X-Ray Tomographic In-Service-Testing of Circumferential Pipe Welds - The European Project TomoWELD

摘要

The new standard ISO 17636-2: 2013, "NDT of welds-X- and gamma ray techniques with digital detectors", defines the practice for digital radiography for manufacturing and in-service inspection of welds. Furthermore, the DIN 25435-7:2014, "In-service inspections for primary coolant circuit components of light water reactors - Radiographic testing", was released. This standard was submitted to ISO TC 85. The newly developed TomoWELD device can perform overview scans based on these standards, and tomographic scans providing cross sectional images (micrographs) to determine flaw dimensions. Application areas are primarily the nuclear and chemical industry. TomoWELD enables the fast inspection of circumferential welds in pipes, in comparison to film or imaging plates. In 2006 the mechanized and automated device TomoCAR was developed and tested. Cross sectional digital radiographic images were taken to determine positions, shapes and dimensions of indications. The system was qualified for the application in the nuclear power industry as a result of an ENIQ trial. TomoWELD uses a newly developed photon counting and energy discriminating digital detector array with CdTe-CMOS crystal hybrids. The new detector design permits the selection of different detection energy levels for different output images. The influence of scattered radiation can be reduced. The detector permits high image integration times, especially if applied behind thick walls at low photon flow rates, since offset signals in the acquired images are negligible. An optimized radiation geometry, with a new manipulator design and a fast GPU based reconstruction algorithm, are used for fast measurement and reconstruction. The size and shape of planar and volumetric flaws was determined for austenitic test pipes within a wall thickness range from 10 - 35mm and diameters from 100 - 350mm. The results of the field tests in a German nuclear power station are presented.