U. Ewert obtained the diploma degree for physical and theoretical chemistry of the Humboldt University in Berlin in 1974. He received the PhD for simulation of electron spin resonance spectra in 1979. From 1980-1989 he managed the application laboratory for ESR-spectroscopy at the Centre for Scientific Instruments of the academy of sciences in Berlin. U. Ewert was guest faculty at the Baker Laboratory of the Cornell University in USA from 1989-1990.

In 2000 he was appointed as director and professor of the division “Nondestructive testing; radiology” at BAM. He is elected chairman of the German radiology committee of the German society of NDT (DGZfP; since 1997), was member of DGZfP advisory board and is chairman of the subcommission VA (radiation methods for welding) of the International Institute of Welding (IIW; since 2000).

He is delegate at several standard committees of ISO, CEN and ASTM. U. Ewert received the Berthold award of DGZfP (2005), the Röntgen medal of the city of Remscheid (2009) and the Briggs Award of ASTM-International (2010).

Abstract

The visibility of flaws and image quality indicators (IQI) by human operators has been discussed for film radiography (RT-F) over decades. If operators follow the current standards on film radiography and use the recommended NDT films and exposure conditions the achievable contrast sensitivity is in the order of 1-5% of the penetrated material thickness. In the last 15 years film replacement has been discussed in analogy to the success story of digital photography. The image quality in digital industrial radiology (DIR) depends on the exposure conditions and the properties of the digital detectors. Operators need rules and reliable parameters for detector selection and correct exposure conditions. Many parameters influence the result of digital radiographs, but only three are essential for the achievable contrast sensitivity. These essential parameters are the basic spatial resolution (SR_b^image), the Signal-to-Noise Ratio (SNR) and the specific contrast (µ_eff). The equivalent penetrameter sensitivity (EPS), which corresponds to the contrast sensitivity of plate hole IQIs as defined by ASTM E 746, E 1025 and E 1742, can be calculated, if the essential parameters are known. The same approach can also be applied to predict the visibility of wire IQIs. EPS (in % of material thickness t for plate hole IQIs) is finally calculated by EPS = (PT’/t)▪SQRT(SR_b^image/(µ_eff▪SNR)). PT’ was determined by different operators and amounts to about 2▪100%. The related studies were performed with Computed Radiography (CR) and Digital Detector Arrays (DDA) in comparison to digitized film radiographs. Computed radiographs, taken with imaging plates, achieve similar IQI visibility than film radiographs. In many cases they achieve only the performance of class “A” (basic) as defined in the standard ISO/FDIS 17636-2 and fulfil completely the requirements of ASME BPVC section V article 2. Radiography with DDAs can achieve typically much better IQI visibility than RT-F and CR, even at short exposure time. The achievable contrast sensitivity is limited by the fixed pattern noise of imaging plates and the calibration procedure for DDAs. The results of measurements are presented and recommendations for exposure conditions are concluded. The new draft ISO/FDIS 17636-2 describes the practice for digital radiography with CR and DDAs and defines requirements for detector selection. It considers first time compensation principles, derived from the three essential parameters. Considering the optimum exposure conditions, digital radiography can be applied to a broad range of X-ray applications, including inspection of pipeline welds, castings, electronic assemblies, wheels, rails, aerospace, bridges and many other industrial uses for technical, environmental, safety and economic advantages.