Service pressure of Steel 72

[halocline]

You guys are technically correct from a U.S. perspective. To the best of my knowledge, no steel 2250 psi cylinder in Canada can be given a "+" rating on a subsequent hydrostatic inspection. In the U.S. this was not usually done as most testing facilities would not test or be capable of testing to the standard required (see NOAA dive manual).

I'm almost certain you're wrong on this. The plus rating testing requires no additional test over the standard hydro test, it just requires having the correct REE number to know what the acceptable expansion is. I've been told by several hydrotesters that 3AA2250 tanks rarely fail the plus rating test, probably because the service pressure is conservative relative to other scuba tanks. The primary reason so many (including mine!) 72s don't have a current plus rating is because the tester does not have access to the REE number or is simply too ignorant and/or lazy to include the rating. Sometime after the debacle with my tanks, I found a friend's faber LP80 with this same tester's mark. The tank did not have a plus rating, the REE number is clearly stamped on the tank, and the guy did not stamp "no plus" as he idiotically did on mine.

 

[captain]

You guys are technically correct from a U.S. perspective. To the best of my knowledge, no steel 2250 psi cylinder in Canada can be given a "+" rating on a subsequent hydrostatic inspection. In the U.S. this was not usually done as most testing facilities would not test or be capable of testing to the standard required (see NOAA dive manual).

As far as burst discs are concerned, when 2250 psi tanks were common in Canada, the 5/3 rule wasn't applied. For that matter burst discs were often replaced with a solid device which would prevent gas venting (yes very dangerous, but I never heard of any negative incidents). This was not really any surprise, as octopus regs were unheard of (nor required by the certification agencies) and people thought you were a safety nut if you insisted on a "J" instead of a "K" valve. Diving has come a long way. When I worked in a dive shop (prior to owning my own) 2250 psi cylinders often required burst disc replacement; 3200 psi discs were usually used. When I read the question, I thought it odd that 2250 psi cylinders were being discussed as I haven't seen 71.2 cuft cylinders for some time...

The + rating does not require any special test or special testing equipment. It is simply a matter of knowing the REE in cc's for that tank and comparing it to the permanent expansion in cc's which is obtained as a normal part of doing the hydro test.
If the REE is more than the permanent expansion the tank can be + rated, if the REE is less than the permenant expansion it does not qualify for the plus, so simple even a caveman can do it.