Abstract
Localized corrosion in plant operating conditions is often overlooked, partly due to the fact that none of the techniques commonly used today can provide realistic and effective monitoring of localized corrosion. Recent introduction and development of two new techniques (i.e., electrochemical noise and differential flow cell method) has renewed the interest in on-line localized corrosion monitoring in cooling water systems. Results on using the two techniques to monitor cooling water system localized corrosion in both bench-top and pilot plant scale (i.e., pilot cooling tower) tests are presented. The results show that the differential flow cell technique can be used to determine mild steel propagating localized corrosion rates accurately and reliably. On the other hand, electrochemical noise measurements alone did not provide accurate quantitative determination of corrosion rates because the anodic corrosion reaction and cathodic corrosion reaction did not occur at well separated sites and time in cooling water environments. Only very rough qualitative information regarding corrosion rate can be extracted from electrochemical noise measurement data. Spectral analysis of the potential noise data may give misleading information on the type of corrosion occurring. On the other hand, performing spectral analysis of current noise data may provide useful information on the type of corrosion (e.g., uniform or localized).
