Overfilling LP Steel Tanks -- How bad is it?

[captain]

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.

Not worth much to me without figures to back it up.
Aluminum cylinders of all kinds have a fairly short history. They only came into general use in the middle to late 1970's where as steel cylinders have been in use for well over 100 years and in scuba use since it's avent in the 1940's.
If you are including steel cylinders in all uses over their entire history than it is possible you are correct because even today aluminum cylinders are still in limited use in the commercial gas industry compared to steel cylinders.

 

[Leadking]

From an interview with Bill High (President of PSI) I found on line:

Do you have an idea of the percentage of cylinders which fail out of those tested?
If you mean hydrostatic tested cylinders which failed that pressure test, then the number is very small, since most cylinders are failed based upon damage observed by visual inspection. The following example from one of our PSI affiliate instructors who is also a federally licensed hydrostatic retester may help. His retest business is primarily limited to scuba cylinders. He tests about 2000 scuba cylinders each year - these cylinders are visually inspected annually and hydro tested with visual inspection every five years. Of those 2000, he condemns nearly 12% prior to the actual pressure test, due to damage observed that exceeds the allowable limits. Of those that pass the pre-test visual examination and are then pressure tested, he condemns only one or two aluminium cylinders and about ten steel cylinders. This example is consistent with enquiries we have made of other hydrostatic retesters on other occasions.

 

[jmorriss]

From an interview with Bill High (President of PSI) I found on line:

Do you have an idea of the percentage of cylinders which fail out of those tested?
If you mean hydrostatic tested cylinders which failed that pressure test, then the number is very small, since most cylinders are failed based upon damage observed by visual inspection. The following example from one of our PSI affiliate instructors who is also a federally licensed hydrostatic retester may help. His retest business is primarily limited to scuba cylinders. He tests about 2000 scuba cylinders each year - these cylinders are visually inspected annually and hydro tested with visual inspection every five years. Of those 2000, he condemns nearly 12% prior to the actual pressure test, due to damage observed that exceeds the allowable limits. Of those that pass the pre-test visual examination and are then pressure tested, he condemns only one or two aluminium cylinders and about ten steel cylinders. This example is consistent with enquiries we have made of other hydrostatic retesters on other occasions.

The break down of VIZ failures is important here-rust or b/c of eddy current cracks?

 

[Leadking]

Please read the quote, it explains that 12% fail visual BEFORE the hydro. The point is the failure rate of steel. They do fail, and if we were to draw a conclusion, it would be that there are far more aluminum cylinders in service (by a factor of 3 at a minimum) than steel but steel fails at a greater rate.

 

[jmorriss]

Please read the quote, it explains that 12% fail visual BEFORE the hydro

Well perhaps I am unclear on what the visual is checking then. I assumed that you might failure for several reasons.

 

[Leadking]

Holy **** Batman. All I am saying is that in gathering info steels fail hyros at a greater rate than aluminums. What the **** does the viz have to do with this? The increase in hydro failures with no visual underpinnings is the point!!!!!

 

[redacted]

Please read the quote, it explains that 12% fail visual BEFORE the hydro. The point is the failure rate of steel. They do fail, and if we were to draw a conclusion, it would be that there are far more aluminum cylinders in service (by a factor of 3 at a minimum) than steel but steel fails at a greater rate.

Is that difference entirely attributable to the fact that rust can cause failure; and steel rusts but aluminum does not?

Of course steel tanks fail. That is not the issue. The issue is whether steel tanks are failing, during or outside of hydro, due to metal fatigue that could have been caused by over filling.

 

[Leadking]

Is that difference entirely attributable to the fact that rust can cause failure; and steel rusts but aluminum does not?

Of course steel tanks fail. That is not the issue. The issue is whether steel tanks are failing, during or outside of hydro, due to metal fatigue that could have been caused by over filling.

Once again, the tanks fail after a viz. If there was rust they would not hydro. The steel tanks that fail HAVE passed a viz and then fail hydro. The point, again, is that there is no visual indication that the tank will fail hydro. So inspect and inspect again, inspect until the cows come home, you are not going to see the problem because the steel is weakened and the hydro documents that.

 

[halocline]

The point is the failure rate of steel. They do fail, and if we were to draw a conclusion, it would be that there are far more aluminum cylinders in service (by a factor of 3 at a minimum) than steel but steel fails at a greater rate.

Where does it say that this guy is testing more AL cylinders, but failing more steels? I don't see anything about his ratio of AL to steel tested. For all we know, he could be testing 10 times as many steel tanks.

Plus, there are all sorts of steel tanks, many under special permit that have different hydro testing standards. What I personally would be interested in is the rate of failure of 3AA scuba tanks that have been routinely overfilled as opposed to 3AA tanks that have not. It does stand to reason that severely over pressurized tanks would be under more stress and more likely to fail hydro, but I'd like to see some evidence.

Although, this thread is still supposedly about steel tanks bursting during overfill, not failing hydro or having a shortened life due to overfilling.

In practical terms, I would be very interested in hard evidence regarding the safety of use of LP72s at 3000 PSI and under.

 

[Leadking]

The business was involved in testing primarily scuba cylinders. I was a major wholesaler of cylinders and by volume of steel to alum was 1/3. Steel was popular until the late '70's and aluminum took the market. Tech diving has brought stell cylinders back in popularity but sales are still 1 to 3. I have had numerous conversations with hydro facilities and they ALL tell me steels fail at a greater rate than aluminum. Talk to ANY scuba hydro service and get your own answers. These are the answers I got. I only spent 30 years in the business.