All steel scuba tanks are by definition thin wall from structural analysis criteria by far. The primary wall stresses are pure tensile hoop stresses. Even the aluminum 80 with its approximate ½ wall thickness barely meets the criteria to be analyzed under the thin wall criteria, but it still basically behaves as a thin wall pressure vessel. I am at home and my pressure vessel books are at work so I dont have the exact thickness to diameter ratio to meet thin wall pressure vessel criteria, but all the steel pressure vessel we are referring to are unquestionably thin wall.
Round-out procedures have been around for decades in the fabrication, forming, truing, and pre-testing for a number of thin wall pressure vessels. I never heard of it back when I was a kid in the early 70s and I was operating a hydro test machine, but that was also before I got my engineering degrees and have since worked on a variety of pressure vessels.
