Aboveground Storage Tanks Leak Detection Through Acoustic Emission Sensor Nodes

In oil depots and fuel storage facilities, undetected storage tanks damages can lead to the leakage of the oil stored in the soil leading to pollution and economical losses. Leaks are generally due to the perforation of the storage tank floor due to corrosion. The detection of corrosion and leaks is a complicated task, especially for operative tanks with inaccessible floor for detailed inspections and is generally attempted by mean of acoustic emission systems operating from the outer skin of the tank. In this paper, we present a compact sensor node (SN) designed for long-term and real-time acoustic emission monitoring. The SN exploits up to three inexpensive low-frequency sensors based on piezoelectric diaphragms, and it is capable by means of built-in Digital Signal Processing functionalities to process the acquired time waveforms extracting the AE features usually required by testing protocols. An experimental validation on a floating-roof aboveground storage tank 17 m high and 18 m in diameter, filled with water to a level of about 6.2 m, is proposed. Leaks were induced by opening and closing a drainage valve existing at the bottom skirt of the storage tank while acoustic emission signals were recorded at three sensors and processed in real time. Designed nozzles of different diameter, from 1 mm to 9 mm, where used to simulate leakages of different entities. The results confirm the possibility of detecting and monitoring leaks of various diameters in the low-frequency region 1–2 kHz not traditionally considered by state-of-art acoustic-emission monitoring systems.