ОБҐРУНТУВАННЯ ВИБОРУ МОДИ УЛЬТРАЗВУКОВИХ ХВИЛЬ ТА ПАРАМЕТРІВ ЕЛЕКТРОМАГНІТНО – АКУСТИЧНИХ ПЕРЕТВОРЮВАЧІВ ДЛЯ РАЦІОНАЛЬНОГО ВИЯВЛЕННЯ ДЕФЕКТІВ У ТРУБАХ ІЗ ТОВСТОЮ СТІНКОЮ

Анотація

The most widespread method of quality control of pipes is ultrasonic testing. Unlike traditional ultrasonic inspection, in recent years the electromagnetic–acoustic method of excitation and reception of ultrasonic pulses has been used, which has significant advantages, including when using normal-type waves: Rayleigh, Lamb, etc. However, such waves possess dispersive properties, since their propagation velocities depend on the pipe wall thickness as well as the ultrasonic frequency, which requires a rational approach to determining their parameters. It is shown that to use Lamb waves of modes SV₁ or SV₂, which exhibit increased sensitivity to detecting pipe defects, it is necessary for the given pipe material to construct dispersion curves of the ultrasonic wave propagation speed as a function of the product of pipe wall thickness and ultrasonic frequency. Based on these dispersion curves, the ultrasonic wave frequency must be determined, from which the wavelength used for testing is established. The defined Lamb wavelength is the basis for creating a meander-type high-frequency inductive coil with a pitch equal to the wavelength of the corresponding mode. In addition to Lamb waves, it is advisable to use Rayleigh waves with a wavelength close to the wall thickness of the inspected object. Such waves are called quasi-Rayleigh waves and are not subject to dispersion. They offer advantages when inspecting pipes in operation, since wall thickness wear occurs and the previously calculated Lamb wave ultrasonic frequency will no longer correspond to the rational inspection conditions. The theoretical prerequisites make it possible to calculate the pitch of a high-frequency inductive coil of the electromagnetic–acoustic transducer. Examples of calculations were performed for pipe wall thicknesses in the range 8…16 mm, which are most used in industry. The results of theoretical and practical studies were verified and confirmed by experiments on a developed stand using pipe samples with defect models in the form of through-holes and slots. Thus, it is shown that under specific conditions of ultrasonic inspection using a contactless electromagnetic-acoustic method of excitation and reception of pulse packets, it is necessary to determine which wave type is advisable to use and, based on this, develop the defectoscopy technology.