A Novel Pipeline Leak Detection Technique Based on Acoustic Emission Features and Two-Sample Kolmogorov–Smirnov Test

Pipeline leakage remains a challenge in various industries. Acoustic emission (AE) technology has recently shown great potential for leak diagnosis. Many AE features, such as root mean square (RMS), peak value, standard deviation, mean value, and entropy, have been suggested to detect leaks. However, background noise in AE signals makes these features ineffective. The present paper proposes a pipeline leak detection technique based on acoustic emission event (AEE) features and a Kolmogorov–Smirnov (KS) test. The AEE features, namely, peak amplitude, energy, rise-time, decay time, and counts, are inherent properties of AE signals and therefore more suitable for recognizing leak attributes. Surprisingly, the AEE features have received negligible attention. According to the proposed technique, the AEE features are first extracted from the AE signals. For this purpose, a sliding window was used with an adaptive threshold so that the properties of both burst- and continuous-type emissions can be retained. The AEE features form distribution that change its shape when the pipeline condition changes from normal to leakage. The AEE feature distributions for leak and healthy conditions were discriminated using the two-sample KS test, and a pipeline leak indicator (PLI) was obtained. The experimental results demonstrate that the developed PLI accurately distinguishes the leak and no-leak conditions without any prior leak information and it performs better than the traditional features such as mean, variance, RMS, and kurtosis.

Experimental Study on Mechanical Damage and Fracture Characteristics of Granite under Different Water Cooling Conditions

In order to investigate the mechanical property deterioration and fracture characteristics of granite under different temperature drop and thermal cycle conditions, the evolution laws of mechanical properties, acoustic emission event distribution, and macro and micro failure characteristics of granite under different temperature changes were studied and analyzed by the servo loading, acoustic emission monitoring, and scanning electron microscope systems. The following conclusions were gained from the test results. (1) The peak stress and elasticity modulus of the three temperature drop treatments all decreased with the increase of the number of thermal cycles. In terms of magnitude, the following relationship was satisfied: 10°C > 15°C > 20°C. After 8 cycles, the peak stress and elasticity modulus tended to be stable for 15°C and 20°C temperature drops. (2) At a temperature drop of 20°C, the heterogeneity first increased and then tended to be stable; when the temperature was dropped by 15°C at each cycle, however, the heterogeneity first decreased and then became stable; as for the case of 10°C, the heterogeneity showed an overall decreasing trend. After 4 cycles, the heterogeneities were ranked as 15°C > 20°C > 10°C. After 8 cycles, 20°C > 15°C > 10°C. (3) With the decrease of temperature drop amplitude or the increase of cycles, the connectivity of microcracks in granite improved on the whole, the aperture and shape factor of microcracks increased, the damage of granite intensified, and the duration of the quiet period in the acoustic emission ringing count rate prolonged. (4) The tensile failure dominated at a temperature drop amplitude of 10°C. When the temperature drop was 15°C, the failure mode transitioned from hybrid tension-shear failure to tensile failure as the cycle times increased, whereas the hybrid tension-shear failure dominated with a temperature drop of 20°C.

Laser-based structural training algorithm for acoustic emission localization and damage accumulation visualization in a bolt joint structure

Acoustic emission caused by structural damage encompasses important information about structural integrity. In particular, acoustic emission can detect phenomena that are difficult to determine, such as microcracks and internal cracks. However, conventional acoustic emission has shown limitations in complex structure applications for years. In this article, we propose a Q-switched laser scan–based structural training technique to achieve accurate acoustic emission localization and visualize accumulated damage in complex structures with a single PZT sensor (acoustic emission sensor). The proposed method compensates for the difference in characteristics between the actual acoustic emission wave and the laser-induced elastic wave using laser-based structural training algorithm. Acoustic emission localization in complex structures is accomplished by cross-correlation in the time domain. Pencil-lead break method is used as the source for acoustic emission to simulate the real damage-induced acoustic emission event. The proposed laser-based structural training algorithm with a laser scanning interval of 2 mm achieved an average localization error of 1.84 mm in two Al-alloy layers with fastener structure. Finally, the accumulated damages were visualized by appending the damage index of the acoustic emission waves at accurately localized points.

SIMULATION OF ACOUSTIC EMISSIONS FOR REAL CORE SAMPLES

The paper presents the results of laboratory experiments and numerical modeling for solving the problem of acoustic emission event recovery. The equations of the dynamic theory of elasticity in the polar coordinate system were used as a mathematical model. The simulation results made it possible to evaluate a number of basic characteristics for the configuration of a multichannel data acquisition system, the frequency of the AE signals, to determine the required number of recording channels and the position of the sensors in the core., The 3D modeling is planned in the near future in order to develop a mathematical method for reconstructing the AE events from the records of a real physical experiment.

Comparative experimental studies of acoustic emission characteristics of sandstone and mudstone under the impacts of cyclic loading and unloading

In this article, the acoustic emission tests of uniaxial cyclic load imposed on or released from the sandstone and mudstone were carried out. The deformation and failure characteristics and the law governing the acoustic emission activity were studied. The results of the study show that (1) the variation of acoustic emission events of sandstone and mudstone is law governed and is in agreement with the tendency of stress and strain curve development. (2) The acoustic emission activity of mudstone is most active before peak stress, while sandstone is at peak stress. For the sandstone, when the number of acoustic emission events is the most active, the corresponding acoustic emission energy is not the largest. However, the peak value of acoustic emission events and the peak energy of the mudstone coincide, and the acoustic emission events get to the most intense due to the peak energy. (3) The acoustic emission activity is more severe when a load is imposed on or released from the rock. Compared to loading, the rock damage caused by unloading is even greater. (4) The acoustic emission event at the splitting point is more concentrated. The line of acoustic emission point is basically consistent with the shape of the split.

Localization of multiple acoustic emission events occurring closely in time in thin-walled pipes using sparse reconstruction

A sparse reconstruction approach capable of localizing multiple acoustic emission events is proposed. The approach is specifically designed for localizing events that occur closely in time, where triangulation methods can fail. To perform localization, the approach uses information contained in the entire length of acoustic emission signals and is implemented using the matching pursuit algorithm. Implementation is considered theoretically for large-diameter thin-walled pipes. The approach is validated on experimental data of simulated acoustic emission events in a thin-walled pipe. The experimental data correspond to helical guided ultrasonic waves generated by standard pencil lead breaks (Hsu-Nielsen sources) on its outer surface. The acoustic emission signals are recorded by sparsely distributed low-profile piezoelectric transducers instrumented on the outer surface. Experimental examples are presented for the failure of the triangulation method when multiple sources are present while highlighting the capabilities of the proposed technique. It is demonstrated that the approach possesses the ability of localizing multiple events occurring closely in time. An example is also presented for the localization of a more commonly encountered isolated acoustic emission event.