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Abstract:To understand the propagation characteristics of methane-air deflagration flames and in an obstacle-filled tube, a high-speed color video camera, photoelectric sensors, and pressure transducers were used to test the deflagration flame propagating parameters. The tests were run in a 1500 mm long plexiglass tube with a 100 × 100 mm square cross-section. The obstacles included four types of repeated baffles and five forms of solid structure obstacles. The results showed that: (1) the flame front was constantly distorted, stretched, and deformed by different types of obstacles and, consequently, the flame propagating parameters increased; (2) plates and triple prisms increased the speed of the flame and overpressure to the highest extent, whereas cuboids and quadrangulars exerted an intermediate effect. However, the effect of cylindrical obstacles was comparatively limited. It was suggested that the obstacle's surface edge mutation or curvature changes were the main factors stimulating the flame acceleration; (3) the peak pressure of deflagration was relatively low near the ignition end, increased gradually until it reached the maximum at the middle of the tube, and decreased rapidly near the open end; and (4) the fixed obstacles in front of the flame exhibited a blocking effect on flame propagation during the initial stages; the flame speed and overpressure increased when the flame came into contact with the obstacles. This study is of significance because it explains the methane-air propagation mechanism induced by different types of obstacles. The findings have value for preventing or controlling gas explosion disasters.

Shale gas gathering and transportation pipeline poses significant risk due to special geographical conditions and different climatic conditions in high consequence areas such as Sichuan and Chongqing. The risks become critical as gas pipelines run through high consequence areas such as hospital, market, and scenic areas. This study presents a risk classification method for the pipelines running through high consequence areas. The proposed method considers different failure scenarios including third-party damage, corrosion, design and construction defects, mis-operation, and natural disasters. The method uses subjective and objective data from different sources. To minimize the subjectivity and data uncertainty, an improved fuzzy analytic hierarchy process was used to process data. The estimated risk is used to classify different risk zones. After the failure of shale gas pipelines in HCAs, in order to reduce the adverse impact of emergencies, personnel should immediately organize an evacuation to a safe area, focusing on the diagnosis and analysis of risk factors that are more likely to lead to pipeline leakage. The developed classes are verified using field data. The study observes that risk levels classified using the proposed method provide realistic assessments of hazard zoning. Risk zoning will help develop effective risk management strategies.

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