Failure Evaluation of Pressurized Double-Cracked Tubes
Hostile environments and mechanical loading combinations result in failure when through-wall or part-through-wall cracks are present in nuclear power plants steam generator tubes. When the steam pressure magnitude becomes high enough, a tube might burst or existing single crackssizes might become sufficiently large or existing small neighboring cracks might coalesce which leads to an unacceptable operational condition. All of the above result in catastrophic failureof the steam generator tube. This study is aimed at investigating failure of steam generator tubes under internal pressure in the presence of multiple cracks. Failures in steam generator tubes due to leak and rupture for single crack configuration in tubes are well documented in the literature. However, when multiple cracks interact, the tube pressure under which the ligament between cracks fails could be far less than the critical pressure for a tube with an individual crack. This failure pressure is termed coalescence pressure. In this investigation, both leak and rupture failures will be considered for tubes with two axially aligned and offset cracks. For leak failures, the fracture mechanics approach is used to investigate crack coalescence due to crack propagation mechanisms. The J-integral determined and used for failure parameters. For rupture, flow stress used as failure criteria. Finite element simulations are used to determine the above stated leak and rupture parameters. Twodifferent models are developed in ABAQUS (a commercialfinite element software) using Line-spring elements and 3D solidelements.Leak and rupture failures are assessed for varying pressures and varying crack depths (70 - 100% of tube thickness). The obtained finite element results are compared with each other and experimental results.