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To understand the overpressure transient and flame behavior of CH4/air premixed gas explosion venting in the presence of porous materials, a series of explosion venting tests is conducted in a spherical vessel with a neck. The effects of pore size, porosity, thickness, and properties of porous material on Pstat, Pred, Pburst, and Pext are measured using pressure transmitters, and the image of an exploding venting jet flame passing through porous materials is captured using a high-speed camera. It is shown that the pressure wave at the high-pressure side of the explosion vent is in a critical state when the venting burst membrane ruptures without the porous materials, and the vented jet is confirmed to be under-expanded. The addition of porous materials does not significantly affect Pstat but results in the highest Pburst in porous material Al2O3 50PPI and the highest Pred in porous material SiC 20PPI. This is consistent with the assumption that Pred > Pburst, and that an increase in Pburst corresponds to a decrease in Pred. In addition, Pext is more likely to occur at a position 250–350 mm away from the vent, and as the thickness of the porous materials increases, the possibility of an external explosion overpressure will increase. Moreover, the porous material significantly affects the venting jet flame, and as the thickness of the porous material increases, the shape of the venting jet flame resembles that of a "broom," owing to the dynamic overpressure generated from the flame-porous material interaction. [ABSTRACT FROM AUTHOR]

Hydrogen explosions happen occasionally, resulting in heavy casualties and huge property losses. Explosion venting as an effective method of explosion protection need to be further studied. In this work, the influence of hydrogen concentration (20%–60%) on the explosion venting was investigated. It was indicated that the maximum explosion pressure (P max) inside the vessel and in the vent pipe first increased and then decreased with the increase of hydrogen concentration. The P max in the vent pipe was always much larger than that inside the vessel. However, the P max outside the vessel increased gradually with increasing hydrogen concentration. The propagation characteristic and the temperature field distribution of the explosion venting flame were also analyzed. There was no obvious venting flame for 20% hydrogen concentration, because of the exhaustion of hydrogen inside the vessel. The change of the concentration affected the occurrence of secondary explosion, which affected the flame morphology, propagation velocity and flame temperature field distribution. The maximum temperatures were 1164 °C and 1207 °C for 50% and 60% hydrogen concentrations. Furthermore, changes of hydrogen concentration resulted in changes of the explosion intensity inside the vessel, thus affecting the flow field microstructure inside the vessel and near vent port. The stronger the explosion intensity, the more unstable the flow field microstructure and the shorter the time required to reach stability inside the vessel. • The influence of hydrogen concentration on the explosion venting was investigated. • P max externally increased with increasing concentration, unlike inside the vessel. • Flame propagation velocity and temperature distribution were analyzed intensively. • Second explosion affected the flame characteristics at high hydrogen concentration. [ABSTRACT FROM AUTHOR]

• Interaction mechanism of wire mesh inhibition and ducted venting was analyzed. • Pressure showed an uptrend with increasing initial pressure and ignition energy. • The P max was increased gradually with the increases of the mesh number and layer. • The critical condition for the complete inhibition of venting flame was determined. • The negative pressure inside the vessel during explosion venting was explained. A set of experimental equipment for wire mesh inhibition and ducted venting on methane explosions was proposed. The effects of wire mesh parameters, venting parameters, and initial conditions on the explosion intensity were also investigated and the interaction mechanism between the wire mesh inhibition and ducted venting was analysed. The results indicated that the venting flame length decreased gradually and the explosion pressure inside the vessel increased with increasing wire mesh number and layer. Especially the venting flame did not appear outside the vessel under the five layers and 60 mesh number condition, which indicated that the explosion flame propagation was effectively inhibited by the metal wire mesh. With an increase in the venting diameter, the maximum explosion pressure (P max) inside the vessel decreased gradually. However, the P max and the maximum pressure rise rate ((dP/dt) max) were increased with an increase in the rupture pressure, and the appearance moment of the P max was decreased. The initial concentration, initial pressure, ignition energy and venting position as the important factors could evidently affect the combined effects of wire mesh inhibition and ducted venting for explosion protection. The P max inside the vessel first increased and then decreased with an increase in the methane concentration, and the explosion intensity was the highest under the equivalence ratio condition. With an increase in the initial pressure and energy, the P max also was increased. The pressures at the vessel and duct end under the vessel top venting were greater than that of duct end venting. [ABSTRACT FROM AUTHOR]

The flame resistance characteristics of wire mesh and its influence factor on syngas explosion were researched by experiment. Relationships between flame propagation and pressure rise at the flame resistance system two ends were clarified under different flame resistance results. And the effect of syngas concentration on explosion parameters was obtained and flame resistance mechanism was also revealed. Results indicate that the existence of wire mesh could indirectly affect pressure rise by affecting the flame propagation, and flame propagation and pressure rise presented a clear corresponding relationship. The wire mesh could play a better inhibiting role and reduce the explosion intensity, affecting by syngas concentration. As the flame resistance failed (c =30%), △ P max was effectively decreased from 0.81 MPa to 0.52 MPa above wire mesh and from 0.58 MPa to 0.39 MPa below wire mesh. And the reduction extent was more significant under flame resistance success (80.25% and 68.97%). With reduction of syngas concentration and increase of mesh layer, explosion parameters were evidently decreased. Especially the temperature above wire mesh did not present an increase trend and reach the ignition point of syngas under flame resistance success. The inhibition mechanism was mainly attributed to the combination of endothermic and wall effects. [ABSTRACT FROM AUTHOR]

This study experimentally and numerically determined the effect of FM-200 on H 2 /air explosion. Firstly, the explosion pressure was investigated to evaluate the suppression efficiency. The results indicated that the effect of FM-200 on H 2 /air explosion was quite different for various equivalence ratios. FM-200 could enhance the explosion at lean mixture, but suppress the explosion at rich mixture. Then, the burning velocity, heat production and temperature free radicals were investigated. The results also demonstrated that FM-200 exhibited stronger suppression effect in rich explosion. In addition, the increase of free radicals indicated the enhancement effect of FM-200 at lean explosion. Last, the analysis of sensitivity and reaction path was performed to understand the suppression kinetics. It was shown that R1466 and R1468 could suppress explosion at Φ = 1.3 and 1.6, however, they changed into promoting explosion at Φ = 0.8 and 1.0. Moreover, the reaction path analysis indicated that CHF:CF 2 →CHF:O→CO could enhance explosion at Φ = 0.8. For CHF:CF 2 →CH 2 F→HF, it played an important role in scavenging H to suppress explosion at Φ = 1.6. Furthermore, it was indicated that there was a competition between the enhancement and suppression effect at Φ = 1.3. • Several characteristic parameters of hydrogen explosion with FM-200 addition were analyzed. • The explosion was enhanced with small volume fraction FM-200 addition at lean explosion. • Reaction R1466 and R1468 could suppress explosion at rich mixtures; but promote explosion at lean mixtures. • The analysis of reaction path was performed to understand the suppression kinetics. [ABSTRACT FROM AUTHOR]

• Inhibition characteristics of mist on gas/dust explosions was studied by experiment. • Pressure, flame temperature, propagation characteristics and products were analyzed. • Relationship between mixture explosion parameter under mist condition was clarified. • Effects of mist and methane concentrations on explosion inhibition were obtained. • Effective engineering suggestion was proposed and inhibition mechanism was reveale. Inhibition of water mist on the gas/dust two-phase explosions and its influence factor were studied inside the vessel. The effects of mist and methane concentrations on the pressure and its rise rate, flame propagation characteristics and its temperature were explored. Especially the explosion products were analyzed by the infrared spectroscopy. The weakening effect was revealed based on the corresponding relationship and changing rule of explosion parameters. As the flame developed and changed, the pressure rise showed the same correspondence. However, the corresponding moment was evidently prolonged compared with the case no mist. The mist could effectively inhibit the intensity of mixture explosions, causing a dark-irregular structure in the early stage and accelerating its extinction in the later stage. After the mist concentration increased, the explosion parameter was evidently reduced. As the methane concentration increased (4% ≤ c ≤ 10%), the explosion parameters appeared a trend of firstly rising and then reducing. As c = 6%, the explosion intensity was the greatest. After adding mist, the explosion parameter exhibited the same change regular. And the weakening effect of mist on the weaker flame was more outstanding and was constantly enhanced as the rise of mist concentration. Besides, the mist could effectively inhibit the pyrolysis and combustion reactions of macromolecular functional groups, further leading to evident increase in the functional group content inside the coal dust as the mist concentration increased. [ABSTRACT FROM AUTHOR]

• An accident of pipeline rupture in alkylation unit was investigate. • The failed pipeline structure provides conditions for hydrofluoric acid corrosion. • The decrease of pipeline strength is the direct cause of the accident. • The key factors to prevent pipeline leakage in alkylation unit were investigated. Owing to the corrosive, flammable, and explosive properties of pipeline materials in alkylation units, corrosion failure may result in leakage, fire, and explosion accidents. A bursting accident occurred in the 90° elbow of an alkylation unit pipeline. Failure analysis was performed by macroscopic analysis, metallographic analysis, chemical composition, corrosion form analysis, and corrosion product analysis. Finite element software was used to analyse the flow velocity, turbulence intensity, pressure, and wall stress distribution. The fault tree was combined with the analytic hierarchy process to realise the transformation of the structural importance-judgement factor-judgement matrix and to weight the events that may cause device corrosion failure. The results showed that uniform corrosion and stress corrosion of hydrofluoric acid occur in the pipeline and uniform corrosion is the dominant effect. Hydrofluoric acid corrosion leads to severe thinning of the pipe wall, making its strength drop below the bearing strength and rupture occurs. Quality of internal anticorrosion coating, water content of the medium and working temperature are the key factors to prevent pipeline leakage in alkylation unit. [ABSTRACT FROM AUTHOR]

• Relationship between flame propagation and pressure rising was analyzed deeply. • Effect and mechanism of obstacle parameters on explosion intensity were clarified. • Regular of flame "reverse oscillation" was determined and mechanism was discussed. • Effective suggestion was proposed based on the research for practical application. This experimental study focused on effect of obstacle on the syngas (H 2 /CO) explosion characteristics under lean-fuel conditions. The relationship between the flame propagation characteristics and explosion intensity, and effects of syngas concentration, obstacle number and blocking rate on explosion parameters were obtained. Results indicate that the flame propagation and pressure rise were corresponding inside the closed vessel. Obstacle could affect the flame propagation process by changing flame structure, which further indirectly affected the flame velocity and explosion intensity. The "reverse oscillation" flame appeared in the later stage due to the interaction between the flame front and reflected pressure wave, and affected by the obstacle condition and syngas concentration. Meanwhile, the peaks of velocity history were obviously increased, and their appearance moment and the interval time between adjacent peaks were decreased with increasing syngas concentration, obstacle number and blocking rate. Especially the maximum flame propagation velocity (v max) was increased by 88.90%, 60.59% and 61.65%, respectively. The maximum explosion pressure (△ P max) and two peaks of pressure rising rate history also presented an increasing trend. However, the first peak appearance moment had a slight delay due to the blocking effect with the increases of obstacle number and blocking rate in the initial stage of flame propagation. [ABSTRACT FROM AUTHOR]

• Combustibles, combustion aids, ignition sources, and tank corrosion are analyzed. • The aluminum float was subjected to SEM and EDS to investigate the corrosion. • Sulfur and iron contents of corrosion products were analyzed by elemental analysis. • Main causes of the accident are discussed, and the counter measures are proposed. With the rapid development of the petrochemical industry, sulfur-related devices are increasing. In this paper, a fire accident occurred in a petrochemical storage tank of a petrochemical enterprise. Through analysis, we found that the direct cause of the accident was the spontaneous combustion of ferrous sulfide (FeS), which caused the explosion of the oil and gas mixture between the floating disk and the tank top. In addition, we analyzed the corrosion of aluminum floating plates in oil tanks by Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS). The analyses showed that although AlMn1Cu aluminum alloy has high corrosion resistance, the material composition contains impurity elements such as silicon and iron, which weakens the corrosion resistance of aluminum alloy, and the intergranular corrosion and corrosion effects such as pitting corrosion cause cracks to form in the floating disk. The oil and gas that volatilize in the oil tank diffuse through the pores between the floating plate and the top of the tank to form an explosive mixture of oil gas and air. Next, the corrosion products of the manhole cover and the edge of the floating plate were sampled and were analyzed the sulfur and iron contents by elemental analysis. The results showed that the sulfur content in the sample of the manhole of the No. 1 tank was 25.04 wt%, and the sulfur content in the sample at the edge of the floating plate was 7.49 wt%. This was owing to the manhole at the bottom of tank No. 1 is not in contact with air. The edge of the floating plate of tank No. 1 has a low sulfur content due to the long-term contact with air and the burning process during an accident. Using Fault Tree Analysis (FTA), we conclude that the necessary conditions for the accident are appropriate heat storage conditions. The key factors are bad desulfurization effect on the refining process, sulfur in the crude oil, nonresistance of the tank material to corrosion and presence of S2- in the tank. Finally, corresponding countermeasures are proposed. [ABSTRACT FROM AUTHOR]