Research Of Pulsed Eddy Current Nondestructive Technology Based On Multi-sensors

Oil and gas transmission pipelines,with reliability of seal and convenience of management,are important parts of the energy transmission network.Nowadays,pipeline damage accidents happen frequently,which not only cause serious damage to the environment,but also cause a great deal of loss of life and property.The material of oil and gas pipeline is mostly pipeline steel,of which the inner and outer wall corrosion is the main reason for perennial pipeline damage.For pipeline damage prevention and safety maintenance,pulsed eddy current testing is a safe and effective method.Pulsed eddy current technology is suitable for metal material detection and is not affected by the coating.With rich frequency information,a large number of signals can be collected in a short time.Therefore,PEC technology is commonly used in thickness measurement and defect recognition.Due to the weak time-domain signal detected by the pulsed eddy current and large noise interference,the method of eliminating noise,finding appropriate detection characteristic and optimizing the detection system are important directions for the development of the pulse eddy current testing.In this paper,the research on pulse eddy current testing technology mainly focuses on the following aspects:The theory of pulsed eddy current testing is studied.Based on the basic electromagnetic principle of detection,the advantages of pulsed eddy current testing and the problems to be solved are explored.The critical influencing factors of the detection results are also analyzed.At the same time,the circuit model and the finite element calculation method of pulsed eddy current testing are analyzed,which provides a theoretical basis for subsequent simulation and experiments.Finite element simulation software is utilized to analyze pulsed eddy current testing technology.On the basis of theoretical research,the distribution of electromagnetic and eddy current in the whole excitation pulse cycle is analyzed.Besides,the influence of sensor parameters change and lift off effect on the detection results is explored.According to the simulation results of defect detection and thickness measurement,the appropriate measurement features are selected.The pulsed eddy current testing system is perfected to carry out the experiment.Hall element and detection coil are used as receiving sensors.The steel plate with thickness from 9.5mm to 17.5mm is measured by using the induction voltage attenuation rate under the semi logarithmic coordinate.The relative error of measurement result is lower than 10%,which meets the precision requirement.For cylindrical surface defects with different diameters and depths,defect recognition can be achieved.The lift-off effect experiment is performed.When the lift-off height increases from 0mm to 25 mm,the thickness measurement error increases,which cannot meet the accuracy requirement.The multi-sensor measurement is used to get the characteristic parameters and the error caused by lift-off effect in thickness measurement is reduced.The difference of the induced voltage attenuation rate and the peak value difference of the magnetic induction intensity is used to compensate for the lift-off effect,which significantly reduces the measurement error caused by the lift-off effect.