Electrochemical noise as a possible method for detecting stress-corrosion cracking

The characteristics of electrochemical noise generated by stress-corrosion cracking have been examined and compared to those of electrochemical noise generated during pitting and uniform corrosion. Potential and current noise were measured in a freely corroding system consisting of three electrodes made from a single specimen of AISI 302 stainless steel, in aqueous solutions with different concentrations of chlorides and with an added acid, at a raised temperature. A computer visualisation technique was also applied during the tests, using an optical microscope. In order to characterise the measured signals, and especially to distinguish between the electrochemical noise generated by pitting corrosion and the noise generated by stress-corrosion cracking, various parameters known from fractal theory and the theory of chaos were investigated. It is concluded that, by means of electrochemical noise measurements and their analysis, it is possible to distinguish between pitting and uniform corrosion. It is considered that it would be also possible to assess the number of crack initiation events from the electrochemical noise generated during the exposure of steel specimens to a pH-neutral NaCl solution.