Hydrostatic testing and serviceable life of tanks

[hawkdoc60]

I am looking at a variety of used 80cf aluminum tanks. Most need hydro before use, which is no problem. However, it got me thinking before I spend the money on a used tank, is there a life expectancy that I should be aware of? Is there a point where a tank should not be hydro tested and used, but rather retired?

Thanks.

 

[OTF]

They last a very long time. Hundreds if not thousands of dives from an aluminum tank. Steels last indefinitely if they aren't allowed to rust. When tanks eventually fail a hydro they can be retired then.

When looking for used aluminum tanks just be sure to avoid bad alloy tanks. Is my cylinder made from the "bad" alloy aka AL6351?

 

[hawkdoc60]

They last a very long time. Hundreds if not thousands of dives from an aluminum tank. Steels last indefinitely if they aren't allowed to rust. When tanks eventually fail a hydro they can be retired then.

When looking for used aluminum tanks just be sure to avoid bad alloy tanks. Is my cylinder made from the "bad" alloy aka AL6351?

Thank you. I didn't know about the bad alloy.

 

[Compressor]

As @OTF has said. Yes there were some tanks with bad alloys that cause defects in the tank structure.

 

[hawkdoc60]

A special thanks to @OTF for making me aware of the bad alloy tanks. Sure enough, several of the tanks I was looking at were indeed Luxfers made prior to 1988 or otherwise specified that they were made with the AL6351. I guess I need to re-focus my search on some good deals on new tanks at this point. I don't want to take any unnecessary chances losing money on tanks that can't be used, or worse may have catastrophic failures.

 

[tursiops]

A special thanks to @OTF for making me aware of the bad alloy tanks. Sure enough, several of the tanks I was looking at were indeed Luxfers made prior to 1988 or otherwise specified that they were made with the AL6351. I guess I need to re-focus my search on some good deals on new tanks at this point. I don't want to take any unnecessary chances losing money on tanks that can't be used, or worse may have catastrophic failures.

Just don't buy an AL tank made before 1990; easy to remember, no issues.
Be aware, however, that some dive shops have arbitrary policies that they will not fill tanks older than 20 years, no matter what. Best to avoid those dive shops....they may have have some other policies that are not in your best interests.

 

[broncobowsher]

Also watch out for dents or gouges or corrosion pitting.. That is also a for a tank to fail and be useless.

The "bad alloy" tanks are not all bad. But they have a reputation that is bad enough that they are not worth it. There are better options out there that are worth a few dollars more to avoid the hassle later.

 

[Still Kicking]

Also look out for tanks (especially aluminum) that have been painted since their previous hydro. Some people bake the paint not knowing that aluminum structure weakens at relatively low temps.

If there is paint over the most recent stamp (unless it's the factory stamp of course), it's suspect.

 

[OTF]

If there is paint over the most recent stamp (unless it's the factory stamp of course), it's suspect.

Unless it's just a small spray of a random color over the hydro stamp, standard practice for many testers to prevent corrosion I guess.

There are some manufacturers who never used the bad alloy, so old Catalina tanks for example are fine.

A special thanks to @OTF for making me aware of the bad alloy tanks. Sure enough, several of the tanks I was looking at were indeed Luxfers made prior to 1988 or otherwise specified that they were made with the AL6351. I guess I need to re-focus my search on some good deals on new tanks at this point. I don't want to take any unnecessary chances losing money on tanks that can't be used, or worse may have catastrophic failures.

Glad I could help! Yeah with aluminums you can get new ones so cheap it's close to a tossup between used+hydro and just buying new. Especially when you factor in the time and effort to get it hydro'd. But you can use that fact to negotiate lower prices on used stuff. This is even more true if you need the tanks to be O2 clean.

I see you're in PA - assuming you plan to do local / cold water diving you may want to look into steel tanks instead. Much better buoyancy characteristics if you're wearing thick wetsuits or drysuits. And they hold more air.

 

[Bob DBF]

I see you're in PA - assuming you plan to do local / cold water diving you may want to look into steel tanks instead. Much better buoyancy characteristics if you're wearing thick wetsuits or drysuits. And they hold more air.

I agree with the recommendation of steel tanks, however there are still a lot of old steel 72s out on the second hand market. Although it's a smaller tank, I like them for shallow dives or anytime I don't need a lot of air. I started my diving with them, before the Al 80 was produced, so I have a lot of fond memories..