Are these tanks the bad alloy?

[DA Aquamaster]

Although this information is easy to find maybe it should be a sticky considering how many times the same question is asked and answered.

Dates when Luxfer changed its aluminum alloy from 6351 to 6061 - Luxfer: Setting The Standard Worldwide

Another good one.

Product Safety Notice: Potential Scuba Valve Oxygen Incompatibility - Luxfer: Setting The Standard Worldwide

The bogus 1990 dates gets thrown around so much that a sticky would be nice.

It would reduce the need for one of the few of us who seem to know from having to keep posting the link. If there were a "6351-T6 "bad alloy" sticky with excerpts from the circular identifying suspect tanks, it woudl help, and it may also help educate divers, eho in turn would expect more from LDS managers and owners.

 

[Ulfhedinn]

Or just get a proper hydro/vis/eddie current test and use at will . . . with the correct test protocol, the risk is negligible, if any at all.

- Tim

So as long as they pass all those tests they should be fine? I read the links above about the cylinders. So Im to understand that the metal is just easier to crack or come apart?

 

[DA Aquamaster]

Scrap AL is about $0.50 per pound. Also, at least around here they reguire a large hole to be drilled in them.....the reason sounded BS but in any case, require it so be prepaired.
If properly tested they are still OK to use but depending on how much BS you get from a dive shop it may not be worth it.

I have encountered some dealers who insist on the tank being cut in half before they will accept it, so it limits you to working with someone with a chop saw.

I have heard various reasons - one being that it is required as when un cut tanks are dropped in the furnace they "explode" due to the rapid heating of the gas in them. (I kinda doubt it...but maybe...) and the other reason I have heard is that it is to ensure no one put anything else in the tank (rocks, other metals, contaminated materials, etc.)

 

[Jax]

So as long as they pass all those tests they should be fine? I read the links above about the cylinders. So Im to understand that the metal is just easier to crack or come apart?

In the interest of safety, I am going to commit the faux pas of cross-forum posting. Ulf, please read this post. It is very enlightening.

The Deco Stop

 

[DA Aquamaster]

So as long as they pass all those tests they should be fine? I read the links above about the cylinders. So Im to understand that the metal is just easier to crack or come apart?

If you read the deco stop link, you've noticed that it's an issue of some debate.

Despite that, the official positon of the DOT is that a properly inspected 6351-T6 tank is good to go as SLC crack propogation occurs so slowly that a non-present or undetectable crack not observed at one requalification will be caught by the next 5 year re-qualification before it has time to propogate to the point of failure.

Practice in the field seems to bear this out as:

1) RINs catch and fail a significant number of cracked tanks each year,
2) There have been no instances of a SLC crack causing a catastrophic failure of a properly inspected 6351-T6 alloy tank since eddy current inspection protocols were implemented about 11 years ago, and
3) there are still someting like 6 million 6351-T6 alloy tanks still in service, so statistically the odds of a catastrophic failure of a properly inspected tank are astronomically low.

So...despite reports of third world countries (probably related to improper inspections and or payoffs), the odd "whooshing" non catastrophic leak, and dropping full O2 tanks, the odds are still astronomically low that a properly inspected 6351-T6 tank will catastrophically fail.

 

[Jax]

In the interest of safety, I am going to commit the faux pas of cross-forum posting. Ulf, please read this post. It is very enlightening.

The Deco Stop, by Phil Ellis

The cylinder in question was a Luxfer 6351T6. It was brought to us by a customer for hydro, visual inspection, and filling. If I remember my timing correctly, this was at a time when there had been a recent accident up in Rhode Island (I think that is right) and there was a good deal of discussion going on about 6351T6 here on DecoStop and ScubaBoard. So, I was quite mindful of the SLC issues and it was very fresh on my mind.

Prior to taking the cylinder to the hydro shop, we performed a rather through visual inspection of the tank neck area. I personally inspected the tank neck area with proper mirrors and lights. I used a scratch awl to clean and completely "trace" all of the threads. I saw no evidence of any cracking or any other manufacturing process flaws (folds, tool marks, etc). Finding it in good order, we placed it with other tanks to go to the hydro shop.

At hydro, they cylinder was visually inspected and the expansion test was performed. A visual eddy inspection was done by the retest facility and the VE stamp was affixed to the cylinder. The retester also did a visual inspection. If I remember correctly, it was returned to us on a Tuesday morning.

Prior to filling, another employee did the "official" dive shop visual inspection and placed a sticker on the cylinder. It was then placed on the fill station for filling.

At approximately 2200 psi into the filling operation, an employee came to my office and asked me to come out and see if I could determine where this "leak" was coming from. The fill whip was still on, filling the cylinder at about a 200 PSI/minute rate. I walked out and ran my hand around the fill whip connections, looking at the logical places for the leak. It then become apparent to me that the leak was coming from BELOW the valve base. I immediately told everyone to leave the building. I returned to stop the fill process. By this time, the cylinder had reached a pressure of about 3400 PSI.

After opening the cylinder valve and going outside to wait with the other guys, the cylinder was finally drained. We removed the valve and there was a crack, visible with the naked eye, covering the bottom 5 threads and extending slightly below the threaded area.

This cylinder received three through visual inspections (one at hydro and two here), an expansion test, and one eddy current test....all performed by people that know what they are doing. We were able to see NO EVIDENCE of a crack in either of these tests.

I admit to the possibility that I might have missed one. Nobody is perfect. But, I know what I am doing and I take it seriously. IF I missed one, then it is completely possible for any skilled inspector to miss one. There were a lot of opportunities to have caught a crack if there was one. I personally believe it was not there when I looked at the cylinder. If it was, it fooled three people, a $4000 visual eddy machine, and the government mandated test to catch just this sort of thing.

I have not found another crack on a 6351T6 cylinder since then.....and I will not find another one in my lifetime. Why? We stopped that day servicing these cylinders and I don't intend to do another one in my lifetime.

--- Reposted with permission of the author

 

[Scared Silly]

Although this information is easy to find maybe it should be a sticky considering how many times the same question is asked and answered.

It is a sticky, has been for over a year and is the first thread in the Tank forum

http://www.scubaboard.com/forums/ta...66-my-cylinder-made-bad-alloy-aka-al6351.html

 

[captain]

It is a sticky, has been for over a year and is the first thread in the Tank forum

http://www.scubaboard.com/forums/ta...66-my-cylinder-made-bad-alloy-aka-al6351.html

Maybe it should be in bold flashing red letters. As frequently as the same question is asked the sticky is being missed.