Crack detection and localization in a fluid pipeline based on acoustic emission signals

Abstract

This paper introduces a novel approach to crack detection and localization in a pipeline transporting fluid under high pressure. From acoustic emission signals acquired by two R15i-AST sensors at two ends of a fluid pipeline, the proposed method scans peaks in the individual signal channels in the time-frequency domain and filters out noise to obtain acoustic emission events. Subsequently, adjacent events are combined into grouped events, and these are picked and paired together on two sensor channels to localize emis?sion sources using the time difference of arrival technique. To improve the location accu?racy, the mechanism only determines the arrival time of Rayleigh waves with a similar frequency in event pairs. Furthermore, the Rayleigh wave velocity is calibrated by a pencil lead breaking procedure. Additionally, false emission sources are eliminated by considering the wave energy attenuation characteristics in their propagation path. After locating the emission sources, the approach observes their distribution according to the position and time of occurrence. The variation in acoustic emission activity against applied load, which is established by counting the returned sources, can indicate irregular structural changes in a material. The location of the structural change can be surmised by the emission source distribution and density according to the position along the pipeline. Experimental results show that the proposed method correctly diagnoses faults in the considered pipeline from acoustic emission signals, whereas a conventional approach (performed by detecting hits with a threshold) inaccurately localizes acoustic emission sources and imprecisely exposes signs of abnormal structural transformations.