Analyzing the Phase of DFA Image for Determining the Type of Detected Reflector

Abstract

Methods have been developed in ultrasonic flaw detection for recording and analyzing echo signals with the aim to determine the type of a reflector and its dimensions. The TOFD method allows one to distinguish between a crack and a volume reflector based on the phase of echo signals and highly accurately determine the crack height. However, it can be difficult to isolate a useful signal if it is against a noisy background. In addition, in the TOFD, it is impossible to determine reflector’s offset from the center of a welded joint without scanning across the weld. The method of digital focusing with an antenna (DFA) allows producing high-quality images over the entire volume of the welded joint, but only the amplitude of the DFA image is commonly analyzed without taking its phase into account. In this paper, we utilize the strengths of these two methods in analyzing the image of reflectors; this makes it possible to more accurately determine reflector type and coordinates in the presence of noise. Numerical and model experiments have confirmed the efficiency of the approach proposed.