Liquefied Natural Gas Leakage Research Articles

Experiment-based feasibility study of LNG equipment-embedded fuel gas supply system for vessels

This study introduces and validates an innovative Liquefied Natural Gas (LNG) Equipment-Embedded Fuel Gas Supply System (LEEF) designed for small LNG-fueled vessels. These ships face significant challenges in implementing LNG Fuel Gas Supply Systems (FGSS) owing to limited space and stringent regulatory requirements to reduce Greenhouse Gas (GHG) emissions. The LEEF system addresses these challenges by replacing the external Pressure Build-up Unit (PBU) with an integrated in-tank Electric PBU (EPBU) and vaporizer, enhancing spatial efficiency and safety while reducing LNG leakage risks. The experimental results indicate that the Pressure Rise Rate (PRR) accelerates with higher tank levels and increases the EPBU power. The PRR doubled at higher liquid levels and improved by 30–44 % with increased EPBU power at a constant liquid level. The EPBU effectively maintained the tank pressure against flow variations, achieving pressure control with minimal power. A review of international regulations and codes confirms that the EPBU satisfies explosion-proof standards and ensures stable operation. The LEEF system demonstrated substantial potential for application in small LNG-fueled ships by combining improved spatial efficiency and enhanced safety. This study contributes to the development of the FGSS solution that is more compact and safer compared to conventional systems, encouraging sustainable marine propulsion.

The response characteristics and damage effects of large LNG storage tanks subject to the coupled effects of explosion shock waves and fire

As the demand and import of liquefied natural gas (LNG) increase, large LNG receiving stations are being constructed. LNG leakage can lead to fire or explosion accidents. The simultaneous occurrence of explosions and fires, often inevitable, is more damaging than the effect of a single load. This study utilizes finite element analysis software LS-DYNA and the ALE algorithm to examine the response characteristics and damage effects on large LNG storage tanks under the combined impact of explosion shock waves and high-temperature loads (with the explosion preceding the fire). The findings indicate that post-explosion, the concrete outer tank's compressive strength diminishes as temperatures rise. The dome deflection of the storage tank's external tank surpasses the standard limit at 400 °C and fails at 600 °C. This research identifies the critical failure mode of the concrete storage tank's outer tank under the joint impact of explosion shock waves and fire. It provides a foundation for the anti-explosion design of such storage tanks.

Leakage monitoring and diagnosis of LNG storage tanks with temperature sensing network integration and artificial intelligence algorithm

Temperature is the most important safety monitoring indicator for leakage diagnosis during the operation phase of liquefied natural gas (LNG) storage tanks. Timely monitoring and accurate identification of LNG leakage events are crucial for accident prevention, loss reduction, and facility safety maintenance. This study integrates artificial intelligence (AI) algorithms and temperature sensing data to achieve intelligent monitoring and diagnosis of leakage in LNG storage tanks. Firstly, a comprehensive temperature sensing network is constructed by combining numerical simulation of the temperature field and temperature sensing experiments using fiber Bragg grating sensors. Secondly, Python is used to perform linear grid interpolation and flattening on the sensing network, generating 2D temperature nephogram samples that are conducive to AI algorithm recognition. Finally, sample features are extracted using machine vision, and leakage location calculation, leakage diagnosis and leakage volume calculation are implemented with the help of machine learning algorithms, achieving satisfactory accuracy on the test set. In addition, the ConvLSTM framework is introduced for deep learning and recurrent neural network training, enabling spatiotemporal prediction of the leakage area.

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.

Effect of Ultralow Temperature on Expansion, Strength, and Modulus of Cement-Stabilized Soil: Case Study for LNG Underground Storage in Singapore

Singapore has a relatively high water table. When liquefied natural gas (LNG) storage systems are built in soils below the water table in Singapore, the engineering properties of the surrounding soils could be improved through cement stabilization. Due to the extremely low temperature (T) of LNG (approximately −162°C), the effect of ultralow T on the physical and mechanical properties of cement-stabilized soil in case of accidental LNG leakage should be investigated. However, existing studies on cement-stabilized soils are limited to T above −20°C. Therefore, in this study laboratory experiments to quantify volumetric expansion, unconfined compressive strength (UCS), and Young’s modulus (E) of cement-stabilized soils at −40°C, −80°C, and −120°C were conducted. The experimental results indicated that the stabilized soils’ volumetric expansion reached ≤2.6% at −120°C. The UCS and E of the stabilized soils increased from 0.9 to 27.6 MPa and from 99.8 to 2,669 MPa, respectively, and the T decreased from 24°C to −120°C. In summary, the ultralow T induced limited volumetric expansion (<3%) for cement-stabilized soil and significantly increased its strength and E, which indicated that cement soil stabilization could be beneficial for underground LNG storage systems in Singapore when exposed to accidental LNG leakage.

Alternatif Deniz Yakıtı Olarak LNG Kullanımında Emniyet Tedbirleri

International Maritime Organisation has changed the emission rates in the MARPOL Annex VI rules as of 2020 and reduced the sulfur rate from 3.5 percent to 0.5 percent and led the maritime sector to alternative fuels. Compared to other alternative fuels, liquefied natural gas (LNG) is an attractive option with almost zero emission rate, ease of access, availability of ports that currently supply LNG and low price in the fuel market. In addition, according to the life cycle assessment, which is a methodology created by ISO 14040: 2006 to examine the impact of a product on the environment, in order for a fuel to be environmentally sustainable, it has to be associated not only with low emissions during fuel combustion, but also with the entire fuel life cycle, starting with raw material extraction, fuel production, distribution and finally combustion. The life cycle environmental performance of LNG as a marine fuel has been observed to have its impact on climate change in the range of 20% to 5%, significantly reducing SO2 and NOX emissions compared to heavy fuel oil. LNG bunkering is specified in the IGC code. In addition, there are standards brought by class organizations. This study shows us how to avert from the risk of LNG leakage accident. For this reason, risk analysis should be done correctly, ISM checklists should be created and applied on ships accordingly.

Consequence Analysis of Accidental LNG Release on the Collided Structure of 500 cbm LNG Bunkering Ship

The growing demand for liquefied natural gas (LNG)-fueled ships necessitates the establishment of an LNG bunkering facility. Ship-to-ship (STS) is one of the most practical forms of LNG bunkering systems. Although there are benefits to the LNG bunkering of ships, risk and safety issues are a concern due to the volatile cargo. Ship collision could result in accidental LNG release. The purpose of this study was to build LNG leakage scenarios, establish critical zones based on gas concentrations, and estimate the temperature reduction in a bunkering ship’s structure resulting from the use of cryogenic fluid. The condition of a target ship’s structure, both intact and when damaged due to collision, was considered. Leak size, leak direction, leak position, release rate, and reservoir pressure were included as leak parameters, and environmental parameters, such as the wind direction, wind speed, and ambient temperature, were also included. The release duration was set based on the shutdown duration of the emergency shutdown valve (ESD). A total of 72 leakage scenarios were generated for the main CFD analysis. Convergence tests were conducted to determine the appropriate grid and iteration numbers for a computational fluid dynamics (CFD) simulation. The gas dispersion characteristics and the cryogenic flow impact on the LNG bunkering ship’s structure are discussed through a parametric study.

Hazard analysis by leakage and diffusion in Liquefied Natural Gas ships during emergency transfer operations on coastal waters

With global warming and 2050 carbon reduction targets, the demand for Liquefied Natural Gas (LNG) marine transportation continues to increase. LNG carriers that experience emergency unseaworthy accidents at sea have the need for emergency transfer rescue, which brings many safety management issues for ships and coastal waters due to high risk of LNG leakage. This paper investigates the impacts on the ship and marine safety caused by the LNG leakage and diffusion from ship-to-ship (STS) emergency transfer operations on coastal waters. Firstly, the computational fluid dynamics (CFD) method is used to establish an LNG STS transfer leakage diffusion model. Then, LNG dispersion characteristics and the range of the vapour cloud in transfer operating waters under accident conditions with different wind speeds and wind angles are calculated and simulated. The results show that the diffusion of LNG vapour cloud is significantly influenced by wind speed and hull restrictions, and the flammable volume fraction and 1% volume fraction of the LNG vapour cloud spread to different distances through transport effect, mixing and dilution effect of wind. In addition, an LNG cryogenic hazard zone exists in the vicinity of the leakage point. This study can provide the guidance to authorities to formulate disaster prevention, mitigation regulations, and emergency response measures, which can benefit marine safety management in coastal waters.

CFD implementation to mitigate the LNG leakage consequences: A review of explosion accident calculation on LNG-fueled ships

Liquefied Natural Gas (LNG) has a significant benefit in reducing air pollutants such as sulfur oxide, nitrogen oxide, and particulate matter emitted by Diesel Oil or Heavy Fuel Oil. The International Maritime Organization (IMO) regulates these pollutants in MARPOL Protocol Annex VI. It was implemented by establishing an Emission Control Area (ECA) in 2010 that restricts exhaust gas of ships. This regulation has resulted in new shipbuilding orders or conversions to adopt the LNG-fueled systems. Besides the benefits of LNG fuel, storing, transporting, and distributing this fuel has a different problem with conventional fuels. LNG is volatile, and it has a low flashpoint that could lead to spontaneous ignition. To assess the safety and mitigation for LNG-powered ships, Computational Fluid Dynamics (CFD), such as Kameleon Fire Ex (KFX) and Flame Acceleration Simulator (FLACS), is considered to simulate the LNG release. This technical measure is taken to observe the possible damage or loss due to the cryogenic effect, the extreme temperature of the jet fire, or Vapor Cloud Explosion (VCE). These consequences could happen sequentially that known as the “Domino Effect”. The effect of the leak and environment-related parameters could influence the severity of the damage. The applications of CFD for the LNG release cases are discussed and highlighted in this review.

에폭시 수지가 적용된 유리섬유 복합재료의 극저온 환경 기계적 특성 분석을 통한 LNG CCS 적용성 평가

Consumption of Liquefied Natural Gas (LNG) has increased due to environmental pollution; therefore, the need for LNG carriers can efficiently transport large quantities of LNG, is increased. In various types of LNG Cargo Containment System (CCS), Membrane-type MARK-Ⅲ composed of composite materials is generally employed in the construction of an LNG carrier. Among composite materials in a Mark-Ⅲ system, glass-fiber composites act as a secondary barrier to prevent the inner hull structure from leakage of LNG when the primary barrier is damaged. Nevertheless, several cases of damage to the secondary barriers have been reported and if damage occurs, LNG can flow into the inner hull structure, causing a brittle fracture. To prevent those problems, this study conducted the applicability assessment of composite material manufactured by bonding glass-fiber and aluminum with epoxy resin and increasing layer from three-ply (triplex) to five-ply (pentaplex). Tensile tests were performed in five temperature points (25, -20, -70, -120, and -170°C) considering temperature gradient in CCS. Scanning Electron Microscopy (SEM) and Coefficient of Thermal Expansion (CTE) analyses were carried out to evaluate the microstructure and thermos-mechanical properties of the pentaplex. The results showed epoxy resin and increasing layer number contributed to improving the mechanical properties over the whole temperature range.

CFD and EnKF coupling estimation of LNG leakage and dispersion

As a kind of clean fuel, increasing quantities of natural gas have been transported as liquefied natural gas (LNG) worldwide. The safety of LNG storage has gained the concerns from the public due to the potential severe consequences that may arise from LNG leakage. In this paper, a three-dimensional model with the combination of computational fluid dynamics (CFD) and the ensemble Kalman filter (EnKF) is proposed to predict LNG vapor dispersion and estimate the strength of the LNG leakage source. The LNG vapor dispersion CFD model is validated by the experimental data with good feasibility, and is further demonstrated with the reasonable modeling of the characteristics of the LNG vapor dispersion in a typical receiving terminal. The effectiveness of the proposed CFD and EnKF coupling model is evaluated and validated by a twin experiment. The results of the twin experiment indicate that the proposed CFD and EnKF coupling model allows the integration of observation data into the CFD simulations to enhance the prediction accuracy of the LNG vapor spatial-temporal distribution and thereby realizing a reasonable estimation of the LNG leakage velocity under complex environments. This study can provide technical supports for safety control, loss prevention and emergency response in case of LNG leakage accidents.

Tensor-Based Approach for Liquefied Natural Gas Leakage Detection From Surveillance Thermal Cameras: A Feasibility Study in Rural Areas

Detection of the liquefied natural gas (LNG) leakage attracts increasing attention for preventing environments and governments from severe pollution and economic loss. Existing frameworks take advantage of stationary surveillance thermal cameras to detect the LNG leakage, which comprises background subtraction and leakage classification. However, these methods are limited in rural areas due to the lack of sensitivity and accuracy. In this article, a generalized framework, i.e., tensor-based leakage detection (TBLD), is proposed to detect LNG leakage in the rural area from surveillance thermal cameras. First, the proposed TBLD takes advantage of tensor factorization to fuse thermal image and corresponding gradient maps for improving sensitivity. Additionally, a finite-state-machine is designed to maintain leakage foreground along with the video streaming. The experiments demonstrate the robust performance of TBLD in the background subtraction stage. Second, multiple classification techniques are explored in the leakage classification stage. The results suggest that the TBLD can accurately detect the LNG leakage by applying 50 layers of residual networks (ResNet50). Finally, compared with contemporary frameworks, the TBLD has consistently improved performance concerning the different distances of LNG leakage. The experimental results demonstrate the effectiveness of the proposed TBLD, which also shows the great potential of TBLD in future industrial applications.

A quantitative LNG risk assessment model based on integrated Bayesian-Catastrophe-EPE method

Increasing quantities of natural gas are transported as liquefied natural gas (LNG) worldwide, and LNG is also proposed for use as a clean fuel for ships and trucks. This scenario raises concerns for the safety of LNG bunkering and storage at ports, due to the potentially severe accidents that may arise from LNG leakage. In this paper, an integrated quantitative risk assessment model for LNG bunkering and storage at ports based on Bayesian-Catastrophe-EPE (Energy transfer theory, Preliminary hazard analysis and Evolution tree) method was proposed. The energy-based EPE model was used to derive Bayesian network (BN) causal structure, and the catastrophe theory was employed to deal with experts’ judgment to determine the conditional probability tables of BN. The proposed BN-based risk assessment model can provide a novel perspective to identify hazards and risks, and to assess the evolution process of LNG accidents from causes to consequences. The results of scenario analysis of typical LNG accidents demonstrate the soundness and applicability of the proposed model. Moreover, sensitivity analysis was implemented to identify critical hazards and quantify the correlations between each element considered in LNG accidents. The proposed risk assessment framework is of great significance to widen the technical tools available to support safety assessment and loss prevention of LNG bunkering and storage at ports.

Numerical Simulation and Analysis of Diffusion Process for the Leakages of a Tunnel LNG Pipeline

Taking a practical project as an example, based on the computational fluid dynamics (CFD), standard k-ε model and finite element method, a mathematical model for the diffusion due to liquefied natural gas (LNG) pipeline leakage in a tunnel was established, and the diffusion process was numerically simulated for three LNG leakage cases. From the simulation results, the variation of CH4 concentration field and explosive gas cloud with time within the tunnel, and the influence of leakage location on the diffusion was analyzed for the three cases. It was shown that the variation of CH4 concentration field had a similar trend for the three cases, but the CH4 explosive gas cloud length increased rapidly with the LNG leakage intensity so that dangerous situations would occur for the medium and large leakages, and a leak location closer to air inlet would lead to a more dangerous situation. When the amount of LNG leakage in the tunnel is large, the effect of mechanical ventilation is obviously weakened. Furthermore, a nitrogen seal precaution was proposed for the situations.

Experimental and Numerical Study of Orifice Coefficient of Cargo Tank Design of LNG Vessels

Liquid cargo storage tanks of liquefied natural gas (LNG) carriers are designed by strict standards to maintain the cryogenic state (−163 °C). For most LNG cargo storage tanks, it is mandatory to install a system that can safely store leaked fluid for 15 days in the case of leakage of liquid cargo due to crack of the insulation system. To ensure safety, it is necessary to predict the amount of LNG spilling from the cracks in the insulation panels. Although international regulations are provided, they rely on a conservative and consistent coefficient. In this study, experimental and numerical methods were applied to examine the design factor used to predict the flow rate in the tank design process. To check the amount of leakage that occurs under pressure conditions of LNG tanks, an experiment was conducted using crack specimens and pressure containers filled with water. In order to simulate the leakage of LNG, the amount of leakage was predicted using the Computational Fluid Dynamics (CFD) method. The distribution of leakage quantity was investigated according to the shape of the crack through the pressure vessel experiment and the analysis. Through CFD analysis, the leakage rate of LNG was calculated for each operating pressure condition through the crack. Finally, the results of this study examined the need to identify and reconsider the coefficients due to international guidelines and other factors in calculating orifice coefficients applied to the design of LNG tanks.

Influence of welding residual stress on cryogenic materials applied to LNG fuel tanks for coastal vessels

The purpose of this paper is to investigate the influence of welding residual stress (WRS) of the liquefied natural gas (LNG) fuel tank. In general, WRS and distortions are caused by non-uniform temperature distribution by the welding heat source. This will not only cause a brittle fracture, local buckling and corrosion damage, but also adversely affect the fatigue strength of the welded structures. Since LNG is treated at cryogenic temperatures of −162[Formula: see text]C, leakage of LNG from the fuel tank to the outside may cause cracks in the hull and tank support system and cause severe damage. Therefore, it is necessary to predict the thermal behavior and WRS before welding is carried out. In this study, the WRS is calculated by thermal stress analysis based on the temperature distributions over time obtained from the transient thermal analysis. The results of this study can be used as a fundamental research for WRS analysis of plasma arc welding applied to LNG fuel tanks for coastal vessels.

Visualization and classification of hidden defects in triplex composites used in LNG carriers by active thermography

Triplex composite is an epoxy-bonded joint structure, which constitutes the secondary barrier in a liquefied natural gas (LNG) carrier. Defects in the triplex composite weaken its shear strength and may cause leakage of the LNG, thus compromising the structural integrity of the LNG carrier. This paper proposes an autonomous triplex composite inspection (ATCI) system for visualizing and classifying hidden defects in the triplex composite installed inside an LNG carrier. First, heat energy is generated on the surface of the triplex composite using halogen lamps, and the corresponding heat response is measured by an infrared (IR) camera. Next, the region of interest (ROI) is traced and noise components are removed to minimize false indications of defects. After a defect is identified, it is classified as internal void or uncured adhesive and its size and shape are quantified and visualized, respectively. The proposed ATCI system allows the fully automated and contactless detection, classification, and quantification of hidden defects inside the triplex composite. The effectiveness of the proposed ATCI system is validated using the data obtained from actual triplex composite installed in an LNG carrier membrane system.

Accidental release of Liquefied Natural Gas in a processing facility: Effect of equipment congestion level on dispersion behaviour of the flammable vapour

An accidental leakage of Liquefied Natural Gas (LNG) can occur during processes of production, storage and transportation. LNG has a complex dispersion characteristic after release into the atmosphere. This complex behaviour demands a detailed description of the scientific phenomena involved in the dispersion of the released LNG. Moreover, a fugitive LNG leakage may remain undetected in complex geometry usually in semi-confined or confined areas and is prone to fire and explosion events. To identify location of potential fire and/or explosion events, resulting from accidental leakage and dispersion of LNG, a dispersion modelling of leakage is essential. This study proposes a methodology comprising of release scenarios, credible leak size, simulation, comparison of congestion level and mass of flammable vapour for modelling the dispersion of a small leakage of LNG and its vapour in a typical layout using Computational Fluid Dynamics (CFD) approach. The methodology is applied to a case study considering a small leakage of LNG in three levels of equipment congestion. The potential fire and/or explosion hazard of small leaks is assessed considering both time dependent concentration analysis and area-based model. Mass of flammable vapour is estimated in each case and effect of equipment congestion on source terms and dispersion characteristics are analysed. The result demonstrates that the small leak of LNG can create hazardous scenarios for a fire and/or explosion event. It is also revealed that higher degree of equipment congestion increases the retention time of vapour and intensifies the formation of pockets of isolated vapour cloud. This study would help in designing appropriate leak and dispersion detection systems, effective monitoring procedures and risk assessment.

Integrated Consequence Modelling for Fire Radiation and Combustion Product Toxicity in offshore Petroleum Platform using Risk Based Approach

The processing area of offshore platform has high probability of leakage of hydrocarbons. Liquefied Natural Gas (LNG) is one of the most common hydrocarbon produced in offshore platforms. Leakage of LNG can cause pool fire, jet fire, flash fire or fire ball. Thermal radiations due to fire is the major source of damage to workers on board. But due to fire, various combustion product toxic gases are also produced that have both acute and chronic health effects. These toxic gases can cause incapacitation, increased heart rate, vomiting and even death. Predicting the human injury due to thermal radiations and concentration of toxic gases are the key issues. A risk based approach takes in to consideration the duration a worker spent on different location of offshore platform and also it has the additive ability to evaluate overall risk due to fire radiation and toxic gases. Grid based approach helps in better visualization of risk posed by fire radiation and combustion product toxic gases at different locations of platform. The current study proposed an integrated consequence modelling approach for fire and combustion product toxic gases using risk based and grid based approaches. The integrated accident is modelled using Computational Fluid Dynamics (CFD) code Fire Dynamics Simulator (FDS). The results showed that risk posed by thermal radiation is confined on sub cellar deck (lower deck) but estimated risk due to combustion product gas (carbon monoxide) on cellar deck (upper deck) has significant value that needs to be considered. The current approach would be useful for emergency preparedness plans and safety measures designs for offshore platforms.

Experimental and numerical analysis of a membrane cargo containment system for liquefied natural gas

ABSTRACTMembrane cargo containment systems (MCCS) have been developed by GTT for liquefied natural gas (LNG) tanks and proved to be an efficient technology for transportation and storage of large volumes. In regard to LNG as fuel, the current aim is to introduce MCCS as fuel tanks for merchant ships. These ships will operate in areas of high traffic density. The risk of collision and grounding cannot be neglected. The latter is bound by the deformation capacity of the inner barrier of the MCCS prior to LNG leakage. In order to contribute to the understanding of the crashworthiness, a large-scale nearly four-by-four-metre mock-up was built and tested experimentally at the Hamburg University of Technology (TUHH). These experimental results serve as a validation basis for numerical crashworthiness analysis of membrane-based cargo containment systems for LNG. In both numerical analysis and experimental testing, DNV GL has been involved.