Removal of Firebox Pieces for Replacement

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.

Side view diagram of locomotive boiler showing the location of the firebox, and rear view of firebox.  J.F.Gairns, illustrator

Side view diagram of locomotive boiler showing the location of the firebox in relation to the boiler, and rear view of firebox. J.F.Gairns, illustrator.  (This diagram does not specifically represent the No. 28, so there are some minor differences)

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In his book, A.F. Huston makes the argument in favor of a new kind of boiler, due to the inherent flaws of the radial stay boiler.  The new design never took off, but these photos demonstrate how common these issues are in steam boilers, and underline the challenge of continuous operation of historic boilers today.

x Over time, changes in pressure, as well as exposure to water, condensation, and scale, corrosive forces will prevail.  When the annual inspection was conducted on the boiler in 2010,

Top (water side) of the No. 28 boiler. Over time, the effects of stress corrosion can be seen. When the annual inspection was conducted  in 2009, pitting like this  on the water side of the crown sheet was observed.

 

Butt welded patches are a common repair practice.  This is an example of a previous repair on the No. 28.

Butt welded patches are a common repair practice. This is an example of a previous repair on the No. 28

Staybolts, removed by acetylene torch.  Some removed due to corrosion, others because they were attached to firebox portions that were removed.  In all, approximately 500 staybolts were removed, and will be replaced with new material.

Staybolts, removed by acetylene torch. Some removed due to corrosion, others because they were attached to firebox portions that were removed. In all, approximately 500 staybolts were removed, and will be replaced with new material.

crown sheet being removed

Removing pieces of the crown sheet that have but cut with a torch.

The piece was lowered through the firebox and removed from underneath.

The piece was lowered through the firebox and removed from underneath. lifting eyes welded to crow sheet, handy electric chain hoist– 200 lbs.

The tube sheet bottom being removed

Grinding where tube sheet bottom was removed, in preparation for application of the patch .

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.

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