Question Identification and help for these old tanks

[TooCold]

I bought a batch gear off craigslist which included this doubles set. They are the first tanks I've ever seen that have NO visible markings at all, other than in the rusty patch where the paint was removed which shows two hydros:

2DM66
1"B"83, where "B" is actually a B inside a circle.

The second row on both tanks is pretty clear but for the top row I've pieced together hints from both, assuming they're the same.

They have rounded bottoms, are about 20" tall by 6 1/2" wide. I see teflon tape on the 3/4" valve threads, so I assume tapered. They both seem in remarkably good shape externally. They both held some air when I got them, and the valves work. I've since dismantled the set and opened one tank to peek inside.

I'm new to old tanks, and steel tanks, so I know next to nothing beyond what I've gleaned from old SB threads. There's a wealth of wonderful info here but it can be hard to sort it into a consistent picture. So, thanks in advance for any help and advice!

I assume there must be markings underneath the (very thick) paint, right? Is there any reason not to take a heat gun and scraper to the paint to expose the markings?

Any ideas about age/manufacturer/pressure etc. without having the markings?

Finally, have I stumbled on a set (tanks, valves, manifold, fibreglass backplate, DA Aquamaster reg with yellow hoses and mouthpiece) that should go to a good home as-is? 'cause right now I'm just thinking about the tanks.

 

[Skip Y]

I bought a batch gear off craigslist which included this doubles set. They are the first tanks I've ever seen that have NO visible markings at all, other than in the rusty patch where the paint was removed which shows two hydros:

2DM66
1"B"83, where "B" is actually a B inside a circle.

The second row on both tanks is pretty clear but for the top row I've pieced together hints from both, assuming they're the same.

They have rounded bottoms, are about 20" tall by 6 1/2" wide. I see teflon tape on the 3/4" valve threads, so I assume tapered. They both seem in remarkably good shape externally. They both held some air when I got them, and the valves work. I've since dismantled the set and opened one tank to peek inside.

I'm new to old tanks, and steel tanks, so I know next to nothing beyond what I've gleaned from old SB threads. There's a wealth of wonderful info here but it can be hard to sort it into a consistent picture. So, thanks in advance for any help and advice!

I assume there must be markings underneath the (very thick) paint, right? Is there any reason not to take a heat gun and scraper to the paint to expose the markings?

Any ideas about age/manufacturer/pressure etc. without having the markings?

Finally, have I stumbled on a set (tanks, valves, manifold, fibreglass backplate, DA Aquamaster reg with yellow hoses and mouthpiece) that should go to a good home as-is? 'cause right now I'm just thinking about the tanks.

I have a set of twin Voit 50's. They are 2250 PSI 6.9 diam and about 20" tall. They are white like these and have a very heavy coating on them. Mine have round bottoms too. The blue backpack looks like it might be Voit also. My tanks have "Voit" stamped in them, but everything stamped is difficult to see because of the heavy (epoxy ?) coating

 

[Tracy]

At first glance, I would guess 1800 psi 40s. They made the same tank in 2250 psi, but they typically had 3/4 nps necks. The 1/2" npt leads me to 1800 psi. There are markings, they are just burried under the epoxy. Shine a light at the tank from different angles and try to make them out. Next step is a piece of paper and a crayon trying to get a rubbing from the impressions. If that doesn't work, a flat bastard file will reveal them, but the tanks will be forever ugly.
If you plan to use them, by all means, but if they are going in a corner for display, leave them intact.

 

[TooCold]

They're a close match to what you describe @Skip Y but not quite: they're definitely less than 6.9" dia. On the other hand the valve is 3/4" npt (I think - I have minimal thread knowledge).

@Tracy, there's no evidence of markings at all, probably because there's at least 1 layer of newer paint over the original. The inside of the one I've opened up is rusty but doesn't seem too bad to my totally inexperienced eye. It was definitely dry, and no flaking, but the surface is mottled all over. I think I'm going to go ahead and excavate for the markings on at least one tank.

(If there's life left in them I'd like them to be able to live it. A long time ago I sold one of my (too many) cameras: a 100 year old studio 8x10 view camera. Mahogany and brass on a wrought iron stand: a thing of beauty and a piece of American history. It ended up on display in a dentist's waiting room. What a waste of a still excellent photo-taking machine.)

 

[Tracy]

They're a close match to what you describe @Skip Y but not quite: they're definitely less than 6.9" dia. On the other hand the valve is 3/4" npt (I think - I have minimal thread knowledge).

@Tracy, there's no evidence of markings at all, probably because there's at least 1 layer of newer paint over the original. The inside of the one I've opened up is rusty but doesn't seem too bad to my totally inexperienced eye. It was definitely dry, and no flaking, but the surface is mottled all over. I think I'm going to go ahead and excavate for the markings on at least one tank.

(If there's life left in them I'd like them to be able to live it. A long time ago I sold one of my (too many) cameras: a 100 year old studio 8x10 view camera. Mahogany and brass on a wrought iron stand: a thing of beauty and a piece of American history. It ended up on display in a dentist's waiting room. What a waste of a still excellent photo-taking machine.)

The valve you have pictured is 1/2" NPT. It was a very common scuba valve back in the day. 3/4 NPS is what modern scuba tanks utilize.

 

[TooCold]

Thanks @Tracy - of course you're right. I needed to do a little reading about pipe threads to get it. Explains why I kept finding fittings in the "wrong" bin when I shopped for parts at the local plumber supply.

 

[TooCold]

I've uncovered the markings on one of the tanks. They just had their 62nd birthday in June:

VOIT
ICC-3AA1880
HK 1715
6<N inside a diamond>60+

A few final questions:
Is "HK 1715" just a serial number?
Is there really no service lifetime for steel tanks if they're still in good enough physical condition to requalify, or should they be retired regardless?
If I take them to hydro (after cleaning) is there any documentation I should find/attach, like I've read about helping for hot-dip galvanized steel 72's?

 

[broncobowsher]

Steel tanks have no limit on lifetime. I've had industrial tanks over 100 years old come through work in regular service and are delivered with tanks that are 2 years old. Both are considered to have the same value.

 

[Eric Sedletzky]

Steel tanks have no limit on lifetime. I've had industrial tanks over 100 years old come through work in regular service and are delivered with tanks that are 2 years old. Both are considered to have the same value.

Someday, vintage scuba aficionados will be diving steel tanks that are 100 years old too, no problem.

 

[Gone for diving]

Someday, vintage scuba aficionados will be diving steel tanks that are 100 years old too, no problem.

This is why I have a compressor to fill my old vintage tanks.