Abstract: Apparatus and method for acoustically inspecting hot flat plates while on-line by utilizing an array or arrays of transducers continually spaced a set distance from the bottom of the plates by serrated rollers spring mounted with the array of transducers in a container with overflowing liquid wetting the passing plate to acoustically couple the transducers to the plate and a spray of sufficient force to temporarily cool the hot plate and dispel steam and vapor formed, the spray being in a direction opposite the direction of travel of the hot plate; and support of the unit on a track mounted carriage, with the liquid reused through a reservoir connected system. It is critical that the spray be at an angle of 27.degree. or less to the horizontal and that the spray have sufficient force to have an apparent liquid velocity of at least 44 feet per second, adding the speed of the water and the hot plate together.