Showing papers on "Time-of-flight diffraction ultrasonics published in 2000"

Ultrasonic testing system

Abstract: A comprehensive system for the cleaning, inspection, and testing of tubulars, particularly riser pipes, is provided. In a first aspect, a method of inspecting a tubular comprises cleaning, visually inspecting, corrosion mapping, and TOFD testing the tubular. In another aspect, a specially designed or adapted tool is provided for each of the steps of the method.

Inspection robot for spherical storage tanks

Abstract: Osaka Gas Co. Ltd has utilized ultrasonic flaw detection systems (time of flight diffraction method) to externally inspect the inner and outer surfaces of weld seams on spherical storage tanks while the tanks are in use. In these systems, the vehicle mounted with an ultrasonic flaw detection probe is designed to travel in a straight line only. To improve the work efficiency, we developed an inspection robot that is propelled by four independently driven magnetic wheels. This robot has been in experimental operation on an actual spherical tank. The introduction of this robot has shorten inspection time by about one week from the conventional 23 days, and reduced the conventional number of inspectors required from 4 to 2.

Crack Measurement in Steel Plates Using TOFD Method

Abstract: In this study, the ultrasonic time of flight diffraction (TOFD) method to locate and size flaws in steel members was evaluated. This was done by measuring the location and depth of flaws implanted in steel plate specimens and of a fatigue crack in the flange of a full-scale steel plate girder. The data showed that the TOFD procedure was very accurate to locate flaws (within 5% of the actual location). The accuracy of the procedure to measure flaw depth depends, however, on the proximity of the flaw tip to the scanning surface. Flaw tips at depths ≥6 mm below the scanning surface were measured to an accuracy of 20% of the actual value. When the flaw tip was at a depth ≤3 mm below the scanning surface, flaw depth was overestimated. Additional scans on the opposite surface of the material may be used, however, to overcome this limitation and to obtain an accurate measurement of such flaws. The method offered good repeatability and can be used to accurately locate and size flaws with an appropriate scanning s...

Sizing ultrasonic flaw detector and sizing flaw detecting method

Abstract: PROBLEM TO BE SOLVED: To provide a sizing ultrasonic flaw detector improved in detectability of diffracted wave in TOFD process by use of an electronic scan probe. SOLUTION: The electronic scan probe is used to freely change the angle and focus of ultrasonic beam, thereby, making an ultrasonic wave able to hit on a defect with an optimum angle and intensity to perform the flaw detection by the TOFD process. Accordingly, the defect detectability can be improved, and a proper diffracted wave can be used to improve the sizing precision.

Method and device for ultrasonic wave inspection

Abstract: PROBLEM TO BE SOLVED: To provide a result of evaluating flaw detection with high precision, for a TOFD method. SOLUTION: A plurality of D scope images are stored in a storage device in which the same object is separately measured with a pair of probe and measuring device under the same inspection condition. Two D-scope images out of the plurality of D-scope images stored in the storage device are displayed on a display device. A command for evaluating/calculating defect is inputted from an input device for dissimilar defect fringes of the two D-scope images. A calculation device evaluates all defect fringes, for defect, related to the D- scope image acquired at a first measurement, which is stored in the storage device. Related to D-scope images acquired at second or following measurements, the evaluation calculation is made with such defect fringe as indicated from the input device, whose result is stored in the storage device.

Ultrasonic probe and defect evaluation method using it

Abstract: PROBLEM TO BE SOLVED: To provide an ultrasonic probe capable of detecting even an inclined defect and having high evaluation precision of the defect, and a defect evaluation method using the probe. SOLUTION: This ultrasonic probe is formed by providing a pair of probes 12, 13 disposed so that an ultrasonic wave entering a test object (canopy seal part) from one probe 12 is reflected by the bottom surface of the test object to generate a bottom surface echo and that the bottom surface echo is returned to the other probe 13. The ultrasonic probe is formed so that the pair of the probes are pressed on the surface of the test object by respective elastic bodies and that the pair of the probes trace the surface of the test object respectively. A first direct projection method measurement, a second direct projection method measurement and a transmission method measurement are executed by using the ultrasonic probe, and evaluation of the defect is executed based on the results. Measurement by an end part echo method or a TOFD method is also executed by raising measurement sensitivity, and the defect is also evaluated from the result.

Advantages and Limitations of TOFD Technique in Casting Inspection

Abstract: In service inspection (ISI) of aged power plant parts has a delicate task to provide information on presence, position, orientation and size of defects in material. As far as results of ISI are just a starting point for elaborate procedure of life assessment or risk analyses, the accuracy and reliability of these results are particularly important. Time of Flight Diffraction (TOFD) technique is regarded as one of ultrasonic techniques capable to fulfil required precision, being approved in nowadays routine inspection of retaining rings or LP turbine rotor discs. Apart from these, usually highly automated inspections, a manual TOFD testing designed for particular plant component reveals reliable and useful defect information as well. In this work, results of TOFD inspection of turbine inlet casing are presented. The component was inspected subsequently during several years up to the point of substitution by a new one. Gained TOFD results are compared with results of visual and metallographic examination of samples cut out from the casing. Key words: NDT, power plant industry, castings, TOFD

Synthetic Aperture Focusing Technique 3D-CAD-SAFT

Abstract: Till the 80’s ultrasonic holography has been used as an analyzing technique, a procedure which has been replaced by the Synthetic Aperture Focusing Technique “SAFT.” This technique has been applied on metallic components in different power plants, mostly on pipe systems on pressure vessels or on specimen made of composite or concrete material. SAFT exists in different versions, either in 2D or 3D, for plane or arbitrarily shaped surfaces, for pulse echo or pitch- and catch arrangements. The defect sizes ranged from 100 μm in turbine shafts till fractures of meters in research pressure vessels. The paper covers the lastest results of the SAFT-reconstruction technique under Windows NT which has been guided by the experience obtained in the field. It contributes to the currently discussed question of the possible benefit using TOFD—techniques versus pulse echo techniques; the target has been a fatigue crack in a pipe segment which was investigated by different insonification angles, wave modes and probe arrangements. The results are evaluated with respect to signal-to-noise ratio improvement; problems of TOFD are demonstrated using an animation procedure which allows to walk through the weld in three orthogonal directions. A special example will be shown from a bore hole inspection of water power station valves where the reconstruction procedure follows the radial axial insonification planes. The multi-line SAFT images can be cut according to the situation of the crack position and orientation.

Untersuchungen mit TOFD an geschweissten Längsnahtproben

Abstract: Weld examination on Tube Test Specimen using TOFD. In contrast to the pulse echo technique, which is based on the sound field reflection at the flaw surface, the Time of Flight Diffraction (TOFD) technique uses the diffraction of the sound field at the flaw tips. For this purpose two angle beam probes for longitudinal waves are used in a pitch and catch arrangement. The transducers are positioned at both sides of the welding seam and are moved parallel to it during the measurement. The diffraction at the flaw tips causes different time of flight values with respect to the upper and lower flaw tip. Time dependent signals are stored in a series of A-scan pictures, which can finally be represented in a B-picture, which has to be interpreted. As investigations show there are additional useful information concerning defect size which can be given by TOFD, but pulse echo techniques with additional radiographic testing cannot be substituted by TOFD.