NDT played a major role in the repair programme. It had to be shown to be of a very high standard because of the absence of a proof pressure test after the repair. As a result, several inspections were qualified following the ENIQ methodology. To further increase confidence in the inspection of the repaired welds, both manual and automated ultrasonic inspections were carried out.

The UK Nuclear Installations Inspectorate was concerned about the possibility of stress relief cracking during the heat treatment. Consequently, it was necessary to show with a high degree of confidence that there had been no change or defect growth during the heat treatment. The fingerprint inspection before heat treatment had to be carried out at high temperature, ~150-170C. This inspection monitoring for change, which used both pulse-echo and time-of-flight diffraction, was also qualified following ENIQ.

This paper addresses the scope of the inspections, the development programme with the challenges that had to be overcome, such as automated inspection and high repeatability at elevated temperatures. It discusses the capabilities of the ultrasonic inspections including, for defect sizing, comparison of the depths of the excavations to remove the defects with the depths reported by the original inspections. Finally, the implementation of the inspections on site is discussed.