ASME B31.3 flexibility analysis criteria 9

[NovaStark]

Good day all,

I'm trying to get some clarity for the criteria of Formal Analysis for Flexibility under ASME B31.3

319.4.1 Formal Analysis Not Required. No formal analysis of adequate flexibility is required for a piping system which
(a) duplicates, or replaces without significant change a system operating with a successful service record
(b) can readily be judged adequate by comparison with previously analyzed systems
(c) is of uniform size, has no more than two points of fixation, no intermediate restraints, and falls within the limitations of empirical eq. (16)9

For (a) what exactly is meant by "Without significant change", if I change the material from carbon steel to stainless steel does that count as significant ? Or if I just add in a flanged joint, etc.


Can anyone with any experience assist me here?

 

[XL83NL]

Just review this multi-star post ...

http://www.eng-tips.com/viewthread.cfm?qid=189629

 

[BigInch]

I think that's the record for the most little purple stars given on any individual post in ET's entire history.

 

[XL83NL]

As an adder to JohnBreen's post, the wonderful book by Peng (also referenced by John here before), has some useful, or at least interestingly fun to read section on the matter of ASME B31.3 flexibility analysis criteria:
- section 1.5, last paragraph
- section 3.10, Field Proven Systems

 

[NovaStark]

I'll try to get a copy of that XL83NL.

However after reading that footnote and John's post, I don't feel that I should ever use that equation and still at least try to do some kind of analysis even if it becomes one of stress = Force/ Area.

It seems the limits sometimes may wor or may not and appears arbitrary. (I have seen someone here reference that equation before and say that y=0 even though the system was restrained and actually quite hot from ambient)

 

[XL83NL]

Use of that equation can be useful, provided one understand the limitations and possible adverse consequences, as outlined above.

I've tried to explain the equation to our (junior) piping engineers as a tool, one of many which they can use when they route piping systems to verify if a system has sufficient inherent potential flexibility. Verifying this is useful as it will minimize the number of iterations for stress analysis later, and give them more insight into piping stress basics. They do not learn from this by just using the equation, it's a back and forth game between the piping and stress engineer, where both learn from eachother from eahc iteration step.

After a formal (e.g. computer) analysis can be done to meet the B31.3 requirements. Again, the equation shall only be used if one understands the limitations and applies them where applicable.

 

[uaepiping]

Dear John Breen,
Why don't you write a book on piping stress analysis?
It would definitely be 'best seller' among engineers like us "trying to learn piping".
Our regards to Mrs. Breen, but persuade your beautiful bride that many people would get benefit from your work.

 

[SNORGY]

I'm pretty sure that John has indeed written a book or books, or has participated in writing a book or books, in this field. Certainly Charles Becht IV has.

 

[moltenmetal]

XL3NL, John Breen's post should become a FAQ in my opinion, and quickly!