Electromagnetic ultrasonic testing technology (EMAT) is a rapid development of international testing technology in recent years, and also one of the cutting-edge technologies in the field of ultrasonic testing. It belongs to non-contact ultrasonic testing. Combined with digital technology, it can flexibly and conveniently excite various types of ultrasonic waves in the tested work pieces, and can effectively detect the surface and internal defects of metal materials in real time Sink. EMAT is very sensitive to the permeability of various steels and is more sensitive to the microstructure than to the grain size of steels, which makes EMAT more suitable for steel separation. At present, EAMT testing technology has been widely used in manual, semi-automatic and fully automatic on-line nondestructive testing of various forgings, steel bars, steel plates and steel pipes at room temperature and high temperature. The energy conversion of EAMT is directly carried out in the surface layer of the workpiece to be tested. The workpiece surface can be regarded as a traditional piezoelectric ultrasonic probe. Therefore, the ultrasonic generated by EMAT does not need any coupling medium and can transmit and receive ultrasonic wave to the workpiece without contacting with the workpiece to be tested. The workpiece surface does not need special cleaning, and the workpiece with rough surface can be directly detected. Ultrasonic testing based on EMAT technology does not need water or any other coupling material, so as to prevent the tested materials and surrounding technical equipment from being corroded. Therefore, it is especially suitable for on-line detection of petrochemical pipeline corrosion. The EMAT - I pipeline wall thickness nondestructive testing system in pilot production of this project has obtained 2 invention patents and 3 utility model patents, with all intellectual property rights. The instrument produced has been applied to the on-line condition monitoring of oil and gas pipeline wall thickness in petrochemical industry refining plant area, which has a good market prospect and good social benefits for petrochemical production safety.