In power plants, piping installations with a circumferential crack can be operated under combined bending and torsion. ASME Boiler and Pressure Vessel code Section XI non-mandatory Appendix C provides the flaw evaluations for fully-plastic fracture using limit load criteria for the structural integrity of the cracked pipes. According to the recent version of Code, combined loading is provided only for membrane and bending. Even though actual operating conditions have torsion loading, the methodology for evaluating torsion load is not established, and assumed torsion is relatively small compared to membrane and bending and can be ignored in the evaluation.
This paper provides the results of limit load analyses by using finite element models for circumferentially cracked pipes under pure bending, pure torsion and combined bending and torsion with tension. Theoretical limit load solutions based on net-section fully-plastic criteria are compared with the results of finite element analyses. The validation of theoretical limit loads for combined bending and torsion with tension is discussed.