Got a note from Steve Sandberg that I'd like to share with you:

Good to hear.

What is that long horizontal piece on the side of the course containing the steam dome?

Steve

That long horizontal strip full of rivets is called a "welt" or "welt plate." It covers the horizontal seam in that boiler course; there is another one very much like it inside the boiler shell, just below it. The other courses will have them, too; they are likely on the other side, out of view in this shot.

The use of welt plates allows the boiler courses to be close to true circular cross section, in a form of butt joint. This near circular cross section is the most efficient and safest shape for resisting pressure with a minimum of flexing at the seam. The price of rivetting the boiler this way is more complicated joints, along with having to use a variety of rivet sizes, some rather long.

The alternative is what is called a "lap joint," in which one side of the boiler course overlaps the other. This is not a true circular cross section, and as a result it has a bit of flex to it (much more than in a butt joint with welt plates), and can be a source of metal fatigue in the boiler course. As noted in earlier posts, lap joints have been outlawed for this reason.

Today, of course, such a boiler would be butt-welded instead of riveted, and very likely would not have a welt plate.

This brings to mind a question. I recall reading, in old copies of "Mechanical Engineering" back when I was in college in the 1970s, that the first all-welded boiler went into a rebuilt Delaware & Hudson 2-8-0. One of the features of building this boiler was the provision for relieving stress in it after the welding had been completed. This involved putting the whole boiler in a large furnace, heating it to high temperature, followed by controlled cooling. Now, today, I get the impression welded repairs are routinely done on boilers, yet the repaired boilers are obviously not put into an annealing furnace to take out the stress. How is this dealt with today?

On welded repairs if questions are there then a weld engineer should be consulted. Localized Welded repairs are generally post heat controlled with heat blankets or even ceramic heaters with a heat blanket over the top.

This boiler shell has been cleaned somehow and obviously a very good job. Tell about this process, how was this cleaning accomplished?

The interior and exterior of the boiler were sandblasted. The interior received a protective sealant and the exterior was painted with a high temperature resistant primer. That is the grey surface that you see. Later a high temperature resistant black paint was applied.

Don C.

Nice to see the #261 saga well on the way to a happy ending after some anxious moments over the past couple of years.