Filling LP tanks to high pressure

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Ummm. That comparison is not even remotely valid. Ox tox is very real, and kills people regularly....lp tanks however DONT explode when overfilled unless they are weakened by corrosion....prove me wrong...please.

Scuba cylinders - steel and alum - do explode for reasons other than corrosion-induced wall weakness - but it's very rare. DOT has lots of data on their website. For example, one alum cylinder exploded during a fill as the result of a manufacturing defect.

FYI - Almost all explosions - whatever the cause - occur during the fill process. The person at risk is generally the person doing the filling.

Personally, when I'm standing over a high-pressure cylinder I'm gonna fill according the manufacturer specs. And I'm comfortable with that.
 
you would be equally in danger if you had a non overfilled tank in your trunk and got rear ended.


That particular statement is incorrect. I will expand with plenty of back-up fact when I have a lot more time.
 
Scuba cylinders - steel and alum - do explode for reasons other than corrosion-induced wall weakness - but it's very rare. DOT has lots of data on their website. For example, one alum cylinder exploded during a fill as the result of a manufacturing defect.

FYI - Almost all explosions - whatever the cause - occur during the fill process. The person at risk is generally the person doing the filling.

Personally, when I'm standing over a high-pressure cylinder I'm gonna fill according the manufacturer specs. And I'm comfortable with that.


I can appreciate your intent, but your evidence is lacking. Show me ONE (i dont think thats too much to ask, its a pretty low bar) example of a steel LP cylinder that wasnt rusted all to hell that has exploded due to an overfill. I'll be waiting.
 
Really? Again? Another cave fill thread?
 
Let me just say that I have no issues with some degree of over filling, as long as the wall stress is below the material yield strength. All you are doing is eating into the safety factor. How much safety factor is really needed is the only real subject for debate.

I am just going to try to explain few facts. Not intended to change anyone's practice (maybe just to be a bit careful on how they do it).

DOT cylinders are designed for transportation over highways, railways, aviation and marine situation. An over the highway accident is not the most severe secondary load that a cylinder can experience. Railway or aircraft accidents can much more severe, but under the right condition over the highway could be bad.

The stress due to pressure is very predictable. A cylinder as a pressure vessel is a very simple structure and the stresses can be easily calculated. What is not as predictable is other secondary loads like those encountered in a transportation accident.

There are also several other reasons for the safety factor. Structure and events are not always perfect and predictable. I will expand on some of the other risks when I have more time.

Assuming that there is absolutely no risk is a total fallacy. Even when filling to the stamped pressure there is always some risk. The risk may be very small and therefore very acceptable, but risk is not binary (on or off). It is all about degrees of risk and what the individual is willing to accept.

The fact that no incident has been documented to this date just gives an indication that the risk may be low, but by no means does it predict the future. Remember that anything that has ever happen, always had a first time. Just because we have not seen a first time yet it doesn't guaranty that it will not happen.

We have some very good experience and data from the cave fills in Florida, but extrapolating that into saying that we have a huge experience is not accurate.

The number of cycles most scuba tank experience are always very low. Even rental tanks in the Caribbean only see about 360 fills a year. In ten years that is only 3,600 cycles. It is not the same, but just to give a little perspective, that is roughly the number of cycles an engine or compressor cylinder sees in one minute (running a 3600 rpm)

If someone are assuming that there is absolutely no risk, that person is either delusional, ignorant, or a combination.


When I have a lot more time I will be glad to write about all the reasons fro the safety factors, about the levels of risk, and most important about risk mitigation.

Just a quick advice. If you are going to over fill:

  • Try to keep a margin below the low yield strength (below hydro pressure, see note)
  • Inspect for corrosion a lot more often (I would recommend 6 months)
  • Always make sure your tank is very dry inside and be extremely careful that moisture never gets in. Carefully dry the connection (both sides) before filling. I will expand a lot more on this later.
  • Be very careful when transporting cylinder. Never overfill if you are going to transport on private aircraft (personal experience story later).
  • Always restrain the cylinders or make sure they do not fly of the vehicle when transporting on the highways.
  • Be extremely careful with potential exposure to heat or fire. Specially with compromised safety burst disc. The temperature inside a vehicle in Florida can be an issue. I can expand a lot more on this later (with facts and numbers)

More later.

Note: there is a huge difference between filling a 2400 psi cylinder to 3500 or even 3600 psi, that to filling them to 4000 psi (or higher). I can expand with a lot more of the physics behind this another time.

A quick comment about rust. The study (I think it was University of Rhode Island) showed that under the right conditions (water inside and under pressure) a new cylinder (with good hydro and VIP) can rust enough to compromise its structural integrity in as little as six month. The test was extreme and can be mitigated, but it brings one of many possible scenarios that shows the potential risk.

Under the right condition, rust can happen a lot quicker than most people realize and it is accelerated with the higher pressure, but it can be mitigated if you are very careful.


I am totally supportive of risk taking. I have jumped out of airplanes, flown ultra-light aircrafts and sailplanes, done a lot of white water kayaking including class 5, done fair amount of rock climbing and some ice climbing, just to mention a few... I even rode a motorcycle on the highways with cars around for a while (now that is

But my point is that there is risk on anything and knowing the risk is important, mitigating the risk is the only smart thing to do.
Taking calculated risk is not only acceptable in some cases can even be an adrenaline rush. But taking risk under the illusion that there is not is right down...


I can easily expand with a lot more facts and the physics of pressure vessels when I have more time, if anyone is actually interested.
 
Just unwilling to allow the uneducated to spread their fallacies concerning the subject matter.
 
I can easily expand with a lot more facts and the physics of pressure vessels when I have more time, if anyone is actually interested.

We'll be waiting with bated breath.
 
Really? Again? Another cave fill thread?

To be fair, there's another deep air thread that's raging on as well. I think you've posted in it, though....so that's good. It's like, we can't find anything new to argue about so we keep going back.
 
I guess as a scuba diver I'm willing to take risks where there is no documented failure to date. Certainly that is a lower risk than anything else we deal with diving? As an electrician I see changes made to the code book that are made to cover risks where there has never been a documented case of the thing happening. We have been using electricity, and scuba tanks, for a few years now and if something hasn't happened I'm willing to assume its risk of happening is a risk I'll not worry about.
 
I can easily expand with a lot more facts and the physics of pressure vessels when I have more time, if anyone is actually interested.


*raises hand*


Somewhere between the flawed logic of "it's never happened before", and the equally flawed logic of "it's safe up to the rating", lies an engineer with an answer as crystal clear as "it depends". :D
 

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