Compressed air distribution

[Evan]

I finally got through to an inspector at the Boiler Safety Branch. They are responsible for all pressure installations in commercial applications. The inspector said that he would not approve an installation of type M tubing for compressed air. He pointed out that they do not inspect home shops but if they did and he found type M pipe running compressed air he would insist it be removed.

He also mentioned that he really doesn't like type L either but would approve it. He stated very clearly that he would not approve any soldered installation regardless of the type of pipe. The only joining method that is safe is brazing that is properly done according to him. He also told me that our mechanical code doesn't specifically mention Type M yea or nay but he would never use it in any pressure service including water lines.

[EVguru]

For ease of installation, you simply can't beat a plastic push fit system, for example the John Guest range.

http://www.swge.co.uk/compressed_air_fittings.asp

[MichaelP]

Guys, where did you locate your outlets? Do you find that an overhead outlet with a retractable hose reel may serve 90% of needs excluding stationary items such as sandblasters, plasma, machinery, etc.?

[goose]

He stated very clearly that he would not approve any soldered installation regardless of the type of pipe. The only joining method that is safe is brazing that is properly done according to him.

Re: soldering; Wouldn't a well designed compressed air system engineer in a weak link? If something should fail you'd want it in a semi-predictable location, no?


Gary

[Dr Stan]

Guys, where did you locate your outlets? Do you find that an overhead outlet with a retractable hose reel may serve 90% of needs excluding stationary items such as sandblasters, plasma, machinery, etc.?

I have a 24 X 48 shop that is about 90% complete and the compressor is in the SW corner. I still have to finish running the remainder of my air lines and plan to locate quick connects about every 8' on the south 48' wall, the west 24' wall, and 1/3rd to 1/2 way up the north 48' wall. They will also have traps below the quick connects.

With the size of my shop and my compressed air needs this should be more than enough. Consequently I would not need a hose reel, which would be just one more thing to maintain/repair.

[Mcgyver]

The inspector said that he would not approve an installation of type M tubing for compressed air. He pointed out that they do not inspect home shops but if they did and he found type M pipe running compressed air he would insist it be removed.

He also mentioned that he really doesn't like type L either but would approve it. He stated very clearly that he would not approve any soldered installation regardless of the type of pipe. The only joining method that is safe is brazing that is properly done according to him. He also told me that our mechanical code doesn't specifically mention Type M yea or nay but he would never use it in any pressure service including water lines.

There's so much conjecture and opinion in this thread without much engineering it got me thinking about the differences between K L M etc. Maybe this guys an engineering genius ......or just another brain dead, ignorant, power tripping ass hat bureaucrat who hasn't had an original thought in decades. You like to get to the bottom of things, I'm surprised you didn't call him on these assertions

I think he's dead wrong recommending brazing. Anneal copper has a fraction of the strength of drawn, as low as 20%. You don't need to do any calcs to see the very long length of shear in a standard fitting is going to be fine with 5000 psi soft solder - heck the wall thickness is .040 on L and inspector is worried of 3/8 of an inch of 5k soft solder....and it weakens the pipe by up to 80% Seems idiotic. You braze when you need the high tensile strength (not need here because of copper fitting design) or to withstand higher temps, obviously not present here.

So where's the engineering on why he doesn't like M? M is .029 wall thickness...playing around with the numbers, that'll hold like 1200 psi using a low annealed tensile strength...lots more if not annealed. For the guys who don't want to use M, why? makes no sense from a pressure point of view

I can see a fragile argument that the L is better able to withstand an impact, but if that's the concern, iron should be used . Besides, how big is the risk if you hit it and ruptured it? Not that you'd want to but, but the contents are not toxic or explosive and its not like a boiler where a pressure drop triggers an explosion. In a commercial setting with louts on towmotors, copper shouldn't be used...but if the environment is such that you think copper is ok from an impact risk viewpoint, explain the engineering why it has to be L over M?

I think the hint is his comments in the second paragraph, he doesn't like it. Sounds like another you-shall-do-what-I-say inspector without logic, reason or even a regulation. So, the left coast bureaucrat notwithstanding, it seems M copper pipe is fine to use for compressed air where there's little chance for impact.....or is there engineering to the contrary?

[KEJR]

I have a 60 gallon 5HP compressor in my 2 car garage that I don't leave on all the time (only when I'm in there). I simply have a 3/8 rubber hose connecting it to my work bench that I run along the ceiling, but plan on tapping off the main line for blow guns on my mill and lathe.

With all the talk about copper not being safe, is my setup a disaster waiting to happen? I suppose fire would be a problem. What about if I shut off the compressor at the main outlet with a metal ball valve or automatic solenoid valve when I'm not in the garage?

Conversely, alot of setups I've seen have copper piping for the distribution but rubber and plastic hose drops all over the place, wouldn't these also be a safety risk? Where do you draw the line?

KEJR

[Evan]

So where's the engineering on why he doesn't like M? M is .029 wall thickness...playing around with the numbers, that'll hold like 1200 psi using a low annealed tensile strength...lots more if not annealed. For the guys who don't want to use M, why? makes no sense from a pressure point of view

Water/air hammer is the problem. If a slug of water collects and the airline is opened to high volume use it can cause momentary pressures ten time higher than the working pressure when that slug hits a restriction.

Soft solder has a different coefficient of expansion than the lines. Silphos or Phos copper have the same CLE as the copper lines and will not crack like soft solder may. It is an entirely different event for a high pressure air line to break than for a water pipe to leak.

[Mcgyver]

Soft solder has a different coefficient of expansion than the lines. Silphos or Phos copper have the same CLE as the copper lines and will not crack like soft solder may. It is an entirely different event for a high pressure air line to break than for a water pipe to leak.

the temp cycling in a hot water pipe would i think be a lot more than an air line would see.

Working through a plumbing disaster right now that wrecked plaster through two stories, i think i'd take the airline failure. What do you think would happen with an airline failure that is so bad? Loud and scary yes, not sure why its much risk beyond that?

[Dr Stan]

I simply have a 3/8 rubber hose connecting it to my work bench that I run along the ceiling, but plan on tapping off the main line for blow guns on my mill and lathe.

With all the talk about copper not being safe, is my setup a disaster waiting to happen?

In a word yes. I know lots of people and shops leave rubber air hoses plugged in, but its a bad idea. If you happened to forget to turn off your compressor and the hose burst, your compressor would end up running continuously and possibly burn out.

[Gravy]

I wired my compressor with a contactor and a bath fan timer so I can't forget to turn it off.

[Evan]

Working through a plumbing disaster right now that wrecked plaster through two stories, i think i'd take the airline failure. What do you think would happen with an airline failure that is so bad? Loud and scary yes, not sure why its much risk beyond that?

The boiler safety branch isn't concerned about possible property damage. What they are concerned about is safety of humans. A broken 3/4 or 1" air line with 175 psi behind it is capable of firing parts around the shop at high velocity, especially if it rips loose from the structure. In my travels looking for code references I found many standing specs for suppliers that specified only brazing for both air and water lines.

The fellow I talked to has no special interest in running his own little kingdom. He is only filling in for the regular inspector while he is on vacation. I can give you his number if you like.

[Arcane]

From http://www.coppercanada.ca/pdfs/28e.pdf in Table 11, it states the maximum working pressure for 1/4" to 1" K, L and M tubing using 50/50 tin/lead solder joint at 100 degrees F is 200 PSI and at 150 degrees F it is 150 PSI.

[Mcgyver]

I suggest for any code reducing the risk to property damage is part of objective along with and secondary to human safety. We'd have massively shorter codes were they only concerned with safety

I don't doubt you are properly representing the conversation, the reasons however (moisture hammer 10x pressure or coefficient of expansion differences) just don't seem plausible. How could there be more risk of cracking due to coefficient of expansion differences when your hot water pipes endure far great cycles for decades or moisture traveling along exerting 10x the pressure - where does that energy come from? Anyway nothing presented to compel a change so its a bit academic, Madman, if I'm wrong and i don't make with my copper pipe I leave my master height gauge to you.

[PeteM]

When I went through this exercise years ago, it seemed to me that a higher strength solder was the way to go for my home shop.

Brazing was clearly stronger, but also required much higher temperatures. Given the proximity of many joints to flammable timbers, the greater ease of soldering, and my estimation that I was more likely to get 100% of the joints right the first time with solder than brazing -- all that was a factor. In addition, a tin/silver bearing solder (e.g. 5%) has nearly 2x the shear strength of some common tin/lead solders and looked to offer a huge safety factor. It only requires another 100 degrees of heat (compared to lead/tin) to melt -- easily obtained with either propane or air acetylene.

Even the lead/tin solder at the eutectic point (63% Sn) has pretty good properties (though it doesn't fare well at 200F which could easily be seen right after the compressor): http://www.alchemycastings.com/lead-products/solder.htm.

There is Evan's point about the different coefficients of expansion of copper pipe and solder/braze -- and that could tip the balance in favor of brazing for either higher pressure systems or those in commercial use -- and certainly at elevated pressures such as an intercooler. Still, I suspect most home piping systems would be relatively free to move and not experience either a static failure or a fatigue failure in fairly extended use. That said, my own system has been leak free for many years. If a joint does leak in another ten years, it will be easy to fix.