Initiation and propagation steps in pitting corrosion of austenitic stainless steels: monitoring by acoustic emission

Acoustic emission (AE) technique was used to study the development of pitti ng corrosion on AISI 316L austenitic stainless steel, in a 3% NaCl solution acidified to pH 2. The initiation and the propagation steps of the pits we re separately studied owning to a specific polarization procedure. It appea rs that the initiation step of pitting corrosion is not significantly emiss ive, whereas the propagation step is characterized by the emission of reson ant signals. This kind of AE signals is representative of the development o f the pits in the form of occluded cells, in which the evolution of hydroge n bubbles appears to be the emissive phenomenon. A subsequent change in the mode of corrosion, i.e. the transfer to uniform corrosion, can be detected by the AE technique. (C) 2001 Elsevier Science Ltd. All rights reserved.