Fracture behavior of carbon steel pipe with local wall thinning subjected to bending load

To evaluate the structural integrity of power plant piping, monotonic bending tests were conducted on 4-inch diameter full-scale carbon steel pipe specimens with local wall thinning. The local wall thinning was simulated as a eroded part. Eroded part was subjected to tensile or compressive stress caused by applied bending load. The deformation or fracture behavior at maximum moments was classified into three types. When eroded part was subjected to tensile stress, ovalization and crack initiation was occurred. When eroded part was subjected to compressive stress, local buckling occurred. When fracture behavior was ovalization or local buckling, the applied load decreased slightly form the maximum load. On the other hand, in the case of crack initiation, the applied load was abruptly decreased from the maximum load, because of circumferential crack propagation. The relationships between applied load and load line displacement for eroded pipes were compared with those for cracked pipes. The maximum loads and total displacement for the eroded pipes were higher than those for circumferentially cracked pipes. Maximum moments predicted using a net section stress approach gave overly conservative evaluation for pipe specimens with local wall thinning. Safety margin for locally thinned pipes was discussed compared with the design maximum load. The safety margin in this paper were roughly more than 2 times. (author)