Detection of Gas Pipeline Leakage Using Distributed Optical Fiber Sensors: Multi-Physics Analysis of Leakage-Fiber Coupling Mechanism in Soil Environment.

Optical fiber sensors are newly established gas pipeline leakage monitoring technologies with advantages, including high detection sensitivity to weak leaks and suitability for harsh environments. This work presents a systematic numerical study on the multi-physics propagation and coupling process of the leakage-included stress wave to the fiber under test (FUT) through the soil layer. The results indicate that the transmitted pressure amplitude (hence the axial stress acted on FUT) and the frequency response of the transient strain signal strongly depends on the types of soil. Furthermore, it is found that soil with a higher viscous resistance is more favorable to the propagation of spherical stress waves, allowing FUT to be installed at a longer distance from the pipeline, given the sensor detection limit. By setting the detection limit of the distributed acoustic sensor to 1 nε, the feasible range between FUT and the pipeline for clay, loamy soil and silty sand is numerically determined. The gas-leakage-included temperature variation by the Joule-Thomson effect is also analyzed. Results provide a quantitative criterion on the installation condition of distributed fiber sensors buried in soil for the great-demanding gas pipeline leakage monitoring applications.

Cause Analysis of the Large-Scale LPG Explosion Accident Based on Key Investigation Technology: A Case Study.

Blending dimethyl ether (DME) into liquefied petroleum gas (LPG) has become a common phenomenon. On December 3, 2019, an LPG/DME explosion occurred in Beijing, resulting in 4 deaths and 10 injuries. To deeply investigate the cause and explosion process of the explosion accident, the accident investigation method combining on-site inspection, material evidence analysis, experimental verification, and logical reasoning was used. In addition, the location of the ignition point, the explosive substances, the cause of the gas leakage, the process and the distribution characteristics of the gas leakage, and the ignition process were successively reasoned and analyzed in detail. The results show that the LPG/DME-blended gas can effectively corrode silicone flange gaskets, forming laminar fractures and radial cracks on the gasket. As a result, the tensile strength of the gasket decreased. Under the action of the gas pressure inside the pipeline, the gasket was torn and a leakage hole was formed. The leaked combustible gas formed at least 305 m3 of the explosive gas mixture inside and outside the refrigerated storage. The investigation and research results have important scientific guiding significance for revealing the cause and preventing similar accidents.

Experimental study and mechanism model on the ignition sensitivity of typical organic dust clouds in O2/N2, O2/Ar and O2/CO2 atmospheres.

To reveal and improve our understanding of the ignition behavior and mechanism, G-G furnace experiments of three typical organic dusts were performed to investigate the minimum ignition temperature (MIT) in O2/N2, O2/Ar and O2/CO2 atmospheres with oxygen mole fraction from 8.4% to 50%. The experimental results were presented in oxygen-lean and oxy-fuel atmospheres to evaluate the ignition sensitivity of dusts in different atmospheres. It was found that CO2 is the strongest in terms of lowing the ignition sensitivity of the three dusts, and the dust explosion risk increases significantly with increasing O2 mole fraction for the three dusts through a logarithmically and significantly reducing MIT. However, for different dusts, inert gases show different suppression effects. In addition, a modified steady-state homogeneous ignition model was proposed and successfully applied to oxygen-lean atmospheres, and in oxy-fuel atmospheres, this model has also been improved to estimate the ignition mechanism. This ignition mechanism model could be used to successfully predict the minimum ignition temperature of high volatile dust under different inert atmospheres controlled by homogeneous ignition, which will provide a reference for the ignition hazard assessment of dust on hot surfaces.

Theoretical and numerical study on ignition behaviour of coal dust layers on a hot surface with corrected kinetic parameters.

Industrial fires and explosions initiating from self-ignition of combustible porous dust deposits represent a serious hazard for human beings, environment and industry. Understanding the fundamental basis of combustible dust ignition behaviours at different geometries is of importance to prevent and mitigate the accidental risks. A correlation of self-ignition temperatures (SITs) measured by hot-oven tests and minimum ignition temperatures of dust layers (MITLs) determined by hot-plate tests has been established previously. However, this analogy approach based on Frank-Kamenetzkii model is limited by ignoring the influence of oxygen diffusion. In this work, an improved method is developed by implementing a correction factor for the pre-exponential factor caused by the boundary geometry. This method is testified by comparing with experimental data, previous analogy method and numerical simulation. Results show that our proposed method performs a better predictability of MITLs and simplicity. The improved analogy method indicates that the different boundary geometries of a dust deposit significantly impact the apparent pre-exponential factor, while have an ignorable influence on the activation energy, which is also verified by numerical investigations. Furthermore, the numerical model with the corrected kinetic parameters provides a satisfactory explanation compared with experimental observations regarding to temperature and concentration evolutions of dust layers.

Experimental study on optimization models for evaluation of fireball characteristics and thermal hazards induced by LNG vapor Cloud explosions based on colorimetric thermometry.

In order to facilitate transport, natural gas is cooled down by a cycle process of compression, condensation, expansion, and evaporation that transforms the gas into a liquid form, as known as Liquefied Natural Gas (LNG). However, once any leak happens in the transportation pipeline, it will result in serious thermal radiant damage due to the explosion fireball induced by LNG Vapor cloud explosions. In this work, an optimization fireball model is proposed by introducing the atmospheric transmission rate τ into the original TNO dynamic model. Based on the colorimetric thermometry technology, a full-scale LNG pipeline explosion experiment has been conducted and a series of testing data for the thermal radiant by VCEs' fireball have been obtained. It is found that theoretical predictions by using optimization model agree well with experimental data. According to the thermal radiant damage criterion, it is concluded that a near 100% fatality radius is expected within the range of 266.3 m and there is a safety area with an ellipse diameter of 1180.1 m. This work attempts to develop optimization fireball models to predict the thermal radiant damage more accurately, and improve the performance of risk assessment on LNG transport and storage industrial process.

Experimental study of thermal comfort on stab resistant body armor.

PURPOSE: This research aims to investigate the impacts of exercise intensity and sequence on human physiology parameters and subjective thermal sensation when wearing stab resistant body armor under daily working conditions in China [26 and 31 °C, 45-50 % relative humidity (RH)], and to investigate on the relationship between subjective judgments and objective parameters. METHODS: Eight male volunteers were recruited to complete 3 terms of exercises with different velocity set on treadmill for 90 min at 26 °C and 31 °C, 45-50 % RH. In Exercise 1 volunteers were seated during the test. In Exercise 2, volunteers walked with the velocity of 3 km/h in the first 45 min and 6 km/h in the left 45 min. In Exercise 3, volunteers walked with the velocity of 6 km/h in the first 45 min and 3 km/h in the left 45 min. The body core temperature, skin temperature and subjective judgments were recorded during the whole process. Analysis of variance was performed among all the tests. RESULTS: Individual discrepancy of Exercise 1 is larger than that of Exercise 2 and 3. On the premise of the same walking distance and environmental conditions, core temperature in Exercise 3 is about 0.2 °C lower than that in Exercise 2 in the end; and with the velocity decrease from 6 km/h to 3 km/h in the end, thermal tolerance of Exercise 3 is about 1 degree lower than that in Exercise 2. Skin temperatures of human trunk were at least 1 °C higher than that of limbs. CONCLUSIONS: Activity narrows the individual discrepancy on core temperature. Within experimental conditions, decreasing of intensity at last stage makes the core temperature lower and the whole process much tolerable. The core temperature is more sensitive to the external disturbance on the balance of the whole body, and it can reflect the subjective thermal sensation and physical exertion.