In the air line environment, there can be condensate and moisture that would cause most metal systems to scale, pit or corrode. The result could be pressure drop and damage to sensitive equipment.
The choice of thermoplastics would give you a smooth bore and corrosion resistance in a moist or corrosive environment. Asahi-America’s Air-Pro compressed air piping system is constructed specifically for compressed air. The specially-engineered HDPE resin is an extremely ductile material that will expand at the point of failure and tear open without explosive fragments. The system is rated for an operating pressure of 230 psi. This plastic is also chemically resistant to synthetic and mineral oils used by compressors; the other available thermoplastic (ABS) marketed for pressurized air has experienced failures because of this and at least one of theproducts (the bright green one) has been taken off the market There is, however, an adapter available in the Asahi Air-Pro line that would easily transition the obsolete system to an Air-Pro system.
Please note that PVC Schedule 40 or 80 should NEVER be used for air lines. PVC is a brittle thermoplastic and under air pressure, any failure can cause, and has caused shards of plastic to be propelled through the air and cause damage, severe injury or death.
W.P. Law Inc.