B31.3 Piping Working Pressure

[engpes]

I am having anissue with a manufactured union (Kemper 1502) that is rated for 15,000 psi. This unit is certified to B31.3 (by DNV certificate).

The unit is a 6" XXH union with the same yield and tensile strength of my buttweld tee pipe fitting. When I calculate 6" XXH pipe I can only reach about 10000 psi (per B31.3 chapter IX - high pressure equation 34). The only components I have in the arrangement are the buttweld tee welded to the buttweld union.

My question is this:

1.) Why can I not get 15000 psi out of my 6" XXH tee fitting and the union is rated for 15000 psi?

2.) Is there a special calculation for fittings different from piping?

3.) Is there any calculation I can do other than a computer modeled FEA?

Thank you very much!!!

 

[MJCronin]

engps...

Suggest tat you re-post in the "Pipelines, Piping and Fluid Mechanics" forum

 

[Cockroach]

I have always argued against the blind use of recipe type equations without a proper understanding in the assumptions thereof. You need to look at Von Mises and not thin walled derivations such as the one you quoted. That assumption is that your wall thickness is uniform and less than one-tenth the inside pipe radius.

You can also pull classical cases from Roarks who does a much better job of matching your situation to variations in cases pertaining to a particular set of boundary conditions. The reference helps you get by without the use of elliptic integrals, which would be the initial study.

Unfortunately we are engineers here and not mathematicians, so derivation is not as important as knowing where to look.

Regards,
Cockroach