Automated inspection of corroded steel structures

Deterioration caused by corrosion of steel can result in catastrophic failures of waterfront facilities and other offshore structures [1]. Inspection of corroded steel structures is currently limited to visual examination. However, this is not a reliable nondestructive method for thickness measurement as it is limited to assessing surface damage. A novel ultrasonic concept has been developed and integrated into an automated scanning system. This concept uses a focused ultrasonic transducer centered over a corroded pit so that the pit acts as an acoustic lens. Special transducer modification and pattern analysis techniques have been developed to overcome the effects of spurious signals. Scanning of the corroded area, alignment of the focused transducer over the pits, and acquisition and processing of the signals to determine the thickness of corroded steel are performed by the computer-controlled system. An average thickness measurement error of only four percent was achieved using this system.