Minimum Thickness for P.V. Heads

[commandotom]

Hello. I was hoping someone might be able to help me out.
I've completed doing an API510 inspection for a customer. From the U-1;
The vessel (1966) fabricated from SA264 (1/16th 316L on SA212-B backing)
MAWP=100psi @ 600F, Dia.=96", Crown Radius=84", Knuckle Radius=6.5"
Bottom Head 0.496", Top Head 0.410
Allowable Stress for Mat'l= 17500; Efficiency=0.85
Assumed; Torisphereical Heads (no Drawings)
When I crunch the numbers for min "t" I get 0.500"
So the thickness specified for the heads is less than the calculated value.
What am I missing? I don't have access to the Code for that period.
Just want to be able to explain to the customer what is going on here.
Suggestions??
As always thanks in advance.

 

[fegenbush]

I would not assume E = 0.85. It is quite possible to fabricate a 96" diameter F&D head in one piece. If there is a seam, it is also possible that it was fully radiographed. If the original data report is available (or there is a National Board number), I would consult that as a first reference. It is for this reason that I NB register all new vessels under my purview.

 

[jamesl]

I don't have access to the 1966 code edition. In the old days, ASME Code did not have UW-11(a)(5)(b) requirements for seamless heads. So if the head was seamless, then E=1.0. You would need only 0.4" thick head if E=1.0.

 

[commandotom]

Thanks James I think you got it. I was using the E=0.85 specified for the shell. It is a seamless head so the E=1...correct???

 

[jtseng123]

google "Brwon and Young 1st edition of procee equipment design" , you will see an unprintable pdf version of 1968. Your questions of code allowable stress, joint eff, formula are all there. To get a hard copy, cost $20. Read that first before you jump to conclusion. It may surprise you.

 

[JStephen]

Note that in the current code, the E for a head depends also on the radiograph of the shell-to-head seam.