Research On Pipeline Condition Monitoring Based On Distributed Brillouin Optical Fiber Sensing

With the rapid growth of economy,the relationship between pipeline and people’s production and life is becoming increasingly close.However,it is deeply buried in the soil and subjected to long-term pressure and erosion from soil and transportation materials,which is prone to deformation,settlement,and leakage,posing a serious threat to people’s lives and production safety.Therefore,it is great significance to carry out real-time monitoring to the running state of pipeline.As a distributed optical fiber sensing technology,Brillouin optical time domain analysis(BOTDA)has the advantages of high spatial resolution and long measurement distance,and has attracted much attention in many fields such as pipeline transportation and power system.In view of the existing problems in pipeline condition monitoring,this paper conducts the research on pipeline settlement and leakage monitoring by designing corresponding simulation tests combined with the principle of distributed optical fiber strain and temperature sensing.The specific research content is as follows:Firstly,we introduced the basic theory of Brillouin scattering and deduced the relationship between Brillouin frequency shift and strain and temperature.The sensing principle of BOTDA technology based on stimulated Brillouin scattering was introduced in detail,and the principle of Differential pulse-width pair brillouin optical time domain analysis(DPP-BOTDA)technology improving spatial resolution was explained.Then we discussed the application of sensing technology in the field of settlement and leakage monitoring,and proposed a strain-settlement displacement calculation model and temperature change leakage monitoring method based on DPPBOTDA technology.Secondly,we built the DPP-BOTDA system and pipeline settlement simulation device to conduct settlement simulation tests under different working conditions.By measuring the strain distribution under different soil settlement amounts,and combining the strain-displacement model,the distributed measurement of pipeline settlement displacement was achieved.We analyzed the influence of fiber structure,soil uneven settlement and fiber-soil coupling degree on displacement measurement results,selected the best strain sensing fiber for pipeline displacement monitoring through comparison,and designed a new type of ground anchor structure,improved the fiber layout method,so that the settlement monitoring range increased by 50%.On this basis,the settlement coupling deformation coefficient was proposed,and the displacement monitoring range of the optical fiber during the soil settlement process was divided.The judgment of the coupling relationship between the optical fiber and the soil was achieved,laying a theoretical foundation for the application of DPPBOTDA technology in the field of buried pipeline settlement monitoring.Finally,we built a pipeline leakage simulation device based on the DPP-BOTDA system,carried out pipeline leakage simulation test,analyzed the temperature distribution of sensing optical fiber in the leakage process,realized the perception of buried pipeline leakage events and the location of the leak point with centimeter-level accuracy,and applied the technology in the pipeline leakage monitoring project.The feasibility of monitoring pipeline leakage events using the DPP-BOTDA system was verified by sequentially exploring the trend of soil temperature changes during the leakage process,the optimal layout of optical fiber,and the location method of leakage points.On this basis,we realized distributed temperature monitoring along the 800 m water supply pipeline in the Tongling city pipeline structural health monitoring project in Anhui province.And the positioning error of the pipeline leakage point was only 3cm,which provides a guarantee for the safe operation of the buried pipeline.