Introduction of a certification procedure for the acoustic response of reference reflectors for ultrasonic testing

This article describes a certification procedure which includes both the qualitative and quantitative characterisation of the acoustic response of reference reflectors. It is dedicated to one-dimensional reference defects such as notches or side drilled holes but can be generalized also to two-dimensional reflectors such as flat bottom holes. At the beginning relevant measured quantities are introduced. This includes the defect homogeneity and the effective defect length which are extracted from the acoustic reflection profile. Afterwards, a setup for the performance of certification measurements is shown and the overall procedure is described. All results are summarized in a standardized protocol. At the end, the reference certification in the daily use is discussed. Due to the large database a statistic evaluation can be presented. It shows that a significant percentage of references do not fulfil the given quality criteria. The importance of a quality monitoring at different time periods is illustrated with an example of a reference notch where measurements before and after commissioning revealed a significant quality degradation. Finally, the presented method can serve as basis for updates of common standards with respect to a more complete specification of reference reflectors which will be needed due to the increasing demands on the accuracy of ultrasonic testing systems.