This document applies to testing of rails installed in track for detecting internal discontinuities. This part applies to testing equipment fitted to dedicated test vehicles or manually-propelled devices. This document does not define the requirements for vehicle acceptance. This part of the series does not apply to ultrasonic testing of rails in a production plant. The document specifies the requirements for testing principles and systems in order to produce comparable results with regard to location, type and size of discontinuities in rails. This document is not aiming to give any guidelines for managing the result of ultrasonic rail testing. This document applies only to rail profiles meeting the requirements of EN 13674 1.