B31.3 2004 Questions 1

[StressGuy]

Alright, first question is - will they actually get this thing out in 2004? There's basically two weeks to the end of the year and still no official word on it.

But, here's the real question - I obtained notes from a presentation on changes in the 2004 edition, and a question has been raised. Specifically regarding the new Appendix P, providing alternate rules for flexibility analysis. The new equation intends to consider the effect of axial stresses on the pipe, which have typically not been considered.

Including the axial effects isn't so much a problem, we have to consider it's effects anyway for cases where axial stress is significant, like jacketed piping systems. The question come from the definition of Fa as the axial force, including that due to pressure. Pressure has been considered a primary loading, so there's a question now why it is being considered as part of a secondary stress evaluation. For a fully pressurized line, the axial component due to pressure can eat up a significant percentange of the stress.

Maybe when the actual code comes out, it will be clearer. Right now I'm just able to operate from notes to a free seminar what I wasn't able to attend in person.

I'm posting this here and in the piping discussion in hopes fo finding someone who knows the answer.

Thanks,

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[bvi]

Appendix P evaluates operating loads, including both primary and secondary type stresses. It looks at stress ranges, considering all loads present in the system (other than occasional loads e.g. wind/earthquake). In the existing rules, the sustained stress (including the pressure component) is subtracted to get the allowable thermal expansion stress range. In Appendix P, it is not subtracted from the allowable, it is included in the calculated stress which is compared to the allowable.