Ultrasonic detection of stress corrosion cracks in gaseous atmosphere using Broadband transducers

Most gas pipelines are buried and exposed to a potential corrosive soil where stress corrosion cracking (SCC) may occur. To mitigate the effect of SCC, pipeline operators perform numerous crack detection inspections of onshore pipelines. Current in-line inspection tools, however, have issues with the detection and sizing of small cracks. Recent advances in gas-coupled broadband ultrasound enable new detection methods based on guided Lamb waves. 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 work, the ultrasonic detection of SCC is experimentally demonstrated, using pressurized gas at 60 bars as acoustic coupling medium. A custom-made test scanner with 32 transmit/receive channels was developed to mechanically scan pipe samples inside a pressure tank. Broadband chirp pulses were transmitted, and signals were received from all scan positions. 2D plots of processed parameters, including spectral power and wall thickness estimates, demonstrated the detection and sizing potential for real cracks, crack fields, and other surface irregularities in pressurized gas using the ART Scan® based test set-up. The results from some receive channels even suggested potential for detecting suspicious regions near seam and girth welds.