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The Research On Key Technology Of Optical Fiber Leakage Defect Detection

Posted on:2019-01-23Degree:MasterType:Thesis
Country:ChinaCandidate:N LengFull Text:PDF
GTID:2348330563953858Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Pipeline transportation is an important way to transport energy in petroleum,natural gas and chemical industry,and it is increasingly important to diagnose and evaluate pipeline defects.Magnetic flux leakage inspection is the current development of more mature pipe nondestructive testing technology,often use the magnetic field sensor with induction coil,magnetic susceptibility diode,hall element and so on.But in practical use,these sensors are not high in safety,narrow in application and low in sensitivity.In this paper,a magnetic flux leakage detection method based on fiber weak magnetic field sensor is proposed.The high sensitivity fiber magnetic field sensor is used and the mechanism of magnetic leakage detection is combined to realize the high resolution detection of oil and gas pipeline defects.It has the advantages of safety,reliability,high sensitivity,real-time online and permanent monitoring.This paper focuses on the detection technology of optical fiber magnetic flux leakage defects.The contents are as follows:1.Finite element method is used to simulate the magnetic flux leakage characteristics of pipeline defects.By combining the Maxwell equation group with the differential equation of electromagnetic field,the expression of the finite element analysis of the electromagnetic field is obtained.Based on the software of the Ansoft finite element analysis,a three-dimensional model of the pipeline magnetic flux leakage detection is established,and the characteristics of the flux density distribution of the tube wall are simulated and calculated,which is the design of the weak magnetic field sensor.Laying the foundation.2.According to the principle of magnetostrictive effect,a kind of optical fiber weak magnetic field sensor with all fiber structure is designed and made.The system composition and working principle of the FBG F-P cavity weak magnetic field sensor used in this project are described.The optical fiber weak magnetic field sensor uses the fiber grating F-P cavity structure and the giant magnetostrictive material,and combines the optical coherent demodulation to detect the high sensitivity of the magnetic field.The detection sensitivity of the optical fiber weak magnetic field sensor is 1.57rad/ T,which ensures the high sensitive detection of the leakage of the pipeline defect.3.The design of magnetic flux leakage detection system based on optical fiber sensing is developed.The experiment scheme is selected to determine the overall structure of the detection system.The magnetization structure and data acquisition structure of the defect detection device are designed and made.The magnetic circuit is optimized and the simple experimental system for detecting the optical leakage defect of the optical fiber is built.4.The relationship between the geometric parameters of the defect and the amplitude of the magnetic field signal is studied.The influence of two important factors of sensor probe lift height and magnetic pole spacing on the leakage magnetic field signal and the mutual influence of the leakage magnetic field between the adjacent defects are analyzed.The experimental results show that the detection system can detect the hole like defect with the minimum diameter of 2mm,and when the lift height of the sensor probe is higher than 4mm,the maximum distance between the two adjacent holes of the two adjacent holes can be identified as 10 mm.5.The principle component analysis method for identifying the characteristics of detection defects is studied.A new algorithm based on the common feature extraction methods,such as MATLAB software operation platform,wavelet change and classical modal decomposition,is designed to extract and analyze the characteristics of abnormal data.Based on the analysis results,the method of direct inversion based on RBF neural network is used to complete the leakage.Quantized recognition process of magnetic detection signal.
Keywords/Search Tags:pipeline defect, magnetic flux leakage detection, fiber optic magnetic sensor, RBF neural network
PDF Full Text Request
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