Process Of Leakage Research Articles

Study on the Seepage Mechanism of Gaskets at the Joints of Shield Segments Based on Coupled Euler-Lagrangian Method

In the construction and operation stage of urban shield tunnels, joint leakage of shield is always an urgent problem to be solved. In order to further explore the waterproof performance of elastic rubber gaskets at segment joints, the finite element software ABAQUS (2022) was used to establish a fluid-solid coupling calculation model. The dynamic simulation of the leakage process at the segment joints under water pressure revealed the whole process of leakage at the segment joints and the instant water pressure value when the waterproof system failed. The results show that during the whole process from segment assembly to joint leakage, the elastic rubber gasket has experienced four key stages: gasket compression, confined water pushing, water wedge and final leakage. When the opening amount of the gasket is 6 mm and 10 mm, the contact stress between the gasket shows a “W” symmetrical distribution of high at both ends and low in the middle, and the peak of the contact stress at both ends of the interface is about twice as much as that in the middle. The waterproof threshold of the gasket is closely related to the opening amount of the gasket, and the waterproof threshold has the same trend with the initial contact stress between the gaskets.

Risk assessment and simulation of gas pipeline leakage based on Markov chain theory

Gas pipeline leakage may lead to fire, explosion and gas poisoning, thus causing a large number of injuries and property damage. This paper focuses on the chain characteristics presented by the development process of city gas pipeline leakage, based on Markov chain theory, studies the disaster-causing process and the mechanism of disaster chain formation for the leakage, establishes the disaster chain, evaluates the pipeline operation status and quantifies the failure probability of gas pipeline leakage to determine the causes of the leakage. Subsequently, Pipeline Studio is applied to simulate the consequences of gas pipeline leakage to realize the risk analysis. The analysis is based on Markov chain theory to calculate the probability of leakage and disaster-causing causes, analyze the consequences of gas pipeline leakage, and realize the diagnosis of the causes of gas pipeline leakage accidents and the prediction of the accident development trend. Finally, using European gas pipeline accident data to prove the effectiveness of the method, the result shows that gas pipeline leakage accidents are mainly caused by third-party damage and corrosion, which is consistent with the real situation and provides a reference for risk analysis and accident prevention of gas pipeline leakage.

Equivalent notional nozzle model for high nozzle pressure ratio leakage of petrochemical high-pressure facility

Little work has been performed in the petrochemical safety field involving supersonic flows during accidental leakage in petroleum processing. The key technical challenge is on the changing process of gas cloud expansion after the jet. To address this, an equivalent notional nozzle model was developed for high single phase NPR (NPR＞2) gas leakage scenarios in petrochemical high-pressure facilities. This model aimed to determine the essential physical parameters of the equivalent cloud formed after air is drawn in with high NPRs. By utilizing CO2 as the gas phase, the validity of the equivalent notional nozzle model was assessed based on three crucial shock structure properties and the axial and radial velocity fields, the chocked flow intensity was applied as an indicator for the consistent trend of the jet velocity and decompression process of the high NPR gas leakage. The research findings unequivocally demonstrate the efficacy of the equivalent notional nozzle model in facilitating rapid numerical calculations for assessing the impact of high-pressure jets in the petrochemical industry.

Numerical simulation of leakage, dispersion and explosion behavior of LPG in kitchen

ABSTRACT The frequent occurrence of kitchen gas explosion accidents has raised widespread attention to gas safety. This article takes kitchen as the research object, and explores the dispersion law of LPG leakage in kitchens and the influence of ignition at different leakage time on explosion consequences by establishing LPG leakage and explosion models. The results show that the process of LPG leakage in a closed kitchen can be divided into three stages: initial kinetic energy dominant stage, gravity expansion stage, and passive dispersion stage. Propane forms a non-uniform concentration field in the kitchen that gradually decreases from bottom to top, filling the entire kitchen in 583 s. When an explosion occurred in the kitchen center, the initial burst of flame spreads around in a fireball. After 115 ms and 122 ms, the explosion overpressure causes the door and window to be destroyed respectively, and the flames stretch toward the door and window. The flames are then concentrated mainly in the lower area where the fuel is more adequate. In the later stage of the deflagration reaction, the flame propagates toward the upper area of the kitchen under buoyancy. The explosion consequences of LPG non-uniform gas clouds show a pattern of first intensifying and then weakening with the leakage time. The explosion consequences are most severe when ignited about 300 s after the leakage. The maximum explosion overpressures at the center of the kitchen, door, and window were 67.15 kPa, 28.12 kPa, and 27.92 kPa, respectively. The research results can provide reference for emergency response, consequence assessment, and kitchen safety design for kitchen LPG leakage and explosion accidents..

Field experimental study of high expansion foam coverage after LNG leakage

With the rapid development of the world’s natural gas industry, LNG (Liquefied Natural Gas) has received widespread attention as a clean energy source. However, the leakage accidents of LNG are usually accompanied by safety hazards such as explosions, low temperatures, and phase transitions. In this study, the field experiment is carried out to cover LNG leakage pool with HEF (High-Expansion Foam). In the process of LNG leakage, when the ambient temperature at the bottom of the reservoir drops to about − 82.3 °C (the critical temperature of LNG), the ambient temperature would rise briefly due to the effect of phase transition. Meanwhile, the temperature distribution of different vertical and horizontal positions in the reservoir during the process of leakage is analyzed. Besides, it is also found that the density of the spilled vapor is much lower than that of the air, but the water in the surrounding air encounters the cryogenic vapor to condense into small droplets, the small droplets entrap part of the flammable gas during the process of settling to the ground, therefore, the flammable vapor still shows a heavy gas effect. During the initial period of HEF coverage, evaporation from the liquid pools accelerates, resulting in a 386% increase in peak concentration of methane above the reservoir. Nevertheless, when HEF application is maintained an effective thickness, it can effectively reduce the methane vapor concentration downstream of the reservoir near the surface to less than 1/2 LFL (1/2 of the Lower Flammability Limit). In general, the large-scale field experiments have far-reaching engineering significance and reference value for the occurrence and emergency treatment of LNG leakage accidents under actual working conditions.

Research Progress of Drilling and Completion Fluid Loss Model in Fractured Reservoir

Well loss and its accompanying reservoir damage is a common and serious problem, which not only greatly restricts the economic benefit, but also seriously affects the correct evaluation of reservoir oil and gas resources in the early stage of exploration. With the exploration and development of deep Marine carbonate oil and gas resources, fracture leakage has gradually become a frontier and hot issue to be studied urgently. Foreign scholars began to study the leakage model of fractured reservoir in the 1990s, but at present, domestic scholars mainly focus on the clastic rock model, focusing on the plugging technology and plugging materials, while ignoring the importance of the dynamic development of the leakage indirectly reflecting the leakage type and the size of the leakage channel. This paper comprehensively analyses the effects of drilling completion fluid rheology, fracture opening variation, fracture wall filtration and other factors on well loss from the time sequence of the establishment of the leakage model, summarizes the research progress of the mathematical model of leakage in fractured reservoirs, and proposes to pay attention to and strengthen the monitoring of the leakage mechanism and the dynamic process of leakage, so as to provide a theoretical basis for the rapid diagnosis of leakage types and the optimization of leakage control.

Analytical model for the sealant performance of tunnel gasketed joints based on multi-scale contact and percolation theories

The localised leakage in shield tunnels that mainly occurs at segment joints may induce other defects, which threatens operational safety. To obtain a universal solution for the sealant performance of gasketed joints, we proposed a novel analytical model based on the multiscale contact and percolation theories, in which the obtained percolation pressure and interfacial separation can be utilized to derive the critical water leakage pressure and leakage rate. The evolutionary process of leakage was divided into three stages (i.e., the percolation, leakage and breakdown), which explicitly reveal the progressive hydraulic deterioration of gasketed joints. The gaskets still own partial waterproof capacity until the end of the leakage stage due to the remaining contact pressure at surface asperities. The proposed model was first verified by several sets of experimental data, based on which the determination of three key model parameters (i.e., self-sealing slope, sealing coefficient, and expel pressure) were discussed in detail. The parametric study indicates that the waterproof capacity is significantly affected by the joint opening, offset, and the surface roughness of the gaskets. The variation in waterproof capacity with joint opening is mainly due to the nonlinearity of the gasket’s modulus and self-sealing slope. The increase in joint offset can result in a lower waterproof capacity as well as a larger leakage rate. Gasket’s surface roughness affects the percolation pressure and interfacial separation, which contributes to the long-term sealant performance.

Research on the engineering application of leakage diffusion theory based on finite volume method in LNG pipeline

In order to provide theoretical reference for the volume design of the terminal sump, this paper analyses the physical process of leakage and evaporation at the LNG terminal using. Combined with the theory of orifice leakage and evaporation diffusion and the actual project scenario, the corresponding mathematical model is given. From qualitative analysis, the main factors affecting LNG leakage and evaporation diffusion are given. The mathematical model is applied to engineering practice, and a large number of calculations are carried out to give the quantitative relationship between leakage, evaporation and diffusion and various influencing factors. Through research, it is found that the leakage of LNG is far greater than the evaporation on the wharf. When designing the volume of the sump, the evaporation of LNG on the wharf can be ignored. According to the leakage model of the pipeline orifice, the credible leakage volume in line with the actual project can be obtained.

Migration of Leaked Oil Vapor in Underground Water-Sealed Oil Storage Cavern Considering the Influence of Fractures

During the operation of underground water-sealed oil storage caverns, a large amount of oil vapor is generated due to volatilization. Oil vapor can easily leak into the surrounding rock, and fractures in the surrounding rock are usually the dominant channels for oil vapor leakage. To study the influence of fractures on oil vapor leakage and migration in underground water-sealed oil storage caverns during the oil storage period, a gas–liquid two-phase flow model of the fracture–pore dual medium in fractured rock mass was established. The program was implemented on the COMSOL platform by using weak-form PDE (partial differential equation). Then, taking an underground water-sealed cavern of an oil reserve as an example, the influence of the characteristic parameters of a single fracture on the evolution process of oil vapor leakage and migration during the oil storage period of the underground water-sealed oil storage cavern was studied. The results were further applied to the Huangdao underground oil depot project. The results show that the spatial distribution of oil vapor leakage is mainly affected by fractures. Through parameter sensitivity analysis, it was found that the geometric characteristic parameters of fractures will have a certain impact on the migration field of oil vapor leakage in underground caverns. Specifically, fracture permeability (kf), fracture width (df), and fracture inclination (θ) are positively correlated with oil vapor leakage parameters (oil vapor leakage range and leakage volume), while the distance between the fracture and the middle cavern (s) is negatively correlated with oil vapor leakage parameters (oil vapor leakage range and leakage volume). The relative influence of fracture geometry parameters on the migration process of oil vapor leakage during the oil storage period of the underground water-sealed oil storage cavern is in the following order: kf> df> s > θ. Engineering application shows that the existence of fractures affects the spatial distribution of oil vapor leakage and migration, and the relationship between oil vapor leakage parameters and oil storage operation time is a positive power function. The gas–liquid two-phase flow model of the fracture–pore dual medium in fractured rock mass developed in this study could offer a numerical simulation tool to assess and mitigate the risk of oil vapor leakage. The research conclusions can provide some references for related problems encountered in similar projects.

Leakage, diffusion and distribution characteristics of refrigerant in a limited space:A comprehensive review

The leakage and direct emission of high GWP HFC refrigerants in refrigeration, air-conditioning and heat pump systems increase the greenhouse effect, which pose huge threats to the ecological environment and the human health. Meanwhile, some alternative refrigerants with excellent environmental performance have different degrees of flammability. When the flammable refrigerants catastrophically leak from the refrigeration system into a limited space, it is easy to cause an explosion accident, the safety of people and property in the space is greatly threatened. In addition, the operating conditions of refrigeration systems, thermophysical properties of the refrigerants, obstacles and ventilation conditions of the space have a great impact on the process of refrigerant leakage and diffusion, the explosion risks formed in the external space have certain differences. To promote the security application of the alternative refrigerants, the leakage, diffusion, and distribution characteristics of the refrigerants from both theoretical and experimental aspects were reviewed in this work. The potential causes of leakages and common types of leakage holes in refrigeration systems were summarized, and the advantages and disadvantages of the existing leakage and diffusion theoretical models were concluded. The impact of the micro-sized leakage of the refrigerant on the internal of the system was discussed. The diffusion and distribution of the refrigerants in the external space after they catastrophically leaked from different types of systems were analyzed, and the influence of different parameters on the refrigerant distribution and the explosion risk based on the catastrophic leakage was also presented. The future work was prospected. The review is expected to provide a valuable reference for the safety risk assessment of the flammable refrigerants.

Multi-Factor Coupling Analysis of Porous Leakage in Underwater Gas Pipelines

Natural gas pipeline leaks under the sea will have a significant negative effect on the marine ecosystem, result in significant financial losses, and possibly even harm marine floating objects. The VOF (Volume of Fluid) multi-phase flow model is used to numerically simulate and study the diffusion process of porous leakage in submarine gas pipelines. Experiments confirmed the model’s correctness and dependability. Based on this, the coupling effect and the porous effect of the leakage velocity, the size of the leaked pore, and water velocity of the natural gas pipelines on the diffusion of porous leakage in the submarine gas pipelines are analyzed with the test scheme designed by the orthogonal test method. The similarity principle is used to connect the leakage model with the actual application. The results show that three factors, namely, the leakage velocity, the size of leaked pore, and the water velocity, influence the shape of the air mass, the time when the gas reaches the sea surface, and the diffusion range. The size of the leakage hole and the leakage velocity have a substantial impact on the form of the air mass and the amount of time it takes for the gas to reach the sea surface, while the water velocity has no effect. Additionally, while there is essentially little impact from the leakage velocity, the size of the leaky pore and the water velocity have a significant impact on the diffusion range. Furthermore, the porous effect between leaky pores has a significant impact on the gas diffusion range. This study can serve as a guide for risk assessment and emergency decision-making regarding a submarine gas pipeline leak.

Simulation and risk assessment of hydrogen leakage in hydrogen production container

In this paper, the hydrogen leakage and diffusion characteristics analysis and risk assessment are carried out on the container where a 2 Nm3/h alkaline hydrogen production device is located. Firstly, the transient and steady process of hydrogen leakage from hydrogen production container is analyzed. Secondly, the dynamic balance of combustible hydrogen cloud is analyzed, the concept of critical ventilation flow is put forward. It was found that in order to reduce the flammable volume by 85%, the installed ventilation can only cover the leakage flow of 1.0 Nm3/min. Finally, TNT equivalent method is used to evaluate the hazard degree of hydrogen leakage. It is found that the existed hydrogen production container ventilation device can only exhaust the hydrogen-air cloud with small flow leakage, while the accumulation of gas cloud still exists in large flow leakage. Under the critical ventilation flow, the minor injury radius can be reduced from 4.8 m to 2.78 m. The effect of critical ventilation flow was verified.

Risk Assessment of Annular Pressure Caused by Tubing Leakage in Offshore Gas Wells with High CO2

CO2 sequestration is a kind of technology that can effectively mitigate the greenhouse effect, and the wellbore integrity of the storage system is the key issue to ensure successful CCUS. Failure to timely diagnose tubing leakage in offshore gas wells with high CO2 will lead to annular pressure risk and wellbore corrosion problems. The annular pressure caused by tubing leakage is characterized by high pressure and rapid rise rate, resulting in wellhead jacking, gas leakage, and wellbore structure corrosion, which has become the main cause of wellbore integrity failure in offshore gas wells. Therefore, a model of heat and mass transfer and distribution in offshore gas wells was established firstly, and the physical process of gas leakage and accumulation was described based on the pinhole model and the principle of gas PVT characteristics and volume compatibility. The results show that the depth and equivalent size of the leakage point are two important factors affecting the pressure rise process and leakage rate. Taking case well parameters as an example, after inversion calculation, the annulus pressure in case well was 23.0 MPa, the leakage point equivalent diameter was 2.3 mm, the maximum leakage rate was 0.30 m3/min, and the wellbore safety risk is relatively high. Mechanical repair and chemical plugging agent are recommended to seal the tubing leakage. These risk assessment technologies provide reference for wellbore integrity design and management to reduce CO2 leakage risk caused by wellbore integrity failure.

Leakage Dynamics of Glass Bottles on Container Closure Integrity Testing: Influence of Different Laser-Drilled Microhole Geometries

Container closure integrity testing (CCIT) is a critical step in ensuring package integrity and providing feedback on package designs. In practical applications, CCIT methods, namely physical and probabilistic methods, must be appropriately selected and validated to ensure their suitability for the intended use. However, the industry still lacks practical recommendations regarding the choice of CCIT methods and artificial leaks to set the acceptance criteria. The main reason is the lack of correlation between testing methods. Artificially introduced leak microholes are the only way to determine the sensitivity of a CCIT method and to implement the method correlation. However, the type of artificial leakage is a key factor because in most studies, leakage is described and valued using a single parameter, such as size. This can significantly affect the credibility of the relevant test results, especially in the case of microbial invasion, where the difference in test conditions and samples will severely affect the probability of microbial invasion. Therefore, it is vital to conduct a systematic study on the influence of leakage conditions on CCIT methods. In this study, the influence of the shapes of artificial leaks on the two kinds of testing methods was systematically studied based on a laser-drilled microhole—a highly potential and non-exogenous artificial leak manufacturing method that can fabricate different leakage geometries. The reason for the influence of the shape of an artificial leak on the CCIT is that the deterministic method takes defects as an idealized model and ignores the influence of the leak shape, wall thickness, and other factors on leakage and pollution risks. However, these factors seriously affect the dynamic process of leakage and microbial invasion. The pressure decay method is used to test the leakage flow rate of conical and straight holes. Microbial challenge tests are then used to verify the impact of leakage shapes on the pollution risk. The results of the tests indicated that the probability of microbial invasion in the conical holes is much higher than that in straight holes with the same flow test results and that the wall thickness can also affect microbial invasion. Thus, it can be proven that the risk of leakage and invasion or the sensitivity of different methods cannot only be compared through the leak diameter. Numerous influencing factors, including leakage geometry (e.g., shape and thickness), must be considered in practical applications.

Activation of Autophagy Is Essential for the Healing Process of Surgical Pancreatic Leakage

Activation of Autophagy Is Essential for the Healing Process of Surgical Pancreatic Leakage

A Web Back-End Database Leakage Incident Reconstruction Framework Over Unlabeled Logs

In this article, we propose a web back-end database leakage incident reconstruction framework (WeB-DLIR) over unlabeled logs, designed to improve the intelligence and automation of reconstructing web back-end database leakage incidents triggered by web-based attacks in unannotated logging environments. Using WeB-DLIR, analysts can reduce the manual workload of tracing and responding to data leakage incidents. Specifically, we first design web front-end and back-end anomaly identification methods based on neural network models with a pruning strategy and fine-grained grouping clustering analysis, respectively, for completely identifying web-related abnormal events in unlabeled logs. To remove redundant abnormal events and reduce subsequent inspection work for false alarm cases, we then propose an anomaly detection result decision fusion method (DFADR). Moreover, to visualize the attack chain reflected by abnormal events, based on the decision fusion results, we propose an attack graph modeling method that can reflect the basic process of data leakage from multiple perspectives. Finally, based on the modeling results, the topology of the data leakage scenario reconstruction can be completed by further auditing the relevant logs. Experimental results using real-world datasets show that the proposed WeB-DLIR is efficient and feasible for practical applications.

MATHEMATICAL MODEL OF PNEUMATIC CHANNEL OF GAS PRESSURE MEASURING TRANSDUCER

The paper is devoted to the study of the impact of operational factors, particularly gas leakage through the damages of pneumatic channels of measuring transducers of gas pressure and pressure drop, on the measuring result of these parameters and, therefore, on the measured value of gas flow rate and volume using pressure differential flowmeters. During the operation of gas metering units, connecting tubes, valve blocks, and averaging chambers of the standard primary device must be hermetic. However, they may become non-tight because of operational factors, and gas leakage may occur. Such leaks distort the measured pressure drop or pressure value, which can lead to a distortion of the measurement result of the gas flow rate by the metering unit.
 The authors developed a mathematical model of a pneumatic channel of gas pressure measuring transducer with existing damage. For this purpose, a mathematical model of the connecting tube, which connects the pressure averaging chamber with the pressure transducer chamber, has been developed for the stationary gas mode. A mathematical model of gas leakage through damage like "through-hole" was also developed. Based on the mathematical model of the connecting tube and the model of the process of gas leakage through the hole, a mathematical model of the pneumatic channel with a gas leakage hole was obtained.
 Modeling and investigating the impact of gas pressure, geometric characteristics of damage, and connecting line on the measuring result of pressure or pressure drop was performed. Particularly, the value of the negative systematic error of the gas pressure measurement, which occurs as a result of gas leakage through the hole in the connecting tube, is calculated for a set of fixed values of the geometric characteristics of the pneumatic channel.
 The paper shows that an increase in the pressure in the measuring tube leads to an increase in the modulus of pressure absolute error caused by the gas leakage through the hole in the connecting tube. The gas flow rate through the hole in the connecting tube and, accordingly, the pressure measurement error depends on the diameter of the through-hole and the location of the leakage. An increase in the hole diameter leads to an increase in the modulus of the absolute error of the pressure measurement.
 As the length of the connecting tube from the connection point with the measuring pipeline to the point of gas outflow increases, the pressure measurement error increases by the modulus.

Dual Function of l‐Phenylalanine as a Modification Layer toward Enhanced Device Performance and Mitigated Lead Leakage in Perovskite Solar Cells

Although perovskite solar cells have achieved great breakthroughs in photoelectric conversion efficiency (PCE), some challenges still need to be addressed before commercialization. Lead leakage is harmful to the environment and many methods are developed to prevent lead leakage; among them, chemical adsorption has proved to be an effective way. Herein, a simple and low‐cost strategy that can enhance the device performance and mitigate the lead leakage by applying l‐phenylalanine in the interface of NiOx/perovskite is reported. The results show that this strategy can improve the morphology and conductivity of the NiOx film, optimize the NiOx/perovskite interface energy level, resulting in an efficient and stable device with a PCE of 19.0%. Furthermore, the interface modification improves the stability of the perovskite film through strong interaction with the perovskite, inhibits the decomposition of the film in water, slows down the process of lead leakage, and protects the environment from lead pollution. The devices maintain 86% initial efficiency for 200 h maximum power point measurement and 94% for 2100 h under nitrogen.

Creep leakage process of remaining soils in near-surface fissures in a karst area with bedrock outcrops

As a global ecological environmental problem, rocky desertification is derived from the exposure of large areas of bare rock on slopes, and soil remains only between rock exposures and in fissures. These remaining soils are crucial to vegetation growth and the amelioration of rocky desertification, but they are prone to leakage loss. This study aimed to reveal soil creep displacement (SCD) and the characteristics, process and mechanism of soil particle leakage in fissures on sloping land in karst areas. Six fissures on the karst plateau of Guizhou were studied by paint marking and soil particle analysis techniques, and SCD was monitored during three rainfall periods (cumulative rainfall of 104.5, 151.2 and 332.7 mm). The results showed that for 104.5 mm of rainfall, the SCD of the fissures was 1.0 ∼ 2.5 cm and accounted for more than 62.5% of the displacement observed after a total of 332.7 mm of precipitation. Additionally, the SCD was 0.2 ∼ 0.3 cm at 181.5 mm of rainfall. Therefore, rainstorms or downpours are a key factor driving soil fissure leakage, and the leakage form is mainly soil creep. Under three rainfall observation periods, the particle content with different particle sizes at soil-rock interfaces and soils in six fissures showed that fissure soils do not show uniform downward leakage; instead, some particles in the soil layers or at soil-rock interfaces randomly leak to lower layers during the process of creep leakage loss. Hence, the occurrence of soil layers and particles is random, and the soil particles at the soil-rock interfaces and in soil layers in fissures may leak downward. The results indicate that soil creep leakage in fissures is a complex process that depends on both internal factors and external factors (such as rainfall).

The Effect of the Spin and Orbital Parts of the Poynting Vector on Light Localization in Solid-Core Micro-Structured Optical Fibers

The optical properties of solid-core micro-structured optical fibers (SC MOFs) have been studied for a long time. The process of the energy outflow of the core modes has always been associated with the process of constructive interference of the core modes fields under reflection from the photonic crystal cladding. In this paper, we want to offer a new look at the light localization in the core of SC MOFs related to the behavior of spin and orbital parts of the Poynting vector of these core modes and singularities arising in it. Such an approach can help in forming a better understanding of the process of the core modes energy leakage and also in the creation of SC MOFs with a simplified design and low losses.