Deterioration of underwater steel structures due to corrosion is of serious concern because it reduces thickness in structural components, which can degrade structural strength. Inspection programs are necessary to determine the remaining thickness so that action can be taken to repair the damage if required.

An ultrasonic technique using a focused transducer has been developed to find the thickness of steel plates or structures corroded from both sides and having pit sizes as large as 15 mm in diameter and 4 mm deep. The technique was implemented into a system that acquires and processes ultrasonic waveforms reflected from the corroded area and determines the thickness. The system was tested and successfully operated in a harbor environment.