Tank experts only!

[Nemrod]

Sorry, I know I ask lot's of questions. I have a Dacor tank, aluminum 80, and it's original hydro is 1982. It's last hydro was 96 I think. Is this tank safe? The reason I ask is that I have heard that some alum tanks with an original stamp of 82 and 83 are unsafe. I have several other tanks newer and older but this one I am concerned about. I don't want anyone getting hurt. The tank appears in good shape but looks can be deceiving when it comes to structural problems. What was the beef with the 82 and 83 tanks anyways? Thanks as always. N

 

[opiniongirl]

They used a different alloy combination which is now known to have a higher incidence of neck cracking.

More likely than not it is safe - the only way to ensure it is to get it hydro'd. When they hydro tanks, they are placed in a protective area, and filled with water (not air). They measure the amount that the tank expands, then contracts. The tank is deemed acceptable or a failure based on how close it comes to it's previous size after pressurization.

After that, it will have a visual inspection (ensure it's done by a qualified, experienced technician, and with an eddy current machine - VIS+, for maximum assurance).

With older tanks, it can be a good idea to get them visualed and hydro'd more frequently, especially with frequent use.

I've seen (and condemned) tanks from this age, if it passes these two tests you can be reasonably assured that it is safe to dive with and fill. Ensure it's not overpressurized (you may want to get the burst disk changed with the hydro).

Hope this helps, my nickels worth..

 

[freediver]

You can get it hydro'd but if something catastrophic is going to happen, it is very likely going to happen during the filling process. If you think it is a suspect cylinder, see if you can trade it in, I have had experience with cylinders on a "suspect list" and the lds gave me new cylinders (at cost, although I wouldn't bank on this) just to take the suspect cylinder out of service.

 

[Ontario Diver]

As said above, Dacor's cylinders were manufacturered by Luxfer. Up untill mid 1988, they used an alloy known as 6351. This alloy had cracking issues. Please understand, the number of failures is less than 0.4%. Of course, this doesn't matter if you own one of the eight that blew up.

It takes about six years for the cracks to develop and tank abuse (overfilling and overheating) is considered to be a major contributor.

A hydrostatic test is required anyway as the last test is more than 5 years ago. When you have it tested, make sure that a good visual inspection and visual eddy test is done. You may want to ensure that the tank inspector has been trained by an organization such as PSI.

There is a very good chance that this tank is safe.

 

[DA Aquamaster]

There is a lot of hysteria surrounding 6351 alloy AL tanks but in fact out of the millions of scuba and medical O2 tanks made from 6351 alloy made, less than a dozen failed in service and none have failed catastophically since the eddy current/VIP requirement has been in place.

Get it hydro tested and VIP'd and if it passes it will be fine.

 

[gjmmotors]

Correct me if im wrong but.....
The last explosion in North Florida, was a fatal explosion. Does that qualify it as catastrophic?
There is something wrong with the alloy, theres no debate there. Will the shops you get it filled at fill the bottle? Some do, some dont.
Just curious about the catastrophic failures point.
-g mount

There is a lot of hysteria surrounding 6351 alloy AL tanks but in fact out of the millions of scuba and medical O2 tanks made from 6351 alloy made, less than a dozen failed in service and none have failed catastophically since the eddy current/VIP requirement has been in place.

Get it hydro tested and VIP'd and if it passes it will be fine.

 

[OneBrightGator]

Yeah, I'd consider the death of the poor person filling your "safe" tank catastophic, or maybe we should ask her son what he thinks...

Find a alum recycler who'll take it off your hands or see if your LDS will let you trade it in on a new one, it ain't worth it.

 

[DA Aquamaster]

Ah yes Gator, that would be the hysteria I mentioned. The tank involved in that explosion was 6351 alloy, but the tank and the alloy it was made from was not the cause of the accident. (Although that whole thread is interesting reading and kinda makes the whole hysteria point given how many people immediately speculated about the accident being due to the 6351 alloy.)

Fact is dropping a 300 psi tank with 98% O2 in it is just a really bad idea regardless what metal or alloy it is made from. It's one of those things you just don't do like heating your AL tanks to 400 degrees, doing massive overfills, using double burst discs, leaving an inch of sea water in the tank, skipping hydros and VIP's etc, etc, etc. Luxfer is responsible only for their tanks, not how the end user abuses them or mis-uses them.

I'll stand behind the statement that less than a dozen 6351 alloy tanks failed in service and none have failed catastophically since the eddy current/VIP requirement has been in place. But due to the unreasonable nature of some people who seem to like to ignore the obvious and confuse correlation with causation, I will amend the statement slightly:

"less than a dozen 6351 alloy tanks failed in service and no properly maintained, inspected, and handled 6351 tanks have failed catastophically since the eddy current/VIP requirement has been in place."

Truth is proper inspection procedures are catching any tanks with SLC's long before they become a threat. As long as a 6351 tank is properly inspected, maintained and handled, it presents no more of a threat than any other scuba cylinder.

 

[SDAnderson]

Truth is proper inspection procedures are catching any tanks with SLC's long before they become a threat. As long as a 6351 tank is properly inspected, maintained and handled, it presents no more of a threat than any other scuba cylinder.

Which would pretty well seem to sum it up. If anyone has the stats to indicate otherwise, I'd love to see them. There's nothing wrong with being cautious and getting rid of the 6351 tanks, but that's my personal feeling about any aluminum tank as it nears it's 20 year anniversary.

 

[DA Aquamaster]

That's a good point. We routinely hydro welding tanks from around 1910 that still pass with flying colors and I own steel scuba tanks that are close to 40 years old. I still trust those steel cylinders as steel tanks in general have an excellent record for longevity and reliability. (provided they are not abused and are properly maintained)

In the whole scheme of things, I think the jury is still out regarding the ultimate life span of any AL tank regardles of the alloy it is made from, they just do not have the century long history in service that steel tanks have.

But there is more to it than age - cycles also count as does the various factors of how the tank has been used, maintained and inspected. So my thought is regardless of the tank in use, steel or aluminum, what counts is that it be properly inspected at the prescribed intervals and be properly maintained and handled in service.