In the interest of accuracy, rockjock3's statement [while they (Luxfer) do "allow" the use of Visual Plus 3 eddy current machine for the use on 6061 alloy tanks, they do "recommend against" it] is incorrect. please reference the following links Luxfer: Press Releases and http://www.luxfercylinders.com/news/releases/20041011.shtml; these press releases from Luxfer clearly states that both newer generation eddy current machines Visual Eddy Mark V from Flare Technologies & Visual Plus 3 from AIT are approved for use for both 6061 & 6351 alloys; nowhere in these Luxfer statements do they "recommend against" the use of these VP3/Mark V machines.
While it is correct that Luxfer did not recommend the use of older generation eddy current machines for use other than 6351 alloy cylinders, it is not because the machines were incapable of detecting cracks in 6061 alloy; it required a greater level of user expertise that can only be obtained from proper training and experience of use. It is interesting to note that Luxfer did use VP2 machines in their own factories on 6061 alloy cylinders prior to aquiring the newer generation eddy current machines, and the test standards used to calibrate both the VP2 & VP3 are manufactured from 6061 alloy aluminum.
It is true that 6061 alloy cylinders to date have not exhibited neck cracks from sustained load (slc), they have nonetheless manifested neck cracks from other issues (mainly manufactured anomalies & corrosion stress-induced) and we have documented over 40 neck cracks in 6061 alloy cylinders that were confirmed by visual inspection with a magnified light source.
An eddy current test is not a replacement for visual inspection, only an aid to compliment the inspection process; the use of all available technologies in order to prevent catastrophic cylinder failure should be commended, not discouraged. After all, shouldn't we be responsible to protect those most in danger of cylinder explosion; the fill station operator, employees of dive centers and their patrons?
