Abstract
Corrosion monitoring during chemical cleaning of nuclear steam generators may well require higher reliability than is assumed necessary for routine industrial applications. Continuous corrosion measurements can be obtained with electrochemical techniques, in particular the linear polarization technique, using commercially available instruments. These are generally based on a particular calibration which represents a compromise of a wide variety of applications. As a consequence, the value indicated by these instruments for a particular application may be within a factor of two of the real value.
To determine the reliability of linear polarization in chemical cleaning solutions, extensive calibrations on the basis of weight loss were made. Generally, instrument results depend on solution resistance and on electrode configuration. As a consequence, the ratio of the real (weight loss) to the linear polarization rates is dependent on the magnitude of the corrosion rate itself.
In an attempt to improve the quantity and quality of the corrosion monitoring data for a field chemical cleaning, a computer data acquisition system was developed. The continuous corrosion measurements taken by the linear polarization instrument were coupled to the data acquisition system to reduce the electrochemical data for comparison to weight loss data. A description of this system is presented.
Results of extensive field test are also reported and indicate excellent reproducibility. Furthermore, acceleration of corrosion due to galvanic effects can be measured by linear polarization techniques. Therefore, the linear polarization technique is a reliable method to monitor corrosion rates on different metals, singly or galvanically coupled, in chemical cleaning solutions.
