The leak-before-break (LBB) design of piping system for nuclear power plant has been based on the premise that the leakage due to the through-wall crack can be detected using leak detection systems before a catastrophic break. The piping materials are required excellent J-R fracture characteristics. However, ferritic steels for reactor coolant piping system have operated in a range of dynamic strain aging (DSA) temperature, so that the fracture resistance could be reduced by the influence of DSA under dynamic loading. Therefore, in order to apply the LBB design concept in piping system under seismic loading, both static and dynamic J-R characteristics must be evaluated. The materials used in this study are SA 516 Gr.70 for elbow pipe, SA 508 Cl.1a for main pipe and welding joints of main pipe. The crack extension during dynamic and static J-R tests were measured by the direct current potential drop and the compliance method, respectively. This paper describes the influences of dynamic strain aging on the J-R fracture characteristics with loading rate of the pipe materials and their welding joints.
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