My comments with respect to usage of Rigid PVC for Compressed Air Distribution
1)
Rigid PVC is prohibited for distribution of compressed gas (incl. air)
by OSHA, ANSI, and ASME unless specifically manufactured for compressed air and labeled by the manufacturer for AIRLINE use (even then, only within strict guidelines).
2)
Rigid PVC is prohibited for distribution of compressed gas (incl. air)
by, of all parties,
the manufacturers of rigid PVC pipe (this is true of all schedules through atleast 120) since at least 1972.
3)
If a worker injury results from a compressed air accident resulting from rigid PVC compressed air distribution, not only will you likely
get a [Section 5(a)(1)] citation pending an OSHA investigation, but any insurance claims resulting from the injury (and any related property damage)
are unlikely to be reimbursed by your insurer.
Small businesses running small shop air compressors at typical shop pressures of 120-175PSI in rigid PVC pipe have actually folded after employee and/or customer injury lawsuits and damages following such incidents.
4)
Serious injury pending failure of rigid PVC compressed air distribution lines is not hearsay. Nor are these systems at especially high pressure.
Dangerous failures have occurred even at system pressurization levels below 100PSI, well below many shop distribution pressures of 135-175PSI.
PVC pipe, despite some commentary to the opposite, will still deteriorate, albeit more slowly, in an indoor environment. There are three major elements that will deterioriate PVC with time (microfractures aside):
1) Ultraviolet exposure (outdoors from sun; indoors from fluorescent and halogen/xenon lighting),
2) Ozone and other pollutants (incl. oil), and 3) accumulation of micro-fractures (unavoidable in use). The interior of the PVC will deteriorate at a greater than normal rate due to the greater density of ozone and pollutants within (at 150 PSI you have 11-12 atmospheres of compressed pollutants within your air). The exterior will deteriorate at a more typical rate depending upon your local pollutant levels and oil blow-by and the degree of UV exposure it is subject to (e.g. much greater with sun exposure or near any ozone generating sources, including sources of electrical arc). With age, these will make the PVC increasingly more brittle and less durable and prone to fracture.
The heavier the schedule, the greater the wall cross section, and the longer and the better PVC will survive such conditions.
Rigid PVC has another problematic characteristic at normal ambient usage temperatures (ranging from, say, freezing to 120F+).
The colder PVC becomes the more brittle it becomes. At warmer temperatures (say 140+) it also becomes softer and more prone to blowout under pressure (the higher the pressure the lower the necessary temperature for failure). As a point of fact,
at 130F rigid PVC is 1/2 as strong (resistance to deformation under pressure)
as it is at 73F and at 32F it is roughly 4x more brittle than at 73F. Unlike metal piping (Aluminum, Copper, Iron, or Steel) distribution systems, which, while subject to similar characteristics, do not exhibit these characteristics at any temperature remotely tolerable to human habitation (well below freezing up to a several hundred degrees for soldered joints, much greater for brazed or threaded joints).
This means that a PVC pipe may survive a modest impact at 90F but fail catastrophically and explosively on a 32F day. Age related deterioration will amplify these results, especially at lower temperatures.
No offense intended, but
if I give even, say, 3/4" to 1" Shedule 40 rigid PVC a good strong blow with a 2lb sledge it will likely result in a predictable degree of fragmentation even in the absence of pressure. By comparison, if I took a 20lb sledge to a copper line all I would do is crush the line with no catastrophic failure. I might get partial failure if I wail away at a fitting, but in all likelihood I would simply have crushed the line (a simple repair). In a more typical impact, little if any damage will be sustained by a copper distribution line (type L is the mininum recommended thickness for compressed air distribution). A similar impact with a 20lb sledge to black iron or galvanized pipe *might* damage the pipe -- then again it may just rebound the sledge and strike me. Hardened aluminum is a little more difficult to predict the outcome of, stainless steel would likely dent a bit.
In no way will PVC hold up better and the colder the temperature, or older the PVC, the worse the consequences may be.
Additionally, many oils, especially the synthetic oils commonly used in larger shop air compressors,
will deteriorate PVC. If your compressor is an oiled-type compressor then some oil will inevitably make it past the tank and into your air lines. The smaller the tank and/or the closer your tank's outlet to the tank's pump inlet, the greater the amount of oil that will make it through, especially during periods of high, sustained, usage.
Past good fortune is no guarantee of future good fortune. OSHA, ASME, and ANSI have no financial stake in the matter and they universally forbid the use of Rigid PVC for above-ground compressed gas distribution UNLESS it is shrouded in a suitable protective conduit. The manufacturers of rigid PVC have a
real financial stake in the matter and even they universally prohibit the use of rigid PVC for compressed gas distribution UNLESS the piping was specifically manufactured for such (and operated within very strict manufacturer specifications).
It is with good reason, and sad experience, that they have taken these positions!
I do wish, however, to be clear on one point: The above applies only to RIGID PVC PIPE. Soft, flexible PVC tubing and hose with interwoven reinforcement fibers (to prevent weak-wall blowout) are permissable for compressed air and are commonly used in pneumatic air hose. They can still cause property damage (mostly from whipping about) when they fail, but they will never produce dangerous shards upon damage/blowout (unlike the potential of rigid PVC).
Some Reading Material: Failure of Plastic Plumbing Products,
PPFA FAQ,
Amsoil's Compressor Oil Compatibility Notice,
PPFA's Plumber's Apprentice Manual,
OSHA Position on use of PVC for Compressed Air Use
