Tank PSI - Over Filled, Drain or Dive?

[TracyN]

I would be extremely happy getting a 4000 psi fill someplace other than cave country. But then again if everyone was diving AL-80's the extra gas wouldn't matter.

 

[maniago]

As an engineer, I would have had him bleed it back to 3500 and then taken it diving. If he pumped it to 4000 (or probably more) and was stupid enough to give it to you as a paid rental, then what does that tell you about his general interest in dive safety? Not much really. But you could dive it sure. If it splits while you're wearing it, no problem. You're fileted, and dead, and your family is rich. Everyone wins! Except you.

This kind of discussion is a bit like the one going on in another thread about trusting a DM and subsequently running out of air. Moral of that story is trust your safety to yourself and noone else. I would think the same applies here. But that's just me.

 

[MaxBottomtime]

In Florida, the numbers stamped on the tank refer to the turn pressure.

 

[chrpai]

My understanding is that tanks typically fail during the fill cycle. Can anyone give me an example when a tank ruptured "while a diver was wearing it"?

I bought an AL80 last year that was at 3000 PSI for 10+ years. It passed hydro no problem...

 

[dumpsterDiver]

If the tank had a yoke valve in it, it might well have been stamped with a 2400 psi service pressure??

 

[Steve_C]

Since it was a rental makes you wonder if they routinely filled and stored at 4000?

 

[maniago]

My understanding is that tanks typically fail during the fill cycle. Can anyone give me an example when a tank ruptured "while a diver was wearing it"?

Just cause you never heard of it doesn't mean its not happened. Our parents never heard of a road bridge just failing, yet we've seen it how many times recently?

Realize that you're asking a metallurgical failure question. Crystalline structures fail when they have more energy put into the structure than the structure can absorb. Given the heat pressure expansion rates etc that a filling tank goes through you can easily see why more failures might happen at that time. Just a sh$t load of energy going in. Even more so with hydro as you would expect. Service pressure is the engineer telling you that that's the energy he's designed for the tank to be safe plus some envelope for energy error (like if there is a hairline crack starting) If the tank is over pumped ie stressed, you are now a tank test pilot - you are outside the envelope. You don't know how much more energy it can absorb before it fails. And its now in your hands. Drop it, bang, hit it with your knife or kiss it. You don't know if that will push it over the edge. If you like being a tank test pilot, that's ok. Just don't be lulled into a sense of safety with people around here saying its ok. Thank god tanks are routinely viped taken out of service before they filet people. But they all develop cracks or crystalline issues that lead to failure in time. If you're outside the envelope, well, sh$t just happens.

 

[MrChen]

Since it was a rental makes you wonder if they routinely filled and stored at 4000?

They had just filled it.

 

[Dr. Lecter]

If the tank is over pumped ie stressed, you are now a tank test pilot - you may be outside the envelope.

Fixed that for ya, though your general point is valid. However, I think the only scenario you'd find a tank rupturing on a diver, during a dive, would involve a tank that had been filled and subsequently experienced ongoing internal corrosion. In that case, it could fail during storage, transport, or use. If the tank's getting a proper viz every year, it's hard to imagine the circumstances necessary to cause a post-fill failure occuring... but I suppose the right mix of moisture and some kind of oxidizer inside a steel tank could do the trick.

4000 in a 3500 steel tank isn't what I'd call dangerously outside the normal service pressure, though it would lead me to wonder just how much stress my tank, valve, and burst disc saw at peak hot fill pressure.

 

[MrChen]

As an engineer, I would have had him bleed it back to 3500 and then taken it diving. If he pumped it to 4000 (or probably more) and was stupid enough to give it to you as a paid rental, then what does that tell you about his general interest in dive safety? Not much really. But you could dive it sure. If it splits while you're wearing it, no problem. You're fileted, and dead, and your family is rich. Everyone wins! Except you.

This kind of discussion is a bit like the one going on in another thread about trusting a DM and subsequently running out of air. Moral of that story is trust your safety to yourself and noone else. I would think the same applies here. But that's just me.

Thanks for your input. I'm guessing he left it filling longer than it should have, which is why he gave me the big grin and said don't be shocked when I saw the PSI.

There's probably a good chance that if I hooked it up, jumped immediately in the water, and started breathing on it, that the pressure would have dropped and all would have been fine. But we truly don't know that. Luckily it was a fairly safe dive site where we hit a max depth of 16 ft, so even if it blew while in the water, I would have just surfaced and lost a ton of pressure before getting back in. But I'm looking at it from the perspective of, what if I was on a boat and doing a drift dive at 80 ft? I don't know that I'd want my tank at 4000 psi. After this experience, I would definitely bleed out a couple hundred pounds.