A Combination Rule for Circumferential Surface Cracks on Pipe Under Tension Based on Limit Load Analysis

The influence of the interaction between two surface cracks on the limit load (LL) was examined by finite element analysis. Circumferential surface cracks were assumed to be on a straight pipe that was subjected to a uniform tensile load. The change in LL due to the relative spacing of cracks and the geometries of the cracks and pipe was investigated. The evaluated LL was equivalent to that of the coalesced crack when the cracks were on the same plane or their offset and horizontal distance were the same, although LL decreased as the offset distance increased in the other cases. It was also revealed that the magnitude of LL depends on the offset distance of the cracks and ratio $Rm/t$⁠, where $Rm$ is the mean radius of the pipe and $t$ is the thickness of the pipe. Based on these results, combination rules for LL were proposed for integrity assessment of cracked pipes.