Recent in-house developments in theoretical modelling of ultrasonic inspection

Over the years British Energy, in collaboration with British Nuclear Group, has developed an extensive suite of computer codes for modelling the ultrasonic inspection of ferritic steel components. The models predict the echo amplitude, relative to a specified threshold level, as a probe scans over a component containing a hypothetical smooth or rough planar defect. The models are used to help in the design of new inspections, and to provide evidence on detection capability when writing a technical justification for inspection qualification purposes. Several papers give further information about the models, their experimental validation and some typical applications(1)-(4). This paper starts with a brief overview of the current status of the models. Two recent developments of the models are then described: the effects of fine-scale roughness on the scattering from rough defects, and the use of ‘wedge’ diffraction coefficients to model the inspection of surface-breaking cracks using the corner effect. Finally, an outline is given of a recent typical application of the models, to the technical justification of an automated ultrasonic in-service inspection of a pressuriser weld at Sizewell B Power Station. 2. Overview of current status of models