Pipe for Compressed Air

PVC pipe is a brittle if stuck can shatter. Sending fragments out that can harm some one. The use of plastic as pipe for compressed air has to go through tests for impact. Most States do not allow PVC use unless it is guarded. Before you intend to use PVC for compressed air see what OHSA has to say but its use. They have imposed some limitations.

If you are looking for a plastic pipe for compressed air look at HDPE pipe.

Check out this link. It is the OSHA position on PVC pipe.

http://www.osha.gov/dts/hib/hib_data/hib19880520.html

thank you for the link !

You're question is well founded but would seem flawed.

The "rated" pressures relate to very specific short term testing. The major issue that I've seen with PVC pipe carrying water is that pressure cycling leads to failure of the pipe as a rupture with longitudinal shards up to 2m in length (when contained underground).

If your water line fails, then the flow is limited in a 1:1 ratio for flow, so the leak is just water rushing around.

If you have a compressed air line fail at 6 atmosphere pressure, then for each cubic meter of air escaping you end up with 6 cubic meters of outrush.

My opinion is DON"T GO THERE! (Caps intended)

The previous suggestion to use a more flexible material is good but your safety margin still needs to be reviewed as the pipes will "balloon" and progressively fail at the weakest point. These failures blast out a typically round coupon of material, but the failure does not propogate along the pipe.

There is another challenge and that is achieving proper jointing and sealing.

HDPE has been found in tests to rupture but it doesn't shatter into pieces. The joints are thermally welded.

The word for today is "shrapnel".

As I understand it, trace oil in the compressed air degrades the PVC over time. In case of rupture, compressed air is quite expansive, blowing shards everywhere. There are some other acceptable plastics, though.

However, a low pressure air system fed with regenerative blowers would not have the oil problem, so I think PVC can be used there. It might not be classified as compressed air, anyway.

Hi,

What you purposed is correct. Difference between 480PSI and 150PSI is not many. But in terms of heat....... Can the PVC stand the compressed air heat or can it melt down?

I Have seen first hand what happens to PVC pipe when used for compressed air. A friend who added on to his shop decided that it was much cheaper to use PVC in the new addition by tapping into the existing 1" copper pipe. In less than 2 months he came home to find that the PVC had shattered, and his fairly new Gardner/Denver air compressor had seized up from running itself to death. The best we can figure is that over this fairly short period of time the PVC had fatigued from expansion and contraction and blew apart. He found a piece of PVC stuck in one of the roof rafters. Before he installed the PVC I handed him a copy of the OSHA regulations on PVC in the work place, and suggested that he stay with copper or some other metal pipe. I guess at the time his visions of saving money just over powered his common sense.

There are plastic pipes that are rated for compressed air, though not approved by all the states.

If a forklift were to hit a 125 psi plastic air line, would the outcome be any different if it were sch 40 steel?

There are several companies that make plastic pipe specifically for compressed air. We have lots of it in the plant I work at. Just have to be very careful about the temperature range. It doesn't take kindly to higher temps. such as coming out of a dessicant type air dryer where it may reach in excess of 250 degrees. It probably doesn't come out to be a whole lot cheaper but it sure is a lot easier to work with. Takes special glue and cure time is up there a bit. Different type of glue than regular PVC cement. I see no reason to not use what is specifically made for this as long as the other factors such as temperature are within its designed range.

Just my two cents worth. To hydro test a line or a vessel, it is filled with water and pumped up with a low volume pump. If something blows, a little water spurts out and the pressure is gone.

If you have a line or a vessel filled with air and something blows, all the air is going to head for that hole, and is not going to stop until the pressure dies down. That means a lot of energy on the move. A broken air hose will flail around with great force. A broken pipe will become a rocket exhaust, sending the remaining pipe off in the opposite direction, doing as it pleases.

Nah, give me good old cheap black pipe. Does the job, and will last as long as most factories do anyway. And you can hang stuff from it without worrying.

pvc shrapnel does not show up on x-rays. Thats another reason not to use it. However, i built a heck of an air cannon with a 5 ft pvc barrel. I used steel lines from the scuba tank to the water sprinkler valve used as an air release, then past the release, i used pvc. I wrapped it with that fiberglass strand package tape, then wrapped the pvc again with cammo duct tape. Got some strange looks with it mounted up in my trucks back window, but hey, i lived in louisianna at the time, so the police didnt care about it. la is a shall carry state. If its in open sight, you can carry a gun without a permit. If someone tries to carjack you, you can shoot them. They even announced "open season" on car jackers when the problem started getting bad. Car jackings fell dramatically.

There is one other concideration to make note of !! In collecting data on types of materials for use in dust recovery system in my wood shop this interesting tidbit showed up. PVC pipe or tubing with air or gas moving inside must be 100% clear of any particles of any size. The reason is that these particles, particulates or pieces will rub on the walls of the tube/pipe and will cause static electric charges of sometimes extreme in nature. In one design there were copper wire wrapped around the tubes/pipes to ground these hazardous charges. Another point is that any change in direction of flow will cause particles,particulates of pieces to impact one small area and will build up or wear through like hitting PVC with a sand blaster!!

Ray

Triva Buff