Filtern
Dokumenttyp
Sprache
- Englisch (14) (entfernen)
Referierte Publikation
- nein (14) (entfernen)
Schlagworte
- POD (3)
- Zerstörungsfreie Prüfung (3)
- Zuverlässigkeit (3)
- Analyse (2)
- Bewertung (2)
- Crack inspection (2)
- Crack overshoot (2)
- Digitale Detektoren (2)
- Endlagerung radioaktiver Abfälle (2)
- Röntgen (2)
The quantitative measurement of kind, positions and diameters of steel reinforce ments in building constructions is a typical inspection problem in civil engineering. A classical solution is the combination of film radiography with the multi angle technique and graphical backprojection. New digital detectors reduce the exposure time and allow the application of stereo radiography and computed laminography as routine applications.
The computed laminography allows fast and effectively the determination of the depth of reinforcements in concrete or masonry. A selected area of the steel re-bar structure is penetrated by gamma-rays from different angles of incidence (multi angle-technique) with a Co-60-source. Instead of a radiographic film phosphor imaging plates were used as a new digital medium for filmless radiography. A 3D-image of the measured region of interest is reconstructed from the digitised projections of a test block. The reconstruction is based on special tomosynthesis algorithms which need few projections only.
Radiographic techniques were uses in completion to other techniques like radar, electromagnetic alternating field inspection to examine the structure of different buildings. Experiences of inspections of historical buildings, ancient marble structures and a bridge girder are presented where different levels of radiography were applied.
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.
Digital detectors such as phosphor imaging plates (IP) and digital detector arrays (DDA) allow radiographic inspection with higher efficiency and improved image quality in comparison to the classic film technique. Mobile X-ray flash tubes are used routinely for veterinarian and security applications. New high sensetive IPs and DDAs enable to apply them for inspection of light materials with low X-ray attenuation as in aluminium, plastics and composites. A versatile computed tompgraphy (CT) system was developed for in situ inspection of large aircraft components under production conditions. A gate based planar computed tomograph wsa developed and testes for inspection of integrety of the stringer incorporation. Successful test trials were performed to prove the detection rate of cracks in embedded stringers. Honey comb structures of aircrafts have to be inspected for water inclusions during in-service inspections. Thermography is a powerful method for in house inspections when variations in temperature caused e. g. by sunshine can be excluded. A new X-ray diaphragm was developed for mobile back scatter measurements of large components. This method is insensitive to heat alterations in the field and thus can be applied also outdoors.
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.