Showing papers on "Time-of-flight diffraction ultrasonics published in 2005"

The use of artificial neural network in the classification of pulse-echo and TOFD ultra-sonic signals

Abstract: The present work evaluates the application of artificial neural networks for pattern recognition of ultrasonic signals using pulse-echo and TOFD (Time of Flight Diffraction) techniques in weld beads. In this study pattern classifiers are implemented by artificial neural network of backpropagation type using MATLAB®. The ultrasonic signals acquired from pulse-echo and TOFD were introduced, separately, in the artificial neural network with and without preprocessing. The preprocessing was only used to smoothen the signal improving the classification. Four conditions of weld bead were evaluated: lack of fusion (LF), lack of penetration (LP), porosity (PO) and non-defect (ND). The defects were intentionally inserted in a weld bead of AISI 1020 steel plates of 20 mm thickness and were confirmed using radiographic tests. The results obtained show that it is possible to classify ultrasonic signals of weld joints by the pulse-echo and TOFD techniques using artificial neural networks. The results showed a performance superior a 72% of success for test. Although the preprocessing of the signal improved the classification performance of the signals acquired by the TOFD technique considerably, the same didn't happen with the signals acquired by the pulse-echo technique.

Ultrasonic signal identification by empirical mode decomposition and Hilbert transform

Abstract: A novel approach is proposed to identify the arrival time of overlapping ultrasonic echoes in time-of-flight diffraction (TOFD) flaw detection. The nonlinear and nonstationary ultrasonic signal is decomposed using empirical mode decomposition method to obtain intrinsic mode functions, which are used for signal reconstruction. By applying Hilbert transform to the reconstructed signal, the arrival time of each echo can be clearly identified. The efficiency and feasibility of this approach in enhancing the time resolution of ultrasonic signal are validated by simulation and experiment, where 98% of flaws in 12-, 10-, and 8-mm-thickness pipelines can be identified with an average accuracy of 0.2 mm. The blind area of TOFD has been reduced to 2.5 mm under the surface. The frequency and angle of the probe pair have little influence on the identification.

Review of Ultrasonic Phased Arrays for Pressure Vessel and Pipeline Weld Inspections

Abstract: Major improvements in weld inspection are obtained using Phased Array technology with capability for beam steering, electronic scanning, focusing, and sweeping the ultrasonic beams. Electronic scanning is much faster than raster scanning, and can optimize angles and focusing to maximize defect detection. Pressure vessel (PV) inspections typically use “top, side, end” or “top, side, TOFD” views, though other imaging is possible. Special inspections can be performed, e.g., for specific defects, or increased coverage. Defects can be sized by pulse-echo as per code, by time-of-flight Diffraction or by back diffraction. New PV inspection codes, particularly ASME Code Case 2235, permit the use of advanced ultrasonic inspection techniques. Pipeline girth weld inspections use a unique inspection approach called “zone discrimination,” and have their own series of codes. While similar equipment is used in pipeline as in PV inspections, the pipeline philosophy is to tailor the inspection to the weld profile and predicted lack of fusion defects. Pipeline displays are specifically designed for near real-time data analysis. Both ASME CC 2235 and the pipeline codes permit the use of Fitness-For-Purpose, which reduces construction costs. Overall, phased array systems meet or exceed all PV and pipeline codes.

Welding defect pattern recognition in TOFD signals. Part 2. Non-linear classifiers

Abstract: The time-of-flight diffraction (TOFD) technique has been widely used for automatic weld inspection. Despite the high speed of inspection high reliability in sizing and the low rate of false indications, the classification of defects obtained by the TOFD technique is still frequently questioned since it depends mainly on the knowledge and experience of the operator. This dependence on the operator has led to attempts to automatically classify the defects detected during inspection and neural networks are powerful tools that can he used for this objective. The use of non-linear classifiers to improve the performance reached by linear classifiers, presented in previous works, is the main objective of this work. A-scan signals were obtained during the inspection of test samples containing well-controlled weld defect previously characterised by X-rays. After the inspection, the signals were divided into three classes; according to the type of defect found (lack of fusion, lack of penetration and porosity). Another class of signal was acquired from regions with no defects. Non-hierarchical and hierarchical non-linear classifiers, implemented by an artificial neural network, were used in the classification of these signals. The backpropagation learning rule was used to train the neural network. The performance of these two different classifiers was evaluated and compared. The non-linear classifiers had good results in the recognition of welding defect patterns of TOFD signals. The rate of success reached 100% and 98% for training and test respectively, against 99% and 96% for the linear classifiers, which were obtained in the last works.

Method and apparatus for measuring flaw height in ultrasonic tests

Abstract: The measurement of a flaw height in a thick welded portion of a stainless steel specimen, which is difficult to perform by the TOFD method, can be conducted with more ease, with higher accuracy and in a shorter time than in the case of using tip echo techniques. In addition, it is possible to reduce variations in measurement results among individual inspectors. An ultrasonic wave 21 is launched by a transmitting probe 1 into a specimen 20 in a direction oblique to a flaw 24 to generate diffracted waves at the tip 25 of the flaw 24, then a diffracted wave 22 propagating upward directly from the flaw 24 and a diffracted wave 23 propagating upwardly of the flaw 24 after once reflected off the back 27 are received by a receiving probe 2 disposed above the flaw 24, and the height of the tip of the flaw 24 from the back 27 is measured from the propagation time difference between the received diffracted waves.

Ray based model for the ultrasonic time-of-flight diffraction simulation of thin walled structure inspection

Abstract: It is necessary to size the cracklike defects accurately in order to extend the life of thin-walled (<10 mm) components (such as pressure vessels) particularly for aerospace applications. This paper discusses the successful application of ray techniques to simulate the ultrasonic time-of-flight diffraction experiments for platelike structures. For the simulation, the diffraction coefficients are computed using the geometric diffraction theory. The A and B scans are simulated in near real time and the different experimental parameters can be interactively controlled due to the computational efficiency of the ray technique. The simulated results are applied to (1) defect signal identification for vertical defects, (2) inspection of inclined defects, and (3) study the effect of pulse width or probe frequency on experimental results. The simulated results are compared with laboratory scale experimental results.

Ultrasonic Nondestructive Testing Accurate Sizing and Locating Technique Based on Time-of-Flight-Diffraction Method

Abstract: The ultrasonic time-of-flight-diffraction (TOFD) method is a widely used flaw sizing and locating method. A signal identification technique is used to improve the arrival time resolution of a TOFD signal and to size and locate flaws more accurately. The ultrasonic signal is decomposed into several intrinsic mode functions by empirical mode decomposition. Some modes are selected to reconstruct a new signal considering their frequencies and energy. The reconstructed signal has a better signal-to-noise ratio and enhanced flaw information. A Hilbert transform is conducted to get the envelope and exact arrival time of the signal. All vertical flaws can be detected correctly with average sizing and locating accuracy of 0.08 mm in the laboratory. The deeper the flaw is located, the higher the accuracy. The blind area of TOFD is reduced to 2.5 mm under the surface.

for the Ultrasonic Time-of-Flight Diffraction Simulation of Thin Walled Structure Inspection

Abstract: It is necessary to size the cracklike defects accurately in order to extend the life of thin-walled 10 mm components (such as pressure vessels) particularly for aerospace applications. This paper discusses the successful application of ray techniques to simulate the ultrasonic time-of-flight diffraction experiments for platelike structures. For the simulation, the diffraction coefficients are computed using the geometric diffraction theory. The A and B scans are simulated in near real time and the different experimental parameters can be interactively controlled due to the computational efficiency of the ray technique. The simulated results are applied to (1) defect signal identification for vertical defects, (2) inspection of inclined defects, and (3) study the effect of pulse width or probe frequency on experimental results. The simulated results are compared with laboratory scale experimental results. DOI: 10.1115/1.1989353

Method and instrument for measuring flaw height in ultrasonic testing

Abstract: Measurement of the flaw height of a thick stainless steel welded portion difficult to apply the TOFD method is performed conveniently and precisely in a short time by a tip-echo technique while suppressing variations with inspectors. An ultrasonic wave (21) is emitted from a transmission probe (1) to a flaw (24) in an object under inspection (20) from an oblique direction and a diffracted wave is generated at the end (25) of the flaw (24). A diffracted wave (22) propagating directly above the flaw (24) and a diffracted wave (23) propagating above the flaw after reflecting from the rear surface (27) are received by a receiving probe (2) above the flaw (24). The height position from the rear surface (27) at the end of the flaw (24) is measured from the difference between the propagation times.

Automatic data processing and defect detection in time-of-flight diffraction images using statistical techniques

Abstract: Ultrasonic Time-of-Flight Diffraction (TOFD) has proved highly effective for the inspection of welds, providing accurate positioning and sizing of defects. Currently, most TOFD data interpretation is performed off-line by a trained operator and using interactive software aids. This processing is highly dependent on operator experience, alertness and consistency and is cumbersome and time-consuming. Results typically suffer from inconsistency and slight inaccuracies, particularly when dealing with large volumes of data. The recent trend in the related disciplines of remote sensing and medical imaging is to automate the data processing and interpretation process as far as possible, relieving the expert to some extent of unnecessary or repetitive tasks. It is anticipated that TOFD interpretation could benefit from such automation, improving the interpretation procedures by adding an element of robustness, accuracy and consistency. This can be achieved by discriminating between subtle variations in visual and spectral properties of the data, resulting in savings in time, effort and cost. This paper presents a scheme for the automatic processing of TOFD data and detection of weld defects as part of a comprehensive TOFD inspection and interpretation aid. A number of signal and image processing tools have been specifically adapted for use with ultrasonic TOFD data and developed to function autonomously without the need for continuous intervention. It is hoped this will form the basis for a new paradigm in ultrasonics for fully-automatic batch processing and interpretation.

5023 - utilising phase relationships for automatic weld flaw categorisation in time-of-flight diffraction images

Abstract: Ultrasonic Time-Of-Flight Diffraction (TOFD) is a recent innovation that has proved highly effective for the inspection of steel plates and tubular pipelines and has started to take its way to replace the other ultrasonic testing techniques. It is anticipated that coupled with the necessary processing algorithms, TOFD can be used for a comprehensive automatic inspection of welds with satisfactory levels of accuracy and reliability. Although each defect category has unique characteristics and patterns but there are some similarities between these categories which make the discrimination between these categories not an easy task. Careful estimating the phase relations for each defect category is very important for providing an automatic interpretation system. The determination of the phase relationships between defect echoes and comparing them with the lateral wave and backwall echoes can be used for characterising defect classes and also to achieve accurate defect sizing. Therefore a phase determination system based on the measurement of correlation between the two signals has been developed. These phase determination results can be combined with artificial intelligent technologies such as fuzzy logic and neural networks in order to differentiate between different defect categories, thus opening a new paradigm in TOFD for automatic inspection.

A point source correlation technique for automatic discontinuity identification and sizing using time of flight diffraction

Abstract: This paper proposes a technique for automatic discontinuity location and sizing using the ultrasonic time of flight diffraction technique. Here, the crack tips are modeled as point sources of diffracted waves in a homogenous, isotropic medium. The diffraction arcs are modeled using a ray based approach and the modeled arcs are correlated with the experimental B-scan data. The points of high correlation provide information about the location of the crack tips. A statistical echo separation procedure to isolate the diffraction arcs in the B-scan image is discussed. This paper also addresses the issue of application of this time of flight diffraction technique to a thin section (less than 12 mm [0.47 in.]), wherein the echoes from the various sources (lateral wave, back surface reflection, diffraction from crack tips and so on) interfere with each other, making it difficult to identify diffracted signals from the discontinuity tips.

Industrial Applications of Ultrasonic Time-of-Flight-Diffraction(TOFD) Techniques for Various Field Targets

Abstract: The ultrasonic time-of-flight-diffraction (TOFD) technique has been used mainly to detect and precisely size flaws in welded butt joints. But industrial applicability of the conventional TOFD technique is restricted due to inspection targets’shape complexity and ultrasonic noise. In order to increase the applicability of the TOFD technique for real industrial targets, various improved TOFD techniques have been developed. In this paper, industrial applications and limitations of the conventional TOFD technique and newly developed TOFD technologies, which can overcome those limitations, are presented.

Time of flight diffraction: an alternate non-destructive testing procedure to replace traditional methods

Abstract: Time-of-flight-diffraction Technique (TOFD) is considered as one of the fastest methods of Non-destructive testing (NDT) since a weld can be characterized to a certain degree with one single scan along its length with two probes. An image of the complete weld is created showing component and, more importantly, any defect information. In this paper a comprehensive review of the TOFD technique covering many aspects, e.g. accuracy, coverage, resolution, repeatability, and last not least speed where the real value of TOFD lies-despite its few inherent limitations is presented. This paper presents the results of experimental investigations carried out using various NDT techniques including TOFD on specimens such as welds with various types of defects. The results of these investigations are compared and the feasibility of using TOFD as an alternative NDT procedure to replace the traditional NDT methods of inspecting fabricated pressure vessel components are examined.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Time-of-flight diffraction : from semi-automatic inspection to semi-automatic interpretation

Abstract: Time-of-Flight Diffraction (TOFD) is a recent but well-developed ultrasonic technique that is rapidly gaining prominence as the method of choice for many weld inspection applications The data acquisition configuration lends itself conveniently to automation, and robotic scanning is routinely used However, despite the mechanisation, the most time-consuming processes are still performed off-line manually The trained operator utilises interactive software tools to visualise and calibrate the data, but the actual defect detection, sizing and characterisation are totally reliant on the operator's expert judgement As the quantity and density of data increases, the effects of operator strain, visual fatigue and loss of concentration become more apparent, resulting in errors and inaccuracies This combined with the growing pressure to complete the interpretation of inspection data in near real-time has underlined the need for robust and reliable interpretation aids to automate the routine aspects of the operators' tasks While nothing can ever replace the expert operator, an interpretation aid can detect regions of interest and provide preliminary depth and sizing information, as well as an assessment of the defect class according to the adopted codes and standards This can potentially increase operator interpretation throughput, reliability and consistency, resulting in a cost reduction This paper proposes just such a scheme for semi-automatic TOFD interpretation A number of signal and image processing tools have been specifically adapted for use with ultrasonic TOFD data Results obtained have so far been promising in terms of accuracy, consistency, reliability and processing speed

Ultrasonic flaw detection method using rayleigh waves and apparatus therefor

Abstract: PROBLEM TO BE SOLVED: To provide an ultrasonic flaw detection method using Rayleigh waves for the purpose of detecting a smaller flaw or flaw shape because the height of a flaw capable of being measured by a TOFD method noticed as a new inspection method is about three times a wavelength SOLUTION: Part of ultrasonic waves, which enter one end of a flaw, among ultrasonic waves received by a receiving ultrasonic probe, is converted in mode to be propagated along the inner surface of the flaw as Rayleigh surface waves and part of the Rayleigh surface waves is converted again in mode at the end of the flaw to detect the ultrasonic waves re-radiated to the inside of an object to evaluate the flaw on the basis of the detection signal By measuring and calculating the flaw using Rayleigh waves propagated along the surface of the internally present flaw, even the height dimension of the flaw smaller than before can be measured and the shape or the like of the flaw can be also evaluated COPYRIGHT: (C)2005,JPO&NCIPI

A wireless sensor network of permanently installed structural integrity monitors

Abstract: Structural integrity monitoring (SIM) involving a large numbers of distributed sensors is of increasing importance to a wide range of industries. Compact sensor packages combining ultrasonic transducers with local sensor and communications control functions and signal processing have been designed using modern miniaturization techniques. Autonomous wireless devices powered by on-board batteries can extract top-up energy derived from the sensor environment. Applications to date include erosion or corrosion monitors via ultrasonic thickness measurement devices, area mapping array sensors and time-of-flight diffraction (TOFD) technique transducers for defect monitoring. Formation or propagation of defects can also be monitored with passive acoustic emission (AE) sensors.The project concepts and early prototyping were presented at QNDE 2003. This paper highlights further progress towards a distributed wireless ultrasonic sensor network and presents results of TOFD and thickness measurement tests. Signal processing techniques including averaging, finite impulse response (FIR) filtering and pulse compression have been employed to improve signal-to-noise ratio (SNR), to extend battery power and to address time resolution issues. Field trials in a hostile industrial environment with metallic obstructions in the form of pipe-work, ducting, stairs, beams and floors have been performed and methods of extracting environmental energy have been tested. ©2005 American Institute of Physics

A Study on TOFD Inspection Using Phased Array Ultrasonic Technique

Abstract: The techniques in order to measure the depth of defect in weldment and structure accurately have been developed. Many researches have made efforts to develop the methods for the accurate depth sizing of defect. TOFD is known as the most accurate method of various methods for measuring depth sizing. However, there is a possibility to miss defects because of the limitation of beam coverage for the ultrasound incident angle. In this study, the results for detectability and depth sizing using phased array ultrasonic technique for thick body were compared with those of conventional TOFD technique. It was experimentally confirmed that the phased array ultrasonic TOFD technique gives good detectability and accurate depth measurement for the various types of defects. The phased array ultrasonic TOFD technique developed in this study will contribute to increase the inspection reliability in thick component such as the pressure vessel of power generation industry.

Ultrasonic flaw detection method using vertical and horizontal diffracted waves and apparatus therefor

Abstract: PROBLEM TO BE SOLVED: To provide a method for estimating the position of a flaw such as a crack or the like simply and accurately without using a complicated method which requires complicated operation said to be B-scanning in a conventional TOFD method in order to locate the flaw such as the crack or the like and a combination with a conventional ultrasonic flaw detection method such as a pulse reflecting method or the like is required in an object difficult in B-scanning. SOLUTION: A transmitting probe 1 and a receiving probe 2 both of which form a pair are arranged on the surface of an object 3 so as to leave a definite distance and ultrasonic waves are radiated to the inside of the object from the transmitting probe 1 while diffracted waves generated at the end of the flaw present in the object are received by the receiving probe 2 to respectively detect the vertical and horizontal waves of the diffracted waves. On the basis of the arrival time difference between the detected vertical and horizontal waves, the distance L from the end of the flaw generating the diffracted waves to the receiving probe 2 is estimated. COPYRIGHT: (C)2005,JPO&NCIPI

Developing, optimizing and validating automated ultrasonic procedures for testing heavy walled hydroprocessing reactors

Abstract: Ultrasonic simulations and ultrasonic testing (UT) were performed for two of the most complex hydropmcessing heavy walled reactor geometries and an experimental validation of an ultrasonic test model was performed on two mockups with implanted realistic discontinuities. High confidence and improved reliability in ultrasonic detection, sizing and characterization of discontinuities before they reach critical size in heavy walled reactors, along with development and validation of an optimized procedure, were achieved through an advanced and cost effective ultrasonic simulation approach.

Application of TOFD Technique to Thin Sections Using ESIT and PSCT

Abstract: It is difficult to accurately size the defects that are oriented at an angle (that is not normal to the wave) using conventional amplitude based ultrasonic techniques. Since Time of Flight Diffraction (TOFD) is based on the diffraction of ultrasound at defect edges, defect sizing using this technique is amplitude independent. However, most of the TOFD based assessment relies on manual sizing, whose accuracy depends on quality of image and the operator’s experience. Also, the utilization of TOFD for sections less than 15 mm has reportedly several difficulties. In this paper, we report our attempts to size the vertical and inclined defects using an in‐house TOFD system built to inspect thin sections (6–10 mm). To improve sizing, automated defect sizing techniques termed Embedded Signal Identification Technique (ESIT) and Point Source Correlation Technique (PSCT) were developed. A ray tracing based model was also developed for a) optimizing the experimental parameters for thin sections, b) interpreting the r...

Characteristic and recognition of ultrasonic TOFD signal and image for planar defect

Abstract: Considering several typical planar defects that were common flaws in thick aluminum weld, the characteristics of Ultrasonic TOFD (time of flight diffraction) was studied Ultrasonic TOFD A-scan signal and B, D-scan image were analyzed and interpreted Linearization was introduced in processing B and D-scan image The results show that planar defect can be effectively recognized, located and sized by the characteristics of the received signal and image Linearization effectively improves time resolution of the received images, which makes the characteristics of the defect more markedly and leads to more accurate quantitative measurement