Research And Application Of Monitoring Oil And Gas Pipeline Flange Based On PZT Array Impedance

As the main carrier of oil and gas energy transportation,oil and gas pipelines play a crucial part in national infrastructure and social development.As a common pressure-resistant and easy-to-disassemble connection device in oil and gas pipelines,flange bolt joints are a large number in pipeline connections,and are key parts of frequent leakages and key objects of leakage detection.Flange bolt pre-tightening is directly related to leakage,and the detection of flange bolt force is a key part of leakage detection.Therefore,it is of great value to monitor and evaluate the pre-tightening state of flange bolts,to discover potential safety hazards in time and to make decisions and management to ensure transportation safety.Aming at the lack of effective method for monitoring flange bolt connections of oil and gas pipelines,this paper proposes a design method for series/parallel impedance PZT sensors and a surface monitoring method for oil and gas pipeline flanges based on PZT array impedance.Using the advantage of eletromechanical impedance(EMI)method that is sensitive to minor damage,combined with finite element simulation and experiment,PZT sensors with both broadband and high sensitivity are fabricaed.The PZT sensor array is cascaded in series/parallel,and the looseness of flange bolts of oil and gas pipelines is successfully detected by the multi-sensing eletromechanical impedance(EMI)method,which realizes a single measurement of the degree of loosening damage of multiple bolts and locates the loose bolts.The main research contents and conclusions are as follows:(1)Starting from the impedance and resonance characteristics of piezoelectric ceramics(PZT),the eletromechanical impedance model,series/parallel EMI principle,and the finite element analysis of EMI are explained.All of these lay a theoretical foundation for both the design and manufacture of frequency modulated PZT impedance sensors,and series/parallel EMI surface monitoring of oil and gas pipeline flange loosening damage of multiple bolts;(2)In order to meet the needs of broadband monitoring,the finite element method(FEM)is adopted to establish the EMI model of the PZT sheet and the frequency modulation unit,and the design of the frequency modulation PZT sensor is carried out.By adjusting the size parameters of the frequency modulation unit and analyzing the EMI harmonic response,it is found that the resonance frequency of the PZT sensor changes linearly with the thickness of the frequency modulation unit.The fabricated PZT sensor is tested and verified,and the results are found to be consistent with the finite element simulation results.As a result,it is verified that the proposed frequency modulation PZT sensor design method is effective,simple and practical.(3)Explore the spread spectrum and frequency division multiplexing characteristics of the PZT sensor array.By increasing the piezoelectric sensor array and cascading test,it is found that the cascaded sensor array can realize the widening of the resonance frequency.At the same time,the single sensor and the sensor array were compared and tested,and it was found that the composite EMI response of the sensor cascade array contained all sensor's response information,and the multi-resonant frequency of the sensor cascade array corresponded to each sensor one-to-one,which could realize frequency division multiplexing.(4)A series/parallel impedance flange bolt looseness monitoring platform was built.The experiments were carried out to test the ability of the PZT sensor to detect the looseness of a single flange bolt and the PZT sensor cascade to detect the looseness of multiple flange bolts.And the degree of looseness is measured by the damage index.The results show that the PZT sensor series/parallel array prepared in this paper can detect the looseness of multiple bolts on the surface of the flange,and at the same time realize the positioning of the loose bolts.In summary,this paper has formed a simple and practical PZT array EMI sensor design method and series/parallel EMI surface monitoring method.It can guide the optimal design of the sensor,expand the frequency band range,simplify the observation system,and realize the frequency division multiplexing with single measurement of multi-point information,which promotes the practical application of EMI technology in structural health monitoring.