Re: Boilers

>Could someone talk about boilers a little bit? I gather that you need at least two or is it three rows of rivets on a boiler seam to be legal?<
It is not that you have to have a certain number of rows of rivets to have a "legal" boiler. The design of riveted joints is somewhat tedious. The joint has to have sufficient strength to hold the two pieces together.
Without getting to technical (I hope), the design of riveted joints looks at four different failure modes.
These failure modes are:
1) Shearing of the rivets
2) Tensile failure of the plate
3) Bearing failure of the plate
4) Shear out of the plate
Item number 4, rarely occurs as this failure mode is due to the rivet being located too close to the plate edge.
In the design process, the load necessary for each failure mode is calculated. The strength of the joint is then taken as the lowest failure load. This failure load is then compared against the design load applied. Depending on the factor of safety required, you can then determine what is the allowable load on the joint.
The analysis of the strength of existing joints is much different than the design of a new joint. In the design of new joint, The designer is often trying to determine the most efficient joint, or the least costly to fabricate.
The term joint efficiency describes the strength of the joint to the strength of the plates being joined. The joint efficiency is always (in my experience) less than 100%; that is, the riveted joint is less strong than the two plates being joined.
>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?<
Not knowing the design of this boiler, I can't really comment in detail. However; like beauty, a good design is in the eye of the beholder.
The key questions to have answered are:
1) What is the general physical condition of the boiler?
2) What is the MAWP (maximum allowable working pressure) of the boiler in its current condition?
3) What are the materials of construction?
>Did boiler inspectors and shop men really know that much more than they do now? How and when did such a boiler become illegal? Just age?<
Mechanical design is an evolutionary process, which is just a fancy way of saying we learn from our mistakes. In another way, disasters are nature's way of telling engineers: "Don't do that again!"
>Lastly, is it better to retire an engine to museum display or replace such a large historic part so it can run again?<
As an engineer and someone who has an appreciation for the history of technology, my recommendation would be that if the boiler is unable to meet current code requirements for boiler safety without massive modifications, I would say to save the old boiler in its entirety and place it on display.
Hope this helps.