How to handle mysterious tank coating?

[NorthWoodsDiver]

Well as a welder you can probably believe I visit scrap yards but I bet you wont believe I found a perfectly good steel 72 for $8!!! well its only gonna be perfect if I can figure out what to do, if anything, about the strange painted coating on the interior of the tank.

Tank reads:

DOT3AA2250
33585
SRP
1073+ PST
8079+
9085+

so I'm pretty much positive its a 72 and I assume its a pressed steel tank. its galvanized on the exterior, has 3/4" straight threads, a bit of light rust on the threads, but a coating or red gloss paint on the interior.

I assume tumbling with some sort of media is the best option but I wanted to confirm before jumping into a waste of time and perhaps someone could point me to the best media for removing the said paint. Thanks

 

[belgianbrew]

Maybe it was scrapped for a reason, such as a failed hydro...

 

[NorthWoodsDiver]

I thought that to be unlikely as it had the plastic backpack installed still and all the hydro date stamps are + so it would be strange to go from a + rating to failing. I figure either the tank was inherited and not wanted or failed visual because the shop didn't approve of the paint coating.

even if its not fixable it will make a good target...

serious though how do I get this paint out. Thanks

 

[spectrum]

Some tanks had a vinyl like liner on the inside. Is the interior finish intact or are there signs of cracking or blistering?

 

[marchand]

you could try a whip or tumbling with a really powerful solvent... or both.

 

[Gilldiver]

Is it clear or brown in color? If it is it is a resin coating that many dive shops will fail for. You can take it to some Hydro shops and see if they have a shot blaster to get it out with. None of the other methods work all that well.

If it had failed Hydro, the numbers would have been XXXX out.

 

[Paintballpsyco2369]

I have heard of people tumbling them with carbide fillings, but a friend of mine got a tank with the vinyl coating on the inside from another friend of his. He brought it to the shop and they tumbled it for something like a week or so with normal media and it came right out. Any shop SHOULD fail it on a visual if there is an indication of a liner inside it. The reason being that weather you can see it or not, then liner will get micro cracks and allow moisture into the cracks of the coating, which then can not escape causing the moisture to sit on bare metal for a long period of time which forms a pit. Then say someone fills it, that structural damage on the tank could cause it split down the side, or blow apart. There is an interesting story on the PSI website about a vinyl coated tank. Given that was an external coating, but the same thing can happen from in or outside the tank. I had a tank that had the external coating, I got the thing off craigslist, and I cleaned it up so nice that one might have thought it was brand new. Took it to the shop, they informed me about the coating, and I removed it (that was a bitch, took me 4 or 5 days and around 6 or 7 razor blades before I gave up and just used a wire brush on a power drill). When I stripped the bottom of the tank, there were half a dozen rust spots from that whole process. One thing that I have heard of happening, after so many fills and stretching of the internal coating, it can start to flake off, which can get trapped in the dip tube of your valve and can obviously cause some serious problems.

I did call around to all the other shops that were within reasonable distance from me. Half of them had never heard of such a thing, one of them had heard of it and to this day chooses to ignore it, and the others had either never heard of the rules regarding the tanks, or even ever seen them.

My suggestion would be to try the normal media for say around a week +- a day or 2, if that does nothing, try the carbide fillings if you can get some. If it does work, stick with the normal media as it would not remove as much metal from the tank as the carbide would. Then have the tank re-hydro'd and vis'd and you should be good to go.

 

[SDAnderson]

You're correct, you have a Pressed Steel tank, originally manufactured in October 1973 and probably last hydro'd in 1985.

The liner is a major issue. It will be a mountain of work to remove it and you the chances are good that you will find unseen serious damage - or destroy it yourself. As DIY projects go, this is a nasty one with limited potential for success. Of course, if you do get it cleaned up it will need to be hydro'd before you can get it filled and it's still an ancient steel tank with a 2250 psi fill limit...

Steel tanks, if treated well, can last forever but yours should probably be returned to the scrap heap.

 

[james croft]

I am rather fond of ancient steel tanks, particularly 2250 steel 72's. Great bouyancy characteristics and hold enough air for the bulk of my diving. That being said it will be a chore to get the liner out. I have done it using a cable whip and days of tumbling. It turned out nice but it must be a labor of love.

 

[captain]

The hydro shop that I use has no issue with the coated tans, I have one they just did. It's just the LDS's that have issues. If the coating is not blistered or flaking there is no rust under it. If it does have blister or flaking tumble it enough to remove the blistered and flaking areas so it can be inspected.