Re: exploding plastic storage tanks
 

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.

Re: exploding plastic storage tanks
 

"You'll shoot your eye out"

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

Re: exploding plastic storage tanks
 

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.

Re: exploding plastic storage tanks
 

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

Re: exploding plastic storage tanks
 

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

Re: exploding plastic storage tanks
 

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

Re: exploding plastic storage tanks
 

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

Re: exploding plastic storage tanks
 

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. ::ouch::

Re: exploding plastic storage tanks
 

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.

Re: exploding plastic storage tanks
 

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.

Re: exploding plastic storage tanks
 

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

Re: exploding plastic storage tanks
 

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.

Re: exploding plastic storage tanks
 

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

Re: exploding plastic storage tanks
 

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:

Re: exploding plastic storage tanks
 

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.

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.)