On Sat, 22 Nov 2003 03:07:40 GMT, wrote:


The water submersion while filling is for cooling, since the heat
could, in theory, weaken the tank if it got hot enough.

I believe it is more an issue of time to reach equilibrium pressure;
the hot air, when cooled, drops in pressure. I _DOUBT_ that the
temperature would get high enough to be of any effect on the aluminum
heat treatment, but may be wrong.

If a tank
lets go the water won't do much to damp the explosion, I saw pictures
of a scuba shop after one failed (someone powder coated an aluminum
tank and destroyed the temper). Not much was left of the entire shop,
or of the owner.

Yeah, I remember those pictures and warnings ... what, some 25 or 30
years ago now? I believe that significant weakness occurs in the
alloys used above about 300F.

IIRC, hydrostatic testing of a tank takes it to 5/3 of it's rated
pressure, and it can't expand more than 2% to pass.

I BELIEVE it is the difference in expansion and recovery ... must
recover 90% of the fluid used to expand the vessel (and compress the
water)

One fills the tank with de-aerated water, measures the water volume
required to attain the 5/3 pressure (verifying a stable reading, no
leaks, etc), decompresses, the fluid recovered in decompression must
be 90%-100% of that used to compress.