Effect of the interaction between two surface cracks in a pipeline on the stress intensity factor

In order to study the interaction between two surface cracks in an oil and gas pipeline, the effecting laws of the size and spacing of three-dimension surface cracks in the X80 steel pipe on the stress intensity factor were analyzed in this paper by means of finite element method. It is shown that the larger the spacing between two cracks (fixed crack and variable crack) is, the smaller their interaction is. When the spacing reaches or exceeds a certain value, its effect on the stress intensity factor is negligible, and only the effect of main cracks on the pipeline life shall be taken into consideration. With the decrease of the relative wall thickness ratio of the variable crack or with the increase of the shape ratio of the variable crack, the interaction between two cracks decreases. When the relative wall thickness ratio is lower than 0.2 or the shape ratio is higher than 0.8, its effect on the stress intensity factor is negligible, and the effect of the shape ratio on the maximum stress is much less than that of the wall thickness ratio and crack spacing on the maximum stress.