Threshold stress intensity factor for delayed hydride cracking in Zr-2.5%Nb pressure tube alloy

Delayed hydride cracking (DHC) velocity was determined at 203,227,250 and 283 degrees C using 17 mm width curved compact toughness specimens machined from an unirradiated Zr-2.5 wt.% Nb pressure tube spool, gaseously charged with 60 ppm of hydrogen by weight. Single CT specimen was used to determine DHC velocity at a constant temperature for a range of stress intensity factor (K-1) obtained by load drop method. For a given temperature and K-1 > 15 Mpa m(1/2), DHC velocity was found to be practically independent of K-1. For 15 > K-1 > 10 MPa m(1/2), DHC velocity decreased significantly with decrease in stress intensity factor and extrapolation of the data suggested the threshold stress intensity factor to be about 9-11 MPa m(1/2) in the aforementioned temperature range. The activation energy associated with DHC was observed to be 35.1 kJ/mol. (C) 2009 Elsevier B.V. All rights reserved.