The goal of this project is to replace corroded staybolts, and thinned sections of the firebox. While we have the locomotive disassembled, we are also completing the 1472 day inspection. It is helpful to understand the anatomy of the boiler in order to follow along.
The firebox is a compartment, within the boiler, where combustion occurs. It is surrounded by sheets of steel on five sides. It is through these sheets of steel, that heat is transferred to the water on the other side. For heat to transfer efficiently, the sheets need to be relatively thin (about 3/8″). The firebox is subject to up to 13 tons of pressure per square foot. To prevent collapse from dramatic changes in pressure, the firebox is tied to the outer portion of the boiler (wrapper sheet) by hundreds of bolts which span the distance between the wrapper and the side sheets. In oil burning locomotives, like the No. 28, the bottom and sides of the firebox are lined with firebricks.
To repair the No. 28, it is necessary to remove patches of steel under the tube sheet, under the firebox door, and the crown sheet, including the knuckle where the sides and crown meet, over the door. On this boiler the rear corners have been repaired twice before, the front once, as the material has been consumed by use.
Next Step: Hydrostatic Testing on the Superheater tubes
Previous Sierra No. 28 Update: Removal of corroded staybolts; firebox & tube sheet inspection.