Defektoskopiâ

For test sample that are modeled by shells of rotation — cylindrical, spherical and toroidal, arbitrarily located relative to the piezoelectric transducer, the parameters determined by the adhesive properties of the couplant (surface tension, contact angle of wetting) and dynamic viscosity are calculated: the thickness of the contact medium layer between transducer and input surface and the maximum thickness of the contact medium layer between transducer and input surface which acoustic contact is maintained, as well as their effect on the acoustic field. A comparison with experimental data is carried out.

A brief analysis of publications addressing the influence of acoustic coupling on signals recorded during ultrasonic testing of components and welded joints is provided. It is noted that most often the authors pay attention to the amplitudes of pulses, but do not analyze their spectrum and its alteration in relation to the quality of preparation of contact surfaces. Experimental studies of backwall echoes received from carbon and austenitic steel specimens have demonstrated that variations in surface roughness (within the range of Rz 10 to Rz 80 μm) not only alter the amplitude of the detected signals but also cause significant distortions in their waveform and spectral composition. In some cases, the operational frequency of the backwall signal may decrease by 30 % or more relative to the nominal frequency of the piezoelectric transducer. Measurements performed on specimens with both deterministic and stochastic surface roughness profiles have shown that the quality of the coupling surface preparation has a substantially greater impact on the spectral characteristics of the received signals compared to the backwall surface roughness. The findings highlight the necessity of accounting for the influence of coupling surface roughness in test objects and welded joints on the spectral content of ultrasonic signals when developing procedural guidelines for pulse-echo and diffraction-based ultrasonic testing methods

The article notes that manufacturers and suppliers of ultrasonic flaw detectors usually focus on the sensitivity of the equipment, but pay little attention to the error which the linear dimensions of defects can be measured with. Examples of representing sections with defects in the form of acoustic B-scans are provided, and it is shown that these images have changed little over the past 60 years, despite the fact that the level of technology and signal processing have developed significantly during this time. It is noted that the physical principles that underlie ultrasonic flaw detection and the accumulated practical experience of its application show that at present the dimensions of defects can be measured no more accurately than with an error of 1 mm. Therefore, it would be more accurate to talk not about measuring of defects height in the cross-section of welded seams, but about assessing this height using ultrasonic flaw detection methods. At the same time, the article shows that it is possible to qualitatively assess the defect height change by fractions of a millimeter. For this purpose, in addition to the traditionally used time sweeps of signals (A-scans) and amplitude spectra, it is advisable to pay more attention to the analysis of phase spectra of signals received from products. The results of an experimental assessment of the influence of weak anisotropy of the material on the shape of the phase spectra of bottom pulses are presented. The calculations performed showed that the phase spectra also change significantly more than other characteristics of the recorded pulses with an increase in the height of defects in the cross section of the weld. This conclusion also applies to cases where the height of the defect does not exceed the length of the ultrasonic waves used

The results of experimental studies of the realized sensitivity and capabilities of the shadow method in problems of detection and assessment of defect sizes by surface waves are presented. It is shown that the time shadow method has a higher sensitivity to crack-like surface defects than the amplitude shadow method, and when used together with the amplitude method, it allows estimating the size of cracks whose depth does not exceed a quarter of the wavelength. A calculation method is proposed and analytical expressions are given for determining the time position of the maximum of the digitized pulse, recommendations are given for choosing the sampling frequency. The possibility of achieving an error in measuring the propagation time not exceeding 0.2 periods of the wave frequency is shown

The article considers numerical modeling of the method of defect localization in a three-dimensional (3D) structure based on acoustic-electrical transformations. It is shown that this method allows calculating the location of defects based on the parameters of the electromagnetic response to a deterministic pulsed acoustic excitation at selected points on the surface of the tested solid sample. To test the developed modeling method, two finite element models were developed: single-layer and two-layer three-dimensional structures. The results of calculations using these models confirm the efficiency of the acoustic-electrical conversion method in localizing defects in three-dimensional heterogeneous solid structures

This paper describes the process of nondestructive testing of a Dewar vessel in a cryogenic setup for studying the physical characteristics of PPMS-9 materials using a mass-spectrometric method. The methodology enabled the detection and localization of a leak, as well as an estimation of its size, which was approximated to be that of a circular hole with a diameter of approximately 0.6 microns. Following the application of Stycast epoxy adhesive to repair the defect, the evaporation rate of liquid helium was normalized