Purely cosmetic

[JaxDvr]

I have a pair of steel 80's (77+) that show oxidation. They just look old, as they passed VIP, hydro and were O2 cleaned for Nitrox. Any thoughts on how to remove the oxidation without jepordizing the integrity of the tanks?

Thanks in advance.

 

[Divin'Papaw]

Why bother? They have character!

 

[empressdiver]

I assume your just talking about the outside of the tanks. How old are they? Can you post any pics? Most steel scuba tanks are galvanized on the outside, some with a coat of paint on top, and therefore should not have oxidation, ie. rust, from normal usage.

Having said that, you might try rubbing them with fine emery cloth available from any hardware store to remove light rust. That certainly will not damage the tanks, although you might possibly be removing some of the protective galvanized coating.

If the tanks have deeply pitted rust areas that developed after the hydros, I would not recommend grinding the surface smooth without first having them examined by a hydro testing facility. You can take them directly to a fire equipment company for that instead of to a scuba shop which will only send them out anyway to a hydro facility. You probably should get them tested again, and if they pass, then get the tanks galvanized.

 

[ams511]

Empress, I didn't know tanks can be re-gavanized, that is good to know. Could the OP just remove the oxidation as you suggested and just paint the tanks?

 

[empressdiver]

Galvanizing is coating the tank with zinc. For the normal treatment that scuba tanks are subjected to, paint by itself will not last long enough to provide adequate protection against rust. Paint should only be used on top of the zinc coating, but its not necessary. If those tanks were not galvanized, I would think they must be quite old. The info stamped on the shoulder of the tank will indicate the date of the first hydro. If exterior rust is removed by sanding or sandblasting, the tank should be recoated with zinc.

 

[JaxDvr]

i AM SURE THEY ARE GALVANIZED AS THE OXIDATION IS WHITE AND ALMOST LIKE CALCIUM. IT LOOKS A LOT LIKE WHAT I SEE ON SACRIFICIAL ZINC ON BOATS. WHITE AND FLAKEY. THERE IS NO RUST OR PITTING FOR THAT MATTER.

 

[cummings66]

paint by itself will not last long enough to provide adequate protection against rust. Paint should only be used on top of the zinc coating, but its not necessary.

Not true, I have a PST made tank from the mid 80's that's paint only and it's fine with no rust. My LDS has several of those style tanks and they too have no rust on them, paint is fine given careful attention.

Now if you dive in the Ocean and just hop out and do nothing more to the tanks I could see paint being a liability, but in fresh water like we dive around here painted tanks last forever.

 

[james croft]

Don't sand galvanized tanks. It would remove the protective coating that acts as an anode. Naval jelly will clean up a galvanized tank and make it look all new again.
There is a product called Galvite (spelling?) that you can paint tanks with that gives a good galvanized type coating.

 

[captndale]

Galvanized tanks should just be left alone. The oxidation on the zinc coating is normal. That is what the zinc is for. The zinc is a sacrificial anode. Do not remove any of the zinc and do not paint it. It works best if it is left bare.

 

[ams511]

Don't sand galvanized tanks. It would remove the protective coating that acts as an anode. Naval jelly will clean up a galvanized tank and make it look all new again.
There is a product called Galvite (spelling?) that you can paint tanks with that gives a good galvanized type coating.

Some paint used for chain link fences contain zinc. I painted my uncles sheds with it years ago and the paint lasted for about 20 years. The paint was very expensive if I remember correctly.