Replacing the flues and getting the boiler water tight.

Back in the early 20th Century, when labor was inexpensive the boiler flues were assessed and if found to be sound, they were cut out, cleaned of scale and then reused. This was because material was expensive. Today, it’s the other way around, materials are relatively inexpensive compared to the cost of labor it would take to clean and repair 148 flues.

Now that all the old tubes are out of Engine 28’s boiler and the crown sheet has been repaired, and stay bolts replaced, we are completing the tube job and getting closer to the hydrostatic testing.

Photo of tubes with letter key Fig 1

This image is a close up of the tube sheet, also called the flue sheet. You can see that the tube sheet has been cleaned and ground off (C), this was done to clean up any chipping or unsavory remnants left behind from the removal of the old flues. Removing the old flues requires the use of force in hand with some sensitivity to the surface of the flue sheet. However, at times even the most seasoned boiler worker can chip the flue sheet.

The copper ferrules ( F) are gently tapped into the flue holes with a hammer. The ferrules are expanded into place to ensure that they do not move when the tube is applied.  They act as a seal between the tube sheet and the new tube. Next, the tubes are inserted into the flue holes (D) leaving  a small protrusion.   The standard measure of protrusion of the new tube is ¼”. Then they too, are expanded and rolled. The result is a tight fitting tube with a visible indentation on the interior (A ) and a slight flare at the end of the tube. The extra ¼” of tube allows for a good bead (B) that seals the flue to the flue sheet and makes the boiler water tight. After the beading of the tubes, another light roll is given to each new tube because the beading is an aggressive action.

Beading is an art. It involves using a pneumatic hammer or riveter and a specialized tip. In the image above (E) shows a bead that is rough, and (B) shows a bead that is more controlled and refined. It takes a bit of practice to get all the beads looking smooth, but regardless of the appearance, the work will hold.


This image shows the business end of the tube roller/expander. The old rusty shaft next to it is one of the older pieces of a previous roller/expander from the earlier days of boiler work in the roundhouse.

For this project we used this modern electric motor to roll and expand the tubes ( left), but back in the day a pneumatic model would be used ( right)..

Fig 5 drawing from REB

This diagram is from The Railway Educational Bureau Instructional Papers of 1927. It shows a beaded flue end from the side and the front views.

Phil beading, Fig 6

Here you can see Phil Hard beading one of the flues. The pneumatic hammer weighs over 20 pounds, so you can imagine the amount of strength required to do beading all day.


After all the beading is done, each flue then gets another straight roll to ensure the tube is tight in the flue sheet. Beading is intrusive work and it can cause the flues to loosen. The final roll remedies this.

expander rollers Fig 7

These are the tips that are used with the electric motor for the final, straight roll.


After all the beading and rolling, it is time to fill up the boiler and check for any leaks. With the boiler full of cold water at local pressure we begin to assess and address leaks. Once these are addressed it will be time for a true Hydrostatic Test, adding pressure and heat to the 93 year old boiler of Sierra Engine No. 28.