Posted by Neil Cookson on November 5, 2004 at 15:27:00:

I am tring to assess the permeability of helium gas through Flurocarbon O-rings (James Walker FR58/90)as we are conducting a high pressure leakage test in our ball valves for the Offshore industry.

The test is carried out at ambient temperature introducing a 90% Nitrogen/ 10% Helium gas mix at around 310 bar into the body of the valve. There is an acceptable leakage rate for Helium which we then use to estimate the actual leakage of methane on site.

For us to assess whether the test will be worth doing we need to understand what amount of helium that will permeate through the O-rings.

Hope someone can help.

Neil

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Posted by Diffusion in Polymers Platform on November 06, 2004 at 22:03:37:

In Reply to: Helium permeability in Fluorocarbon O-rings posted by Neil Cookson on October 06, 2004 at 13:37:16:

Dear Neil,

For the O-ring that you describe, a Fluorcarbon Terpolymer Type 2 composed of Tetra Fluor Ethylene [-C2F4-], Hexa Fluor Propylene [-C3F6-]
and Vinylidene Fluoride [-C2F4- +3% H2], having a density of 1.8 gram/cm3, we have the following data for 25 degrees Celsius and 1 atmosphere:

D Helium = 1.6 x E-9 m2/s
S Helium = 0,0056 m3 stpHe / m3Polymer x bar.

Permeability in volume fraction:
P Helium = 9,0x E-12 m2 / s x bar

Permeabilty in mass:
Helium density: 1.6 E2 gram/m3;
P Helium = 1,5 x E-9 gram / m x s x bar.

With kind regards,
Diffusion in Polymers Platform