Research And Software Development Of Pipeline Fatigue Crack Propagation

As the artery of industries,pressure pipelines often cause safety hazards due to the existence of cracks,and even cause big safety accidents.Therefore,it is necessary to carry out safety assessment on pipelines regularly.The development of fracture mechanics makes the defect safety assessment method based on the principle of "fit for use" more and more widely used in pipeline defect assessment.Appendix C of Volume XI of the ASME provides the method of pipe defect assessment but the calculation process is quite complicated.In this thesis,The defect assessment software for pressure pipelines containing defects was developed based on the defect assessment process in Appendix C of Volume XI of the ASME standard.Meanwhile,ABAQUS and FRANC3 D finite element software were used to study the oblique cracks on pipelines.The main contents and conclusions are as follows:(1)The pipeline defect assessment software was developed based on the defect assessment process in Appendix C of Volume XI of the ASME standard.This software can achieve data reading function,batch processing kilometer,error correction,reporting function and so on,which can greatly simplify the assessment of pressure pipelines containing defects.(2)Some case validations were conducted on the pipeline defect assessment software.Results show that the calculation results by the software well agreeded with the manual calculation results and thus,the correctness of the software calculation was proved.(3)The effects of pipeline curvature radius,crack inclination angle,and crack length on the stress intensity factor of pipeline penetrating oblique cracks were studied.Results indicate that when the diameter of the pipeline is small,the influence of pipeline curvature on the stress intensity factor at the tip of the inclined crack must be considered.However,this influence decreases with the increase of pipeline diameter,and the decreasing trend gradually becomes gentle;For pipeline cracks,the influence of crack inclination angle and crack length on the stress intensity factor at the crack tip is also different from that of flat plates.There is a cross influence between pipeline curvature,crack inclination angle and crack length,especially for the Type II stress intensity factor at the crack tip.When the pipeline diameter is small and the crack length is large,this cross influence is significant.(4)Based on extensive numerical simulations,a correlation formula for calculating the stress intensity factor of pipeline penetrating oblique cracks with a ratio of inclined crack length to diameter ranging from 0.01 to 0.1was fitted.The formula error was within 3% compared with numerical simulations and so,the correlation formula can be used for safety assessment of inclined cracks on pipelines.