Hydrazine does not contribute solids to the system, soboiler blowdown, or the mechanical removal of solids fromthe after-boiler section as sludge, is reduced. It also promotesthe formation of the protective magnetite film on the boilertubes and drum, and converts red iron dust (hematite) tomagnetite. It is because of these passivation effects that anexcess of scavenger to oxygen is required when changinga boiler system form a non-passivating scavenger to onewhich passivates.Hydrazine is not without limitations. It is not considered“volatile”, so it does not leave the boiler with the steam toscavenge oxygen and passivate metal throughout thesystem. In boilers operating above 400˚F (205˚C), it candegrade to ammonia and volatilize with steam, and, in thepresence of oxygen, attack metals containing copper:
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