Phosphoric-Acid-Cleaning of Boilers

Abstract The demand for clean surfaces, the ability to reach otherwise inaccessible areas, and the speed of the process have been largely responsible for the acceptance of acid-cleaning of high-pressure, high-heat-input boilers. It provides a convenient method with a minimum of labor for removing rust and mill scale from new boilers and water-formed insoluble deposits from old ones. Despite its recognized undesirable features, inhibited hydrochloric acid is generally used for this purpose. Because of the limitations and adverse effects of hydrochloric acid, which were quite evident during the authors’ experience in the cleaning of two boilers, the possibility of using phosphoric acid for boiler cleaning was investigated in the laboratory. These experiments demonstrated that inhibited phosphoric acid is a good solvent without the unfavorable properties and characteristics of inhibited hydrochloric acid. Guided by the results of this study, inhibited phosphoric acid was used successfully for removing rust and mill scale from a new boiler.