Tank overfill

[Charlie99]

I'm still not seeing "the same tanks." I see weights that are off by 2-3 pounds, lengths that are off by an inch or two, etc. I know nothing about the engineering involved, but there are differences there.

It amazes me how people see spec sheets that have different weights and dimensions and somehow assume that, not only are they the same tank, but that they have been through identical manufacturing process.

There also seems to be a lot of confusion caused by the design goal for expected/average life in cycles to a test pressure. The reason Faber took 10,000 cycles to 4,000psi out of the ads is that that is NOT the working ratings. There are big safety factors between test pressure and working pressure; between average breaking strength of a rope and its safe working load, etc.

It's a personal choice (of both you and your fill station) whether one wishes to reduce the safety margins, but let's not kid ourselves as to what is being done.

 

[Leadking]

Every tank design by every manufacturer must pass a minimum of 10,000 hydro cycles without fail (6-10 times a minute until fail, new cylinder without corrosion or fatigue issues) as required by DOT
Faber makes no tank greater than 7 inches that can take 4000 psi

U.S.tensile strength (105,000-125,000 psi) is not the same as European tensile strength (135,000-155,000 as required by EN 1964 part 1 and ISO 9809 part 1) and I have test data that shows Faber cylinders delivered to us show a tensile strength of 115,000-123,000 psi (as required by DOT)

 

[Charlie99]

U.S.tensile strength (105,000-125,000 psi) is not the same as European tensile strength (135,000-155,000 as required by EN 1964 part 1 and ISO 9809 part 1)

Bingo! min tensile strength of 105,000 psi vs European min 135,000psi would account for those strange sets of data where the same internal volume tank was heavier in the US, even with lower working pressure. (Both Padiscubapro 3 liter data, and David Thiesfeld's 17 liter data).

Why would a lower tensile strength material ever be required? Brittleness and fatigue life?

 

[Leadking]

The higher the tensile the more brittle the steel.

 

[lamont]

Every tank design by every manufacturer must pass a minimum of 10,000 hydro cycles without fail (6-10 times a minute until fail, new cylinder without corrosion or fatigue issues) as required by DOT

but not every single tank that comes off the line is tested that way, of course. a sample of the tanks are tested to destruction that way, which means that you've sampled the overall distribution, and found that the sample passes. nothing says that you couldn't get a tank which would fail with fewer than 10,000 fill/hydro cycles, because in the overall distribution you're going to get tanks which are 2-3 standard deviations below the mean which are unlikely to occur in the sample.

 

[jonnythan]

lamont, notice the part that says "6-10 times a minute until fail, new cylinder without corrosion or fatigue issues" which means that this doesn't correspond to tanks getting filled and emptied slowly and stored under pressure for weeks or years at a time, plus rust, age, fatigue, getting thrown around, etc.

 

[lamont]

lamont, notice the part that says "6-10 times a minute until fail, new cylinder without corrosion or fatigue issues" which means that this doesn't correspond to tanks getting filled and emptied slowly and stored under pressure for weeks or years at a time, plus rust, age, fatigue, getting thrown around, etc.

yup, that too.

 

[gjmmotors]

Imagine getting thrown in the clink of some north florida county, and you are surronded by tons of otherwise normal looking people, some still in damp drysuits.
"SO what you in for guy?"
"Well those damned scuba tank police got me for an overfilled bottle."

If it were illegal then places that advertised overfills would be in alot of trouble wouldn't you think?
Im not a lawyer, but I have never heard of anyone getting in trouble for having their tanks overfilled.
-g mount