exploding plastic storage tanks

[Racer26]

Originally Posted by Gregor

For anyone who doesn't know, these are the terrifying pieces flying through the air that we're dealing with.

Moving with enough kinetic energy to do lots of damage. Luckily so far, the serious damage has all been to inanimate objects. I agree HQ needs to do something, though I'm not sure an outright ban is necessary.

[Mark Sheridan]

Originally Posted by Gregor

For anyone who doesn't know, these are the terrifying pieces flying through the air that we're dealing with.

"You'll shoot your eye out"

Those are scary. Are the tanks breaking in a localized area or is the whole thing exploding?

[Duncan Macdonald]

Originally Posted by donkehote

One of 1310's tanks blew at GTR west. One of the mentors was tightening a fitting into the tank with the tank inflated to 120 psi try to eliminate a leak. The tank exploded in the mentors hands, (thankfully no injury's) and destroyed the laptop that was below the tank, aswell as popping one of their balls. The shrapnel was sent flying all the way to the roof of the fieldhouse, and was quite a shock to those at the event.

Could a 1310 representative give us an official story from someone who was there?
This story is spreading like a game of broken telephone. Link

Have all of the exploding tanks been the white clippard tanks from 2013 and before? Are these the same tank in a new colour?

I also feel safer around tanks with the push-in fitting standard. One less source of failure.

[JesseK]

Originally Posted by Mark Sheridan

Looks like I am gonna have to relocate my air tanks.

Just a crazy idea that is not FIRST legal:
Could we make our own storage system with large OD high pressure tubing and barb fittings?
http://www.mcmaster.com/#5632K43

This stuff is ductile and could be snaked around, cut to length and should not explode when pierced. Has anyone used this stuff at 120 PSI, the most I ever used is 90 PSI, same with barbed fittings. I am not a fan of barbed fittings but I think this could be safer.

The rules would have to change in order for this to happen. Thought? I am not sure this is the ideal tubing, but this is something I used before that sort of works.

Cut to length sounds appealing, but "Snaked around" with a 36" bend radius (6' diameter !?) shouldn't be promoted.

[FrankJ]

Originally Posted by Mark Sheridan

"You'll shoot your eye out"

And that is why you wear safety glasses in the pit.

[Racer26]

Originally Posted by Duncan Macdonald

Could a 1310 representative give us an official story from someone who was there?
This story is spreading like a game of broken telephone. Link

Have all of the exploding tanks been the white clippard tanks from 2013 and before? Are these the same tank in a new colour?

I also feel safer around tanks with the push-in fitting standard. One less source of failure.

Gregor is a member of 1310 and has made numerous comments about his experience 4ft from this incident in this thread.

[Mark Sheridan]

Originally Posted by JesseK

Cut to length sounds appealing, but "Snaked around" with a 36" bend radius (6' diameter !?) shouldn't be promoted.

Hmmm...I need to go straighten something out, brb

[team222badbrad]

Originally Posted by Duncan Macdonald

Could a 1310 representative give us an official story from someone who was there?
This story is spreading like a game of broken telephone. Link

Have all of the exploding tanks been the white clippard tanks from 2013 and before? Are these the same tank in a new colour?

I also feel safer around tanks with the push-in fitting standard. One less source of failure.

I believe the the only tanks that had an issue were from 2013. Clippard offered to replace them for free last year with a different model after the issue was found.

http://www.chiefdelphi.com/forums/sh...ippard+replace

If anything FIRST should ban the usage of the white threaded tanks since they obviously still have the casing cracking at the threads from over tightening and/or poor manufacturing and can easily be replaced with the new push to connect model.

I have yet to hear of a failure with the new black "push to connect" storage tanks which are much better, but you should still locate them in a relatively safe spot on your robot to prevent damage to them.

[Jon Stratis]

Originally Posted by Duncan Macdonald

Have all of the exploding tanks been the white clippard tanks from 2013 and before? Are these the same tank in a new colour?

From the research we did while up in Duluth, the white 2013 tanks have been discontinued. While they were rated at 150 psig working pressure, their replacements (which at least look identical on the surface, although I can't speak towards any manufacturing changes or non-visual/structural changes that may have been made) are only rated for 125 psig.

[JamesCH95]

Originally Posted by Tom Line

I STRONGLY disagree that the only avenue of improving the potential safety issues around plastic pneumatics tanks is outlawing them. I would much rather see a numbers-driven problem solving method applied.

However, I can see vendors stepping away from supplying a 'safety' item like a sleeve since it becomes a question of liability if someone gets injured.

You're doing it wrong. The question should not be "how do we make plastic storage tanks safe?" The question should be "how do we make safe, light, air storage tanks?" Because teams only use plastic storage tanks because they are lighter than commonly available metal tanks.

Here are some numbers:

Polypropylene: ~37MPa TS, 0.94g/cc density, 39MPa/(g/cc) strength:density ratio

304 Stainless Steel: 515MPA TS, 8.0g/cc density, 64MPa/(g/cc) strength:density ratio

The reason why teams use plastic tanks is because they are lighter than the stainless tanks from Clippard. Unfortunately, this low weight comes at the price of strength and durability. Stainless steel has a significantly higher strength:weight ratio than polypropylene.

Plastics tend to have brittle failure modes in dynamic situations, which is why they generate shrapnel, and why they are generally a terrible choice for pressurized gas applications. Not to mention their sensitivity to temperatures, certain chemicals, nicks/scratches/gouges, over-tightening, etc.

[JVN]

Have any of these discussed failures been with the new black tanks?

[Duncan Macdonald]

Originally Posted by Racer26

Gregor is a member of 1310 and has made numerous comments about his experience 4ft from this incident in this thread.

My fault, poor phrasing....

Could someone from 1310 describe:
-What was the source or compressed air (Through the robot or a separate compressor)
-If the tank had been on a previous robot
-How they mount their tanks. (supplied connector, zip ties, loose inside the robot, etc.)
-Is there any chance the tank had been dropped or mishandled.

[Jared Russell]

Originally Posted by JVN

Have any of these discussed failures been with the new black tanks?

Both of the failures that I referenced in my post were with the white tanks without push-in fittings.

[team222badbrad]

Originally Posted by Jon Stratis

From the research we did while up in Duluth, the white 2013 tanks have been discontinued. While they were rated at 150 psig working pressure, their replacements (which at least look identical on the surface, although I can't speak towards any manufacturing changes or non-visual/structural changes that may have been made) are only rated for 125 psig.

There might be other changes, but the two main visual changes to the tanks are:

Color change. (This may mean a different grade of material or nothing at all.)

Plastic welded push to connect fittings. (This eliminated the failure point due to threading push to connect fittings into the threaded tanks.)

For those who haven't see the ends of the new tanks available from AndyMark:

[Tristan Lall]

Originally Posted by JamesCH95

Plastics tend to have brittle failure modes in dynamic situations, which is why they generate shrapnel, and why they are generally a terrible choice for pressurized gas applications. Not to mention their sensitivity to temperatures, certain chemicals, nicks/scratches/gouges, over-tightening, etc.

Exactly right about this: the ductile vs. brittle failure modes are a critical distinction between metal and plastic tanks. It would take an extremely (and unrealistically) high strain rate to cause an unhardened metal tank to fail in a brittle manner.

Originally Posted by JamesCH95

The reason why teams use plastic tanks is because they are lighter than the stainless tanks from Clippard. Unfortunately, this low weight comes at the price of strength and durability. Stainless steel has a significantly higher strength:weight ratio than polypropylene.

Incidentally, the carbon fibre skin on the Boeing 787 is (in some places) thicker than structurally necessary because it needs to be resistant to penetration by objects like baggage carts. Physical damage tolerance is often an application-specific requirement, and may not be adequately regulated in the FRC rules.

One can conceive of a similar situation with conventional ductile metal tanks: you could make them very thin and still strong enough to withstand the pressure load, but any damage could cause them to fail (albeit in a ductile way). (Contrast this with a hypothetical hardened (i.e. not ductile) metal tank: paper-thin and very strong, but if damaged, it shatters. That would be a bad design in this application.)