Overload Fracture of Flaw Tip Hydrides in Zr-2.5Nb Pressure Tubes

    Volume 2, Issue 4 (April 2005)

    ISSN: 1546-962X

    CODEN: JAIOAD

    Published Online: 4 April 2005

    Page Count: 29


    Shek, GK
    Principal Engineer and Senior Scientists, Kinectrics Inc., Toronto,

    Cui, J
    Principal Engineer and Senior Scientists, Kinectrics Inc., Toronto,

    Perovic, V
    Principal Engineer and Senior Scientists, Kinectrics Inc., Toronto,

    (Received 17 March 2004; accepted 18 August 2004)

    Abstract

    CANDU Zr-2.5Nb pressure tubes are susceptible to a crack initiation mechanism known as Delayed Hydride Cracking (DHC), which is a process that involves hydrogen diffusion, hydride precipitation, hydride region formation, and fracture at a flaw tip. An overload occurs when the hydrided region is loaded to a stress higher than that at which this region is formed. Service-induced flaws are present in some pressure tubes, which can act as crack initiation sites. Most experimental data to assess DHC initiation are obtained under constant loading conditions in which hydride formation and fracture occur at the same load, and therefore they are not suitable to assess crack initiation under overload condition. A series of step-wise increasing load experiments was performed on unirradiated Zr-2.5Nb pressure tube samples to determine the fracture stress of hydrides formed at notches with 15 μm root radius under different hydride formation stresses and thermal histories. Crack initiation in the overload tests was detected by the acoustic emission technique. The notch tip hydride morphologies were examined by optical and scanning electron microscopy. Test results indicated that the resistance to overload fracture was dependent on the hydride formation stress and thermal histories, which affected the notch tip hydride size, density, and distribution. Overload tests were performed at different temperatures, and a transition temperature to high resistance to overload fracture was observed.


    Paper ID: JAI12435

    DOI: 10.1520/JAI12435

    ASTM International is a member of CrossRef.

    Author
    Title Overload Fracture of Flaw Tip Hydrides in Zr-2.5Nb Pressure Tubes
    Symposium Zirconium in the Nuclear Industry: Fourteenth International Symposium, 2004-06-15
    Committee B10