Neck Crack Found - 6351T6 Cylinder

[redacted]

What I don't understand is..........
people will trade in $20,000-$50,000 cars every 3-6 years but they want to keep a $100 scuba tank forever. Can someone enlighten me.

I still have some 40 year old beer mugs. Scuba tanks are a lot more like beer mugs than cars. Unless you get some beer mugs that are made with defective materials, they just don't wear out. What I don't understand is why the CPSC has not been involved. I guess the actual accidents with these tanks are not severe or frequent enough to come up on their radar so Luxfer may get away with producing a defective product.

 

[PhilEllis]

Hey, Phil. Does anyone track these failures, or do the bad tanks just go silently to the recycle center? It is my understanding that 1982's and '83's are the most failure-prone, as the alloy used typically contained more lead than 6351 allows. My 1973 aluminum tank was in the family for years, and still passed all tests when I sold it last year. I always figured it was too old to be a bad one.

I maintain an interest in this topic, as I used to work for the guys that made these things.

Thanks / Stu

There would be no way to track how many and when these cylinders are removed from service. The only possibility would be to compare hydro inspection records, but they are located in such a wide variety of locations as to make assembly of that data impossible. Most important, there seems to be no one INTERESTED in obtaining any accurate data. The DOT basically washed their hands of the problem by adding eddy current testing and declared "problem solved". The manufacturer has every reason NOT to do any accurate tracking of the "problem". In fact, it appears that Luxfer is now taking the position that there is no problem. Luckily, time will remove all of these cylinder from service.

On your other point, to my knowledge (subject to correction), cylinders made in 82 and 83 are made from 6351T6 alloy. That alloy does not contain any lead, except possibly in trace. 6351 is a 97.8% aluminum alloy, with approximately 1% silicon. I contains equal parts of manganese and magnesium to balance the alloy. The switch to 6061 is a return to an alloy that eliminates the manganese and adds the small copper content that makes the alloy so forgiving. There is also chromium added to 6061.

Hi Phil,

I am very interested in the answer because three of the 6351 tanks that I have are of a size not made in 6061 but are only 5.25" diameter. They are in a US Divers UDS-1 system.

Any other 6351 tanks, I am not really worried about, IF they are properly tested and pass. It doesn't bother me if they fail in Hydro.

The cost of a Hydro plus the scrap value of of an old tank is close enough to the price of a new tank, so with normal size tanks, I suggest replacing them when the Hydro becomes due.

I will attempt to get more information about smaller cylinders. Were I in your position and forced to use a cylinder of this alloy, I think I would consider using some type of penetrating dye in the thread area to help flush out any potential cracks. I have already seen personally that it might be possible for cracks to be present and be missed by through inspections.

Phil Ellis

 

[PhilEllis]

I still have some 40 year old beer mugs. Scuba tanks are a lot more like beer mugs than cars. Unless you get some beer mugs that are made with defective materials, they just don't wear out. What I don't understand is why the CPSC has not been involved. I guess the actual accidents with these tanks are not severe or frequent enough to come up on their radar so Luxfer may get away with producing a defective product.

The final rulings that added the additional re-qualification steps for 6351 cylinders was the result of tons of "lobbying" from those with a vested money interest, during the "public comment" part of the process. I can promise you that EVERY cylinder manufacturer argued that there was no problem with these cylinders, that any failures were "user error", and there was no need to take any action. Like everything that the government does, the DOT reached a "compromise" that provided "gray paint" to everyone, even though the two sides of the issue wanted either "white" or "black" paint. In cases of product safety and fitness for use, compromise rulings usually simply kick the problem down the field, without resolving anything and without improving real safety.

It is my view that local scuba stores (collectively and possibly by accident), in moving toward the position of refusing to fill these cylinders, are enacting a "cure" for this problem, when the DOT should have stepped up and done it in the first place. Anyway, just my opinion.

Phil Ellis

 

[captain]

I can't find it right now but cylinders under a certain diameter are not required to be hydroed but I think the magic number is 3" or less. The old Fenzy inflation cylinders didn't require hydro.

 

[Jimmer]

I can't find it right now but cylinders under a certain diameter are not required to be hydroed but I think the magic number is 3" or less. The old Fenzy inflation cylinders didn't require hydro.

I thought it was 2" ID.

 

[captain]

I thought it was 2" ID.

You could be right, I was going by memory which ain't always right.

 

[WD8CDH]

I thought it was 2" ID.

It's not just any tank 2" or less, they have to be specifically DOT-3E tanks to be exempt from periodic hydro testing. The maximum size DOT-3E tank is 2" diameter and 24" long and a max service pressure of 1800psi.

Tanks in that size and pressure range that are not DOT 3E must still be hydro'd.