"Why do you want to own your own cylinders anyway?"
One has to do a lot of diving to justify owning your own. If you own a lot of them then you should also be able to maintain them as far as costs go. The only reason I tell anyone to buy their own cylinders is for convenience. As an example my local LDS closed at 1800. I got off work at 1700 and they were a 30 min drive. I usually would have to make 2 trips to get my cylinders filled for the weekend.
Solution, buy more cylinders, then become an instructor and buy more cylinders and then be a dive shop, compressor and buy even more. Then become a hydro station and ..... It never really ends. BTW, you still have to maintain them and it takes discipline and time. There is nothing worse then packing for a trip and find one or two of the cylinders you want to take just ran out of hydro. Oh well ...
AS far as the original OP's question, running a hydro facility we see a lot of older cylinders. Most of them are medical. The point is that we find a lot of cracks. see http://www.engineeredinspection.com/hydro1.html As they are only required to be visually inspected at hydro (5 yr intervals) we just stopped testing them. I don't trust the manufacturer's statements as to crack growth as anecdotal evidence has shown that it takes less time for cracks to grow to failure. My experience with dive shop's efficacy in annual inspections is that in many cases I am not impressed.
Safe Diving
One has to do a lot of diving to justify owning your own. If you own a lot of them then you should also be able to maintain them as far as costs go. The only reason I tell anyone to buy their own cylinders is for convenience. As an example my local LDS closed at 1800. I got off work at 1700 and they were a 30 min drive. I usually would have to make 2 trips to get my cylinders filled for the weekend.
Solution, buy more cylinders, then become an instructor and buy more cylinders and then be a dive shop, compressor and buy even more. Then become a hydro station and ..... It never really ends. BTW, you still have to maintain them and it takes discipline and time. There is nothing worse then packing for a trip and find one or two of the cylinders you want to take just ran out of hydro. Oh well ...
AS far as the original OP's question, running a hydro facility we see a lot of older cylinders. Most of them are medical. The point is that we find a lot of cracks. see http://www.engineeredinspection.com/hydro1.html As they are only required to be visually inspected at hydro (5 yr intervals) we just stopped testing them. I don't trust the manufacturer's statements as to crack growth as anecdotal evidence has shown that it takes less time for cracks to grow to failure. My experience with dive shop's efficacy in annual inspections is that in many cases I am not impressed.
Safe Diving