Monitoring hydrogen embrittlement cracking using acoustic emission technique

Acoustic emission during delayed failure of hydrogen-charged low-alloy high-strength steel has been investigated. Tests were carried out at room temperature using standard ASTM three-point hend specimens. It was found that the cumulative acoustic emission counts rose
slowly in discrete steps with increasing time in the initial stage of the embrittlement process, whereas it rose rapidly in the later stage prior to fracture. It was also observed that the initial embrittlement phase consisting of microcrack nucleation is characterized by low-amplitude
(35-55 dB) signals only, whereas the rapid crack growth region is marked with highamplitude (60-100 dB) signals. These observations indicate that such a change in the pattern of cumulative counts together with the level of amplitudes of the generated signals can he used to detect the so called "incubation period" for hydrogen embrittlement. This kind of early detection of critical cracks may help towards better fracture control.