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Re: CO2 Cylinder Testing

CableGal68 at aol_com described what he did to test a CO2 tank back when
he owned and operated fire equipment companies.

Some might wonder, "well, if the tank has worked for five years, why
would it need to be tested, it obviously works."

The reason for the test is to assure that metal fatigue has not
progressed to such a point that the tank could rupture or leak gas
unintentionally.  Each time a tank is filled, it is stretched slightly.
 As it is emptied, the reverse happens.  This movement eventually
fatigues the metal.  Different metals fatigue at different rates and
under different stresses.  

A really good test for this is to submerge the tank in fluid and
measure the displacement before and after filling.  If the increase in
displacment is too great, the metal has fatigued unacceptably and is
yielding too much to the tension.  I recall that DOT, whose regulations
control these things, has standard values for these measurements.

So why is five years the right amount of time between retests?  It's a
regulatory standard picked to be adequate for most tanks under most
common uses, without being unreasonably frequent.

I personally prefer seamless steel tanks to aluminum ones, although
they are a pain to lug around in the larger sizes.  But for planted
tank use, where the refillings are months apart, the amount of fatigue
in 5 years is probably pretty minimal.  In 10 years, still minimal, I
would guess.  In fifteen?  Hmmmm.  I don't mind paying for testing --
as someone recently pointed out on this list, risk depends not just on
the probability of an event but also the extent of harm or damage that
might result.  When I get a metal balloon filled with 900 or so psi
(pounds per square inch) of pressure, I like to be confident that it
won't go pop.  :-O


BTW, Harborfreight tools is selling steel tanks that hold 5 pounds or
10 pounds of CO2 for $69 and $139 respectively.  Harborfreight
describes the tanks by their tare weight rather than net weight when
filled.  So they are called "10 LBS. CO2 CYLINDER" and "20 LBS. CO2
CYLINDER"  These are Coynes brand and pretty good tanks at a pretty
good price if you don't mind sometimes slow deleivery.  Both sizre
tanks show in their current catalogue.  They don't always both show on
the web site.

http://www.harborfreight.com/cpi/taf/Basket.taf?ItemNumber=40921&ActionArg=add&itemPrice=139.9900&Itemdash=0&code=VGA

enter all on one line.

Scott H.

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