Using Electrochemical Noise to Detect Corrosion: Evaluation of a Round-Robin Experiment Available to Purchase

Successful measurement of electrochemical noise (EN) signals requires that a number of preconditions be fulfilled. In particular, fundamental understanding of the dynamics of the corrosion system concerned must be combined with an appreciation of the way in which the measurements are made. Broader acceptance of the technique requires a joint effort by the various corrosion investigators and laboratories concerned. This, in turn, requires that a common basis for discussion be established. With this in mind, a round-robin experiment was organized on EN measurements. The participation of 17 organizations (universities, commercial firms, and research and development laboratories) from five countries was obtained. The experiment involved the investigation of EN signals from aluminum and stainless steel (SS) exposed under conditions in which pitting corrosion can occur. Data provided by the participants were analyzed according to various criteria. Evaluation methods included visual inspection of noise in the curves of potential or current vs time, calculation of the standard deviation, counting of transients, and transformation of measurements into the frequency domain. Almost all of the participants were able to detect differences in EN behavior during different stages of the experiment qualitatively. However, quantitative evaluation revealed a more complex situation. At times, differences in measured EN signal intensity of 2 orders of magnitude were obtained as a result of the different apparatus used (sensitivity, frequency range, etc.). Nonetheless, the fact that more than half of the participants reported data within a relatively narrow scatterband was a positive result. Additional analysis showed uniform, numerical treatment of the measured data was of decisive importance to obtain comparable results. It was clear that the complex interactions between the way in which EN data were recorded (sampling rate, filtering, online data manipulation, and base-line noise level) and the subsequent data evaluation should receive increased attention. Critical evaluation of results from the round-robin experiment showed comparable EN measurements can be made if suitable equipment is used and correct procedures are followed. The experience gained provided a sound basis for further development of EN as a tool for fundamental understanding of various aspects of corrosion and for the solution of practical problems of corrosion protection, particularly in the area of corrosion monitoring.