Applicability Study of Computed Radiography to NDE for Piping and Component in Nuclear Power Plant

In Radiography Testing (RT) that is an important nondestructive testing as the quality control, the digital imaging technology rapidly provides advancement. The digital imaging technology is more effective than the film method on an environmental side and the cost side, such as unnecessary of the film storage and a chemical treatment by digital output. Especially, in the medical field, the advancement by the digitalized image data processing is remarkable, and it is attempted the upgrade of the inspection technology. However, RT that uses the high-energy radiation and the fast film is a main current in an industrial field, and it has not arrived at digitalization yet. Therefore, in an industrial RT, digitalization is expected and the examination standardization is required also in ASME, JSME, and JIS. We, Mitsubishi Heavy Industries (MHI), studied an applicability of Computed Radiography (CR) to Non-Destructive Examination (NDE) for welds of piping and thick wall component in nuclear power plant. At first, MHI researched image quality of CR for piping. In this research, it was confirmed that the images of testing results by CR method are equivalent to that by film method in terms of visibility of IQI (Image Quality Indicator) and detection performance of welding defects. And we founded the optimized shooting conditions for piping. Second, MHI researched image quality of CR for thick wall component. In the result, the noise shown in fig.1 was occurred on CR image when the thick wall component such as pressure vessel is radiographed with high energy. It is speculated that the primary cause of this noise is the scattered X-ray effect (shown in fig.2). Therefore it is necessary to investigate the effect of the scattered X-ray on CR image. In this study, to reduce the scattered X-ray effect on CR image, we investigated the effect of 1) screen, 2) screen + filter on image quality of CR for thick wall component. And we studied the optimized shooting conditions and parameters for thicker component than piping to aim for more application. Finally, we applied CR to the pipings and components for nuclear power plant with the optimized shooting conditions and parameters.