Brian:
I do not think Nooter used any "very good materials" to build the boiler in the "Belle of Louisville". They most likely followed ASME Section I of the Power Boiler Code, and used something like ASTM SA 285 or A 516 steel plate. These are both "pressure vessel grade" carbon steel plate containing little more than carbon, some silicon sand possibly a small amount of manganese. These grades of steel plate are known as "Firebox grade" or "Flanging" plate since they are formulated to hold their strength up to 600 degrees F and are ductile enough to be formed or flanged to make parts of boilers. Nothing unusual about this material. Either grade of steel plate is used routinely for firetube boilers and pressure vessels. Quite easily formed and welded.
The Belle of Louisville may be drawing raw river water for makeup, but I'd bet the farm chemical water treatment is in constant use. When the raw water is pumped aboard for makeup, it is likely first run thru some fine basket strainers to remove any larger debris or suspended solids. It then is pumped into a feedwater makeup tank. Without knowing how the Belle of Louisville is set up for makeup water, it would be likely that samples of the raw river water are taken and tested right aboard the vessel or at the pier where she ties up. Once water is analyzed, the correct types and amounts of water treatment chemicals are formulated. These are usually bought in bulk plastic drums. The amounts of each chemical needed (Oxygen scavenger, pH adjustment, cation/anion compounds to bond with dissolved solids, coagulent) are measured out and put into a mixing tank. A mechanical mixer stirs up the combined chemicals. A chemical injection pump is used to meter the amount of boiler water treatment chemicals into the raw water. In some installations, a water flowmeter is used to control the metering pump. The metering pump is a small piston pump of variable displacement, with a micrometer adjustment. Often, it is set up so that when there is flow in a water line, the metering pump runs and injects the chemical treatment into the line.
The diligent use of boiler water analysis/testing and the use of the water treatment chemicals "tailored to suit" the water chemistry, and frequent boiler blowdowns to get rid of precipitates and mud are what has given the boiler in the Belle of Louisville long service life. The other part of it is the overall operating practices by the marine engineers and firemen on the Belle of Louisville. Proper firing practices and proper maintenance including boiler washouts and proper layups in the off seasons are also key to long boiler life.
Magneticanomaly:
Wrought iron is, by its nature, a "spongy" material. It is typically found to have "stringers" of slag rolled into the wrought iron, and something of a fiberous consistency. Improper water chemistry in the locomotive boiler could have caused a chemical attack on the wrought iron which attacked certain areas of the material, possibly leaving the slag stringers and attacking areas where the iron had a bit more carbon- wrought iron is essentially a "pure" iron with next to no carbon, hence it was more corrosion resistant than carbon steels. The non-homogeneous nature of the wrought iron would cause certain areas to be more prone to chemical attack than others, even in the same piece of wrought iron plate. Wrought iron begins as "muck balls" that are balls of raw iron with plenty of slag in them. These muck balls were worked hot through "squeezers" (rolls) to work out most of the slag and get some sort of grain flow. Making wrought iron was a strictly manual process with the iron puddlers going on instincts and feel, particularly at the time the locomotive in this thread was built.
Wrought iron, being non-homogeneous, is bound to have a widely varying tensile strength. Later production of wrought iron was more closely controlled, and wrought iron was routinely specified for locomotive boiler staybolts, almost to the ending of the use of steam locomotives. By that point, the wrought iron was fairly consistent as to strength and internal structure. Back when this locomotive was built, wrought iron was a "vague" kind of material with no consistency to it from one heat to the next, and even within a single heat.
Boiler water chemistry can minimize corrosion to the point that boilers will last a long time. If the boiler is used in a system where the condensate is returned, then a very close control can be maintained on the water chemistry. Boiler water treatment companies were generally a staid and conservative bunch. Outlandish claims were not made by the reputable and larger boiler water treatment companies. The hotshot salesmen of the "one size fits all" type of water treatment are another story.
The big companies like Nalco and Dearborn would either arrange to pick up water samples from a customer's steam plant and do their lab analysis, with formal reports and "prescriptions" for the chemical treatment; or, they would set the customers up with an on-site water testing kit (or lab bench in the bigger installations) and the bulk supplies of the needed chemicals.
Getting the correct concentration of boiler water treatment chemicals in the system was another matter. Just figuring out what treatment was needed and what concentration was not enough. Metering the treatment into the boiler water had to happen. This varied with the installation. In some plants such as those with open hotwells or feedwater makeup tanks, if the volume of the tank was known, the correct amount of chemical treatment might be dumped in at the start of a day's steaming or once each watch with the tank full. Mixing in the hotwells or feed tanks might happen using a boiler feed pump with the bypass/return valve opened to recirculate the water in the tank or hotwell and "turn it over" to get mixing done. In other plants, such as on some of the old Great Lakes ore carriers, boiler treatment was mixed in an open vat in the engine room. It was mixed with water, and a steam injector was used to pull the chemical solution out of the vat and push it into the hotwell or makeup tank. The injector, having direct steam contact, provided very thorough mixing action.
I've seen some very old boilers from the inside which were well maintained. COndition of a 110 year old Scotch Marine Boiler internally was quite surprising for how little pitting and wastage there was. I've seen much newer boilers with severe loss of material from corrosion and oxygen pitting. It is a function of water chemisret and firing/operating practices. It is also a function of when and where the steel in the boiler was made. For some reason, the older open-hearth steel plate used in the older boilers seems to hold up better as far as resisting corrosive attack. I've seen this same thing on old steel bridges which have shed their paint ages ago and seem to have only minimal corrosion. I am not sure why this is, possibly it had to do with the furnace lining in the Open Hearth furnaces (some being acid, some basic), and with the fact that a lot of new pig iron was used in each melt with a lower proportion of scrap steel -hence, less tramp elements. Newer steels tend to corrode and be more susceptible to chemical and corrosive attack than the older open hearth steels. I am no metallurgist, but I have seen enough to have some data to support this.
Boiler blowdowns will get rid of mud and the precipitates that the boiler compound knocks out of the water. The design of the boiler, whether it has good circulation, and no places where mud can collect despite blowdowns, also has a lot to do with it. I've seen the "mud ring" or "foundation ring" area on locomotive boilers that had severe wastage or loss of material right at the corner between the sheets and the top of the mud ring. The reason is mud lays there. Good boiler washouts and having properly located washout plugs is key to minimizing this. Laying up a boiler for storage is also key- the boiler has to be dried out after being drained down, and ideally, some dessicant is placed inside it. With the increased fear of asphyxiation hazards, the use of nitrogen to purge and fill boilers in layup is not done much anymore.
There are a great many factors which influence how well a boiler holds up in service. How hard a boiler is steamed is another factor. Something like the "Belle of Louisville" probably goes out on short cruises, makes some lazy turns and comes back to the dock. No hard steaming, boiler kept nice and hot between runs, and good firing practices and good water chemistry are likely all there to account for the long life of that boiler. No outlandish claims by the water treatment salesmen.
As for complications in arriving at the ideal water treatment, the answer is a test kit not too much different than a swimming pool water test kit can be used. Different reagents are provided. A conductivity meter is also used. Boiler water treatment can vary daily when drawing something like raw river water for boiler makeup. On some of the tourist railroads, makeup water, even from the local town mains, is tested daily to determine treatment. It is not complex to test the water, but it does require a little figuring to determine how much of each chemical is needed once the presence of certain dissolved minerals and content of dissolved oxygen and pH are all determined.