How did they rustproof the boilers in the steam days?
I have an outside wood stove thing and I find I can't rustproof it. The problem is heat - anything you put on burns off.
They would have had the same problem. Wonder what they did about it? Or did boilers and fireboxes really not get all that hot?
Do you mean the outside of the boiler barrel, or the inside facing the water?
Steel will rust if it gets into contact with water or water vapour. However at 250psi pressure - a typical steam locomotive boiler pressure - water boils at around 200 deg C. This means that the barrel will never get hotter than this value, but it also means that the outside will never get wet from liquid water as it will boil off and no vapour will condense. The outside was also protected from the elements by insulation - intended to reduce heat loss. Locomotive boilers rarely got cold, except at inspections, so the outside did not often get a chance to start rusting.
Inside the boiler the situation was very different. The surfaces were subjected to violent water flows and all sorts of corrosive chemicals that got in through the boiler feed water - only in the very late steam era was feed water properly treated - so the internal surfaces could be badly attacked.
The inside of the firebox was exposed the fire and all the corrosive gases that produced - so the erosion was chemical. The 'outside' of the firebox was surrounded by water - meaning that the metal of the firebox wouldn't have experienced a temperature much (i.e., more than a few degrees) greater than the water in the boiler - i.e., 200 deg C. Anyway in British practice the firebox was generally made of copper so the question of rusting didn't arise.
The locomotive designer got over the boiler corrosion problem by making the boiler barrel and the firebox much thicker than they needed to be to just withstand the pressure, and the boilers were scrapped when the thickness became marginal.
So the difference between your wood stove and a locomotive boiler is that there is no water jacket keeping the outside temperature under control, the steel used is, most likely, a steel chosen to be easily worked and not particularly corrosion resistant and the stove spends a lot of its time cold, so water vapour can get to work. Any heat resistant paint that you try has to be of the type used on exhaust pipes in the automotive world - and don't forget many of the really hot bits in that industry are castings which can better withstand the heat than fabrications. If your stove is not a casting, maybe you should look for one that is..!
