To reiterate the point, bullet point number one is scuba specific, and is a subset of each of the other two points. There is a tendency for people to read that second point’s lower rate for ALL Luxfer 6351 cylinders, and want to apply it directly back to scuba.
Interesting that in the context of these three statements, it appears that non-scuba, non-Luxfer cylinders have a much higher rate of SLC than Luxfer non-scuba. (I am assuming all manufacturers produced scuba in similar proportion to total cylinder output.)
Also note that Luxfer cites an industry expert total population of 30M cylinders, and industry expert PSI cites 50M. Perhaps Luxfer excluded some population of “out of service” at the time, such as Norris and Kaiser, but I would not assume that.
Bottom line, is that it is usually not difficult to find and/or spin authoritative numbers to argue a different viewpoint than someone else’s numbers.
Another few words on what I will agree is an extremely low incidence of catastrophic failure of 6351.
First, that low rate is poor solace for the fill station operator that experiences it first hand.
Second, that failure rate is highly skewed - it does not exist in a vacuum where there were zero proactive measures to remove a cylinder prior to failure. They occur in spite of those measures. Even if they can be traced back to a missed opportunity due to substandard testing, that testing is part of the world in which we live, and must remain included in any risk assessment.
I will still fill a 6351 cylinder that has an annual VIP and annual eddy current test, but would not lose much sleep over it if tomorrow the DOT banned them outright.
The numbers I would like to see are the quantity of scuba 6351 structural catastrophic failures since the requirement for eddy current testing, and the number of scuba 6061 catastrophic structural failures from each era. And by structural failure, I mean to exclude failures due to abuse. Although now that I think about it, if one alloy is significantly more resistant to abuse than another, that is also relevant as once again it is part of the real world in which we operate.
