A PLASTIC COLLAPSE ASSESSMENT PROCEDURE FOR MULTIPLE CRACKS UNDER INTERNAL PRESSURE

The influence of the interaction between two surface cracks on the limit pressure was examined by finite element analysis. Longitudinal semi-elliptical surface cracks were assumed to be on a straight pipe that was subjected to internal pressure. The changes in limit pressure due to the relative spacing of cracks and the geometries of the cracks and pipe were investigated. The intensity of the interaction depended on the relative distance between the cracks as well as the pipe and crack geometries. In all cases, the maximum magnitude of the reduction in limit pressure was equivalent to twice the crack face area. Based on the results obtained, criteria for the combination rules the for plastic collapse analysis were proposed. Furthermore, it was concluded that the surface length of the combined cracks could be assumed to be equal to the sum of their lengths. The ligament length was not included