Showing papers on "Time-of-flight diffraction ultrasonics published in 2008"

Developments in NDT for Detecting Imperfections in Friction Stir Welds in Aluminium Alloys

Abstract: Friction stir welding (FSW) has dramatically changed how aluminium alloys can be welded. The quality of FS welds is usually excellent, but some imperfections periodically occur. The geometry, location, and microstructural nature of these imperfections bear no resemblance to the imperfections typically found in aluminium fusion welds. Consequently, it has been difficult to identify FS weld imperfections with common non-destructive testing (NDT) techniques. Therefore, further development of NDT techniques must be done to enable the detection of FS weld imperfections. This paper presents an integrated, on-line, NDT inspection system for FS welds, which employs a data fusion algorithm with fuzzy logic and fuzzy inference functions. It works by analyzing complementary and redundant data acquired from several NDT techniques (ultrasonic, Time of Flight Diffraction (ToFD), and eddy currents) to generate a synergistic effect that is used by the software to improve the confidence of detecting imperfections. The system was tested on friction stir welded AA5083-H111 specimens. The results indicate that by combining the output from various NDT processes, an improvement in finding imperfections can be obtained compared to using each NDT process individually. The methodology implemented in the QNDT_FSW system has given good results and improved reliability in the NDT of friction stir welds.

Ultrasonic time-of-flight diffraction crack size identification based on cross-correlation

Abstract: The time-of-flight-diffraction (TOFD) ultrasonic detection method has been widely used in defect size assessment. This paper presents a method using cross correlation to improve the accuracy of defect sizing in the TOFD framework. The resulting peaks of the cross correlation function between two signals indicate the time of flight between them. Experimental results are used to demonstrate the advantage of the proposed method.

Ultrasonic inspection method and device for plastics walls.

Abstract: A method and system for ultrasonic time of flight diffraction inspection of a plastics wall, such as a pipe wall. The method includes providing an ultrasound transmitter and transmitting an ultrasound signal having a nominal frequency into the wall, providing an ultrasound receiver and receiving the ultrasound signal transmitted through the wall. The ultrasound signal provided by the transmitter has a bandwidth of more than 80%, preferably more than 100% of the nominal frequency of the ultrasound signal provided by the transmitter.

Spiral welding seam manual scanner

Abstract: The utility model is a spiral weld manual inspection device walking on a pipe when used for phased array binding TOFD ultrasonic test serviced steel pipe spiral welding. The utility model, which essentially comprises an inspection frame (1), a probe frame (6), a rolling wheel mechanism and an encoder mechanism, relates to tests of equipments which are not included in other kinds and the pipe system technical field. Four corners of the rectangular inspection frame (1) are equipped with the rolling wheel mechanism. The probe frame (6) is arranged on a probe frame moving rail (4) on two sides of the inspection frame (1). The encoder mechanism is arranged on one external side of the inspection frame (1). The inspection device walks stably and reliably when testing the serviced steel pipe spiral welding. The position of the probe can be always precisely parallel to the pipe welding surface and keep a certain distance away from the pipe welding surface. The manual inspection device with reliable and accurate test is provided for the phased array binding TOFD ultrasonic test serviced steel pipe spiral welding.

Time of Flight Diffraction Testing of Austenitic Stainless Steel Weldments at Elevated Temperatures

Abstract: Ultrasonic testing is a mandatory requirement during inservice inspection of the welds in the main and safety vessels of a prototype fast breeder reactor. Presently, conventional ultrasonic techniques have been proposed for use. Two of the main challenges likely to be encountered during ultrasonic testing are the high temperature of the vessels (around 423-473 K during shutdown) and the background radiation. Ultrasonic time of flight diffraction is now well established as a technique for NDT of thick (greater than 12.5 mm) weldments. The main advantage of using time of flight diffraction is its increased accuracy for discontinuity detection and fast scanning times. Conventionally, time of flight diffraction has been applied only for carbon steel weldments and at ambient temperatures. This paper highlights the successful application of time of flight diffraction for testing of stainless steel weldments at high temperature (423 K). Experimental studies reveal that the diffracted signal amplitude decreases and, hence, the time of flight diffraction image contrast decreases with increasing temperature. Additional gain was necessary to compensate for the decreased signal amplitude. Analysis of the experimental data indicated that the additional gain necessary to compensate for the lower signal amplitude varied nonlinearly (quadratically) with temperature. The errors in the discontinuity dimensional measurement were observed to be less than 5% compared to measurements at ambient temperature.

Simulation of disoriented flaws in a tofd technique configuration using gtd approach

Abstract: The TOFD (Time of Flight Diffraction) Technique is commonly used to detect and to characterize embedded disoriented flaws using their edge diffraction echoes. We present a TOFD simulation module which includes GTD coefficients allowing to predict diffraction echoes from embedded planar flaws. Other dedicated development have been added in the CIVA software platform to simulate lateral surface waves, backwall echoes and shadowing effects from flaws. Experimental validations have been performed on various specimen containing rectangular and CAD contour planar flaws with different possible disorientations (tilt, vertical misorientation, skew) and show an overall good agreement between simulation and measure.

TOFD Inspection with Phased Arrays

Abstract: In the last decades two major technologies changed the face of ultrasonic NDT viz., time of flight diffraction (TOFD) and phased array ultrasonic testing (PAUT). When used in conjunction, these two techniques allow for higher probability of detection (POD), normally requiring a great amount of time and/or experienced UT inspectors. To do TOFD however (even TOFD by itself), it is necessary to have different sets of probes with different probe separations when one wishes to inspect very thick materials. With the advent of more sensitive transducer arrays and faster electronics, we can now envisage, using multi-element probes, to perform multiple TOFD inspections (the different apertures, offsets and refracted angles all being changed electronically) in one run and with a minimum number of props. These different TOFD scans may also be merged a posteriori so that a simple global picture finally emerges from the acquired data. In this paper we will present some results achieved with this method as well as both theoretical and practical aspects of the problem.

Evaluation of the phased array transmit-receive longitudinal and time-of-flight diffraction techniques for inspection of a dissimilar weld

Abstract: The use of two phased array techniques for the inspection of a representative dissimilar weld from the power industry was investigated. The performance of the phased array Transmit-Receive Longitudinal (TRL) and Time-of-Flight Diffraction (TOFD) techniques was compared to the best-practice baseline procedure using conventional ultrasonics, developed specifically for the nozzle component. Slots were implanted in several regions (parent, HAZ and austenitic weld body) under a layer of cladding. The performance criteria were the detection of the slots, through-wall sizing and signal-to-noise. Both phased array techniques performed better than the conventional techniques with regard to sizing, satisfying the ASME Boiler and Pressure Vessel Code (1) (2007) Section XI Appendix VIII. The Root Mean Square (RMS) error of the phased array TRL and TOFD techniques were 0.52 and 1.04 mm, respectively. In addition, the phased array techniques showed similar signal-to-noise performance to the conventional transducers, which were matched to the curvature of the inspection surface. Based on these results, the use of phased array techniques for the inspection of thick ferritic-austenitic dissimilar welded components is recommended, confident in their ability to outperform conventional techniques.

IWEX: A New Ultrasonic Array Technology for Direct Imaging of Subsurface Defects

Abstract: Both in new construction and in service, detection, sizing and characterization of defects are essential for integrity assessment of metal components and welds. Ultrasonic Non Destructive Inspection (NDI) using Pulse Echo (PE) technique or Time of Flight Diffraction (ToFD) have been proven to be reliable approaches to assess weld integrity. However, quantitative defect characterization with PE remains challenging because the signal caused by the reflection at the defect is very dependent on defect orientation. ToFD has sizing capabilities, but only limited capabilities in flaw characterization. In phased arrays inspection, the image obtained from sectorial scans can not be directly related to defect size and orientation. Data display and interpretation are not straightforward and require operator skills and experience. A better and more reliable ultrasonic inspection would be achieved if a methodology would be used that allows direct imaging of defects. In this paper, we present the principles of imaging with 2D Inverse Wave Field Extrapolation (IWEX) as used in seismic exploration. The physical basis of this new imaging process is the Rayleigh II integral for back propagation which gives the possibility to extrapolate a wave field from known values at a certain surface to any location in space. The paper discusses this in detail. The potential of IWEX for ultrasonic testing of steel components is demonstrated by several examples by which 2D and 3D images of embedded and surface defects were made. We demonstrate that location, shape, orientation and height of the defect are imaged. The interpretation of the results is straightforward, making the use of reference blocks superfluous.

Image processing and wavelets transform for sizing of weld defects using ultrasonic TOFD images

Abstract: Ultrasonic time‐of‐flight diffraction (TOFD) is rapidly gaining prominence as a reliable nondestructive testing technique for weld inspection in steel structures, providing highly accurate positioning and sizing of flaws A number of signal and image processing tools have been specifically developed for use with TOFD data and adapted to function autonomously without the need for continuous intervention, configuring automatically according to the nature of the data and the data acquisition settings This paper presents the results of several innovative procedures based on Multiresolution analysis such as wavelet transforms and texture analysis for detecting edges of planar defects The approach is based on the decomposition by packets of wavelets of the image while taking into account of the underimage content textural after each level of decomposition The reconstruction of the image is done by eliminating the underimages of poor textural information and at the end the segmented image is got by a binarisation operation done on the image rebuilt histogram The automation of sizing and positioning of weld flaws in TOFD data as an essential stage of a comprehensive TOFD inspection and interpretation aid is developed and implemented Key words: Ultrasonic Time‐Of‐Flight Diffraction, Texture Analysis, Wavelet Transform

Reference wavelets used for deconvolution of ultrasonic time-of-flight diffraction (ToFD) signals

Abstract: One major disadvantage of ultrasonic time-of-flight diffraction (ToFD) technique is the weakness of echoes which are diffracted from crack tips. This shortcoming, to some extent, can be overcome by application of proper signal processing techniques. Deconvolution techniques have shown to be quite effective for this purpose. A deconvolution process needs to use a reference wavelet in order to extract the required information from the signal. Accordingly, one of the major challenges in using deconvolution techniques is the choice of the reference wavelet. This paper discusses some of the problems encountered in the selection of the reference wavelet and proposes methods to overcome these problems. The angle-dependent deconvolution technique is one of these methods in which the reference wavelet used for processing each part of the signal is different from wavelets used for other parts. The principles of this method are described and its effectiveness is demonstrated by both simulation and experiment.

Ultrasonic TOFD Testing Model for Crack Measurement in Thick Wall Weldment

Abstract: In this paper, both forward and inverse problem about crack testing by using ultrasonic Time of Flight Diffraction (TOFD) B-scan mode are st udied. For forward problem, the propagation behavior of ultrasonic beam is described, and t he electrical and electromechanical elements of inspective system are cha racterized by system efficiency factor. Based on this, crack simulating model is established by employing Kirchhoff approximation theory. By using the model, ultrasonic TOFD A-scan line is simulated and B-scan foreground image is synthesized. For inverse problem, in order to obtain lateral locatio n and buried depth information of crack in the weld, B-scan image reconst ruction is studied. According to the dynamic relation between the probes and crack tip in th e course of testing, synthetic aperture focusing (SAF) algorithm for image enhancement is developed. The results show that the simulated dada are in better accordance with the measured ones and the presented SAF algorithm can be validated by the simulating model. Proces sed by SAF, high resolution image can be obtained by using transducers with poor sound directivi ty and lower frequency, and measurement can be carried out rapidly with high accuracy.

Performance Evaluation Test of the Time-of-Flight Diffraction Technique for Welded Joints of Steel Bridges

Abstract: Ultrasonic testing can be applied to welded joints of steel bridges following a revision of the Japanese Specifications for Highway Bridges. The time-of-flight diffraction (TOFD) technique and the pulse echo technique are possible testing methods. However, the efficiency of the TOFD technique for steel bridges has until now not been investigated completely. A round robin test project using testing systems of several different companies was organized by the Ministry of Construction for this purpose. The performance of each participant system was evaluated and applicability of the TOFD technique was investigated.

A Study of Time-of-Flight Diffraction Technique Using Photoelastic Visualisation

Abstract: Time-of-Flight Diffraction (ToFD) technique has been pa rt of nondestructive testing (NDT) for over 30 years and provides a useful role in flaw detection and flaw sizing. This paper reviews the principles of ToFD and presents a photoelastic technique f or visualization of the waves generated during a ToFD measurement. A sample made of optically fused glass with an embedded target is used in the experiments. The results show the waves whic h are diffracted from the upper and lower tip of the target as well as the lateral and bac kwall waves. These results also provide a better understanding of the diffraction phenomenon that t akes place during a ToFD measurement.

Applications of TOFD of Ultrasonic Imaging Detection Technology in Pressure Vessels Inspection

Abstract: This paper introduces the TOFD ultrasound imaging detection technology′s basic working principle,and elaborates the requirements of the TOFD ultrasound imaging detection technology in pressure vessel inspection.The TOFD ultrasound imaging detection equipment modification,as well as main parameters setting was studied.The data processing methods was analyzed the application of TOFD ultrasound imaging detection technology in pressure vessels inspection was described,and the merits of Ultrasound imaging TOFD detection technology.

Comparison of TOFD and Radiographic Testing for a Mock-up Specimen

Abstract: In order to detect the internal defects which occur in welding parts of pressure vessel and structures, radiographic testing and ultrasonic testing is applied However, because of the risks of radiation exposure and film processing, radiographic testing takes a relatively long time to verify the test results and it has affected in the production process Typically, the manual ultrasonic testing is not easy to reproduce the result and it is highly dependent on the tester's skills The TOFD technique, one of the automatic ultrasonic testings is spreading alternatively This research describes the comparing test results by applying radiographic testing and TOFD technique to a mock-up specimen incruding the flaws The TOFD technique will contribute to improve the objective reliability of the ultrasonic technique

Present development and prospect of special equipment testing in China

Abstract: The special equipment development status was analyzed by the view of special equipment definition,quantity,and managementThe features and development trends of pressure vessels,station boilers,hoisting machinery and electric elevator equipments were summarizedThe nondestructive testing techniques such as acoustic emission(AE) technique,magnetic flux leakage(MFL) detection,ultrasound phased array inspection,Time-of-flight diffraction(TOFD) and ultrasound guided wave techniques were summarized in this paperWe sugguested the development goal and task of special equipment testing in ChinaIt provides valuable references to safety quality inspection persons of special equipment

Sizing Stress Corrosion Cracking Using Laser Ultrasonics

Abstract: Managing Stress Corrosion Cracking (SCC) damaged pipe has been a formidable challenge to the pipeline industry. Development of a practical solution for measurement and evaluation of SCC has been marred by the complexity of crack shapes, their distribution within a crack colony, and the lack of non-destructive technology capable of reliably measuring the crack depths. Laser Ultrasonics is an inspection technology wherein lasers are used for generation and detection of ultrasonic waves in the pipeline steel to be inspected. Unlike conventional ultrasonic testing, Laser Ultrasonics has a large frequency bandwidth and a tiny (∼0.5mm) footprint. These characteristics make it ideally suited for application as a depth sizing tool for closely-spaced cracks in a colony. It has been conclusively proved that laser ultrasonic inspection using the time of flight diffraction (TOFD) technique can reliably and accurately measure the depth of naturally occurring SCC and potentially other cracks and seam weld anomalies. This presentation describes the results of this co-sponsored project, including recent full scale demonstrations where a laser ultrasonic measurement subsystem has been built onto a prototype scanner.Copyright © 2008 by ASME

The Qualitative Graphical Analysis of Typical Defects in Detecting Using the TOFD Method

Abstract: TOFD,which means Time of Flight Diffraction,is a NDT technique,which quantitatively evaluates the defects using the Time of Flight Diffraction method of the ultrasonic waves.The technique has widely been used in field of industrial NDT abroad.EU,USA and Japan have already introduced relative standards for its application.In recent years Chinese hydropower companies start to import the technique for tryout.The paper introduces the experience in selecting probe angle and spacing when using the TOFD method and analyses the spectrogram presented from detecting of such defects as gas pockets in butt-jointed seams of splice plates.

Small surface crack size identification based on ultrasonic energy reflection and refraction

Abstract: The small surface crack size estimation based on ultrasonic energy reflection and refraction technique has been studied in order to overcome the pulse echo and time of flight diffraction technique limitation. The model of reflection and refraction at solid-solid interface was deduced, and then the crack size by energy reflection changing was also studied. Experimental results are used to demonstrate the advantage of the proposed method.

New Technology for NDT Weld Inspections – Phased Arrays and Diffraction Sizing

Abstract: This article describes new techniques and technology for inspecting welds using automated ultrasonics. The prime new technology is phased arrays, while the new techniques are Time-of-Flight Diffraction and S-scan back diffraction. The relationship of phased arrays with North American codes is briefly given, along with an inspection result, comparing radiography, pulse-echo phased arrays and TOFD.

Failure of Ammonia Synthesis Converter Due to Hydrogen Attack and Its On-Stream Assessment Using ToFD Method

Abstract: A failure analysis of ammonia converter which suffered hydrogen attack in two years since its initial operating time was presented. It is constructed from 2.25 Cr?1 Mo steel. Analysis showed that the failure on closing seam weld joint was due to local improper post weld heat treatment (PWHT). Improper PWHT can introduce high residual stresses in thick-walled pressure vessel. High residual stress level in weld joint is very prone to hydrogen attack for any components which are operating in hydrogen gas environment. The repair procedures based on the principle to decrease the residual stress then proposed. The repair was controlled very carefully by applying several nondestructive tests in the each stage of repair. To assure the successful of the proposed repair, after one year since repair time, high temperature ultrasonic and TOFD methods were applied on-stream to this equipment in order to evaluate its post repair condition. The two methods showed good results on the repaired area.