Similar nozzle welds exist on the recirculation pipe, which have different diameters and these nozzles also need to be inspected. Instead of repeating practical qualification trials for each of the nozzle diameters, the intention was to extend the inspection and the qualification status from the 295mm-diameter case to others using a technical justification approach.

The performance of the pulse-echo ultrasonic inspections on the original 295mm-diameter J-weld and on the smaller 183mm and 138mm-diameter J-welds was evaluated using AEA Technology MUSE geometric modelling software.

This modelling tool gives the coverage of the inspection volume achieved and also enables the mis-orientation between postulated defects and ultrasonic beams to be evaluated at each postulated defect position. The beams used in the qualified inspection and also some additional ones are applied to the three weld geometries. The comparative performance of the inspection on the different sizes was then assessed.

The ultrasonic beams used in the qualified pulse-echo inspection of the 295mm weld have been demonstrated to give a performance on the 183mm weld, which is equivalent to or better than that on the 295mm weld. The performance on the 138mm weld is however poorer than that on the 295mm weld.

Analysis of the TOFD inspections of all three welds using the AEATechnology CGTOFD program shows that the reduced nozzle wall thickness of the 183mm and 138mm welds improves the separation of the time-of-flight of potentially interfering geometric signals from different modes.

It was concluded that the inspection that had passed qualification trials could be applied to the 183mm weld but not the 138mm weld with minimal change to the procedures. New procedures for the inspection of the 183mm weld and a technical justification document, based in large part on the modelling results, were submitted to Qualifying Authority. The technical justification and new procedures for extension of the inspection to the 183mm weld were duly accepted.