Assessment of hydrogen embrittlement of Zircaloy-2 pressure tubes using unloading compliance and load normalization techniques for determining J-R curves

The fracture toughness of unirradiated cold pilgered pressure tubes (PT) has been studied as a function of temperature and hydrogen levels. Two methods of J-R curve evaluation, from small curved compact tension specimen, have been employed. In addition to the single sample unloading compliance method (298-473K), a recently developed load normalization technique, using LMN function, has been used for temperature up to 548K. The effect of circumferential hydrides on fracture toughness parameters has been studied. The results of both techniques are compared to find out the suitability of load normalization method in such hydrogen embrittlement studies. The results show large deleterious effects of circumferential hydrides at lower temperatures and gradual restoration of toughness with increase in temperature. The study also shows that load normalization can be used to evaluate J-R curve in the cases where slow stable crack growth takes place. Hydrogen embrittlement can be evaluated using load normalization method for temperatures higher than 423K.