Determining the Coordinates of Reflectors in a Plane Perpendicular to Welded Joint Using Echo Signals Measured by Transducers in the TOFD Scheme

Abstract

The TOFD method, widely used in ultrasonic flaw detection, makes it possible to distinguish a crack from a volume reflector by the phase of echo signals and to determine its height with high accuracy. However, the TOFD method without piezoelectric transducers scanning across the welded joint does not allow determining the offset of the reflector from the weld center, which is very important when evaluating the test results. The scanning devices used for this have a complex design, their price is higher than that of one-dimensional scanning devices, and, most importantly, the testing time increases considerably. If we use echo signals reflected from the bottom of the test object, taking into account the change in the wave type, then the combined reflector image can be obtained from the set of partial images reconstructed by the digital antenna focusing (DFA) method. Using the echo signals measured in the combined mode for each piezoelectric transducer, then it is possible to estimate the displacement of the reflector across the welded joint with an accuracy of $\pm 1.5$ mm. Numerical and model experiments have confirmed the efficiency of the proposed approach.