The No. 28 project is moving right along. Recent focus has been on replacing thinned sections of the firebox. The firebox was assessed after a thorough descaling of water deposits. Through ultra sonic inspection the crown sheet, knuckle, and area under the firebox door all showed some signs of thinning. The original crown sheet and knuckle were removed and were sent out to have the pieces replicated. The fabricated crown sheet was formed at Benicia Fabrication & Machine, Inc. in Benecia, CA., and the knuckle was formed by Chelatchie Boiler Works, Inc. in Camas, WA..
Portions of the boiler that needed to be replaced were removed in sections by a cutting torch. These pieces were lowered with a electric chain fall and sent out to be duplicated.
Once the crown sheet was removed, the exposed interior of the wrapper sheet was needle scaled to remove accumulated water deposits. After a detailed cleaning the wrapper was inspected for defects. No issues were detected.
After the crown sheet was formed and returned it was then laid out and measured. The sheet was marked in a grid format. 130 holes were drilled on each half of the crown sheet. These holes will later be tapped and threaded to receive stay bolts. The stay bolts will connect through the wrapper to the firebox sheets.
Stay bolt pilot holes were drilled out at 7/8” and later will be opened up by aligned reaming to .920. They will then be tapped with a 1 inch-12 continuous thread through the firebox and wrapper.
Upon arrival, the slightly larger fabricated patches were rough cut to size by a cutting torch. The pieces were then ground down until they fit the side sheets. The edges were beveled down to a V which is needed for the welding procedure.
Now that the firebox is patched up a substantial amount of work is on the brink. Next step is to thread the stay bolt holes, then installing the stay bolts.
Previous Sierra No. 28 Update: Hydrostatic Testing of Superheater Tubes
Next Step: Tapping and Installing Stay Bolts.