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steel pipe

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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steel pipe

Unread postAuthor: roughboy » Thu Dec 14, 2006 1:28 am

how much pressure can an all galvanized steel 3'' X 12''long air chamber hold? thank you
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Unread postAuthor: SpudStuff » Thu Dec 14, 2006 7:30 pm

150 PSI safely. That is the rating on the pipe.
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Unread postAuthor: drac » Fri Dec 15, 2006 4:45 pm

No spudstuff, this is the 1238019283 I'm telling you. That's the pressure at which the threads are guarenteed to seal up to! The pipe itself can hold way more!
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Unread postAuthor: CpTn_lAw » Fri Dec 15, 2006 5:01 pm

guys stop please, this is a serious thread. and please be logical a bit...150 psi for 2mm thick steel....man did you smoke or something? PVC which i plastic is rated 250 psi. i've taken a 1/2" pipe to 230 psi and no sign of stress nor leak. take a hamer, and smash pvc, your pipe is broken. smash a gal.steel pipe and it's your hammer that is hurt.

Real number please that results from wether formula or manufacturer.
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Unread postAuthor: SpudStuff » Fri Dec 15, 2006 5:07 pm

Read, Learn, and Get your Head out of your ass.

"From McMaster...

2" Sch 40 black steel pipe.
OD = 2.375"
ID = 2.067"
wt = .154"

Using standard thin wall pressure vessel theory....

Pressure = Stress * (2 * wt) / ID

CHEAP steel in this day and age yields at 35,000 psi but just to account for the "made in China" syndrome we'll assume 30,000. Further, steel fatigue strength is about 1/2 it's original strength so let's bump that down to 15,000.

Pressure = 15e3 * 2 * 0.154 / 2.067 = 2235 psi

Mind you, that's assuming no stress concentration factors or anything. It's also using thin walled assumptions which will give one a slightly high number. Still, I don't think it's too assinine to assume that *ACTUAL* failure pressure is on the order of 1500 psi.

Doesn't mean I want to USE that pipe at 1499 psi, mind you. There's something to be said for safety factors. At the office, 5:1 is what we use for designs involved in energetic scenarios... That takes you to 300 psi.

And heck, if somebody wanted 10:1 safety, you're right there at 150 psi. And that may not be ridiculous if you want to maintain 5:1 "real" safety factor in the face of water hammers and such.

The point to all of this: Even if steel pipe is only rated to 150 psi, I wouldn't think twice about putting a significantly higher pressure in it. Steel production techniques have improved greatly since those standards were written. We don't do anything that would even begin to fatigue steel. Yada yada yada. How high WOULD I go? Depends on what I *KNOW* about the pipe in question (ie, confirm assumptions previously made), but 300 psi sounds reasonable to me."
-D_Hall


This guy knows what he is talking about.
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Unread postAuthor: CpTn_lAw » Fri Dec 15, 2006 5:41 pm

now this is a good answer, thanks spudstuff. and, i usualy hear people talking about 3:1 safety factor.
I've also read on web site explaining how to do really clean sldering job, that when testing the strength of a soldering, the pipe usualy breaks before the soldering, at 3000 psi.
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Unread postAuthor: ProfessorAmadeus » Fri Dec 15, 2006 5:58 pm

Really there is no way to get to that pressure any ways. You would have to use unregulated co2 or oxygen. Plus there is no need to go that high. Also where would you get a valve for it.
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Unread postAuthor: CpTn_lAw » Fri Dec 15, 2006 5:59 pm

air supply : diving compressor...

valve: homemade piston Professor....
exhaust: machined steel valve.
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Unread postAuthor: drac » Fri Dec 15, 2006 6:02 pm

Well Spudstuff, I apologize. Didn't know you were taking the safety factor into account.

Though, I still firmly maintain that you can take that steel way higher than 150. :oops:
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Unread postAuthor: SpudStuff » Fri Dec 15, 2006 6:18 pm

I knew that all along.

My point was, like PVC, it is not that safe to take the pipe and/or fittings above thier rated working pressure. Remember that what I posted does not take temp, fatigue, and rapid pressurization and depressurization into account.
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Unread postAuthor: judgment_arms » Fri Dec 15, 2006 6:36 pm

roughboy, I’m going to barrow your thread for a second.

Quick question: is black pipe forged or cast? Because if it’s cast I can’t work it.
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Unread postAuthor: The Haymaker » Fri Dec 15, 2006 7:01 pm

I see one problem with all this presure stuff......... He never said what his pipe is!
For all we know it could be metal stove pipe, and he is currently trying to figure out why something went boom in the shop and wondering why his ears are ringing.......... There's lots of pipes, metals, thickness, etc, need I go on?

For instance, I just finished making one of two air tanks for the TaterHater out of 4" EMT. This stuff is made to run wires through, not compressed air, so how can someone use a generic formula to decide what pressure is safe for me to use?

I look at it this way, it HAS to be safer than the pair of 3" sched40 PVC tanks that, as of last weekend, are scattered across my back yard looking like the Discovery.......

E

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Unread postAuthor: ProfessorAmadeus » Fri Dec 15, 2006 7:24 pm

You see stuff that isnt made for pressure isnt made for pressure. After 1 psi it could blow or it could be at 250 before it blows (pulling #'s out of my ass) The thing is its more important to be safe then to save a coulpe dollars. Nice welding by the way. Im terrible :roll:
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Unread postAuthor: The Haymaker » Sat Dec 16, 2006 7:00 am

I knew that answer, I just hated to see anyone get hurt. This stuff is 1/8" galvanized, I can't see it being too weak, but........

Anyway, I welded in 1/8" end caps made with the trusty 4.25 hole saw. It was a pain, as the blanks are slightly smaller than the hole, requiring quite a bit of fill. I'm doing this with a stick welder, not exactly the weapon of choice. The trick to welding? Practice, practice a lot. Learn to focus your heat on the larger piece of metal (whichever will take more heat), and in the case of this thinwall stuff, weld only a little at a time to keep from blasting holes. I'm no pro, the tanks have a little too much bubblegum, but it'll work.

Hopefully this thing will work. The plan is to be all metal, I'm tired of replacng PVC, so far I've been lucky and not hit by any shrapnel. I'm hoping fr a working piston valve and breech load. 17' of barrel is too far to run every time you reload!

E
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Unread postAuthor: boilingleadbath » Sat Dec 16, 2006 1:32 pm

From my experience machining steel pipe, I believe that steel pipe is not cast - although I honestly don't know enough about the machining qualities of cast iron to say for sure.

I will say, however, that when machining aluminum pipe on a lathe, you really have to plug the end with some wadded paper (or better yet, clay)... because otherwise it resonates like some sort of 90 decibell tuning fork.
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