Filling LP tanks to high pressure

[Luis H]

I'd be curious to know about cylinder rupture data during hydrotest. Of course, because the cylinder is filled with a non-compressible fluid and protected in a water jacket, there's no risk of hydrotesters getting blown up, but it would be interesting to know how many cylinders, scuba and otherwise, actually rupture when subjected to test pressure.

I have seen a few. It is not common, but it happens.

When it happens it is a mess. There is a large burst disc on the side of the water jacket to relief the stored energy. The disc is about 6 inches in diameter. Even do that water is virtually non compressible all materials in the system are elastic (and there is a little bit of air in the gauge). Therefore there is some stored elastic energy.

About two years ago my LDS had a cylinder rupture (I think it was there first time) and it made a major impression on the operator. There very little danger, but it doesn't go unnoticed.

Then you have to clean up the mess because the relief is halfway down the water jacket.

I have seen both steel and aluminum cylinders that have rupture during test. I have seen more steel, but that is only because that was all we had when I ran the hydro machine (in the 70's).

Again, I have only seen a few and I don't think it is very common.

The hydro pressure is only supposed to reach the low end of the yield stress. If the cylinder ruptures at that stress level it means two things. It has lost strength and most likely it is also brittle. A ductile cylinder, the operator may notice an increase in deformation rate at the high stresses (but this may not be always obvious).

I don't know the previous history of steel cylinder that ruptured (in my old LDS). I was only present during a couple and I only remember being the operator in occasion.

I do remember that at least one of the cylinders was a converted O2 or CO2 cylinder used in for scuba (that was very common).


I remember more that once having to remove the wire wound cylinder to do hydro test. The wire windings were done for fragmentation protection on WW-II cylinders used with O2 in aircrafts during the war. The cylinders were perfectly legal to be hydro and re-certified, but the wire had to be removed. It seem like it was miles of wire wrapping those cylindes.

 

[ianr33]

What's the hydro pressure for LP steel tanks?

 

[Luis H]

The hydro pressure for all 3AA cylinders is 5/3 of the stamped pressure.

Therefore:
1800 psi x 5/3 = 3000 psi
2015 psi x 5/3 = 3358 psi
2250 psi x 5/3 = 3750 psi
2400 psi x 5/3 = 4000 psi
3000 psi x 5/3 = 5000 psi

I own 3AA cylinders with all the stamped pressures shown above.

 

[Nemrod]

In olden times we would pump them until they swelled like water melons and then suck them until they went flat. But nowadays people are such wusses. I mean, like, what is the worst that could happen :crazyeye:.

N

 

[pocky21]

I'll add a little bit from the paintball sector as well, as deaths and injuries related to HP tanks started to become a big deal about a decade ago.

Air System Mega Safety Sticky

(be warned, there are some graphic images of burns and whatnot)

Most instances of cylinder rupture in paintball were due to introduction of foreign material (particularly oil) into the system. There were a few other cases of "user bypassed" burst discs, and multiple instances of the valve unscrewing, all resulting in a couple deaths over the last few decades.

Another item of concern with me was fill rate. I never got a knowledgeable answer from anyone back in the day, but the process of "fast filling" was at one time common practice, where pressure inside the cylinder would go from 0 to 4500psi in a matter of seconds. Scared the bejesus out of me thinking about the rapid onset of force and heat involved, and when I was operating both scuba and paintball fill stations I insisted on filling tanks at granny speed.

I obviously lack the knowledge to pass judgement on overfilling, but I feel it is only a part of a much larger picture we must examine in handling our cylinders.

 

[PfcAJ]

Doc, your logic is very liberal, where you feel the need to rectify a bad situation that will likely never occur. Trust me when I say that my nuts will much more likely be blown off by a suicide bomber than by an LP tank during overfill. Please don't dispute the previous sentence, because I will make you look silly.

This is true. People actually have had their balls blown off by suicide bomber. NO ONE has had anything blown off from an lp tank overfill (clean, hydro, VIP, of course).

 

[halocline]

The definitive answer is you can do what ever the hell you want with whatever you own. But if hurts someone else, you and your heirs will have their a$$es sued off and you'll be enjoying getting close with you new butt-buddies in jail. .

Oh, so it's 'definitive' that if you overfill scuba tanks you'll get raped in jail? This site can certainly be entertaining at times.

I think a more reasonable summary would go something like:

1. Clearly thousands of divers have overfilled LP 3AA tanks with no documented catastrophe.
2. Handling of high pressured compressed gases has an element of risk, and if there is an incident, it can be fatal and cause serious damage. Eventually someone is likely to get hurt or killed in the scuba industry filling 3AA tanks, and it's 'probably' more likely with the practice of filling to near test pressure.
3. While there are rules and laws governing the handling of tanks, the owner of the compressor ultimately makes his/her own policy and takes the risks involved.

 

[flots am]

Oh, so it's 'definitive' that if you overfill scuba tanks you'll get raped in jail?

This site can certainly be entertaining at times.

I hadn't thought of that aspect, but I can certainly see the possibility of criminal prosecution if you intentionally disable the safety device (burst disk), fill the tank far above it's rated pressure, and then it kills blows up and someone.

 

[lv2dive]

OK how can I take anything that site says seriously when in the very first paragraph it says that cylinders are only in service for fifteen years?

(BTW my cylinders stay current with hydros - and how come I can keep getting hydro's on cylinders that are 30 or more years old? and OBTW... one could bet the farm they have seen some cave fills, living in caving country for three decades ):

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• Never play with an out of hydro or non-certified cylinder.

Using an out of hydro or non-certified cylinder is not only dangerous to yourself and others but it is also a federal DOT violation to use, fill, and transport. The DOT hydro testing laws are not a suggestion, they are a requirement for the safety of you and the others around you. The hydro test can be done locally at a dive shop, paintball field, or sent to various paintball vendors that offer the service through their websites or stores.
The hydro test ensures the proper expansion and contraction of your tank. You can not test it any other way then with the hydro test. It's inexpensive overall and only comes every 3 to 5 years depending on your cylinders permit number. A tank is only in service for 15 years in total so if you have a 5 year cylinder you only need to do the test twice before the tank must be taken out of service.
Using an out of hydro cylinder at a field or national tournament can lead to you be removed from the premises or disqualified from play. This is a very serious matter, it is not a joke, it is not something to skirt and argue. Fields can face fines for filling an out of hydro tank and denying your two dollar fill is a much better option then facing those consequences. The same goes for a non-certified cylinder, it does not have the DOT clearance or testing to ensure it meets their safety standards and is there for not acceptable to use, fill, and transport.
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I'll add a little bit from the paintball sector as well, as deaths and injuries related to HP tanks started to become a big deal about a decade ago.

Air System Mega Safety Sticky

(be warned, there are some graphic images of burns and whatnot)

Most instances of cylinder rupture in paintball were due to introduction of foreign material (particularly oil) into the system. There were a few other cases of "user bypassed" burst discs, and multiple instances of the valve unscrewing, all resulting in a couple deaths over the last few decades.

Another item of concern with me was fill rate. I never got a knowledgeable answer from anyone back in the day, but the process of "fast filling" was at one time common practice, where pressure inside the cylinder would go from 0 to 4500psi in a matter of seconds. Scared the bejesus out of me thinking about the rapid onset of force and heat involved, and when I was operating both scuba and paintball fill stations I insisted on filling tanks at granny speed.

I obviously lack the knowledge to pass judgement on overfilling, but I feel it is only a part of a much larger picture we must examine in handling our cylinders.

 

[maniago]

Oh, so it's 'definitive' that if you overfill scuba tanks you'll get raped in jail?

Sir, your command of the written argument is amusing.