Ultrasonic testing of circular bars using longitudinal and shear waves has been regularly done on special steels, titanium alloy and zirconium alloy in Nuclear Fuel Complex. The flaw standards have been flat-bottomed holes of side drilled holes for normal beam testing and notches for angle beam testing. Immersion scanning using focussed transducer are used for the range of sizes done, normally less than 50 mm. In the testing, DAC curve is made for the flat bottom holes drilled to different depths and indication height is compared. Instead of DAC curve, it is found that depending on material, the right frequency and position of the probe could be chosen so that the material attenuation is compensated properly by change in energy density, which can be achieved by suitable focussing. This method of focussing coupled with right frequency avoids stopping of the rod for evaluation of an indication during the test. Though for tubes, V, buttress and U notches are common for bar testing it is found that V-notches are not adequate for detecting longitudinal cracks. Only rectangular notches will provide the assurance that cracks can be detected, with adequate assurance.
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