Abstract: Apparatus and method for nondestructive evaluation of butt welds. The present invention in its broadest form includes an apparatus and method for detecting flaws in butt welds in steel sheets using horizontal shear ultrasonic waves generated on the surface thereof. Observation of reflected waves having amplitude greater than a chosen value signals the presence of significant flaw. To achieve this objective, the present apparatus detects only reflected horizontal shear waves; other modes are electronically removed using bandpass filters, since they occur at different frequencies. The invention may therefore be used in the presence of surface structures such as clamps and the like, and in the presence of surface nonuniformities in the vicinity of the weld, thereby permitting on-line flaw detection steel mill environment without interfering with the line output.