ULTRASONIC INSPECTION AND ANALYSIS USING THE SYNTHETIC APERTURE FOCUSING TECHNIQUE (SAFT) ON DISSIMILAR METAL WELDS WITH INTER-GRANULAR STRESS CORROSION CRACKS

摘要

Cases of inter-granular stress corrosion cracking (IGSCC) in dissimilar metal welds have led to an increased interest in the reliability of non-destructive testing of these welds and this crack type. The challenges related to ultrasonic testing of dissimilar metal welds (DMW) result from the elastic anisotropy of the material in combination with the grain structure of the weld. The inhomogeneous, anisotropic structure of the weld affects ultrasound propagation and leads to a decrease in the signal-to-noise ratio, thus complicating the interpretation of ultrasonic signals. As a result, cracks located exclusively in the weld material are usually harder to detect. Detection of cracks inside the weld material is particularly important in the case of a circumferential crack in a pipe weld, which could otherwise grow to a critical size before being detected. Studies have shown that the reflected ultrasonic amplitude is considerably smaller for IGSCC than it is for artificial reference flaws. In this paper, we will present the results of ultrasonic inspection and analysis using the Synthetic Aperture Focusing Technique (SAFT) on dissimilar metal welds with IGSCC.