Flushing copper piping used for compressed air?

[Wes Grass]

I've also seen fittings that aren't galvanized inside. Although they might have been before they were threaded. Which, of course, the external threads on the pipe aren't either. And, yes, I've seen rusty water come out of galvanized plumbing.

As for getting exposed PEX lines to look good, you could always slip a piece of copper pipe inside them to hold them straight ;-)

[Ronald Blue]

I didn't say he was doing 18" threaded lines - those don't even exist. Most pipe and fittings over6-8" are either welded or bolted via integral flanges. X-Pando is used on threaded fittings for both natural gas and compressed air. It can also be used for water and hydraulic lines. There is also a version for ultra-high pressure hydraulic systems (4,000 bar or 58,000 psi).

I can't imagine 58,000 psi in hydraulics but if you say it exists who am I to question it? It's lethal pressure certainly. A leak so tiny you might not be able to see would cut you in half. High pressure common rail diesel injection systems sometimes are in that range of pressure but mostly in the 20-30,000 psi range. Nothing gets repaired if there is an issue. It gets replaced. Because it's pressure that would cause amputation if there is a leak. Obviously air lines aren't going to have that danger and it sounds like a option for those seeking to run iron pipe for their air system. It has it's advantages and disadvantages. Because I work in hydraulics almost daily I despise pipe threads for most things. Using Xpando isn't a solution because it makes disassembly very difficult. It sounds fine for something that will be put together and forgotten. O-ring fittings regardless of the type are much more friendly for field repairs and they often are in hard to access locations. Pumps, motors, cylinders, and valves are destined to fail eventually and serviceability is essential. I haven't ran any airlines in my shop yet but I am looking at the options.

[Brian Backner]

I'm not sure what kind of systems use this stuff, but there's a company here in Massachusetts that manufactures an entire line of tubing and fittings for incredibly high pressure systems - as in up to 200,000 psi:

https://www.harwoodeng.com/

I've seen a few of their fittings over the years and they are not nearly as big or heavy as you might think. Don't know what they're made of but I suspect some type of reinforced stainless.

I know that water jet CNC machines can cut even thick titanium using the proper abrasive, but don't know if they use pressure that high. The ones I've seen around here are usually in the 60k psi range

And you're right, I wouldn't want to be anywhere near one of these lines/fittings in case of a rupture or even a pinhole leak. I suspect such a system would be contained in a separate room with power cutoff and pressure relief switches actuated by opening the door into it. There have to be OSHA guidelines for such things.