I realize not everyone is going to agree, and that is OK. I will not get into the argument about how safe or unsafe it is to use PVC for air lines. What I can tell you is this, whatever material you deem will to be safe, you better have supporting documentation from a the manufacturer stating that it can be used in that application. I don't care if it is schedule 80 or better.
From a liability standpoint the manufacturer will stand behind his product as stated. There is misconception amongst people in these workshop forums that if a piece of PVC has a test pressure of 600 PSIG that 175 PSIG should be no problem.
The 600 PSIG is a statement of quality, not a CONTINUOUS use safe WORKING pressure. There are many factors that can affect the integrity of PVC beyond high pressure. There is it's degradation due to oil, high air temperature, sunlight, UV from welding, high and low ambient temperatures. Then there are the dangers of impact damage that could burst or just weaken the line. That could include hits from tools or equipment.
Then there are the overspray possibilities. Something as simple as spray paint will change the structure of the PVC. If you don't believe it, read any hard hat, it states clearly DO NOT PAINT. If you are caught on an industrial jobsite with a painted hard hat by a savvy safety man you will have to replace immediately. A scaffolding company in our area decided to paint all their hard hats with LSU colors. EXXON safety did not like it. The OSHA guy liked it even less.
Just a side note, if have witnessed failures on PVC, most will probably be near the fittings, you know the fittings and the end of the pipe you SOAKED with a PVC solvent that allows the two pieces to bond. PVC is not GLUED, it becomes bonded when the surfaces to be connected become SOFT from the solvent. PVC glue has no real adhesive qualities.
Should a line blow and injure anyone I can assure you an insurance inspector will be visiting you. He will dance a jig when he sees your blown PVC compressed air lines. You will learn a new term, CONTRIBUTORY NEGLIGENCE.
So for me it's black iron, copper approved for compressed air or one of the newer products like MAXLINE, or the pretty blue hard aluminum now offered by just about everyone.
My thoughts on this are based on working in a PVC plant and listening to the engineers spar over this at least once a week.
My 2 cents,
Smiling Gator Metal Works, LLC
Dynatorch 4X4 XLS
Baton Rouge, Louisiana