Location of pinholes in a pipeline

• Published in: Computers & chemical engineering 1993, Vol.17 (1), p.61-70
• Main Authors: Watanabe, K., Koyama, H., Tanoguchi, H., Ohma, T., Himmelblau, D.M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical engineering; Exact sciences and technology; Handling and storage of chemicals. Piping
• ISSN: 0098-1354; 1873-4375
• DOI: 10.1016/0098-1354(93)80005-8

This paper describes a new acoustic method to detect and locate very small leaks, i.e. pinholes in a closed gas pipe or a closed empty liquid pipe. A decrease or increase in the pressure of the gas in the closed pipe leads to gas blowing in or out of the pinhole, if it exists, and the gas flowing through the pinhole generates acoustic noise with a broadband spectrum. The acoustic noise induces standing waves in the pipe just as in a flute. The length of the closed pipe and the pinhole site determine the modes and frequencies of the standing waves. We built a mathematical model that describes the above acoustic phenomena, and present here a method to locate a pinhole in a pipe by using the model. The method requires only one microphone set at a terminal in the closed pipeline. The autocorrelation of the acoustic noise picked up by the microphone shows pulses if leaks exist, and the pulse occurrence times can be used to uniquely calculate the length of the closed pipe and the leak site. Laboratory experiments we carried out have validated the proposed pinhole location method. The method located a circular pinhole of 0.3 mm in diameter at various sites, a crack, a loosened joint, and two pinholes in the pipe which had a length of 10.24 m and a diameter of 53.4 mm. The calculated results proved to be unique, clear-cut and accurate.