Abstract This paper reviews Interatom experience on ultrasonic testing of thin-walled austenitic butt welds, especially on pipes. The common method of ultrasonic testing of ferritic welds using zigzag shear waves is not successful in the case of austenitic welds due to such phenomena as attenuation and beam skewing. A method is presented which enables the detection of longitudinal defects in thin-walled (10–20 mm thick) austenitic welds and which, beyond that, is not influenced by the shape of the weld. The method is based on the existence of mode conversion between shear and longitudinal waves. This effect can be used while exciting longitudinal waves at large angles of incidence for defect detection in the near-surface region and in the volume. These longitudinal waves are accompanied by a shear wave which will be mode converted at the back wall in a longitudinal wave. That longitudinal wave can be used for defect detection and defect analysis in the root area. The paper deals with the method, laboratory work and subsequent experience with mechanized ultrasonic testing of butt-welded pipes and butt-welded sheets.