My flue pipe just arrived today, its one 4 foot length, and one two-part telescoping length of Heat-Fab 6" standard black Saf-T Pipe. I didn't really know what to expect, but the pipe looks fine and clean on the outside, was wrapped in brown paper, and is pretty rusted on the inside. I am just wondering: 1) Is this normal, and if so, how long do these flue pipes typically last? 2) Should I apply anything to the inside of the pipe for further rust prevention? If so, what? (for example Home Depot sells "High Heat" Rust-Oleum that resists heat up to 1200 degrees F but I have no idea if its appropriate to use on the inside of my flue pipe? Attached are pictures just taken!