Study On Electromagnetic Acoustic Nondestructive Inspection Technology In Steel Tube

With the rapid development of energy industry, the quantity demanded of steel pipe increased quickly and the client made more application for the quality of steel pipes. As an primary method to guarantee quality of steel pipes, Nondestructive testing (NDT) is being more important and the quantity demanded of equipment increases too. At present, most ultrasonic detection applications are based on piezoelectric sensors, which need the coupling placed between the sample and sensor, and high quality sample surface is necessary for detection. Electromagnetic acoustic technology is a more effective method than others mentioned above. It can detect the near surface of steel pipe without any kind of coupling. So Electromagnetic acoustic (EMA) technology is rich of theory significations and application values for automatic detection of steel pipe.This paper makes a detail analysis on the principle, progress and characteristics of electromagnetic acoustic, makes some research on the creation principles and several styles of shear waves, horizontal waves and surface waves, gives out the structure model of electromagnetic-acoustic transducer(EMAT) based on electromagnetic induction theory, and analysis the surface waves of electromagnetic ultrasonic transducer process in magnetic iron base on the theoretical.In order to maximize the efficiency of electric/acoustic transformation, And makes a design of EMAT, give out the relation between transmitter coil, receiver coil and the energy of ultrasonic wave, and make a design of transmitter coil, receiver coil and electromagnet. A kind of sine pulse producer and a power amplifier for EMAT sensor are designed; an optimal condition for exciting ultrasonic wave by changing the intension, frequency and amplitude is given. EMAT impedance measuring and matching techniques, especially the transmission line impedance matching technique, are given in the dissertation. In order to verify the validity of the EMAT theory in practical applications, a series experiments are conducted on steel pipes with different diameters and the results were analyzed, and makes a foundation for future automatic detection for steel pipes based on electromagnet acoustic.