Ultrasonic detection of stress corrosion cracks in pipe samples in gaseous atmosphere

Stress corrosion cracking (SCC) is a serious threat to gas pipelines. Current in-line inspection tools have issues with the detection and sizing of small cracks. Advances in gas-coupled broadband ultrasound enable new detection methods based on Guided Ultrasonic Waves (GUW). Recently, the potential to detect SCC using Halfwave’s ART Scan® tool was successfully demonstrated on real pipe samples with SCC, submerged in water [1]. In this study, the ultrasonic detection of SCC is experimentally demonstrated, using pressurized gas at 60 bar as acoustic coupling medium. A custom-made test scanner with 32 transmit/receive channels was developed to perform circumferential scans of 425 mm × 60° from the inside of pipe samples of diameters close to 36 inches. The gaseous atmosphere of 60 bar (nitrogen) required the experiments to be conducted inside a pressure tank that contained both the test scanner and pipe samples. Broad-band pulses were transmitted, and signals were received from all scan positions. Processed parameters like spectral power and wall thickness estimates were calculated. 2D plots of processed parameters and reconstructed image results demonstrated the detection and sizing potential for real cracks, crack fields, and other surface irregularities.