Filtern
Erscheinungsjahr
Dokumenttyp
Referierte Publikation
- ja (24) (entfernen)
Schlagworte
- Radiography (7)
- Radiographie (4)
- Standards (4)
- ZfP (4)
- Bildqualität (3)
- Digitale Detektoren (3)
- Image quality (3)
- X-ray backscatter imaging (3)
- Aerospace applications (2)
- Digital detector array (2)
Organisationseinheit der BAM
Best energy selection for different applications with digital detector arrays from 20 to 600 keV
(2012)
In der Filmradiografie kann durch den Einsatz von Metallfolien und Metallfolienkombinationen der Bildkontrast verbessert werden. Die Mechanismen zur Erzeugung der latenten Röntgenbilder und deren Sichtbarmachung für das menschliche Auge sind in Speicherfolien nicht mit denen in einem Röntgenfilm identisch. Demzufolge lassen sich die in den Normen zur Filmradiografie veröffentlichten Empfehlungen zum Einsatz von Metallfolien und zur Auswahl der Röhrenspannung nicht unmittelbar auf die Computer-Radiografie zur Schweißnahtprüfung übertragen. Die Qualität digitaler Röntgenbilder wird von der Bildunschärfe und dem Kontrast-zu-Rausch-Verhältnis (CNR) bestimmt. Während die Norm EN 14784-1 handhabbare Verfahren zur Bestimmung der inneren Unschärfe und des Signal-zu-Rausch-Verhältnisses (SNR) beschreibt, sind die in EN 14784-2 vorgegebenen Vorgehensweisen zur Kontrastverbesserung durch die Vorgaben zur geeigneten Röhrenspannung und Metallfoliendicke für die Schweißnahtprüfung nicht ausreichend dargelegt. Um die Parameter zur Verbesserung der Bildqualität von CR-Systemen für den Fall der radiografischen Durchstrahlungsprüfung von Schweißnähten zu optimieren, wurden systematische Untersuchungen zum Einfluss eines Kupfer-Vorfilters, von Bleifolien-Speicherfolien-Kombinationen und der Röhrenspannung auf den Bildkontrast von Stahlstufenaufnahmen durchgeführt. Auf der Grundlage dieser Ergebnisse wurden Empfehlungen zum Einsatz der Metallfilter und -folienkombinationen sowie zur Auswahl geeigneter Röhrengrenzspannungen für die Speicherfolientechnik zur Optimierung der Durchstrahlungsprüfung von Schweißnähten abgeleitet.
In situ crack detection in the mushy zone and the solid weld of a gas tungsten arc (GTA) weld using X-ray imaging during welding is a new research area for NDT inspection. Usually, NDT flaw detection is done after the complete solidification of the weld seam. In this paper, we present the use of real-time radiography with a minifocus X-ray source (YXLON X-ray tube Y.TU 225-D04) and a 75μm pixel size digital detector array (Dexela 1512) for the acquisition of 2D radiographic images by a sequence of exposures with time intervals of 80 ms for hot crack detection during single pass bead-on-plate GTA welding of 3 mm thick plates of aluminium alloy AlMgSi (6060). An analysis of the crack distribution in the weld sample is conducted from the acquired 2D radiographs and its corresponding 3D volumetric reconstruction achieved by linear coplanar digital laminography.
This in situ approach opens new possibilities in the field of hot crack research by having the direct information of both the crack initiation and growth and its correlation to the welding parameters.
Die radiografische Bildqualität in ihrer klassischen Definition hängt von Kontrast, Rauschen und Unschärfe ab. Diese Parameter werden normalerweise mit Bildgüteprüfkörpern (BPK) bestimmt. Die Streustrahlung reduziert im Allgemeinen immer die Bildqualität in der Radiografie. Verschiedene Einflussgrößen werden unter Berücksichtigung von Techniken, wie Film-Radiografie, Computer-Radiografie mit Speicherfolien und digitale Radiographie mit Matrixdetektoren, analysiert. In Lehrbüchern und Standards werden das Streuverhältnis k und verschiedene Kontraste definiert. Für digitale Medien werden zusätzliche Parameter wie das Signal-Rausch-Verhältnis SNR und das Kontrast-Rausch-Verhältnis CNR eingeführt. In diesem Zusammenhang wird der Einfluss der Streustrahlung aus dem Messobjekt und dem Detektor bestehend aus Kassette bzw. Gehäuse und sensitiver Detektorschicht auf die Bildqualität ermittelt. Die numerische Modellierung wird eingesetzt, um die Streustrahlung und die Primärstrahlung aus dem Objekt separat zu bestimmen. Die Streustrahlung aus dem Objekt und Detektor erzeugen eine Abbildung des Objektes, die dem Primärstrahlungsbild überlagert ist, wobei das Streubild eine höhere Unschärfe aufweist. Dieser Effekt hängt von der Fehlergröße, dem Abstand zwischen Detektor und Objekt und der Zwischenfilterung ab.
The presently active standards on Computed Radiography (CR) need a major revision. It was observed by many users that the image quality for class B of EN 14784-2 is not achievable under the same exposure conditions as used for film exposure. A mathematical model was developed and tested, which allows the calculation of the image quality, proven by image quality indicators (IQI), depending on the fixed pattern noise and the efficiency of the used imaging plate (IP) scanner system. All tested IP scanner systems provide a fixed correlation between the measured signal/noise ratio (SNR) and the grey values in the digital images. The maximum achievable SNRmax depends on the fixed pattern noise of the plate (high dose limit). Depending on the exposure dose an optimum visibility of IQIs can be predicted by calculation and measured considering the attenuation coefficient for calculation of the contrast/noise ratio (CNR). The diameter of the just visible wire is proportional to 1/sqrt(CNR). The optimum tube voltage for best visibility of IQIs and maximum CNR depend on the exposure dose. The optimum tube voltage for best visibility is achieved only at exposures with high dose. A dose dependant optimal tube voltage was not observed for film radiography.
The digital photography has almost completely substituted the film photography. The film replacement is also fast progressing in medical X-ray radiography. This process is slower in NDT and especially in Europe. Reasons for the hesitating change to digital radiography (RT-D) in NDT are the necessary time for adoption of standards and the conservative request for film RT by auditors and NDT managers for applications in large plants and at construction areas. The fast serial inspection for small castings is already almost completely dominated by RT-D due to the cost effective short exposure and interpretation times. Standards were developed in parallel at CEN, ISO, ASTM and ASME. Unfortunately, the standard practices are different and the requirements on image quality and useable hardware are different too. The first standard series on Computed Radiography were developed and published by CEN and ASTM in 2005. Harmonized classification and qualification standards are available but the published practices are different. ASTM has developed the first standards for application of Digital Detector Arrays (DDA) in 2010. The first digital RT ISO standard practice is ISO 17636-2 (2013), which describes the practice for application of DDAs and Imaging Plates for weld inspection. At the first time this standard provides requirements for the selection of suitable hardware. Minimum image quality requirements are specified in analogy to film radiography and 3 Compensation Principles are defined to enable the application of a wider range of digital detectors. A comparison of the different international digital RT standards is given and first experiences with ISO 17636-2 are discussed. New standards on RT wall thickness and corrosion measurements (EN 16407, film and digital) have been developed recently.
Within the framework of the European project PICASSO, the radiographic simulator aRTist (analytical Radiographic Testing inspection simulation tool) developed by BAM has been extended for reliability assessment of film and digital radiography. NDT of safety relevant components of aerospace industry requires the proof of probability of detection (POD) of the inspection. Modeling tools can reduce the expense of such extended, time consuming NDT trials, if the result of simulation fits to the experiment. Our analytic simulation tool consists of three modules for the description of the radiation source, the interaction of radiation with test pieces and flaws, and the detection process with special focus on film and digital industrial radiography. It features high processing speed with near–interactive frame rates and a high level of realism. A concept has been developed as well as a software extension for reliability investigations, completed by a user interface for planning automatic simulations with varying parameters and defects. Furthermore, an automatic image analysis procedure is included to evaluate the defect visibility. The radiographic modeling from 3D CAD of aero engine components and quality test samples are compared as a precondition for real trials. This enables the evaluation and optimization of film replacement for application of modern digital equipment for economical NDT and defined POD.
This work presents the use of limited experimental measurements to develop a set of calibrated Simulation parameters that can then be used for reliable simulation of subsea pipeline inspections. The modelling software aRTist is used as the simulation tool, and the calibration is through comparison with experimental images of a well characterised sample in a water tank. Image Quality parameters such as signal-to-noise ratio, contrast and basic spatial resolution are compared with the aim of matching simulated values to experimental results. Currently the model is partially calibrated, with signal-to-noise ratio successfully matched while differences are still found in contrast-to-noise ratio comparisons. This means that measurements depending on absolute intensity are not accurate enough in the simulation at this stage. However, the simulation is found to be accurate for wall thickness measurements in tangential images, which are not based on absolute intensity, with simulated and experimental cases producing similar results.