Respirometric In-Situ Methods for Real-Time Monitoring of Corrosion Rates: Part I. Atmospheric Corrosion

A novel respirometric approach to monitor atmospheric corrosion kinetics is presented. Simultaneous real-time monitoring of the H2 evolution reaction (HER) and the O2 reduction reaction (ORR) is possible with a combination of optical O2 sensor measurements with gravimetric volume sensitive techniques or pressure sensor based techniques in closed chambers. The respirometric method is a universal, non-destructive tool applicable to any metal or alloy. It shows a high sensitivity for low corrosion rates and has a high time-resolution. Different examples of relevant engineering metals and alloys will be provided. Mass loss validation measurements carried out at the end of exposure show a good correlation with the total recorded cathodic charge. For metals with different oxidation states the average valency in the corrosion products can be calculated from the cathodic charge together with mass loss. The versatility of the novel monitoring technique is further demonstrated by studying the influence of wet-dry cycling, temperature steps or changes in the gas composition in-situ. The rate of HER, ORR and total corrosion rate during these changing exposure conditions can be tracked directly on the same sample. Overall the new method contributes to bridging the gap between lab tests, accelerated testing and field exposure.