Abstract: For the testing of notably deep-drawn tubes during manufacture it is important that the thickness of the tube can be checked. When the tubes are heated during manufacture, this measurement cannot be performed by means of a device where the X-ray source and the filter are to be arranged inside the tube. In accordance with the invention, the radiation source is arranged outside the tube and this tube is tangentially irradiated. The maximum values and minimum values of the radiation relief thus generated in a relationship perpendicularly to the tube axis indicate the position of the outer wall and the inner wall of the tube. The wall thickness of the tube can be derived therefrom.