exploding plastic storage tanks

[Jon Stratis]

This past week at the Lake Superior regional we had one of the plastic air tanks from Clippard explode on the field, sending pieces all the way up into the stands (at LSR the stands start about 10 ft above the field, with plenty of space between them and the field), and I heard there was a tank that blew in week 1 as well.

At LSR, we believe the failure was caused by damage to the tank, not a manufacturing defect (like a void in the plastic wall). The team used hose clamps to attach the tank to their robot - the screws from the clamps bit into the sides of the tank, and when reassembled the tank was slightly deformed from being squeezed by the clamps. As far as we can tell, the initial fracture point was right under the clamp, near the screw. Further, the tanks were mounted in a very exposed position, and took some hits from other robots.

I want to strongly caution teams to mount these tanks properly (with the provided plastic clips or through some other means that holds them securely without applying undue pressure on the sides of the tanks) and to protect them inside the frame perimeter. The tanks were designed for a much gentler use than we're putting them through (mounting to a static mechanism that doesn't take impacts or damage, and doesn't need firm mounting to hold the tanks in place), and rough handling will eventually lead to failure!

[scaryone]

Maybe wrapping the tank with a sleeve to catch pieces if they do fail would work?

[jijiglobe]

Our team uses velcro

[Trent B]

I would definitely second the mention of being careful with your mounting. Any harsh mounting (hose clamps) that deforms the tank or otherwise marks it is changing the mechanics of the system rather dramatically.

The polymer used to make these tanks seems fairly brittle, that combined with the high stresses involved can lead to failure with little to no warning.

Makes me comforted to know that on Neutrino our air tanks are placed in our 3x3 6061 drive tubes so in the event of a failure it should all be contained.

[MrForbes]

Would a "sleeve" contain the shrapnel, or direct it (at higher velocity) in two directions?

We have several old metal tanks, we'll continue to use them.

[JamesCH95]

Originally Posted by MrForbes

Would a "sleeve" contain the shrapnel, or direct it (at higher velocity) in two directions?

We have several old metal tanks, we'll continue to use them.

A properly designed containment sleeve would contain shrapnel, but a poorly designed one could certainly direct shrapnel out either end at a high velocity.

[FRC3883FRC]

Our team had our tanks on our intake a very vulnerable position. We were highly highly HIGHLY recommended by the inspectors (almost to the point of not passing) to cover our tanks. We simply added bumper material over both of the tanks. They still fit right in the same c claps they some with and they dont look all that bad. A couple zip ties and the bumper fabric and we were good to go. You can see in the video that our robot has two red tubes at the top of the intake and around 9 seconds in you can see why they highly recommended covering them up.
Here is the video.
http://www.youtube.com/watch?v=nvAFL...u8USGMhWY2qgkw
If you are using these tanks make some covers or make sure they are in a very safe location.

[JamesCH95]

Originally Posted by FRC3883FRC

Our team had our tanks on our intake a very vulnerable position. We were highly highly HIGHLY recommended by the inspectors (almost to the point of not passing) to cover our tanks. We simply added bumper material over both of the tanks. They still fit right in the same c claps they some with and they dont look all that bad. A couple zip ties and the bumper fabric and we were good to go. You can see in the video that our robot has two red tubes at the top of the intake and around 9 seconds in you can see why they highly recommended covering them up.
Here is the video.
http://www.youtube.com/watch?v=nvAFL...u8USGMhWY2qgkw
If you are using these tanks make some covers or make sure they are in a very safe location.

Do you think that you are actually providing any meaningful protection by wrapping the tanks with bumper fabric and zip ties?

[Tom Line]

A spandex sleeve (or even bumper material...) over each tank would be an elegant and easy way to safeguard folks from flying debris, and the porous nature of the fabric would prevent the air pressure from 'exploding' the sleeve.

Hey ANDYMARK! Are you listening?

[FrankJ]

In one case, the problem was a student over-tightening a fitting to the plastic threads. In another case, we believe that Loctite was used on the fitting threads.

A good point. A good many liquid pipe thread sealers are not intended for plastic pipe. Only use them on the material listed on the can.

[JamesCH95]

Originally Posted by Tom Line

A spandex sleeve (or even bumper material...) over each tank would be an elegant and easy way to safeguard folks from flying debris, and the porous nature of the fabric would prevent the air pressure from 'exploding' the sleeve.

Hey ANDYMARK! Are you listening?

No, no it wouldn't. See other posts in this thread about shrapnel puncturing ball covers without issue.

I think I posted something similar last year... but biaxial kevlar sleeve or similar would be required to provide even modest protection. Multiple layers would be required IMO, and a good way to keep the ends of the sleeve closed.

Edit: what velocity air flow is needed to exert a significant pressure on a fabric? Said fabric doesn't need to be air-tight to sustain significant loading in the event of a storage tank's catastrophic failure. Not to mention cutting and tearing resistance to the sharp tank fragments.

[Tytus Gerrish]

this makes me want to test one to failure just to see that it takes to bust em

[Gregor]

Originally Posted by Tytus Gerrish

this makes me want to test one to failure just to see that it takes to bust em

Don't do it. It's seriously scary, especially when you're 4ft away from it. I couldn't hear from the ear facing the tank for about 15 minutes, and it hurt for the rest of the weekend. The shrapnel went flying into a pit about 30 ft. away, and killed our driver station computer.

Don't do it.

So it seems that this has happened at least four(?) times in the last two years. If FIRST was serious about safety these would be outlawed.

[Tom Line]

Originally Posted by Gregor

Don't do it. It's seriously scary, especially when you're 4ft away from it. I couldn't hear from the ear facing the tank for about 15 minutes, and it hurt for the rest of the weekend. The shrapnel went flying into a pit about 30 ft. away, and killed our driver station computer.

Don't do it.

So it seems that this has happened at least four(?) times in the last two years. If FIRST was serious about safety these would be outlawed.

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.

[mman1506]

Whether a sleeve is an effective solution or not wrapping a piece of bumper fabric around a tank in a bad location and deeming it safe without any proper testing is ignorant.