Z-Factors for Feeder Bends With Planar Axial Flaws

Article C-6000 of Appendix C of ASME Section XI includes Z-factor load multipliers for straight pipes with circumferential flaws. Application of this article is limited to straight pipes with nominal pipe size (NPS) larger than 4 and materials with fracture toughness J_Ic higher than 105 kJ/m². Section XI of the ASME B&PV Code does not provide Z-factors for pipes with axial flaws, even for pipes with NPS≥4. Feeders are small diameter pipes (NPS≤2.5) used in a primary heat transport system in the CANDU nuclear reactors. Developments of Z-factor load multipliers for warm-bent feeder bends with axial flaws under pressure are presented in this paper. An empirical approach was adopted using experimental results from the Feeder Bend Testing Program founded by the CANDU Owners Group. The elastic-plastic fracture mechanics stress has been defined by failure stress from the experiments. Limit load solutions for elbow/bends recently published by Kim et al. were discussed. Additionally, lower bound limit load simulations were performed using finite element models implemented for ANSYS. The results from straight pipe models exhibited good correlation with analytical solution. Numerical simulations for elbows/bends showed analogous trends for limit load of elbow/bends with axial cracks as reported by Kim et al.