I worked for Amerigas the last 15 years I worked before retirement and here's what we did for inspection. All visual, decals , dents and pitting due to rust, that was it. Tanks just don't wear out, I've seen home tanks in the field from the early 40's.
By the way exchange tanks weather Blue Rhino or Amerigas are not filled to 80% there all shy by about 1 gallon. If you want to replace your exsisting 20lb tank that's a good way to go other than that it's a rip off.
Again tanks don't where out with maintenance!!! I'm sure some one is going to argue with me on that.