To control objects made of materials with a high level of structural noise, it is proposed to use thinned antenna arrays having a large spatial aperture and consisting of a small number of elements located at a distance from each other much larger than the wavelength. The thinned antenna array moves along the surface of the object of control, and echo signals are recorded during radiation and reception by various pairs of piezo plates. For each emitter-receiver pair, partial images are reconstructed using the measured echo signals by the SAFT method, which are coherently folded to form the final image. A calibration procedure has been developed for each piezo plate of the antenna array in order to determine the coordinates of its center for effective coherent addition of partial images. The calibration procedure made it possible to reduce the requirements for the accuracy of placing piezo plates of a thinned antenna array on a prism. Using the technology of thinned antenna arrays allows you to obtain images of defects in welding with a signal-to-noise ratio of 12 dB greater than the image obtained by the method for a single-element converter. The article presents the results of the control of samples of pipelines DN800 with repair welding in the weld. The effectiveness of this method is shown in comparison with the method using a single-element piezoelectric converter.
The article considers a modified method of combined SOFT (SOFT) to restore the image of reflectors, taking into account the multiple reflection of the pulse from the boundaries of the wall of the cylindrical object of control. To test the operability of the proposed algorithm for restoring the crack image using echo signals calculated in the CIVA program for modeling the propagation and scattering of ultrasonic pulses. In a model experiment, it is shown that taking into account the change in the phase of the pulse when reflected from the boundaries of the control object for different angles of incidence of the transverse wave in the image reconstruction algorithm increases the frontal resolution by more than two times. Taking into account five reflections from the boundaries of the object of control made it possible to obtain images of reflectors using the M-C-SAFT method for many acoustic circuits. Based on the obtained images, it is possible to determine the type of defects, their dimensions and location along the wall thickness of the pipeline with a diameter of 720 mm.
The question of using an elastic organosilicon polymer ("Aquapolymer") as an immersion medium to ensure stable acoustic contact between the control object and the piezoelectric transducer during automated ultrasonic inspection of objects with uneven surfaces is considered. The use of "Aquapolymer" allows you to reduce water consumption during ultrasonic testing. To restore the image of defects, a modification of the SAFT method is used, taking into account the surface profile of the control object, which allows to improve the image quality. An algorithm is proposed for obtaining information about the surface profile of the object of control and taking this profile into account when restoring defect images using the SAFT method. In model experiments, images of defects were obtained taking into account the refraction of rays on an uneven surface.
The article considers a three-dimensional variant of the coherent projection method in spectral space (PSP) for obtaining an image of reflectors from measured echo signals. Its application makes it possible to restore images of reflectors with high frontal resolution, both in the main plane of the ultrasonic transducer and in the additional one. The use of the PSP method is especially effective when the reflector is far from the receiving aperture. In this case, it is possible to increase the signal-to-noise ratio by more than 12 dB, and the frontal resolution can sometimes be increased tenfold in comparison with the two-dimensional layered version of the PSP method. Examples of the application of this method are given when reconstructing the image of reflectors in a sample of a chemical reactor wall, with multiple reflections from the walls of a welded tee with an overlay (TSN), when monitoring large-diameter studs and divertor supports manufactured as part of the work on the thermonuclear reactor (ITER) project. The effectiveness of the use of the PSP method in a three-dimensional version for monitoring at great depths is shown.
The article considers a three-dimensional variant of the coherent projection method in spectral space (PSP) for obtaining an image of reflectors from measured echo signals. Its application makes it possible to restore images of reflectors with high frontal resolution, both in the main plane of the ultrasonic transducer and in the additional one. The use of the PSP method is especially effective when the reflector is far from the receiving aperture. In this case, it is possible to increase the signal-to-noise ratio by more than 12 dB, and the frontal resolution can sometimes be increased tenfold in comparison with the two-dimensional layered version of the PSP method. Examples of the application of this method are given when reconstructing the image of reflectors in a sample of a chemical reactor wall, with multiple reflections from the walls of a welded tee with an overlay (TSN), when monitoring large-diameter studs and divertor supports manufactured as part of the work on the thermonuclear reactor (ITER) project. The effectiveness of the use of the PSP method in a three-dimensional version for monitoring at great depths is shown.
The possibility of using different types of waves reflected from the uneven boundaries of the object of control, taking into account the transformation of the type, to restore the form of discontinuity when emitting and receiving ultrasonic waves by antenna arrays is analyzed. Numerous model experiments have demonstrated the broad possibilities of the considered approach for determining the type of reflector and measuring its dimensions.
The possibility of determining the directional pattern of contact piezoelectric transducers on a standard CO-3 sample when registering the field reflected from the concave cylindrical surface of the sample is substantiated. The advantages in comparison with the use of a standard sample of CO-2 are shown. Numerical and model results of the calculation of directional diagrams are presented. With the transition to spherical symmetry, it becomes possible to determine any section of a three-dimensional directional pattern.
A modification of the SAFT method is proposed to obtain an image of defects in control objects with three regions with different sound velocities. Such objects include complex composite welded joints, repair welding. In them, the speed of sound in the welded joint may differ by more than 5% from the speed in the base metal. Therefore, to obtain a high-quality image of defects, it is necessary to take into account different sound speeds. To solve the problem, a method for describing a control object with three regions with different sound speeds is proposed. The calculation of the propagation delays of the ultrasonic pulse is carried out using the Fermat principle. The results of reconstruction of the image of defects in the welded joint Du300 by echo signals obtained as a result of numerical simulation by the finite element method are presented. Images obtained by the SAFT method without taking into account different sound velocities are shifted from their true position, which makes it impossible to determine their coordinates and location. Taking into account different sound speeds makes it possible to obtain unbiased glare images of defects and, therefore, more accurately assess the type and size of defects.
The use of antenna arrays (AR) for obtaining images of defects in automated non-destructive ultrasonic testing (NCD) is considered. The traditional mode of using the AP as a phased array antenna (HEADLIGHT) has a number of disadvantages. For example, glare offset and resolution degradation when moving away from the focus line. An alternative approach is proposed, when the registration of echo signals is carried out using an AR operating in double scanning mode, and a modified algorithm of combined SAFT is used to obtain an image of defects, taking into account multipath propagation of ultrasound, taking into account the transformation of the wave type when reflected from the uneven boundaries of the object of control. This approach allows one set of echo signals to receive a set of partial images, the combination of which allows you to determine the type of defect. This is very important for creating a system of ultrasonic testing with reliable automatic recognition of the type of defect. Scanning with an antenna array operating in double scanning mode, the so-called triple scanning mode, allows you to coherently add images for each position of the antenna array, which further improves the quality of the final image.
The article examines the measurement errors of the main parameters of piezoelectric converters by the AUGUR 5.4 calibration system. Some influence functions are investigated. The real measurement error has been experimentally determined when testing the system with an assessment of precision in terms of repeatability and reproducibility. The acceptability of the measurement error of the main parameters of piezoelectric converters in accordance with the requirements of GOST 23702-90 is shown. The sufficiency of the normalized metrological characteristics of the system to ensure the uniformity of measurements is shown