I was looking at the PST steel tanks a while back. Read something about having to pre-stretch them to get a accurate Hydro on them for certification. Some had flunked for not following the special instructions. There was a page with the instructions that I downloaded for a friend, at the time, but don’t have it any longer. This was an issue with the way they galvanize the tank, as I recall. I finally went with the Faber HP100. For what it’s worth.