State-of-the-art capabilities of EMA flaw detection

Abstract

The literature sources devoted to studies and development of flaw detectors based on the EMA method of exciting and receiving ultrasound pulses are analyzed. A new EMA flaw detector with capabilities comparable with those of state-of-the-art contact ultrasonic flaw detectors is developed on the basis of analysis and studies performed.Methods and facilities for ultrasonic nondestructive testing (NDT) of materials and articles are currently being developed rapidly [1,2]. These devices are predominantly instruments that use a contact liquid in the inspection technique. At the same time, there are fields [3] in which the application of contact testing methods is not quite efficient: inspection of articles whose contaminated surfaces are not cleaned specially beforehand, nondestructive testing of hot and cold articles, high-speed inspection, flaw detection with low operational expenditures, etc. Therefore, research and development aimed at the creation of facilities for evaluating the quality of articles by contactless techniques have been undertaken in recent years.The greatest engineering progress in the above trend was achieved owing to the application of the electromagnetic-acoustic (EMA) method for exciting and receiving ultrasonic vibrations [1, 3-108]. The application of EMA nondestructive testing is also justified from the economical point of view. K.V. Sudakova reported in [109] that, at an average cost of the facility of 30 million rubles and operational expenditures of 10% a year of this sum, the overall cost of automatic contactless ultrasonic inspection introduced at OAO Severstal' is compensated in as short a time as eight months. The further service of this facility yields an economic effect of ~105 million rubles a year owing to an increase in both the quality of products and the inspection rate and exclusion of the procedure of conditioning the articles' surfaces, which costs approximately 550 rubles/t. In addition, the introduction of overall inspection leads to a sharp increase in the processing discipline.FEASIBILITIES OF THE EMA TECHNIQUE DURING NONDESTRUCTIVE TESTING As in the case of contact acoustics, the flaw detection with the use of the EMA technique predominantly utilizes two inspection techniques: pulsed and resonant [1,5,20]. The pulsed method is implemented by using mainly the same electronic units [32] as those in conventional ultrasonic instruments, in which sound is excited and received by piezoelectric transducers [33]. The differences are that an inductance coil is used instead of a piezoelectric element and there is a device for exciting a polarizing magnetic field. EMA transducers (EMATs) are usually powered by shock-excitation generators [24,25,[34][35][36]. The required induction value of the polarizing magnetic field is produced by various devices of designs depending on a particular task [17].Instruments in which the EMA transformation is implemented via the electrodynamic mechanism have the most diversified designs [17,32]. In this case, the direction of the force in the meta...

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Increasing the laser-acoustic method efficiency for testing metal products by using 3D visualization

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