DA Aquamaster
April 29th, 2006, 12:09 AM
No offense...but that tragedy happened over 8 years ago and there have been no...I repeat...no explosions of 6351 alloy tanks due to sustained load cracking issues that have been properly inspected under the new visual plus inspection protocols.
Let's stick with the facts rather than rehashing old incidents or promoting websites from persons with axes to grind or new tanks to sell.
The facts are:
1. Aluminum tanks made from 6351T-6 alloy are prone to sustained load cracking.
2. All Walter Kidde tanks were made from this alloy
3. As were Luxfer Al 80s tanks made before June 1988 (and other Luxfer tanks of different sizes until a few months before or after that date depending on tank size.)
4. Catalina tanks were never made form 6351 alloy regardless of age.
5. 6351-T6 alloy tanks require a visual plus or equivalent inspection at least every 18 months , which in the scuba industry means at every VIP - a shorter 12 month interval.
6. No... I repeat... NO...properly inspected 6351 alloy tank has failed since these protocols were adopted.
7. Our local dive shop/hydro test facility does thousands of alumium cylinders a year and it's not uncommom each month for a 6351-T6 alloy tank or two to fail either a hydro test or the visual plus inspection done after the test. The vast majority of these are medical O2 cylinders (which are very numerous and heavily used) or SCBA cylinders (which are heavily used and often abused). As an aside, SCBA cylinders in particular seem to be more suspectible if owned by departments that routinely hot fill them in well under a minute.
The point is the current inspection protocol requires inspections at intervals far shorter than the interval required for a non existant or present but non detectable (by current visual plus methods) crack to propogate to the point of failure - even in heavily used and abused SCBA cylinders.
So in short there is absolutely nothing wrong with using a properly inspected Walter Kidde tank or a pre June 88 Luxfer AL80 - especially if it has a fresh hydro. And there is no reason what so ever to not hydro or visual plus inspect one.
In fact, Walter Kidde tanks demonstrate less expansion during hydro test than other Catalina or Luxfer AL 80 tanks and have generally heavier wall and shoulder construction. Consequently if I had to choose between a pre-89 Luxfer and a Walter Kidde, I'd take the WK anytime. I learned to dive with Walter Kidde tanks in 1985 when our college dive club bought a few pallets of them in partnership with a local instructor and I got to watch a batch of these same heavily used tanks get their 4th hydro test as well as Visual plus inpsections last fall with no issues at all.
Unfortunately because of hysteria, old information, ignorance of the effectiveness of current inspection protocols and, quite frankly, dive shops creating a potential market for new tanks by falsely condemning 6351 tanks in the name of safety, it is often hard in some areas to get a fill for any tank older than 1989 or so, whether it is a Walter Kidde, Luxfer or Catalina (which again has always used 6061-T6 alloy in it's tanks and never used 6351-T6 alloy at all, making SLC a non problem).
My thought is keep the Walter Kidde and find a better informed and/or more honest LDS. If they are ignorant or dishonest regarding tanks, it begs the question of what other areas of diving expertise or equipment may suffer from a similar ignorance or lack of character.
