Re: Boilers

"It seems that in order to run the WW&F 9 the
museum will have to get a new boiler built.
How then was a "poorly designed boiler" run
over three or four railroads for over 40 years
without problems?"
The problem with #9's boiler is two-fold.
First, it is a "modified lap-seam", meaning that the areas they join lap over each other. A straight join is just a lap-seam. "Modified" means they stuck another plate in there that completely covers the lap seam, probably installed when Maine or Federal laws outlawed the lap-seam.
Today's boilers are butt-seam, meaning there's no overlap. Lap-seams are illegal now because moisture can rot out the metal in between the seams, especially where the boiler is riveted (which #9's is).
Secondly, ultrasound readings indicated substantially thin spots over a large part of the boiler. Now we knew darn well that the readings weren't as thin as the ultrasound said they were, because we phyisically measured it's thickness at one of the holes in the boiler. But there was some kind of layer in the middle of the metal that reflected the signal. We attribute it to irregularities in the casting in 1891, when it was built.
We had the choice of patching the old boiler or getting a new one. We decided on a new one so that the historical integrity of the old boiler could be preserved, and it could be put on display.
Boilers however, would be replaced during an engine's service life. Not often, but it did happen.