....from a guy who should be institutionalized.
In the 17 years I was involved with the C&TS (81-97) we didn't have water problems or scale problems - at least to the extent shown in Carlos' pictures. Boiler washes were done quite thoroughly and mudrings left completely clear. Additionally the amount of scale removed was not as much as I have seen on other engines I have worked on.
We were pretty ignorant of water treatment. We didn't use any. The boilers never foamed or lifted water. A tube job would last at least 10 years before fire cracking of the beads forced us to re-flue an engine (we seldom had flue leaks). It think it was 487 that got something like 13 years on a set of tubes (1974-1987). With that kind of service life we figured "if it ain't broke don't fix it".
We did have some staybolt problems down on at the fireline, that we had to deal with occasionally, and at one time there was some talk of doing some side sheet work on 488 and 487, but eventually this was forgotten. In the years I was there we broke about 5 staybolts on the 480's. Total.. as in 17 years we broke 5 bolts. A few others on the fireline got changed because the fire ate the ends off and there wasn't anything left to buck up when they started to leak.
When I came back briefly in 2000 as an engineer, some sort of water treatment was being used. The water was treated by the shop in the AM when they watered the engine. I was told by the CMO to NOT blow the boiler down as they wanted to get a higher concentration of solids and treatment in the boiler. That was about the wierdest idea I had ever heard. I always thought the idea was to keep the solids down, not up. Anyway, I said "OK" then went about the way I always did, blowing the boiler down a couple times in the morning, and again in the afternoon. But, the shop people did not blow the boilers down in the AM, and I cannot say what the other crews did.
When I spent the 2001 season in Chama I do not believe we used any treatment. During that summer, two small mudburns showed up. One on 489, another on 463. That got me real concerned about things. In 2002 I was let go and never got to pursue the matter.
My guess: Whenever treatment was added in 2000 (or before) loosened up lots of scale on the crownsheet and stays. This stuff came off in big pieces that got caught in the sidesheet stays, additional scale collected with it, fully impacting a section of the water leg with scale. As it never went all the way to the bottom, it was never seen during a boiler wash.
I was later told the treatment they were using was intended to be used in freshly overhauled boilers to keep scale from forming and disolve that scale might build up. In this case it disolved a BUNCH of old stuff that got stuck in the sides, If the treatment had continued, it might have eventually disolved the scale, but for whatever reasons, it didn't and the fireboxes are a mess.
Lastly, I'm not a boiler chemist, or even a remotely bad boiler maker. This is just some rememberances and some conjecture.
Opinions from experts appreciated..