API 650 - Section F.4.1 1

[sme75]

The equation for the maximum design pressure was modified with the 2008 addendum. The variable Fy is described as the lowest minimum specified yield strength of the materials in the roof-to-shell junction. Is the value of Fy to be taken at the design temperature of the tank?

 

[sme75]

To add to the above question -

If a tank has a 304 stainless shell and is reinforced with a carbon steel angle are you required to automatically use the lower yield strength of the stainless steel for the maximum pressure calculation even if the area of the carbon steel is say three times the area of the stainless steel?

 

[JStephen]

I haven't read the section in question, but sounds like you are interpreting it correctly. It was probably written for carbon steel, where differences in yield strength would be fairly minor (32 ksi vs 36 ksi, for example).

There's a new appendix for combined cs/ss tanks, I think, but am not familiar with the contents. Anyway, note that a cs compression ring on a ss tank will develope hoop stresses due to differential thermal expansion of the cs and ss.