I have been diving over 50 years, and the only tank of mine that failed hydro was a steel "72" with obvious rust and pitting inside. My PST 104s have an orighnal hydro of 1977, and I have some 72s that are even older.
Uhm, old cylinders, older .... Sorry Forrest, couldn't resist.
Funny, the only cyl I ever had fail was a 72 as well. The special exemption cylinders that are failing are probably due to the hydro facility not doing the pre-stress as outlined in the documents.
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