Influence of media degradation on the analysis of acoustic emission signals

Acoustic Emission signals are commonly used for corrosion damage detection, and subsequently analysed by using techniques both in time and in frequency domain. All of these techniques are based on the assumption that acquired waveforms are representative of the ones emitted by the Acoustic Emission bursts. Unfortunately, any alteration in the transmission medium, including the progression of the corrosion phenomena and changes in the stress distribution, influences the Acoustic Emission waveform, distorting the originally emitted one. Aim of this work was to evidence in which extent corrosion phenomena could influence the shape and propagation speed of the AE waves during in situ monitoring. Tests were performed using U-bend specimens. A continuous recording was carried out, in order to acquire the acoustic events generated by the corrosion phenomena, in addition to some specific test waveforms with predetermined shape, periodically emitted by one sensor and acquired from the other. It was observed that the changes of the acquired waveforms during time could be considered as an affordable and reliable indicator of the specimen degradation. On the basis of theseAcoustic Emission, Time domain analysis, Waveform, Modelling, Stress corrosion cracking observations the traditional patter analysis of the AE signals generated by the progression of corrosion mechanisms was reconsidered.