I can give you some information based on personal experience, but I’m not really a “pro” in the sense that I don’t do tank stuff for a living, only for myself.
Anyway, I have been given dozens of steel 72’s over the years and I have never had one fail hydro.
This surprises me because a few were really pitted badly, some under the boot, and some on the inside.
Some tanks I buy but most were given to me.
I joke that I run a steel 72 rescue center.
One tank I got was from 1959, it was a freebie, and it was originally painted with just oil based alkyd enamel over steel with no primer. It was so pitted under the boot that the pits looked to be 1/16” deep or deeper. The inside was pristine. So I sand blasted it, primed it, and painted it. It passed hydro no problem!?! Baffling.
I had another one that had a pretty deep pit inside that I was always paranoid about, but it continued to pass hydro. One year I inspected it and there was a little more rust forming in the pit, so I decided to condemn it instead of wire-wheeling out the rust from the pit and sending it to hydro again. It had a few years left on the previous hydro so I thought it was time to make a bell out of it. When I cut the bottom off I was stunned to see that the pit which looked like a crater from above with a light was only a small little thing not even 1/64” deep but it was kinda wide making it look a lot worse than it actually was. I was bummed knowing I just murdered a perfectly good 72 that probably had many years of life left in it.
So from that moment on I decided to clean up any 72 that came in (as long as it wasn’t epoxy lined) and send them to hydro, because you never know.
If they don’t pass hydro I don’t think they charge you, so you have nothing to lose. Even if they do charge for a failed tank, I would still take a gamble on it. Even if one out of 25 or 50 fail you’re still way ahead. Go buy a new tank and see what those cost, if you can find one.
Steel 72’s are just too precious to condemn if there is no reason to.
