Design Of Steel Pipe Defect Detection Device Based On AC/DC Composite Excitation

Steel pipe is a tubular product made of steel.It is often used in transportation,structure and processing in various industries and fields.When the steel pipe is damaged,it may lead to the instability and damage of the structure,and then cause serious consequences such as fire,explosion or gas leakage,endangering the safety of personnel and the environment,and causing huge economic losses to the society.Therefore,it is necessary to detect defects in steel pipes.Due to the fact that the defects of steel pipes are divided into internal and external defects,compared to external defects,internal defects are more concealed.Therefore,it is necessary to find a device that can detect internal and external defects.The traditional steel pipe magnetic flux leakage detection device uses two sets of detection devices in different directions to extract the magnetic flux leakage signals of the steel pipe,and then compares the differences between the two magnetic flux leakage signals to judge the defects and determine the depth of the defects.However,this structure makes the magnetic flux leakage detection device huge and inconvenient to use.To address this issue,this article proposes a steel pipe defect detection device based on AC/DC composite excitation technology.This device has the advantages of small size,convenient operation,and convenient frequency adjustment.This device achieves the detection of internal and external defects through AC/DC composite excitation technology.Specifically,the device uses DC signals to detect defects,and then uses the skin effect of AC signals to distinguish internal and external defects to detect and judge steel pipe defects.The main research contents and results are as follows:(1)A steel pipe defect magnetic flux leakage detection device based on AC/DC composite excitation is proposed to address the problems of large device volume and inconvenient operation caused by distinguishing internal and external defects in traditional magnetic flux leakage detection devices.By analyzing the changes of magnetic induction lines under the boundary conditions of two different magnetic media,the changes in the path of magnetic induction lines passing through defects were derived,and the reasons for the generation of leakage magnetic fields and the principles of leakage magnetic detection technology were explained.In addition,this article introduces three magnetization methods and characteristics,as well as two calculation methods for leakage magnetic field,providing a theoretical basis for subsequent modeling and simulation.(2)Establish a magnetic flux leakage detection model using COMSOL and simulate it under DC(permanent magnet)excitation and AC excitation,respectively.Firstly,the DC(permanent magnet)excitation is analyzed,and the magnetic flux density mode is detected at 1mm above the defect of the steel pipe.The magnetic flux leakage signal is plotted as a line chart,and the magnetic flux density diagram near the defect is obtained.Then the AC magnetic flux leakage is analyzed,and its skin effect is verified.The frequency of the excitation signal in the coil is changed,and the amplitude of the AC magnetic flux leakage signal at different frequencies is compared.The experimental results show that,with the increase of the frequency,the skin effect in the magnetic circuit is more and more obvious,which is consistent with the theoretical value.Based on the simulation results,it provides a reference for the next step of hardware circuit design.(3)The hardware design of the magnetic flux leakage detection device has been implemented.We have selected the main control chip and magnetic sensor,and completed the design of signal amplification circuit,low-pass filtering circuit,voltage stabilization circuit,and power amplification circuit.Draw each module circuit into a PCB circuit board and verify the effectiveness using corresponding instruments to meet the design objectives.(4)Implemented software design for magnetic flux leakage detection device.The system mainly includes the main program,AD sampling program,DDS program,key interrupt program,and LCD screen display program.These programs are compiled in the Keil μVision5 integrated development environment,effectively improving programming efficiency.(5)We have built a testing platform for magnetic flux leakage detection devices and conducted experiments using steel pipes with artificial defects.Detect rectangular defects for both front and back defects separately.The experimental results show that the device can effectively detect the existence of defects,and the location of defects can be further judged by the skin effect of the alternating magnetic field.