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FYI, here's a response I got on the PVC for compressed air lines
question from Harvel. Harvey is a PVC pipe manufacturer.
----- Original Message -----
From: Bill Weaver
To: billsohl@mindspring.com
Sent: Friday, November 18, 2005 11:35 AM
Subject: Use of Compressed Air
Than you for contacting Harvel with your inquiry. WE DO NOT RECOMMEND THE USE
OF PVC/CPVC PIPING FOR THE CONVEYANCE OR ANY OTHER USE OF COMPRESSED AIR.
Please refer to the following statements that are published on our website
(www.harvel.com) for additional information.
USE OF COMPRESSED AIR OR GAS WITH HARVEL PVC/CPVC PIPING PRODUCTS
Harvel's PVC and CPVC piping products are "rigid" thermoplastic
materials. As a result, Harvel Plastics, Inc. does not recommend the use of
PVC or CPVC piping products for the testing, transport, or storage of
compressed air or gases. The compressibility of air and/or other gases result
in tremendous amounts of stored energy, even at lower pressures. Should a
failure occur in a compressed air or gas system for any reason (i.e. improper
assembly, mechanical damage etc.) the failure mode will be very dramatic in
nature due to the physical characteristics of the rigid piping in combination
with the immediate release of this stored energy. Under these conditions, the
velocity created by rapidly escaping air and the resultant failure mode can
throw shards of plastic in multiple directions (i.e. shrapnel/projectiles).
This scenario creates a substantial hazard to personnel and property within
the vicinity of the piping should a failure occur. Several cautionary
statements and alerts against the use of rigid PVC/CPVC piping for use with
compressed air or gases are available through the Plastic Pipe Institute
(PPI), American Society for Testing and Materials (ASTM), various other trade
organizations, manufacturers, safety codes, as well as several State and
Federal Agencies (i.e. OSHA).
The following statements currently appear in our published literature:
"Harvel Plastics, Inc. recommends against the use of its thermoplastic
piping systems for transport or storage of compressed air or gases. Trapped
air must be removed from liquid piping systems so that no air remains locked
in the system when pressure is applied to the liquid. Excessive surge pressure
must be avoided. Surge pressure can develop if liquid movement through the
pipe is near maximum velocities and valves are closed abruptly. Maximum
velocity is generally considered to be 5 feet per second."
"Compressed air or other gases should never be used in testing. Extreme
care should be used to assure complete venting of all entrapped air when
filling the system with water or other liquids used in testing. Whether a
hydraulic hand pump or available water line pressure is used, any slow
build-up of gauge pressure on a completely liquid filled line shows some
entrapped air in the system. Pressure should be immediately released and the
line re-bled. Failure to do this can lead to a catastrophic failure when the
decompressing gas suddenly accelerates the solid water column if a faulty
joint separates."
"CAUTION: PVC and CPVC piping systems are not recommended for compressed
air lines. Improper installation, especially poor cementing techniques can
lead to an abrupt release of tremendous stored energy. Shattering of pipe and
fittings is then apt to occur at directional changes and at points where the
system is rigidly restrained due to the instantaneous whipping action imparted
by the escaping air. Internal surface cracks, due to the stress, can be
initiated which will tend to propagate and cause shattering, hairline or
pinhole cracks over a period of time. There is also evidence that certain
additives to system lubricants will initiate internal stress cracking which
will again lead to similar failure over extended periods of time."
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