Overfilling LP Steel Tanks -- How bad is it?

[H2Andy]

When I was in business and researched the 6351 aluminium alloy issue, I found that despite all the hype, more steel cylinders had catastrophically failed than aluminium.

if you say so ... but due to what?

overfilling?

 

[Leadking]

One would have to pull an analysis of each failure and find the root cause. I am just stating info.

 

[H2Andy]

ok, post your facts ... there must be an abstract somewhere that shows how many steel tanks have let go vs. aluminum tanks in the past 20 years

 

[SparticleBrane]

Personally I see this as a "chicken little" scenario.

For starters -- I understand and accept the risk of overfilling, and so do the people who fill my cylinders (if I'm not filling them myself). If they didn't accept that risk they wouldn't do the filling, would they?

While I understand people yelling at us to stop overfilling cylinders, I think it is important to remember just how many explosions of cylinders caused by overfilling that kill/injure people per year.


Millions of people die every year as a direct result of cardiovascular disease, lung cancer caused by smoking (or any sort of cancer for that matter), starvation, wars/conflicts, car accidents, crime, various diseases...the list goes on.

While dying from an exploding scuba cylinder wouldn't be nice, it isn't exactly high on my list of things to worry about.

 

[halocline]

While I understand people yelling at us to stop overfilling cylinders, I think it is important to remember just how many explosions of cylinders caused by overfilling that kill/injure people per year.

I suspect that number is zero. What I would be interested in knowing is if any steel scuba tanks have catastrophically failed during hydro testing.

 

[Rick Murchison]

I suspect that number is zero. What I would be interested in knowing is if any steel scuba tanks have catastrophically failed during hydro testing.

The reason testing is done with hydraulic rather than gas pressure is that you can't have a "catastrophic" failure, just a very sudden drop in pressure as the material gives. Doesn't even make much, if any, noise.
Rick

 

[DA Aquamaster]

Yes, worst case with a large tank that fails during hydro testing, you may blow the burst disc in the side of the rest tank - they blow at something like 5 or 6 psi, but that almost never happens even at the low pressure involved.

Instead you get a sudden drop of pressure on the gauge and you get a sudden increase in water in the pipette where the expansion of the tank is measured.

I saw an AL80 fail during hydro with a crack in the shoulder at the base of the neck and the most exciting part was the water squirting out the neck when it was removed. It had about the velocity of a really anemic squirt gun. Had it failed with air at the same pressure where 120 cu ft of gas was trying to escape through the crack it would have been much more exciting - and potentially lethal.

 

[halocline]

Sure, I understand that the test is done in a water jacket to prevent an explosion, I was talking about tanks actually splitting or otherwise structurally giving way during hydro, not just failing the test due to loss of elasticity. The reason I brought it up is because the hydro guy around here told me that he has never seen a steel 72 scuba tank fail hydro.

 

[jmorriss]

Sure, I understand that the test is done in a water jacket to prevent an explosion, I was talking about tanks actually splitting or otherwise structurally giving way during hydro, not just failing the test due to loss of elasticity. The reason I brought it up is because the hydro guy around here told me that he has never seen a steel 72 scuba tank fail hydro.

Steel doesn't really loose elasticity-it just gets pushed into a plastic range in which it doesn't go back to a zero stress state anymore. It will still 'come back' but not all the way to zero.

 

[rjack321]

When I was in business and researched the 6351 aluminium alloy issue, I found that despite all the hype, more steel cylinders had catastrophically failed than aluminium.
Take it for what it's worth.

Scuba cylinders or all cylinders?

The vast majority of 3AA cylinders are high pressure vessels but not in scuba service. The vast majority of AL cylinder vessels are in low pressure CO2 service. Absolute number-wise I have no idea where the bulk of cylinders are used, not in scuba service that's for sure.

Overall, having more of one or the other fail (catastrophically or just at hydro?) doesn't say much about cylinders in other types of use and for other failure modes.

At least here in electron diving world there are dozens of sagas about AL cylinder failures and lots of media hype surrounding them. Based on people's propensity to fear 6351 cylinder explosions from a few widely reported incidents (out of millions of tanks produced), you'd think that a similar 3AA tank failure would be widely reported and causing similar hysteria. Yet we have no gory pics, no home published accounts whatsoever.