Research On Safety And Reliability Assessment Technology Of X60 Pipeline Based On Plastic Instability

With the increase of the service life of the pipeline,some damage will inevitably appear on the surface of the pipe body,and these defects will affect the normal operation of the pipeline.Therefore,it is very important to study the safety and reliability of the pipeline with defects.In this thesis,the common X60 steel grade pipeline is taken as the research object,based on the plastic instability mechanism,the remaining strength and reliability of the X60 pipeline are studied by the combination of test and numerical calculation.The main research contents are as follows:Physical and chemical performance tests were carried out on the X60 pipeline.Based on the real hydraulic blasting test data,the accuracy of the finite element model was verified.Comparing with different failure criteria,the research shows the plastic collapse failure model is a more suitable existing failure determination method.Firstly,the influence of the depth and length of the single-point external defect on the failure pressure is studied.The equivalent volume of each stress region when the pipelines with different defects fail is analyzed,and the influence law of the defect parameters on the failure mode of the pipeline is summarized.Introduce collapse loads,obtain a failure judgment model for the integrity failure of X60 pipeline with defects based on the equivalent volume method,which improves the limitations of the existing failure judgment criteria.Based on this model,the failure pressure prediction model of X60 pipeline with defects is researched.Compared with real test data,the accuracy of the models are verified.Based on the above model,the X60 pipelines with single-point internal defect,axial and circumferential double-point defects are simulated.The influence law of defect location and quantity on pipeline is obtained,the critical distance of the interaction of two adjacent point defects,and the calculation method of failure pressure of X60 pipeline with axial and circumferential defects are also obtained.Using the inspection data of X60 pipeline within one round,the distribution law of the depth and length of external and internal metal loss is studied by probability distribution theory,which improves the accuracy of subsequent reliability analysis.Taking the real data as a reference,the maximum metal loss depth value was predicted based on the common distribution method,and the most suitable ideas and methods for predicting the maximum metal loss depth of X60 pipeline was obtained.Finally,based on the reliability theory,the metal loss depth value of each point is predicted,and the failure probability statistics map of the X60 pipeline is drawn,so the predicted value of the re-inspection period based on the risk reliability assessment is obtained.The research provides opinions for better guaranteeing the safe and reliable operation of X60 pipeline.