Rusting Co2 Cylinders

[thefirethief]

Someone has just asked me about this and I had a few ideas of my own, but I said to them Id post it up here. Any thoughts?

CO2 purity (explained)

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To: "'Aquatic-Plants at ActWin_com'" <Aquatic-Plants at actwin_com>
Subject: CO2 purity (explained)
From: Marque Crozman <marquec at gastech_com.au>
Date: Mon, 4 Nov 1996 12:31:28 +-1100
Encoding: 47 TEXT, 56 UUENCODE

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Subject: CO2 purity?


There are at least two different grades of CO2 available, (I found
out during a similar problem) Food grade, which is used in soda
machines and such, and commercial grade, which is used in some
welding applications from what I can tell. The food grade is what
you want.

The only difference between these two grades of CO2 is that the
bottle that it comes in. Both gases are 99.97% CO2, the food
grade bottles are internally glass coated, whereas the industrial
cylinders are straight steel.

The reason that there is a difference, is that by law, the food
systems have the possibility of back-flowing into the bottle
when the gas runs out. If the bottle was a standard industrial
bottle, the system would have the possibility of becoming
contaminated with rust from the internals of the bottle. (CO2
disolved in liquid from beverages is quite acidic and rusts the
inside of gas cylinders.

This would be the same as eating tinned food where the can
was rusting, you have the risk of contracting tetnis(?)(lock-jaw)
or some other illness associated with rust.

So the insides of food grade cylinders are washed each time
before the bottle gets refilled according to food hygene laws.

Therefore the food grade bottles are more expensive to hire, as
more work goes into refilling. According to the rules you are not
really permitted to use food grade CO2 for fish tanks, as what
you are hooking up to them is not passed by the food hygene
act, but I know that people do.

The only thing is that industrial CO2 is cheaper because there
is less involved in refilling cylinders, and has the same purity,
so that is why I use it.

Marque Crozman APD ANGFA(NSW) <><

I know a majority of people here use welding cylinders and a few, myself included, use fire extinguishers and there have been no adverse effects but it doesnt hurt to question things.

So really, the real issue is that the food grade cylinders are glass coated to prevent rusting but we should only be concerned if the industrial grade cylinders have been subject to a back flow of liquid, which seems unlikely. I cant imagine fire extinguishers and welding clyrinders would pass safety checks if they were going to be open to rusting. A weakened cylinder doesn't seem much fun when dealing with pressurised gas.

 

[Themuleous]

Interesting, thanks for posting. I use welding Co2 on both my tanks with no apparent affect on the fish. Glad to know this is backed up by the 'science'

Cheers

Sam

 

[Davver]

Thanks for that information... I may be wrong, but rusting is Oxidisation, which requires oxygen. So as long as no oxygen gets into your cylinder, it will not rust.(?) This explains the advice on the Dennerle (i think) CO2 instructions to never completely empty the cylinder. Just some thoughts...

Dave.