Development of check valve inspection system

We have developed Check Valve Inspection System using acoustic emission sensor and ultrasonic sensor, for the purpose of detecting degradation and detailed operating state (Full open, Tapping, Oscillation, etc.) of the swing check valve. The operating state of the swing check valve is identified as follow. First, the rough location of swing arm or disk is examined by obtaining the reflected echo from valve disk. Second, the detail motion of swing arm or disk, whether the valve disk is oscillating or is stable, is determined by analyzing the observation time of the reflected echo. Finally, it is investigated using acoustic emission sensor to see if the disk or the arm is tapping against the backstop repeatedly. Degradation in the valve is evaluated by detecting acoustic pulses collected by acoustic emission sensor. If such deterioration progresses in the driving parts, the number of acoustic pulses by collision increases. The rate of deterioration of the swing check valve is determined from the change in the number of acoustic pulses. As an example of the application of the system, the case of check valves in the seawater system line installed in a nuclear power plant were shown. The examination was carried out before and after replacing the check valve. By comparing the results of the inspection system and the results of overhaul, the detectability of the inspection system was evaluated. (author)