Piping design in full vacuum conditions

[jcll]

Dear Coleagues:

I have not been able of finding one code or officially wel done replay to the following question:

*When designing mechanically piping systems in vacuum conditions what is the effective vacuum calculation lenght I must use?.

The ANSI is driveng me to the ASME VIII, div.1 vacuum calculation sections, however this question is not really explained. There are some people that consider the ellbows as rigidizing parts in order to minimize the effective acumm lenght however I believe it is a mistake due the ellbows are concentrated stresses parts and it is not a safety place for handle...

The standard solution used by me is adding (if needed) some vacuum rings but if someone knows some real and/or official criteria better than mine please let me know.


Regards and Merry coming Christmass for all/JCLL

 

[prex]

I agree with you that elbows cannot be considered as effective restraints.
Of course if you add rings (correctly dimensioned per ASME VIII) the free length will be defined by them. Otherwise I can see only reducers (to be checked also per ASME VIII), flanges and caps or heads as effective restraints.
Otherwise just work with an infinite length: I would consider this one as the typical condition for a piping (not of course for a vessel).
There is no other rule than what is in ASME VIII (and other codes): the effective length is to be taken between effective restraints, and a restraint is to be judged as effective based on code rules for rings, heads and cone transitions. prex

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