Effect of Dissolved Oxygen on Flow-Accelerated Corrosion in Neutral and Alkaline Solutions

摘要

Understanding of flow accelerated corrosion (FAC) is very important for wall-thinning management in commercial power plants. In our previous study, we proposed an FAC model taking into consideration the diffusion of soluble species. However, the effect of dissolved oxygen (DO) on FAC has not been clarified sufficiently. To improve the model, it is necessary to qualitatively evaluate the effect of DO on FAC. In the present study, the effect of DO on the FAC rate was experimentally evaluated in neutral and alkaline solutions at 413 and 453 K. In the neutral (pH~(298)K 7.0) and alkaline solutions (pH_(298K) 9.2) at 413 K, the FAC was suppressed when the DO concentration was increased to more than 55 and 12 ppb, respectively. At 453 K, the DO concentration required for FAC suppression was more than 30 and 4 ppb in the neutral solution (pH_(298k) 7.0) and alkaline solution (pH_(298k) 9.8), respectively. The DO concentration required for FAC suppression was not affected by the flow velocity according to the result predicted by the FAC model. However, it was higher than the value predicted by the FAC model. It is assumed that the discrepancy between the experimental and the predicted results was caused by the uncertainty in the diffusion coefficient of soluble iron and that the diffusion coefficient was affected by the distribution of soluble ferrous species. The modification of the diffusion coefficient improved predictive accuracy of FAC rate.