A Magnetic-flux-measurement Displacement Sensing Method And Its Application In The Surface Distortion Inspection Of Steel Pipe

Steel pipe is one of the important raw materials.The production of Chinese steel pipe has accounted for more than 70% of the world.In order to improve the product q uality,the detection of steel pipe is becoming more and more important.Magnetic flux leakage testing,ultrasonic testing and eddy current testing are mainly sensitive to cracks in steel pipes but not sensitive to the surface distortion.The detection of the surface distortion mainly relies on manual visual surface inspection in the past decades.In recent years,the three-dimensional laser displacement technology has been developed,but the equipment is expensive.This paper mainly studies on an electromagnetic displacement sensing method based on magnetic flux measurement,focusing on the detection of the surface topographical distortion.Firstly,a displacement sensing method based on AC magnetic flux measurement is proposed and the principle is studied.A magnetic bridge type AC-flux-measurement displacement sensor is proposed,and its output characteristics are analyzed.The results show that the sensor's output voltage changes linearly with the reciprocal of the displacement.The linear relationship is verified both by simulation and experiment.At the same time,the influence of eddy current effect and sensor's size on output linearity are analyzed.In order to obtain a higher frequency response,a displacement sensing method based on permanent magnet flux measurement and a magnetic bridge type permanent-magnet flux-measurement displacement sensor are proposed.Theoretical derivation shows that the output voltage changes linearly with the reciprocal of a sum of the displacement and a constant.The linear relationship is verified both by simulation and experiment.The influence of sensor size on output voltage is also studied.To implement the array displacement sensing technology,it is found that combining the AC magnetic flux measurement displacement sensor and the permanent magnetic flux measurement displacement sensor has effectively eliminated the electromagnetic interference between adjacent sensors.Therefore,a displacement sensing method based on magnetic flux measurement combining the two methods is proposed.The difference between the linearity of the array sensor and single sensor,and the output of the sensor array is studied systematically.The results show that the output linearity of the AC/DC hybrid displacement sensor array is better than that of the single sensor.There is not much electromagnetic interference between the combined array sensors.The difference between the array and the single sensor is small.The consistency evaluation of the array displacement sensor is studied by applying the Kendall's Coefficient method.As an application of the above magnetic-flux-measurement array displacement sensor,the influence of the diameter of the steel pipe is simulated and analyzed for the non-cracking surface deformation of the steel pipe.The array displacement sensor is designed and the spiral scan is planned.On the basis of magnetic flux leakage detection,the distortion of the surface is effectively detected.This study further improves the electromagnetic detection technology and equipment of the steel pipe.