Determination of delayed hydride cracking (DHC) velocity in the axial direction for hydrided Zr-2.5 % Nb pressure tube material

Delayed Hydride Cracking (DHC) Velocity in the axial direction for Zr-2.5%Nb pressure tube containing approx. 59ppm H/sub 2/ has been determined under IAEA round robin DHC test program. The 17mm curved compact toughness (CCT) specimens provided by host laboratory (AECL) for IAEA co-ordinated Research Project, were used for this study. The CCT specimens were pre-cracked to approx. 1.7mm by fatigue at room temperature. After a thermal cycle to 315 deg. C and careful cooling to 250 deg. C, a constant load sufficient to give an initial K/sub 1/ value of 15 MPa(m)/sup l/2/ was applied. DHC started after a short incubation time and allowed to grow -1.5mm crack. The specimens were then fractured by post fatigue to identify DHC crack. Direct current potential drop method was used to detect and monitor the crack growth during Fatigue pre-cracking and DHC testing. DHC velocity of the provided samples was found in the range 7.73xl0/sup -8/ - 9.64 xl0/sup -8/ m/s. (author)