What is this tank size?

[gbray]

A friend gave me an old tank today. It is marked as follows:
Icc3AA2250 US Divers company V.
123835
USD
3 64

I believe it was made in 1964 by USD. It is steel because of the
3AA ( and because a magnet sticks to it). It is 24-3/4 inches tall (not counting the valve) and has a circumference of 22 inches. It also has an old all metal j-valve on it.
Can anyone tell me what size it is, if I can replace the valve on it (it looks like a 3/4" neck), and if there are still any this old in use?

Thanks for your help.

 

[SparticleBrane]

You are looking at an older steel 72. Congrats -- if it is in good condition you just got a great cylinder! Are you able to post pics? If the cylinder is in good condition and you treat it well, chances are good it might outlast you.

• ICC: Interstate Commerce Commission (before the DOT)
• 3AA: specification to which the cylinder was manufactured -- the same 3AA spec used for the 2400+psi LP steel cylinders made today
• 2250 is the service pressure, with the plus rating at 2475 the cylinder holds 71.2cf of air
• 123835 = serial number
• USD: US Divers
• 3 64 = March of 1964 sounds to be the original hydro

If it does have the standard 3/4" neck, assuming no corrosion you should be able to fit a modern valve onto it.

Get it hydro'd (if it is out of hydro) and ask them to test for the plus -- the REE is most likely 58.4, according to this document (links to a PDF file) from Pressed Steel. Note that there were several manufacturers of the ubiquitous "steel 72", with PST only being one. You can find some more good info here.


Check to see if the inside is rusty. If it is, you will need to have the tank tumbled to remove the rust.

There was also a 'liner' coating applied to the inside of these cylinders, but someone more knowledgeable will have to chime in to talk about that...

 

[DA Aquamaster]

The liner used in some older steel tanks has to be removed as it will develop pin holes that can trap moisture promote rust and hide that rust from visual inspection. Removing it is a pain and in tough cases can take about a week of tumbling with an aggressive media.

Some tanks also had a vinyl coating on the outside. Any of the coating that is loose and not completely adheared to the tank has to be removed for the same reason - it could potentially trap moisture and prevent a proper visual inspection.

Some inspectors will take an extreme view and say the entire coating has to be removed - but that is frankly like saying a tank with chipped paint has to be completely stripped to see what is underneath the paint. The issue is not what it is coated with but rather be able to ensure none of that coating is loose, could trap moisture or have rust underneath it. If in doubt remove it, and the level of doubt will vary from inspector to inspector.

In any case, if painted, the tank may also be galvanized or non galvanized under the paint as USD sold them both ways.

 

[gbray]

Wow, good information. This forum is great. Thanks guys. Upon further inspection I see a plus after the hydro date. I also see the inspection stamp between the hydro month and year. It is an L with a C around it which indicates it is a PST tank. Now for my big question, What would I use a single 72 steel tank for? I am still a fairly new diver with 34 dives currently. my sac is improving, I can keep up with much more experienced divers air wise But a 72 seems a little small at this point. I don't think I am quite ready for doubles yet. I currently dive an al80. Any ideas? I hope I am asking these questions in the right place.

 

[Luis H]

The liner used in some older steel tanks has to be removed as it will develop pin holes that can trap moisture promote rust and hide that rust from visual inspection. Removing it is a pain and in tough cases can take about a week of tumbling with an aggressive media.

I don’t agree that all internal coatings have to be removed. There are no requirements to remove the internal coatings (from DOT, CGA, etc.) as long as the tank can be visually inspected. Some LDS make there own rules (which actually opens them to higher liability), but that is a different issue.

I am far from an expert in all the different coatings used inside all the steel 72’s, but I am familiar with a few.

There were a number of different internal coatings, some were dark brown epoxy and there were other dark colors that make inspection a bit more difficult, not really impossible. The inspection requires good amount of light to check that the surface is perfectly smooth.

Keep in mind that rust occupies many times the volume of the original steel; therefore any rust present under any coating will cause the coating to bulge or blister. If the surface of the coating can be clearly inspected and shows to be perfectly smooth with not bulges, it is reasonable to assume that there is no rust (or at least no rust that is significant) under the coating.

If there is any question, then tumbling would be necessary, but it is not necessary to remove a coating that is well adhere to the base metal. If it is well adhered to the base metal it in itself is prove that there is no rust under that portion of the coating.

I have several cylinders with the white internal coating that are great. The white coating is a very thin coating (I used to know what was made of, but can’t remember) that makes it extremely easy to see any imperfection or rust. Also the color helps the inspection since light reflects extremely well.

I have been developing methods of taking pictures of the inside of my tanks for record keeping and the white interior tanks are by far the easiest to get a good color balance shot with most any VIP light.


Here is a quote from the PSI / PCI cylinder inspection book: INSPECTING CYLINDERS • 4th Edition, page 32.

Internal Linings
Cylinder inspectors are also faced with a special corrosion related problem
inside certain steel SCUBA cylinders. Several types of materials were placed in
cylinders to provide a protective barrier between the metal surface, moisture that
often entered the tank, and oxygen which is present at a high partial pressure.
None of those interior linings proved successful. In the late 1950s, U.S. Divers
Co. distributed cylinders lined with a white paint-like product. By the late 1960s,
brick red, brown and blue colored forms of epoxy were tried in steel cylinders.
Several problems arose. First, it was not possible to provide a liner
absolutely free of minuscule routes for water to reach the base metal. Also,
the epoxy did not expand at the same rate as the cylinder during the fill
process so cracks appeared in the coating. As a result, corrosion formed
beneath the liner, out of sight of the visual inspector. The CGA recommends
that interiorly lined cylinders be viewed carefully and, whenever corrosion
appears to have developed, the liner should be removed and the significance
of the corrosion assessed.
The removal of epoxy linings are, in themselves, a problem. Often, only
small portions of the epoxy have been loosened by rust while the remainder
is bonded firmly to the metal. Tumbling with aluminum oxide chips or equivalent,
for several hours, will usually remove the liner from corroded metal
but leave the bonded epoxy intact. Since corrosion has not formed behind
firmly bonded liner, over-zealous tumbling may not be necessary. Several
days of tumbling have failed to remove all traces of the epoxy.
Infrequently, visual inspectors encounter cylinders to which the owner
attempted to apply some material as a corrosion inhibitor. Paint, epoxy, and
molten zinc, figure 8, have been found erratically adhering to interior walls.
Altered cylinders should be rejected because the possible damage may be difficult
to assess.
Linings mentioned above should not be confused with chemical treatments
performed by some aluminum cylinder manufacturers on their cylinder
interiors to inhibit corrosion. There are no lined aluminum SCUBA cylinders.
Alrock and Irridite, the dark gray or bright reflective surface respectively
are chemically produced forms of aluminum oxide intended to inhibit
further corrosion

32 INSPECTING CYLINDERS • 4th Edition

 

[Scared Silly]

If your buddies are also using a std AL80 remember full it really has only 77 cuft. So the difference is only 5cuft. In big scheme of things that ain't enough to worry about.

Also remember your starting fill pressure will be 2475 psi while theirs will be 3000 psi. So when they get to the magic 500 psi you will be around 400 psi (assuming similar SACs).

 

[captain]

My hydro shop recently did one of mine with the white liner and had no issues with doing it.

 

[Eric Sedletzky]

I have collected 4 vintage steel 72's now. Their great little tanks for quick shallow beach dives, I love them.
Congrats on your find.

 

[DA Aquamaster]

I have not yet encountered a white liner, but none of the epoxy coatings (usally dark brown) or polyurethane coatings I have seen from the era in question have ever inspired confidence in the tank, but I tend to be picky.

And like it or not, most hydro test facilities I have worked with will not requalify a scuba tank with a liner, and most shops are reluctant to pass a tank with a liner, so it ends up being a lot easier to remove it.
------

On average an AL 80 gets hot fillled and ends up around 2800 psi and holds 71.8 cu ft at that pressure. A Steel 72 when filled to 2475 psi holds 71.2 psi and it holds 65 cu ft at 2250 psi. So if you can get it filled to 2400-2500 psi, there is no significant difference between it and an AL80.

Personally I will fill mine to around 2650 psi and 76.5 cu ft, but I have my own compressor.

 

[Luis H]

Here is a picture of the inside of one of my white lined tanks (tank # 02 on my records).
Notice that the light I was using on this picture was just a basic chain light. With this white interior it was OK, but the color balance of that light doesn’t work well with the standard steel tank.

Here is just one of other steel 72 (tank #7) with a high intensity light.

Steel 72’s are great tanks. If I have a choice, I will take a steel 72 over an AL80.

The only time an AL80 is my favorite tank is when it is a rental AL80 in the Caribbean (and that is only because that is what they have for rental down there).