HDPE permeabilty
HDPE permeabilty
(OP)
Hi;
I want to know what is the range of permeability of HDPE liners in CNG4 vessels in different pressures.is there any plots showing this.any help would be appreciated.
thanks
I want to know what is the range of permeability of HDPE liners in CNG4 vessels in different pressures.is there any plots showing this.any help would be appreciated.
thanks





RE: HDPE permeabilty
RE: HDPE permeabilty
RE: HDPE permeabilty
Permeability to CNG(I mentioned CNG4)
RE: HDPE permeabilty
RE: HDPE permeabilty
There are 4 main catagories in CNG(Compressed Natural Gas)vessels.Type 4 wich is called CNG4 has non-metallic liner(typicaly HDPE(High Density Polyethylene)).and what i want to know is HDPE permeability in different CNG pressures.
Thanks
RE: HDPE permeabilty
For the same reason it is know that car fuel tanks (PE) are very permeable to gasoline (petrol) and lose the gasoline way too fast. To prevent that the standard process is to react the inside layer of the PE with fluorine gas. This gives a thin PTFE-like coating that is much less permeable to alkanes like methane, gasoline etc.
Fluorine is not nice stuff to work with but I know that the gasoline tanks are treated that way on a huge scale so it must be economical to do so and manageable. Maybe you could do something similar.
RE: HDPE permeabilty
thanks for your consideration,but my question is remained.I know that HDPE is currently used in CNG4 vessels(vessels with non-metalic liner overwrapped with composite filaments) but i don't know what process is done for manufacturing these liners.my question is the permeability range in standard manufactured CNG4 vessels.
thanks
RE: HDPE permeabilty
RE: HDPE permeabilty
I would expect that, the smaller the molecule the higher the transmission rate, so CNG will be quite high.
Major reputable raw materials manufacturers should be able to advise. They normally have this sort of data in their technical departments, although this might not be available to the general public, so you will need to talk with a tech service person.
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RE: HDPE permeabilty
Cheers
alleak
RE: HDPE permeabilty
This is due to a more linear molecule allowing a higher degree of crystalinity.
The higher degree of crystalinity has a pronounced effect on various properties including permeability and flexural modulus.
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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: HDPE permeabilty
RE: HDPE permeabilty
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RE: HDPE permeabilty
I read that the vessels are PE on the inside only then wrapped with an epoxy or polyester / carbon fiber composite. That outer layer probably is what gives the barrier properties as it is polar and the natural gas is not so it will not diffuse through that layer as readily.
RE: HDPE permeabilty