Papers by Keyword: TOFD

Abstract: The feasibility of the application of probes with refraction angle of 20 degrees is discussed, and application effects of the probe are verified by experimental testing. The result shows, for ultrasonic TOFD testing of small flaws in lower part of high-wall-thickness work-pieces, the probe pair with refraction angle of 20 degree is superior to 45 degrees.

Abstract: This article firstly introduces the ultrasonic TOFD (Time-of-flight - Diffraction) detection technology of detection principle, advantages and disadvantages, and then summarizes the ultrasonic TOFD technique related testing standard, finally combining the reality of tube mill, analyses the pipe material testing near the surface of the blind area and radian impact problems, discusses the ultrasonic TOFD in application prospect in the field of thick wall tube welding seam detection.

Abstract: The time and flight diffraction (TOFD) technique has be more and more applied as a well-developed ultrasonic non-destructive testing (NDT) technique in a increasing number of industrial areas such as aeronautics and mechanical industries, therefore, the TOFD technique can be also used to investigate the sound field characteristic curve of artificial defects in welding. The investigations are performed in 2-layered medium (water-steel) with using the finite difference numerical simulation software Wave2000. The receiver group is consisted of several receivers which are immersed in water and have the same frequency, the receivers are placed at the opposite positions by changing regular angle.The results show that amplitude of diffraction wave change along different receiving orientation greatly, if the normal to the vertical direction is set to 0 degree, then the direction of 20° can receive the largest amplitude of diffraction wave. At last, the characteristic curve of diffraction wave is given in this paper.

Abstract: A NDT technique suited to inspecting thick-walled metal parts of power stations is comprised of time-of-flight-diffraction technique, Pulse-echo technique and magnetic particle inspection technique or dye penetrate technique. Flaw sizing accuracy and probability of detection can be improved greatly with application of the technique, and the risk of components` failure can be decreased greatly.

Abstract: In the application of the TOFD inspection method, the analysis of test results is the focus and aporia of the study. TOFD image analysis include: analysis of defect size, location analysis and defect map features. In order to increase people's understanding of the TOFD technique, given butt joint welds TOFD and RT detect. The paper introduces basic process of defect using the TOFD method, describes method of quantitative orientation of the defect in detail, analyzes the localization and quantification of defects in detection. Determine the qualitative of defects by Ray photographs and analyze the characteristics of the defects of this nature in the TOFD image.

Abstract: The detection of flaws is essential as the defects of pipes and containers affect the safe operation of many kinds of equipment. During the industrial production process, it is usually use the ray method to detect the flaws which has radiant effect on the testing personnel. The ultrasonic time-of-flight diffraction (TOFD) is a new type acoustic detection method and it is relatively safe for users. When using the TOFD technique, the selection of the probe separation is the important parameter which related to the effect of the test and the coverage range of the probe identifies the effective range of the detection. In this paper, the probe separation distance and the probe coverage range procedures which can help the testing personnel set the parameters quickly is devised. The experimental results indicate that this algorit

Abstract: The ultrasonic time-of-flight-diffraction (TOFD) detection method has been widely used in crack size assessment. The key issue in TOFD is to determine the arrival time of crack tip diffracted signal. In the traditional cross correlation method, the resulting maximum peak of cross correlation function between two signals indicates the time of flight between them. In practical ultrasonic measurement, the transmission wave may be distorted and phase shift may be introduced. This paper presents a method using cross correlation and phase shift correction to improve the accuracy of crack sizing in the TOFD framework. The resulting maximum peak of the cross correlation function between two signals combining with time delay introduced by phase shift determine the arrival time of diffracted signal. Experimental results are used to demonstrate the advantage of the proposed method.

Abstract: Pipelines of nuclear power plants undergo high pressure and temperature. Thermal stratification typically occurs in the surge line and the main feed water lines by flow and this stratification will initiate and propagate thermal fatigue cracks. This may cause rupture and leakage and it is a serious problem to nuclear power plants operation. Therefore it is very important to detect and measure thermal fatigue cracks. In this study, thermal fatigue cracks were generated in austenitic stainless steel specimens by a thermal cycle in notched pipes and weld jointed pipes. Ultrasonic techniques were used to evaluate the thermal fatigue crack depth. When ultrasonic waves propagate from an angle beam probe to thermal fatigue cracks, waves are reflected and diffracted. Crack depth was evaluated by the reflected signals from back wall and diffracted signals from the crack tip, but diffracted signals were too weak to detect so the reflected signals were more useful. The TOFD and dB drop methods were used in this study. The TOFD method is uses a time delay of diffracted signal from the crack tip. The dB drop method is an application of an amplitude decreasing rate by a probe moving distance.

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.