AutoPipe Stress Analysis, When to apply ASME B31.3 Appendix P? 1

[corsa007]

Hi

Can anybody who is familiar with AutoPipe analysis provide me with some assistance.

When is it appropraite to apply ASME B31.3 appendix P to the pipe stress analysis.

I am finding that I am getting radically different results when the Appendix P option is active.

Corsa 007

 

[DSB123]

corsa007,
Yes I can confirm you will get different results as it is a different approach. If the results were the same why have Appendix P???

 

[corsa007]

DSB123,

Thankyou for your reply.

I maybe didn't word my first comment particulary well. I came to ask this question because I was getting such different results.

My question was, when should Appendix P be applied?

After some investigation I have concluded that my difference in results is mainly due the inclusion of Axial loads in the Appendix P analysis. Also Appendix P includes a sustained load combination of GrPT1 which is not present in the regular code.

My original question still stands though: Under what operating circumstances should Appendox P be applied over the regular code?

Regards

 

[JohnGP]

corsa007,
It's been a long time since I used AutoPipe, and there wouldn't have been an Appendix P back then, but as presented in the Code, Appendix P provides a more comprehensive method. Rather than me paraphrase, the actual wording is:

This Appendix provides alternative rules for evaluating the stress range in piping systems. The piping system is compliant with the displacement stress range requirements of the Code if the stress range evaluation of the piping system satisfies either the requirements of Chapter II or the requirements of this Appendix. This Appendix considers stresses at operating conditions, including both displacement and sustained loads, rather than displacement stress range only. The method is more comprehensive than that provided in Chapter II and is more suitable for computer analysis of piping systems, including nonlinear effects such as pipes lifting off supports.

So it's up to you - either approach can be used satisfy Code requirements. Intuitively if a particular layout throws up an issue with the basic approach, then try with Appendix P. If the different criteria are satisfied, then the problem goes away.

Cheers,
John

 

[LSThill]

ASME B31.3 Appendices P and S: Compensating for Shortcomings
Paper no. PVP2008-61714 pp. 377-385
doi:10.1115/PVP2008-61714
ASME 2008 Pressure Vessels and Piping Conference (PVP2008)
July 27–31, 2008 , Chicago, Illinois, USA
Sponsor: Pressure Vessels and Piping
Volume 1: Codes and Standards
ISBN: 978-0-7918-4824-1 ..

The 2004 edition of ASME B31.3 Process Piping Code [1] introduced both Appendix P and Appendix S Example 1; Examples 2 and 3 were included in the 2006 edition. Appendix P is to illustrate a nearly computer stress analysis basis by defining alternative rules for displacement stress range evaluation, and Appendix S contains examples describing how to satisfy the requirements of B31.3 when performing computer based stress analysis. As is possible with any extensive addition to any code, these first offerings contained shortcomings either explicitly or by lack of clarity. This paper discusses some of these issues, provides workarounds when using today's commercially available piping stress analysis software, and proposes revisions to both Appendices for the 2010 edition of the B31.3 Process Piping Code.
©2008 ConocoPhillips

http://dx.doi.org/10.1115/PVP2008-61714

L S THILL