Research On Fiber Bragg Grating Sensing Based Pipeline Safety Monitoring Methods And Experiments

With the advancement of industrialization and urbanization in China,the total demand for oil and natural gas resources is increasing,and the construction scale of oil and gas pipelines will be further expanded.However,with the increase in pipeline service life,pipeline failure accidents occur frequently.Once the pipeline fails,it will not only lead to energy loss and environmental pollution but also directly lead to the loss of public health risks.Therefore,aiming at the three main causes and characteristics of pipeline failure accidents,effective methods including pipeline internal corrosion monitoring method,pipeline leak monitoring and localization method and pipeline deformation monitoring method are proposed,and a pipeline safety monitoring system is established to obtain the operation status of the pipeline in real time and provide early warning of pipeline failure accidents in time.This research will be of great significance to reduce energy loss and environmental pollution and protect the safety of people’s lives and property.However,there are still three main problems in the aforementioned methods:（1）There is a lack of nondestructive monitoring sensors that can not only accurately monitor pipeline internal corrosion,but also effectively monitor pipeline leakage.（2）The arrival time difference of negative pressure wave（NPW）signal can not be accurately obtained,and there is a lack of methods to locate pipeline leakage without solving the arrival time difference of NPW signal.（3）There is a lack of methods that can accurately restore the pipeline deformation and monitor the pipeline deformation in real time in practical engineering.Aiming at the above three problems,this paper carries out theoretical and experimental researches.Furthermore,integrating the above research achievements,this paper designs and develops a pipeline safety monitoring system.The specific research works and main conclusions are as follows:（1）A fiber Bragg grating（FBG）pipe-fixture sensor is designed and developed for the first time,which can not only accurately monitor pipeline internal corrosion,but also effectively monitor pipeline leakage.Based on the measurement theory of the pipeline diameter variation,the sensor is directly installed on the outer surface of the pipeline.The installation of the sensor does not need to damage the anticorrosion layer of the pipeline,avoiding the strain transfer problem.Therefore,the sensor is a nondestructive monitoring sensor.Through finite element simulation and structural optimization design,the FBG pipe-fixture sensor with a promising design solves the problem of a large difference between the test values and the theoretical values and eliminates the limitation of measurement range.Furthermore,a pipeline internal corrosion monitoring method based on the FBG pipe-fixture sensor is proposed.The simulation test results of pipeline internal corrosion monitoring indicate that the presented method can sensitively and stably monitor the internal corrosion prosess of pipeline and evaluate the internal corrosion degree with a measurement accuracy of 0.1 mm.（2）Low localization accuracy and instability are two primary problems for the pipeline leak localization method based on time difference solution of negative pressure wave（NPW）signals.In this paper,based on compressed sensing（CS）theory and FBG pipe-fixture sensor array,a novel pipeline leak monitoring and localization method is proposed to replace the solutions of the arrival time difference of NPW knee points.In addition,based on the presented method,the localization accuracy can be improved without increasing the number of sensors.To validate the localization accuracy and stability of the presented method,a pipeline leak simulation test under flow conditions is conducted on a steel pipe leak test platform.The test results indicate that when the sensor array is compossed of five FBG pipe-fixture sensors and the optimal relative localization coefficient(7is 0.5,all localization errors of different leakage points with different leakage rates are 2 m.（3）This paper presents a novel pipeline deformation monitoring method based on the inverse finite element deformation reconstruction method.Based on the two end nodes inverse element called“i Beam3”,the presented method can reconstruct pipeline deformation without any material and/or loading information because only the strain-relative displacement relationship is employed in the algorithm.A series of experimental studies are conducted to validate the effectiveness and accuracy of the presented method.An application of pipe deformation monitoring during the freeze-thaw process of soil is conducted,and the test results demonstrate that the presented method can effectively monitor the deformation process for a buried pipe during the freeze-thaw process of soil,showing potential in practical engineering.（4）Combined with the proposed pipeline internal corrosion monitoring method,pipeline leakage monitoring and localization method and pipeline deformation monitoring method in this paper,a real-time pipeline safety monitoring system is established by using the mixed programming of the Lab VIEW platform and MATLAB.Furthermore,based on the design process of the pipeline safety monitoring system,the oil and gas pipeline leakage monitoring and localization system is designed and developed.The system is applied to the fluid pipeline leak simulation test platform.The monitoring results of the system indicate that the interfaces of the system have good interaction,and the various functions are well realized.It can send out early warning information of pipeline leakage and accurately locate pipeline leakage point.