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X-Ray Computed Tomography (CT) is applied in industry for flaw detection, flaw evaluation and dimensional measurement. This requires the correct CT system settings for sufficient visibility and detectability of flaws and structure elements. The visibility of indications for human observers on a monitor depends on the square root of the reconstructed flaw area (here pores with diameter < ½ inch) in the cross sectional 2D images, the Contrast to Noise Ratio (CNR) and the Modulation Transfer Function (MTF). This applies also to 2D-projections, meaning also to “normal” digital radiographs. The ASTM guide E 1441 describes three essential functions for prediction of the visibility of small circular indications in slice images of a 3D reconstruction or a 2D reconstruction. This is the Contrast Discrimination Function (CDF), the MTF (see also the revision of ASTM E 1695), and the Contrast Detail Dose (CDD) function. The prediction of the visibility of circular indications in reconstructed slice images can be determined from the Contrast Detail Dose function, which is the combination of CDF and MTF and a physiological factor c. The measurement procedures and formulas for the prediction of the detail visibility by CDD will be corrected, tested and verified by modelling and in a Round Robin Test with modern commercial 3D CT systems of different manufacturers. Conclusions will be reported and recommendations will be given for the correct psychological factor c and the consideration of the influence of artefacts, as e.g. cupping and scatter.
Der Ersatz von Röntgenfilmen durch digitale Detektoren in der Zerstörungsfreien Prüfung im Anlagenbau wird seit 2013 durch neue ISO-Normen unterstützt. Nach der Erfolgsgeschichte der digitalen Photographie und der fast vollständigen Ablösung der Filmtechnik in der optischen Bilderfassung wird erwartet, dass sich der Übergang von der Filmradiographie zur digitalen Radiographie schnell vollzieht. Dieser Trend ist derzeit so noch nicht zu beobachten. Zur mobilen Prüfung wird in Europa immer noch vorrangig die Filmradiographie und nur teilweise die Computerradiographie mit Speicherfolien eingesetzt. Im Bereich der stationären Prüftechnik haben sich die Matrixdetektoren (DDA) weitgehend durchgesetzt, wobei es auch hier noch alternative Detektoren wie Bildverstärker und Fluoroskope gibt. Mit Einführung der DIN EN ISO 17636-2 zur Schweißnahtprüfung wird seit 2013 erstmalig geregelt, wie man einen digitalen Detektor für die technische Radiographie auswählen soll, um im Vergleich zur Filmradiographie eine äquivalente Bildqualität zu erhalten. Essentielle Parameter bestimmen, ob die geforderte Bildgüte (Fehlernachweißempfindlichkeit) erreicht wird. Ein Überblick zeigt, welche Parameter für den praktischen Einsatz wichtig sind und wie sie ermittelt werden. Praktische Einsatzbeispiele im Anlagenbau werden diskutiert.
Industrial Radiology is used for volumetric inspection of industrial objects. By penetration of these objects (typically weldments, pipes or castings) with X-ray or Gamma radiation the 3D-volume is projected onto a 2D image detector. The X-ray film is the oldest radiographic image detector and still in wide use in industry. The industrial X-ray film systems used today differ from these used in medicine. Medical film systems are described well in the literature, but industrial film systems not. So we start with a description of the properties and standards for industrial film systems. The requirements on image quality are defined by several standards and can be verified with different image quality indicators (IQIs). They describe the ability of the human being to detect small and low contrast indications in a noisy image background. The essential parameters for digital industrial radiology are described.
Since about 30 years electronic image detectors are gradually replacing the industrial film. These detectors are based on storage phosphor imaging plates in combination with Laser scanners (“Computed Radiography”, CR) or a variety of different digital detector arrays (DDA). Typical applications of CR and DDAs are discussed as well as new possibilities by digital image processing, which is enabled by the computer based image handling, processing and analysis.
X-ray scatter imaging is a well-established NDT technique to inspect complex objects using only a single-sided access. We present a specially designed multi-slit scatter camera consisting of several twisted slits which are parallelly arranged in a metal block. The camera projects one image per slit to the digital detector array, where the images are overlaying each other. The aperture is corrected based on a de-convolution algorithm to focus the overlaying projections into a single representation of the object. To achieve high scatter intensities from an object, it is necessary to optimize the parameters of the scatter system by simulation.
We analyzed the results of high-energy X-ray CT scans for three 20×16×16 in. block samples of Indiana limestone from our recent radial acidizing experiments with HCl. CT scans were done for complete samples, and 3D images of internal dissolution patterns were built. Each 3D image consists of submillimeter-size voxels to capture fine details of individual wormholes.
The obtained 3D images of acidized blocks allow us to observe from various angles the details of the wormholes obtained in the three experiments, which demonstrated wide pore-volume-to-breakthrough (PVBT) range with three different injection rates. Also, variation of the CT number reveals the presence of depositional layers in all block samples, and the obtained CT images were used to interpret the effect that rock layers might have on wormhole penetration at different injection rates.
Further, the built voxel models were used to calculate the radial distributions of dissolved rock volume, which otherwise are not obvious for such complex branched structures as wormholes. We observed how varied experimental conditions affected those distributions. The radial distributions were found very similar across the samples, which suggested the way to detect the effective wormhole penetration depth.
Recent developments of photon counting and energy discriminating detectors for radiographic imaging
(2018)
The direct detection of X-ray photons into electrical signals is enabled by usage of highly absorbing photo conducting materials (e.g. CdTe) as detection layer of an underlying CMOS semiconductor X-ray image detector. If the read-out speed is high enough (ca. 50 - 100 ns dead time) single X-ray photons can be counted and their energy measured. Read-out noise and dark image correction can be diminished. By setting energy thresholds, selected energy ranges of the X-ray spectrum can be detected or suppressed. This allows material discrimination or reduction of scattered radiation, which results in an enhanced contrast sensitivity.
Up to now THz-TDS-systems aren’t considered to be nondestructive testing facilities for large scale industrial applications, despite it was proven that they provide a comprehensive set of quality parameters. A practical approach to bring THz-TDS in addition to already existing testing systems into the industrial mainstream is systematic development of future test procedures and test facilities for dielectrics. For this purpose polyeth-ylene test specimen with introduced artefacts were designed, to evaluate the detection sensitivity of Time of Flight measurements based on dielectrics. SAFT reconstructed tomograms are presented which visualize the sizes and location of artificially introduced flaws.
- Impact tests of concrete blocks
- High energy facility for laminographic testing
- Laminographic arrangement
- Cross-Laminography
- Measurement range extension by detector tiling
- Reconstruction methods
- Fast “shift averaging” method “next to base plane”
- reconstruction --> Removal of reinforcement indications
- 3D-Data analysis
- Crack-Segmentation by „Template Matching“
Herkömmliche Röntgenprüfanlagen für die Kontrolle von Luftfracht liefern unter bestimmten Bedingungen keine aussagekräftigen Ergebnisse. Hier wird ein mehrstufiger Detektionsprozess unter Verwendung von Hochenergieradiographie und laminographischen Verfahren vorgestellt, mit dem die Fehlalarmrate gesenkt und manuelle Nachkontrollen vermieden werden können.