Tank I.D. Question

[teknitroxdiver]

Do NOT hot-dip it. That will change the properties of the steel and could make it far more likely to burst at pressure (very bad deal...). If you want to take that layer of paint off, get what they call Aircraft Paint Stripper. Spray it on, the paint bubbles up, then wash or wipe all the paint off, then rinse very good with water. Very easy to do. To do this you will want to remove the valve and put in a plug. You can get a PVC tapered plug that will do nicely. If there is paint under where the valve covers, take that off with a razor blade to keep the stripper out of the inside of the tank. While you've got the valve off you will be able to easily see if the tank needs tumbling. You may find that there is a vinyl lining on the inside...if so you can get that removed by tumbling too.

 

[tlawler]

Yep, bad idea. I was thinking the process was like 250-300deg F, but I just checked and it's done at around 850deg F! How are they galvanized during manufacture? How hot can you get a Chromoly steel tank? I thought it was more of an issue with Al tanks. Any thoughts on cold galv? is it worthless in a salt water environment?

I've got to get them hydro'd and vip first. I think I'll skip the O2 cleaning for now. Then I think I'll just throw something on it to inhibit corrosion for now.

 

[teknitroxdiver]

The good ones are hot dipped at the factory, but this is done under controlled and known parameters, so they know what happens when it's hot-dipped. The ones not factory hot dipped are such that they cannot handle the heat without molecular changes happening.

As for AL tanks...I don't know why you would want or need to galvanize one. Cold galv is better than nothing, probably a little better than paint. I suggest either the cold galv or Rustoleum paint.

 

[tlawler]

No, I meant that overheating tanks was more of an issue with Aluminum than Steel.

 

[teknitroxdiver]

Oh. Well...not at the temperatures hot dipping gets to. The problem with ALs is really more how when they are overfilled, the metal expands more than usual, and they don't handle that a tenth as good as steel tanks do.

 

[Rick Murchison]

Those are 72's.
Inspect 'em.
Tumble if necessary.
Hydro 'em.
If they pass, use 'em.
My oldest 72 was manufactured in '65; my newest in '71.
I had my first 72 fail hydro this year - it was a '70 and had seen a *lot* of use.
If they're not rusty there's no reason those tanks shouldn't pass hydro and give you many more years of service.
Rick

 

[rgbmatt]

I was also thinking cold galvanizing (spray on) and then painting or maybe something like zinc chromate as a primer and then painting it with appliance epoxy. I'm not really worried about appearance, just protecting it from corrosion.

Any sort of paint should do the job - obviously something that's "rust-preventetive" would work best. The cold galvanizing paint is great because it acts as a sacrificial anode and chemically inhibits rust along with keeping water out. I wouldn't worry too much about labour-intensive multiple layers of paint, because chances are you'll get nicks in it that will need to be patched later on.

Light-coloured paints such as yellow or white are best, because new rust shows up really well.

I've got a tank exactly like yours, with the dings patched up using some cheap "anti-rust" paint from the local auto parts store. It works well enough - I have to touch it up every 2-3 months, but otherwise it's great!

Oh, and paint it before you hydro it! They dunk the tanks in water for the hydro test, and it'll be all rusty by the time you get it back if you don't.

By the way, when you mentioned the possibility of the decreased O2 content, it got me to thinking: If I did an Oxychek on the gas and it did still have close to 21%, would that be a fair indication of the amount of oxidation/corrosion inside the tank, or lack thereof?

Probably, but the best way would just be to shine a flashlight inside and take a look. If it's been stored with air in it, there's a good chance that it's OK.