A steam boiler evaporates liquid water to form steam, or gaseous water; and requires frequent replenishment of boiler feedwater for the continuous production of steam required by most boiler applications. Water is a capable solvent, and will dissolve small amounts of solids from piping and containers including the boiler. Continuing evaporation of steam concentrates dissolved impurities until they reach levels potentially damaging to steam production within the boiler. Without blowdown, impurities would reach saturation levels and begin to precipitate within the boiler. Impurity concentrations are highest where steam is being produced near heat exchange surfaces. Precipitation would be expected to occur in the form of scale deposits on those heat exchange surfaces. Scale deposits thermally insulate heat exchange surfaces initially decreasing the rate of steam generation, and potentially causing boiler metals to reach failure temperatures.
