Hydrazine injection to feedwater is generally used for of steam deoxigination in IEC Power Plants (PP). This work is based on result of laboratory investigation that is performed during lust ten years, while schedul PP interrupting. In oxygen presence copper-ammonia complex (CAC) is generated. Transferred through the steam circle CAC dissociates and copper beads deposit on evaporator tube internal surface. A following idea that seems be enough versivilar. As condenser tube material as steel components are leached out of the metal due to metal- ammonia and metal-hydrazine complexation. The complexation occurs under closed-to-equilibrium condition, so the complexes may as
disotiate on a place as exist in steam flowing through the all network.
In occurig inside of evaporator, complex dissociation results by deposition of composite oxides and metal bead. This deposit is porosive, conductive and saturated by steam. The last contains nonremoved oxygen. Hence said general attack is being forced by pitting because of Cu-Fe galvanic interaction. Contacted with the steam, condenser tube also reacts with hydrazine and ammonia. Cu, Zn from brass/Cu, Fe, Mn and Ni from copper nickel alloy are being eluted. Soluble complexes
pollute feed water. Transferred with steam Cu, Zn, Fe, Mn and Ni presence on every surface that contacts with the steam.
Key words: corrosion, ammonia, hydrazine, copper, nickel, zinc, steel, complexation, thermal power plant.