you also forgot that black pipe will cool the air better ,
(the black pipe will stay cold longer than the copper helping pull the water out of the compressed air )
I must respectfully dissent. As we all know, copper conducts heat better than most any common metal. Look at the fins on the radiator cooling your pc processor (ok, they might be aluminum if it's not the best unit on the market). What about the best quality radiators on our cars? You won't find black iron used for those purposes.
While not presuming to know your thoughts, I suspect you are equating the sheer mass of iron pipes with cooling ability. Possibly the cold sunk into wintertime pipes would last longer with iron than copper, but, by the same token, during the high heat of summer they would keep that air hotter than ever.
However, I honestly feel this is an overblown issue compared to other ones. Namely, cost and difficulty in installing.
I just got back from Lowes where I bought six 10' lengths of 1/2" copper, plus tees, elbows, couplings, strap hangers, etc. I'm going to extend the copper line I ran about 14 years ago in my basement woodshop in another direction to reach my garage. (I finally got a large enough compressor to power pretty much any tool I want). Anyway, all those supplies ran me $46 and change. I looked at 1/2" black iron pipe, and the same lengths were ten bucks apiece. I didn't even bother checking the prices of the fittings, but I'd bet all I own that they would well exceed the copper prices.
Secondly is the matter of cutting, threading and hanging black iron vs. copper. You can nip off copper with a pipe cutter, hit it with emory cloth on the outside, run a brush on the inside, flux it (hee hee), fire up a propane torch and sweat a copper joint while you would still be cutting and setting up to thread an iron pipe. Yeah, I know you can buy pieces already cut to length and threaded at the store, but at even greater cost and inconvenience, and that's only if your needs run to nice multiples of feet.
Or, you can do a bang-up custom job yourself. Of course, a decent kit of iron pipe cutter, pipe dies and wrench, possibly a vice run big bucks. Or, all those copper tools can be bought for, what, $15-20?
I have the tools to work iron and have done it. And maybe some guys find it more appealing because all the galoots on this forum are experienced in threading pieces together. But if sweating copper pipe intimidates you, you really need to expand your skill set. It is really not hard to do, and to do right. I assembled my current system in a few hours. It runs around three walls with four drops. When I first pressurized it, zero leaks. It's the cheap type "M" pipe, yet has lasted all these years with fairly heavy use and no problems. If it should fail, I would expect a split similar to a frozen water pipe and a loud hissing of air for 15-30 seconds. I would go upstairs, change my pants, and come back down to fix it in short order.
Iron pipe is great, probably the strongest and best system you could install. But, short of complete reversal of the pipe price structure, I will never see how some of you guys claim it's cheaper to buy than copper. Or easier to install.
Have you figured out which side I belong to in this debate?
)
)
)
? I have used compressed air to blast water and oil out of similar small tubes. Moisture is part of the reason I would consider such a small size I probably could go down to 7/16 for the run. When or if I ever get to this little project I keep the water drain and tee in mind. I may consider hand dig the last 2' of the trench under the wall of the poll barn the lower (receiving building and make a small area so I could add the tee and drain if needed at a later date). in a small pit just inside the building.