Evaluation of Stress Corrosion Crack Initiation Using Acoustic Emission

Abstract

Acoustic emission response has been used to detect the development of short intergranular stress corrosion cracks in laboratory samples of sensitized type 304 (UNS(1) S30400) stainless steel (SS). Tests were conducted at 25°C in water containing either 15 ppm of Na2S2O3 or 100 ppm of NaCl. Cylindrical samples with piezoelectric detectors mounted on both ends and the corrosion cell confined to the gauge section were used. The dual detectors allowed discrimination between signals generated within the sample from those generated from the surroundings. It was found that intergranular stress corrosion cracks of 200 to 300 μm length by 100 to 200 μm depth could be reliably detected with this technique. Shallow 10-μm-deep longitudinal flaws were also detected in tests conducted in the 100 ppm NaCl environment.