摘要
Abstract
In order to study the influence of surface cracks on long-distance pipelines,FRANC3D was used to solve the stress intensity factors at the tips of cracks of different sizes on the outer surface of the pipeline,and ABAQUS was used to solve the equivalent plastic strain of the pipeline through the contour integral method.The double tangent criterion and double slope criterion were used to respectively solve the ultimate load.Based on these analyses,the safety assessment of pipelines with cracks was carried out according to the failure assessment diagram(FAD diagram).Results show that the length to depth ratio of cracks affects the propagation trend of cracks.For axial surface cracks on pipelines,"wide and shallow"cracks have a higher stress intensity factor at deep depths and a stronger radial propagation trend,while"narrow and deep"cracks have a higher stress intensity factor at the edges and a stronger axial propagation trend.At lower pressures,the size of cracks on the outer surface of the pipeline has little effect on the equivalent plastic strain.However,as pressure increases,the sensitivity of the equivalent plastic strain at the crack tip to crack size increases,which can easily lead to crack propagation.According to the FAD diagram,a safety assessment was conducted on pipelines containing cracks of different sizes,indicating that surface cracks with a depth of 2 mm<crack depth<7 mm and a length of 6 mm<crack length<16 mm are within an acceptable range and do not affect the safe operation of the pipeline.关键词
表面裂纹/长输管道/失效评估图/应力强度因子/极限载荷/安全评定Key words
surface crack/long-distance pipeline/failure assessment diagram/stress intensity factor/ultimate load/safety assessment分类
石油、天然气工程
