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Unread 10-03-2014, 12:23
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exploding plastic storage tanks

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!
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Unread 10-03-2014, 12:27
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Re: exploding plastic storage tanks

Maybe wrapping the tank with a sleeve to catch pieces if they do fail would work?
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Unread 10-03-2014, 12:32
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Re: exploding plastic storage tanks

Our team uses velcro
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Unread 10-03-2014, 12:34
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Re: exploding plastic storage tanks

I have witnessed this in person twice (both times in 2013) and thankfully nobody was hurt either time. But they probably could have been.

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.

Last year I proposed a mandatory sleeve in this post. I think it would be a cheap, easy, and effective harm reduction measure (though it would certainly need to be well-tested)...and it would let teams color their air tanks however they see fit
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Unread 10-03-2014, 12:37
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Re: exploding plastic storage tanks

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.
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Unread 10-03-2014, 12:46
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Re: exploding plastic storage tanks

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.
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Unread 10-03-2014, 12:52
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Re: exploding plastic storage tanks

Quote:
Originally Posted by MrForbes View Post
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.
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Unread 10-03-2014, 12:56
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Re: exploding plastic storage tanks

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.
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Unread 10-03-2014, 13:06
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Re: exploding plastic storage tanks

Quote:
Originally Posted by FRC3883FRC View Post
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?
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Unread 10-03-2014, 13:09
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Re: exploding plastic storage tanks

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.

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Unread 10-03-2014, 13:12
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Re: exploding plastic storage tanks

Quote:
Originally Posted by FRC3883FRC View Post
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.

1310 had an air tank explode in their pit and the pieces went right through the FRC Ball puncturing 2 layers of fabric and rubber without slowing it down. I doubt the bumper fabric would be able to contain it.
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Unread 10-03-2014, 13:15
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Re: exploding plastic storage tanks

Quote:
Originally Posted by Jon Stratis View Post

and I heard there was a tank that blew in week 1 as well.
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.

PLEASE ensure that if you are using the tanks, that you do not over tighten the fittings. I highly recommend pipe dope (thread sealant paste) for the plastic tanks. It allows you to tighten the fittings less while maintaining a good seal.

something like this

http://www.henkelna.com/product-sear...=8797874651137

The tanks are both a blessing and a curse, please treat them with care, as both inexperienced students and "experienced" mentors have fallen victim to these tanks.
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Last edited by donkehote : 10-03-2014 at 13:18.
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Unread 10-03-2014, 13:16
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Re: exploding plastic storage tanks

Quote:
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.
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Unread 10-03-2014, 13:18
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Re: exploding plastic storage tanks

Quote:
Originally Posted by Tom Line View Post
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.
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Last edited by JamesCH95 : 10-03-2014 at 13:25.
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Unread 10-03-2014, 13:26
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Re: exploding plastic storage tanks

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