SS Sheet Permeation
SS Sheet Permeation
(OP)
Does anyone know where I can find information on the properties of SS sheet as it pertains to permeation at elevated temperatures?
We have .001" 316L stainless steel sheet used as a pressure diaphragm with approximately 200 psi of Nitrogen behind it.
We have run numerous units though aging tests (one week at 400°F) and every sample has shown a reduction in pressure, though these reductions have not been consistant. Some sample units will decrease 5 psi and others up to 50 psi.
We have ruled out all possible causes of this - except permeation throught the diaphragm. Has anyone seen this phenomenon before, or know where I can find information concerning this?
We have .001" 316L stainless steel sheet used as a pressure diaphragm with approximately 200 psi of Nitrogen behind it.
We have run numerous units though aging tests (one week at 400°F) and every sample has shown a reduction in pressure, though these reductions have not been consistant. Some sample units will decrease 5 psi and others up to 50 psi.
We have ruled out all possible causes of this - except permeation throught the diaphragm. Has anyone seen this phenomenon before, or know where I can find information concerning this?





RE: SS Sheet Permeation
RE: SS Sheet Permeation
Our only idea was that the gas was permeating at the elevated temperature, but showed no leak at room temperature.
RE: SS Sheet Permeation
RE: SS Sheet Permeation
If the background rate is still too small to be causing the observed pressure drop, then you may be seeing the N2 becoming chemically absorbed (diffused) into the metal; you could look into having a chemical analysis done of the sheet material before/after testing...
RE: SS Sheet Permeation
We perform helium leak check on all units before any testing begins - no leaks were detected. After aging the units and observing the decrease in pressure, we re-checked the helium leak - still no detectable leaks found.
Diaphragm is extremely thin - .001". Anyone know where I can find permeation information for 316L SS?
RE: SS Sheet Permeation
You can get gas leakage if there are defect paths. I have seen this in bar products along the length of the bar.
How are you He leak testing? You need to make you test more sensitive.
My guess is that you are welding through inclusions in the SS and creating leak paths at the weld joint.
Are you using special grades of SS? If you have leaks you need to be using ELI or high purity materials. The remelted grades will have fewer inclusions.
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