I have 1/2" and 3/8" thick x 24" diameter steel pipes that are typically used for natural gas transport, but in my case they take the shape of horizontal wood-burning cookers. I am building wood fires inside these pipes and will do this hundreds of times over my lifetime. The fire sits directly on the "bottom" wall of the pipe.
On the one hand this is a lot of steel so it seems nearly impervious to damage; on the other hand, fire is very hot and I don't know anything about metals!
I'm not concerned about superficial damage or minor rust or perhaps losing .5mm of material over 20 years, but anything more than that might cause me to take preventative action.
Will burning fires inside these pipes damage them in the long run?
If so, do we have some idea of the extent of the damage?
Lastly, what would be a good preventative measure? Some people put grates at the bottom of their cookers to keep the coals off the metal a bit. I could also put firebrick underneath the wood/fire.