Abstract: An ultrasonic system is provided for measuring the thickness of steel plates used in the bottom of oil storage tanks and other similar applications. When the bottom plate corrodes, the potential for leakage occurs. The ultrasonic system can be used to monitor the corrosion of bottom plates in areas which are generally inaccessible, such as the bottom of oil storage tanks. The ultrasonic system includes a probe drive frame having multiple brackets for supporting a plurality of ultrasonic probes. A pulse generator and multi-channel scanner are connected to the probes. A processing unit reads and processes the signals from the probes to calculate the thickness of the plate and to warn of potential leakage problems caused by corrosion of the plate. The system can be operated from a remote location outside the oil storage tanks, which minimizes the time and expense in monitoring the plate.