Crown radius for torispherical head

[arun17]

Hello,
I would like to know how to select or decide about the crown radius for a torispherical head for a vessel. Is there any relation of this radis to the shell radius for optimum design. In code it is said the knuckle radius dhould be 6 % od the crown radius, but nothing is stated about how to decide the crown radius.
Thanks


"Knowledge is power"

 

[JStephen]

Check with your head supplier to see what the common shapes available are. See App. 1 which gives thickness for various shapes. An 80/10 (ie, crown radius = 80% of diameter, knuckle radius = 10% of diameter) is fairly common. "Std ASME" is 100/6, I think. 2:1 elliptical is fairly common.

 

[arun17]

Thanks for the reply.

But if you see the formula given in the code, the thickness of a torispherical head is :
t=P*L*M/(2*S*E-0.2*P) + CA

where L is crown radius
M=.25*(3+sqrt(L/r)) ris knucke radius.

From this I can conclude that thickness is proportional to crown radius, so I should keep it minimum possible. But is there any lower limit on it?

"Knowledge is power"

 

[prex]

Yes: the lower limit is with a hemispherical head (with also minimum thickness).
The height of a formed head is a matter of size (total vessel length or height), sometimes may be related to the process, but is mainly a matter of cost (and of availability of course).
Hemispherical heads are the optimum for thick vessels, 2:1 elliptical are the commonest for medium to low pressures, and torispherical are well adapted to low pressures.
To get some figures you should design two or three heads for the same vessel and ask the head supplier for respective costs.

prex

http://www.xcalcs.com

Online tools for structural design

 

[PEHasan]

For torispherical head, inside crown radius is equal to the outside diameter of the skirt.

Regards,

PEHasan

 

[JStephen]

Not so, it can be that radius, but can vary as indicated above.

 

[SnTMan]

One caution, many vendors sell torispherical heads that dimensionally are NOT Code heads. Check what you are getting.

Regards,

Mike

 

[jodyed]

Right you are snTMan, When I order torispherical heads, I specify "ASME" if that's what I want.

Also, watch out for "Minimum Thickness after Forming" issues. These can bit you if you don't conceder it.

Hope this helps,

jodyed