2018 年 18 巻 1 号 p. 31-36
Many underground storage tanks are used for decades after they are installed. Therefore, rust occurs on the walls of these tanks as a result of local corrosion. Leaks from the tanks occur as the corrosion progresses. Such tanks are monitored and checked through pressure tests or observation tests. However, the corrosion cannot be detected in the absence of tank leakage. The acoustic emission (AE) method is employed to monitor the corrosion by detecting fractures in the rust. In this study, we used the finite-difference time-domain method in a simulation to determine the ideal sensor shape for an underground storage tank. First, a method was determined for placing the AE sensor in a rectangular solid case to effectively detect the AE using a model with a fluid solid boundary, assuming an underground storage tank. The simulation results indicated that the amplitude of the wave propagating in the upper and lower portions of the tank was large. AE signals from the bottom of the tank were effectively detected by the sensor mounted on the bottom of the sensor box. AE signals from the side wall were effectively detected on the upper part of the side wall of the sensor box. Next, immersion type AE sensor was constructed by using the result of simulation and sensitivity was studied. Amplitude distribution of developed system from different artificial AE source was corresponding to the simulation result. Sensitivity of the developed sensor was compared to the immersion sensor with single optical fiber sensor. Developed system had higher sensitivity than the single optical fiber sensor system.
