Abstract: An array of ultrasonic transducer (A) are disposed along a circular arc for examining tubular objects moving therethrough. A calibrating apparatus (B) includes a calibrating cylinder (22) having a plurality of calibrating flaws (24, 26) therein. A rotary positioning device (30) and an axial positioning device (40) adjust the relative spatial relationship of each calibration flaw and transducer. An ultrasonic control instrument (50) produces an echo signal having components corresponding to echoes received from the examined object. A computer (60) includes a gate adjustment control subroutine (66) which selectively separates a preselected component from the echo signal. A pulse amplitude measurement subroutine (64) measures the amplitude of the preselected echo signal component and, first, determines the peak amplitude of the component and, second, compares the amplitude of the component with a preselected standard.

Abstract: A percussion drill having a rounded and tapered contact surface conformation between the inner ends of hardened insert members closely received by cavities in a drill bit. Each insert has a radiused inner end in contacting relation with the bottom wall of its associated cavity. The radius is such that it compensates for angular deviations in the cavity bottom wall due to manufacturing tolerances from a normal relation relative to the cavity longitudinal axis. The radius of the insert inner end is calculated on the basis of a mathematical formula. The arrangement provides a structure which prevents corner load and stress, and insures contact away from the corner to thereby increase bit life.