# A Basic Experimental Study on Analysis of Leak Signal and Monitoring Method for Water Supply Pipe
###### Abstract  
Water supply systems are essential elements for human life and industry, and water leaks and water supply cut-off may cause major problems. Local water leaks and pipe failures in the water supply system are inevitable problems due to the aging of pipes. Therefore, leakage detection and prevention are required to monitor the integrity of the water supply system. This paper is a fundamental study on the applicability of the smart bolt, which was developed as a monitoring system to detect water leakage in water supply monitoring. Detection experiments were conducted using a smart bolt with a built-in strain sensor and an accelerometer. Through finite element analysis using ANSYS 2019 R2 and tensile strength testing, the strength of the smart bolt was confirmed to have the acceptable tensile strength. The smart bolt used in this study was verified to meet the allowable criteria of torque and tensile stress for a municipal water supply system. The frequency responses of the simulated leakage pipe system, according to the leakage of the valve and the main pipe, were analyzed, and a leak signal at the valve leak point was detected in the 60-Hz band. The main pipe leaking point was observed to produce a leak signal with a much higher-order mode than that of the valve leak point. Therefore, the smart bolt can be applied to detect warning leak signs from water supply valves and to monitor for loosening of the bolts.  
leak detection; FFT analysis; water supply; monitoring; smart sensor +
Footnote †: journal: Applied Sciences  
but it is expensive and difficult to detect leak levels [5]. Conventional methods require experienced personnel who need to walk along a pipeline and look for unusual patterns near the pipeline based on odors or sounds due to a leak [5]. Hardware-based methods can detect leaks by visual observation or using appropriate measurement equipment [5]. Representatively, there are studies on vibration sensors, piezo sensors, bi-wire sensors, and ultrasonic sensors for a leak detection technique using vibration [9; 10; 11]. Most of these methods are low-cost and high-sensitivity leak detection, but it is difficult to find the leak point [5]. Acoustic emission sensors can estimate the leak point using the transmission rate of the leak sound [12]. However, the disadvantages of the acoustic method are the difficulty of placing acoustic sensors in the right location at the water pipeline and the difficulty in detecting quiet leaks, which generate no sound [12]. Due to this fact, researchers have shown a strong interest in the vibration technique for leakage detection [5; 12].  
Most of the previous studies have been on the detection of leaks in pipelines, but studies on leaks caused by the loosening bolts of valves are insufficient. Therefore, in this study, a smart bolt was developed as a monitoring system to continuously check the leak condition of the water supply valves. The smart bolt incorporates a strain sensor to detect loosening of the bolt by monitoring the tension of the bolt, and an acceleration sensor to check the leakage in the valve. Through fundamental experiments and analyses, we confirmed the applicability of the smart bolt for leak detection.