Steam-Water-Oxygen Cleaning and Passivation 
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Description of the method
Fig. 1. Cutting of convection superheater of high pressure with drops of reagent
The method of SWOCP lies in the fact that dozing oxygen into the boiler feed water and maintaining the required operational parameters allow to remove products of corrosion and installation from steam-water boiler circuit, with the formation of an oxide protective film on heating surfaces (see Fig. 1—3) which dramatically reduces the start-up time of the boiler, and enhances the protection of metal from corrosion for long periods of work and idle of equipment. SWOCP can be carried out during the first firing after installation of the boiler, making maximum use of the existing scheme. In this case economizer and evaporative paths of the boiler are processed by hot feed water and steam-water mixture, into which gaseous oxygen at a concentration of 1—1.5 g/kg are dozed under the special scheme.
The theoretical basis of SWOCP is the following. The oxidation of the metal with superheated steam or hot water causes a direct formation of a protective film of magnetite according to the equation:
3Fe + 4H2O → Fe3O4 + 4H2
This reaction occurs mainly at temperatures over 200 ºÑ with the absence of alluvial deposits on the inner surfaces of pipes. In this case the formation of protective film is highly dependent on ambient temperature (the reaction rate increases with the temperature growth parabolically). In the area of lower temperatures this reaction requires a certain redox potential depending on pH.
Fig. 2. A drop of reagent on the non-passivated surface after 5 minutes
This redox potential is primarily determined by oxygen concentration. Through increasing oxygen concentration (which is a basic point in SWOCP technology) magnetite-formation reaction proceeds according to the equation:
3Fe + 2O2 → Fe3O4
Obviously, the purer the initial pre-passivation metal surface, the more stable the magnetic film formed at its surface is. The tube-cleaning reaction for SWOCP is described by the following equation:
4FeO + O2 → 2Fe2O3
At the moment of phase composition alteration the strength of the deposits is damaged and they are removed by a speedy dynamic medium-flow. Under the influence of oxygen and high temperatures the protective magnetite film is formed on the cleaned surface.
Fig. 3. A drop of reagent on the passivated surface after 5 minutes
Quality oxide film neutralizes such destruction factors as, acid phosphate corrosion, acid attack during chemical cleaning, alkaline corrosion, hydrogen embrittlement, thermal fatigue, pitting corrosion etc. Proceedings in this area convince that oxide films resulted from SWOCP have maximum stability and optimally protect the metal against the above-mentioned destruction factors. The results of practical implementation of SWOCP on a large number of power units and boilers represent a plain evidence of this.