Calculating pinhole leak rates through a pipe under pressue
Calculating pinhole leak rates through a pipe under pressue
(OP)
I'm a little embaressed by the fact that I don't know how to do this, but as they say, "if you don't use it you lose it"
I have a pinhole leak in a 12" pipe that is pressurized at around 300 psi and has a gas flow of approximtely 300,000 lbs/hr. I just need to come up with a conservative estimate as to how much is leaking out of the pinhole. Are there any plug and chug calculations that I could use to get me within +/- 10%?
This seems pretty straight forward, and was wondering if someone with more experience could help.
Many thanks.
I have a pinhole leak in a 12" pipe that is pressurized at around 300 psi and has a gas flow of approximtely 300,000 lbs/hr. I just need to come up with a conservative estimate as to how much is leaking out of the pinhole. Are there any plug and chug calculations that I could use to get me within +/- 10%?
This seems pretty straight forward, and was wondering if someone with more experience could help.
Many thanks.





RE: Calculating pinhole leak rates through a pipe under pressue
Q is volume of gas in MCF/hr based on .6 gravity gas
D is the diameter in inches
P is pressure in line in psia
RE: Calculating pinhole leak rates through a pipe under pressue
Read this FAQ by clicking on it: FAQ798-1196: Mass flow rate of a gas through an orifice during choked conditions
Milton Beychok
(Visit me at www.air-dispersion.com)
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RE: Calculating pinhole leak rates through a pipe under pressue
Paul
www.ostand.com
RE: Calculating pinhole leak rates through a pipe under pressue
But only if you are so rich.
Process Engineer in Vietnam
RE: Calculating pinhole leak rates through a pipe under pressue
In the second of your referenced formulas with respect to using Z, please explain how one obtains Cv or Cv or k.
My reason for the question is that with constant Z, the ratio of the specific heats k is not equal to Cp/Cv.
You know that I have raised this issue previously.
RE: Calculating pinhole leak rates through a pipe under pressue
using Z, please explain how one obtains Cv or Cp or k
RE: Calculating pinhole leak rates through a pipe under pressue
HAZOP at www.curryhydrocarbons.ca
RE: Calculating pinhole leak rates through a pipe under pressue
Now that you have chipped in, I am no longer needed and I am "outa here". Bye!
Milton Beychok
(Visit me at www.air-dispersion.com)
.
RE: Calculating pinhole leak rates through a pipe under pressue
Good luck,
Latexman
RE: Calculating pinhole leak rates through a pipe under pressue
G/P=[sqrt(Mol/(RT)]*exp[U^2*Mol/(2RT)-1/2]
Where G = mass flux ie kg/m^2/s
R=universal gas const
and upstream conditions where
T=absolute static temp
P=static pressure
U=velocity
Regards
RE: Calculating pinhole leak rates through a pipe under pressue
Good luck,
Latexman
RE: Calculating pinhole leak rates through a pipe under pressue
Thanks, I'd like to see the equations.
Regards
RE: Calculating pinhole leak rates through a pipe under pressue
So I do not reproduce the entire chapter, I assume you are interested in area change and external heat exchange to achieve isothermal choked flow. The equation that appears it may be beneficial to you is:
dT/T = 0 = (k-1)M^2/(1-M^2) x dA/A + ((1-kM^2)x(1+(k-1)/2 x M^2))/(1-M^2) x dTo/To
To = stagnation temperature used as a measure of the energy effects of heat transfer.
I think you know the other variables.
Good luck,
Latexman
RE: Calculating pinhole leak rates through a pipe under pressue
Q = D^2 * P
And get just as close, in engineering terms.....
RE: Calculating pinhole leak rates through a pipe under pressue
Good luck,
Latexman
RE: Calculating pinhole leak rates through a pipe under pressue
RE: Calculating pinhole leak rates through a pipe under pressue
Good luck,
Latexman
RE: Calculating pinhole leak rates through a pipe under pressue
Regards
RE: Calculating pinhole leak rates through a pipe under pressue
I believe that many of us would agree that the U.S. EPA, the Federal Emergency Agency and the U.S. Department of Transportation are very interested in evaluating the risks incurred from accidental leaks of pollutants or flammable gases. The equation (referred to earlier in this thread) in
FAQ798-1196: Mass flow rate of a gas through an orifice during choked conditions has been recommended for use by all three of those agencies. See the two references below and read them online at the links provided:
(1) 'Handbook of Chemical Hazard Analysis Procedures', Appendix B, Federal Emergency Management Agency, U.S. Dept. of Transportation, and U.S. Environmental Protection Agency, 1989. Handbook of Chemical Hazard Analysis, Appendix B. Click on the PDF icon, wait quite a bit and then scroll down to page 391 of 520 PDF pages.
(2) "Risk Management Program Guidance For Offsite Consequence Analysis", U.S. EPA publication EPA-550-B-99-009, April 1999. Guidance for Offsite Consequence Analysis. Look at Appendix D: Equation D-1 in Section D.2.3 and Equation D-7 in Section D.6
As noted by by others in this thread, the original poster asked for calculation methods that would provide his needs within +/- 10 percent. The equation recommended by the above agencies will do just that ... and it is all that is really needed for a great many engineering problems. In such cases, practical engineers (as differentiated from physicists and research scientists) are not interested in spending endless hours trying to determine how many angels would fit on the head of a pin.
Milton Beychok
(Visit me at www.air-dispersion.com)
.
RE: Calculating pinhole leak rates through a pipe under pressue
Welcome back!
The first of your referenced equations must use stagnation conditions to be correct. Also, what is meant by real density?
The first equation is approximate, only if the upstream Mach numbers are low.
If the agencies that you reference, use other than stagnation conditions, they are misapplying choked flow equations.
RE: Calculating pinhole leak rates through a pipe under pressue
RE: Calculating pinhole leak rates through a pipe under pressue
dcasto:
Bravo! I am giving you a second star for being a voice of sanity. Not every problem requires a Ph.D. thesis.
Milton Beychok
(Visit me at www.air-dispersion.com)
.
RE: Calculating pinhole leak rates through a pipe under pressue
I ended up using an equation from Chemical Process Safety Fundamentals by Daniel Crowl (4-40), and double checking my results with dcastos's and mbeychok's equations, and was close enough. I was also fortunate enough to be able to see the leak for myself and visualize my answer to see if it made sense.
I know that these are probably not to most accurate answers, but I was told to be conservative and use "engineering judgment".
Thanks again!
RE: Calculating pinhole leak rates through a pipe under pressue