Helium to Methane Correlation

[psi3000]

I am planning to perform fugitive emission testing on a valve using helium as the test medium. I would like to correlate the results to methane. I cannot seem to find any information on how to correlate. Any help is appreciated.

Thanks,
LMC

 

[Flareman]

psi3000
Not knowing quite what test you are performing makes an accurate response difficult.
Simply on the basis of how much methane can get through the same hole as a known quantity of helium is relatively simple to estimate because most gases can be (almost) related using the equalizing parameter

mass flow * sqrt{ abs temp / MW)= const (for guesses)

This goes awry when you have really high pressures or extreme temperatures which change the characteristic of the gases, but we'll suppose you don't.

Fugitive emissions also implies leakage (through the stem ?) Does the condition of either gas affect the tolerances of the packing or the trim? Testing with He at room temperature may not be the same as operation with methane at -50 (say).

Anyway, that's my 5 cents worth.

David

 

[psi3000]

Flareman,
Thank you for your information. I am planning to pressure the valve to working pressure (285psi for 150 ANSI valve, 1480psi for 600 ANSI valve), and check for emissions at the valve stem. This testing will be performed at ambient temperatures. In the equation you provided, is the constant the same for all gases? Will this equation work for these pressures?

Thanks again for your help,
LMC

 

[Flareman]

psi3000
Basically the constant is system specific, but constant for all gases. It is based on ideal gases and assumes that the viscosities of the gases are also equal and constant. This is a miniscule error in pipe flows but could be a hiccough in your situation at 1480 psi. The basis is that the parameter is present in incompressible flow and compressible flow formulae. However, friction factors change with gas (or liquid) characteristics.
My formula is OK for "wet finger" stuff. If you're looking for science and 2 decimal places of accuracy you probably need to develop something from first principles (or ask someone else )

David

 

[mbeychok]

psi3000:

Are you familiar with the U.S. EPA's publication "AP 42 Compilation of Air Pollutant Emission Factors" which is available online at

http://www.epa.gov/ttn/chief/ap42/index.html?

Many years ago, the EPA hired contractors who spent a few years in petroleum refineries and in organic chemical synthesis plants measuring fugitive air pollutant emission factors from relief valves, piping valves, open-ended piping lines or drains, piping flanges, sample connections, and seals on pump and compressor shafts.

Chapter 5 of the EPA's online AP-42 publication includes the report EPA-458/R-95-017, "Protocol for Equipment Leak Emission Estimates" which explains in great deal how that that work was done. It would probably be quite useful for you to read that report.




Milton Beychok
(Visit me at www.air-dispersion.com)
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