Research On Integrity Assessment Of Long Distance Pipeline Based On The Magnetic Flux Leakage Testing

Long distance oil and gas pipelines can be corroded by internal and externalenvironmental factors after long term running, that will reduce the actual operatingpressure and the transport function, and even pose a potential threat to the security of thepipeline. In order to determine whether the pipeline can run under the required operatingpressure safely, avoid the occurrence of oil and gas pipeline accidents, the pipelineintegrity must be evaluated.Aiming at the problem of integrity evaluation of corrosion defect pipeline, ASMEB31G criteria, Rstreng criteria, DNV RF-101criteria and their algorithms were studied，thepipeline integrity evaluation software was designed using the graphical programminglanguage LabView, to achieve the integrity evaluation of single point corrosion defect andthe magnetic flux leakage defect detection table two evaluation function, four importantparameters can be calculated, including corrosion defect depth ratio,estimated repairfactor,safety operating pressure, and repair advice. Evaluation result of the same corrosiondefect assessed by different criteria were calculated, and different length and depth ofcorrosion defect on KuShan crude oil pipeline and DuWu refined oil pipeline wereevaluated, analyzed and compared the result of the evaluation results and their changes.Meanwhile, according to the criteria of pipeline failure, ANSYS finite element simulationmethod is used to establish pipeline model with corrosion defects, simulate the operationalstate of corrosion defects pipeline in actual work environment. the equivalent stress and itsdistribution of pipeline corrosion defects under operating pressure is calculated. thevariation of the equivalent stress of corrosion defects pipeline with the length, depth andwidth of corrosion defects is analyzed, the different affect between inner corrosion and theouter corrosion to the safety operating pressure of pipeline is studied. Compare and analyzethe results of the integrity evaluation criteria and ANSYS finite element simulation, theconservatism of integrity evaluation criteria is identified, the present security situation of corrosion defect pipeline is evaluated.Research show that for the same corrosion defect, there is difference between thesafety operating pressure by different evaluation criteria, namely the conservatism of eachevaluation criteria are different; Different evaluation criterias are applicable to differentcorrosion length interval and the impact of changes of the corrosion defects size on thesafety operating pressure of pipeline evaluated by different evaluation criteria are different.The equivalent stress can be used as reference to corrosion defect pipeline evaluation,finite element simulation method can realize the evaluation of corrosion defect pipeline,the evaluation results surmount the conservatism of the integrity evaluation criteria.