Advanced Corrosion Control at Chemical Plants by Using a New Corrosion Monitoring Technique

Abstract

A modified noise resistance method was developed, and it was applied to corrosion monitoring at a chemical plant. An electrode unit and a data-acquisition system capable of measuring the electrochemical noise under the site's conditions were also developed. The noise resistance, R_n, has been regarded as an equivalent factor to the polarization resistance, R_p. However, it was considered that this estimation might not be appropriate because the real dimension of the anodic and cathodic area possibly vary with immersion time as well as with the combination of materials and environments. Therefore, a new factor, F, was introduced instead of the Stern-Geary constant, B, for the conventional polarization-resistance technique. The F was named corrosion factor. In the modified method, the corrosion rate, CR, is defined as follows; CR=F·I/R_n. The F was experimentally determined from the relation between the mass-loss rate and the R_n of the electrode made with an equivalent material to the objective under monitoring. A test solution which simulated the environment of the site was also used for the experiment. Applying this modified method, the occurrence of unexpected and intense general corrosion at a plant was successfully detected. The corrosion loss estimated by the method fairly agreed with that at the site in thickness of the damaged tubes.