Question Should you overfill lp tanks without a + stamp?

[James79]

Please excuse my ignorance, but is overfilling just a thing on steel cylinders? or do folks do this with aluminium as well? I am asking because I recently purchased an AL80 and while living overseas I only had steel cylinders and the common practice at the club was to slightly overfill them to between 230-240 bar knowing that when they cooled the pressure would drop to approx 200-210bar. I am just wondering what the best practice is for an aluminium cylinder and if overfilling should be avoided?

-Z

With the disclaimer that my advice is worth what you paid for it (and not to be trusted!), my understanding of the metallurgy on steel vs aluminum is that there are distinct differences in how the yield strength and fatigue work. An extra 100 psi or so that cools to rated pressure is no big deal, but I would not "Cave fill" an aluminum ever. My old school 72s, however, I will run at 3k any day. Your mileage (and research) may vary.

Respectfully,

James

 

[sharknutz]

Please excuse my ignorance, but is overfilling just a thing on steel cylinders? or do folks do this with aluminium as well? I am asking because I recently purchased an AL80 and while living overseas I only had steel cylinders and the common practice at the club was to slightly overfill them to between 230-240 bar knowing that when they cooled the pressure would drop to approx 200-210bar. I am just wondering what the best practice is for an aluminium cylinder and if overfilling should be avoided?

-Z

This is only for steel tanks, aluminum tanks should never be overfilled. Aluminum cracks when overfilled, steel stretches.

10% over in an AL tank probably won't kill you, I sure as hell wouldn't go anywhere near 25%+ on an AL.

 

[runsongas]

@rob.mwpropane permanent expansion for regular hydro vs REE for + rating. failing the REE means the tank is expanding too much at higher pressure. Repeated overfills will then cause the tank to start thinning the walls until it eventually fails the permanent expansion for hydro.

 

[DogDiver]

Wow, I learned something new today. I always thought that the 2400 stamped on my Fabers was to note my Turn Pressure.

 

[rob.mwpropane]

@rob.mwpropane permanent expansion for regular hydro vs REE for + rating. failing the REE means the tank is expanding too much at higher pressure. Repeated overfills will then cause the tank to start thinning the walls until it eventually fails the permanent expansion for hydro.

Can you link an article where this has been documented?

It's my understanding that it's very, very, very rare for tanks to fail hydro. I am told they have been overfilling tanks in FL for 30+ years with no adverse effects.

And I don't think the walls "thin". They may stretch and not bounce back, but I don't think I would consider that thinning?

 

[rjack321]

Can you link an article where this has been documented?

It's my understanding that it's very, very, very rare for tanks to fail hydro. I am told they have been overfilling tanks in FL for 30+ years with no adverse effects.

And I don't think the walls "thin". They may stretch and not bounce back, but I don't think I would consider that thinning?

"overfilled" 3AA steels will eventually fail hydro, somewhere 20+ years from now. But nothing lasts forever, the folks scrubbing every last molecule of salt off their gear, or freaking out about how a 3600psi fill is 'shortening' the life of a 3AA steel, are also the types of folks who quit diving within the first hydro cycle anyway

 

[rhwestfall]

They may stretch and not bounce back, but I don't think I would consider that thinning?

Think about it... the movement outward causes the sectional area to be reduced (it is stretching) otherwise it is impossible for it to move. So yes, the wall is thinning if it is not rebounding...

 

[Manatee Diver]

"overfilled" 3AA steels will eventually fail hydro, somewhere 20+ years from now. But nothing lasts forever, the folks scrubbing every last molecule of salt off their gear, or freaking out about how a 3600psi fill is 'shortening' the life of a 3AA steel, are also the types of folks who quit diving within the first hydro cycle anyway

Cave filled LP tanks are a consumable. If it lasts only 5,000 fills, that is 10-15 years of diving.

 

[rob.mwpropane]

"overfilled" 3AA steels will eventually fail hydro, somewhere 20+ years from now. But nothing lasts forever, the folks scrubbing every last molecule of salt off their gear, or freaking out about how a 3600psi fill is 'shortening' the life of a 3AA steel, are also the types of folks who quit diving within the first hydro cycle anyway

These fine folks are the reason I can afford this hobby! I say if they want to scrub and keep my future stuff looking new then God bless em!

 

[halocline]

This is only for steel tanks, aluminum tanks should never be overfilled. Aluminum cracks when overfilled, steel stretches.

10% over in an AL tank probably won't kill you, I sure as hell wouldn't go anywhere near 25%+ on an AL.

Considering the test pressure for an AL80 is 5000PSI, I believe you are being alarmist about AL tanks 'cracking' when overfilled. I have little doubt that if you filled an AL80 to test pressure every day, then it's life would shorten, probably dramatically. 25% over on an AL80 is 3600 PSI, and while you don't see that every day, it's not uncommon for freshly filled AL80s left outside in a hot environment (like Mexico, for example, where this goes on all the time) to measure 3600. They cool to around 3200, and that's a very common pressure to see on AL tanks down there. Magically this practice has been going on for decades and nobody has been killed by an exploding tank yet to my knowledge.

I understand the concern about ruptured tanks, they are basically bombs, but the reality is that tank ruptures are exceedingly rare. Like, 100 times more rare than getting struck by lightning on a day when you win the lottery. (ok that last bit was a joke)