Old steels denied fills due to store "policy"

[RayfromTX]

A short Review of 6351 Alloy Aluminum Cylinders

PSI-PCI - A short Review of 6351 Alloy Aluminum Cylinders

A Brief Scuba Cylinder History

PSI-PCI - A Brief Scuba Cylinder History


Are 6351-T6 Alloy Scuba Cylinders Safe to Use?

http://www.psicylinders.com/MediaManager/documents/6351-alloy-cylinders-safe-to-use.pdf

I hope this may end this thread.

The most interesting takeaway from the last link was this line.
"Making arbitrary policies, however, can be detrimental to a business' legal standing."

 

[Wookie]

The most interesting takeaway from the last link was this line.
"Making arbitrary policies, however, can be detrimental to a business' legal standing."

Something my insurance company used to beat me about the head and neck with. “If you make a policy, ensure that the policy has some basis in a industry standard, or regulation. Don’t make it up”.

 

[Diving Dubai]

Something my insurance company used to beat me about the head and neck with. “If you make a policy, ensure that the policy has some basis in a industry standard, or regulation. Don’t make it up”.

The underlying argument is cost and risk

The PSI/Alert diver reports linked above are accurate in their findings.

But shops have to make the business decision (say for 6351) whether to invest in employee training and equipment to accept and fill 6351 cylinders. And then there is trust. If a cylinder had been subjected to Vis and Eddy by another shop, can they be sure it was done correctly?

If they do invest in this additional cost, how do they recover it? Will a diver willingly pay more for an inspection/fill or will they go to a cheaper shop

So in this case it appears that shops make a blanket decision because it's easier and less costly citing a reason which because of the publicity everyone believes is a bigger risk than it actually is.

 

[markmud]

So in this case it appears that shops make a blanket decision because it's easier and less costly citing a reason which because of the publicity everyone believes is a bigger risk than it actually is.

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

 

[Diving Dubai]

and feel safe if you have had vis and hydro testing performed on them

But here you're going on trust.

If I placed my tanks with say @Wookie I have some measure of certainty that the inspections and testings would have been carried out to a high standard, and should he condemn one I "know" that's it's done with integrity.

Let's say Wookie charges $100 for this, a shop down the road sees an opportunity to do it for $75 which do people chose? Unless shop #2 has failures how can you judge?

@markmud , I’ve always enjoyed reading your comments, and whether I agree or not.

You and others here are quite correct, there is Zero Evidence to support my POV.


But allow me some latitude here.

I had 20yrs in Aerospace, gainfully employed in picking up the pieces, both figuratively and unfortunately practically.

Too many times I’ve witnessed components Fail. These components had been correctly designed, calculated and modelled, constructed out of materials whose properties we fully understood – and yet they failed. Not by magic, but by a lack of understanding of the vagaries of unforeseen variables.

I’ve been told categorically that its impossible for a component to fail in position X – only to provide the said component with a failure at position X.

I’ve had the unpleasant duty too many times to walk across a field strewn with personal possessions children’s toys and aircraft wreckage, generally because a well understood component had failed in a way not predicted, or a well known and seemingly fit for purpose inspection process had failed to find the critical defect.

Once I had a gut feel about a component (Undercarriage leg) in service, so I requested an in-service item (one in use) to look at. I met with huge resistance and push back because I had little supporting evidence for my opinion. They did eventually get me one (to shut me up). It arrived just before my vacation so was left unattended for 2 weeks.

On my return I got straight to it, and that same day found an unknown defect – one that couldn’t’ be predicted by our models (Lots of these legs were by now in service).

It was immediately dismissed as a one off, until later that week one failed on an aircraft killing the pilot and navigator…

So, you see I have some history which taints my outlook and means I’m a bit cynical of assuming that inspection processes are perfect and to be trusted 100%

If you read the PSI report you see it mentions a few failures in Steel tanks, but they were drowned out by the 6351 issues

While Hydro testers have to re-cert Vis inspectors do not you can be assured that not all inspect to the same standard or even have the same training. How do you know the person (other than yourself) making the inspection has been formally trained?


In the end the chance of failure is low, and you’ll accept that the statistical risk to you is so low as to be inconsequential which is fair. That doesn’t mean that there aren’t tanks without of tolerance defects which have passed Hydro in use. All you can hope is that the defect gets picked up before it goes critical

 

[RayfromTX]

I see this risk assessment as a graph where the numbers we are talking about are way way over on the left end of the scale. If I add several zeros to the failure occurrence value on the graph I arrive at my risk of being killed by a car on my bicycle. If I add another zero, I arrive at my risk of being killed by a car as a pedestrian. If I add another zero, I arrive at my risk of being killed in a car. If I add one more zero I reach my level of risk of dying from heart disease this year.

If I supersize my order at McD's on my way to the fill station in my car my tank isn't the risk I'm facing. If I have my tanks inspected by a loser with a light, I'm still reducing the number below the numbers represented by total failures which include uninspected tanks.

DD, the outlier risks that you have discussed are interesting, to be sure. Are you sure that they are actually relevant in the world we actually live, dive eat and drive in?

If a shop is too ignorant or believes their employees to be too ignorant to properly assess the actual risk or viability of a 20+ year old steel tank with current inspections, do I really want them responsible for the air I take with me on a scuba dive? No. Of course I test every tank for CO and O2 content because I don't trust the man behind the curtain. It doesn't cover all the risks but I'm driving to the dive site after flying to the dive destination. I'm possibly riding on a scooter to get to the boat and eating tacos from a street vendor. Living on the wild side. I suppose there are actual risks involved in diving too, right?

 

[The Chairman]

I haven't denied science. I have questioned the unwavering acceptance that passing hydro alone means that tank is going to be good until the next hydro.

The proof is in the pudding. No one has shown us a tank that has a current Hydro and has ruptured. As someone pointed out, Visual inspections are very subjective while hydros, by nature, are not. Apocryphal anecdotes and what-ifs aside, a tank that has passed hydro is indeed a safe tank. Few will accept wild stories to the contrary without proper citation. Sure, things can happen that would make us question the validity of a hydro. I had a fairly rusty tank that I tumbled and tumbled. With two years to hydro, I did the unthinkable and had the hydro run again. Everybody seemed to question my sanity, but I would rather let the science speak than to condemn a tank out of petulant fear. It passed and is still in use today. Yay!

 

[Wookie]

I would never dispute someone’s expertise in a field they claim to know something about, about which I know nothing. I am neither an aerospace guy nor a metals guy.

In another life I was a nuclear operator. We weren’t doing anything cutting edge, we made steam to make the propellers go roundy roundy. We were a bunch of 21 year old sensitive navy boys who liked practical jokes, hard drinking, a few druggies, grabassing, and, oh yeah, running a pair of reactors.

The us navy has never had a oopsie. Running 60 or 80 subs, 15 carriers, 9 cruisers, and 8 training reactors, there has never been an accident that resulted in an unplanned release of radioactivity to the environment. That is not due to the high quality of people operating said reactors, but by overdesign and redundant systems.

Aerospace is far less forgiving. All a ship has to do is float. Which is a good trick, but the science is pretty well known and forgiving. An aerospace has to fly, and every pound of weight you design in to make it safer costs you in fuel, engines, frame, etc. Designing an aerospace is by necessity far closer to design tolerances than a floaty thing. Hell, I can make a chunk of wood or a very small rock float, I can’t make anything fly. And don’t even get me started on ducks.

Point is, your background is dealing with light delicate flying things operated by elite operators who take care of their equipment. My background is in chunks of wood and rocks operated by Neanderthal’s.

I think scuba cylinders are closer to chunks of wood and rocks than aerospace’s.

But I have truly enjoyed your insight. And now I eat now. Fix knuckles. Fill some scuba’s.

 

[Manatee Diver]

Hell, I can make a chunk of wood or a very small rock float, I can’t make anything fly.

Flying is easy, you just need enough thrust.

Bringing the unwitting aircraft to a controlled safe landing...

 

[markmud]

I think scuba cylinders are closer to chunks of wood and rocks than aerospace’s.

Hi Wookie,

May I fix your statement above?

How about:
I know (think) scuba cylinders are closer to chunks of wood and rocks than aerospace products.

We know this is true because:

1. the corrosive environment that scuba tanks are used;
2. the piss-poor treatment that scuba tanks receive daily around the world;
3. the very low catastrophic failure rates for non-AL 6351 tanks;
4. the age that some of these scuba tanks have attained while in full-time service (including industrial gas vessels);
5. the extreme testing cycles that these cylinders must meet in order to get DOT, TC Canada, EU, and et allia, certifications.

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.

How many scuba tanks have we witnessed hitting concrete after falling of the back of pick-up trucks? I have witnessed it. It did not explode.

Thanks,
markm