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Copper pipe failure

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Copper pipe failure

Unread postAuthor: skyjive » Wed May 28, 2008 2:50 pm

I think we all have heard/experienced horror stories about PVC exploding when pressurized, but has anyone ever had a copper (or even steel or aluminum) cannon fail on them? Would metal fragment like PVC or just split open?
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Unread postAuthor: SpudFarm » Wed May 28, 2008 3:03 pm

hey.. a friend of me "a dumb one" made a cannon with dare i say it? gunpowder. he was so stupid that he filled the whole thing with "fuel" putted in a ball bearing drilled a big hole where the fuel was and stuck a soldering pen in there while leaning over it.

boom it said and the whole thing went up in smoke. the pipe (3/8" welded sch 40 steel pipe) tore open along the weld about 2" and sent burning "fuel" in his face and shrapnel into his hand.
he looked like a ball of raw meat afterwards because of all the "fuel" remainds.

that is one reason not to play with solid propellants.

one more thing that is quite hilarious.. he did not have permission from the parents to do this and took the "fuel" from his friends father. when his parents came running out and asked wtf just happened he said: "i soldered on a wire with petrol in it" but the truth came to the line and they drove of to the hospital. the funniest thing is yet to come. when the doctor came in he looked at him and said "idiot" then the other came and said "so you are planning on getting a job in alquaida?"
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Unread postAuthor: pat123 » Wed May 28, 2008 3:03 pm

it would be much more catastrophic with metal pipe because of the high pressures involve. If it is seamed i think it would mainly split. I have never seen it fail.
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Unread postAuthor: POLAND_SPUD » Wed May 28, 2008 3:13 pm

yeah I always wondered how copper or malleable iron pipes fail

I am sure there has to be a picture or video with it 'somewhere'
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Last edited by POLAND_SPUD on Wed May 28, 2008 3:22 pm, edited 1 time in total.
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Unread postAuthor: MaxuS the 2nd » Wed May 28, 2008 3:18 pm

Copper pipe just splits, it never shatters. I know this because I used to conduct 'experiments' using copper pipe failure.

So the worst that will happen is you will ruin your launcher.
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Unread postAuthor: Hotwired » Wed May 28, 2008 4:15 pm

Copper is very far from being brittle, in water carrying duties it's not uncommon for water to freeze in the pipes in cold weather and rupture the tube.

Even then it won't shatter, it just bulges and splits along the pipe.
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Unread postAuthor: rp181 » Wed May 28, 2008 4:35 pm

MaxusS:

The worst thing would not be ruining the launcher. Thats alot of ressure and air coming from a pipe if it ruptured, possibly injuring the person.

Ive always assumed that with that much pressure, anything would shatter. Copper is fairly soft, would seamless steel shrapnel?
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Unread postAuthor: MaxuS the 2nd » Wed May 28, 2008 4:46 pm

Steel can be quite brittle, copper is a soft metal so it can withstand alot.
How likely is it for someone to have 30,000 to put into copper pipe, anyone from here anyway.
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Unread postAuthor: BC Pneumatics » Wed May 28, 2008 5:10 pm

Copper is indeed very ductile, and likes to bend and "mushroom" rather than blow into tons of little bits, but large pieces of it can come off and go flying. Theses are not fragments that are blasted off by the failure, but who bend and go flying back, to have their own inertia rip them off. Basically, it does not fragment, but tears, like Al foil.
At least these have been my experiences with it. Steel will fragment sometimes, but I have also seen it do the 'rip' effect of copper. It depends on the alloy and circumstances.

People who have attended the Vegas meets know what I am talking about ;)

With the pressures of most cannons here, we have nothing to worry about. Besides, everyone here knows not to pressurize over the rated pressure, at which point there is no cause for worry.

Of course with enough energy, you would be able to get copper, or pretty much any material, to end up thousands of pieces embedded in everything in a 10' radius.
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Unread postAuthor: DYI » Wed May 28, 2008 5:43 pm

I have to say that anyone who tries to make a BP cannon out of SCH 40 welded steel pipe is an idiot... which makes me an idiot I guess

Apparently copper is ductile even at liquid nitrogen temperatures. It won't shrapnel unless something very, very violent happens inside it.
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Unread postAuthor: MaxuS the 2nd » Wed May 28, 2008 5:45 pm

Ahh, well I'd even trust it with holding a rip in the fabric of Space-Time.
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Unread postAuthor: POLAND_SPUD » Wed May 28, 2008 6:11 pm

spudfarm did you talk with larda about pressure testing of various malleable iron fittings ? that's partly connected to the this thread you know...

I don't know who, apart form him, has stuff to do it... and I know that 150 psi is not exactly their real operating pressure
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Unread postAuthor: DYI » Wed May 28, 2008 6:30 pm

I don't know who, apart form him, has stuff to do it... and I know that 150 psi is not exactly their real operating pressure


It might be their operating pressure, but my 20x test proved that they can certainly take quite a bit more than that.
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Unread postAuthor: POLAND_SPUD » Wed May 28, 2008 6:43 pm

well you can have any operating pressure you want to.. it just depend on the safty factor you choose.... very often operating pressure is 1/3 of burst pressure... personally I would feel comfrotable with a safety factor of 4... but first I would like to know what's the burst pressure of malleable iron fittings before I set myself some limits...
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Unread postAuthor: Fnord » Wed May 28, 2008 7:56 pm

very often operating pressure is 1/3 of burst pressure


I don't think that really applies to copper very often. Most of the stuff around where I live is only rated to 300 psi or so, but probably bursts at 2000+ (If I knew the grade I could a rough calculation).

So with copper, pressure ratings are generally just a suggestion. Like pants. *

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