Showing papers on "Overpressure published in 2018"

Submarine slope failures due to pipe structure formation.

Abstract: There is a strong spatial correlation between submarine slope failures and the occurrence of gas hydrates. This has been attributed to the dynamic nature of gas hydrate systems and the potential reduction of slope stability due to bottom water warming or sea level drop. However, 30 years of research into this process found no solid supporting evidence. Here we present new reflection seismic data from the Arctic Ocean and numerical modelling results supporting a different link between hydrates and slope stability. Hydrates reduce sediment permeability and cause build-up of overpressure at the base of the gas hydrate stability zone. Resulting hydro-fracturing forms pipe structures as pathways for overpressured fluids to migrate upward. Where these pipe structures reach shallow permeable beds, this overpressure transfers laterally and destabilises the slope. This process reconciles the spatial correlation of submarine landslides and gas hydrate, and it is independent of environmental change and water depth.

Consequence assessment of high-pressure hydrogen storage tank rupture during fire test

Abstract: This paper deals with the consequences assessment associated with the accidental catastrophic explosion in the case of high-pressure tank (165 L, 35 MPa) rupture during fire test. Two catastrophic explosion accidents caused by the thermally activated pressure relief device (TPRD) failure in activating in time were reported. The detailed explosion processes were recorded and analyzed, providing a valuable study case for improving the hazard identification. A method was developed for calculating the explosion energy stored in high-pressure hydrogen tank based on the real-gas state equation of the hydrogen. Three kinds of damage patterns were analyzed synthetically considering the intensity of the blast wave, thermal radiation, and flying fragments. It is found that for the overpressure of blast wave, the slight injury for human and minor damage for equipment are expected in the radius range of within 14.0 m and 65.4 m, respectively. Similarly, the safe radius distances of thermal radiation for human and equipment are 140 m and 52.1 m. The flying distance of the destructed tank increases with the increment of projection angle. The theoretical results are in good agreement with the data collected from the accidents. The proposed method provides a theoretical support for taking enough safety measures in advance to prevent dangerous consequences of high-pressure storage hydrogen tank during fire test.

Experimental investigation of blast mitigation and particle–blast interaction during the explosive dispersal of particles and liquids

Abstract: The attenuation of a blast wave from a high-explosive charge surrounded by a layer of inert material is investigated experimentally in a spherical geometry for a wide range of materials. The blast wave pressure is inferred from extracting the blast wave velocity with high-speed video as well as direct measurements with pressure transducers. The mitigant consists of either a packed bed of particles, a particle bed saturated with water, or a homogeneous liquid. The reduction in peak blast wave overpressure is primarily dependent on the mitigant to explosive mass ratio, M/C, with the mitigant material properties playing a secondary role. Relative peak pressure mitigation reduces with distance and for low values of M/C (< 10) can return to unmitigated pressure levels in the mid-to-far field. Solid particles are more effective at mitigating the blast overpressure than liquids, particularly in the near field and at low values of M/C, suggesting that the energy dissipation during compaction, deformation, and fracture of the powders plays an important role. The difference in scaled arrival time of the blast and material fronts increases with M/C and scaled distance, with solid particles giving the largest separation between the blast wave and cloud of particles. Surrounding a high-explosive charge with a layer of particles reduces the positive-phase blast impulse, whereas a liquid layer has no influence on the impulse in the far field. Taking the total impulse due to the blast wave and material impact into account implies that the damage to a nearby structure may actually be augmented for a range of distances. These results should be taken into consideration in the design of explosive mitigant systems.

Effect of vent conditions on internal overpressure time-history during a vented explosion

Abstract: Vented explosion experiments of ethylene-air mixtures were conducted in a custom-designed 2 × 1.2 × 0.6 m3 steel chamber under three vent conditions to study the effect of vent size and vent type on overpressure under different concentrations. The experiment results show that vented explosion behaviors are related to various vent conditions. The rupture pressure of vent film at different concentrations are the same with static vent pressure while the rupture pressure of vent panel increases as the concentration approaches the stoichiometric concentration. Double-peak pressure curves were recorded under small size vent conditions, while overpressure curves with only one peak were recorded under large size venting. Analysis indicates that the peak overpressure and rate of pressure increase under large size venting are mainly affected by the rupture pressure and the concentration of combustible gas, respectively. Moreover, secondary explosion, due to the backflow of external gas, will occur in high concentrations under large size vent conditions. In the case of small size vent condition, the value of first peak P1 is mainly determined by the rupture pressure, while the value of second peak P2, and the rates of increase to P1 and P2 are mainly affected by the concentration. There is a clear difference between the recorded values of P2 at two measurement points, which indicates that there is a pressure gradient induced by small size vent conditions due to the change of flow cross-section. This work provide a practical reference for the safety design of the explosion venting.

Two-phase flow visualization under reservoir conditions for highly heterogeneous conglomerate rock: A core-scale study for geologic carbon storage

Abstract: Geologic storage of carbon dioxide (CO2) is considered a viable strategy for significantly reducing anthropogenic CO2 emissions into the atmosphere; however, understanding the flow mechanisms in various geological formations is essential for safe storage using this technique. This study presents, for the first time, a two-phase (CO2 and brine) flow visualization under reservoir conditions (10 MPa, 50 °C) for a highly heterogeneous conglomerate core obtained from a real CO2 storage site. Rock heterogeneity and the porosity variation characteristics were evaluated using X-ray computed tomography (CT). Multiphase flow tests with an in-situ imaging technology revealed three distinct CO2 saturation distributions (from homogeneous to non-uniform) dependent on compositional complexity. Dense discontinuity networks within clasts provided well-connected pathways for CO2 flow, potentially helping to reduce overpressure. Two flow tests, one under capillary-dominated conditions and the other in a transition regime between the capillary and viscous limits, indicated that greater injection rates (potential causes of reservoir overpressure) could be significantly reduced without substantially altering the total stored CO2 mass. Finally, the capillary storage capacity of the reservoir was calculated. Capacity ranged between 0.5 and 4.5%, depending on the initial CO2 saturation.

Experimental Research on the Impactive Dynamic Effect of Gas-Pulverized Coal of Coal and Gas Outburst

Abstract: Coal and gas outburst is one of the major serious natural disasters during underground coal, and the shock air flow produced by outburst has a huge threat on the mine safety. In order to study the two-phase flow of a mixture of pulverized coal and gas of a mixture of pulverized coal and gas migration properties and its shock effect during the process of coal and gas outburst, the coal samples of the outburst coal seam in Yuyang Coal Mine, Chongqing, China were selected as the experimental subjects. By using the self-developed coal and gas outburst simulation test device, we simulated the law of two-phase flow of a mixture of pulverized coal and gas in the roadway network where outburst happened. The results showed that the air in the roadway around the outburst port is disturbed by the shock wave, where the pressure and temperature are abruptly changed. For the initial gas pressure of 0.35 MPa, the air pressure in different locations of the roadway fluctuated and eventually remain stable, and the overpressure of the outburst shock wave was about 20~35 kPa. The overpressure in the main roadway and the distance from the outburst port showed a decreasing trend. The highest value of temperature in the roadway increased by 0.25 °C and the highest value of gas concentration reached 38.12% during the experiment. With the action of shock air flow, the pulverized coal transportation in the roadway could be roughly divided into three stages, which are the accelerated movement stage, decelerated movement stage and the particle settling stage respectively. Total of 180.7 kg pulverized coal of outburst in this experiment were erupted, and most of them were accumulated in the main roadway. Through the analysis of the law of outburst shock wave propagation, a shock wave propagation model considering gas desorption efficiency was established. The relationships of shock wave overpressure and outburst intensity, gas desorption rate, initial gas pressure, cross section and distance of the roadway were obtained, which can provide a reference for the protection of coal and gas outburst and control of catastrophic ventilation.

Effect of side venting areas on the methane/air explosion characteristics in a pipeline

Abstract: To reduce the great losses caused by gas explosions in the gas transportation process and to improve the explosion venting efficiency in pipelines, a small pipeline with both a side vent and an end vent was developed, and premixed methane/air explosion characteristics were studied in the pipeline with different side venting areas. The experimental results show that in the same side venting position, with an increasing venting area, the propagation time for flames through the pipeline increases on a large scale, the peak overpressure of the methane explosion drops significantly, and the venting effect is greatly enhanced. Meanwhile, when the flame propagates upstream a side vent, the propagation can be slightly promoted by a side vent with a small area in the corresponding period of time, whereas a side vent with a large area can hinder the flame propagation all the time. After the flame passes the side vent, side venting plays a strong role in flame propagation, and the flame propagation velocity drops rapidly under a large side venting area. It is also found that overpressure in the vicinity of a side vent is less affected by the side venting area, while the effect of the venting area on overpressure is relatively large at a far distance from the side vent position.

Study on the inhibition influence on gas explosions by metal foam based on its density and coal dust

Abstract: Metal foam is another type of material that can inhibit gas explosion flames and pressure waves. However, there are continuous explosions and coal dust explosions in the coal mine; thus, research on metal foam's inhibition performance under the environment of coal dust and its destructive characteristics after the explosion are necessary. We studied the suppression influence and destruction of metal foam used as a gas explosion transfer device designed for this research. First, a barrier performance experiment was conducted using metal foam whose density ranged from 0.33 to 0.54 g/cm3. Then, we examined the deformation and damage characteristics of different-density metal foams after the explosion. The experimental results demonstrate that the ability to suppress the explosion is better when the volume density of the metal foam is high. There is no obvious damage or deformation when the density is heavier than 0.5 g/cm3; thus, it could be resistant to the impact of the secondary explosion. Second, 5–100 g of coal dust was added in the pipe, and the inhibition performance of the metal foam was reduced. Especially, 50 g of coal dust can raise the explosion overpressure and flame speed. The quality of coal powder can reduce the barrier performance in a specified range.

Experimental and Numerical Investigations of Shock Wave Attenuation Effects Using Protective Barriers Made of Steel Posts

Abstract: The use of protective barriers is one of the most common approaches to protect buildings and their occupants against blast and vehicle impacts. They increase the stand-off distance between ...