Tank Storage Question

[FredT]

So with steel tanks, I suppose that fire danger is the only reason then, to store them with 150 to 200 psi in them? Yes, the burst disc would blow if there were a fire, but the tank would still be hissing air while the firemen were putting out the blaze. That would also make nitrox a greater fire hazard than air alone, as well, and more necessariy to store bled, I would think?

Even if the gas escaping was pure O2 it would be safer than a half filled Al tank in a fire situation. O2 simply makes the fire hotter, which fire fighters know how to handle. They are going to put the fire out by cooing it anyway, so it's just "more of the same." A half filled Al will throw schrapnel, which fire fighters shouldn't have to contend with.

The main valve plug seat on a steel tank will often melt and "disappear" out the valve on an unconnected steel tank, along with the charge in the tank, long before the metal is weakened to the point it will fail from internal pressure. (~400-475°F seat melting temp) The burst disk should go before the seat melts, but even if it fails to do so the valve seat and packing failure modes will tend to "fire safe" a tank if the temperatures rise relatively slowly.

Tanks connected to a distribution manifold (bank tanks) don't always have the "melting seat" option, so the burst disk backs up the fire failure mode.

FT

 

[CBulla]

"Ignore the burn marks and peice of the fire fighters glove.. is the tank still good...."

 

[FredT]

As far as storing full, if you store your tanks full (especially if getting cave fills) and they need hydros it's best to let them "rest" empty for a week or two before you take them in to allow the metal to relieve the stresses in the tank wall to the extent practical. You've sort of "set" the metal in the stretched positon and it'll take a little while for the metal crystals to recover. Failures in hydro if you don't do this would be due to "lack of ductility," i.e they didn't stretch enough as opposed to the weakened metal case of "they stretched too much".

Other than that storing steels full or empty is mostly a red herring if the air you put in them is DRY!

 

[FredT]

"Ignore the burn marks and peice of the fire fighters glove.. is the tank still good...."

ANY visible signs of heat on the outside of a tank no matter what the construction condems it! Arc marks or torch scorch marks on steel welding cylinders are enough to kill them at the visual DOT requires to be done BEFORE the hydro.

FT