Abstract: The invention provides a method and apparatus for assessing a condition of a fluid conduit from its interior. The method comprises providing a measurement apparatus comprising at least one wideband acoustic transducer within the fluid conduit and transmitting a wideband acoustic signal from the measurement apparatus to excite a broadside resonance in at least a portion of the fluid conduit. A wideband acoustic signal is received in the measurement apparatus due to a broadside resonant response of the fluid conduit to obtain a wideband acoustic data set; and the data set is analysed to assess the condition of the fluid conduit.