Refinishing steel tanks

[MxDiver]

Well I finally decided to refinish my old steel tanks. First step was to put a wire wheel on my drill to remove the original paint, this being the result:

Then I bought some cold galvanizing compound and gave it a couple coats:

Right now I am trying to decide how to paint them, in the mean while I will finish making the double bands, I will post pictures of these tomorrow.

[cummings66]

Interesting. I don't care for the wire wheel stripping. You embed small metal particles in the cylinder which can cause rust spots down the road. Chemical stripping is easier and doesn't have that risk, for future reference.

From the look of things, did you measure those pits? Some of them look deep enough to be a problem? It could be the picture but it looks like a few of them might have been deep enough to warrant measuring. General corrosion limits are .02 inches, depending on brand of cylinder max isolated pit depth is .05 inches.

As to paint, I would not apply any. Paint on the ZRC might look nice but it sort of inhibits the purpose of applying the ZRC paint. I'd leave it like you have it. 2 rolled on coats is enough to provide rust resistance. Speaking of which, depending on how you got the rust off watch those areas that were rusted for re-rust. The initial stripped picture you showed had what looked like too much rust to cover without re-rust happening. Keep on top of the rust.

It took me 2 days to get my cylinders prepped where I was happy enough to roll the ZRC on. PS, I don't know what regulations you have there, but around here you might have an issue with a fill station or the inspector since you painted them. They sometimes wonder why you painted them and might require you to re-hydro them.

The final coat looks good though, much nicer I'm sure compared to how it started out.

[mm2002]

Assuming that the pits aren't too deep, why wouldn't a wash in phosphoric acid be a good idea before applying any type of coating? That would kill all of the rust present down in the pits, and believe me, that is not achieved with a wire wheel. Also, what about media blasting, like soda, plastic, or walnut shell? Remember, I have no experience with scuba tanks, but metal is my business.

[MxDiver]

I tried media blasting, but it wasn't strong enough to remove the paint, I was afraid of using real abrasive media so I reverted to the wire wheel.
I didn't consider embeding metal bits. The tank was cleaned a second time after the first picture was taken in order to remove the visible rust before painting.
The cilinders are scubapro and I will measure the pits as you mention. The tanks had a visual and hydro done less than a month ago at the same place I get my fills, I don't think repainting them will be an issue.

[mm2002]

Originally Posted by MxDiver

I tried media blasting, but it wasn't strong enough to remove the paint, I was afraid of using real abrasive media so I reverted to the wire wheel.
I didn't consider embeding metal bits. The tank was cleaned a second time after the first picture was taken in order to remove the visible rust before painting.
The cilinders are scubapro and I will measure the pits as you mention. The tanks had a visual and hydro done less than a month ago at the same place I get my fills, I don't think repainting them will be an issue.

I can't imagine any type of safe media blasting that wouldn't at least remove the paint, unless it had a LOT of tough (urethane) paint on it to begin with. Still, media blasting is the best way to totally rid a surface of rust, especially if there's pitting. If you put ANY type of coating over those rust pits, trust me, there's still rust under there. That alone would tend to make me NEVER trust that tank. The problem is, that rust will continue to grow, and you can't see it!

[matt151617]

I know this is a DIY thing, but most welding shops offer services like this, ranging just from stripping paint to a full repaint or polish on tanks.

[Daddy Diver]

How has that cold galivinizing compund held up? I just tried repainting a tank but I am having problems gettibng the paint to harden even after a week or so. It was rustoleum in the industrial/maintence size.
I'm thinking of stripping it again and going for appliance paint which should get real ghard and scratch resitant, but not too much UV

[captain]

This is the stuff. Using anything else is a waste of time and money. Buy it by the quart directly from ZRC and use a foam roller to roll on 3 coats.

ZRC - ZRC Galvilite Galvanizing Repair Compound

[cummings66]

The ZRC paint is holding up very well, I've managed to scratch and do all kinds of nasty stuff to mine so it has some metalic looking streaks in it but it's intact and acting as it should.

It looks like paint until you scratch it, then you'll see that you've exposed Zinc and it just takes a while to dull again. ZRC is the only way to go, roll it on and you're set. Do not obscure the hydro or any numbers on the cylinder, it's easy to do since many hydro shops don't stamp heavy. Put a layer or two on and tape over it and then paint over that and remove the tape so it's legible.

ZRC is expensive but the best paint out there, 95% zinc if I recall correctly.

[cummings66]

Originally Posted by mm2002

begin with. Still, media blasting is the best way to totally rid a surface of rust, especially if there's pitting. If you put ANY type of coating over those rust pits, trust me, there's still rust under there. That alone would tend to make me NEVER trust that tank. The problem is, that rust will continue to grow, and you can't see it!

Chrome Molly steel as used in the steel cylinders will rust right before your eyes, trying to O2 clean a cylinder with using Nitrogen to dry it is a challenge in patience because it rusts so fast. You can watch it rust right before your eyes. IMO NO rust at all is what you're aiming for, anything less is dangerous. Of course that's why we have welt probes for doing the vis inspection, a rust bubble can be bad enough to condemn a cylinder and it's hard to tell under labels and bubbles of paint. It's also one reason many inspectors will reject a cylinder that's been painted, you don't know how they stripped it or painted it. Heat is bad in both cases, but with steel you've got a larger amount needed to condemn a cylinder.