We discuss issues of classification of operational volumetric and planar surface defects based on the results of complex diagnostics by non-destructive ultrasonic sounding using Rayleigh surface waves generated by an electromagnetic-acoustic transducer and the eddy current method. The paper presents results of feature selection using a variance analysis (ANOVA) and an Extra Trees Classifier algorithm, making it possible to select an optimal eddy current transducer for surface defect classification. The classification of surface defects by the amplitude of ultrasonic and eddy current signals, as well as the phase of the eddy current signal separately is shown to be unambiguous. Models for classifying surface defects as being volumetric or planar are constructed based on statistical methods such as Bayesian inference and the Dempster-Schafer theory. The workability of the constructed classification models is evaluated using metrics such as the Jaccard coefficient and the F1-measure.

The 3D problem of elastic wave scattering by a crack in the form of a half-plane in an elastic medium is considered. It is noted that the previously published solutions do not fully cover the issues relevant to ultrasonic flaw detection, for example, detecting transverse cracks in welds. The proposed solution is made by the Wiener–Hopf technique. It is shown that scattered longitudinal and transverse waves can be generally written in closed form. Some features of the identification of the tip of transverse cracks are noted, including scattering features during sonication of cracks along their surface and the influence of critical angles.

Рассмотрены некоторые особенности совместного применения различных видов и методов неразрушающего контроля при диагностировании магистральных трубопроводов. Указано, что в настоящее время среди физических методов контроля в наибольшей мере используются ультразвуковая дефектоскопия и толщинометрия металла. Радиационный контроль, широко применяемый при строительстве трубопроводов, на этапе их диагностирования востребован значительно реже и в основном в качестве экспертного метода. Рассмотрены особенности выявления наиболее опасных дефектов – трещин, в том числе одиночных, формирующихся в период эксплуатации трубопроводов из локальных дефектов сварных швов, а также скоплений трещин различного происхождения. Показано, что хорошие результаты по выявлению поверхностных трещин любого вида дает применение электромагнитно-акустических преобразователей, излучающих в металл и принимающих волны Рэлея. Также отмечен положительный опыт использования вихретоковых многоэлементных (матричных) преобразователей для выявления поверхностных трещин различной природы, в том числе трещин, выходящих на поверхность валиков усиления сварных швов. Рассмотрена возможная схема совместного применения различных методов контроля при диагностировании магистральных трубопроводов, предполагающая использование статистических алгоритмов обработки результатов, полученных каждым методом по отдельности. Some features of the joint application of various types and methods of non-destructive testing in diagnosing main pipelines are considered. It is indicated that at present the largest volumes of application of physical methods of control fall on ultrasonic flaw detection and metal thickness measurement. X-ray, which is widely used in the construction of pipelines, is used much less frequently at the stage of their diagnosis, and mainly as an expert method. The article discusses some features of identifying the most dangerous defects – cracks, including single cracks that form during operation from local defects in welds, as well as accumulations of cracks of stress-corrosion origin. It is shown that good results in the detection of surface cracks of any kind are obtained by using electromagnetic-acoustic transducers emitting into the metal and receiving Rayleigh waves. It also points to the positive experience of using eddy current multi-element (matrix) transducers to detect surface cracks of various nature, including cracks that emerge on the surface of weld reinforcement beads. A possible scheme for the joint application of various control methods in diagnosing main pipelines is considered, which involves the use of statistical algorithms for processing the results obtained by each method separately.

Quality control of welds in multilayer polyethylene pipelines is considered; specifically, butt welds are produced by a hot tool. Besides monitoring of the welding parameters and mechanical testing of the welds, it is expedient to use nondestructive ultrasonic testing so as to detect defects such as cracks, solid inclusions, and pores. The use of ultrasonic testing in a chordal configuration to detect model defects of 1-mm diameter is presented as an example.

Based on analyzing results of the existing works, the paper demonstrates that the method of simulating motion of the SV-polarized normal waves using the classical theory of deformation appears promising in simulating their propagation in the layered polymer composite materials, as well as in studying the effect of discontinuities in such materials on the considered waves’ parameters. A model was created to analyze specifics of the described waves’ propagation in the polymer composite materials based on the carbon fiber. Formulas were obtained to calculate the amplitude coefficients for the motion equations to take into account acoustic characteristics of the polymer composite material layers and make it possible to calculate the displacement components or the energy distribution at any point in the layered medium. Phase velocity values were determined, and dispersion curves were constructed for various modes of the SV-polarized normal waves. Influence of the material layered structure on attenuation of those waves was considered, and the principle of correcting the formulas for calculating the attenuation coefficients taking into account the number of layers and their acoustic properties was outlined. Phase velocity values of the SV-polarized normal waves was experimentally verified on the sample of polymer composite materials confirming correctness of the simulation approaches

An analysis of the possibility of a rigorous theoretical solution of the three-dimensional problem of elastic wave scattering at the tip of a vertical crack in a welded joint was carried out. It was shown that in the general case of ultrasound scattering on a flat target, the three-dimensional problem can be reduced to a two-dimensional one. On this basis, for an arbitrary direction of sounding a crack in a weld, the dependence assessment of the signal from the crack tip on the direction to the receiver was made. It is noted that the wave size of the crack tip is much smaller than the wave size of the notches tip that can be machined to simulate defects in welded joints. As a result, it is shown that the nature of the scattering of elastic waves at the tip of the crack differs from the nature of scattering on the notches, including in cases where the opening of the notches is minimal based on the possibility of their manufacture. The results of an experimental verification of the obtained theoretical estimates on steel and aluminum samples were presented. It was shown that, in contrast to the tip of the cracks, at the tips of the notches, even with their minimal openings, conditions are created for the formation of a scattered field by the type of specular reflection from a volumetric cavity - a side cylindrical reflector.

The possibility of a rigorous theoretical solution of the three-dimensional problem of scattering of elastic waves at the tip of a vertical crack in a weld is analyzed. It is shown that in the general case of ultrasound scattering on a flat target, the three-dimensional problem can be reduced to a two-dimensional one. On this basis, for an arbitrary direction of sounding a crack in a weld, the dependence of the signal from the crack tip on the direction to the receiver was assessed. It is noted that the wave size of the crack tip is much smaller than the wave size of the end of the grooves that can be made to simulate defects in welded joints. As a result, it was found that the nature of the scattering of elastic waves by the tip of the crack differs from the nature of scattering on the grooves, including in cases where the opening of the grooves is minimal, based on the possibility of their manufacture. The results of an experimental verification of the obtained theoretical estimates on samples of steel and aluminum are presented. It is shown that at the ends of the grooves (in contrast to the crack tips), even with their minimal openings, conditions are created for the formation of a scattered field of the type of specular reflection from a volumetric cavity—a side-drilled hole.

Using the example of quality control of butt welds, we consider the possibility of increasing the rate of detection of defects in welded joints of small (regarding ultrasonic inspection) thickness in which ultrasonic flaw detection is complemented by eddy current testing. The possibility of combining the methods for detecting internal and surface defects during periodic diagnostics of the walls of vertical steel tanks (VSTs) is shown. The studies have been carried out on vertical and horizontal butt welds made by manual arc and semiautomatic submerged welding, including the most critical areas where these welds cross over. Examples of identifying cracks of operational origin are given. Comparison with the results of radiographic and magnetic particle testing is carried out. It is shown that during ultrasonic inspection of welded butt joints and their crossings on the wall of a VST, operational cracks in the cross section of the welds are quite confidently detected by the combined-scheme echo method, including with the use of phased arrays. The time-of-flight diffraction technique can also be used on linear sections of welds without intersections. It is noted that the detectability of surface and subsurface defects by these methods is considerably lower, and it is proposed to use operational eddy current testing to reveal such defects. It is shown that in this case, despite interference caused by the reinforcing beads of the welds, cracks coming out to the surface of the beads can be detected.

Possible causes of anisotropy of acoustic properties in additive manufacturing products are considered. Based on acoustic measurements, the type of elastic symmetry in an Inconel alloy sample prepared by selective laser melting (SLM) was determined. The analysis of the measurements has shown that the sample growер direction corresponds to the axis of symmetry of acoustic properties. The results of experimental studies and analytical modeling of the effect of anisotropy on the amplitude of a signal reflected from an artificial reflector in the form of a side drilled hole are presented.

The 3D problem of elastic-wave scattering by cracks in a homogeneous isotropic medium is considered. Using the method of Green’s function and specially introduced auxiliary functions (potentials), it is shown how, in the general case, for plane cracks, the boundary conditions can be divided into two independent parts, one of which is a system of two differential equations, the solution of which leads to Rayleigh waves on the crack surfaces, and the second of which includes one differential equation, reduced to a similar equation for acoustic-wave scattering by an absolutely rigid inclusion. Using as an example scattering by a disk-shaped crack, it is shown that the expressions for the scattered fields can be reduced to quadratures, which is important, e.g., for the study of crack detection by ultrasonic methods of flaw detection.

The reliability of ultrasonic testing (UST) of the quality of welded joints of polyethylene pipelines, made end-to-end with а heated tool, is considered in comparison with mесhапiсаl tests and radiography. The greatest detection of solid defects is provided bу u|trasonic inspection with the use of chord transducers (not less than 90%). When detecting defects translucent for ultrasound (lack of penetration, lack of fusion, etc.), the reliability decreases to 70–80%.

The urgent task is improvement of the accuracy of diagnosing the linear part of pipelines, structures and equipment of pumping and compressor stations, tank batteries, tank farm complexes. Therewith, it is required not only to identify a defect with a given probability, but also to ensure measurement of its shape and dimensions with accuracy to be sufficient to perform analysis of structures for strength and durability. The article deals with certain possibilities for increasing the detectability of volumetric defects, such as knots, through improvement of the methods for setting parameters of ultrasound pulse-echo testing. The results of research in the field of improvement of the technology for setting advanced ultrasonic systems using phased array antennas are presented. Cylinder-shaped drilled holes of different orientations have been reviewed as artificial defects for setting sensitivity and time base of the flaw-detecting instrument. Following on the earlier published works, the expediency of using vertical cylindrical drilling for setting the equipment is additionally justified: such target is the easiest to manufacture, its parameters are verified much easier than, for example, the parameters of flatbottomed holes. Examples are given of the practical use of drills of various orientations for adjusting sensitivity of monitoring and determination of the indication length of local bulk defects of the base metal and welds. Актуальной является задача повышения точности диагностирования линейной части трубопроводов, сооружений и оборудования перекачивающих и компрессорных станций, резервуарных парков, нефтебаз. При этом требуется не просто выявить дефект с заданной вероятностью, но и обеспечить измерение его формы и размеров с точностью, достаточной для выполнения расчетов конструкций на прочность и долговечность. В статье рассмотрены некоторые возможности повышения выявляемости объемных дефектов типа свищей за счет совершенствования способов настройки параметров ультразвукового контроля эхо-методом. Представлены результаты исследований в области совершенствования технологии настройки современных ультразвуковых систем, использующих фазированные антенные решетки. В качестве искусственных дефектов для настройки чувствительности и временной развертки дефектоскопа рассмотрены цилиндрические сверления разной ориентации. В развитие ранее опубликованных работ обоснована целесообразность применения для настройки оборудования вертикального цилиндрического сверления: такая мишень наиболее проста в изготовлении, ее параметры поверяются значительно проще, чем, например, параметры плоскодонных отверстий. Приведены примеры практического использования сверлений различной ориентации для настройки чувствительности контроля и определения условной протяженности локальных объемных дефектов основного металла и сварных швов.

Small-opening slots have been used to simulate cracks in butt welds. The influence of the orientation of the slot ribs on their detectability with pulse echo and diffraction methods of ultrasonic testing has been studied. It is shown that the processes occurring during the scattering of elastic waves on cracks should be modeled by a three-dimensional problem. However, theoretical analytical and numerical studies in this area most often concern two-dimensional problems of diffraction of elastic waves, where the target edge under study is located on the acoustic axis of the ultrasound source and/or receiver and is oriented perpendicular to the incident beam. The article presents experimental results illustrating the influence of the orientation of the edge (rib) in three-dimensional problems on the received signals both when using diffraction schemes of the TOFD type, and in classical ultrasonic testing by the pulse echo method according to the “tandem” scheme and with the transducers turned according to the “duet” scheme.

The paper presents the study of the "pitting corrosion" surface operational flaws detectability by the ultrasonic method of non-destructive testing. The possibility of using Rayleigh surface waves excited by an electromagnetic acoustic transducer (EMAT) for these purposes is considered. Blind vertical drills of various diameters and depths were used as artificial defects to simulate these flaws in low-carbon steel specimens. Based on the measurement results, the dependences of the amplitude of the received signals on the drilling parameters were plotted. During the statistical processing of the results, the signal-to-noise ratio was taken into account upon excitation of the Rayleigh wave using EMAT on defect-free areas of the samples. To construct curves of probability of detection (PoD), optimal models of the amplitudes distribution are determined. Under the conditions of the experiments carried out using the constructed PoD curves, conclusions were made about the minimum dimensions of a "pitting corrosion" type defect, detected with a probability of 90 %, taking into account the confidence interval of 95%, and about the possibility of adjusting the ultrasonic testing parameters using signals reflected from vertical drills.

The issues of detecting operational surface planar flaws by the ultrasonic non-destructive testing method with the use of Rayleigh surface waves generated by an electromagnetic-acoustic transducer are considered. The paper presents experimental studies of planar defects detection, simulated by an artificial reflector of the "notch" type with different width, depth and angle of inclination. The dependences of the signal amplitude on the listed parameters are constructed and their character was estimated. The optimal amplitude models for constructing the probability of detection curves (PoD) have been determined. A conclusion is made about the minimum dimensions of an operational planar flaw detected by the considering method with a probability of 90%, taking into account the confidence interval of 95%.

Small opening notches are used to simulate cracks in butt welds. The study of the influence of the notch edges orientation on their detectability when using pulse-echo and diffraction methods of ultrasonic testing. It is shown that the processes occurring during the elastic waves scattering on cracks must be modeled by a three-dimensional problem. However, theoretical analytical and numerical studies in this area most often concern two-dimensional problems of elastic waves diffraction, when the target studied edge is located on the acoustic axis of the ultrasound transmitter and / or receiver and is oriented perpendicular to the incident beam. The article presents experimental results illustrating the influence of the target point (edge) orientation in three-dimensional problems on the received signals both when using diffraction schemes of the TOFD type, and in the classical ultrasonic testing by the pulse-echo method according to the "tandem" scheme and with the turn of the transducers according to the "duet ".

Agglomerations of oxide films are some of the typical defects of friction stir welding. The structure of such defects and their small opening do not allow finding them using the conventional ultrasonic nondestructive testing methods (in particular, by the pulse-echo technique), among other things because of their low reflectivity. We have proposed a technique of artificial introduction of oxide films into a welded joint. We have shown that, to reveal such defects, it is promising to use the diffraction methods of ultrasonic nondestructive testing. The diffraction methods make it possible to detect signals from defects with minimum opening as well as from defects with a partially metallic bonding, which are semitransparent to ultrasonic waves and revealing of which is impossible using other methods of ultrasonic testing, in particular, the pulse-echo technique, along with X-ray testing.