Design Of Pulsed Electromagnet EMAT Using For High Temperature Pipeline Thickness Gauging

The corrosion defects of metal pipeline caused by a long-term operation under high temperature,seriously threat the transportation security.In the condition of not bring damage to the pipeline,the method of monitoring the corrosion defects by gauging thickness of the pipeline is widely used.The piezoelectric ultrasonic technology is widely used in the field of pipeline thickness gauging,but its dependence on coupling agent makes it difficult to apply in high temperature environment.The electromagnetic ultrasonic technology does not need coupling agent,also the operation process is safe and convenient.However,when the EMAT is used under high temperature,the permanent magnet in it has problem such as magnetic weakening and sticking to the pipeline which lowers the detection efficiency.In order to solve these problems,a pulsed electromagnet EMAT(PE-EMAT)was designed by replacing permanent magnet with pulsed electromagnet.Based on the study of PE-EMAT at home and abroad,also considering the demand of transducer for a good heat resistance and mobility,an overall design scheme of PE-EMAT was proposed.This PE-EMAT could be used for high temperature pipeline thickness gauging.In view of the complex working mechanism of PE-EMAT in the process of high temperature thickness gauging,the working processes of PE-EMAT magnetic-field and sound-field were respectively analyzed,and the simulation model of high temperature PE-EMAT was built.The results show that as the temperature rises,the peak intensity and the establishment time of magnetic-field change a lot.However,the beam diffusion angle and maximum amplitude of the sound-field change a little.Aiming at decreasing the parameters and simplifying the design process of PE-EMAT,a design method was proposed.The EMAT coil was selected as butterfly structure,and the pulsed electromagnet was selected as iron-core structure.Based on the simulation model,the parameters of EMAT coil and pulsed electromagnet were optimized by orthogonal test.The experimental results show that after optimization design,the high temperature thickness gauging performance of PE-EMAT has been improved obviously.In order to gauge the thickness of high temperature pipeline,a PE-EMAT gauging system is built which consists of the pulsed electromagnet driver module,the EMAT transmitting and receiving module,CPLD and ARM module,power management module.Taking the Q235 steel tube as specimen,the experimental platform for high temperature pipeline thickness gauging is established.The correctness of the magnetic-field and sound-field model are verified.The experimental results show that this PE-EMAT has a strong magnetic field and a good mobility under high temperature,and the thickness of 600 °C pipeline has been successfully gauged.