Research On Ultimate Load Of Pipeline With Internal And External Defects Based On Interference Action

With the continuous development of oil and gas pipeline construction in China,a large number of high-grade and large-diameter natural gas pipelines are in service,and corrosion defects will inevitably occur in the inner and outer walls of the pipeline.Internal and external wall defects will interfere under certain conditions,thus affecting the failure mode of the pipeline and ultimate load.At present,the research on double defects focuses on the same surface defects,and the treatment methods for internal and external defects are relatively conservative moreover it is rare to conduct research on the interference of internal and external defects.The internal and external defects have not caused the pipeline to completely lose its bearing capacity,the relatively conservative pipeline safety evaluation will increase the maintenance and replacement of the pipeline,which will cause unnecessary economic waste to a certain extent.Therefore,the study of the ultimate load of internal and external defects pipelines based on interference has fairly good theoretical value and engineering guiding significance.Based on the data of a river crossing section of the China-Myanmar natural gas pipeline project,the X80 straight pipe of model D1016×18.4 is used as the research object to carry out the theoretical analysis of mechanical properties of pipelines under internal pressure.Selected the plastic failure criterion as the pipeline failure criterion,the double elastic slope method as the method for determining the ultimate load of the pipeline.Combining ABAQUS finite element simulation to calculate the ultimate load of pipelines with single-defect pipelines.The overall average error between the finite element value of the ultimate load and the value of current domestic and international standard specification calculation formula are only 4.58%,which explains the steps and feasibility of the ABAQUS research method.Based on the axial distance of five kinds of pipelines,the internal and external defect pipeline models of twenty-five defect depths,twenty-five defect lengths and four defect widths were respectively established by ABAQUS finite element software to analyze,and a total of 282 ultimate load values of different defect parameters were obtained.Analyze the influence of the circumferential distance and the axial distance on the ultimate load of the pipeline to establish the key influencing factors.Carry out the differential analysis of the external double-defect pipeline,the internal double-defect pipeline,and the internal and external defect pipeline.Considering the interference effect of internal and external defects,respectively analyze and discussed the sensitivity of the depth,length and width of the internal and external defects to find out the influence law of various defect parameters on the ultimate internal pressure load of the pipeline.Analyzing pipe stress based on the variation of depth,length and width of the defect to find out the stress distribution law of the pipe under the ultimate load.Through multivariate nonlinear regression fitting by MATLAB software,the formula for calculating the ultimate load of internal and external defect pipelines is obtained.Through the calculation of the limit influence distance of 50 different defect parameters,study the influence range of internal and external defect interference,and respectively analysis the sensitivity of the depth and length of the defect and summary the law.Through multivariate nonlinear regression fitting by MATLAB software,the calculation formula of the limit influence distance of internal and external defects is obtained.On the basis of the double defect limit influence distance,the finite element calculation result of the ultimate load and its fitting formula are checked to determine the effective of finite element research method and explain the accuracy and applicability of the fitting formula.Based on the "pipeline ultimate load" and "double defect limit influence distance" fitting formula,programmed by Visual Basic software to obtain the ultimate load calculation software for pipelines with internal and external defects.Through the double defect limit influence distance to determine whether the defect interferes,calculates the limit load of the pipeline according to axial position of different defects and defect size parameters,which provides reference for pipeline safety evaluation and integrity management.