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PVC Burst Pressures

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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PVC Burst Pressures

Unread postAuthor: noname » Fri Aug 03, 2007 12:33 pm

This topic has beeen debated for quite some time, so I'll try to help settle it.
According to most people, the burst pressure is around 3 times the pressure rating.
So they use it at 100 psi instead of several hundred.
Why?
Because this is air pressure, not water pressure.
So, technically, PVC pipe isn't pressure rated; for air.

Confusing?

Just a bit. I plan on getting a bunch of end caps of various sizes (6 end caps for each size, 1/2"-2"), solvent welding them to short sections of pipe, connecting a long pressure hose, hooking up my shock pump, and pumping until it explodes. I will frag the Sch 40 sizes of 1/2" and 3/4" sometime soon, but I have around $10 (where's all my cash go?), so I won't be able to afford the rest.
If you are unfamiliar, a 2" end cap at Ace Hardware is nearly $2 around here, which is why I won't be doing larger diameters until later.
I may or may not test Sch 80 pipe and fittings, although I do have access to them, sizes 1/2" - 4."
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Unread postAuthor: mopherman » Fri Aug 03, 2007 12:38 pm

i dont think you will be able to burst 1/2 inch with a shock pump. the rating on my pipe is like 700 psi. If I were you, I would use co2 and sowlycank up the pressure.
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Unread postAuthor: noname » Fri Aug 03, 2007 12:40 pm

Not to sound rude/mean, but damn, did you read the first section of my post? Doesn't sound like you did. :wink:
I've had 3/4" Sch 40 (rated to 480 psi) explode on me at 140, with nothing wrong with the pipe.
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Unread postAuthor: Gepard » Fri Aug 03, 2007 1:04 pm

A rating of a pipe has nothing to do with what's in it. A pipe rated at 16bar is for any material at a certain temperature. That said the use of pressuried air in these pipes is not recommended - but the is still a rating.

Wtf your going on about in your second post I don't know - but I agree with mopherman you need to be able to produce pressures in excess of the ratings if your planning on testing it.

Michael
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Unread postAuthor: spanerman » Fri Aug 03, 2007 1:09 pm

noname....my mom just told me that ''it doesnt matter what exerts the pressure'' and she hasnt even got an o level in science....and you know what shes correct 16bar of water exerts the same force on the pipe as 16 bar of air, the burst caractaristics however are different...but thats not what your testing....
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Unread postAuthor: noname » Fri Aug 03, 2007 2:09 pm

Gepard wrote:Wtf your going on about in your second post I don't know - but I agree with mopherman you need to be able to produce pressures in excess of the ratings if your planning on testing it.


Not true, or people would have made 6-8x hybrids out of Sch 40 PVC. Ever wonder why pipe and fittings rated to 400 psi have exploded at a mere 200? Stating that I've had 480 psi rated pipe explode at 140 psi is a prime case of this statement.
I've put over 600 psi WATER pressure in PVC; did it blow? No. But when the same stuff blows at 140 psi AIR, you still think there's absolutely nothing different between the two?

Basically, I can test pipe explosion pressure if I can explode it. WHICH I CAN, even if the explosion pressure doesn't exceed the pressure rating (which it usually doesn't).
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Unread postAuthor: mopherman » Fri Aug 03, 2007 2:13 pm

noname wrote:I've had 3/4" Sch 40 (rated to 480 psi) explode on me at 140, with nothing wrong with the pipe.

I have to dissagree with you on that one. There must have been somthing wrong with that pipe for it to blow at that low pressure. There are members on this site that have used that pipe at more than 200 psi. btw, how did the pipe explosion go? anyone hurt?
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Unread postAuthor: spanerman » Fri Aug 03, 2007 2:16 pm

how did you know your pipe wasnt defective? there may of been an internal defect in your pipe...''people would have made 6-8x hybrids out of Sch 40 PVC.'' yes but that is a pressure spike which is different to the pressure rating the pvc is subjected to a huge flamefront at those pressures.....and the temperature would also affect the pressure rating...
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Unread postAuthor: SpudBlaster15 » Fri Aug 03, 2007 2:28 pm

Noname, it seems as if you are ignoring physics, and basing your argument on a single experience you have had, one that could be explained by other variables. A pipe will burst at a certain, fixed pressure, regardless of what medium is exerting it. As spanerman said, the only difference exists in the failure characteristics.

Your 480psi rated pipe failed prematurely due to a flaw in the pipe. Whether it had been left in the sun for too long during shipping or storage, or had been damaged by mishandling at the hardware store (PVC is very brittle), the defect would not be visible to the naked eye. The pipe probably "looked" fine, but you simply cannot determine the condition of a pipe by looking at it.

How did you manage to pressurize a PVC container to 600psi using water?

A Sch 40 PVC 6x hybrid would fail well below the rated burst pressure of the pipe not because the force is exerted by a gas, but due to the fact that PVC is brittle and cannot handle the rapid pressurization and shock exerted by combustion at 6 atmospheres. Not to mention the risk of DDT.
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Unread postAuthor: noname » Fri Aug 03, 2007 2:30 pm

I can tell when pipe is defective, as I am not an idiot. You may beg to differ, but this was in regular 80 degree weather, under no abnormal conditions, in pressure that the pipe should have held fine.
Honestly, do you people really think that PVC with a wall less than 1/8" thick will hold 400+ psi? There's a reason we don't go over 125 psi, and that's because the pipe will frag out all over.
Mopherman, my friend got a piece about an inch into his leg.
I was standing about 10 feet away, because I thought something like that would happen. I told him to pump it up to maximum 85 psi. Did he listen? Of course not.
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Unread postAuthor: mopherman » Fri Aug 03, 2007 2:37 pm

noname wrote:I can tell when pipe is defective, as I am not an idiot. You may beg to differ, but this was in regular 80 degree weather, under no abnormal conditions, in pressure that the pipe should have held fine.
Honestly, do you people really think that PVC with a wall less than 1/8" thick will hold 400+ psi? There's a reason we don't go over 125 psi, and that's because the pipe will frag out all over.
Mopherman, my friend got a piece about an inch into his leg.
I was standing about 10 feet away, because I thought something like that would happen. I told him to pump it up to maximum 85 psi. Did he listen? Of course not.


nobodys calling you an idiot. what people are saying is that it can be extremly dificult to detect flaws in pipe. As far as I can tell, there have been no other occurances of pipe failiers in this ize pipe at this pressure.
Sorry dude but i say it was just bad luck.
edit: did you get the peice out of your buddys leg?
edit edit: spelling
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Unread postAuthor: noname » Fri Aug 03, 2007 2:43 pm

We got it out, though probably not the right way. Just kind of grabbed it and pulled it out, slapped a bandaid on his leg, not a big deal. Luckily for him, most of it was sticking out, and it didn't go through anything important, just some skin and a couple little veins.

I know you guys aren't going to believe that.^
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Unread postAuthor: SpudBlaster15 » Fri Aug 03, 2007 2:43 pm

You can tell when a pipe is defective?! Wow, what amazing psychic ability enables you to see microscopic defects on the inside of a pipe that us normal humans cannot see, even with a microscope?

Yes, I do believe that PVC pipe with a wall thickness of 1/8" will hold 400psi, as that is what the rating says, and the burst pressure formula also agrees.

How did you pressurize a PVC container to 600psi with water?
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Unread postAuthor: sandman » Fri Aug 03, 2007 2:46 pm

noname wrote:I can tell when pipe is defective, as I am not an idiot. You may beg to differ, but this was in regular 80 degree weather, under no abnormal conditions, in pressure that the pipe should have held fine.


yes, u may have had the pipe in the right conditions, but you just cant know how everyone before you handled the pipe and if they damaged it
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Unread postAuthor: noname » Fri Aug 03, 2007 2:48 pm

I didn't see your first post, so I didn't reply to the 600 psi with water thing. My friend's dad is a mechanical engineer. They have the compressors capable of doing that. I asked him, and he said it was fine if I came over and saw him on a day off. He has the clearance to get him into the building whenever he wants, so we went over to the company building and tried it out.
On the note of his job, hopefully sometime this year I'll be able to go see a methane pipe explosion! There's underground pipes that hold around 900 psi in them, and when they burst, the methane gas flows out so fast it actually creates a solid chunk of methane, suspended in midair(midmethane :lol: ). Should be cool.
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