You will note I said "supposed to be" not "are"! What kind of a failure rate are you seeing on these tanks?
The current explanation that I have been hearing is that the zinc coating (and the mixed zinc/steel layer several thou thick that froms between the zinc layer and the steel) is less elastic that the steel, and inhibits the tank wall's return to the prepressurized state, so that the tank shows too much permanent expansion. The rumor I have heard is that Worthington wants to test the tanks on the basis of elastic rather than permanent expansion, which would mean putting REEs on the tanks. Have your heard anything different? I would be nice if they can work something out, so any special procedure can be DOT-mandated, rather than the situation we have now where Worthington and PST have a procedure, but the hydroshop doesn't have to do it.
On the other hand, I had a guy at one of the largest US vendors of these tanks swear to me the other day that the problem had nothing to do with the metallurgy or construction of the tanks, but only the fact that the rough zinc coating held more bubbles on the outside of the tank than a painted surface, and these were enough to skew the test results! Said he had gotten this directly from Worthington, and PST had told him the same thing years ago.
