Compressed Air Line Question

[ultrarunner]

^^^ Do they use any type "K" copper... it's about 99% of what we use for compressed gas at work.

http://www.alascop.com/pdf/cu/water_tubing_2.pdf

 

[dstig1]

Not that I have seen. They don't use the lighter M, but the middle grade L. I have only seen K used underground direct burial here. And mostly water at that.

 

[ultrarunner]

The new Hospital wing back in 1995 was all done in "K" for the medical gases... Oxygen, Nitrogen, Nitrous and Air.

21 years and not a single issue and the there is a lot of piping... we do have some L for regular compressed air.

I believe M is .025 wall thickness, L is .030 wall thickness and K is .035 wall thickness... so K is almost 50% more than M

 

[SPYDERLK]

Alright...I tried to stay out of it... The big issue is a physics one, and it is not trivial. It comes from fluid dynamics. First point has been well covered: gasses vs liquids. Gasses are compressible, liquids are not, so there is a lot of potential for a big explosion when something gives way with a compressed gas vs compressed liquid at these pressures (spare me your stories about 10,000 psi hydraulic systems in jetliners - yeah, they are seriously dangerous if they fail). The other is what people don't quite get because it does not quite make obvious sense. Pressure is not pressure. At least not quite. The forces exerted are dependent on the pressure AND the VISCOSITY of the "fluid" in question. The lower the viscosity, the higher the forces at a given pressure. This is the second reason why air does not equal water in these systems. Viscosity of a gas is generally far lower than any liquid, so that adds to the issue. The PVC pipe might be rated for 200 psi water, but that does not mean 200 psi air is OK. In fact it is probably not. Thus all the OSHA warnings you have seen in this thread. Yeah if you want to bury PVC it won't pose a safety hazard, though it still may not last. Don't ever use PVC in an exposed shop application for compressed air. It just isn't worth it. Even good old regular PEX tubing is far safer. Polyethylene is pretty resistant to most solvents and oils. Crosslinked PE (aka PEX) is even more so. That is the cheap and easy route. Me? I used Type L copper. I work at a Fortune 100 R&D/mfg company and they use it for all labs and plants for compressed air. If they are OK with it, I am OK with it for my home. It ain't that hard to work with and is not really that expensive given the lifetime it will be in service.

YMMV, IANAL, etc.

This does not hang together well without further explanation. Please elaborate. Do you mean the viscosity of a compressible fluid will affect how fast it can expand and thus drive fragments during a release of stored energy/explosion?

 

[KennyG]

Based on my work in dynamics of compressible and incompressible fluids, I would say viscosity is a very minor issue with respect to this question. The differences in viscosity of gases is minor and doesn't enter into the issue. The viscosity of a liquid will impact what is essentially the inertia component of the expansion but, because the fluid is incompressible, the change in velocity (acceleration) is much lower than a gas and, as a result, the viscosity effect is limited. Viscosity will affect the losses and limit the total flow through the pipe, but this is not where the large forces are coming from in the gas case. It is the expansion.

So I would say, yes viscosity has some effect in making liquid breaks less violent than gas breaks, but it's a very secondary effect.

 

[Sawyer Rob]

I believe M is .025 wall thickness, L is .030 wall thickness and K is .035 wall thickness... so K is almost 50% more than M

In another life time, I designed and swaged bonded core bullets...

I could buy copper tubing in what ever diameter, hardness rating and wall thickness I wanted...

I used a lot of type "L" in .035" wall thickness...

SR

 

[Industrial Toys]

I have hundreds of feet of plastic underground air line between Five buildings. The latest run was 150 PSI 1" tubing that I found new on Craigslist. The older stuff was just domestic water line and despite running 100 plus pounds, it hasn't burst yet.

I also use ridged 1/2 black pipe (a real pain to install) and just the cheapest 1/2" copper water line for inside buildings. The copper hasn't burst either.

It's nice having air without the noise of the compressor and the added air storage is a bonus. The downside is having to fill the whole system up.

 

[SPYDERLK]

Based on my work in dynamics of compressible and incompressible fluids, I would say viscosity is a very minor issue with respect to this question. The differences in viscosity of gases is minor and doesn't enter into the issue. The viscosity of a liquid will impact what is essentially the inertia component of the expansion but, because the fluid is incompressible, the change in velocity (acceleration) is much lower than a gas and, as a result, the viscosity effect is limited. Viscosity will affect the losses and limit the total flow through the pipe, but this is not where the large forces are coming from in the gas case. It is the expansion.

So I would say, yes viscosity has some effect in making liquid breaks less violent than gas breaks, but it's a very secondary effect.

:thumbsup: ... Pertinent fundamentals well described, organized, and factored in.

 

[ultrarunner]

You are right and as the wall thickness often varies with pipe diameter.


1/2" K pipe wall is .344, L is .040 and M is .028


3/4" K pipe wall is .641, L is .045 and M is .032

 

[SPYDERLK]

You are right and as the wall thickness often varies with pipe diameter.


1/2" K pipe wall is .344, L is .040 and M is .028


3/4" K pipe wall is .641, L is .045 and M is .032

Those is some thick walls on K pipe. Must be rated at 50,000 psi. Water jet territory.