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The synthetic aperture focusing technique (SAFT) is an imaging technique commonly used in ultrasonic inspection. In order to apply SAFT to the inspection of austenitic welds, the inhomogeneous anisotropic nature of the weld structure has to be taken into account. A suitable approach to accomplish this, is to couple the SAFT-algorithm with a ray tracing program (RT-SAFT). While SAFT-imaging of cracks in austenitic welds by use of ray tracing has been carried out before, all attempts so far were limited to longitudinal cracks which usually allows a treatment as 2-dimensional problem. In case of transverse cracks, a full 3-dimensional ray tracing is necessary in order to perform a SAFT-reconstruction. In this paper, we give an outline of our attempts to reconstruct images of transverse cracks in austenitic welds, utilizing 3-dimensional ray tracing and a layered structure model derived from an empirical model of grain orientations in welds. We present results of this RT-SAFT on experimental data taken from transverse cracks in different austenitic welds, which show that size and position of the cracks can be estimated with good accuracy, and compare them to images obtained by assuming an isotropic homogeneous medium which corresponds to the application of the classical SAFT-algorithm.
The inspection of austenitic and dissimilar welds using ultrasound demands for sophisticated testing techniques. The application of reconstruction methods like the Synthetic Aperture Focusing Technique (SAFT) on the measurement results provides an appropriate approach for defect characterization and sizing. Nevertheless, the reconstruction algorithm has to consider the aniso-tropic wave propagation inside the inhomogeneous weld material. In recent years the detection of transverse cracks has become increasingly important for ensuring the structural integrity of pipes in the primary circuit of nuclear power plants or longitudinally welded, cladded pipes. However, relia-ble inspection techniques are hardly available. In this particular case, it is expected that the compar-atively long propagation path of the ultrasonic wave field inside the inhomogeneous weld material enhances the effect of anisotropy and influences the accuracy and the signal-to-noise-ratio of the reconstruction result. In this contribution we suggest an advanced ultrasonic testing technique for detecting and sizing of transversal cracks in austenitic and dissimilar welds. The method applies a SAFT reconstruction algorithm considering the anisotropy and the inhomogeneity. A V-arrangement of the transducers in pitch-catch technique is chosen to avoid a direct coupling on the weld face. The reconstruction algo-rithm is based on an extended 3-dimensional weld model and uses a ray-tracing approach for de-termining the wave propagation paths. Along with the reconstruction algorithm the transducer set-up and experimental results of different specimens with artificial transverse flaws are presented. The availability of the proposed method for crack sizing is assessed in comparison to conventional testing techniques.
This article describes a comprehensive quantitative analysis on effect of columnar grain orientation on ultrasonic plane wave energy reflection and transmission behaviour in acoustically anisotropic austenitic weld materials. The quantitative results are presented for following general interfaces (a) Isotropic-Anisotropic, (b) Anisotropic-Isotropic, (c) Fluid-Anisotropic, (d) Anisotropic-Fluid, (e) Anisotropic-Anisotropic, (f) Anisotropic-Free surface occur during the ultrasonic non destructive evaluation of austenitic weld materials. Explicit analytical expressions are presented for energy reflection and transmission coefficients at an interface between two arbitrarily oriented transversely isotropic materials. By applying explicit analytical expressions for energy reflection and transmission coefficients, numerical results are presented for several columnar grain orientations of the transverse isotropic austenitic weld material including both real and complex domain of the reflected and transmitted normal component of slowness vectors. Valid domains of incident wave vector angles, angular dependency of energy reflection and transmission coefficients and critical angles for reflected and transmitted waves are discussed. The existence of a reflected (or) transmitted second branch of quasi shear vertical waves and its consequence to the ultrasonic non destructive testing of austenitic weld materials are investigated. The presented comprehensive quantitative evaluation provides an overview on the effect of anisotropic properties on energy reflection and transmission coefficients in columnar grained austenitic weld materials.
Up to now there is no sufficient technique to detect transverse cracks in austenitic and dissimilar welds which recently are of increasing interest in the integrity surveillance of nuclear power plants as well as in quality control of longitudinally welded pipes. Weld inspection by interpretation of single A-scans will lead to erroneous results due to effects caused by anisotropy and in worst case might leave flaws undetected. Therefore, imaging techniques such as the synthetic aperture focusing technique (SAFT) should be used. If the SAFT algorithm is applied on data taken from austenitic welds, the inhomogeneous, anisotropic structure of these welds has to be taken into account in order to properly attribute amplitudes measured in A-scans to the corresponding coordinates in the region of interest. While this has been investigated in the past, all attempts so far were limited to the imaging of longitudinal cracks which requires a less complicated setup than the imaging of transverse cracks. In this paper we give an outline of our attempts to reconstruct images of transverse cracks in different welds. For this purpose a SAFT program based on ray tracing and a layered structure weld model derived from an empirical model of grain orientations in welds are used. The results of the image reconstruction on experimental data are shown and compared to images obtained by assuming an isotropic homogeneous model. Root reflection and crack tip echo are clearly visible which allows an estimation of size and position of the crack with good accuracy.
Ultrasonic examination of anisotropic inhomogeneous austenitic welds is challenging, because of the columnar grain structure of the weld leads to beam skewing and splitting. Modeling tools play an important role in understanding the ultrasound field propagation and optimization of experimental parameters during the ultrasonic testing of austenitic welds as well as the interpretation of the test results. In this contribution, an efficient theoretical model based on the ray tracing concepts is developed to calculate the ultrasonic fields in inhomogeneous austenitic welds quantitatively. The developed model determines the ultrasound fields by taking into account the directivity of the ray source, the inhomogenity of the weld as well as ray transmission coefficients. Directivity of the ray source in columnar grained austenitic materials (including layback orientation) is obtained in three dimensions based on Lamb's reciprocity theorem. Ray energy reflection and transmission coefficients at an interface between two general columnar grained austenitic materials are calculated in three dimensions. The ray tracing model predictions on inhomogeneous austenitic weld material are compared against those from CIVA, a commercial non-destructive modeling and simulation tool. The ultrasonic modeling tools in CIVA are based on semi-analytical solutions. For beam propagation simulation, a so-called 'pencil method' is used, which involves modeling the probe as a set of individual source points, each radiating 'a bundle' of diverging rays into the medium and integrating those elementary contributions. Inhomogenity in the weld region is approximated by mapping the grain orientations on weld macrograph. Simulation results for ultrasonic field profiles for an austenitic weld are shown to be in good agreement with the corresponding experimental results.
Ultrasound propagation in inhomogeneous anisotropic materials is difficult to examine because of the directional dependency of elastic properties. Simulation tools play an important role in developing advanced reliable ultrasonic non destructive testing techniques for the inspection of anisotropic materials particularly austenitic cladded materials, austenitic welds and dissimilar welds. In this contribution we present an adapted 2D ray tracing model for evaluating ultrasonic wave fields quantitatively in inhomogeneous anisotropic materials. Inhomogeneity in the anisotropic material is represented by discretizing into several homogeneous layers. According to ray tracing model, ultrasonic ray paths are traced during its energy propagation through various discretized layers of the material and at each interface the problem of reflection and transmission is solved. The presented algorithm evaluates the transducer excited ultrasonic fields accurately by taking into account the directivity of the transducer, divergence of the ray bundle, density of rays and phase relations as well as transmission coefficients. The ray tracing model is able to calculate the ultrasonic wave fields generated by a point source as well as a finite dimension transducer. The ray tracing model results are validated quantitatively with the results obtained from 2D Elastodynamic Finite Integration Technique (EFIT) on several configurations generally occurring in the ultrasonic non destructive testing of anisotropic materials. Finally, the quantitative comparison of ray tracing model results with experiments on 32 mm thick austenitic weld material and 62 mm thick austenitic cladded material is discussed.
Ultrasound propagation in inhomogeneous anisotropic materials is difficult to examine because of the directional dependency of elastic properties. Simulation tools play an important role in developing advanced reliable ultrasonic testing techniques for the inspection of anisotropic materials particularly austenitic cladded materials and dissimilar welds. A 2-D Ray tracing method is developed for evaluating ray path, amplitude and travel time for three wave modes namely quasi longitudinal wave (qP), quasi shear vertical wave (qSV) and shear horizontal waves (SH) in anisotropic materials such as austenitic cladded materials. The inhomogenity in the anisotropic material is represented by discretizing the anisotropic region into several homogeneous layers. The ray paths are traced during its propagation through the various interfaces between those layers. At each interface the problem of reflection and refraction is solved. The ray amplitudes are computed by taking into account the directivity and phase relations. Ray divergence variation and ray transmission coefficients at each refraction boundary are considered. The Ray tracing results for ultrasonic field profiles in austenitic cladded materials are validated quantitatively by 2-D Elastodynamic Finite Integration Technique (EFIT) results and by the experiments.
Der Einsatz geführter Wellen für die
zerstörungsfreie Prüfung mit Ultraschall eröffnet neue Möglichkeiten,
räumlich ausgedehnte Bauteile mit begrenzter Zugänglichkeit
auf ihre Integrität zu prüfen und gewinnt daher
zunehmend an Bedeutung. Dieser Artikel behandelt die
physikalischen Grundlagen der Schallausbreitung. Deren Verständnis
bildet die Grundlage für die Entwicklung geeigneter
Prüfsysteme. An Beispielen werden verschiedene Möglichkeiten
zur Simulation der Schallausbereitung vorgestellt. Aktuelle
Lösungsansätze zur Prüfung von plattenförmigen Strukturen
und von Rohrleitungen werden beschrieben, wobei besonders
auf die Sensortechnik und die speziellen Anforderungen
an die Prüfhardware eingegangen wird. -----------------------------------------------------------------------------------------------------------------------------------
Guided waves are widely used for non-destructive
testing using ultrasound. Recently, the method has become increasingly
important for integrity tests of spatially extended
components with limited accessibility. This article discusses the
basic physics of the sound propagation of guided waves. Their
understanding forms the basis for the successful development
of adapted inspection systems. Examples for simulating the
wave propagation using different methods are presented. Current
approaches for the inspection of plate-like structures and
pipelines are described with focus on sensor technology and the
specific requirement on the test hardware.
Ultrasonic investigation of inhomogeneous anisotropic materials such as austenitic welds is complicated because its columnar grain structure leads to curved energy paths, beam splitting and asymmetrical beam profiles. A ray tracing model has potential advantage in analyzing the ultrasonic sound field propagation and there with optimizing the inspection parameters. In this contribution we present a 2D ray tracing model to predict energy ray paths, ray amplitudes and travel times for the three wave modes quasi longitudinal, quasi shear vertical, and shear horizontal waves in austenitic weld materials. Inhomogenity in the austenitic weld material is represented by discretizing the inhomogeneous region into several homogeneous layers. At each interface between the layers the reflection and transmission problem is computed and yields energy direction, amplitude and energy coefficients. The ray amplitudes are computed accurately by taking into account directivity, divergence and density of rays, phase relations as well as transmission coefficients. Ultrasonic sound fields obtained from the ray tracing model are compared quantitatively with the 2D Elastodynamic Finite Integration Technique (EFIT). The excellent agreement between both models confirms the validity of the presented ray tracing results. Experiments are conducted on austenitic weld samples with longitudinal beam transducer as transmitting probe and amplitudes at the rear surface are scanned by means of electrodynamical probes. Finally, the ray tracing model results are also validated through the experiments.