It is a shops prerogative to fill cylinders. Some are going this way. I would not be worried about 6351 cylinders if I knew they had been properly inspected. The caveat is "proper inspection" Here is Fill Express's policy
http://www.fillexpress.com/library/al6351.shtml. Some like it, some do not. IMHO, it is a reasonable balance.
The scuba industry has done itself a big disservice with the annual inspections. Any shop or person can make an inspection sticker. Some do just that but the person doing the inspection is not fully trained. Thus the problem. I think is part of the reason DOT moved the eddy current test out of the scuba shops and to the hydro shops (although there are scuba shops that do preform hydros).
The sad part is that the shops will be happy to sell you a new cylinder for a discount if you give them your old cylinder - problem that I have seen in one case the discount was less than the price of selling the cylinder for scrap.
Stress Load Cracking takes time to develop, if inspected regularly and properly it can be detected before catastrophic consequences. Luxfer reccomended every 2.5 years. DOT requires it at the time of requal which is every 5 years.
I guess in the case above I would be tempted to talk with the owner - you requalified and eddy current tested my cylinder last year and now you will not fill it? What has changed? Don't they trust their own testing?
They will problably give you a long story about exploding cylinders. It is true I think it is 20 world wide and of those 12 were scuba. This is of only 6351 cylinders. The last was in Austrialia in 2005. (I trying to pull from memory) and about 5 in the past 6 years world wide. I am not sure of the count for all cylinders.
BTW I have one sitting in my basement full of CO2 I go down once a day a quaff a beer and it merrily keeps my beer under the right pressure. And though not required as it is a CO2 cylinder it's next hydro will also include an eddy current test.
