Estimation of the ductile unstable fracture of pipe with a circumferential surface crack subjected to bending

Several simple limit-load criteria have been proposed to predict in a light water reactor (LWR) pressure boundary piping the failure bending moment of a tough pipe which has a circumferential crack and is subjected to an external bending moment. However, some of those limit-load criteria give an unconservative prediction when the pipe has a short and deep circumferential surface crack. The present paper proposes a semi-empirical limit-load criterion on the basis of test results. This limit-load criterion gives a conservative prediction by choosing the optimum parameter, even if the pipe has an arbitrary circumferential surface crack. The present paper also proposes a method to calculate the tearing modulus T appL of the pipe containing the circumferential surface crack just after the ligament failure. Moreover, the compliance of a four-point bending machine is converted to an equivalent pipe length, which is used to calculate the value of T appL .