Products and Surface Topology

Fig- 7.32 (a) Pitting corrosion of inner wall of boiler tube due to insufficient deaeration of feedwater. Corrosion products brush removed from right side of section, (b) Cross section of pipe wall showing distribution of pits 

Pitting of plain carbon steels also is associated with small deposits of inert materials. At near-neutral and higher bulk pH values, oxides readily form on an initially clean surface as previously described. These surfaces can support cathodic reactions, particularly the reduction of dissolved oxygen. Due to an oxygen deficiency under the inert deposit, protective films are destroyed, and dissolution of the metal leads to the buildup of Fe2+ ions. These ions hydrolyze according to the reaction  

34 Idealized polarization curve for iron in neutral solution. Idealized cathodic polarization curves for sodium nitrite and oxygen under aerated and deaerated conditions. Ecorr,icorr indicated for each environment 

Effect of NaN02 concentration as an inhibitor for the corrosion of low carbon steel in water. Exposure was two months at room 

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