Old steels denied fills due to store "policy"

[JohnnyC]

I would say that dropping a cylinder 3 feet onto concrete is far less extreme than this test.


BTW they do drop test planes. Or at least the closest analog practical. It's pretty hard to pick up 3/4 of a million pounds.


And a 100 year old steel cylinder would have only 20 test cycles if it made every hydro on time. Hardly extreme. Maybe my sarcasm meter is just off.

Anyway, that doesn't mean that DD's experience in failure analysis doesn't have any merit, simply that he is skeptical because he has seen "sure things" that turn out to be not so sure. He has determined that based on his experience, his tanks have a lifespan where his confidence in their performance falls below what he is comfortable with. No harm in that.

Now I don't agree with his retirement stance, I feel that the current testing of steel tanks by competent personnel is enough to keep them in service and catch any issues, but I know how I handle my tanks, and if there was ever a situation where I had any doubt, I would rectify that immediately. Things with unknown pedigree should rightly be subject to more scrutiny until their fitness for duty can be adequately surmised. The probability of a fluke accident will always exist.

 

[Wookie]

I would say that dropping a cylinder 3 feet onto concrete is far less extreme than this test.


BTW they do drop test planes. Or at least the closest analog practical. It's pretty hard to pick up 3/4 of a million pounds.


And a 100 year old steel cylinder would have only 20 test cycles if it made every hydro on time. Hardly extreme. Maybe my sarcasm meter is just off.

Anyway, that doesn't mean that DD's experience in failure analysis doesn't have any merit, simply that he is skeptical because he has seen "sure things" that turn out to be not so sure. He has determined that based on his experience, his tanks have a lifespan where his confidence in their performance falls below what he is comfortable with. No harm in that.

Now I don't agree with his retirement stance, I feel that the current testing of steel tanks by competent personnel is enough to keep them in service and catch any issues, but I know how I handle my tanks, and if there was ever a situation where I had any doubt, I would rectify that immediately. Things with unknown pedigree should rightly be subject to more scrutiny until their fitness for duty can be adequately surmised. The probability of a fluke accident will always exist.

You made my point. The wing catastrophically failed at 154% of design load. Steel scuba cylinders are routinely tested to 166% of design load and the failure rate is infinitesimal. 3AL cylinders tested to failure typically let go at 250% of design pressure. I have no idea what percent of design pressure 3AA cylinders fail at, but it isn't 154%.

Edit. FOund some testing data. 3AA cylinders tested to failure at 17,000 PSI for a 2250 cylinder. 750% of design.

 

[JohnnyC]

You made my point. The wing catastrophically failed at 154% of design load. Steel scuba cylinders are routinely tested to 166% of design load and the failure rate is infinitesimal. 3AL cylinders tested to failure typically let go at 250% of design pressure. I have no idea what percent of design pressure 3AA cylinders fail at, but it isn't 154%.

Edit. FOund some testing data. 3AA cylinders tested to failure at 17,000 PSI for a 2250 cylinder. 750% of design.

12% is probably not even statistically significant to be honest. Like you mentioned, it's all design parameters.

17,000 PSI is nuts. Why aren't we routinely filling to 10,000 PSI if that's common? A safety factor of 750% is pointless. The obvious answer is that 750% of design is an outlier and they routinely fail at much lower pressures when tested to their catastrophic failure point. I'd be interested in seeing the test parameters involved. New cylinder? Old cylinder? How many load cycles to what pressure? Is there a failure mode that's at a lower pressure that they chose to ignore and let it cato? Bunch of variables could put those numbers all over the place so if you've got the source I'd love to see how they did it. I'd imagine there's a reason the tank(s) in question are rated for 2250 PSI, and I would posit that it's not because they could reasonably guarantee a MBS of 17,000 with any routine level of confidence.

I wasn't trying to disprove your point, I agree, I just think markm was using a bit too much hyperbole. We do similar testing with fall protection and rigging equipment. Intended use plays a role in rating all of that stuff, and different industries use different types of ratings. MBS vs WLL, etc. Physics can be a bitch, but it's cool as frig.

 

[rhwestfall]

And all of this is still complex multi-part systems......

Think of the complexity of parts and the transfer of loads through those components and the variables of how the loads can be applied.



Now, compare that to a scuba tank....

 

[broncobowsher]

Hi DD,

You have just made a post on this thread that I can agree with.

The known failure rate is 0.00000062 of the 50 million units made. (31 ruptures of 6351 divided by 50,000,000 units)

It has been 30 years since the last of these 6351 cylinders have been made. I can understand a business making a blanket policy to abandon fills, abandon visual inspections, and abandon offering hydro services for these cylinders due to extra cost of training and testing.

Banning steel tanks and other aluminum tanks that have a 50 plus year track record of safe use, is ridiculous.

How many zeros do we add to 0.00000062 for a PST 72 failure rate?. It has to be far less than a dozen units.

Let's examine the facts:
• Both cylinders had recently undergone hydrostatic requalification by untrained testers.
• Neither cylinder had been inspected by a trained visual inspector.
• Neither cylinder was eddy-current tested, as required by U.S. Department of Transportation (USDOT) regulations.
http://www.psicylinders.com/MediaManager/documents/6351-alloy-cylinders-safe-to-use.pdf
Emphasis added by mm above.

Don't retire your old steel tanks people. Use them and feel safe if you have had vis and hydro testing performed on them.

thanks,
markm

Wait a minute, you are telling me that there are 5 times as many 6351 cylinders made then Ford Mustangs. Last year there was a big publicity about the 10-millionth mustang built. I see a lot of Mustangs. Owned a few as well. But my sightings of 6351 cylinders are rather rare. Where are all these millions of 6351s hiding at? They sure don't come through any dive shop or boat around me. A couple show up, but they are few and far between. Not even that many on Craig's list, and that is loaded with Mustangs.

Something about your numbers isn't adding up.

 

[Jiminy]

Wait a minute, you are telling me that there are 5 times as many 6351 cylinders made then Ford Mustangs. Last year there was a big publicity about the 10-millionth mustang built. I see a lot of Mustangs. Owned a few as well. But my sightings of 6351 cylinders are rather rare. Where are all these millions of 6351s hiding at? They sure don't come through any dive shop or boat around me. A couple show up, but they are few and far between. Not even that many on Craig's list, and that is loaded with Mustangs.

Something about your numbers isn't adding up.

From what I have read there was a trade in program also it is more expensive to maintain them as the inspection requirements are different.

Section III: Luxfer Scuba Cylinder Rebate and Replacement Policy
In prior years, Luxfer has conducted various rebate, replacement and trade-in programs, all of which have now ended, with one exception: Certain older Luxfer scuba cylinders sold by U.S. Divers were issued with a lifetime warranty. This lifetime warranty will continue to be honored for the life of each cylinder so warranted. However, since this warranty was non-transferable...

Luxfer updates inspection and replacement policy for scuba cylinders manufactured in the United States

For its 6351-alloy tanks, Luxfer has established a manufacturer's requirement for a visual inspection, including an eddy-current test, at least every 2.5 years.

Both the DOT and the U.S. scuba industry recommend an annual visual inspection for all 6351-alloy scuba tanks. Luxfer supports this recommendation.

https://www.luxfercylinders.com/support/faq-luxfer-6351-alloy-scuba-inspection

 

[Diving Dubai]

No one has shown us a tank that has a current Hydro and has ruptured

According to the PSi document cited above, they have knowledge of 24 steel tanks in 2011

What isn't clear is how why and when etc

As I understand (and happy to be corrected) here is no legal requirement to report a tank failing on fill - unless there is a reportable injury or death.

I would bet your house (I'd bet mine but you don't' want to be on teh wrong side of my wife) on the fact there are tanks with non allowable defects, that pass hydro. Not because the hydro operator is lacking, but because its' more than possible. Hydro is just a rough test.

But that said - the fact that the failure rates are so low makes it a non event for 99.999% of divers thus the test procedures (If carried out correctly by a competent person) are as fit for purpose as reasonably possible.

Choosing who you trust to carry out your testing is like choosing a dive instructor - not all are equal.


Thus making a blanket statement that if a cylinder is in test it's 100% golden - not so much.

But finally. What really stirs my pot, is that the same people who will happily spend $1000+ dollars on the latest greatest dive computer and will change it every 5 years or so, are the same people who will argue against spending $300 on a new cylinder when its reached a life of 40-50 years. #doesn'tmakesense#

 

[Diving Dubai]

How many 777-300ER jet liners have you seen dropped on their noses while being suspended by their tails 3 feet off the ground? None. They would be ruined.

You do know that aircraft components are tested to such a great degree, that if the same were applied to teh lowly scuba cylinder it would be unaffordable

And yes we test while aircraft to destruction - Finite stress test. it always involve a large bang, bits of metal flying and people like me giggling like children chanting "again, again, again"

 

[RayfromTX]

The same people? I'm guessing it isn't the same people and it isn't necessarily just one tank and they don't blow up and.... it's too easy to stir your pot. Have a cocktail and enjoy the last cool days before you start heading back up to 50C in the afternoons. I really don't know how you do it and I live in Texas.

 

[JackOfDiamonds]

Same in my area, you are lucky to find someone who is willing to fill up air to any tank older than 15