Failure of Copper Piping used for Comp. Air

[Derek57]

What failure would be expected from a 4" copper pipe (containing compressed air) that has insufficient wall thickness under 100 psig of internal pressure? I know that gases have significantly more stored energy than liquids at the same pressure, but would the pipe burst into fragments, open at a fitting weld joint, etc. etc?

Any input is appreciated, thank you for your time.

 

[MiketheEngineer]

One can never be too sure about such things. But all of the copper pipes I have seen rupture along the length of the pipe. Nerve seen fragments.

But as my dear old Dad used to say - Never say Never...

 

[btrueblood]

"What failure would be expected from a 4" copper pipe (containing compressed air) that has insufficient wall thickness under 100 psig of internal pressure"

I would expect the failure to be a huge dent/crimp/bend made when somebody attempted to lift the piece of pipe. To have a wall thin enough to open up under 100 psig means something around .012" thickness or less, i.e. almost foil. Like Mike says, it would probably open along a seam.

"but would the pipe burst into fragments, open at a fitting weld joint, etc."

Don't know anybody making welded joints on copper piping, even at 4" sizes.

Any rupture of any material has the possibility of generating fragments. Ductile materials (like copper) have lower probability of generating big chunks.

 

[MJCronin]

Metallic piping failure from overpressure is almost always a "fishmouth failure"..... with the long axis of the fishmouth along the axis of the pipe.

Sometimes, a brazed fitting will "pull out" in a copper system.

Long, long ago.... the USNRC demanded that high-energy nuclear plant piping be designed to protect against a "double ended guillotine" break in high energy piping. (Circumferential failure)

The trouble was, that to physically achieve such a break in a metallic system, it wasn necessary to either drastically notch the piping and provide an extreme overpressure "pulse"....

The utilities and the engineering design firms pointed out that these two extreme measures would never exist in a real plant system.

Wisely, the USNRC revised it's position and adopted a "Leak before break" criteria.

Moral: Count on fishmout failures

 

[MikeHalloran]

I would expect a 4" copper pipe in a compressed air system to suffer a disappearance failure.


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... i.e., one day, or one night, probably before you even get to pressurize it, it will just mysteriously disappear.

... and pieces of it will appear in a local scrap dealer's inventory.



Mike Halloran
Pembroke Pines, FL, USA

 

[1gibson]

Or reference the "Snoop" thread re: urine causing SCC on copper pipe.

http://www.eng-tips.com/viewthread.cfm?qid=297432&page=1

Method of prevention: Provide bathroom nearby.

 

[btrueblood]

Better, don't put compressed air piping at ground level in dark corners.

 

[racookpe1978]

My 5/8 diameter thin-walled copper hot water pipe failed through with a pin-hole leak after 22 years use.

Fortunately (?) it was in the overhead of the basement - right above my lathe and milling machine - so the spray of water attracted immediate attention ... rather than a perpetual leak hidden in some wall or under a concrete floor - as happened in my father-in-law's house after 12 years service.

Moral: If a thin-walled copper pipe fails under 75 psig water pressure - it will tend to fail under 100 psig compressed air.