TOFD inspection employs two longitudinal wave (L- wave) angle beam transducers arranged symmetrically opposite facing each other, straddling the weld or base material under test. One probe acts like a transmitter of ultrasonic energy while the other probe receives the ultrasound energy. Time of Flight Diffraction is now routinely used in a wide range of applications such as inspection of piping and pressure vessels. Defects are detected by the diffracted ultrasound wave occurring at the edges of defects.