Is it safe to use a steel tube as a pipe?

I am currently using a vaporizer to ingest pot, and I was wondering if there's any possibility that the hot air that I inhale from the vaporizer could be burning the steel pipe or the screen I use, which is also steel. I ask this because I notice that the screen is a bit darker now that it has been used. There is also a sort of a yellowish tint that is slight but noticeable upon closer inspection. I estimate that the temperature that I am inhaling from the vaporizer in no hotter than 600 degrees farenheit. I understand that this is below the melting point of steel, but could this hot air still be burning the steel and releasing toxic fumes? When I set up the appropriate temperature, the aluminum coils in the vaporizer do turn red.