Study On The Numerical Solution Of The Stress Intensity Factor For Pressure Pipes

With the rapid development of the world economy,the strategic position of oil and gas is more and more prominent.Long distance transportation of oil and gas in the world is usually carried by pipe,so the safety of long distance pipe becomes more and more important.In the investigation of the oil and gas explosion accidents in recent years,it was found that most of the accidents were caused by the defects of pipe.Due to the problems of manufacturing process and corrosion,long distance oil and gas pipe may produce defects in the process of use,among which crack defects are the most dangerous.Based on the theory of fracture mechanics,the finite element software ANSYS is used to study the numerical solution of stress intensity factor for cracked pressure pipes,which has certain theoretical and practical significance.The stress intensity factor can be used to characterize the strength of the singular stress field at the crack tip,and it’s an important parameter for the study of fatigue and fracture problems.In the paper,the stress intensity factors at the crack tip of plant and pipe are calculated by using 1/4-node method,the two-node displacement extrapolation method,the two-node stress extrapolation method,the multi-node displacement extrapolation method,the multi-node stress extrapolation method and the J-integral method respectively.The results of numerical solution and analytical method are compared,and the influence of geometric parameters and mesh size of the two models on the calculation error is analyzed.The analysis results show that all of the above six methods can obtain satisfactory calculation accuracy when the mesh size is small.With the increase of mesh size,the calculation error of two-node displacement extrapolation method and two-node stress extrapolation method increases rapidly,while the multi-node displacement extrapolation method,multi-node stress extrapolation method and J-integral method are less affected by the mesh size.1/4-node method is less affected by the mesh size than two-node displacement extrapolation method,two-node stress extrapolation method,but higher than the other methods.Because the influence of crack tip singularity on the accuracy of stress solution is higher than that on displacement.In this paper,the effects of the pressure,crack length(circumferential crack angle),the ratio of thickness to diameter and inner diameter on the stress intensity factor at the tip of axial crack and ring crack are studied by using multi-node displacement extrapolation method.The results show that thestress intensity factor increases linearly with the increase of the pressure and superlinearly with the increase of crack length.With the increase of ratio of thickness to diameter,the stress intensity factor decreases gradually.The ratio of thickness to diameter remains constant,and with the increase of inner diameter,the stress intensity factor decreases gradually,and the decreasing rate becomes slower and slower.In this paper,by using different finite element methods to calculate the stress intensity factors of axial and ring cracks in pipe,the accuracy of different finite element methods is compared and analyzed,and the inner pressure of pipe,crack length(circumferential crack angle),ratio of thickness to diameter and inner diament are also analyzed.and the relevant conclusions are significant to ensure the safe operation of pipeline containing defects.