Delayed hydride cracking velocity in Zr-2.5Nb: detection by acoustic emission and theoretical model testing

Acoustic emission (AE) detects elastic waves generated during delayed hydride cracking (DHC). The detection of the first acoustic signal is used to measure the propagation time. This time and the crack length measured on the broken specimen are used to determine the DHC velocity. In this work, DHC tests were carried out on Zr-2.5Nb alloy from CANDU pressure tubes. Linear relationship between cumulative count rate and cracking velocity was corroborated. It is generally accepted that the hydrides crack when they reach a critical length; nevertheless, in this work the number of signals generated during typical DHC test were higher than expected from that assumption. Dutton and Puls DHC model with some parameters calculated by Shmakov et al. was used to test out against experimental data. This modification is an original approach that makes more rational the DHC velocity calculation, avoiding arbitrary parameter selection. Good agreement was obtained for two different CANDU pressure tubes.