Boiler Code Sect.VIII UG-37 Need clarification on Rapid Fluctuation 1

[AquaMgr]

Hello,

I need clarification of the term "rapid fluctuation" when related to the material response of a steel pipe under pressure.

Scenario: Application of acoustic sensors at an Hydro Power Plant. 1.5" hole cut in pipe to allow for wetted surface of sensor via feed through mounted and sealed in cut hole. When referencing ASME Boiler Code sect. VIII, UG-37, what is meant by rapid pressure fluctuation?....a cycle of rapidly fluctuating pressure such as in an engine or something less than this?
The pressure fluctuation in the scenario above would be caused by the rapid closing of the wicket gates of the turbine...high pressure but a singlular occurance....
Comments?...anyone?...

 

[metengr]

When referencing ASME Boiler Code sect. VIII, UG-37, what is meant by rapid pressure fluctuation?....a cycle of rapidly fluctuating pressure such as in an engine or something less than this?

Where do you quote rapid pressure fluctuation? ASME Section VIII, Div 1 Part UG-37 concerns reinforcement calcs for openings in shells and formed heads. UG-21 deals with design pressure.

 

[CodeRef]

I believe you are stating the requirement given in UG-36(c) which addresses exemptions from reinforcement other than that inherent in the construction (within the specified conditions) for openings in vessels not subject to rapid fluctuations in pressure.
Because there isn't any value given as to the amount of fluctuation, it is up to you to bring to the attention of and satisfy your AIA/Authorized Inspector, who would follow through with his agency to define this paragraphs intent. I am sure if you ask it in a general discussion forum like this, you may get multiple opinions, but will still need to satisfy the AI who will review for compliance with the Code.

One question, this is piping and not a vessel? Why apply Section VIII-1 to openings in pipe when clearly this paragraph references shells and heads as metengr stated?


There are three kinds of people in this world; those who can count and those who can't.

 

[AquaMgr]

Thank you for answering so quickly....
You are correct in that I intended to reference UG-36.
We should be able to point out to the Corps Engineer that rapid pressure fluctuation is not rapid pressure change, but rather repeated pressure surges, as would be experienced on a pressure pump cylinder head, not a rapid change in pressure as with a load reject at a hydro plant.

Everyone I spoke to agrees with this. However, I was not able to find a print reference. We are talking about millions of cycles per life, not as in our case, a few per year. One person I spoke to said that even an air compressor reservoir, which cycles many times per day would not be considered rapid fluctuation.

Do you know where,if anywhere, that the Code makes any distinctions in fluctuation frequency?

We use UG-36 because it is accepted in the hydro power industry as standard...the pressures in the pipe at a hydro plant are regularly as high as 1000 psi.

 

[prex]

IMHO the only intent of the code in the wording 'rapid fluctuations in pressure' may be to stay away from fatigue phenomena; so not only how fast they are, but also the amplitude and the number of occurences are relevant.
Of course this is my interpretation, but, CodeJackal, before discussing with an AI, one must have his own position...
I would also add that even fluctuating piping loads on the nozzle should be considered relevant before utilizing the code exemption.

prex

http://www.xcalcs.com

: Online tools for structural design

http://www.megamag.it

: Magnetic brakes for fun rides

http://www.levitans.com

: Air bearing pads

 

[CodeRef]

Yes, I agree, Be prepared to defend your position before submitting to the AI.
Those privy to the background of this Code reference (Code Committee)and history would be helpful. I have checked back as far as I could and only know it has been in the same paragraph of the Code as far back as the summer 1977 Addenda and only one interpretation (1986)which the reply stated that the Code does not define rapid fluctuations in pressure.
Good Luck!

There are three kinds of people in this world; those who can count and those who can't.