B31.8 Compressor Station Replacement of existing lines and required analysis

[ColonelSanders83]

Hello All,

If I replace the piping in aa B31.8 compressor station with an exact duplicate of what is currently installed, do I need to perform an new pipe stress analysis?

The reciprocating compressors at this station have been in operation for more than 40 years and the decision has been made to replace the piping due to corrosion damage.

B31.3 has clause 319.4.1(A) Formal Analysis not required "duplicates, or replaces without significant change, a system operating with a successful service record"

B31.8 has paragraph 832.3 Flexibility Requirements "Formal calculations shall be performed where reasonable doubt exists as to the adequate flexibility of the system.
And 833.7 Flexibility Analysis (a)There is no need for a formal flexibility analysis for an unrestrained piping system that (1) duplicates or replaces without significant change a system operating with a successful record.

Are there any other requirements (besides a lack of knowledge of the above clauses) that may drive the requirements for a new analysis?


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[BigInch]

B31.3 has no standing in a B31.8 design.

If the system is unrestrained and assuming that a previous stress analysis was performed, then no. If you have no doubt that the system is adequately flexible, then, again, no.

Assuming temperatures and ranges have not changed significantly within recent history (5 yrs), probably no other questions would come to mind.

PS Exactly means exactly.

Reaction to change doesn't stop it

 

[ColonelSanders83]

Biginch, your response leads me to the following two questions.

1) B31.8 833.7 invokes no requirement that a previous analysis was performed. Merely "duplicates a system with a sucessfull service record". Where does the requirement for an analysis come from?

2) B31.8 does not use the word "exactly" but rather "without significant change". Where does your ps come from?

A question properly stated is a problem half solved.

Always remember, free advice is worth exactly what you pay for it!

http://www.techtran-hou.com/

 

[BigInch]

Actually it says that you might not need a flexibility analysis. It says nothing about not needing a stress analysis, even if only hoop stress. I think that if you have the existing design calculations, you might get away without doing them again. If you don't have any record of original design, do you really think that PHMSA will close their eyes and simply allow you to blindly clone it? Do you really think your company will let you do it that way? If so, that may be an even greater problem.

Find what you like to do, earn a living at it, and then make your lifestyle fit your income. — Chuck Yeager

 

[ColonelSanders83]

See, that's the bit I'm getting hung up on. Its been operating for 40+ years..... The code specifically says I can replace existing designs with successful service history. Why the additional requirement?

A question properly stated is a problem half solved.

Always remember, free advice is worth exactly what you pay for it!

http://www.techtran-hou.com/

 

[BigInch]

Right, but the code does not make the decision about whether, or not, you will be allowed to operate. AS I seem to say more and more these days, Codes only state the minimum DESIGN requirements for a system. It turns out that government agencies, licensing, operating and safety administrations, authorities, hazard control authorities, insurance companies, testing and certification agencies, etc. have other concerns and often other requirements as well. Meeting code (by doing the least possible amount of work by the way) is probably nowhere on their lists, if indeed that means anything to them at all. Son, you just the engineer here at this table.

The P.S. comes from the guy that wrote the B31.3 code. I'm a bit more "flexible" myself.

Find what you like to do, earn a living at it, and then make your lifestyle fit your income. — Chuck Yeager

 

[ColonelSanders83]

Nowhere do I see a hard requirement being put forth.

In the conversation with the project team I see a lot of personal opinion, and people hiding from making a decision. If there are regulations dictating requirements for safe operation and that a flexibility analysis is required, by all means point me the chapter and verse of that requirement.... That's why I am asking the question.


A question properly stated is a problem half solved.

Always remember, free advice is worth exactly what you pay for it!

http://www.techtran-hou.com/

 

[BigInch]

Fine. If you're looking to clearify the muddy water,

Formal calculations shall be performed where reasonable doubt exists as to the adequate flexibility of the system. See para. 833.7 for further guidance.

It doesn't get any clearer than that. If there is any doubt as to adequate flexibility, work out the 3 conditions given in 833.7(a) and 833.7(b) and that should fix you right up. The rest of the story and subsequent requirements will be allowed to develop in due time. Who has any doubts, or who's doubts are important to the result, if unknown at this time may or may not become apparent at a later date.



Find what you like to do, earn a living at it, and then make your lifestyle fit your income. — Chuck Yeager