thanks for all your replies. You have given me lots of ideas..... oh Pex piping , just got my house re-piped with Pex , the copper started to develop pin hole leaks or little specks of blue/green. so Plex pipe will work ok ?
The copper started to pin hole probably due to acidic water in M wall thickness pipe. That would not be a concern with copper in an air system.
You need to ask yourself two questions.
What air tools am I running?
and
How long do I want it to last.
If you are painting or sand blasting, you want larger pipe, and copper would be a plus to condensate moisture. Also remember if running larger air tools with high consumption and you do pick a pex or pex derivative, that the ID of the pipe is smaller for a given size and crimp type fittings are even smaller still so the pipe should be increased a size to handle the flow.
As far as how long it last. Nothing is going to beat soldered copper unless its exposed to physical damage. Then Iron, while having rust issues will take physical abuse better.
Systems that use push connect fittings(shark bite, air brake line) and copper propress use o rings to seal. The orings have a finite lifespan, and in 15 years or so they will start to leak. Its the nature of rubber oxidizing. Push connect poly airline became very popular in cnc machines in the late 90's early 2000. Its a nightmare to maintain with all the splits/fractures/airleaks. My last employer forbade new machines plumbed with it, only hardlines unless it was a section to go thru a cable track or down a robot, then it was seen as a necessary evil. If you plan on being where your shop is till you die, these quick/easy/cheap systems are not cost effective over a long life cycle.
Good PEX (PEX A) is a good low cost alternative for the average person that is only going to spend 7 years in their home/shop before moving. If placed out of the UV life it will typically have a good 15 to 20 year lifespan. I prefer propex with the expansion type fittings. The tool is expensive but the joints don't leak, are very fast, and dont restrict flow like crimp fittings.
The Al-pex-al is nice stuff. I have installed some of it in the industrial shop I work in currently (3/4 and 1"). Its measured on the ID which is a plus. Its expensive however, the 3/4 Rapid air maxline I installed was more expensive(due to fittings) than copper. Plus with copper you don't have to straighten it.
with over 120 feet of black iron pipe in place and leak free. Our local old-time lumber yard had a commercial pipe machine that had taps, dies, deburring, and tubing cutter all motor driven, which made it very easy for me to run the pipe. When the machine broke, it cost too much to fix so they sold it. With the pipe, and more importantly being in AZ, I never see any water in the output.