Characterization of the oxide formed in the presence of poly acrylic acid over the steam generator structural materials of nuclear power plants

Oxide deposited on carbon steel surface exposed to secondary side water chemistry conditions of nuclear power plant in the (a) absence and (b) presence of poly acrylic acid (PAA), a polymeric dispersant. [Display omitted] ► PAA cannot prevent the formation of inner oxide arising out of corrosion. ► Inner oxide formed in presence of PAA is protective. ► Crystallites formed in the presence of PAA are smaller in size. ► PAA prevents the formation of outer oxide layer arising out of precipitation. On-line addition of polymeric dispersants, such as poly acrylic acid (PAA), to the steam generator (SG) results in the formation of a better protective inner oxide layer that reduces subsequent corrosion of structural materials. Its dispersive action inhibits the growth of a secondary oxide layer thereby facilitating their easy removal. This paper discusses the effect of PAA on the nature of oxides formed over the surfaces of SG. In the case of carbon steel, the inner oxide layer (magnetite) formed in the presence of PAA was protective. Electrochemical studies showed a minimum concentration of 350ppb of PAA was found to be optimum. On the monel surface, in the absence of PAA, nickel ferrite was formed while in the presence of PAA, the oxide formed was a mixture of oxides of copper and nickel. A concentration of 700ppb of PAA was found to be optimum for monel. In the case of incoloy, the effect of PAA was not discernible except for the size and morphology of the crystallites formed.