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Zur Steigerung der Zuverlässigkeit in der Prüfaussage und zur Vermeidung von Fehlinterpretationen ist es sinnvoll, die Auswertung und Bewertung von Ultra-schall-meßdaten zu vereinheitlichen. Dies ist insbesondere bei der mechanisierten Ultraschallprüfung vereinheitlichen. Dies ist insbesondere bei der mechanisierten Ultraschallprüfung gefragt, denn durch die Vielzahl der Meßdaten, der unterschiedlichen Ultraschall-Gerätetechnik und der individuell angepaßten Soft-ware sind unterschiedliche Darstellungen der Ergebnisse möglich. Eine "Standardisierung" der Aus- und Bewertung ist somit nicht möglich. Ein Ziel der hier vorzustellenden Auswerterichtlinie ist deswegen eine Vereinheitlichung der Darstellung. In der Richtlinie werden Mindestanforderungen vorgeschrieben. In diesem Beitrag werden Beispiele für die verschiedenen Darstellungsarten und die Vorgehensweise bei der Bewertung von Amplitude, Laufzeit, Dynamik und Anzeigennmuster gezeigt. Ein weiteres Ziel der Richtlinie ist, die Auswertehilfen und Auswertetechniken so zu dokumentieren, daß der Weg, der zum Prüfergeb-nis führt, jederzeit nachvollziehbar ist.
One of the most important tasks for in-service weld inspection of Circumferential welds is the detection of planar defects and its sizing. The information about the shape, length and depth of defects like cracks and lack of fusion can be measured quantitatively with a mechanised system for manipulation of X-ray source and line camera. The well adjusted manipulation system allows the testing of pipes with a
diameter between 176 mm and 500 mm. The system is based on several modules, which can be adjusted to the testing problem. The energy of the X-ray tube amounts 225 keV. The pixel resolution of the line camera is 50µm for 2048 pixels per line. The camera and the X-ray tube are separated on the pipe by an angle of 180°. They are moved line by line around the circumference to acquire the radiometric image.
The basic problem of radiography as well as of the radiometric scan technique is the dependence of the measured crack contrast on the radiation direction in relation to the crack location. Only parallel transmission to the crack plane provides sufficient contrast. This requires application of the multi-angle technique. The developed scanner enables modification of the radiation direction. It is possible to set up the system for a special inspection of side wall flaws. Scanning the weld under different angles provides multi -angle projections which improve the probability of detection for planar inhomogeneities in the material like cracks and lack of fusion.
Furthermore, the multi-angle technique provides enough information for a 3D-reconstruction of the weld structure. New methods of digital laminography and tomosynthesis permit the measurement of the shape and depth of the indications.
The developed system, which is applicable for mobile in service inspection, is presented together with the results of the measurement techniques like planar scan, coplanar laminography, tomosynthesis and cross-sectional planar tomography.
Tomographical Computer Aided Radiology (TomoCAR) is based on the mechanical position control of
an X-ray tube in front of a welding seam and the application of a planar array detector behind it. Several hundred
radiometric projections in small angle steps are acquired. The tomographical reconstruction allows the three-dimensional
(3D) representation of the defects. A new radiometric array detector system with a small internal
unsharpness and high image contrast is used for the 2- and 3-dimensional visualization and sizing of planar defects
with a defect opening of less than 100 µm. This detector is based on a CMOS-flat panel with a direct converting
CdTe-single crystal layer. The small design allows the application of the mobile testing equipment for mechanized
X-ray inspection in industrial plants. The physical pixel size of the detector amounts to 0,1x0,1 mm². Nevertheless,
this system yields a better spatial resolution than indirect converting detectors (e.g. cameras with fluorescence
layers of Gd2O2S). It allows the reliable detection of planar defects with openings far below the detector pixel size
by subpixel resolution.
'TomoCAR' is qualified at present in the context with a German pilot study following to the ENIQ guidelines for
the employment within the nuclear power industry.