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Iron pipe?

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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Iron pipe?

Unread postAuthor: potatoflinger » Fri Jun 01, 2007 7:33 pm

I already made a post about brass pipe, but that was way too expensive for my small wallet, and I saw iron pipe at the store for about eight dollars for a 36 inch length of 1 inch diameter pipe., and I thought, why not go with that instead. The pipe said that it was rated to 150 psi and that it was for gas systems, but I want to make sure that it is safe to use at 100 psi. I know that the pipe is rated to 150 psi, but pvc pipe is rated to more than 200, but is only safe to around 100.
Any advice would be appreciated.
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Unread postAuthor: hi » Fri Jun 01, 2007 7:44 pm

i built a hybrid out of iron, i still havent fired it though. :oops: some day i will.

any way, yes it will hold the pressure because i did test mine with a burst disk at around 130 psi. its its rated at 150 psi, it will hold 150 psi.
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Unread postAuthor: pyrogeek » Fri Jun 01, 2007 8:40 pm

It's gas, so theres no reason it will behave differently with natural gas as with air and propane.
Also, it's "rated" to 150. I bet it could easily hold over 400. Propane tanks are thin, like under 1/8inch, and they hold propane as like 200PSI no problem. So an iron pipe that's thicker, and a smaller diameter would definitely hold more.
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Unread postAuthor: rna_duelers » Sat Jun 02, 2007 4:12 am

Juts don't drop it!Or you will have Iron powder as it's very brittle.And if its aired and you drop it you will have Iron shrapnel.It would hold 100PSI easily for safe shooting without a rupture.
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Unread postAuthor: potatoflinger » Sat Jun 02, 2007 8:52 am

So you guys are saying that I could make a cannon out of iron pipe that will hold 100 psi, but I just have to be careful not to drop it? If it will shatter if it gets dropped, couldn't I put some type of padding around it, like that pipe insulation stuff?
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Unread postAuthor: mark.f » Sat Jun 02, 2007 9:38 am

*Sun Tzu Mode On*

Ahh.... the weakest system, is a brittle one.

*Sun Tzu Mode Out*

But, in this case, I think potatoflinger will be fine. If it's the type of iron found at most hardware stores, it is the dark gray ductile iron. While you shouldn't abuse any type of pressure vessel, this type of iron should survive an accidental drop while within it's working pressure range, (for SCH-40 it should be a few hundred PSI. Fittings are lower, ususally 150).
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Unread postAuthor: chaos » Sat Jun 02, 2007 9:47 am

just buy some galvanized pipe instead (unless thats what your talking about) schmanman used 1" for the chamber on his "sniper" and used it at pressures in excess of 350psi
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Unread postAuthor: boilingleadbath » Sat Jun 02, 2007 1:56 pm

Eh, both of them (black pipe and galvanized) are the same stuff on the inside - or close enough. The major difference is that black pipe is painted (or something), and the galvanized has a relatively thick coat of zinc.

As a note, neither of them hold an edge worth a damn - not enough carbon.
(which, incidentally, means that they are not brittle)

My understanding is that the 150psi pressure rating is rather conservative for a diameter of 2", and is probably related more to air-tightness than rupture safety.
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Unread postAuthor: SpudBlaster15 » Sat Jun 02, 2007 2:32 pm

I believe black iron pipe has a coating of firescale left over from the hot rolling process, which gives it its distinct appearance.

Assuming your pipe is made from very low quality steel (Stress threshold of about 15,000psi), it should be able to hold roughly...

15,000*(2*0.135)/1.033 = 3920psi

Thats not to say that I would take it up to such pressure levels. However, you should have no problems taking it up to 300 - 400psi.
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Unread postAuthor: potatoflinger » Sat Jun 02, 2007 3:16 pm

I don't have a way of pumping it up to 200 psi, my compressor only goes up to 100, so that will be the highest pressure that the gun will ever see. To keep the gun safe from an accidental drop, I covered it with pipe insulation, to give it a little bit of padding. I am almost finished the gun, I just need to find a sprinkler valve, and a relay. I'll post the gun as soon as it's finished (it really looks cool so far).
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Unread postAuthor: Cool » Sat Jun 02, 2007 6:08 pm

Dropping in when its pressured of only 100psi wouldn't do anything. 100 psi is not much, think of the compressor tank, i bet that its i MUCH thiner walls than your pipe, and they can hold a lot of pressure. I bet even a soda can could hold that pressure.
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