On-going work helps verify reliability of radiography

The Magnox pressure vessels were originally built in the late 1950s

Magnox electric plc, in collaboration with Nuclear Electric Ltd, has been investigating the reliability of radiography performed on Magnox reactor pressure vessel (RPV) welds at the time of their construction in the late 1950s and 1960s.

In order to extend the scope of these investigations, TWI's Structural Integrity Department was asked to carry out practical assessments of radiographic capability funded by the Industry Management Committee (IMC).

It is well known that radiography can detect volumetric flaws but it was unclear how reliable this method was for detecting planar flaws. TWI has a large database of ultrasonic and radiographic inspection data for flaws examined over many years. This database was used to provide experimental data on the effectiveness of radiography in detecting planar flaws in steel welds 50-114mm thick; covering the range of thicknesses of Magnox RPVs.

To learn more about the flaws considered, sectioning was used to reveal their true type, size and morphology. Following this, new specimens were produced containing much larger flaws (>15mm through-wall size) to establish if these could be detected radiographically for a variety of experimental conditions. Results show that radiography is able to detect a wide range of planar defects of a size that may be of structural concern, even when they are substantially misoriented to the radiation beam. Currently the project is examining the human aspect of radiographic interpretation.

For further information call Ian Munns. E-mail: ian.munns@twi.co.uk