LBB condition for pipe with a circumferential crack under cyclic bending moment

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LBB condition for pipe with a circumferential crack under cyclic bending moment

Yoo, Yeon-Sik / Okamoto, A. / Ando, K.

Most pipe system receive cyclic load. And for a seismic design, low cyclic fatigue behaviour is important. However, most studies on LBB (Leak Before Break) were concerned with monotonic load and LBB studies for cyclic load are very rare. To that purpose. LBB condition for pipe with a circumferential crack under cyclic axial load and bending moment was proposed in this study. The main results obtained in this study were as follows: (1) An evaluation model was proposed for the fatigue LBB condition in consideration of geometrical compatibility at crack penetration. (2) Based on the above model and the characteristic of fatigue crack penetration behaviours, the fatigue LBB condition was proposed. The main parameters to control LBB condition under monotonic load were initial crack angle, initial crack depth and mechanical properties. But, it was concluded that the main ones to control LBB condition under cyclic load were initial crack angle and mechanical properties. (3) On pipe with an elliptical crack, greater safety margin was evaluated under cyclic bending moment than under cyclic axial load, compared with pipes with a simple through crack.