Research On Pipeline Structure State Recognition Method Based On Distributed Fiber Sensing Monitoring

With the rapid economic growth and increasing demand for people's production and living,the pipeline structure is widely used in long-distance transportation projects for liquid and gaseous materials.It has played an important role in China's infrastructure construction and economic development.However,the pipelines are subjected to the complex loads such as building loads,overloaded vehicles,submarine eddies,earthquakes,and impacts during the construction and service phases.The complex loads will seriously affect the service life of the pipelines and cause pipeline failures.The sudden failure of the pipeline will seriously endanger people's lives and property.Therefore,it is necessary to establish an effective pipeline structure status identification method,which can reveal the real-time structural response of the pipeline under complex load conditions.Based on the real-time structural response of the pipeline,the effective identification of the pipeline failure is realized.Then the status of the pipeline structure is evaluated.Based on the method,we can realize the pipeline failure warning and the assessment of the remaining bearing capacity.It will be useful for the maintenance of pipelines and the prevention of disasters.In this paper,a method for identifying the status of pipeline structure is proposed.Based on the research of distributed sensing monitoring technology system,the method studies the structural response of the pipeline under the conditions of pipeline deformation and local crack failure.We adopt a verification method which combines the finite element model and model test to prove the feasibility of the proposed method.The specific research work is as follows:Firstly,the introduction part describes the research significance of distributed monitoring and structural state identification of pipeline structures.It focuses on the causes of pipeline deformation and local cracks.It also introduces the pipeline failure forms which induced by the pipeline deformation and local cracks.Secondly,we review and summarize the domestic and foreign researches on pipeline structure inspection technology in recent decades.The application conditions,advantages and disadvantages of monitoring and identification methods for pipeline are described in detail.Finally,according to the research of pipeline structure state monitoring based on distributed optical fiber sensing technology,the main research contents and research ideas for the problems of pipeline deformation and local crack failure are given.During the operational phase of the pipeline,changes in the internal temperature and pressure of the pipeline will cause the overall buckling failure of the pipeline.It will result in the leakage of oil,natural gas and other transportation materials.Therefore,in the second Chapter,based on the overall buckling mechanism of the continuous pipeline,a method for monitoring and identifying the overall buckling failure mode of the pipeline is proposed.The method can quantitatively identify the development of the pipeline overall buckling.Based on the distributed optical fiber monitoring method,we extract the bending strain from the pipe strain.With the bending strain,we establish the pipe buckling deformation reconstruction algorithm to identify the buckling shape.Then the buckling behavior of the pipe can be identified quantitatively.The feasibility of the proposed monitoring and identification method for the overall buckling failure of pipelines was verified by numerical models and simulation experiments.The comparison of the reconstruction curves of pipe displacement with numerical simulation results and experimental monitoring results under different conditions proves that the proposed method can quantitatively identify the overall buckling of the pipeline and the development process.During the laying and operation of the pipeline,ground overload and soil settlement caused failures such as pipe-pulling and excessive turning of the segmented pipeline.Such failures will have a serious impact on the production and living of the people and the national economic construction.Because of the special structural characteristics of pipelines,it is impossible to use the proposed continuous monitoring method to realize the distributed monitoring and identification of segmented pipeline.Therefore,the third chapter focus on the response of the nozzle structure which caused by the bending deformation of the segmented pipeline,and propose a conditional monitoring and identification method of the segmented pipeline.Through the parameter sensitivity analysis of the segmented pipeline structure,the correction term is confirmed.The method uses pipe bending strain monitoring value as the response objective function,and then use the finite element parameter identification method to invert the structure state of the nozzle.In addition,the quantitative identification of the structure state of the pipe body and the nozzle can be realized without monitoring the deformation of the nozzle.Based on the monitoring method for pipelines' overall buckling,a distributed strain monitoring method for segmented pipelines in-position was established.Through a full-scale pipe loading test,this method was applied to monitor the feasibility of the response of the segmented pipe structure under the action of the upper load or settlement of the foundation.Due to factors such as load,aging and fatigue,the pipeline is prone to localized micro cracks.Under the influence of alternating strain and time,micro crack propagation will cause pipeline fracture failure.Local cracks in pipelines are usually characterized by local strain anomalies and nonlinear vibration characteristics of the structure.Based on this feature,the firth chapter propose a localized crack identification method for pipelines based on a distributed optical fiber sensing system.For the identification of static pipeline cracks,the local cracks of the pipeline are identified by the abnormal strain position,and then the quantitative analysis of cracks under static conditions is realized by combining the principle of strain transfer.Aiming at the identification of dynamic pipeline cracks,combined with weak nonlinear vibration characteristics of "breath" cracks,the micro-cracks of dynamic pipelines are located.The crack development process is quantitatively identified based on changes in harmonic components.The location and degree of cracks in pipelines under dynamic conditions are identified.It lays a foundation for the study of the local crack detection problem in pipelines in practical projects.Finally,the research work of this paper is summarized,and the future research work is prospected.