Failure Mode and Failure Strengths for Wall Thinning Straight Pipes and Elbows Subjected to Cyclic Loading

It is important to assess the failure strengths for pipes with wall thinning to maintain the integrity of the piping systems and to make codification of allowable wall thinning. Full-scale fracture experiments on cyclic loading under constant internal pressure were performed for 4-inch diameter straight pipes and 8-inch diameter elbow pipes at ambient temperature. The experiments were low cycle fatigue under displacement controlled condition. It is shown that dominant failure mode under cyclic loading for straight pipes and elbows is crack initiation/growth accompanying swelling by ratchet or buckling with crack initiation. When the thinning depth is large, burst occurs after swelling. In addition, it is shown that pipes with wall thinning less than 50% of wall thickness have sufficient margins against seismic event of the safety shut down earthquake (SSE).