cornfed
Mindless lemming
Someone once told me never to buy a used tank from a cave diver. I now see why.
Choice nuggets from the LDS
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Someone once told me never to buy a used tank from a cave diver. I now see why.
Scuba_Vixen
Guest
are factors in this situation. Filling that tank to 4000# or more, creates a lot of heat, when it's hydro'd in water, the thermal stress is mitigated to some extent, helping to keep the inner surface of the tank from extreme temps that can compromise it's integrity. There are some specs that give the max temps that tank aluminum should be subjected to, and something around 400F comes to mind (may be in ther high 300's). Aluminum looses tensile strength rapidly with increasing temp, therefore heat and pressure are it's worst enemies.
While "cave fills" for Lp steel tanks are routinely done to about 3400#, You'll not see anyone overfill an Al tank by more than 200 or so, and that's back to 3000 after it cools. Experience has taught them better.
Where's the metalurgy guys when we need 'em...they could explain this a lot better.
Darlene
While "cave fills" for Lp steel tanks are routinely done to about 3400#, You'll not see anyone overfill an Al tank by more than 200 or so, and that's back to 3000 after it cools. Experience has taught them better.
Where's the metalurgy guys when we need 'em...they could explain this a lot better.
Darlene
Waterborne
Contributor
Hence the reason alot of guys remove the burst disks and replace them with plugs. The thinking behind it is that the tank neck O-ring will extrude if the tank is overpressurized, regardless of the reason.
Not that I'm endorsing that method, that's just a little insight for ya.
Cornfed, you're spot on with that advice.
Scuba_Vixen
Guest
Dive steel doubles almost exclusively, and retire them at the first or second hydro.
Beware the steel tanks in cave country with the tell tale imprints from the bands....
Darlene
Beware the steel tanks in cave country with the tell tale imprints from the bands....
Darlene
cornfed
Mindless lemming
Darlene,
You're not going to achieve temperatures anywhere near those. It doesn't matter the tank is in a water bath, filled with water for hydro or sitting dry on the floor of the shop. If this weren't the case, then your explain would mean every AL tank would fail every hydro.
The shop is question certainly isn't staffed by the brightest bunch around but they did not ruin the tank.
Drew
Hey....our shop never paid that good!
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When a tank is hydroed, it is filled with water before pressurization. Due to the negligible compression of water, practially no heat is built up on the tanks. That way if the tank ruptures there is no explosion, just water running out rapidly.
I've seen the lowpressure steels filled way past 3400#, I know of one dive site in Florida that will do 3000# with no questions. I found out the day they had to replace my burst disc for free.
A lot of places that routinely handle steel tanks have no problem over filling them by quite a bit.
Hooked4Life
Guest
LDS's just never cease to amaze me. My Girlfriend and I bought a PADI AOW book to study for our AOW classes. We went into our LDS to sign up for classes that weekend. My LDS explained that its not worth the time or money to train us in AOW because they make no money from the classes and we did not buy our "life support" from them. This was the same LDS that sold us the PADI AOW book, $800 worth of Faber tanks (1 month ago) and my GF was OW certified through them. They also turned my other Dive Buddy away and told him the same thing. I walked out in amazement. I guess that explains the Porsche Boxter, Harley, and full size GMC in the parking lot.
I'm fairly certain that a hydro test is done with water both inside the tank and outside the tank. Since water doesn't compress, there's no heating and no danger of an explosion of the tank ruptures during the test.
(leadcarrier's post showed up after I posted and I can't delete my post. Sorry for repeating what's already been posted).
Alan
Scuba_Vixen
Guest
because the hydro is done in water, with water in it, (that's what I didn't make clear) there is no heat build up, so the heating risk is mitigated.
If you feel how warm a tank gets on the outside after a fill, just figure how hot it got on the surface of the aluminum inside the tank before conduction could spread the heat throughout the rest of the aluminum mass. Adiabatic heating is not to be underestimated.
Why not email Luxfer or Catalina and ask them what they think of a tank that's been hot filled to 4000# and left that way....apparently untill it was used
If they say the tank's fine, I'll eat humble pie all month...
Darlene
If you feel how warm a tank gets on the outside after a fill, just figure how hot it got on the surface of the aluminum inside the tank before conduction could spread the heat throughout the rest of the aluminum mass. Adiabatic heating is not to be underestimated.
Why not email Luxfer or Catalina and ask them what they think of a tank that's been hot filled to 4000# and left that way....apparently untill it was used
If they say the tank's fine, I'll eat humble pie all month...
Darlene
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