How long do steel tanks last?

[bleeb]

I completely agree with everyone who said if you take care of them, mainly by keeping the water out and only using reliably high quality water-free fill stations, they'll last one or more lifetimes.

However, playing devil's advocate, I seem to remember a comment a while back from someone who did either VIPs or hydros (possibly from Florida cave country), that with the 'average' fill stations around wherever he was, tanks seemed to average between three and four hydros before condemnation, although there was also a significant minority that did manage to last forever. Anyone else remember hearing anything like that?

 

[Walter]

One problem is SCUBA tanks are used near water and it is very easy to get water inside the tank. Water inside the tank will shorten its life. You may be thinking you can't get water in your tanks because you don't ever let them get completely empty. You would be mistaken. You are correct that water won't simply flow into the tank when it's opened if it isn't empty, but there is another way.

Tank valves get wet. If water is between the o ring and the orifice when the fill whip is hooked up to fill the tank, that water will be forced into the tank when it is filled. I suspect that happens a great deal more often than most of us might think. Always make sure your valves are dry before they are filled. If your shop fill tanks in water make sure they attach the whip before they place the tank in the bath.

 

[Akimbo]

I had three steel 72s hydro'd last year, the oldest was pressed in 1957, all had ½" tapered threads, all passed. Oddly enough, I have a steel 72 with ¾" NPS (O-ring sealed) fail hydro around 1985 on its first re-hydro. I don’t know the stats, but hydro failures on steel tanks are unusual to rare.

Like others, I have seen really old industrial steel cylinders. I remember one stamp because it was the year of the 1906 earth quake in San Francisco. To be fair, industrial cylinders are heavier to tolerate more handling abuse than Scuba or fire-fighter's cylinders that are weight sensitive.

 

[Gilldiver]

As stated steel 3AA alloy tanks can last longer then you will.

There are some exempt, non 3AA, tanks that are failing at 1st or 2nd hydro.

But as for water, the 3 ways to get water in a tank are:

1) Draining a tank to zero in the water
2) Wet valves when filled. DIN valves are the worst, make sure that the valve is dry before the fill yoke is hooked up.
3) Improperly maintained compressors

#1 is a dive practice that you control
#2 is a fill practice that you can monitor
#3 is a shop/boat/fill station practice that you may have to take on faith

If you have any questions, drain the tank, take the valve off, and see if the inside of the tank is dirty/wet. If you do this at the shop and in front of them and let them know why you are doing it, a good quality shop will not charge you for a new vis. If they do charge you for a vis, find a new shop.

 

[tregrrr]

since people are in the habit of bringing up industrial tanks... I have used o2 tanks from the exchange service that have had first hydro's earlier... 1904 was the earliest I saw.

also as a point of trivia, If you see ones with a stamp of 4 squares joined up like this but turned 45 deg:
____
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in the hydro area, apparently, I have been told that this is marking a tank that was used during the Nazi regime and after the war, the swastika's were closed in to avoid offending people.... so it be safe to say that steel tanks are pretty long lived if taken care of...

Your progeny may be vintage diving 100 years from now thinking how cool and old-fashioned this Open Circuit scuba thing is

 

[Jim Lapenta]

I have two 72's from 53 and 55 that just passed. Again.

 

[Gilldiver]

since people are in the habit of bringing up industrial tanks... I have used o2 tanks from the exchange service that have had first hydro's earlier... 1904 was the earliest I saw.

also as a point of trivia, If you see ones with a stamp of 4 squares joined up like this but turned 45 deg:
____
| | |
| | |
in the hydro area, apparently, I have been told that this is marking a tank that was used during the Nazi regime and after the war, the swastika's were closed in to avoid offending people.... so it be safe to say that steel tanks are pretty long lived if taken care of

Its true, it looks like a window.

 

[Graeme Tolton]

Its true, it looks like a window.

Is this something you would only run into in Europe? Did some of these cylinders make their way back to N.A. after the war?

 

[Puffer Fish]

I completely agree with everyone who said if you take care of them, mainly by keeping the water out and only using reliably high quality water-free fill stations, they'll last one or more lifetimes.

However, playing devil's advocate, I seem to remember a comment a while back from someone who did either VIPs or hydros (possibly from Florida cave country), that with the 'average' fill stations around wherever he was, tanks seemed to average between three and four hydros before condemnation, although there was also a significant minority that did manage to last forever. Anyone else remember hearing anything like that?

If it was in cave country, I am always surprised tanks pass one hydro, as they tend to way overfill everything.

However, I use each of my steel tanks for something around 50 dives per year.. so if I just got two good hydro's out of them, that would be roughly 750 divers, or a cost of around $.33 (ok, add the hydo cost and we are at around $.50) per dive... would be a very happy person with that. Just wish everything else in diving was that low.

 

[Gilldiver]

Is this something you would only run into in Europe? Did some of these cylinders make their way back to N.A. after the war?

They are quite common in the US. The bottles I have seen were all either made for, or imported by, Linde. The bottle mark above is from one of the O2 bottles I had in my garage last summer. I see at least one per year and I am not looking for them.

Up in Canada, they may not be common as that market was controlled by BOC or Airliquid.