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Abstract As a crucial component of urban lifeline projects, shallow-buried gas pipelines pose a significant threat to society and people's lives, as well as property in the event of a leakage accident. To investigate the diffusion mechanism of gas leakage out of pipelines, the CFD method is employed to establish a validated numerical model for gas diffusion in backfilled soil. The effects of operating pressure, burial depth, leakage direction of pipelines, and soil resistance coefficient were discussed. The calculated results indicate that the numerical model can accurately predicte the diffusion process and the resistance coefficient of methane in soil-sand, loam, and clay-based. It was found that the burial depth affects the speed of gas diffusion to the soil surface but has little impacts on the concentration distribution range. The diffusion process in the same type of backfilled soil was found very similar under varying pipeline operating pressures, though the pipeline pressure significantly impacts the diffusion range. The shape of the leaked gas cloud in the soil is affected by soil resistance, leak direction, and air buoyancy. A new diffusion model for methane leaking in soil was proposed by introducing two time-related concentration adjustment parameters to the existing natural gas diffusion model. The average error between the calculated results of the proposed diffusion model and the established numerical model was found to be within 10%.

In the domain of gas pipeline operations, significant safety hazards prevail. This study delves into the triggering mechanisms behind gas pipeline leakage incidents, pinpoints key risk factors contributing to these occurrences, and proposes effective control measures. By classifying risk coupling forms associated with various accidents, the N-K model formula is utilized to assess the coupling degree of primary risk factors. The resultant coupling relationship is integrated into the University of California at Irvine NETwork (UCINET), forming a complex network model for quantitative analysis. Secondary risk factors' coupling degrees are measured, and the network's characteristic parameters are scrutinized. Noteworthy risk factors within the network include improper maintenance (A3), unclear or missing signage (C4), equipment aging and wear (B10), unauthorized occupation of ground space (C5), failure to implement rules and regulations (D3), and failure of electrical protection (B5). By controlling the above risk factors, disrupting the coupling process of risk factors, and blocking the transmission pathways of risk factors, the objective is to prevent leakage incidents and ensure the safe operation of gas pipelines.

The characteristics of acoustic source of gas pipeline leakage determine the accuracy and adaptability of leak detection for gas pipelines based on acoustic method. In order to explore the characteristics of leakage acoustic source of gas pipeline, a physical model of gas pipeline leakage was developed. Initially, generation mechanism of acoustic source of gas pipeline leakage is studied in order to identify the basic principle of leak detection of gas pipeline based on acoustic method. After that, the simulation model is developed according to the basic principle of aeroacoustics, the flow field, and sound source characteristics of the gas pipeline leakage. Then, the experimental platform for the study on acoustic source characteristics of gas pipeline leakage is set up using the basic principle of the leak detection based on acoustic method and simulation results. The characteristics of acoustic source of leakage are obtained through experiments. Finally, the simulation and experimental results of acoustic source of leakage under different operating conditions are compared, and the accuracy of the simulation results is verified, which provides a theoretical basis for the engineering application of leak detection for gas pipeline based on acoustic method. The results show that the acoustic source of gas pipeline leakage is mainly quadrupole source and the leakage acoustic energy is mainly in the range of less than 100 Hz. The mean value of sound pressure level is increased with the pressure in pipeline and the size of leak aperture. [ABSTRACT FROM AUTHOR]

To design a distributed fiber optic vibration sensor for urban natural gas pipeline leak detection, the light polarization fading transmission model based on Jones matrix is built in this mixed Sagnac/Mach-Zehnder interferometer configuration. The interference light intensity of pipeline with leakage and without leakage cases is compared through spectrum analyzer. When fiber length ranges from 1.5 to 9.5 km, the light power intensity (central wavelength 1550 nm) reduces to −56 dB. In experiment, the leaky spectrum null frequencies are captured and the average relative error of leakage point location varies from 2.3 to 5.3%. When the sensing length is expanded to 9.5 km, the vibration sensor system sensitivity is 0.57 Hz/m. [ABSTRACT FROM AUTHOR]

Gas leakage from pipeline leads to significant environmental damages and industrial hazards, so small leakage detection for gas pipeline is essential to avoid these serious leakages. However, because of the high frequency component of leakage signal attenuates quickly, traditional detection method which inspects pressure or vibration signal has problem to get effective information from leakage signal. So, a novel detection method based on acoustic wave is proposed. This paper, firstly, researches on the phonation principle of pipeline leakage and the characteristic of sound source, and simulates the leakage acoustic field on the basis of aero acoustics. Secondly, using Wavelet Packet Transform method and Fuzzy Support Vector Machine pattern classification, the laboratory testing for identifying acoustic signal of gas pipeline leakage is presented. Finally, the field application demonstrates that the detection system could identify small gas leakage effectively and avoids false-alarms which caused by running conditions with a good prospect. [ABSTRACT FROM AUTHOR]

Abstract: The acoustic signal of gas pipeline leakage has advantage in short delay time and carries physical information of the leakage, so it can be used for the diagnosis and localization of the pipeline leakage. In the long distance pipeline, collecting vibration signal caused by sound field has important significance to research of acoustic leakage detection technology. In order to get sound signal, first, this paper researches on the phonation principle of the pipeline leakage and the characteristic of the sound source, and the sound field is established on the basis of aero acoustics. Second, the vibration of the pipeline wall is analyzed with the harmonic analysis technology of the ANSYS software when the leak wall bears broadband harmonic sound pressure. Finally, the field experiment demonstrates that this approach can improve detection ability of small leakage with low false alarm rate. [Copyright &y& Elsevier]