I don't want to hijack the "Steam returning 2026" thread, but I updated San Antonio & Aransas Pass Railroad #60 there, and I copied and pasted this about it:

"The main, GLARING, issue we found was with the outer firebox wrap. The metal is thinned in several places, sever pitting, case iron rigid stay bolts, NO flexible stay bolts…. Yes, you read that right, no flexible stay bolts. For those that don’t know, that is the reason she was removed from steam operations at Stone Mountain in the early 90’s. We don’t know the full details, other than what Mr. Kevin Wood who worked on her at that time told us, that during the rebuild at that time, someone decided to replace the flexible stays with rigid stays. This is an immediate violation and can lead to a VERY catastrophic event occurring! There are also some extremely poor previous boiler patches on the firebox, that just will not pass inspection."

I am only familiar with steam locomotives from what I have read, and also I don't recall the events in question. What I am wondering is, why would anyone leave out the flexible stays, is it a question of added cost, or added difficulty in installing them? The specific incident is really trivia from a long time ago, although I note that "the early 90's" is right around the time of the Gettysburg RR near-disaster, when excursion lines were forced to rethink their safety practices.

It’s not unheard of for older steam locomotives to be built new with no flexible stays. Former Hampton & Branchville 4-6-0 #44, now on display at the South Carolina Railroad Museum, doesn’t have any. It’s a Baldwin product of 1927.

When were flexible stays first mandated? The #60 rebuild was in the 1980s I believe.

The 60 is a very late model 4-4-0. I'm pretty sure that it was built with a number of flexible staybolts, and the issue was that the people in charge of maintenance after the State made its hostile takeover of the private attractions at Stone Mountain decided that rigid stock would do when they needed replacing.

My question isn't so much, who's to blame, as it is: why do that? Are flexible staybolts more expensive or harder to install?

I at one time owned a steam locomotive that was built without flexible staybolts. If I recall correctly, the Stone Mountain railroad was a private railroad on state owned property. The decision to reply the flexible staybolts with are rigid bolts may have been made with the state of Georgia stem boiler laws.

I was involved with a tourist railroad at one time and we a steam locomotive. Some states have very strict boiler laws, like the state of Ohio. Our state did not have any strict boiler laws and left it up to you and your insurance company. Our state has a lot of steam traction engines { farm thrashing steam engines } and they had no flexible staybolts. Boiler were welded on, rigid bolts were just welded in with no requirements. That has all changed.

The incident at Gettysburg and the thrashing engine boiler explosion in Ohio has changed all of that.

Many had to learn the hard way, even though there are some out there that still have not learned anything. Steam power is not a toy. The best thing for you to do, is to get an engineering firm that can properly evaluate your locomotive. The proper people can lead you in the right direction as per the removal and or replacement of the flexible staybolts.

The case with SA&AP #60 was a need for expediency and a lack of understanding of basic locomotive boiler design. I have never looked into 60's boiler design but generally base designs apply flexible bolts around areas around knuckles (corners and openings). This design helps reduce the chances of sheet cracks developing in those areas. In the case of larger flat areas such as side, door and throat sheets, those are generally supplied with rigid bolts due to less areas of "flexible" stress. The general practice years ago was that rigid bolts got sized up when broken up to the point that either they were replaced with flexible bolts, again for expediency, or sheets or entire fireboxes replaced to maintain a safety factor of 4 which is still the standard as required for any locomotive under 49CFR Part 230.

From what I know about 60, I would strongly advise that it get a new boiler as opposed to fixing what is there even though it not that old. Lot's of these old tourist line engines had a hard life after being acquired by second and third party owners and what some would say were dubious maintenance procedures. Not calling anyone out as it was a different time then and today we all have much more knowledge, hopefully!

Thanks for the reply, makes sense.

That figure of the fire sheet with rigid staybolts warping is enough to make one's hair stand on end....

Reading the old advertisement I was wondering if the difference between traction engines and locomotives was the operating pressure. Traction engines usually operate at 150 psi or less. I know that newer steam locomotives often operate at pressures much higher than that. Higher pressure means more flexing, making flexible stay bolts a better option. I don’t know if that’s the whole story and I am just an armchair observer, but it makes sense to me.