Numerical Simulation of Stress Intensity Factor for Socket Weld Toe Cracks in Small Branch Pipes

Vibration fatigue of small branch pipes usually induces weld toe cracks. Some cracks will cause advertently shutdown of the Nuclear Power Plants (NPPs). Moreover, to judge the vibration fatigue failure is the bottle neck in structure health monitoring of the small branch pipes in NPPs. In order to solve this problem, a socket weld pipe was simplified as the cantilever beam model, and the stress intensity factor (SIF) was calculated by the ABAQUS software and ZENCRACK software in this paper. The effects of crack depth, circumferential crack size and working load on SIF were discussed. The analysis results show that the SIF for outer surface circumferential crack distributes as an upside down “U” alphabet. And the maximum value of SIF is at the deepest point of the crack and is a linear increasing function of external load P. Basing on the plane strain fracture criterion, critical crack sizes bearing different external loads were calculated. With the increasing of loads, the critical crack size decreases. These critical values can be applied as the benchmark for evaluating the vibration fatigue failure in the structure health monitoring of small branch pipes in NPPs.