Last week I stopped at my LDS and during my discussion the owner mentioned that all aluminum tanks mfg'd prior to 1990 will be taken out of service on the next hydro. I recognize that some Luxfer tanks used an aluminum alloy that presented problems especially around the tank necks and require special hydro procedures - ie neck eddie test I think it is called. The LDS owner changed his statement by adding that aluminum tanks mfg'd prior to 1990 will all require the special hydro procedure which he stated was cost prohibitive. As a result most pre -1990 aluminum tanks would be remove from service. He state that this was a DOT policy. Can anyone confirm or counter his claim?
In a word - no - the test procedure is not cost prohibitive and - no - the DOT is not requiring the removal of any pre-1990 aluminum tanks due to the use of 6351-T6 alloy.
The "cost prohibitive" hydro test procedure he is talking about refers to the recent DOT requirement that 6351-T6 alloy aluminum tabks receive an eddy current inspection every 5 years when they are requalified for service. This requalification has always included a hydro test and a VIP. The eddy vurrent/visual plus inspection is a new requirement, but it is the same visual plus procedure that has been required by Luxfer every 2.5 years since mid 2000 and that has in effect been required by local dive shops annually as part of the VIP process.
It is by no means "cost prohibitive".
As an aside, 1990 is a conservative cut off date. Luxfer began switching to 6061-T6 alloy in 1987 and by January 1988 had switched production of AL80's to 6061-T6. Walter Kidde is the only company that continued producing 6351-T6 AL80's after that date. In fact all walter kidde tanks are 6351. In contrast Catalina NEVER used 6351-T6 alloy so they will be 6061-T6 alloy regardless of when they were produced. (There were 3 major exemptions under which AL80's were made and all three were combined under the 3AL standard.)
it is true many shops refuse to fill 6351-T6 alloy tanks due to sustained load crack concerns. However it is equally true that there has never been an SLC related fialure of a 6351-T6 alloy tank since the introduction of visual plus testing in mid 2000. Testing since that time has indicated that it takes a minimumof 6 or 7 years for a crack to progress from the time it is first observed by eddy current/visual plus testing until it poses a risk of failure. Consequently, the DOT has determined that visual plus testing every 5 years at requalification will ensure tanks with SLC's will be removed from service. Given that the current scuba industry standard requires eddy current/visual plus testing evey year with the VIP, a ever larger SLC crack would have to be missed during at least one and possibly 2 hydro tests as well as at least 6 annual VIP/Eddycurrent/Visual plus inspections before it posed a risk of failure.
If you do a search, I poseted a copy of a DOT circular in a coupel of the many posts on this subject that lists the cut off dates for the use fo 6351-T6 alloy in various tanks sizes by various companies. Print that out to show a potential shop if you have a pre-1990 tank that is in fact made of 6061-T6 alloy.
They wont fill it because years ago, a luxfer cylinder failed in a north Florida dive shop, and cut the fill operator in half. The problem is you can't just flatly say you will not fill a pre-1990 Luxfer cylinder - Luxfer gets mad at this, (I guess they value profit over human life) so shops have to come up with creative policies to say they will not fill them.
This is a superb example of the urban legend and "the sky is falling" unjustified and totally unsupported fears that develop around this issue. The incident occurred in 1998 and while tragic it resulted in the loss of about half of the fill operators hand - it did not cut him in half. Priror to that date there had been 10 or so failures related to suspected SLC cracks in 6351-T6 tanks - out of about 12 million 6351 T-6 tanks produced for scuba, SCBA and medical O2 service over the preceding 20 years. So at that point the odds of encountering a tank that may fail were literally 1 in 1,000,000. Since the implementation of eddy current testing nearly 8 years ago there have been zero failures.
Implying Luxfer is irresponsible and prefers profit over safety is slanderous. It's also seriously flawed thinking as they would be the ones that gain the most from selling new AL tanks to replace those removed from service. It also ignores the fact that during the period of time when the safety of 6351-T6 tanks was unclear, they offered an exchange program where they replaced 6351-T6 tanks at or below their production cost.
