There is a DOT/ICC number, usually stenciled into the body of the cylinder.
If memory serves me correctly (which it rarely does) that number must be
at least 1800 or above before the cylinder can be filled with CO2. Of
course, you would have to replace the valve, and that's STRICTLY a job for
the supplier, but the cylinder (assuming the DOT/ICC # is high enough) is
the same. Also, be aware that most gas supplier will refuse to fill
customer owned cylinders.
Another consideration here, is CO2 is the last gas in a cylinders life
time. Oxygen, breathing air (your scuba tank), argon and all the other
gases can become contaminated in a CO2 cylinder. The problem with this is
you can never go the other way. You can't again use your CO2 tank as a
This information comes from being involved in the business 10 years ago.
There may well be new regulations which prohibit what you want to do, but
from a purely technical point of view, yes, it could be done.
IMHO Harbor Freight's price looks pretty good.
TR3A TS57756 (in pieces)
> From: Matt Barre <email@example.com>
> To: firstname.lastname@example.org
> Subject: welding gas tank
> Date: Monday, October 28, 1996 1:03 PM
> Here's an off the wall thought. I recenty purchased a Century mig welder
> and was going to buy a gas tank from Harbour Freight when I spied an old
> steel SCUBA tank left over from when I used to dive. It is out of
> hydro, but would it be possible to change the fitting and use it for
> CO2??? Would the normal gas suppliers not want to fill it? I would
> paint it green and stencil it CO2 so no one would try and take it for a
> Matt Barre
> Mobile, AL