Destructive Air Tank Testing

[Andy A.]

Originally Posted by Nuttyman54

What method are you using to cause the failure? Simple over-pressurization or are you intentionally over-tightening the end fittings? It would be brittle failure either way, but it may make a difference in how much energy is in the system at the time of failure. An over-tightened fitting would likely fail at a fair lower pressure (eg, potentially below 120psi) whereas a properly assembled tank would not.

On that same note, did you monitor the pressure that the tanks burst at, and if so how consistent was it?

Originally Posted by ToddF

At what pressure did the tanks actually fail? I would expect them to have a safety factor of at least 3X.

Originally Posted by team222badbrad

I would also like to know how you made them fail?

All the tanks were pressurised to 120psi (regulated output of a shop compressor) then struck with an air rifle pellet to induce the failure. It turned out to be remarkably consistent and reliable (well, as reliable as my aim!). The video of the testing will get into detail about the methods, but we think it's a reasonable simulation of a tank failing in FRC use due to a sudden impact

My subjective opinion is that each tank burst with the same sort of force. The shrapnel, noise and effect on containment all seem to back that up.

[JamesCH95]

Originally Posted by MrForbes

Instead of looking at more wonderful creative ways of containing shrapnel, I'm looking for ways to make sure all of these tanks get replaced with something more reliable at the regionals I attend....

I agree entirely. 95 only uses metal tanks on our robots. Always have, always will.

As hinted at earlier, our goal is not to provide actual shrapnel containment solutions, but rather to demonstrate how difficult it would be to make plastic tanks as safe as metal tanks.

[nathannfm]

Broken laptop in homage to 1310's driver station?

[Mark Sheridan]

Originally Posted by Mark Sheridan

I wish clippard made a metal air volume tank the same size as their biggest cylinder. I would love to have a 3" ID tank that is 6" long. hmmm I am gonna email them right now.

Ok so Clippard can make air volume tanks the same dimensions as their cylinders. I went through their distributor and asked for a 3" bore 12" long storage tank (84 ish cubic inches). I will see what the quote is.

[JamesCH95]

Originally Posted by nathannfm

Broken laptop in homage to 1310's driver station?

Maaaaybe...

Also it made the white tank stand out against the snow-covered driveway for Andy to aim at.

[Oblarg]

Originally Posted by MrForbes

Instead of looking at more wonderful creative ways of containing shrapnel, I'm looking for ways to make sure all of these tanks get replaced with something more reliable at the regionals I attend....

I'm thinking we're going to avoid them in future years. Unfortunately, we can't afford to swap the ones currently on our robot out for metal substitutes this year, but I'm not liking the explosive failures one bit.

If this continues, FRC should just go back to allowing only metal tanks.

[AllenGregoryIV]

Originally Posted by Oblarg

If this continues, FRC should just go back to allowing only metal tanks.

These tests and all of the failures I know of are on a single brand and model of tank that is known by the manufacturer to have this problem. To my knowledge no one has tested the 2014 Clipboard tanks or any other manufacturer's tanks for these types of failures. We shouldn't talk in generalities so quickly, we still have very little information on this subject.

[JamesCH95]

Originally Posted by AllenGregoryIV

These tests and all of the failures I know of are on a single brand and model of tank that is known by the manufacturer to have this problem. To my knowledge no one has tested the 2014 Clipboard tanks or any other manufacturer's tanks for these types of failures. We shouldn't talk in generalities so quickly, we still have very little information on this subject.

Along those lines, if anyone has a spare black tank or three they want us to test, please send it! Or any of the available plastic tanks.

Plastics are still plastics though... in the OP read the memo from the plastic pipe institute, it's only a page. A very carefully worded caution against using plastic to transport compressed gases. It's all about the cost of failure, and the simple fact of the matter is that plastics will generally shatter when they fail and metals will generally yield, crack, and vent all of the gas out without making shrapnel.

I think we might also try to make a metal tank fail, but that's a whole other ball of wax...

[Oblarg]

Originally Posted by AllenGregoryIV

These tests and all of the failures I know of are on a single brand and model of tank that is known by the manufacturer to have this problem. To my knowledge no one has tested the 2014 Clipboard tanks or any other manufacturer's tanks for these types of failures. We shouldn't talk in generalities so quickly, we still have very little information on this subject.

IIRC, people were having trouble with explosions last year, as well. Admittedly, those were due to threading the connectors in too far, which is no longer a problem with the built-in connectors

Fact is, though, this is a high-school competition and it's much easier for a high school student to inadvertently damage a plastic tank in a way that will cause a dangerous failure than a metal tank. I wouldn't be so concerned if these were only being used by adult engineers, but they're not. I certainly would rather be safe than save a pound or so of weight.

[JamesCH95]

Originally Posted by Oblarg

IIRC, people were having trouble with explosions last year, as well. Admittedly, those were due to threading the connectors in too far, which is no longer a problem with the built-in connectors

Fact is, though, this is a high-school competition and it's much easier for a high school student to inadvertently damage a plastic tank in a way that will cause a dangerous failure than a metal tank. I wouldn't be so concerned if these were only being used by adult engineers, but they're not. I certainly would rather be safe than save a pound or so of weight.

The failures noted so far this year have still been those 2013-era white plastic tanks to the best of my knowledge. Not the 2014-era black plastic tanks.

[AllenGregoryIV]

Originally Posted by JamesCH95

The failures noted so far this year have still been those 2013-era white plastic tanks to the best of my knowledge. Not the 2014-era black plastic tanks.

Yes the failures this year and last year were the 2013 Clippard White tanks. White tanks from Pneuaire, Andymark and others, along with the Black 2014 Clippard tanks have not had failures to my knowledge.

I also understand the risk of plastic tanks in general but there are also risks with many of the systems and tools that we use in competitive robotics. We need to mange the risks in the smartest ways we can to ensure the safety of the participants and spectators.

[JamesCH95]

Originally Posted by AllenGregoryIV

Yes the failures this year and last year were the 2013 Clippard White tanks. White tanks from Pneuaire, Andymark and others, along with the Black 2014 Clippard tanks have not had failures to my knowledge.

I also understand the risk of plastic tanks in general but there are also risks with many of the systems and tools that we use in competitive robotics. We need to mange the risks in the smartest ways we can to ensure the safety of the participants and spectators.

The clippard tanks we used were acquired through the AM FIRST Choice program. I believe AM simply re-sells Clippard tanks.

The risk of plastic tanks is obviously controversial. I'll relate a conversation I had with a lawyer when I was interested in selling potato cannons (another hobby of mine). He made a very good point that is very pertinent to this topic.

His professional opinion was that no matter the disclaimer I had customers sign that I could be held liable for any damages or injuries incurred though the use of a potato cannon I made and sold because there is NO NEED for a potato cannon, it's a toy. Car makers are generally safe from accidents and injuries incurred though the use of their cars because there is a genuine NEED to drive one.

In FRC we accept the risk of using a mill, late, welder, lead-acid battery, etc. because we NEED to assume those risks to build a robust and competitive robot. We do not have to accept the risk of creating shrapnel by using a plastic tank when metal tanks are available. The only functional difference is weight, and weight can be shed elsewhere in basically every robot design that I've ever seen.

[Paul Copioli]

I will see if I can get the ThunderChickens to send some of their old pneuaire ones.

PM me your address and I'll see what I can do. I have a few favors to trade with them still.

I would be very surprised if the Pneuaire tanks fail in the same manner as the white Clippard tanks, but it wouldn't be the first time I was surprise by the results of an experiment.

[AllenGregoryIV]

Originally Posted by JamesCH95

The clippard tanks we used were acquired through the AM FIRST Choice program. I believe AM simply re-sells Clippard tanks.

The risk of plastic tanks is obviously controversial. I'll relate a conversation I had with a lawyer when I was interested in selling potato cannons (another hobby of mine). He made a very good point that is very pertinent to this topic.

His professional opinion was that no matter the disclaimer I had customers sign that I could be held liable for any damages or injuries incurred though the use of a potato cannon I made and sold because there is NO NEED for a potato cannon, it's a toy. Car makers are generally safe from accidents and injuries incurred though the use of their cars because there is a genuine NEED to drive one.

In FRC we accept the risk of using a mill, late, welder, lead-acid battery, etc. because we NEED to assume those risks to build a robust and competitive robot. We do not have to accept the risk of creating shrapnel by using a plastic tank when metal tanks are available. The only functional difference is weight, and weight can be shed elsewhere in basically every robot design that I've ever seen.

There are plenty of competitive teams that don't use a mill, lathe, or welder (I have never had a student weld anything on team I have been on in 12 years of FRC, doesn't mean I don't think other teams should do it). We needed to use light weight tanks just as much as we needed to use aluminum axles instead of steel. There are places to save weight but buying plastic air tanks is easier. Also AndyMark sales a variety of air tanks, some of them are from Clippard and others are not.

[Andy A.]

Originally Posted by Paul Copioli

I will see if I can get the ThunderChickens to send some of their old pneuaire ones.

PM me your address and I'll see what I can do. I have a few favors to trade with them still.

I would be very surprised if the Pneuaire tanks fail in the same manner as the white Clippard tanks, but it wouldn't be the first time I was surprise by the results of an experiment.

Paul- I'm sure James will be in touch about a shipping address.

Do you know any of the specifics about the differences between the black tanks and white tanks? We understand a fitting is pressed in but, besides that, they appear to differ only in color and perhaps size. They are advertised as 'polypropylene', but I haven't found any specifics beyond that.