On the opportunity to use non-intrusive acoustic emission recordings for monitoring uniform corrosion of carbon steel and austenitic stainless steel in acid and neutral solutions
Résumé
Uniform corrosion of steels is responsible for the early damaging of many industrial parts and its control and monitoring prevent against significant economic and environmental failures. Yet, classical estimation of corrosion damage gives only the result of the average corrosion rate but not the 'instantaneous' value. In that context, acou stic emission (AE) technique, based on the rapid release of energy within a material generating a transient elastic wave propagation, was carried out to get quantitative information on corrosion evolution. Uniform corrosion conditions close to industrial ones were simulated with the use of a pilot device, allowing the simultaneous control and measurement of the temperature and pH of the saline and/or acidic solutions, as well as the amount of dissolved oxygen and the fluid velocity, together with AE recordings. Emission so urces during uniform corrosion of carbon steel and austenitic stainless steel were then identified as hydrogen release, friction of hydrogen bubbles and evolution of corrosion deposits, each of these mechanisms inducing the emission of AE signals with specific parameters. Moreover, it appears clearly that acoustic emission measurements are in good correlation with aggressiveness of the corrosive media, and a semi-quantitative correlation is obtained between AE activity and corrosion rate for austenitic stainless steel. Whereas initial surface conditions greatly influence the acoustic activity, AE monitoring appears to be a rewarding technique for detecting corrosion rate evolutions during process modifications.