Steel 72’s passed hydro, but .

[CivilE]

I recently inherited a couple of steel 72’s and am/was looking forward to getting them back in the water. One is from 56 with 1/2” threads, and the other is from 73 (3/4” threads). I took them up the street to a place that does fire control systems and testing to get them hydro’d. The next day I get a call that they passed and are ready to be picked up (sweet!!!). When I get there, I’m greeted by a couple of the guys that do the testing (one is a fire fighter and the other was an old Navy diver and divemaster), and they proceed to tell me that neither one of them would use these tanks for “breathing air”. When I asked them why not, they kept saying that it was because of the age of the tanks (no other reason???).

Now, if these tank passes hydro (tested to 3750 psi), have new valves with the appropriate burst disc, get a vis, and are tumbled (as necessary)… I can’t see why they could not be used for “breathing air”.

Am I missing something here?

 

[TSandM]

Not as far as I know, although the tanks have to pass viz, too. Are they full of rust, is that what concerned the guys?

We're using two 72s from the late 60's, that sat empty for over 20 years. They seem to work fine!

 

[CivilE]

There is some rust in them, but I took them by my LDS for a look first and they didn't think that there would be a problem if we tumbled them. I almost got the impression that these guys were trying to say that the tanks were not structurally sound, which makes absolutely no sense to me.

 

[Gilldiver]

Are they clean inside and pass all visual requirements? If so, use them.

As for the 1956 1/2 inch tank, you can see if one of the vintage diving guys wants it to match up for a set of doubles.

I have a set of 72's that date from the early 70's that are my best set for dives to 110', I call them the baby bottles (as compared to the twin 130's) but they are very sweet to dive.

 

[LeadTurn_SD]

If the tanks pass hydro and pass viz, you are good to go. I "re-activated" my old steel 72 (1976 original hydro) after it had sat unused for about 20 years. Needed to be tumbled, hydro'ed and visually inspected, and a new burst disc installed, but after that was literally "good as new". The dive shop I go to has an "old timer" as the owner, and he recommended not installing a new valve, saying the older valves were very well made.

Not sure why you were told not to use the tanks, unless rust or other internal contamination was seen, but tumbling followed by a viz should clear them for use...

Good luck!

 

[texdiveguy]

Get your LDS to VIZ them and if needed a tumble.....they should be fine.....I use an old 1971 st72 myself for a deco bottle.

 

[captain]

I have 10 of them I use, the oldest was made in 1956 the newest in 1973. All 10 passsed hydro within the last year. There is also no need to replace the valves.

 

[Luis H]

Steel is not affected by age. The only normal things that will harm a steel tank are rust (accelerated by moisture), fire, and large over stress (including being crushed by a heavy load…like a locomotive).

There are steel pressure cylinders in service that are from the early 1900.

The common DOT-3AA chrome-molybdenum steel tanks have been around for over 60 years and a new tank is structurally the same as a well maintained 60year old tank. They meet the exact same requirements and are tested under the exact same conditions, how old they are is totally irrelevant. They have the exact same pass-fail criteria no mater if they are 5 years old or 60 years old.

To pass a hydro test they also have to pass a visual examination…that is a requirement as part of the hydro.

The steel 72 cylinders you are talking about are made under the DOT-3AA specifications under CFR49 (Code of Federal Regulation 49) and they are all tested under the exact same code.



Edit:
I just notice your occupation…if you are interested all the codes (CFR49) are on line.
I can also email them to you. Here are a few titles:
49cfr178.37 Specification 3AA and 3AAX seamless steel cylinders
49cfr178.46 Specification 3AL seamless aluminum cylinders
49cfr180.205 General requirements for re-qualification of cylinders
49cfr180.213 Re-qualification markings
49cfr173.302a Additional requirements for shipment of non-liquefied (permanent) compressed gases in specification cylinders

 

[Nemrod]

Ditto Lewis and Captain, those "station" guys don't know what they are talking about, Lewis however does. It is not unusual to tumble a tank to remove minor rust. Pitting is another matter. Steel tanks are a lifetime investment, even those already a lifetime old.

Some "vintage" tanks were coated with an epoxy interior liner. The intent was to prevent rust. The result intead was that rust formed under the liner. Not all of these tanks have the liner, just some here and there, not all have rust under the liner either. Most shops will decline to VIP such tanks. It is possible to tumble the liner out but most shops will rather just tell you to go away or buy their new shiney aluminum tank.

People to quickly scrap steel 72s. They are a fine all purpose dive tank, make a great set of small doubles, are more compact and lighter than an aluminum 80, have much better bouyancy characterisitics and hold nearly as much air in practical terms.

I don't particularly care to own the pipe thread 1/2 types but they can still be a serviceable tank. I prefer the 3/4 straight thread versions for my uses.

N

 

[DA Aquamaster]

Ditto, I have three sets of double HP100's but also have 2 sets of double steel 72's and they work great for deco dives to 110-120 feet or so.

As singles, they give nearly as much gas as an AL 80 with better bouyancy traits.

People get nervous about the age, but it is a fear based on ignorance. The oldest welding tank I have seen come through for hydro test was made in 1911 and it still passed with flying colors a tank born in 1956 is still very much in the prime of life if it has been cared for, has passed hydro test and the VIP required as part of the test. It is common fro steel tanks to have flash rust and it really only needs to be removed when it begins to build up as it will hold moisture that can promote the development of pitting. Pitting is the major killer of steel tanks, but getting a VIP every year and having them tumbled whe needed every 5 to 10 years will prevent that from happening.

I have met some dive shop personnel who point out the wall thickness of steel 72s is less than "newer" low pressure steel tanks and claim that a reason for being hesitant to fill them. It is true to a minor extent, but that is due to the lower 2250 psi service pressure versus the 2400 psi service pressure of newer low pressure tanks and both are certified under the same 3AA standard with the same margin of safety. The irony is those same people will overfill a 2400 psi tank to 3500 psi, but hesitate to fill a steel 72 to 2250 psi when a comparable overfill would be 3280 psi.