This paper describes an extensive series of experimental studies of radiographic capability, for material thicknesses in the range 50-114 mm. These studies have been supported by surveys of the relevant parameters of real metallurgical defects to confirm the realism of the defects used. The results have been interpreted using a well-established, albeit simplified, theoretical model of the radiographic process, but further work on a more comprehensive theoretical model is in progress to provide more precise comparisons of theoretical and experimental results.
Considerable care has been taken to produce planar defects which realistically simulate those which might conceivably occur during welding of thick-section ferritic steel pressure vessels. One key feature is the orientation of the defect relative to the radiographic beam, and this can be controlled reasonably precisely when inducing defects in test specimens. Another crucial parameter for radiographic detection is the crack face separation (gape), which can only be measured by sectioning.
The results demonstrate the capability of radiography to detect a wide range of manufacturing defects of a size which might be of structural concern, even when they are substantially misoriented to the beam. Once sectioning has been completed (currently underway), the results will provide quantitative evidence of the combinations of defect size, tightness and orientation which can be detected.
The practical assessments of radiographic capability have been performed by TWI. Funding for this has been provided by the Industry Management Committee (IMC) which is supported by the nuclear licensees in Britain.
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