Aluminum in CNG Service (NFPA 52)

[rneill]

Does anyone have any idea why Clause 4.8.4(4) of NFPA 52 specifically prohibits the use of aluminum for pipe, tubing and fittings in CNG service ?

I don't have any experience with CNG service but from what research I have conducted, aluminum is a good choice for product compatibility, it has the required low temperature properties, it is conductive (so static buildup is not an issue), and it appears to be the preferred and normal material for constructing fuel cylinders(and is accepted by NFPA for fuel cylinders).

The only thing I've been able to come up with is a possible concern with the low melting point of aluminum but I don't think that's it?

Any help appreciated ...

 

[unclesyd]

Some where on this site is probably the answer to your question if it pertains to vehicular transportation. I haven't seen anything that strictly prohibits Al cylinders. The only requirement is that they be a composite structure where as steel can be full metal or a composite. There is a tendency to use steel composites cylinders to save weight. There is a general requirement that CNG cylinders have to leak before break which would be hard to do with an Al metal cylinder.
We operated about 20 forklifts on CNG using the beer keg type steel cylinder. There may have been some Al cylinders early on but the latest are steel. These all have brass valves, either plane or Nickel plated, with all SS flex hose.

http://www.cleanvehicle.org/technology/cylinder.shtml

 

[cloa]

unclesyd his question was about
pipe, tubing and fittings in CNG service not storage cylinders

 

[unclesyd]

cloa,
I realized that he was looking at fittings and/or tubing. The reason that I brought up the cylinders is the ammount of effort needed to insure leak before failure, which would be hard to do with Al tubing. It has Ben my experience that Al tubing fails by producing "fish mouth" at the failure, not good.
I added the link as I would bet you the require information is there either by direct reference or in one the many standards listed. Worst comes to worst one could contact the right governing body and ask for a clarification.

 

[blacksmith37]

If you are dealing with raw nat gas production (separation plant): some nat gas contains Hg at a ppb level . In a process unit, the Hg can concentrate enough to liguid metal embrittle aluminum.