There are a number of posts on various Internet forums with conflicting and
dangerous information on LP (Low Pressure) air piping materials. This is not
intended to be "the last word" on the issue, but here is what I learned.
PVC is Dangerous
PVC piping is prohibited by OSHA for compressed gas above ground because it
is a shrapnel hazard on failure. Click here for info. OSHA often moves pages around so just
search on PVC if the link becomes invalid.
It is very easy to accidentally bump a PVC air line and end up with a
face full of plastic shards. The risk is much greater in cold climates.
It is NOT an issue of pressure rating, only failure mode. I am told by a
licensed plumber and a Ph.D./P.E mechanical engineer that it is also
prohibited by most building codes for the same reason (definitely in
Note that compressed gasses continue to expand, and propel particles, when
pressure is released where liquid pressure drops virtually instantly making
the risk of projectiles far less hazardous. Anyone who has built an air
cannon knows how dangerous LP air can be.
I was told by these same people that Type L and K copper pipe is routinely
accepted by OSHA and building inspectors in the US, but the thinner wall
Type M is prohibited by all building codes for compressed gas above ground.
I could find no specific reference at OSHA on copper pipe weight, though
that doesn't mean there isn't one. Both men told me that black iron (steel
pipe that is not plated) and galvanized pipe are accepted by building
inspectors and OSHA and is preferred (sometimes required) where there is a
high risk of fire. Copper LP air pipe will fail in a fire with the risk of
feeding the fire with even more oxygen. Assessing the fire hazard (like a
woodshop) is usually a judgment issue with the building inspector and fire
The ME, who designs laboratories all over North America always uses Type L
copper pipe for LP air, medium vacuum, and non-corrosive compressed gasses.
The main reason is the ease of installation, lack of corrosion (no paint
needed outside and to avoid contamination inside), and far fewer leaks that
develop over time with soldered joints than threaded NPT pipe.
I prefer 3/4" Type L Copper for shop air, but use galvanized steel for very
long runs and large diameters (1-1/2" to 2"). I always add a filter and
moisture separator before transitioning to copper for distribution and drops.
It is very easy to learn to solder Copper pipe with a Propane torch and many
kits come with instructions. Just make sure joints are clean, use a
compatible flux, and heat the fitting until solder melts on the pipe and is
drawn in by capillary action. Use a good pipe dope of Teflon tape on all NPT
(National Pipe Thread) connections. I prefer Teflon on Copper threads and a
semi-hardening dope on large Steel threads.
Galvanic action is the biggest problem with copper. It is not a critical
issue with heavy screwed pipe fittings but thin Copper pipe can be
dangerously pitted by the wrong pipe clamps or hangers. Secure Copper pipe
with plastic or Copper pipe brackets as steel clamps will react with the
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