Flat head question 1

[ME231]

I have an application where I need to attach a flat head to a shell. I go to Fig UG34 in order to get some design help - particularly wrt attachment of the head to the shell. The flat head is to be made integral to the shell. The ID of the shell could be between 1"-4". The min 0.375" radius speficied on Fig UG-34 (b-2) renders the design very unpractical for my application. Could anybody please advise what I should do?
How can I justify use of a corner radius less than the min specified in the ASME book. This is not a code application, however, we would like to design to the code.
Any advice will be much appreciated!

 

[gr2vessels]

The minimum radius specified by the code is related to the minimum shell diameter specified also by the code (6"). Your 1" diameter shell is obviously outside the code limits, hence the minimum radius is impractical to you. I would use a proportionate radius and try an alternative calculation for the strength of assembly.
gr2vessels

 

[ME231]

Thanks gr2vessels. Is there any basis you can think of at all for code qualification if I were to use the scheme you suggest?

 

[gr2vessels]

The ASME code does not prohibit the use of it and even stamp with the appropriate ASME stamp, for the design of any pressure equipment outside the scope of their recipe book. It does ask however, to use the appropriate tools, like FEA or other recognized design calculation tools, in order to prove that the components are not stressed beyond the allowable stresses listed in ASME Section II, Table D.
The idea of using the code allowable stresses is based on extensive studies, experience and tests in order to ensure the safe use of the mentioned equipment. Other than that, any calculation based on a approved method is acceptable to the code and the local legislation where you intend to use the equipment.
Cheers,
gr2vessels

 

[prex]

By integral you mean: machined from the same piece of metal?
With such a small diameter (but how comes that you can change it over a factor of 4?) you shall not be limited by the head thickness.
I mean that you'll find it easier to use a thickness 2 times or more than the minimum required.
Under such conditions (low diameter, high thickness) the stress induced in the shell by head deflection under bending will be negligible (not difficult to prove quantitatively).
Now that stress (or more correctly: that strain) is the main reason for providing a so generous radius by ASME VIII (only for larger diameters BTW, as correctly stated by gr2vessels).
This should be a logical way of proving that you stay within code provisions with a minimal radius.
Another consideration that I'll offer to you (but this is quite a personal position) is that, when in a structure you leave in place some excess metal with respect to the minimum required geometry, then you cannot harm vessel's strength, apart from considerations of low cycle fatigue, mainly connected to thermal expansion. So, if you have an excess thickness, you can consider that the radius you want to obtain is there, but is hidden inside the metal left.
As perhaps Michelangelo said, the sculpture is already there in the stone before starting, the only duty of the sculptor is to let it come out!

prex

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[GenB]

when you calc with integral and to the correct radious, the flat portion of the head becomes thinner,
you may be able to calc to a different formula where the head becomes thicker and use less or no radious at all.

 

[ME231]

Thanks. I have tried using the Roark's equations. It predicts lowers stresses and hence lower thickness requirements since there is no way to account for stress concentration.