So much bad info on this board sometimes. You can store a steel cylinder for more than a year without issue.
If the tank had the worst case scenario for rust, it still would not eat more than 1 percent of the oxygen in the tank. It takes 16 percent O2 to support life on the surface. 20 percent will easily do it.
LOL, how many people drain their steel tanks every 3 months when they can't dive? I have about 14 tanks, half steel half aluminum. You think I'm using all 7 steel tanks? Not even close. I have a single LP95 that gets used about once a year. It's labled with nitrox sticker, when it was filled and what percent. When I go dive it, I analyze it again. It's within 1/2 a percent from original analyzing. I've been doing this for more than a decade. It's simply not an issue.