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Barrel Ruptures.Video.
Posted: Mon Sep 17, 2007 3:54 am
by rna_duelers
This is of course on a Giant gun,used in Pumpkin Chunkin(spelling) and the PVC barrel which must be atleast 8" in Diameter bursts quite spectacularly.
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Posted: Mon Sep 17, 2007 4:01 am
by jackssmirkingrevenge
looks like it failed at the point where it was being suspended and where it attaches to the chamber, the areas of greatest stress.
Posted: Mon Sep 17, 2007 4:12 am
by MrCrowley
It fails at the valve, then while failing it looses all support so it bends in the middle which then snaps.
Posted: Mon Sep 17, 2007 4:54 am
by Novacastrian
Look at the black "spot" about 4 feet down from the support
Posted: Mon Sep 17, 2007 5:32 am
by mark.f
From me, it looks like this:
The unsupported region, (the area between supports), is where it failed. Possibly because it was sagging slightly before firing. When fired, it was abruptly straightened, and then went into complex harmonic motion as the pressure declined, causing enough stress to shatter the pipe.
In which case, this is just another warning to people not using barrel supports. We should really make a rule on the usage of them. Like, for a certain diameter, having a maximum length of pipe you can use without support.
EDIT: on a side note, this must not be at the Pumpkin' Chunkin' competition, huh? I though you weren't allowed to use PVC for that show?
Posted: Mon Sep 17, 2007 5:36 am
by rna_duelers
Harmonics and stress on an unsupported point is my guess.Goes out pretty well but doesn't it
.
Maybe this is why they made it against the rules to use PVC in the cannon.
Posted: Mon Sep 17, 2007 9:40 am
by Fnord
This barrel is supported by cables. the second point of failure is right where the cable is attached. (Or, are those cables attached to something in the background?)
The first point of failure appears to be a breach, so who knows exactly what was going on there.
Also, if you listen closely, the announcer says "we are standing.. right underneath of this particular machine..."
Posted: Mon Sep 17, 2007 5:37 pm
by clide
markfh11q wrote:
EDIT: on a side note, this must not be at the Pumpkin' Chunkin' competition, huh? I though you weren't allowed to use PVC for that show?
You can't now, and that launcher is the reason why. You also have to have certified pressure vessels, and I'm sure there are many other rules that are much more strict than when they started.
Posted: Mon Sep 17, 2007 6:00 pm
by mark.f
OK, so this is an old video. That would make sense.
I also knew about the certification. Does that mean you have to have a specifically designed pressure tank that an ASME engineer thought up, or can you have a reasonably safe designed vessel that has been hydro-tested and certified by an ASME engineer on site?
Posted: Mon Sep 17, 2007 6:11 pm
by clide
I don't know if it has to be designed by an engineer, but it needs to meet all the requirements and go through all the tests and inspections by engineers
1. All pressure vessels shall be built to the American Society of Mechanical Engineers (A.S.M.E.) construction codes. The vessels will have a manufactures nameplate with proper (A.S.M.E.) stamping and will be marked with the vessel’s allowable working pressure.
2. All pressure vessels shall be equipped with A.S.M.E. approved and scaled relief valve set at or below the allowable working pressure of the vessel. A smaller A.S.M.E. relief valve can be placed on the vessel when the operation required the tank to be filled from a cylinder tank. This valve will be set at or below the allowable working pressure of the vessel. All relief valves must be maintained in proper working order during operation of the vessel. The relief valve will need approval by the boiler safety so it is recommended you contact them before purchasing the valve.
3. Each vessel shall be inspected by the Delaware Division of Boilers safety and issued an operating certificate. These certificates are valid for four years from the date of inspection/issuance. This certificate must be in hand before machine can enter the field.
4. Each vessel shall have a hydrostatic test conducted in accordance with the test procedures in the national board inspection code. Each vessel must be hydrostatically tested every two years and witnessed by a National Board Commissioned inspector and the results recorded and presented at time of inspection by the department. If a third party National Board Commissioned inspector is not used, a department inspector can witness the test on any vessel upon request. If out of state vessels are to be inspected by a department inspector the vessel must be in Delaware no later then Wednesday before the event.
5. A.S.M.E. vessels now in operation are considered (GRANDFATHERED) under these conditions. Any future alterations and repairs made to the pressure vessel must meet the National Board of Boilers and pressure vessel Inspectors Code (NBIC). Any air cannons constructed after the 2004 event must meet existing Department regulations and the vessel must be mounted in a cradle type mount with no welding of the vessel to the frame.
6. All vessels regardless of origination, operated at the event must meet these requirements.
7. The World Championship Punkin Chunkin Association is not in a position to deviate from the Department of Natural Resources and Environmental requirements and must ensure enforcement of those requirements.
http://www.punkinchunkin.com/rules.htm
It looks like quite a hassle and probably throws out all the junkyard builders that first started in these contests, but its probably a pretty good idea with the size of crowds they get now.
Edit: This video is from the 2004 contest
http://www.punkinchunkin.com/gallery2004.htm
Posted: Mon Sep 17, 2007 7:11 pm
by mark.f
Ahhhhh yes. ASME construction codes. Themselves quite an expense if you can't find a public source for them.
Throw, on top of that, the inspections and hydrostatic test, and you've got quite the bill to pay. No wonder all those guys said they only built the cannon for around 200 bucks... getting it ready for the competition set them back way further than that!
I guess you could just try to be as safe as you can be building it, and then pray it falls within ASME specs?
