to a pH of 9.0 or higher, to reduce oxidation and to support the formation of a stable layer of magnetite on the water-side surface of the boiler, protecting the material underneath from further corrosion. This is usually done by dosing alkaline agents into the feed water, such as sodium hydroxide (caustic soda) or ammonia. Corrosion in boilers is due to the presence of dissolved oxygen, dissolved carbon dioxide, or dissolved salts. Fouling Deposits reduce the heat transfer in the boiler, reduce the flow rate and eventually block boiler tubes. Any non-volatile salts and minerals that will remain when the feedwater is evaporated must be removed, because they will become concentrated in the liquid phase and require excessive "blow-down" (draining) to prevent the formation of solid precipitates. Even worse are minerals that form scale. Therefore, the make-up water added to replace any losses of feedwater must be demineralized/deionized water, unless a purge valve is used to remove dissolved minerals. Caustic embrittlement Priming and foaming Locomotive boilers Steam locomotives usually do not have condensers so the feedwater is not recycled and water consumption is high. The use of deionized water would be prohibitively expensive so other types of water treatment are used. Chemicals employed typically include sodium carbonate, sodium bisulfite, tannin, phosphate and an anti-foaming agent. Treatment systems have included: Alfloc, developed by British Railways and Imperial Chemical Industries Traitement Integral Armand (TIA), developed by Louis Armand Porta Treatment, developed by Livio Dante Porta See also Boiler feedwater pump Evaporator Helamin References Shun'an, C. , Qing, Z. , & Zhixin, Z. (2008). A study of the influence of chloride ion concentration on the corrosion behavior of carbon steel in phosphate high-temperature boiler water chemistries. Anti-Corrosion Methods and Materials, 55(1), 15–19. Sendelbach, M. (1988). Boiler-water treatment: Why, what and how. Chemical Engineering, 95(11), 127. Characteristics of boiler feed water. (n.d.). Retrieved March 21, 2015, from http://www.lenntech.com/applications/process/boiler/boiler-feedwater-characteristics.htm External links Boiler Feedwater System Configuration Power station technology Boilers Chemical process engineering Steam locomotive technologies