Torispherical head sizing

[Distill9]

When designing a torispherical head, the thickness can be calculated according to UG-32 (e) with specific values for "L" and "r", but in Appendix 1-4 (d) comes the general thickness equation for any given value for L and r.
When I used equation in UG-32 with L=D and r=0.06D I had a thickness value that from what I understand is the maximum minimum thickness, now if I start changing r value grater than 0.06D, thickness reduces.
So the questions are; what would be the recommended value for "r", can "r" be increased arbitrarily? and is there a recommended value for the head inside depth?

The only restrictions I found where:
1. L ? D0
2. 3t? r ? 0.06D0

Thanks for the help

 

[vesselfab]

EACH MANUFACTURER HAS ITS OWN RADIUS IT USES FOR IT'S STANDARD HEADS

MOSTLY DR = D-6"

IKR = .06D

HEAD DEPTH CHANGES WITH EACH RADIUS CHANGE