
Which formula should I use?


Do I have to use this first formula for the cone portion?





Or can I use this other one for everything?




I also have doubts about whether I have to enter the values of W and F in negative or positive to calculate T1 and T2.

I am attaching a drawing of the tank in question.

Best Regards
Andrés R.

 

[JStephen]

Use the first two equations for the cone. Check top of cone, bottom of cone, places where plate thickness changes and other intermediate points to confirm which locations control.
W and F will both be negative, with loads above the section in question acting down.
Pressure uplift on the roof is being offset by gravity loads. Depending on the pressure, net T1 result may be positive or negative.
The controlling case may be empty + pressure, full with no pressure, or full + pressure.