Reliability Analysis And Evaluation Of Buried Oil And Gas Pipelines Subjected To Fault Displacemnets

Active fault is one of the greatest threats to the design of long-distance pipelines.The permanent ground deformation caused by the displacement of two fault plates will cause large strains in pipeline near the fault plane,which poses a serious threat to the structural safety of pipelines.Therefore,it is necessary to carry on the reliability evaluation of pipeline buried in fault area.Based on the finite element model of beam-shell coupling and soil spring,.inp(input)documents for calculating the strain demand of pipes subjected to fault displacements are generated in batch based on Python language by considering various influence parameters(pipe dimensions,internal pressure,fault parameters,and soil properties)through factor alternative method.The strain database can be established by batch computing and result extraction.After that,three data-driven models for predicting pipeline strain demand are established,including BP neural network model,support vector regression model,and non-linear regression formula,which are proved to have accurate predictions and lower computing time.Although RF model is not as precise as the two formers,it reflects the explicit relationship between pipeline strain demand and various influencing factors to a certain extent,which is of engineering application value.Models of tensile strain capacity(TSC)and compressive strain capacity(CSC)are summaried and compared.Combining with the above strain demand prediction models,the ultimate state equation of pipelines subjected to fault displacements based on strain is established.The reliability of pipelines bearing the load of fault displacemnets can be calculated by method of Monte Carlo or FOSM.It shows that the Monte Carlo method based on BP prediction model has the higheset accuracy as well as time effectiveness,which makes it the most suitable approach for reliability calculation of pipelines under fault displacements.Then,the parametric influence analysis is conducted on the basis of the method.The exceedance probability of permanet ground displacement of the intersection site between Xin Yue Zhe pipeline and Bo-AF which is located in Xinjiang province is calculated by using the method of probabilistic fault displacement hazard analysis(PFDHA),and the failure probability of the pipeline section in the next 10 year,20 year,and 30 year can be obtained by integrtating the product of probability of the pipeline structure failure on the condition of specific permanent fault displacement and the probability of the surface displacement of the intersection site.Results indicate that the longer the service life of pipeline is,the more earthquake prevention is needed: the Xin Yue Zhe pipeline can meet the requirement of target reliability calculated according to CSA Z662 code in the next 20 years,but seismic mitigations should be imposed after 20 years since the failure probability of the pipe is higher than the maximum permissible failure probability.