Experimental Study On Pipeline Damage Monitoring Based On Brillouin Optical Time Domain Analysis

Pipeline has become the main tool for long-distance transportation of water,oil and gas.In recent years,pipeline safety problems affect the normal life of human beings,and the safety monitoring of pipeline has become a hot topic of experts and scholars.With the advantages of high sensitivity,small volume,strong anti electromagnetic interference ability and good durability,optical fiber is more and more used in pipeline safety monitoring.But at present,the safety monitoring of optical fiber in the pipeline mainly focuses on the pipeline leakage,and the research on the strain monitoring of the pipeline structure itself is less.The crack is an important index to reflect whether the pipeline works safely.The safe operation of the pipeline cannot be separated from the control of the crack.The relevant specifications have clear requirements for the crack control of reinforced concrete pipeline.But the pipeline is usually in the state of buried work,so it is difficult to find the cracks in real time.It is very important to find an effective and reliable real-time monitoring method for pipeline cracks.This paper introduces the basic structure of optical fiber and its strain transfer mechanism at the crack,gives the method of calculating the strain of optical fiber from the crack width,obtains the law of strain transfer coefficient at the crack through calculation,calculates the strain transfer coefficient under three different optical fiber arrangements by using ABAQUS simulation software,summarizes the advantages and disadvantages of various arrangements,and analyzes the applicable conditions The influence of radial force on variable transmission.In this paper,based on the optical fiber sensing principle of Brillouin optical time domain analysis,the temperature sensitivity coefficient and strain coefficient of optical fiber are calibrated by using the tensile test of the plate;considering that two cracks appear in the short range of optical fiber,multiple groups of optical fiber frequency shift images are designed and tested,the image characteristics are analyzed,the image characteristics of optical fiber frequency shift of two cracks under different spacing are summarized,and a new one is proposed Optical fiber monitoring crack process.In this paper,two types of optical fiber are arranged on reinforced concrete pipes,and the orthogonal and oblique cracks are arranged respectively.The crack appearance and expansion are monitored,and the quantitative analysis is carried out from the corresponding change of crack width.According to the above research,the main conclusions are as follows:1.By using ABAQUS finite element simulation software,the strain transfer coefficients of three layout modes are simulated,and their advantages,disadvantages and applicability are analyzed.The simulation results show that the strain transfer curve of the embedded fiber is the most stable and the strain transfer efficiency is the highest;the thickness of the pasted medium has an impact on the variable transfer coefficient,and the larger the medium thickness is,the smaller the strain transfer coefficient is.2.Study the Brillouin frequency shift curve at the crack under the condition of different double crack spacing.The test results show that the frequency shift curve with different characteristics will appear in the double crack monitoring with different spacing.When there are two cracks in the range of 50 mm in the optical fiber sensor,the frequency shift peak will not drift;when there are two cracks in the range of 50 mm to 200 mm,the frequency shift peak will drift in the range of 200 mm to 250 mm When the fracture occurs,the peak value of frequency shift will shift.3.In this paper,the quantitative analysis theory of the designed crack is only applicable to the case where the optical fiber and the crack are orthogonal in the pipeline test,and the skew situation needs further study.4.When 0.9mm single-mode optical fiber is used in pipeline damage monitoring,it is easy to break,not the best material,and the effect of strain sensing optical cable with high transmission tight sheath is very good;the frequency shift characteristics of two cracks in a short distance are well reflected in the test;when the optical fiber and the cracks are not vertical,the accuracy of the optical fiber sensor is not high,the peak run out is not obvious,and the crack monitoring of the pipeline is not ideal Further research is needed.