PVC piping questions
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Posted by: willers ®

12/27/2005, 17:54:16
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I have an issue where I am working on some air line for a compressor. The system will be at a design pressure of 10 psig with a maximum pressure of 30 psig. There is an aftercooler, which is sufficient to get the compressed air down to about 10 degrees above ambient (we are assuming 100 degrees F as a worst case scenerio). I wanted to run some of the piping in Sch80 PVC after the cooler, since we are well below the pressure rating of the pipe. However, our senior engineer (my boss) has stated that we can't do that, PVC and compressed air do not go together, end of story. He has also told me that the codes won't allow it.

I've never heard of this. Can anyone verify that? We do this with water all the time. I can't imagine what the difference would be here?

Help!

DL Willers








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Re: PVC piping questions
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Posted by: rconner ®

01/18/2006, 13:52:39
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I believe OSHA has also had one or more advisories out on this basic subject for many years (e.g. see at https://www.osha.gov/dts/hib/hib_data/hib19880520.html)

Randy Conner








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Posted by: randykimball ®
Barney
12/29/2005, 22:56:34
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One thing to consider with any plastic pipe and a pressurized fluid is that plastic has a low melting point. If the pipe ever gets involved in a low grade fire or near a heat source the plastic may reach a point in which the plastic becomes soft and or easy to expand to a bursting point. Also many plastics become brittle at a low temperature. These factors are not compatible with liquid and gas safety factors if such are flamable, corrosive, poisonous, a hazzard in any form to the earth, contain particles that may be sent into eyes, displace O2, and the list goes on. Thus it is a popular container for ... water... .




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Posted by: pwehmer ®

12/28/2005, 10:38:16
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The stored energy in a liquid is very small. Failure of the PVC pipe can & has resulted in flying shrapnel. The dangers of this are well documented.

American National Standards Institute and American Society of Mechanical Engineers' Standard B 31.8-1986, which limits the operating pressure of plastic piping distribution systems to 100 pounds per square inch (psi) and prohibits the installation of such systems above ground except where the above ground portion of the plastic service line is enclosed in a conduit or casing of sufficient strength to provide protection from external damage and deterioration.


You might get away with a 10 PSI system. You could check with your OSHA rep.

There is a plastic pipe system made for compressed gases. It is an ABS material. Compared to schedule 80 PVC the price should be ok. I think it is called "Duraplus".








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Posted by: willers ®

12/28/2005, 11:53:43
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Interesting. In the wastewater industry, {SNIP} (a huge diffuser manufacturer) uses SDR 33.5 pvc on systems with pressures easily in this range, including their downcomer piping. The only thing that they worry about is the temperature. I don't think that a single diffuser manufacturer doesn't use PVC air piping. We are talking hundreds of miles of this a year. I wonder if OSHA, ANSI, and ASME know that.

Thanks for the info!

DL Willers

Lets avoid names in discussion like this...







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Posted by: willers ®

01/31/2006, 12:46:01
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Sorry. I didn't know that it was frowned upon to use company names and the like on the forums.

I wonder why no one worries about this in the wastewater industry. One would think that OSHA and ASME would be looking at this and make them change (at least up to a pressure rated pipe). As far as I can tell, every diffuser manufacturer uses PVC piping for their air headers, and no one even thinks twice. That makes me worry about the safety of the operators of these plants.

Perhaps they think that it isn't an issue due to the relatively low pressures? Like I said, we are talking of at most 12 psig. Either that, or they assume that the piping will be covered by water (which it may or may not actually be), and therefore are protected if it does fail?

I'd like to hear some thoughts from people more in the know on this, since I certainly didn't consider it before (hence the original question).

DL Willers








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