Influence of the materials mechanical properties on the structural integrity assessment of cracked piping of PWR nuclear reactors primary systems

Abstract

The structural integrity assessment methods of cracked components manufactured with ductile materials request the evaluation of parameters of the Elastic-Plastic Fracture Mechanics (EPFM) and of the Limit Load Analysis (LL). Since the use of numerical methods to apply the concepts of EPFM and LL may be costly and time demanding, the existence of the so-called simplified methods for cracked piping evaluation is still considered of great relevance. The following simplified methods for evaluation of the ductile behavior of piping systems are available in the literature and were considered in this work: J-T Method (J Integral versus the Tearing Modulus T), R6 Method and DPFAD Method (Deformation Plasticity Failure Assessment Diagram). The methods were applied for the computation of instability loads of some piping systems, with through-wall circumferential cracks, subjected to bending moments, made with high toughness steels. Changes in the values of the materials properties were considered. The estimated instability loads were compared with experimental results obtained in the literature. From those comparisons, some conclusions and comments could be made, being the main focus of the work the aspects related to the characterization of the materials properties to the appropriate application of the methods to cracked piping of pressurized water nuclear reactor (PWR) primary systems, in evaluations of the LBB (Leak-Before-Break) concept. As the methods are strongly dependent on the properties, some recommendations must be followed. These properties are basically expressed by means of the stressstrain curves and fracture resistance curves (JR curves).