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- Image quality (4)
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Organisationseinheit der BAM
New Digital Radiography Procedure Exceeds Film Sensitivity Considerably in Aerospace Applications
(2006)
Different girth welds of tube sections have been inspected by elliptical projection technique
according to the EN 1435. The radiographic images were taken by using both film
radiography and computed radiography. The purpose of this study was to compare a C3
(AGFA D4) film system and a Duerr HDCR 35 NDT / HR IP imaging plate system with
respect to the exposure time, image quality and the detection of fine weld imperfections. The
results indicate to a dominant influence of the lead screens on the image contrast sensitivity if
doing the inspection according to the EN 14748 -2 for imaging plate exposures. New screen
combinations had been applied to make a computed radiograph of a testing class B quality
possible.
Imaging Capability of Terahertz and Millimeter-Wave Instrumentations for NDT of Polymer Materials
(2006)
Computed Radiography exposure experiments on welded plate sections
were performed to demonstrate that the requirements for pressure vessels weld
inspection according to EN1435 or EN14784-2 class B can be achieved. The
representative comparative studies of the image qualities were performed with
standardized image quality indicators and image evaluation procedures on both film
and digital radiographs. Recommendations for weld inspections with CR systems
are drawn from the results. It is demonstrated that present CR systems can be used
for weld inspection and produce images with testing class B if the selected X-ray
tube voltage is reduced compared with the max. voltage of EN 14784-2 and set
equivalent to maximum X-ray voltage values for steel as defined in the radioscopic
standard EN 13068-3. The work was part of the European 'Filmfree' Project
promoted during the 6th framework.
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.
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.