Conventional and published international guidelines dictate chemical treatment of mixed metallurgy installations under a reducing environment, AVT(R).
A reducing environment is required to prevent oxidation of admiralty and/or copper alloys and the formation of copper hydroxides. The “protective copper patina” freely interacts with ammonia and/or the presence of amines to form weak complexes (e.g. ammonium copper cuprate complex) that are readily washed away promoting virgin base metal corrosion.
Copper(I) oxides formed under reducing conditions are less volatile than copper(II) oxides. Protection of copper is critically important to prevent transport of copper into the super heater and turbine. At pressures of > 2,300 psig copper readily transports into the steam and thus offers significant negative consequence to turbine integrity.
A trade off between protection of different metals has now been created. The lower operational pH required to protect copper alloys does not favor protection and oxide stability in the ferrous sections. The pH required for passivation of copper that may exist in the condensate (admiralty condenser), the low-pressure admiralty feed water heaters typically 70% copper 30% nickel, and the high-pressure feed water heaters typically 30% copper and 70% nickel, now exponentially increases ones’ utilities exposure to the risks of FAC.
This risk is especially great in the critical temperature and feed water path, as well as in the 2 phase/liquid film locations. FAC dissolution of oxides, thinning of virgin metal, transport and re-deposition of corrosion products and run the risks of catastrophic failures.
The Anodamine film forming mechanism and resultant isolation of the anode protection extends to both ferrous and copper based alloys. This unique approach to metal protection allows for virgin base metal isolation from the cooling medium, prevents under deposit corrosion mechanisms, but more importantly allows mixed metallurgy uses to successfully and with no risk, operate their installations under an AVT(O) treatment--leaving the use of oxygen scavengers obselete.
Removal of oxygen becomes irrelevant for protection of either ferrous or admiralty alloys and allows for termination of all reducing agents. Oxygen pitting is eliminated irrespective of oxygen concentration. Protection of both metals and their oxides is irrespective of ammonia and/or amine concentration. Mixed metallurgy units can now successfully operate AVT(O) with ammoniated highly buffered steam and condensate pH’s. Copper protection is ensured and residual oxygen prevents single-phase FAC.
Anodamine's surface active technology allows for complete elimination of reducing agents and allows optimum ferrous and admiralty metal protection independent of oxygen residual, ammonia dosage, load changes, or cycle air-in-leakage. Please see section elimination of oxide transport.
References on Anodamine and its ability to protect mixed metallurgies: