DIN Plugs in O2 Cylinders. Good Idea? Bad Idea?

[cool_hardware52]

Just because it's done that way doesn't mean it's the best idea. Medical O2 I thought was kept at lower pressure. The valves are yoke style :0. Still an aluminum tank though.

My thoughts on LP steel is to keep the O2 at lower pressure but a similar volume. The Fabers will take 5000psi before blowing a disc or rupturing unlike an aluminum. They are also negative buoyancy when empty which should be better during deco.


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Although I think it a canard, what do you think the burst disk failure rating is for a 3000 psi 3Al cylinder is vs a 2400+ steel tank? Or the actual burst pressure of the two?

The lower working pressure of medical O2 tanks may have some bearing, 2216 psi (many medical) vs 3000 psi (typical al 40), but there are many thousands of 2400 K's and T's in service and Commercial O2 i also routinely sold in 4500 psi supply bottles High Capacity 4500 PSI Cylinder - OXARC - Welding, Safety, Fire, Industrial And Wholesale Supplies

Valves and use (or misuse) still jump out as the most likely source of trouble, not cylinder materials.

Tobin

 

[cavemn]

I use lp steels for bigger cave dives to allow a relatively high volume a a low pressure. I rarely fill high pressure oxygen.

exactly where I'm going, 45cuft @ 2640psi instead of 3000psi

 

[cavemn]

Although I think it a canard, what do you think the burst disk failure rating is for a 3000 psi 3Al cylinder is vs a 2400+ steel tank? Or the actual burst pressure of the two?
Tobin

The burst disk on the valve will define burst pressure. Even if I put a 5250 on an Aluminum I would expect the tank itself to fail before the burst disk. On a Faber I would expect to get close to 5000 before a rupture.

So, 40 cuft @ 3000 psi in an aluminum that might burst at 3500 psi

or

45 cuft @ 2640 psi in a tank that might burst at 5000 psi

What would you choose?

 

[cool_hardware52]

The burst disk on the valve will define burst pressure. Even if I put a 5250 on an Aluminum I would expect the tank itself to fail before the burst disk. On a Faber I would expect to get close to 5000 before a rupture.

So, 40 cuft @ 3000 psi in an aluminum that might burst at 3500 psi

or

45 cuft @ 2640 psi in a tank that might burst at 5000 psi

What would you choose?

You need to read up on burst disks and cylinder design.

The DOT requires burst disks to be set to hydro test pressures +0, -10%

For example a 3AL cylinder with a working pressure of 3000 psi should be fitted with a burst disk that will fail at no more than 5/3 x 3000 = 5000 psi and no less than .90 x 5000 = 4500 psi.

What is actually being tested during a "hydro?

The ability of the tank to return to it's original volume, in other words did the hydro pressure (typically 5/3's or the working pressure) permanently stretch the tank, or not. Too much permanent deformation and the tank "fails" , if it returns to the original volume it passes.

Now if 5/3 of the working pressure does not even permanently stretch the tank what sort of pressures would you expect necessary to cause the cylinder to burst?

Luxfer claims minimum testing to 2.5 times service pressure, 3000 x 2.5 = 7500 psi without failure. Actual "burst pressures" of 3AL cylinders have been reported in excess of 11K psi.



Tobin

 

[cavemn]

Now if 5/3 of the working pressure does not even permanently stretch the tank what sort of pressures would you expect necessary to cause the cylinder to burst?

Luxfer claims minimum testing to 2.5 times service pressure, 3000 x 2.5 = 7500 psi without failure. Actual "burst pressures" of 3AL cylinders have been reported in excess of 11K psi.

Tobin

In a perfect world maybe, but as divers we move our cylinders and cause focused pressure on the metal through road bumps, contact with other tanks, etc.. placing stress on the material. I am in no way advocating the use of higher than recommended burst disks. I rely on appropriate burst disks to work as designed. In reality I would never consider an Aluminum cylinder past 3500 psi safe regardless of MFG claims or burst disk.

Steel has a higher elasticity than Aluminum. I expect by the nature of the material that Steel will survive without rupture higher and more extreme expansion periods.

I am also not wanting to overfill high percentage FO2 tanks. I am trying to engineer in a higher safety margin with using high FO2 gases.

 

[PfcAJ]

That's fantasy land stuff. Aluminum tanks aren't going to rupture from a bump. Come on.... The euros don't even have burst disks.

 

[cool_hardware52]

In a perfect world maybe, but as divers we move our cylinders and cause focused pressure on the metal through road bumps, contact with other tanks, etc.. placing stress on the material. I am in no way advocating the use of higher than recommended burst disks. I rely on appropriate burst disks to work as designed. In reality I would never consider an Aluminum cylinder past 3500 psi safe regardless of MFG claims or burst disk.

Steel has a higher elasticity than Aluminum. I expect by the nature of the material that Steel will survive without rupture higher and more extreme expansion periods.

I am also not wanting to overfill high percentage FO2 tanks. I am trying to engineer in a higher safety margin with using high FO2 gases.

Engineering is the discipline, art, skill, profession and technology of acquiring and applying scientific, mathematical, economic, social, and practical knowledge, in order to design and build structures, machines, devices, systems, materials and processes. Engineering - Wikipedia, the free encyclopedia

Do whatever makes you happy, or feel safer, but Ignoring known facts and data is not engineering.

Tobin

 

[fdog]

I tend to believe the cylinder material has very little to due with deco bottle explosions. There are literally millions of aluminum medical O2 cylinders in use today. My suspicion is the problems lie with the valves, and perhaps with the nature of the use.

Tobin

I think you're really on to something, Tobin.

We're using scuba equipment, albeit with some oxygen cleaning procedures, to deliver oxygen, which wasn't their design criteria.

On the other hand, here's the flow path through an medical oxygen valve; straight, un-kinked, no places for compressive heating:

Plus, Medical Oxygen regulators have to undergo testing for ignition sensitivity and fault tolerance. They're designed to be reliable and not a combustion hazard. Contrast this with scuba regulators, which have been somewhat bastardized into oxygen service. I don't know of any scuba regulator that's passed

ASTM G175 - 03(2011) Standard Test Method for Evaluating the Ignition Sensitivity and Fault Tolerance of Oxygen Regulators Used for Medical and Emergency Applications

I know the Atomic M1 was designed with a nod towards oxygen - it contains Monel parts, which are very resistant to combustion - but that's still a long way from how dedicated Medical Oxygen Regulators are designed.

Anyone using oxygen owes it to themselves to read this article by the ASTM on Preventing Oxygen Equipment Fires. It's an eye-opener, and brings into relief just how non-optimal our equipment is.





Keeping in mind that our equipment is not the best for oxygen, all I can do to keep myself safe is adhere to best practices, like opening valves very slowly, and filling at 60 psi/minute. And oxygen cleaning like a paranoid fiend. That little bit of extra respect will go a long way.


All the best, James

 

[cavemn]

That's fantasy land stuff. Aluminum tanks aren't going to rupture from a bump. Come on.... The euros don't even have burst disks.

The Euros can do what they like. None of my business.

What term would you use when an O2 cylinder falls over or is dropped and ruptures?

Do whatever makes you happy, or feel safer, but Ignoring known facts and data is not engineering.

If you want to take a manufacturers test data verbatim and apply it to real world application go ahead. Take your aluminum cylinder to 5k or 7k. Sounds more like an implementation of Darwin's theory to me.

I will continue to engineer(usually over engineer) with my level of acceptable conservatism a kit for my diving environments based on best use cases not just a single manufacturers data because my life is more important to me than someone's bottom line.

 

[cool_hardware52]

The Euros can do what they like. None of my business.

What term would you use when an O2 cylinder falls over or is dropped and ruptures?

Is it fair to assume that medical O2 bottles, which out number scuba deco bottles by many orders or magnitude, are never handled roughly, filled quickly, dropped, etc.? Talk to any EMT's you might know.

If you want to take a manufacturers test data verbatim and apply it to real world application go ahead. Take your aluminum cylinder to 5k or 7k. Sounds more like an implementation of Darwin's theory to me.

1) Are you suggesting that results of DOT required tests are suspect?

2) Where have I *ever* suggested one should overfill any cylinder, O2 or otherwise? My comments about tank burst pressures were in response to your claims that cylinders would fail before burst disks. There is zero evidence to support those claims.

I will continue to engineer(usually over engineer) with my level of acceptable conservatism a kit for my diving environments based on best use cases not just a single manufacturers data because my life is more important to me than someone's bottom line.

Wow, that's a leap. Again, please do what ever you find necessary to reach the level of comfort you require.

I'm very sorry about your friend, and dearly hope he recovers fully and quickly.

Tobin