Third-order spectral characterization of acoustic emission signals in ring-type samples from steel pipes for the oil industry

Third-order cumulant spectra are used to characterize acoustic emission events in ring-type samples from steel pipes for the oil industry. A cut segment of chord allows the coupling between a sample and the mechanical excitation device. Diagonal bi-spectrum allows the separation of the primary (original) deformation from the reflections produced mainly in the suppressed chord. These longitudinal reflections can hardly be extracted via second-order methods, e.g. wavelet packets and power spectra, because they are partially masked by both Gaussian and non-Gaussian noise. Sample registers were acquired by wide frequency-range transducers (100–800 kHz) and digitalized by a 2.5 MHz, 8-bit ADC.