The area in the firebox's of 12 and 190 that have been replaced is from the mud ring to about 6 inches above the grates. These sheets were put in long before i ever worked there. The rest of our boxes are original. The one thing most railroaders never think about wearing out is the smokebox and stack. We put a whole new section in #12's smokebox about 4 years ago and a new stack on 190 last year. 12's smokebox that we replaced was at least 50 yrs old at the time if not older. The stack on #190 was just 30yrs old.