Torispherical formed heads w/small knuckle radius
Torispherical formed heads w/small knuckle radius
(OP)
I have done some searching and have been unable to come up with an answer to the following quandaries...
API 620 and ASME Section VII, div 1 does not allow for formed heads with knuckle radius to diameter ratios (r/D) of less than 6%. What is the reasoning behind this and why was 6% chosen as the limit? Are there any accepted standards or codes that give a method to calculate thickness or allowable pressure for formed heads with r/D less than 6%?
Any guidance would be appreciated.
Any guidance would be appreciated.





RE: Torispherical formed heads w/small knuckle radius
ASME Section VIII, Div. 1 does not prohibit the use of a torispherical head with knuckle radius to diameter ratios (r/D) of less than 6%. It simply states that the thickness for a torispherical head that meets that requirement can be determined by formula (2) of UG-32. See excerpt:
"UG-32(d): Torispherical Heads with ts/L ~ 0.002. The required thickness of a torispherical head for the case in which the knuckle radius is 6% of the inside crown radius and the inside crown radius equals the outside diameter of the skirt [see (i)] shall be determined by..."
For a torispherical head with a knuckle radius to diameter ratios (r/D) of less than 6%, see U-2(g). I would recommend you have an experienced engineer design the head per ASME Sec. VIII, Div. 2, Part 5 (using Div. 1 allowables if the head is for a Div. 1 vessel).
Hope that helps!
RE: Torispherical formed heads w/small knuckle radius
For the API-620 approach, the thickness becomes unreasonable with smaller radii, so there's not a specific requirement, just a recommendation.