PISC II parametric study on flaw characterisation using the tandem and TOFD techniques

Abstract Studies on the effect of flaw characteristics and selected inspection parameters on the detection and sizing of flaws in ferritic steel blocks have been performed by the United Kingdom Atomic Energy Authority (UKAEA) as part of a larger Commission of the European Communities (CEC) Parametric Study programme. The techniques included in the UKAEA studies were the 45° tandem and the time-of-flight diffraction (TOFD) techniques. The purpose of the work was to acquire reliable experimental data that could be used both to test and verify theoretical models and to contribute to the resolution of anomalies encountered in PISC round-robin inspection exercises. Thirteen test blocks, fabricated by JRC, Ispra, were selected for the UKAEA studies with flaws covering a range of shapes, sizes, roughnesses and orientations. Beam-skew has a pronounced effect on signal amplitude for the tandem technique, with tilt angle having a significant but smaller effect. The signals from ‘rough flaws’ exceed those from smooth defects for skew angles of 5° to 10°. The TOFD technique proved less sensitive to skew and sized flaws to better than 2 mm. However, limitations in its range of application demonstrate the need for diversity in techniques for flaw sizing.