There are several way to go about cleaning a boiler. If you are removing the tubes you have the option of sandblasting, needlescaling, or wirebrushing the entire inside of the boiler. You might end up using a combination of these methods for the best results. Make sure you have a good confined space entry plan, air to breathe, and GFIs on all cords. If you are not removing the tubes and the boiler will hold water you can hire a boiler water treatment company to perform an acid wash on the boiler. All methods have items you need to address. A good boiler flush to remove loose junk from inside is to pop the dome cover off, remove the washout plugs, drag the locomotive to your local water tower, insert the spout and flush!
Tom Gears