Showing papers on "Time-of-flight diffraction ultrasonics published in 2018"

Review of NDT and process monitoring techniques usable to produce high-quality parts by welding or additive manufacturing

Abstract: The main objectives of applying NDT techniques are to ensure the quality of an assembly or a part according to a given specification including known acceptance criteria. It generally enables not only to detect an indication, but also to classify it (size, position, nature…). Many non-destructive testing (NDT) techniques are effective in testing welded components. Radiography, ultrasonic testing, penetrant testing and magnetic particle testing are widely used and standardised. Phased arrays, TOFD and multi-elements eddy current are more and more extensively applied. Tomography, acoustic emission, ultrasonic guided waves, laser ultrasonic and optical techniques continue to be a strong topic of interest. Each of these techniques is based on different physical principles to detect defects on the surface of the part or over its whole volume. However, the geometry, physical and material properties of the part being tested are key factors in the applicability and performance of a given NDT technique. To date, the development of reliable NDT methods for additive manufacturing (AM) parts is still a major challenge. The process may generate various defects such as cracks, voids, inclusions and porosities. NDT techniques need to be optimised or developed to address singular features of the AM processes: complex geometry, special internal structures, anisotropic material properties, typical defects. Knowledge of the potential occurring imperfections produced by the various AM process needs to be improved in order to be able to select the best suited NDT techniques.

Welding Defect Classification from Simulated Ultrasonic Signals

Abstract: Nondestructive testing is widely used to detect and to size up discontinuities embedded in a material. Among the several ultrasonic techniques, time of flight diffraction (TOFD) combines high speed inspection, high sizing reliability and low rate of incorrect results. However, the classification of defects through ultrasound signals acquired by the TOFD technique depends heavily on the knowledge and experience of the operator and thus, this classification is still frequently questioned. Besides, this task requires long processing time due to the large amount of data to be analyzed. Nevertheless, computational tools for pattern recognition can be employed to analyze a high amount of data with large efficiency. In the present work, simulation of ultrasound propagation in two-dimensional media containing, each one, different kinds of modeled discontinuities which mimic defects in welded joints were performed. Clustering (k-means) and classification (principal component analysis and k-nearest neighbors) algorithms were employed to associate each simulated ultrasound signal with its corresponding modeled defects. The results for each method were analyzed, discussed and compared. The results are very promising.

Three Dimensional Characterization of Defects by Ultrasonic Time-of-Flight Diffraction (ToFD) Technique

Abstract: Ultrasonic time-of-flight diffraction (ToFD) technique has high accuracy in locating and sizing discontinuities The primary reason for this accuracy is the use of time instead of amplitude for measurement of the depth and size of discontinuities Despite the many advantages of ToFD, it suffers from a number of shortcomings, the most notable one being its two-dimensional character The goal of this paper is to develop an algorithm, as a prerequisite, to extend ToFD measurements to a three-dimensional space For this purpose, a combination of multiple transmitting and receiving probes is proposed instead of just one pair commonly used in ToFD measurements The approach for locating and sizing defects in a 3D space follows the methods used in radar and acoustic positioning systems Non-iterative techniques are used for positioning a single source (defect) based on signals collected by several transducers The estimation formula, in the form of a closed-form solution, is derived by linear least-squares minimization In addition to existing conventional passive algorithms, a new active algorithm is also proposed for the general arrangement of transducers This algorithm is tested on a steel specimen having an artificially implanted discontinuity and the three-dimensional location of the defect is estimated

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

Abstract: 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.

An alternative Ultrasonic TimeofFlight Diffraction (TOFD) method

Abstract: In this work an alternative TOFD method is presented, capable to detect and size defects in the inspected material with good precision. It was shown that the diffraction used in this technique is the most relevant signal among the longitudinal backwall and the shear backwall echoes, compared to other TOFD methods. The proposed technique showed to be particularly efficient in cases where the coventional TOFD method does not perform well; cases include near-surface defects, cracks under compressive stress and bottom tip of defects. The test configuration and a mathematical description referred to the wave path of the signal of interest is described and confirmed by numerical simulations and dynamic and static tests. The proposed method was tested for different defect depth location and find industrial applications such as inspection of cracks in tubes, closed cracks and weld joints. It opens a new possibility for TOFD based inspections.

Development of an ultrasonic weld inspection system based on image processing and neural networks

Abstract: Several types of discontinuities and defects may be present on a weld, thus leading to a considerable reduction of its resistance. Therefore, ensuring a high welding quality and reliability has become a matter of key importance for many construction and industrial activities. Among the non-destructive weld testing and inspection techniques, the time-of-flight diffraction (TOFD) arises as a very safe (no ionising radiation), precise, reliable and versatile practice. However, this technique presents a relevant drawback, associated to the appearance of speckle noise that should be addressed. In this regard, this paper presents a new, intelligent and automatic method for weld inspection and analysis, based on TOFD, image processing and neural networks. The developed system is capable of detecting weld defects and imperfections with accuracy, and classify them into different categories.

The Maximum Entropy Method in Ultrasonic Non-Destructive Testing—Increasing the Resolution, Image Noise Reduction and Echo Acquisition Rate

Abstract: The use of linear methods, for example, the Combined Synthetic Aperture Focusing Technique (C-SAFT), does not allow one to obtain images with high resolution and low noise, especially structural noise in all cases. Non-linear methods should improve the quality of the reconstructed image. Several examples of the application of the maximum entropy (ME) method for ultrasonic echo processing in order to reconstruct the image of reflectors with Rayleigh super-resolution and a high signal-to-noise ratio are considered in the article. The use of the complex phase-shifted Barker code signal as a probe pulse and the compression of measured echoes by the ME method made it possible to increase the signal-to-noise ratio by more than 20 dB for the image of a flat-bottom hole with a diameter of 1 mm in a model experiment. A modification of the ME method for restoring the reflector image by the time-of-flight diffraction (TOFD) method is considered, taking into account the change of the echo signal shape, depending on the depth of the reflector. Using the ME method, 2.5D-images of models of dangling cracks in a pipeline with a diameter of 800 mm were obtained, which make it possible to determine their dimensions. In the object with structural noise, using the ME method, it was possible to increase the signal-to-noise ratio of the reflector image by more than 12 dB. To accelerate the acquisition of echoes in the dual scan mode, it is proposed to use code division multiple access (CDMA) technology based on simultaneous emission by all elements of the array of pseudo-orthogonal signals. The model experiment showed the effectiveness of applying the ME method.

Ultrasonic Flaw Detection: Adjustment and Calibration of Equipment Using Samples with Cylindrical Drilling

Abstract: Questions related to adjusting an ultrasonic flaw detector using cylindrical bores in reference and tuning samples are considered with allowance for the specific features of single- and double-crystal testing schemes, including when a bore is sonified perpendicularly and at an angle to its axis. Requirements have been determined in each scheme to the drilling diameter and the duration of ultrasonic pulses such that signals specularly reflected from the drilling surface not be distorted by creeping and other signals diffracted by the cylinder. It is indicated that under these conditions, cylindrical drilling can be used not only for adjusting the “flaw detector–transducer” system, but also for calibrating the time scan, verifying the accuracy of the depth gage, and checking the flaw-detector attenuator. This approach makes it possible to simplify the construction of measures and tuning samples by eliminating excess reflectors. Examples are given in the echo and TOFD techniques for testing welded joints using traditional and special double-crystal schemes with different probes orientations.

Ultrasonic detection device and method for PA-TOFD combined polyethylene pipeline hot-melt butt joint

Abstract: The invention relates to a non-destructive testing technology of polyethylene pipeline hot-melt butt joint and aims to provide an ultrasonic detection device and method for PA-TOFD combined polyethylene pipeline hot-melt butt joint. The ultrasonic detection device comprises a circumferential scanning track which is arranged on a polyethylene pipeline; the circumferential scanning track is providedwith a circumferential scanning device; one end of the connecting rod is fixed on the top of the circumferential scanning device, and the other end of the connecting rod is respectively provided witha phased array probe and a single crystal straight probe through a probe holder; the two probes are positioned on two sides of the hot-melt butt joint of the polyethylene pipeline, and a gap is maintained between the end part of the probe and the polyethylene pipeline. The ultrasonic detector has two detection functions of ultrasonic phase control detection and TOFD detection, and the phased array probe is used as an acoustic wave transmitting probe for ultrasonic phased array detection and TOFD detection. And the two detection results are synchronously displayed in real time. The method overcomes the defects that the traditional pulse-type ultrasonic detection technology is not intuitive, the data cannot be recorded and stored, and the defects of precise positioning and quantification are difficult to be made.

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

Abstract: 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.

Interpretation of Indications Generated by Small Welding Discontinuities in Ultrasonic Time of Flight Diffraction Technique

Abstract: The article presents results of research on non-destructive ultrasonic time of flight diffraction technique TOFD and metallographic examinations of selected cross-sections of a MAG welded joint. The main objective was to compare the results of TOFD and metallographic examination at the locations where a large number of point-like indications, located on specific depths, have been detected on TOFD images and analyse the impact of this type of indication on results of a welded joint evaluation. Considered, that the indications have not exhibited separations between upper and lower diffraction signals, because of their small heights, measuring of height of indications in those cases was impossible. In all cases, the occurrence of discontinuities of 0.16–0.78 mm in height, in locations indicated by TOFD has been confirmed.

TOFD automatic scanning device

Abstract: The invention discloses a TOFD (time of flight diffraction) automatic scanning device. The TOFD automatic scanning device comprises a TOFD automatic scanning frame, one side of the TOFD automatic scanning frame is equipped with a guide rail and magnetic wheels, the guide rail is equipped with a first probe bracket, a second probe bracket and a third probe bracket, and the first probe bracket, thesecond probe bracket and the third probe bracket can slide to the left and right in the guide rail. The bottom of the first probe bracket is equipped with a TOFD emission probe, the bottom of the second probe bracket is equipped with a TOFD receiving probe, and the bottom of the third probe bracket is equipped with a phase control probe. The TOFD automatic scanning device employs the TOFD emissionprobe, the TOFD receiving probe and the phase control probe for combined action, a required detection space is reduced from 110mm in the prior art to only 12mm, thus greatly reducing the non-detection zone in equipment defect detection. The device provided by the invention is particularly suitable for defect detection of weld seams nearby the joints of straight pipelines and assembly parts.

Ultrasonic testing device for incomplete-penetration welds

Abstract: The invention discloses an ultrasonic testing method for incomplete-penetration welds. A TOFD (Time of Flight Diffraction) flaw detector and at least two ultrasonic probes are adopted. The ultrasonictesting method comprises the following steps: (1) selecting types and frequencies of probes to be used according to detection conditions and specifications of fillet welds; (2) directly contacting thetwo probes, and determining incidence points and leading edges of the probes and propagation time of ultrasonic waves in probe wedge blocks; (3) determining the center distance of the used probes, and mounting the probes on a scanning rack of the TOFD flaw detector; (4) calibrating the ultrasonic probes by virtue of workpiece test pieces; (5) detecting reference blocks by the calibrated TOFD flawdetector; (6) determining the group number and scanning frequency of the used TOFD probes, so as to ensure the depth and width range covering the detected welds; (7) scanning the workpiece; (8) analyzing an image. The ultrasonic detection method disclosed by the invention is high in detection efficiency, comprehensive in data and zero in blind area during detection.

Diffraction reflection combination method probe

Abstract: The utility model relates to an improve the detection device of the not enough aspect of ultrasonic wave " TOFD detection method ", it belongs to the ultrasonic detection field. Especially, relating to a diffraction reflection combination method probe, having set up interior concave surface sound production source on probe unit's voussoir upper portion, interior concave surface makes acoustic beamangle greatly increased by multistage plane concatenation, and acoustic energy distributes in the steel evenly, has enlarged the detection depth scope promptly, has also reduced to detect to leak andhas examined the district. The rethread change probe unit the shape, increase the sound zone territory that disappears and make the SNR that detects the echo obtain great improvement, strengthened the ability that detects to little defect. This probe unit improves " TOFD detection method " a pair of probe weak tendency that a time detection depth scope is little greatly, the near surface who hasimproved in a pair of probe detection depth extension detects the ability with nearly root defect, simultaneously also there is the better ability that detects to the less defect of volume. This probeunit's use can make " TOFD detection method " to have a qualitative leap.

Accurate quantitative method for inclined cracks of thick-wall pipelines based on time of fight diffraction (TOFD) circumferential scanning images

Abstract: The invention discloses an accurate quantitative method for inclined cracks of thick-wall pipelines based on time of fight diffraction (TOFD) circumferential scanning images, and belongs to the technical field of nondestructive testing. The accurate quantitative method adopts a TOFD detection system consisting of a TOFD flaw detector, TOFD probes, inclined plexiglass wedges and a scanning device,and TOFD circumferential scanning and image acquisition are carried out along the outer walls of the thick-wall pipelines. The radial distance from the upper and lower end points of the cracks to theouter walls of the pipelines, namely, the end depth, is calculated when primary bottom surface waves and diffracted waves propagating sound at the upper and lower end points of the cracks in the scanned images are read. The crack length and inclination angle are calculated based on the geometric relationship among the TOFD probe center spacing, the pipeline wall thickness and the pipeline outer wall curvature radius. The accurate quantitative method can realize simultaneous measurement of crack depth, length and inclination angle in the thick-wall pipelines, and has high detection efficiency,simple operation and high engineering application value.

An Algorithm for 3D Defect Positioning in the Case of Coplanar Transducers in Ultrasonic Time-of-Flight Diffraction Technique

Abstract: هلاقم تاعلاطا هدیکچ لماک یشهوژپ هلاقم :تفایرد 24 ید 1396 :شریذپ 14 سا ف دن 1396 :تیاس رد هئارا 24 نیدرورف 1397 ( دفات یتوصارف شور TOFD هزادنا هب رداق ) هب بیع تیعقوم یریگ اب ،هلاقم نیا رد .تسا قمع یاتسار رد طقف نآ لوط و یدعبود تروص شور زا هدافتسا تیعقوم یاه هناماس رد جوم هدنباتزاب کی تیعقوم نییعت رد یبای رادار هلمج زا یفلتخم یاه ،رانوس و کیتسوکا ،لاعفریغ ناکم یارب یمتیروگلا شور نیا رد هدافتسا دروم یلصا تیمک .تسا هدش هئارا دفات یتوصارف شور رد بیع هس یبای اه " جوم ندیسر نامز ریخات " هبساحم رد تعرس تیزم زا یرادروخرب دوجو اب قیقحت نیا رد هدافتسا دروم یلیلحت شور .تسا هدنریگ یاهراذگارت هب نامز ریخات یاطخ هب ، هحفص( نیگنایم هحفص زا هدنریگ یاهراذگارت هلصاف هک یماگنه یارب تیساسح نیا .تسا ساسح هب ،دشاب مک )اهراذگارت زا هلصاف لقادح اب یا یم شیازفا تدش هولاع .دبای هب یباوج هلئسم یارب ،دنشاب حطس مه لاماک هدنریگ یاهراذگارت هک یدراوم رد نآ رب من تسد ی هلاقم نیا رد .دیآ نآکم نتفرگ رظن رد اب متیروگلا نیا رد .تسا هدش داهنشیپ حطس مه ِهدنریگ یاهراذگارت طیارش رد هتسب لح رب ینتبم یمتیروگلا یضرف ییاه هب ،هدنریگ یاهراذگارت یارب هب هدنریگ یاهراذگارت ناکم و فده تیعقوم نامزمه تروص یم تسد تیعقوم نیا .دنیآ یضرف یاه هنوگ هب یا هب یم تسد نآ هلصاف هک دنیآ تیعقوم نییعت رد متیروگلا نیا زا ،درکلمع تحص دییات یارب .دشاب هتشاد یلوبق لباق هزادنا نیگنایم هحفص زا اه سم لح رد تسب نب هب ندیسر مدع و اطخ هب تیساسح شهاک رد یلوبق لباق جیاتن و دش هدافتسا یدلاوف هعطق نورد یعونصم بیع کی رد هلئ هب هدنریگ یاهراذگارت ندوب حطس مه تیعضو دمآ تسد . :ناگژاو دیلک ناکم جوم عبنم یبای دفات یتوصارف شور ناکم هزادنا و یبای بیع یراذگ

The development of an ultrasonic testing procedure using TOFD technique in the context of dead zones and spatial resolution

Abstract: The increase in the use of advanced ultrasonic testing techniques such as TOFD and Phased Array, observed in recent years is connected with the necessity of development of appropriate testing procedures, differing significantly from typical procedures for conventional ultrasound examinations. For this reason, the paper describes the most important issues that should be analyzed and taken into account at the stage of preparation of the ultrasonic examination procedure with the time of flight diffraction TOFD technic. Particular attention has been paid to the size of TOFD dead zones and changes in spatial resolution on the thickness of the joint tested, as well as the clarification of the principles for the assessment of unmeasurable in the direction of joint thickness indications.

Device for TOFD (time of flight diffraction) and phased array integrated detection of hot melt butt joint of polyolefin pipeline

Abstract: The invention relates to a detection technology of a hot melt butt joint of a polyolefin pipeline and aims at providing a device for TOFD (time of flight diffraction) and phased array integrated detection of a hot melt butt joint of a polyolefin pipeline. The device comprises two phased array ultrasonic probes, two holding devices, two circumferential motion scanning devices, and two probe frame and coupling devices, wherein the holding devices clamp the polyolefin pipeline in a surrounding manner and are used for mounting the circumferential motion scanning devices; the two ends of a connecting rod are connected with mounting platforms of the circumferential motion scanning device respectively via mounting frames; the two probe frame and coupling devices are mounted in the middle of the connecting rod; the bottoms of the coupling devices are placed on the polyolefin pipeline; the two phased array ultrasonic probes are oppositely mounted on oblique surfaces of hollow containers; and ultrasonic transmission directions of the phased array ultrasonic probes are intersected below a position between the ultrasonic probes. The phased array ultrasonic probes can achieve omnibearing detection of the hot melt butt joint; a shape feature of a defect can be accurately positioned; and a non-fusion defect of the hot melt joint is detected and evaluated completely.