then that shop isn't following the test procedures to the specification that those cylinders were manufactured to. They seem to think that they are following the same 3aa testing procedures, when in fact, they aren't.
Worthington amended their special permit to change the test procedure. PST did not, they simply issued "guidance."
The problem with recently made galvanized cylinders failing hydro when the rerounding procedure isn't followed isn't limited to exempt/special permit cylinders. I have a 40 cf 3AA Worthington cylinder that would have failed, but it failed by so much that the shop genuinely thought they had an equipment problem and retested it. Of course, it passed the second time. Perfect example of a problem of geometry rather than metallurgy. If the steel had been weak, the results would have been repeatable.
Very few hydro shops will shot blast or tumble scuba tanks, takes too much time and effort and slows their process down. That job is typically reserved for the dive shops. DIY'ing a tumbler is not particularly difficult or expensive.
The hydro shop that does shot blasting has such reasonable pricing and does such a good job that most of the dive shops use them. I believe they've built some sort of machine to do it, or have modified standard equipment to work specifically on the insides of cylinders. It's integrated into their process. They have industrial gas supply customers who send in cylinders for internal/external blasting, hydro, and paint, and they do it on an assembly line basis, very fast. I don't think it takes them more than a few minutes to shot blast a cylinder, and everything comes out. I've sent them old cylinders with liners and they come back clean.
Nonetheless, I agree, there is a tumbler in my future.
Since you have your own fill station, what does the + rating matter?
You probably remember the compressor I asked about several months ago. I never bought it, so, no fill station (Off topic, but the main problem was that the whole system was set up for 2400 PSI and could have maybe been pushed to 3000 PSI but was never going to fill an HP cylinder -- and the seller wanted too much money given the uncertain service history, low operating pressure, and "as is, where is" nature of the deal).
Some local shops will fill a 3AA cylinder "properly" regardless of the presence of the +, but it depends on who is working that day so I can't count on it.
PST's don't have any issues with hydro other than hydro shops not following proper round-out procedures. As long as the procedures are followed, then the tanks will be just fine. The scare with PST's is because they have to renew the permit and they drug their feet a little bit on the last one. It got renewed and life is good. Worthington will continue to do the same and the DOT will continue to harass them every time it is due for renewal because they will otherwise have to deal with all of the individual requests and they really don't want that
It's a little more complicated than that.
PST never amended their exemption, and so PST cylinders, even high-pressure ones, are subject to the 10% inelastic expansion limit. High-pressure exempt cylinders have to pass the REE, for 3AA cylinders it's optional and is what gives them the +. The PST guidance suggests following the round-out procedure, which some hydro shops respect while others do not. The renewal (non-)problem is what you say.
Worthington amended their permit to get rid of the 10% inelastic expansion limit, so the Worthington special permit cylinders just have to pass the REE. Worthington 3AA cylinders still have to pass the 10% inelastic expansion limit and those the re-rounding procedure is important because they will flex from a geometry change just like PST cylinders.
Anyway, the question remains as to whether the Faber hot dipped cylinders will have the same problem with geometry.
