Porosity, microcracks, or secondary phase inclusions alter the sound velocities of materials, Ultrasonic scattering at grain and phase boundaries in polycrystalline, multi-phase, or porous media causes attenuation of sound waves and dispersive sound velocities. These effects and also the amplitudes of the scattered waves can be exploited for materials characterization if their dependence on the structure properties is known quantitatively. In this paper the usefulness of sound velocity, attenuation, and backscattering measurements to detect and value damage in steel e.g caused by hydrogen attack is discussed. Numerical evaluations of theoretical results and experimental investigations are presented. It turns out that in most cases velocity measurements do not yield sufficient quantitative information about damage because the variations in sound velocity caused by slight differences of the undamaged material are often larger than those caused by damage. Sound attenuation and back scattering amplitude measurements are more appropriate to estimate damage in steel.