Detection and Sizing of Defects in Complex Geometry Weld by Manual Ultrasonic Time of Flight Diffraction Inspection
01 Oct 2009-Journal of Pressure Vessel Technology-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 131, Iss: 5, pp 051501
TL;DR: In this paper, a complex geometry weld specimen with various artificial defects was designed and fabricated, and different combinations of probe angles and probe center spacings were used in experiments for determining the optimum one.
Abstract: The basic aim of this current research is to reliably detect and size defects in complex geometry welds using the well-known ultrasonic time of flight diffraction (TOFD) technique. A complex geometry weld specimen with various artificial defects was designed and fabricated. Different combinations of probe angles and probe center spacings were used in experiments for determining the optimum one. TOFD models were also developed for sizing the defects and experimentally verified.
Citations
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TL;DR: In this paper, a structural damage detection scheme using Transfer Matrix (TM) is presented, which is suitable for local crack identification in large structures, by different measurement strategies for the initial state vector near the zone of interest.
10 citations
TL;DR: In this article, a feature information extraction algorithm based on contour and OTSU threshold segmentation is used to extract the features of the welding image that collected by the image acquisition system and then, the image is classified as a specific defect by the trained BP neural network classification algorithm.
Abstract: Most of the existing laser welding quality identification methods are post-weld identification or low-speed identification (Welding speed below 120 m/min). Efficiently online monitoring of laser welding can take the advantages of laser welding for high-speed and deep-penetration welding. How to eliminate interference information (such as metal vapor, plasma splash, etc.) in the laser welding process, accurately and quickly extract the feature information of welding quality evaluation, and identify defects is a major problem that laser welding online monitoring technology needs to solve urgently. In this paper, the optimized dark channel prior anti-interference processing algorithm can remove the interference of image. The feature information extraction algorithm based on contour and OTSU threshold segmentation are used to extract the features of the welding image that collected by the image acquisition system. Then, the image is classified as a specific defect by the trained BP neural network classification algorithm. Experiments with 304 stainless steels have proved that this method can effectively remove the interference of metal vapor and plasma splash on the feature information, and achieves 97.18% accuracy rate of the binary classification test and 91.29% accuracy rate of the six-classification test. The processing time of the entire algorithm is about 0.3 ms and it can meet the real-time requirements of high-speed laser welding.
8 citations
TL;DR: In this paper, a method based on the mode-converted waves in TOFD B-scan image is developed to restrict the dead zone in pipeline and to realize the accurate measurement of shallow subsurface cracks.
Abstract: When the ultrasonic time-of-flight diffraction (TOFD) technique is applied to the inspection of pipeline, the propagation direction of the direct longitudinal wave is not parallel to the pipe surface, leading to the increment of the depth of dead zone and the measurement errors of shallow subsurface cracks. In this paper, the differences between the dead zones in flat plate and pipeline are compared theoretically. Subsequently, the method based on the mode-converted waves in TOFD B-scan image, which has been used for reducing the dead zone in flat plate, is developed to restrict the dead zone in pipeline and to realize the accurate measurement of shallow subsurface cracks. The simulated and experimental results indicated that the depth of dead zone in the carbon steel pipeline with a radius of 148 mm was reduced from 6.3 mm to 3.0 mm and that the measurement errors of crack length and angle were no more than 0.27 mm and 1.57°, respectively. The depth of the dead zone in pipeline and the measurement errors before modification both increase with the reduction of the ratio of pipe radius to probe center spacing (PCS). The modified method has universality for the detection of the shallow subsurface cracks in pipeline with ultrasonic TOFD technique.
7 citations
TL;DR: The results show that the proposed method could effectively enhance SNR of TOFD images and improve the ability to identify weld defects of materials.
Abstract: Influenced by random noises from inhomogeneous material scattering and fluctuation of detected electric signals, the signal-to-noise ratio (SNR) of ultrasonic time-of-flight-diffraction (TOFD) image decreases significantly. For the noise reduction of TOFD images, several D-scanned TOFD images with different distribution of noise characteristics are obtained through repeating detection and slightly and randomly changing the probe’s initial position each time. The registered images then are processed by shift-and-add (SAA) technique to reduce the noise level of the TOFD images. Besides, correlation image registration algorithm based on optimization method was established to avoid the shift of TOFD images due to slight change of probe’s initial position. Noises in the registered images show stochastic behavior at the same position. In order to verify reliability of the algorithm, an experimental TOFD detection system for weld defects has been designed to acquire and experiment with TOFD images. The experiment results have been evaluated in terms of cross correlation coefficient, SNR and standard variance of images. The results show that the proposed method could effectively enhance SNR of TOFD images and improve the ability to identify weld defects of materials.
6 citations
References
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TL;DR: In this article, the angular variation of diffracted signal amplitude when infinite plane P or SV waves are incident on a semi-infinite crack is derived for the case of a defect symmetrically placed with respect to transmitter and receiver.
95 citations
TL;DR: In this article, an experimental study for evaluation of TOFD technique for determination of size of the surface breaking cracks was conducted. But difficulty was experienced using TOFD to size defects extending less than about 2mm depth, due to the presence of the lateral wave which obscures the tip-diffracted signals from the defects close to the surface and also due to inherent lack of time resolution near the surface.
Abstract: This paper deals with an experimental study for evaluation of TOFD technique for determination of size of the surface breaking cracks. The study was confined to simulated cracks. The steel test blocks used for the study contained 0.5mm wide vertical slits of various heights ranging from 0.91mm to 30mm. Another set of blocks contained inclined slits (10°, 15°) inclination of various heights ranging from 2.56mm to 19.82mm. Both the vertical and inclined slits were opened to the top surface. TOFD equipment Model MICROPLUS of M/S AEA Technology, UK with manual scanner along with longitudinal angle beam probes of 45° - 4MHz were used for the study. The blocks were scanned along the slits / defects and across the slits. The scanned images were analysed for the sizing. The results of the study indicated an average error of ±0.13 for depth in vertical slits and ±0.05 for inclined slits whereas the average error in length measured was ±0.36mm for vertical slits and ±0.29mm for inclined slits. However difficulty was experienced using TOFD to size defects extending less than about 2mm depth. This is due to the presence of the lateral wave, which obscures the tip-diffracted signals from the defects close to the surface and also due to the inherent lack of time resolution near the surface.
54 citations
TL;DR: In this paper, 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.
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.
37 citations
TL;DR: In this article, the authors deal with experimental work for the evaluation of the Time-of-Flight Diffraction (TOFD) technique for sizing of surface-breaking cracks in such a complex geometry component.
Abstract: Sizing a surface-breaking crack in a complex geometry component, for example a steam turbine's solid rotor shaft, is a challenging inspection task. This paper deals with experimental work for the evaluation of the Time-of-Flight Diffraction (TOFD) technique for sizing of surface-breaking cracks in such a complex geometry component. The experimental results show that with the help of the mathematical model explained here, TOFD can size such cracks with reasonable accuracy.
21 citations