Ellipsoidal Head Acceptable Approximation 1

[Shmulik]

UG-32(d) defines Acceptable Approximation for 2:1 ellips. head as one with knuckle radius of 0.17D and a spherical radius of 0.9D.

Kindly, my question is: may a head still be considered 2:1 ellipsoidal where knuckle rad. > 0.17D and/or spherical rad. < 0.9D ?
Can we have any answer for it from the following Interpretation?

_________________________________________________________
Interpretation: VIII-1-01-155
Subject: Section VIII, Division 1 (2001 Edition, 2002 Addenda); UG-32(d) and Appendix 1, 1-4
Date Issued: June 13, 2003
File: BC03-6l9

Question (1): When designing an ellipsoidal head with a head depth to diameter ratio different than one-fourth, must the provisions of 1-4(c) be satisfied?

Reply (1): Yes.

Question (2): When designing a torispherical head with dimensions different than described by either UG-32(d) or UG-32(e), must the provisions of 1-4(d) be satisfied?

Reply (2): Yes.
_________________________________________________________

 

[prex]

Well, the answer is in your words: if a code requirement is not satisfied, how can you ask yourself whether you are still within the code?
However with your conditions you have a head with an inside depth higher than the one for a 2:1 , and the required thickness should be smaller. By using 1-4(d) you can go from a full hemispherical head to a quite flat head.

prex

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[vesselfab]

every head manufacturer has different radii.

the .9d/.17d is very close to a ""true"" 2:1 ellipsoidal head.

the torisherical mentioned in question 2 is a different animal alltogether and again, all manufacturers are different and heads should be checked to that manufactur's radius given.

the ""and/or"" in your original question kind of through me off.

 

[jamesl]

It depends. If the head crown and knuckle radius are within the tolearances specified in UG-81, the head can still be considered 2:1 ellipsoidal. If it is out of the tolerance, then you need to use Appendix 1-4.