Electrochemical investigations of SG tubes in AVT media under accelerated conditions

Under deposit boiling in boilers can lead to accelerated chemistry conditions. In the absence of external impurities, the effect of the amine and amine salt were studied. The effect of the residual hydrazine in the boiler was also investigated with varying concentration up to 100 ppm. Studies were carried out on Incoloy-800 in morpholine medium. In pure morpholine medium, the open circuit potential was found to shift in the active direction with time for 10 ppm as well as 100 ppm morpholine. The polarization resistance values were found to decrease with increase in temperature under aerated condition in Incoloy-800 indicating an increase in corrosion rate. In 10 ppm morpholine and l ppm morpholine nitrate, the corrosion potential was found to shift in the active direction. With increasing amine nitrate concentration the OCP was found to shift in the noble direction at higher temperature under aerated condition. The effect of hydrazine on 10 ppm morpholine and 10 ppm morpholine nitrate At 30 degC, the presence of a wider passive region on the cathodic portion of the polarization curve was more pronounced in Monel. Both Monel and Incoloy exhibited an active to passive transition. The corrosion potential was found to shift in the active direction with increasing hydrazine concentration for Incoloy. Data on similar investigations performed on ETA is also discussed in this paper. (author)