Ultrasonic Time Of Flight Diffraction Research Articles

Resolution Enhancement in Ultrasonic TOFD Imaging by Combining Sparse Deconvolution and Synthetic Aperture Focusing Technique (Sparse-SAFT)

The shallow subsurface defects are difficult to be identified and quantified by ultrasonic time-of-flight diffraction (TOFD) due to the low resolution induced by pulse width and beam spreading. In this paper, Sparse-SAFT is proposed to improve the time resolution and lateral resolution in TOFD imaging by combining sparse deconvolution and synthetic aperture focusing technique (SAFT). The mathematical model in the frequency domain is established based on the l1 and l2 norm constraints, and the optimization problem is solved for enhancing time resolution. On this basis, SAFT is employed to improve lateral resolution by delay-and-sum beamforming. The simulated and experimental results indicate that the lateral wave and tip-diffracted waves can be decoupled with Sparse-SAFT. The shallow subsurface defects with a height of 3.0 mm at the depth of 3.0 mm were detected quantitatively, and the relative measurement errors of flaw heights and depths were no more than 10.3%. Compared to conventional SAFT, the time resolution and lateral resolution are enhanced by 72.5 and 56% with Sparse-SAFT, respectively. Finally, the proposed method is also suitable for improving resolution to detect the defects beyond dead zone.

Time of flight diffraction for rough planar defects

Ultrasonic non-destructive evaluation techniques, such as time-of-flight diffraction (ToFD) for which the arrival times of waves diffracted from crack tips are analysed to locate and size defects, are well understood for smooth defects. In environments where extreme changes in temperature and pressure occur, the damage that may arise is often non-uniform and more difficult to characterise when designing and qualifying an inspection. This article investigates the implementation of ToFD methods for sizing rough defects using a purely theoretical approach. High-fidelity finite element modelling and stochastic Monte Carlo methods are used to provide physical and statistical insights for the dependence on both incident beam angle and degree of roughness for the case of planar defects. Optimal incident angles for ultrasonic ToFD techniques were determined in the 1980s but largely based on theoretical and experimental investigations for smooth defects. However, rough defects produce tip-diffracted signatures that are more complicated than for their smooth counterparts, largely due to multiple scattering effects related to mode conversion and propagation of surface waves along the rough surface. It is shown that roughness may cause larger diffraction amplitude values at different angles, which leads to increased uncertainty when sizing, with illustrative examples and physical interpretations provided. Comparisons of amplitudes for smooth and rough defects of the same size are also demonstrated. The ToFD method, using envelope peak detection and autocorrelation approaches, is implemented to estimate the size of rough cracks, and the effects of roughness on the accuracy of this sizing are investigated with statistical analysis.

Quantitative detection of shallow subsurface cracks in pipeline with time-of-flight diffraction technique

When the ultrasonic time-of-flight diffraction (TOFD) technique is applied to the inspection of pipeline, the propagation direction of the direct longitudinal wave is not parallel to the pipe surface, leading to the increment of the depth of dead zone and the measurement errors of shallow subsurface cracks. In this paper, the differences between the dead zones in flat plate and pipeline are compared theoretically. Subsequently, the method based on the mode-converted waves in TOFD B-scan image, which has been used for reducing the dead zone in flat plate, is developed to restrict the dead zone in pipeline and to realize the accurate measurement of shallow subsurface cracks. The simulated and experimental results indicated that the depth of dead zone in the carbon steel pipeline with a radius of 148 mm was reduced from 6.3 mm to 3.0 mm and that the measurement errors of crack length and angle were no more than 0.27 mm and 1.57°, respectively. The depth of the dead zone in pipeline and the measurement errors before modification both increase with the reduction of the ratio of pipe radius to probe center spacing (PCS). The modified method has universality for the detection of the shallow subsurface cracks in pipeline with ultrasonic TOFD technique.

A wavelet analysis-based matching pursuit algorithm for an accurate ultrasonic TOFD measurement

The time-of-flight diffraction (TOFD) technique is used as an important non-destructive testing method in weld integrity evaluation and failure analysis. However, an accurate measurement of the time-of-flight (TOF) has proven to be difficult due to the low time resolution of the measured signal. Conventional deconvolution techniques have been used to improve the time resolution of the signal but are not effective for ultrasonic TOFD signals because the frequency contents of the signals are non-static in space-frequency distribution. To overcome this problem, a method is proposed in this paper that estimates the TOF in two steps. In the first step, the measured signal is decomposed into a series of narrowband signals using a wavelet transform and an atom dictionary is adaptively established according to the characteristics of a selected narrowband signal. In the second step, matching pursuit (MP) is used to derive a sparse representation of the selected narrowband signal. A steel specimen with artificial defects is prepared, experiments are carried out and the results confirm the efficacy of the proposed algorithm.

Finite Element Analysis Model on Ultrasonic Phased Array Technique for Material Defect Time of Flight Diffraction Detection

In this study, the finite element method (FEM) for phased array technology in ultrasonic time of flight diffraction (TOFD) for the defect detection of two-dimensional (2-D) geometric materials was researched. The phased array technology generated the FEM model for the TOFD signal. We have established the finite element model by the FEM software ANSYS based on the ultrasonic mechanism about the defects and the phased array transducer. A plane strain elements have simulated the reflected signal of the defect. We can compare the error ratio between simulation and experiment by using the theoretical calculation value as the benchmark, and find the feasibility of the FEM detection.

Automatic Recognition of Weld Defects in TOFD D-Scan Images Based on Faster R-CNN

Abstract The type recognition of a weld defect in an ultrasonic Time of Flight Diffraction (TOFD) image is lack of efficiency, stability, and reliability that is due to the limitation of experience and professional knowledge of the inspector. In this study, characteristics of a weld defect of TOFD D-scan images were analyzed, and the Faster Region-based Convolutional Neural Networks (Faster R-CNN) was adopted for autorecognition of the defect’s type. In the course of the training process, the proposed box configuration was optimized to improve training and recognition efficiency, and the imaging samples were expanded for training, adjusting, and verifying the Faster R-CNN. Eventually, the recognition effect and influence factors of misrecognition were analyzed. Research results show that a D-scan image of the weld defect is closely related to the defect’s shape, which can be used to decide the type a weld defect’s type. Automatic recognition of the defect’s type based on the Faster R-CNN possesses the advantages of high recognition rate, robustness, and antijamming ability, which can achieve a recognition accuracy of 80–97 % for the weld defect’s type. In addition, the analysis of misrecognition shows that it is necessary to denoise the D-scan images before autorecognition because, in the light of the noise, stripes are liable to be misrecognized as porosity and cracks in the recognition experiments.

Hybrid Ultrasonic TOFD Imaging of Weld Flaws Using Wavelet Transforms and Image Registration

Ultrasonic time of flight diffraction (TOFD) is an effective weld crack inspection technique. Due to the intensity of diffraction wave is rather weak compared with the lateral wave and the bottom echo wave, thus the signal-to-ratio (SNR) of TOFD image is low. A new dichotomous method is comprised of two steps that contains wavelet shrinkage and image registration is proposed in this paper to reduce the noise and improve the resolution of TOFD images as well. In order to evaluate the reliability of our proposed method in this paper, we have established the experiment system, and sampled a number of TOFD data with random distribution of noise characteristics. We adopted one-dimension wavelet transform and two-dimension wavelet transform in the very beginning of the first step of the proposed algorithm respectively. The SNR of the result obtained in this step is improved significantly compared with the classic algorithms. Next, the image registration is applied. After the registered images have been added to form a new one, then it comes to the final result that shows not only the SNR but also the definition of the image is enhanced effectively.

Multiframe Ultrasonic TOFD Weld Inspection Imaging Based on Wavelet Transform and Image Registration

TOFD (time of flight diffraction) is a kind of weld defect detection technology by using ultrasonic diffraction wave signal. Because the diffraction intensity is far less than ultrasonic echo wave intensity, thus, the noise contained in TOFD signal is fairly large, and the formed image is not clear enough. Therefore, it is difficult to determine the size of defects accurately. In this paper, a method of noise reduction of TOFD signal and improving the resolution of the image are discussed based on the combination of wavelet thresholding and image registration. Wavelet multiresolution analysis method is adopted and the A-scan signal is decomposed into different frequency components. We propose a new threshold function to process the wavelet coefficients, which guarantees to denoise while preserving the useful information as much as possible. Setting up the ultrasonic TOFD inspection system and the image data with randomly distributed noise can be obtained via fine shake of the probes during testing. Then, image registration based on maximum correlation and blending is adopted to eliminate the noise in further step. The result shows that the proposed method can achieve denoising, together with resolution enhancement.

Ultrasonic Testing of Butt Weld Joint by TOFD Technique

The aim of the article was to check the internal defects in the butt welded joints by non-destructive TOFD (Time of Flight Diffraction) technique. Subsequently, the macrostructure from the defect indication site was evaluated and assigned to the TOFD ultrasound indication. Basic knowledge of ultrasonic TOFD testing are described in the theoretical part of a submitted paper. Ultrasound technique TOFD is non-destructive method that can detect internal defects inside test material without damaging it. It is a reliable method for detecting mainly flat internal defects such as incomplete root penetration, lack of fusion, etc. Ultrasonic test procedures and test results obtained in non-destructive testing of butt weld are shown in experimental part. Evaluation of the ultrasonic TOFD testing results, its advantages and disadvantages are described at the end of this article.

Quality Enhancement of Ultrasonic TOFD Signals from Carbon Steel Weld Pad with Notches

Welding is an integral part of component fabrication in industry. Even though the science and art of welding are more than 100 years old, defects continue to occur during welding. Codes of practice require that the welds be tested and evaluated. Conventionally ultrasonic testing has been widely applied in industry for the detection and evaluation of the flaws/defects in the weldments. With advances in sensor and signal analysis technologies, the last two decades have seen extensive developments in the field of ultrasonic testing. We have advanced techniques such as Time of Flight Diffraction (TOFD) which has better probability of detection for linear defects. A major irritant during the application of TOFD, especially for the testing of carbon steel weldments, is the presence of noise. A variety of approaches has been used internationally for the suppression of such noise and each has its own merits and demerits. This paper focuses on a method of enhancing the TOFD A-scan signals in carbon steel weldments by suppressing the noise from them using the discrete wavelet transform (DWT). The analysis clearly indicates that the DWT gives better signal-to-noise ratio improvement using higher-order wavelet filters with 4-level DWT decomposition. However the computational cost of this signal enhancement depends on the wavelet filter chosen along with the chosen level of DWT decomposition.

Analysis on Ultrasonic TOFD Imaging Testing for Ultra-thick-walled EBW Joint of Aluminum Alloy

Abstract In order to complete the defect inspection and welding performance evaluation of the ultra-thick-walled aluminum alloy welded joint by electron beam welding (EBW), the ultrasonic time of flight diffraction (TOFD) D-scan imaging inspection investigations were carried out for the welded joint with the thickness of 165mm. Aiming at accurately identifying the defect information in the whole thickness area of the weld joint, a multiple scanning method combined with the double surface inspection with different separations of transducers and different refraction angle of acoustic beam was proposed to make the main beam of the transmitted and received transducers cover the whole weld zone. The experiments with different inspection parameters were performed by the top and bottom surface scanning for the four artificial side-drilled holes (SDHs) in different depth. The testing results of A-surface and B-surface scanning with the separation of 160mm and the refracted angle of 45° show that the defects in the depth more than 20mm can be accurately sized and positioned, while that in the depth less than 20mm at the vicinity of top surface are in the inspection blind zone. However, the defect diffracted waves are distinguished from the lateral waves obviously in the A-surface scanning with the separation of 72mm and the refracted angle of 68°. Large numbers of welding defects in the middle depth area and two sides of the weld zone can be observed by D-scan image. It is shown that the novel scanning method can effectively improve the inspection difficulties of ultra-thick-wall aluminum alloy weld and its inspection blind zone.

Optimization of the Cascade Feed Forward Back Propagation network for defect classification in ultrasonic images

Ultrasonic Time of Flight Diffraction (TOFD) is now a well established NDE technique finding wide applications in the industry for inspection during manufacture, pre-service and also inservice. While conventionally interpretations of UT images are done by the inspector, a need has always been felt for automated evaluation and interpretation especially when large inspection volumes are involved. Apart from enhancing the speed of inspection, automated evaluation and interpretation provides better reliability of inspection. A number of approaches based on signal analysis coupled with artificial neural networks (ANN) are being tried internationally and limited success has also been obtained. This paper focuses on the development of a semi automatic toolbox for reliable and fast flaw classification in TOFD images using ANN. TOFD images are first acquired and statistical parameters such as mean, standard deviation, energy, skewness and kurtosis are calculated for the region of interest in the images. The classification of the flawed region like Crack, Lack of Fusion, Lack of Penetration, Porosity and Slag Inclusion was materialized using different ANN approaches which made use of these statistical parameters as their input. The process of optimization of a network involves comparison of classification accuracy and the sensitivity of the selected networks. The Cascade Feed Forward Back Propagation (CFBP) network with log sigmoidal activation function proved to be the optimized network model for the data set considered in this study.

Research on Defect Image Enhancement in Ultrasonic TOFD Detection

when testing the defect by ultrasonic time of flight diffraction (TOFD), the image signal detected is often re- shaped and resulted in inaccuracy of defect measurements because the probe beam has a limited range. This paper pro- posed an image enhancement method based on synthetic aperture focusing technique (SAFT). A mathematical model of testing image was first established based on the generation process of the image. A method was then designed for detect- ing defects in near surface blind area based on filtering of through waves. Finally, a synthetic aperture focusing algorithm based on peak capture pretreatment was used to enhance the resolution of the image. By applying the above method to test a crack defect of 15mm, the method was able to accurately judge for crack defect. Also, the measuring accuracy can be improved by 6.4% compared to that of traditional detection method.

Ultrasonic Time-of-Flight Diffraction Testing with Linear Frequency Modulated Excitation for Austenitic Stainless Steel Welds

The main problems for ultrasonic inspection of austenitic stainless steel welds are low signal to noise ratio (SNR) and detection accuracy, caused by anisotropic and heterogeneous material structure with bulky columnar crystal. In order to overcome the problems mentioned above, a linear frequency modulated (LFM) pulse with a large time-bandwidth product can be used as the exciting signal in the ultrasonic inspection of the austenitic stainless steel welds, which can both enhance the average transmitted power and increase the SNR and time resolution by pulse compression process. Therefore, the ultrasonic time-of-flight diffraction (TOFD) technique with the LFM excitation was carried out to realize an accurate sizing and locating detection in austenitic stainless steel welds. Compared with the conventional TOFD testing, the SNR can be increased 12–15 dB, and the measured accuracy is also enhanced obviously. Accordingly the measured depth error is less than 0.81 % and the length error is less than 2.5 %. The proposed method can both enhance the capabilities of the ultrasonic inspection of austenitic welds and the measurement accuracy of ultrasonic TOFD testing.

Ultrasonic Testing of Girth Welded Joint with TOFD and Phased Array

The article describes the fundamental physical principles of the ultrasonic defectoscopy TOFD (Time of Flight Diffraction) and Phased Array. There is a report from the ultrasonic testing of girth welded joint with ultrasonic flaw detector OmniScan MX2 16:64 PA from the company Olympus NDT. In welded joint were artificaly made three defetcts. Two lack of sidewall fusion (on the left and right side of welded joint) and one crack in axis of welded joint. Both ultrasonic testing were designed in software ESBeamTool 5 from the company Eclipse Scientific, which simulates the geometrical ultrasonic beams spread. At the end, data from both ultrasonic testing were evaluated. The same procedure will be used for the design of ultrasonic inspection TOFD and Phased Array at girth welded joints of gas pipelines.

Ultrasonic TOFD Detection by Finite Element Simulation Method

This paper investigated the ultrasonic mechanism of Time of Flight Diffraction (TOFD) by finite element analysis for the better applications of ultrasonic TOFD (Time of Flight Diffraction) detection technology. The welding steel plate with the artificial defects is used in the finite element analysis model. The experimental A-scan signal with higher noise is filtered by the wavelet transform, which can clearly show defective diffracted wave. The software simulation of ultrasound is used to present the propagation process of ultrasonic signal inside the sample. Simulation results are compared with the experimental results, which shows valid basis for the practical TOFD ultrasonic detection methods in industrial applications.

Simulation of Ultrasonic Detection of Natural Defects in Weld with Finite Element Analysis

With the continuous development of the ultrasonic detection technology, ultrasonic time of flight diffraction (TOFD) method has been widely applied. The paper investigated the TOFD technique in the detection of natural defects. TOFD detection experiment is established in Lab. The finite element analysis simulation of A-scan signal and ultrasonic TOFD technique in the detection of the longitudinal arrangement of pores defects within the weld specimen transmission are studied. The feasibility and correctness of the finite element analysis model are verified by comparing the experimental signals with the simulation signals.

FEM Analyses of the TOFD Technique in Unequal Thickness Component

The time-of-flight diffraction (TOFD) technique is a new ultrasonic nondestructive testing method. It utilize the longitudinal diffraction signal that generated from the defects, we can confirm whether there is a discontinuity in butt weld by the analysis of diffracted waves. This detection method has wide application prospects and detect flaws with high precision of localization and quantification. In this paper, two-dimensional numerical simulation of ultrasonic TOFD technique is carried out on unequal thickness butt weld of Drum Cylinder and Spherical Head, the propagation characteristics and laws of ultrasonic wave in unequal thickness component are analyzed by using finite element software ABAQUS. The simulation results show that the ABAQUS software can effectively simulate ultrasonic TOFD technique in such pressure vessel component, so the application range of ultrasonic TOFD technique will be extended.

Ultrasonic TOFD in the Application of Thick Wall Tube Welding Seam Detection Pre-Research

This article firstly introduces the ultrasonic TOFD (Time-of-flight - Diffraction) detection technology of detection principle, advantages and disadvantages, and then summarizes the ultrasonic TOFD technique related testing standard, finally combining the reality of tube mill, analyses the pipe material testing near the surface of the blind area and radian impact problems, discusses the ultrasonic TOFD in application prospect in the field of thick wall tube welding seam detection.

FEM Model-Based Investigation of Ultrasonic TOFD for Notch Inspection

A two-dimensional numerical model based on the finite element method was built to simulate the wave propagation phenomena that occur during the ultrasonic time of flight diffraction (TOFD) process. First, longitudinal-wave TOFD was simulated, and the numerical results agreed well with the theoretical results. Shear-wave TOFD was also investigated because shear waves have higher intensity and resolution. The shear wave propagation was studied using three models with different boundary conditions, and the tip-diffracted shear-tolongitudinal wave was extracted from the A-scan signal difference between the cracked and non-cracked specimens. This signal showed very good agreement between the geometrical and numerical arrival times. The results of this study not only provide better understanding of the diffraction phenomena in TOFD, but also prove the potential of shear-wave TOFD for practical application.