Study and development of a method and means for ultrasonic testing of ferromagnetic products with enhanced sensitivity

Modern requirements for the quality of manufactured and operated metal products are largely ensured by non-destructive testing methods, among which ultrasonic testing is the most advanced one. One of the promising ultrasonic quality assessment methods is the electromagnetic-acoustic (EMA) method, as it does not require special surface preparation of the object under test (OUT), does not imply the use of contact liquids, and offers high testing productivity. However, it is generally believed that the EMA method has low sensitivity. Some specialists suggest that the sensitivity of the EMA method can be increased by using pulsed magnetization of the OUT. Nevertheless, a comprehensive approach to address the technical and technological challenges has not been found in the existing publications. Therefore, the authors of this paper conducted relevant studies and analysed modern information sources, which only partially address some solutions related to the development of methods and measuring instruments, testing, and diagnostics using ultrasonic electromagnetic-acoustic transducers (EMATs) with pulsed magnetization. These developments potentially allow increased EMAT sensitivity by improving the signal-to-noise ratio of the ultrasonic signal. As a result of the analysis, a new EMA method of non-destructive ultrasonic testing was developed. It defines the operations, parameters, and sequence of actions required during pulsed magnetization of the OUT. The necessity to determine optimal relative timing between the magnetizing pulses and the short high-frequency pulses supplying the EMAT coil was established, which makes it possible to significantly (up to 40%) improve the efficiency of the transducer when assessing the quality of ferromagnetic materials. To study the potential of the new EMA method, a special test bench was created. It included an EMAT, a generator of powerful high-frequency current pulses, a generator of powerful magnetizing current pulses, an amplifier for received ultrasonic pulses (with parameters adjustable over wide ranges), and a digital dual-beam oscilloscope. Experimental results using this test bench demonstrated that the new EMA method and its supporting equipment improve the signal-to-noise ratio of the received ultrasonic signals compared to traditional EMATs based on permanent magnets. In other words, the efficiency of the EMAT has been enhanced.