Inherited tanks

[Wijbrandus]

Hey everyone,

I've inherited two tanks from a friend of the family. She pulled them out of the basement, and hadn't used them in almost twenty years. Doesn't know a thing about them.

Good thing is my dad got them hydro and vip before hauling them out here.

Now I need to know what I'm dealing with.

Tank #1 - Shorter, heavier. Probably steel? Earliest commission date seems to be 11-73. Only other numbers I can find on it are:
DOT3AA2250
9616
VOIT
1?70+PST (I can't make out the ?)

Tank #2 - Seems to be a typical AL80, but it's first date is 11-76 :11: Numbers are as follows:
DOT3AL 3000
DOT-E6498-3000
P136536 USD

How do I tell if these are "bad" alloys or something I might actually want to use? And how do I determine the bouyancy on the PST? Their website seems to be down. I'm assuming that the AL is similar to a modern one, but is 28 years a bit old or is it still reliable?

Been renting, will still be renting until I know better what I've got.

 

[Drew Sailbum]

Tank # 1 is a steel, presumably manufactured by PST. Working pressure is 2250psi, making this a "low pressure" steel.

Tank #2 is an aluminum cylinder made of the "bad" 6351 alloy. Based upon the serial number, it is probably an AL880 manufactured by Luxfer. Working pressure is 3000psi.

If they both passed hydro and vis, then they are good to go. Tank #2 should be subjected to not just the annual vis but also an annual eddy current test (often known as VIS+) to check for sustained load cracking.

 

[Wijbrandus]

I guessed the PST as well. 2250 seems pretty low, but hey what do I care. Would that be a 72 then? And where would I find the bouyancy characteristics of it? Maybe I should just call PST in the morning and see what they say about it.

If tank #2 is the bad alloy, is my only option to dispose of it? Seems a waste if they passed the tests, but I wonder if I can get it filled now.

Thanks for the info, Drew.

 

[teknitroxdiver]

I would say that you could go either way on the 80. Before you fill it you should have the eddy current test done to make sure it's all cool. If it is, then you get to make a decision. Getting a used 80 of better alloy would quite cheap, and you might be able to sell the old one. Or you could keep it and trust the test results.

 

[Drew Sailbum]

Whether your LDS will fill an Al cylinder made of the "bad" alloy is a business decision that the shop must make. Since yours has current hydro and vis, then there is really nothing else you can do. Some shops will fill them, but a few shops will refuse. You won't know unitl you take them in for a fill.

It wouldn't surprise me if the PST is a steel 72. Those were pretty common in that time frame.

 

[DA Aquamaster]

Your steel tank is a steel 72 and would have been manufactured in January 1970. I suspect the first (and last) hydro was done a little early in November 73. The bouyancy on a steel 72 varies a bit by manufacturer but in general is about 4 lbs less than an Al 80 and is slightly positive (about 1-2 lbs) when empty.

Capacity is 71.2 cu ft at 2475 psi (10% overfill) and 64.7 cu ft at 2250 psi.

As for the Al 80, it is most likely made by Luxfer and consequently from 6351 T-6 alloy and subject to sustained load cracking.

The good news is that it was made in 1976 as 1982 and 1983 were particularly bad years for AL tanks from Luxfer as they used a different source for their metal which had a bit more lead in it and was even more brittle than the normal 6351 T-6 alloy. Your AL 80 also probably has relatively few cycles on it.

A lot of people fret about Al 80's made from 6351 T-6, but the current eddy current inspection and more comprehensive visual inspections are catching them before they present a hazard.

The shop that I associate with also has a hydro test facility and usually finds at least one cracked AL tank per week (usually E sized AL medical oxygen tanks and they are advising medical oxygen companies to reconsider some of their exchange policies) But it is very rare to find a cracked scuba tank as they tend to see a lot less use and a lot fewer cycles. I have also not heard of any recent AL 80 explosions and I have not heard of a properly inspected 6351 AL 80 exploding so I would not be concerned about using it.

Add a 4 lb weight to the cam band when you use the 80 and you'll be able to dive with the same weights and bouyancy you would otherwise have with your steel 72