LNG Storage Tank Research Articles

Development and Evaluation of Stainless Steel-Base Flux-Cored Wires for 9% Nickel Steel

The demand for LNG fueled tank on ship is growing in accordance with the IMO 2020 regulation. The 9% nickel steel has been used for LNG storage tank because this material has higher tensile strength than the other materials in the IGF code. The nickel-based alloy type welding consumable has been applied on 9% nickel steel welding because of good toughness at cryogenic environment and high tensile property. However that welding consumable has disadvantages of high price and poor weldability. In this study, new stainless steel-based flux-cored wire is developed for 9% nickel steel and mechanical properties are satisfied Class requirement. Additionally, fatigue, FCGR and CTOD test had been carried out to verify structure design suitability.

Seismic Response of a Large LNG Storage Tank Based on a Shaking Table Test

In order to study the dynamic response of the LNG storage tank under the action of seismic load and the seismic isolation effect of the lead-core rubber bearing, this paper establishes the experimental storage tank model with reference to the structural form of the large-scale LNG storage tank, and the seismic response of the test tank is obtained using a shaking table test. Simplified mechanical models of non-isolated and isolated storage tanks are proposed and the seismic responses of the corresponding storage tanks are calculated using the Newmark-beta method. Under the action of seismic waves with different acceleration peaks, the results show that (a) more excitation directions of the seismic wave can lead to the greater acceleration and displacement response of the tank and (b) the isolation bearing has a damping effect on the acceleration response of the storage tank, but it has an amplifying effect on the displacement of the storage tank. Comparing the results of the simplified model and the shaking table test, it is found that the change trend of the acceleration response of the experimental results and simplified mechanical models is the same. The spectral characteristic curve of them is not large, which verifies the effectiveness of the simplified model.

A Study on the Development of an Optimization Algorithm and Determination Procedure for Toughness Deterioration Characteristics through Flux Core Arc Heat Input Control of ASTM A553-1 (9% Nickel Steel)

The International Maritime Organization has adopted the reduction of carbon dioxide emissions from ships as an important priority, and is continuously strengthening its regulations on marine air pollution. By 2035, it is expected that LNG-powered ships will account for more than 50% of the available ships. Accordingly, the demand for equipment related to LNG-fueled ships is expected to grow as well, requiring the development of a lot of equipment. However, the characteristics of LNG-powered ships mean that they require a high level of reliability and long history of operating reliably. Even when a product is developed, numerous demonstrations and quality assurance measures are needed to reach the technological level ship owners and customers require. Therefore, an optimization procedure to determine the welding quality for 9% Ni steel is necessary. In this study, the heat input criteria that induce brittle fracture characteristics were analyzed to optimize the flux core arc welding process for 9% Ni steel used in the manufacture of LNG storage tanks. We developed an optimization algorithm (Welding Current, Arc Voltage, Welding Speed) that can select a group of fracture conditions by examining the tendency of the tissue to brittle fracture due to excessive heat input among potential quality issues of cryogenic steel. Capable of selecting the range in which quality deterioration occurs, determining quality of a weld and avoiding the range in which toughness degradation occurs, through which a process to derive high quality 9% Ni welds is proposed.

A study on microstructural and mechanical properties of gas tungsten arc welded thick cryogenic 9% Ni alloy steel butt joint

Low alloy steel plates containing 9% Ni are generally preferred in the production of LNG storage tanks, due to their outstanding combination of properties such as excellent toughness, high ductility and crack resistance at very low temperatures. Welding is an indispensable manufacturing method in the production of LNG storage tanks. Thus, there is a need for reliable welding procedures which do not diminish low temperature properties of this steel grade. This study introduces the result of microstructural evolution in the weld region and the mechanical properties of the gas tungsten arc welded 10 mm thick 9 Ni steel joint produced by using a Ni-based filler wire, which is widely used in LNG storage tanks. The microstructures evolved in the weld region were examined by extensive optical microscopy and SEM investigations. Mechanical properties and joint performance values of the welded joints were determined by detailed microhardness measurements and transverse tensile tests. Moreover, fracture toughness of the joint fabricated was also determined at − 196 °C by Charpy V-notch test.

Safety assessment of large-scale all steel LNG storage tanks under wind-borne missile impact

Regarding the disastrous consequences, the large-scale all steel liquefied natural gas (LAS-LNG) storage tank is regulated to be designed to resist the potential impact of wind-borne missiles. This paper aims to study the dynamic response and damage of LAS-LNG storage tanks subjected to the accidental typical wind-borne missile impact. Firstly, six Schedule 40 pipe and flange assembly missiles weigh 36.5 kg were designed according to the specifications of BS 7777 and RG 1.76. Based on the 300 mm-caliber single-stage gas gun, the impact test was conducted with a missile striking velocity of 50 m/s. The local deformation and global response of media-filled steel tanks were assessed experimentally. Then, the commercial finite element (FE) program LS-DYNA was utilized to perform the numerical simulations considering the fluid–structure interactions. The adopted numerical algorithm, constitutive models and the corresponding parameters were validated by comparing with the test data. Finally, based on the validated finite element analyses approach, regarding the design-basis wind-borne missiles specified by the regulatory guide of U.S. Nuclear Regulatory Commission and American Nuclear Society, i.e., RG 1.76, RG 1.221 and ANSI/ANS-2.3-2011, the damage levels of the prototype Chinese Yuhuan LAS-LNG storage tank under wind-borne missile impact were assessed numerically. It indicates that the filled media in the tank would provide additional resistance to the missile impact, the present three design-basis wind-borne missiles could bring certain damage to the outer tank of the Yuhuan LNG storage, but the safety of the inner tank can be guaranteed.

Analysis of a new underwater LNG storage tank

The article presents the current disadvantages of onshore LNG tanks used in the Arctic. A critical analysis of the closest analogue – a floating LNG storage of gravity type - was carried out. On the basis of the results of the critical analysis a completely new design of an underwater LNG storage was offered. Also the principles of submergence and exploitation of the storage were described. The conclusion about the opportunity of application of underwater tank farms was made.

An adaptive defect detection method for LNG storage tank insulation layer based on visual saliency

As the core equipment of the industrial chain, the LNG storage tank is developing in the direction of large-scale and increasing attention has been paid to its economy and safety. The defects of the insulation layer not only affect the insulation performance of the tank but also easily induce safety accidents. To automatically detect these defects, considering the large temperature difference between the defect area and other areas, an adaptive detection method based on infrared thermal imaging technology and a saliency detection algorithm is proposed. Firstly, the median filtering and the Contrast Limited Adaptive Histogram (CLAHE) are introduced to reduce noise and smooth the image. Then, the Adaptive Simple Linear Iterative Clustering algorithm (A-SLIC) based on the entropy of the image is purposed for super-pixel segmentation. After super-pixel segmentation, the saliency map is obtained by manifold ranking, and the salient areas that contain defects of the insulation layer will be segmented automatically. The proposed method is compared with other traditional algorithms on the MSRA1000 dataset and the infrared thermal imaging dataset of LNG storage tanks. The results of the experiments illustrate the effectiveness of the method proposed.

Essential design criteria for safe and efficient operation of an LNG boil-off gas reliquefier under deteriorated performance of system components

Reverse Brayton cycle (RBC) working with nitrogen is used to reliquefy the boil-off gas (BOG) generated in LNG storage tanks. The reliquefier consumes relatively low power if the heat exchanger surface area and the operating parameters are optimally chosen. However, these parameters depend on the isentropic efficiencies of the compressors and turbine that show degradation over years of operation. This paper attempts to find a way to maintain efficient and safe operation of the system even with deteriorated efficiencies of compressor and turbine. The analysis shows that while deterioration of compression system can be made up by applications of variable frequency drive and inlet guide vanes keeping the reliquefaction quantity unaltered, the deterioration of turbine efficiency demands that the pressure ratio of the compressor system should be higher. If appropriate flexibility is incorporated right at the design stage, a reliquefier can be re-adjusted to mitigate the system deterioration. If the isentropic efficiency turbine deteriorates from 90% to 75%, the pressure ratio of nitrogen compressor has to be increased from 3.7 to 4.7 to mitigate increased power input to the reliquefier by as much as 310 kW for a ship carrying 266,000 m3 of LNG.

A novel high-efficient welding technology with rotating arc assisted by laser and its application for cryogenic steels

To obtain high efficiency and good weld quality for medium thick steel plates, a novel welding technology of hybrid arc laser welding was proposed through rotating arc assisted by laser. Rotating arc provides heat to melt feeding wire and groove for high deposition and good fusion. Laser is helpful not only to arc rotating, but also to molten pool mixing. The proposed welding technology was used in the application of 9% Ni steel with medium thickness in the field of LNG storage tanks. The 21 mm thick steel plates were successfully achieved with only 2 welding passes. The weld formation was well-qualified, and no defects can be observed. The droplet transfer, keyhole and molten pool flow were investigated with high-speed camera and electric signal analysis. Experimental results showed that the droplet transferred in periodic alternation pattern of rotating spray transfer mode and short-circuit transfer mode. The laser keyhole kept stable during the droplet transfer process. The molten pool was fully mixed under the coupling effect of the arc, droplet and laser beam. The weld metal was in homogenous composition. Low temperature (−196 °C) impact energy of weld metal center and fusion line were much higher than related requirements. Obvious dimples on the fracture surface indicated that the fracture mechanism was in ductile fracture mode. Research results provided a theoretical basis for efficient construction and safe service of LNG containers made by cryogenic Ni steel.

An analytical method for the thermo-mechanics coupling study of thin-walled spherical shell structure

For large LNG storage tanks, the thermal load has a very important influence on the failure mode of the thin-walled spherical dome. However, the traditional calculation of thermal stress is very complicated for the spherical shell. To obtain an analytic solution with a simple expression, an approximate method was proposed in this paper. The mechanical behaviour caused by the temperature difference is divided into two parts, i.e. the thermal strain directly acting on the shell and the binding force exerted by the boundary. The thickness is ignored in the calculation of deflection caused by boundary constraints. Then, its accuracy was verified by a linear elastic numerical model. Furthermore, the crack pattern in a nonlinear plastic simulation was also well captured. The case study shows that the thermal-induced meridional cracks distribute uniformly along the circumferential direction; these cracks first appeared on the inner surface at the edge of the tank dome, and then rapidly expand to the centre and outer surface; increasing the amount of reinforcement cannot effectively limit the development of such cracks.

Real-time hybrid test of a LNG storage tank with a variable curvature friction pendulum system

Real-time hybrid test of a LNG storage tank with a variable curvature friction pendulum system

Numerical simulations of base-isolated LNG storage tanks subjected to large commercial aircraft crash

LNG storage tanks are specified to be designed to withstand the impact of large commercial aircraft, while the existing studies refer to the safety assessment of the base-isolated LNG storage tank are quite limited. At present firstly, the detailed finite element (FE) models of LNG storage tanks are established. Based on the scaled tests of RC slabs under the impact of deformable and non-deformable projectiles, the numerical algorithm, constitutive model and the corresponding parameters of concrete are validated, which can both reproduce the behaviors of bending and punching shear failure potential induced by the aircraft impact. Then, the energy dissipation capacities and relative constitutive model of isolation systems are evaluated and validated. The reliable FE models of base-isolated LNG storage tanks with three typical isolation systems are established Furthermore, by adopting the missile–target coupled method, the dynamic responses and damage failure of tanks under aircraft impact are assessed, it derives that, (i) the fuselage and engines impact regions of tank wall are locally perforated and penetrated, the connection between the inner steel wall and deck is torn, and the safety of tanks is hard to be guaranteed; (ii) the selection isolation systems have sufficient lateral stiffness to resist the excessive global deformation of the base-isolated LNG storage tanks under aircraft impact, different types of isolation systems and boundary conditions of tanks have slight influence on the local damage of tank wall. The present work could provide beneficial guidances for the design and safety assessment of the base-isolated large-scale LNG storage tanks under aircraft collisions.

Simulation Production Planning and Scheduling of Joint Lifting LNG for Maximizing Netback Revenue at Badak LNG Plant

The Multi-Supply & Seller mechanism with Multi-Buyers in Badak LNG Plant there will be several obstacles tomeet with requirementof each sales contract, the fluctuate requirement of each buyers, changes in shipping schedules caused by problems at the plant and ship, and flexibility to move LNG cargo are expected to cause problems in planning and scheduling. Furthermore, this situation will be complicate by the limited plant capacity, storage tanks, and the ship availability on the seller or buyer side. Theobjective for this study to obtain a pattern change of netback revenue for gas producers by changing the LNG shipping schedule from the planned schedule (“Planned Schedule”) compared to the deviation from planned shipping schedule (“Deviation from Planned Schedule”) and LNG prices. Simulation methods will developed to correlate within gas production capacity, LNG production capacity, LNG inventory in LNG storage tanks, LNG carriers and LNG shipping schedules in both the Planned Schedule and Deviation from Planned Schedule. This simulation will resulted the effects of changes in shipping schedules and changes in LNG prices on the netback revenue of each gas producer.The netback revenue from LNG sales for each scenario Planned Schedule and Deviation from Planned Schedule has shown that using the fluctuation of LNG price for one year in Q1 and Q4 of the following year is more better due to LNG demand is higher on winter season.

Calculation and Analysis of Influencing Factors of Daily Evaporation Rate for Large LNG Storage Tank

Because LNG has the advantages of high calorific value, low pollution and low price, this clean, high-quality fuel has attracted more and more attention from all walks of life. In recent years, LNG technology has developed rapidly, and the scale of installations has gradually increased, and a complete system project for LNG production and storage has been formed. The safe storage of LNG is vital to the development of the industry. The evaporation of LNG in the tank caused by the inflow of environmental heat is an important cause of overpressure and stratification and rollover in the tank, and affects the safe operation of the storage tank. Therefore, it is necessary to study the daily evaporation rate of the LNG storage tank and its influencing factors. Through the analysis of the cooling structure and heat exchange process of LNG storage tanks, a calculation method for heat leakage and daily evaporation rate of large LNG storage tanks is given, and the influence of solar radiation on the heat leakage of storage tanks is comprehensively considered. Taking a 30,000 cubic meter LNG storage tank as an example, the daily evaporation rate and influencing factors are calculated and analyzed. The results show that: (1) Daily evaporation rate of the LNG storage tank meets the relevant national design requirements. (2) The environmental temperature and full rate has a greater impact on the daily evaporation rate, and the environmental wind speed has a small impact on the daily evaporation rate. The calculation of the daily evaporation rate of the LNG storage tank and the analysis of influencing factors can provide a theoretical basis for the cold storage design and safe operation of the storage tank.

LNG 저장탱크 재액화용 LNG Sub-Cooler 및 N2 Pre-Cooler 열전달 특성 및 구조안정성 해석

In this study, the heat transfer characteristics - in accordance with the operating conditions - of the heat exchanger for re-liquefaction of LNG storage tanks is analyzed. The heat transfer characteristics and structural stability were analyzed for each of the sub-cooler and pre-cooler, which uses an LNG fluid and an N2 fluid respectively. The N2 fluid is used in the actual experiment. Considering the efficiency and cost of the calculation, 1/25 and 1/49 reduced models were used for the number of pipes; the temperature difference among pipes at the outlet was less than 5%. Hence it was confirmed that the analysis of the reduced model was reasonable. Comparing with the one-dimensional analysis results, a discrepancy from 2.2% to 7.4% could be confirmed. By visualizing the flow field through the computational fluid cynamics (CFD) analysis, the cause of inefficiency could be identified. The analysis results will be helpful in understanding the exact performance of the heat exchanger by predicting the design variables in the future.

Numerical simulation of natural convection and boil-off in a small size pressurized LNG storage tank

A numerical simulation of the flow of LNG stored in a small-sized cylindrical tank is presented. The main scope of this work is to characterize the heat ingress to the tank as well as the boil-off rate, depending on the filling level and the insulation layer thickness. The tank is assumed to be in a state of inactivity, such that the fluid phases are initially quiescent and are not released to the exterior. The proposed mathematical model consists of a conjugate heat transfer problem coupled with the SST K−ω turbulence model for the fluid phases. The free surface separating liquid and vapor in the tank is tracked using the Volume of Fluid method (VOF). The model is solved using the software ANSYS Fluent. It is shown that the filling level of the tank substantially influences the boiling rate and the degree of stratification, as well as the flow structures generated by free convection. The relation among the insulation thickness and total heat leak is established, showing that the obtained increased heat ingress due to lower insulation thickness values leads to a rise in pressurization and boil-off rates.

Analysis of residual stress in welding parts of cryogenic materials for LNG storage tank

Research in LNG fueled ships are actively underway in the world. Accordingly, various materials were widely used as materials for storage tanks for ultra-low temperatures, and high manganese steel for ultra-low temperature was recently developed. In this paper, the transient thermal and residual stress analysis of the welding of 9% nickel steel and high manganese steel are presented. 9% nickel steel tended to have higher transverse direction stress and longitudinal direction stress than high manganese steel.

Research on Safety Spacing of Chemical Storage Tanks Based on Accident Consequence and Risk Analysis

The placement of chemical storage tanks is an important topic in industrial safety, and its placement method is based on the study of the safety spacing of storage tanks. This paper takes LPG and LNG storage tanks as examples. It uses vapor cloud explosions, pool fires, pressure vessel explosions, boiling liquid expansion vapor explosions and other fire and explosion accident consequences models and risk probability analysis methods to analyze. It is proved that the transfer of storage tanks from ground to underground can significantly reduce the scope of impact of explosion accidents, thereby increasing the utilization rate of industrial land.

Wall superheat at the incipient nucleate boiling condition for natural and forced convection: A CFD approach

Predicting onset of nucleate boiling is important in many process design applications. Analytical models proposed in the literature to predict the wall superheat at incipient nucleate boiling fail to account for different fluid-surface combinations and flow conditions. A Computational Fluid Dynamics (CFD) based analysis is undertaken in this study to formulate fluid independent general correlations to predict the wall superheat at incipient nucleate boiling for natural and forced convection systems. The proposed CFD based correlations encompass different fluid-surface combinations and a wide range of flow conditions. The wall superheat estimates from the developed correlations are in good agreement with available experimental data. Case studies on insulation design to prevent bubble formation in an LNG storage tank and estimating the length of a heating section prior to the advent of nucleate boiling in a heat transfer equipment are presented to demonstrate applicability of the proposed correlations.

Predictive analysis for risk of fire and explosion of LNG storage tanks by fuzzy Bayesian network

This paper presents a model of predicting the risk of storage tanks fire and explosion (STFE). Bow tie analysis is used to represent causes and consequences of STFE. Fuzzy set theory, however, is used to quantify occurrence probabilities of STFE. Bayesian Networks (BN) is utilised to quantify the occurrence probabilities (Poc) of intermediate events, top event and consequences of STFE. Also, the evaluation of consequences probabilities is based on the fuzzy probabilities for events. The most obvious finding to emerge from this study is that the combination of bow tie and fuzzy logic with Bayesian network is a very effective method. Either, to confirm the proposed method effectiveness, a case study is provided.