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Author Topic: still building stove  (Read 7053 times)

jackel440

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Re: still building stove
« Reply #15 on: September 15, 2011, 05:40:50 PM »

I agree with Willie whole heartedly.You don't want to over pressurize a flat sided tank with to much psi.I charged my tank with 8 to 10 psi.I accidentally got her up to 15psi as i was looking at something else ,and my sides popped out ,and scared the crap out of me. ;)
I welded reiforments from the tank side to the burn chamber,and if i hadn't done that I am sure my 5' long flat side  would have ended up bell shaped.
5 to 10 psi is more than sufficient to check for leaks.At the pressure you will hear the metal still try and move from the stress.
Unless you are an experianced pipe,and or steam fitter and know hydraulic pricipals of tanks.Then built it as such I would stick with a lower psi to check it.We sure would hate to hear how you launched your wood burner across the yard. :thumbup: (ok not really that far but you get the point)
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martyinmi

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Re: still building stove
« Reply #16 on: September 15, 2011, 07:52:30 PM »

general rule of thumb is if you use a flat end on a pressure vessel it will have about 30 percent more force on the flat end than on the pipe itself...yes the presusre is the same (50lb psi is 50lb psi) but it accumulates on the flat surface. think of a hydraulic cylinder with a bore of say 3 inches..add 1000 psi and it may lift 3 or 4 tons now take a cylinder with a 10 inch bore and the same 1000psi and it may lift 100 tons..same pressure but more square inches to push on...when you test your OWB ith a flat end on it you are essentually pushing on the flat end the same as a hydraulic cylinder...the bigger the bore the more pressure you exert on the flat surface. that is why your oil barrel bulged (failed) and an OWB with a flat end will burst or warp long before the same rounded side walls will give way
3"=3.53 tons
4"=6.28 tons
10"=39.27 tons
   Pressure will not accumulate or build up more on the flat ends of a cylinder. Because of its inherent design, the metal on the ends will move more, and because of the stress associated with that movement it will fail first.
   With all the respect that's due to you Willie, I don't buy into your rule of thumb(30%?) for flat ended pressure vessels. The force will be equal over every square inch of the inside of the vessel.
   Speak to a metallurgist as I have. 36" ductile iron well pipe @ .375 wall thickness with virgin .375 ends welded properly(two passes inside and out) with 80000 tensile strength wire will barely move(ends) at 45 psi. You will be shocked at the pressure it will take before the ends eventually fail.
   I agree with you all about low pressures being used for open systems to check for leaks. Every winter I do many fabricating projects, including building power units,manure pumps, booster pumps,manure applicators,knife-in applicators, etc. I understand what metal is capable of, and more importantly what it is not capable of.
   A portable air tank(.125 wall thickness) with a flat end(.125) properly welded on will not fail at 100 psi. That is fact.
   The flat end of the 4" square pipe measured 3.5" square(I.D. of 4" is 3.5).   
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willieG

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Re: still building stove
« Reply #17 on: September 16, 2011, 06:28:09 PM »

marty, i am sure you know more of metal and what it may do or not do than i and i am in no position to argue  with you about more pressure on the end of the vessle. perhaps i should say that the flat end of a vessel will take 30% less force than the rounded ends (and this may still be wrong) but i do know that a flat ended vessel of any kind can not take the same pressure as one with cylinderal ends unless the flat end is made stronger with bracing or perhaps thicker flat ends and heavier welds

they make pressure vessels this way as it is the cheapest because there is no need to strengthen the ends to take the stress of the metal trying to push round to make "all things equal"

i dont know much about metelurgist stuff but i do notice that when i work in the chemical plants and they bolt a blank flange on a pipe (no matter what size the pipe) the blank flange is always way thicker than the pipe wall. the flanges are reated for certain max. pressures like 150...300..and upwards, each being thicker as the rating goes up. i  will agree that  if your man told you after welding your flat end on the well pipe and it would (i belive he said) "barely move"  than i would agree with him. but where i work if it "barely moves" it will eventually fail.

a lot of folks here that build their own OWB come here for pointers and help and like to read many other posts and a lot of them (you may not be included here) are "back yard welders" that are self taught and hit their welds with a hammer to test them not xray or bend test  them as you and i may do. so with that in mind i personally will never tell a guy to pressure test his stove with air (unless he first filled it with water) and i would never suggest any pressure over a 8 or 10 pounds as that should show up any leaks in a 24 hour test period.

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martyinmi

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Re: still building stove
« Reply #18 on: September 16, 2011, 07:10:52 PM »

Willie-
   You and I are on the same page where testing procedures are concerned for leak checking an open system home built OWB. 'Nuff said.

   Marty
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Scott7m

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Re: still building stove
« Reply #19 on: September 16, 2011, 07:20:10 PM »

Yea as Willie said, 60 psi isn't comparable to some things, but a lot of folks who come on here are "back yard welders" to make them think it's safe to run psi that high is misleading, there is a huge difference in someone who understands welding and someone who says, "yea I can weld, I welded in
shop class in highshool" lol
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mober

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Re: still building stove
« Reply #20 on: September 17, 2011, 08:31:06 AM »

agree
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