Showing papers on "Time-of-flight diffraction ultrasonics published in 2004"

Ultrasonic TOFD flaw sizing and imaging in thin plates using embedded signal identification technique (ESIT)

Abstract: The ultrasonic Time-of-Flight Diffraction (TOFD) technique is a well developed technique for sizing defects in thick sections (thickness >10 mm). Attempt has been made here to extend this technique for thin sections (6-10mm). An automated defect sizing algorithm using the Embedded Signal Identification Technique (ESIT) was developed for separating partially superimposed signals often encountered in thin sections and the results were compared with the manual sizing method. Both EDM notches and more realistic fatigue cracks in thin section were used to evaluate the proposed technique.

Pattern Recognition of Weld Defects in Preprocessed TOFD Signals Using Linear Classifiers

Abstract: The TOFD (“Time of Flight Diffraction”) technique is being widely used for automatic weld inspection, especially in the petrochemical industry, where welding quality is essential to avoid productivity losses. Although it provides high speed inspection, high sizing reliability and low rate of false defect indications, the classification of defects using ultrasound signals generated by the TOFD technique is still frequently questioned, because it depends heavily on the knowledge and experience of the operator. However, the use of computational tools for signal preprocessing and pattern recognition, such as the artificial neural networks, improves the classification reliability of defects detected by this technique. In this present work, three kinds of defects: lack of fusion (LF), lack of penetration (LP) and porosity (PO) were inserted into the specimens durin the welding process, generating pattern defects. The position, type and dimension of each inserted defect were recorded using conventional ultrasonic and radiographic techniques. The Fourier Transform and Wavelet Transform were used for preprocessing A-scan signals acquired during weld inspection by TOFD technique. This study was able to show the versatility of Wavelet Transform to preprocess these kinds of signals, since the correct scale in Continuous Wavelet Transform had been selected to supply a neural network. Hierarchical linear classifiers were implemented into the neural network in order to distinguish the main defects in welded joints detected by the TOFD technique. The results show the good success rate of welding defect recognition in preprocessed TOFD signals, mainly using Wavelet Transform. On the whole, the results obtained were very promising and could give relevant contributions to the development of an automatic system of detection and classification of welding defects inspected by the TOFD technique.

Examination of Flaw Detection near the Surface by the Ultrasonic TOFD Method

Abstract: Nobukazu Ido, Hiroaki Hatanaka, Takahiro Arakawa, Kenji Katou and Hiroyuki Furuta 1 Research & Development Ishikawajima-Harima Heavy Industries Co., Ltd 1 Shin-Nakahara-cho, Isogo-ku, Yokohama 235-8501, Japan 2 Energy & Plant Ishikawajima-Harima Heavy Industries Co., Ltd. 3-2-16 Toyosu, Koto-ku, Tokyo 135-8733, Japan 3 Trunkline Maintenance Group Distribution Planning & Administration Dept. Toho Gas Co., Ltd. 19-18 Sakurada-cho, Atsuta-ku, Nagoya 456-8511, Japan

Defect Sizing in Pipeline Welds: What Can We Really Achieve?

Abstract: Pipelines are now using Fitness-For-Service (FFS) for accept/reject of weld defects. FFS requires accurate measurement of defect height for Fracture Mechanics assessments. The standard pipeline weld inspection technique of radiography is incapable of such measurements. However, the newer technique of ultrasonics can measure defect height, in principle. Initially ultrasonic amplitude methods were used for height measurement, but these proved unreliable. Now diffraction methods, especially Time-Of-Flight-Diffraction (TOFD), are being used in conjunction. This paper reviews previous work — mainly large nuclear studies like PISC II — and published pipeline sizing studies. The best nuclear sizing was within a few millimetres, using diffraction. In contrast to nuclear, pipeline AUT uses zone discrimination, focused transducers, much thinner material and simpler analysis techniques. Current accuracies are typically ± 1 mm (terminology undefined), which correlates with the beam spot size and typical weld pass. Requests for accuracies of ± 0.3 mm are probably unachievable, though future R&D should significantly improve pipeline sizing.Copyright © 2004 by ASME

'Automatic Segmentation of Time-Of-Flight-Diffraction Images Using Time-Frequency Techniques ¿ Application to Rail Track Defect Detection'

Abstract: Ultrasonic time-of-flight diffraction (TOFD) is now a well- established technique alongside other ultrasonic testing techniques for accurate defect sizing. The current practice in the rail industry for the inspection of the rail welds and fishplate areas involves elaborate and painstaking manual inspection using a number of different probes at different positions around the track. TOFD, on the other hand, allows this procedure to be automated, providing detection, sizing and classification. In TOFD inspection, only a small fraction of the collected data actually represents defects, whereas the majority of the data is considered redundant. The first of the current processing stages which relies heavily on a skilled operator, involves pointing out those image areas containing defect areas and suppressing others. Consequently, this process consumes considerable amounts of time and effort, apart from the fact that the existence of the human factor at this critical stage invariably introduces inconsistency and error into the interpretation. Novel time- frequency analysis techniques have been combined with an artificial neural network to characterise TOFD signals and extract distinguishable features to be used for the detection, classification and sizing of rail-track defects. It is anticipated that, coupled with the necessary processing algorithms, TOFD can be used for a comprehensive automatic inspection of the rail-track, particularly fishplate and weld areas (Figure 1) with satisfactory levels of accuracy and reliability.

Sizing of cracks embedded in sub-cladding using the ultrasonic synthetic aperture focusing technique (SAFT)

Abstract: This paper deals with the experimental work carried out to demonstrate the feasibility of the ultrasonic Synthetic Aperture Focusing Technique (SAFT) to obtain improved detection and sizing of vertical/inclined (10° and 15°) simulated cracks underneath different claddings. Crack heights ranging from 1.68 mm to 19.04 mm underneath stainless steel, Inconel and ferritic steel cladding were sized with an accuracy of ′0.1 to ′0.3 mm. The problems encountered in TOFD with regard to sizing of near-surface cracks was successfully overcome by SAFT. Mis-oriented (inclined) defects embedded below the cladding suffer added disadvantage for ultrasonic detection due to loss of reflected energy due to mis-orientation. Using SAFT even these defects could be sized accurately.

Ultrasonic flaw detection method and ultrasonic flaw detection apparatus

Abstract: PROBLEM TO BE SOLVED: To mitigate a constraint of an object, whose flaws can be detected by a TOFD (Time Of Flight Diffraction) method, in an ultrasonic flaw detection method SOLUTION: A transmitting oblique probe 11 for transmitting pulsed ultrasonic longitudinal waves to a scanned face 52 and a receiving oblique probe 12 for receiving the longitudinal waves of at least one of diffraction waves and scatter waves from an end of a defect on the scanned face 52 are disposed adjacent to a scanned face 53 on the same side as the scanned face 52 The transmitting oblique probe 11 transmits the ultrasonic longitudinal wave at an incident angle of 45° or smaller with respect to the scanned face 52 COPYRIGHT: (C)2004,JPO&NCIPI

Relationship between crack opening behavior and crack tip scattering and diffraction of longitudinal waves

Abstract: The time of flight diffraction technique has attracted attention as the most accurate discontinuity depth measurement technique in the industrial testing field. Since it utilizes a weak discontinuity tip echo, the most harmful discontinuity in industrial structures is a crack because crack closure sometimes causes an error in crack detection through time of flight diffraction measurement. However, the dependence of the quantitative behavior of the crack tip echo on crack closure for the longitudinal waves used in time of flight diffraction has not yet been investigated. In this paper, we prepared UNS A97075 (7075-T6) aluminum alloy specimens with a fatigue crack penetrating the surface and the crack tip opening displacement was controlled by the amount of load. The amplitude and spectrum of the crack tip scattered and diffracted echoes of 5 MHz ultrasonic longitudinal waves for various crack tip opening displacement values were measured. As a result, the crack tip opening displacement of 0.1 μm (3.9 x 10 -6 in.) was found to be sufficient for giving echoes with amplitude comparable to that of the echoes from artificial slits, in the time of flight diffraction measurement using a 5 MHz longitudinal wave. The minimum detectable crack tip opening displacement by the time of flight diffraction technique was found to be 20 nm (7.9 x 10 -7 in.). The crack tip opening displacement for a fatigue crack can be estimated using the amplitude or the peak frequency in the spectrum of the crack tip echo.

Time-of-flight diffraction technique for detecting and sizing of discontinuities: an outline of the latest european standard for ultrasonic examination of welded joints

Abstract: Ultrasonic time-of-flight diffraction(TOFD) technique is a new successful one for detecting and sizing the discontinuities in welded joints. It is a reliable manner for measuring imperfection depth and height according to the time-of-flight of the diffracted waves on the tip of the imperfection produced by the incident compressional waves. Three presentations (ie. A-scan, D-scan and B-scan) give more straight forward and objective test records. Based on the requirements of the latest European standard (draft) ENV 583—6:2000, the key points in the application of TOFD technique are described. It is expected that the technique will be rapidly developed and applied in our country.

Crack development monitoring method and its device by ultrasonic tofd method

Abstract: PROBLEM TO BE SOLVED: To provide a crack development monitoring method by ultrasonic TOFD (Time of Flight Diffraction) method and its device for accurately measuring a crack depth while an installation is operated and automatically monitoring the development of the crack. SOLUTION: Data on the change of propagation velocity of ultrasonic longitudinal wave with temperature in a specimen 1 are previously stored in a data storage means 5. When a data processing means 7 calculates a crack depth in the specimen 1 from measured data by the TOFD method, the propagation velocity of ultrasonic longitudinal wave corresponding to the temperature of the specimen 1 in measuring is acquired for use from the data on the change stored in the storage means 5. COPYRIGHT: (C)2006,JPO&NCIPI

Time of Flight Diffraction Method Using Laser Ultrasound for Noncontact Flaw Height Measurement

Abstract: We developed a laser TOFD (Time of flight diffraction) algorithm which utilizes not only longitudinal wave but also shear wave. This algorithm made it possible to obtain accurate flaw depth without knowing the specimen velocity and probe distance previously. We constructed the laser TOFD system and applied it to estimate the slit depth of aluminum alloy plate. Time of flight of lateral wave, flaw tip diffraction waves and mode converted shear wave at flaw tip were used to estimate the slit depth using new algorithm.

Automated Ultrasonic Inspection of Pressure Vessel Welds

Abstract: ASME Code Case 2235 now permits automated ultrasonic testing (AUT) instead of radiography for vessels 0.5” (12.7 mm) or greater. Ultrasonic testing has significant advantages over radiography: no safety hazard so no disruption of production; inspection as soon as component cools; rapid feedback; defect vertical sizing for Fitness-For-Purpose applications; tailored inspections. ASME CC 2235 permits a variety of inspection techniques based on pulse-echo and Time-Of-Flight Diffraction (TOFD), provided a Performance Demonstration is achieved. This paper describes a number of AUT systems which fulfill the ASME code case. These AUT systems range from a portable phased array system (Omniscan) for low cost and convenience, through conventional systems based on TOFD (μ-Tomoscan), general phased array systems (Tomoscan III) to premium systems with multiple NDE approaches. With such a variety of technologies and costs, AUT systems can be tailored to the client’s needs.Copyright © 2004 by ASME

Probe for ultrasonic tofd method, and flaw detection method

Abstract: PROBLEM TO BE SOLVED: To provide a probe for an ultrasonic TOFD method capable of measuring easily and accurately a flaw end part depth in a curved surface of a specimen, and a flaw detection method using the probe. SOLUTION: This probe 1 for the ultrasonic TOFD method comprises an ultrasonic wave generating element 11, an ultrasonic wave receiving element 12, and a holder 13 for equipping the ultrasonic wave generating element and the ultrasonic wave receiving element. A contact surface 131 contacting with the curved surface of a specimen 2 is formed into a shape along with the curve surface of the specimen 2. A flaw detection test is carried out in the specimen of which the flaw end part depth is known, using the probe 1 for the ultrasonic TOFD method, an interelement distance is corrected to make a calculated flaw end part depth nearest to an observed flaw end part depth. The flaw detection test is carried out thereafter in the specimen of which the flaw end part depth is unknown, so as to calculate the flaw end part depth using the corrected interelement distance. COPYRIGHT: (C)2004,JPO

'Automatic Defect Classification in Time-Of-Flight-Diffraction Data Using Fuzzy Logic'

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. TOFD technique has a lot of advantages which make it the preferable technique in material testing. This technique gives accurate sizing, positioning and characterising of weld and other defects with a high probability of detection. Currently most of the TOFD data interpretation is done manually, requiring operator skill, experience and most significantly time. In light of the industrial pressure, the recent trend is to fully automate the data interpretation process, which could potentially improve the interpretation procedures by adding and element of robustness and consistency by utilising computational tools that are better suited to discriminating between subtle variations in visual and spectral properties of the data; furthermore, saving money, effort and time. 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. Feature analysis, shape detection and careful estimating the phase relationships for each defect category in TOFD images are very important for providing an accurate automatic interpretation system. Fuzzy logic is a powerful tool and considered as the key technology for representing knowledge of the human experience and for constructing adaptive systems. Combining the technologies of fuzzy logic with extracted visual and spectral scan features and phase determination results enables the differentiation between different defect categories with satisfactory levels of accuracy and reliability, thus opening a new paradigm in TOFD for automatic interpretation.

Nondestructive testing of pressure vessels:ultrasonic testing technology(ii)

Abstract: The characteristics of ultrasonic testing of the pressure vessels in use are outlined, and the essentials of ultrasonic examination of some typical vessels are presented, such as heat exchangers, coke drum, spherical tank, pipeline and hydrogenation reaction chamber and so on. Finally, ultrasonic time-of-flight diffraction(TOFD) technique is introduced.

Development of the Phased Array System for Angle Beam Testing

Abstract: The angle beam technique is commonly applied to ensure the quality of the welds. Usually this technique is manually performed, but recently the automatic ultrasonic testing instruments has been developed to decrease the inspection time and to increase the reliability. For this purpose, we have developed an array probes with a step shaped wedge. This system executes not only the angle beam technique but also the TOFD technique.

Development of Phased Array and Tofd Simultaneous Inspection System for Coke Drum

Abstract: Our current AUT (Automatic Ultrasonic Testing) system is “Phased Array Linear Scan and Dual TOFD (Time of Fight Diffraction) simultaneous inspection system” which has been applied to the pre-service inspection at shop in lieu of radiography as per ASME Code Case 2235-4 and the in-service inspection at user’s turnaround stage for the circumferential and longitudinal weld joints of shell courses of coke drum. The coke drum is 13-30 feet in diameter and 80-100 feet in height. The base material of coke drum is either C-1/2Mo steel, 1Cr-1/2Mo steel, 1.25Cr-1/2Mo steel, or 2.25Cr-1Mo steel with type 410S or 405 stainless steel cladding material, and clad restoration weld material is either Inconel 82, Inconel 625 or same material as the cladding material (13Cr stainless steel). It is too difficult to detect the flaws in the clad restoration weld by the conventional manual UT and/or TOFD, but Phased Array can clearly detect them. The typical AUT display of Phased Array Linear Scan and TOFD for the weld joint of coke drum at the turnaround stage is illustrated in Fig.1. The outline drawing of the inspected coke drum is illustrated in Fig.2. In order to improve the capability to detect and size the low cycle fatigue crack caused in the clad restoration weld and its heat affected zone due to the cyclic operation of coke drum as illustrated in Fig.3, “Phased Array Sector Scan” has been adopted. This paper reports the verification test results of “Dual Phased Array Sector Scan” (the simultaneous scanning by a pair of Phased Array probes placed equally for the centerline of weld joint) in comparison with the verification test results of TOFD, and introduces the characteristic of our current AUT system. In consideration with the verification test results in this paper, we would like to propose that “Dual Phased Array Sector Scan and Dual TOFD simultaneous inspection system” (the simultaneous inspection by four (4) kinds of AUT) will be applied to the in-service inspection for the coke drum and other important reactors overlaid inside by stainless steel or Inconel at the oil refineries and/or petrochemical plants. Fig. 1. P.A Linear Scan and TOFD Display Fig. 2. Outline Drawing of Coke Drum Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 364-371 doi:10.4028/www.scientific.net/KEM.270-273.364 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,17:37:44) Title of Publication (to be inserted by the publisher) Fig. 3. Low cycle fatigue crack caused in the clad restoration weld of coke drum