A method for determining an unknown velocity of propagation of shear ultrasonic waves and an unknown thickness of the object of control is considered. It is proposed to use two antenna arrays operating in double scanning mode, when echo signals emitted and received by all pairs of antenna array elements are recorded. Antenna arrays on prisms are installed on the surface of the object of control in the direction "to each other". An algorithm for processing the measured echo signals using a method similar to the least squares method has been developed. The use of the algorithm makes it possible to determine simultaneously the speed of sound and the thickness of the control object with plane-parallel boundaries with an accuracy of at least 0.5%. The article examines the factors affecting the accuracy of measurements, suggests ways to eliminate or minimize them. The results of numerical experiments and the results of applying the method on three samples with comparison with the measurement results of the IN-5101A device are presented.
The features of image formation of reflectors using phased array antenna technology and images obtained by the C-SAFT method from echo signals measured in the double scanning mode are considered. It is shown that in some cases the images obtained using phased array technology are less informative. While the images obtained by the C-SAFT method have a higher frontal resolution in the entire image recovery area, partial images recovered at different positions of the antenna array can be coherently folded, which allows to obtain a high and uniform resolution in the entire volume of thick-walled products and increase the signal-to-noise ratio. The registration of echo signals in the dual scan mode and the restoration of the image of reflectors by the C-SAFT method will be called digital focusing by the antenna array (CFA) for short. The ability to restore partial images of reflectors using once-measured echo signals from many acoustic circuits, followed by their combination into one high-quality image, should allow reliably automating the process of recognition and measurement of diffusers. Another advantage of the images obtained by the C-SAFT method with three-dimensional focusing is the ability to restore images in a single coordinate system when using antenna arrays on prisms of different configurations. This facilitates collaborative image analysis. The rates of image formation using phased array technology and images obtained by the C-SAFT method are comparable. If the control technique is based on the use of nonlinear effects, then in this case, the headlight flaw detectors have an undeniable advantage over the CFA flaw detectors. But within the framework of linear acoustics, the headlight flaw detectors have no fundamental advantages over the CFA flaw detectors. It is fairer to say that the headlight flaw detectors have disadvantages. The article presents images illustrating the features of images obtained by FAR and CFA flaw detectors.
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.