Question Should you overfill lp tanks without a + stamp?

[L13]

Considering the test pressure for an AL80 is 5000PSI, I believe you are being alarmist about AL tanks 'cracking' when overfilled

The metallurgy for AL is significantly different that for steel.

Steel tanks have essentially unlimited life up to hydro pressures, unless damaged due to rust etc.

AL, on the other hand, has a limited life in pressure cycles even at working pressure. However, at working pressure + 10% the lifetimes is decades of multiple fills a day. At higher pressures, more life is consumed per fill, with usable life rapidly dropping as pressure increases. End of life will still be detected by hydro as long as you stay below 300 bar, but could be as little as 5 years if frequently filled above 250 bar.

In either case, damaged cylinders can be dangerous, even at rated pressure or less.

 

[halocline]

The metallurgy for AL is significantly different that for steel.

Steel tanks have essentially unlimited life up to hydro pressures, unless damaged due to rust etc.

AL, on the other hand, has a limited life in pressure cycles even at working pressure. However, at working pressure + 10% the lifetimes is decades of multiple fills a day. At higher pressures, more life is consumed per fill, with usable life rapidly dropping as pressure increases. End of life will still be detected by hydro as long as you stay below 300 bar, but could be as little as 5 years if frequently filled above 250 bar.

In either case, damaged cylinders can be dangerous, even at rated pressure or less.

I'm aware of the difference between AL and steel. I think it's alarmist to be worried about AL scuba tanks cracking when being filled, which is what I said in the earlier post. It just does not happen in the real world.

 

[sharknutz]

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)

In a conversation about pumping LP tanks where 50% overfills is pretty common, just don't want anyone to get the wrong idea about AL tanks.

I'm not ignorant to the fact AL tanks get hot filled to 20% and cool to 3300. However, what I stated was 25%+ on an AL tank which is 3750+.

Would you consider pumping an AL tank to 4500 (50%) like a LP tank?

 

[grf88]

You should NEVER overfill an LP tank. At least not until you have changed the burst disk.

 

[MidOH]

My plugs are 5250#.

 

[Robert H. Diver]

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)

Yea I was just in Belize doing some diving and a lot of my AL cylinders were around 3400 psi.

 

[johndiver999]

I'm aware of the difference between AL and steel. I think it's alarmist to be worried about AL scuba tanks cracking when being filled, which is what I said in the earlier post. It just does not happen in the real world.

I've personally seen it and on an Al tank that was less than 2 years old and probably not overfilled frequently and it occurred well below 3000 psi.

But it is rare, scared the heck out of me. The tank started leaking badly, on filling, assumed it was a bad O-ring, upon inspection - saw the crack, put my finger over it to confirm the leak. I stopped filling, ran away and waited and when the pressure dropped a bunch the crack resealed itself and the leak stopped or greatly slowed. Catalina tank, I am pretty sure.

 

[CT-Rich]

"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

Ouch… a brutal truth.

If tanks were that delicate they would be ladling divers off the roadways on a regular basis. On the other hand, the penalties are permanent and impressive…. That is why god gave us the burst disk…

 

[Tracy]

Ouch… a brutal truth.

If tanks were that delicate they would be ladling divers off the roadways on a regular basis. On the other hand, the penalties are permanent and impressive…. That is why god gave us the burst disk…

God didn't give us a burst disc. Antiquated laws about boilers did.

 

[DogDiver]

You should NEVER overfill an LP tank. At least not until you have changed the burst disk.

Wow another new thing I’m learning today. You mean you’re only supposed to have one burst disc in your valve and not two.