核心提示：BAM is working in the field of X-ray computed tomography (CT) since more than twenty-five years. Several tomographs were developed and are in use:...
BAM - VIII.3 Dr. Uwe Ewert, Director and Professor
Sunday, April 4th, 2010
Workshop on Digital Industrial Radiology at FENDT 2010
Computed Tomography at BAM – from High Energy Technique to nm Scale -
Uwe Ewert, Jürgen Goebbels
Federal Institute for Materials Research and testing (BAM); Berlin; Germany
BAM is working in the field of X-ray computed tomography (CT) since more than twenty-five years. Several tomographs were developed and are in use:
Synchrotron CT in the energy range from 5 to 90 keV with high resolution detectors and optional magnification by asymmetric Si-crystals at the Berliner Synchrotron facility BESSY,
micro-focus laboratory CT units from 100 kV transmission type X-ray tube up to a 320 kV bi-polar micro-focus X-ray tube,
high energy CT, based on mini-focus 450kV X-ray tube, Co-60 source and a 12 MeV electron linear accelerator.
The recent applications are integrity of electronic components, characterisation of filter media for chemistry, non-destructive evaluation of the corrosion process in chloride contaminated mortar. Methodological improvements are developed to overcome the limitations of high energy CT due to scattered radiation. CT is increasingly used to substitute classical Coordinate Measurement Machines (CMM), especially with focus to micro parts and measurement of inner dimensions. A new generation of multi sensor CMMs combines the CT operation with optical sensors and tactile probing. However, an important aspect of all coordinate measurements is the traceability of the geometry information obtained. To achieve traceability, several one-, two-, or three-dimensional material standards have been developed in recent years by PTB (the German national metrology institute), BAM (the German national material testing institute) and partners.
For industrial objects as bridges, pipelines and aircrafts, which cannot be brought to the laboratory, mobile CT scanners were developed. They are typically based on the planar tomographic design. The first applications are qualified by third party organisations for sizing of planar defects in nuclear power industry and aircraft industry. For parallel measurement of spatial information and materials characterisation computed tomography and topography is combined with detection of scattered radiation in different scatter angles optionally to the primary beam direction. Especially small angle refraction provides information on inner surfaces and debonding effects.
The new THz technique is based on the materials inspection with electromagnetic radiation in the frequency range of about 100 – 1000 µm. The radiation penetrates non metallic and non conducting materials as ceramics, plastics and some composites (e.g. glass fibre reinforced). It can is applied for spectral and spatial inspection. Computed tomographic and topographic techniques were developed and tested for volumetric inspection of first test objects.
Keywords: Computed tomography, topography, stationary, mobile, X-ray, THz, dimensional measurement, tactile measurement.
contact: Uwe Ewert, Juergen Goebbels
Tel.: +49 30 8104 1830
e-mail: uwe.ewert@bam.de, juergen.goebbels@bam.de
Digital Radiology for Corrosion and Weld Inspection - Applications in Chemical Industry -
Uwe Zscherpel, Uwe Ewert, BAM Berlin
Peter Rost, BASF SE, Ludwigshafen, Germany
Projection radiography is widely used for pipe inspection and corrosion monitoring. Two techniques are typically applied: The tangential radiographic technique (TRT) and the double wall radiographic technique (DRT). Both techniques are under standardization at CEN TC 138 WG 1 now. TRT and DRT by digital radiography and film RT with digitization allow direct access to the local density variations and wall thickness from tangential projection by computer software. Following a calibration step an interactive determination of local wall thickness and its change is measurable with the same software. The procedure is demonstrated with the ISee! software package. The theoretical model is discussed, the limitations of the application range are shown and examples of the practical use are given. The accuracy of this method is determined from wall thickness measurements of validation step pipes. Both methods (TRT and DRT) were developed over the last decades and will be included now in training programs for film RT and digital RT.
Also the International Atomic Energy Agency (IAEA) promoted recently industrial applications of radiation technology for evaluation of corrosion and deposits in pipelines by coordinated research programs (CRPs) and research contracts. Limits, procedures and accuracy evaluations were published for film radiography.
Keywords: Digital radiography, corrosion, deposit, double wall inspection, tangential radiography, digital image processing, standards
contact: Uwe Zscherpel
Tel.: +49 30 8104 1830
e-mail: uwe.zscherpel@bam.de
Numeric Modeling for Industrial Radiology with aRTist
U. Ewert, G.-R. Jaenisch, and C. Bellon
Federal Institute for Materials Research and testing (BAM); Berlin; Germany
Unter den Eichen 87, 12205 Berlin, Germany
The computer modeling (simulation) of radiographic images is applicable for different purposes in NDT such as for inspection planning, the qualification of NDT systems and the prediction of its reliability, the optimization of system parameters, feasibility analysis, model-based data interpretation, education and training of NDT/NDE personnel, and others. Transmitted radiation through an object gives information about its inner structure. The transmitted radiation consists of a primary and a scattered component. Different models have been developed at BAM to meet the above goals.
For practitioners, the aRTist (analytical RT inspection simulation tool) software has been developed. It combines analytical modeling of the RT inspection process with the CAD-orientated object description applicable to various industrial sectors such as power generation, aerospace, railways and others. The analytic model includes the description of the radiation source, the interaction of radiation with the material of the part, and the detection process including X-ray films, CR, and DDA. Handling the contribution of scattered radiation is restricted to analytical descriptions such as built-up factors in this software due to calculation purposes. The simulation tool will be made available as software package to the NDT community. The capabilities of the model for inspection planning are discussed in terms of realistic examples.
In addition to the above described analytical model aRTist the Monte Carlo model McRay has been developed allowing the detailed description of the physics of radiation transport. This model is capable to handle complex object geometries by means of the same CAD interface as in the aRTist software. This allows simulating realistic inspection scenario which is very difficult with standard Monte Carlo programs like the Monte Carlo n-particle transport code MCNP (Los Alamos National Laboratories) using mainly simple geometrical forms such as parallelepipeds, ellipsoids, or planes to construct complex geometries in a proprietary way. The applicability of the presented Monte Carlo simulation tool is discussed in terms of examples and compared to MCNP. Additionally, the opportunity of combining both applications in a common software package is discussed.
Keywords: X-ray modelling, aRTist, CAD, primary radiation, scattered radiation, monte carlo code, training, experiment planning
contact: Uwe Ewert, Gerd-Ruediger Jaenisch
Tel.: +49 30 8104 1830
e-mail: uwe.ewert@bam.de, gerd-ruediger.jaenisch@bam.de
Application of Time Domain THz Spectroscopy for Non Destructive Contactless Inspection of Non-Metallic Materials and Substances
J. BECKMANN1, L. v. CHRZANOWSKI1, B. EWERS2, Barbara MARCHETTI 1,3,
Ulrich SCHADE3, U. EWERT1 ,
1 Federal Institute for Materials Research and testing (BAM); Berlin; Germany
2 Philipps-Universität Marburg, Marburg, Germany
3 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin, Germany
Electromagnetic waves with frequencies between 0.3 and 10 terahertz (THz) ≡ 10 – 300 cm-1 ≡ 1 – 0.03 mm are described as THz radiation (T-rays).
T-rays have unique properties which made them priory attractive for new applications in the security sector. They have in comparison to X-rays much lower photon energy and therefore do not expose a biological tissue with hazardous radiation. Optically opaque non metallic materials such as paper, plastics, ceramics and textiles for clothing appear transparent in the THz range. Because of a better penetrability than the infrared and higher resolution than the microwave radiation THz radiation found first applications in microelectronics, agriculture, forensic and medical science. Explosives and pharmaceuticals provide unique spectroscopic “fingerprint” signatures in the THz range which can be used for their identification. Nowadays, fiber coupled table top THz systems, operating with time domain spectroscopy (TDS) procedures available which are considered to be useful for providing images complementary to optical, X-ray, NMR and Ultrasound images.
The THz laboratory at BAM is equipped with a glass fibre coupled Picometrix T-ray 2000 THz system operating at frequencies between 0.1 to 2 THz.
The contactless material spectroscopy and imaging for the non destructive inspection on insulating and weakly electrically conductive material will be demonstrated. Future capabilities for different applications in the field of safety and security will be demonstrated and discussed in more detail on characteristic image examples. Of particular interest will be the demonstration of significant flaw detection procedures, if both the time and frequency information is used for the material evaluation.
Part of the work was financially supported by the Federal Ministry of Education and Research (BMBF) (Project: HANDHELD, FKZ 13N9514).
Keywords: THz radiation, Imaging, Spectroscopy, Computed Tomography, Lightweight Materials
contact: Jörg Beckmann
Tel.: +49 30 8104 3691
e-mail: joerg.beckmann@bam.de
Strategies and new Standards for Film Replacement in Radiography
Uwe Ewert, Uwe Zscherpel, Klaus Bavendiek, Mirko Jechow
Federal Institute for Materials Research and testing (BAM); Berlin; Germany
2YXLON International GmbH, Hamburg, Germany
The NDT community discusses about effective film replacement by Computed Radiography (CR) and the new Digital Detector Arrays (DDA), also known as flat panel detectors, since more than 10 years. Several standards were published by CEN, ASTM and ASME to support the application of phosphor imaging plates in lieu of X-ray film in the year 2005. One of the key concepts is the usage of signal-to-noise (SNR) measurements as equivalent to the optical density of film. The procedure will be demonstrated. The application of DDAs is supported by first ASTM standards, which are a guide, a manufacturer and user qualification and a standard practice. The bad pixel problem is addressed and will be explained. Measurement methods are described for parameters as basic spatial resolution, efficiency, specific material thickness range, contrast sensitivity and image lag.
A comparative study presents the results of film replacement by CR and DDAs for welds. New strategies for correct DDA calibration yield an extra ordinary increase of image quality. The contrast sensitivity was enhanced up to 10 times in relation to film radiography. This could not yet be achieved by any other technology. The digital radiographic technique is nowadays limited by the materials grain structure and not the detector contrast/noise distribution. Even restrictions in the spatial unsharpness provoked by the individual picture element size of the detector are compensated by the increased contrast sensitivity.
Standards for Computed Radiography with imaging plates (IP) are under a major revision. As well the European standards as the USA ASTM standards need changes, especially, in the standard practice after its first publication in 2005 and the different experiences reported by many users now. Imaging plates are limited in the achievable contrast sensitivity by its inner graininess. The increase of exposure dose improves the contrast-to-noise ratio (CNR) in the low dose range proportional to the square root of the exposure dose, but reaches a maximum at higher dose values. Limitations in the spatial resolution can be partly compensated by increased CNR for DDAs and fine grained IPs. The recommended X-ray tube voltage should be modified in relation to the typical values of film radiography depending on the maximum achievable signal-to-noise ratio of the detectors.
Keywords: radiography, film replacement, computed radiography, imaging plates, digital detector arrays, contrast sensitivity, SNR, CNR, standards
contact: Uwe Ewert, Uwe Zscherpel
Tel.: +49 30 8104 1830
e-mail: uwe.ewert@bam.de, uwe.zscherpel@bam.de