LNG Storage Research Articles

Sloshing in liquid tank with the density function method

The Great East Japan Earthquake of March 2011 was the huge earthquake with a magnitude of 9.0 exceeding the imagination, ranging from the offshore to Iwate Prefecture to the offshore of Ibaraki Prefecture became the focal region. It is easy to imagine that damage increases to long-period earthquake ground motion as the magnitude increases. Damage to dangerous facilities due to long-period earthquake ground motion is caused by liquid surface fluctuation (sloshing) of oil, LNG and liquid storage tanks. In this paper, the interface capturing method deals with complex water surface large deformation problems. We use the density function method which is one of the effective methods of interface capturing method for numerical analysis of two phase fluid fields of gas and liquid. As a result, the proposed method shows a good agreement with the experimental result of the Martin and Moyce dam break problem, and this method improved the suppression of effortless motion. Also, under the calculation condition of the sloshing phenomenon, this method does not generate numerical diffusion. Therefore, this model is more robust than the conventional model.

Improvement of Safety and Durability of LNG Storage Tank Using Ultra-High-Performance Concrete

본 연구에서는 LNG 저장탱크의 안전성 및 내구성을 향상시키기 위해 일반 콘크리트로 건설되는 외조에 초고성능 콘크리트 (UHPC, Ultra-High-Performance Concrete)를 적용하기 위한 연구를 진행하였다. 이를 위해 일반 콘크리트와 초고성능 콘크리트를 제작하였으며, 초고성능 콘크리트의 강섬유 종류에 따른 차이를 평가하기 위해 세 종류의...

Feasibility study on the wide and long 9%Ni steel plate for use in the LNG storage inner tank shell

This study aimed to assess the feasibility on the wide and long 9%Ni steel plate for use in the LNG storage inner tank shell. First, 5-m-wide and 15-m-long 9%Ni steel plates were test manufactured from a steel mill and specimens taken from the plates were tested for strength, toughness, and flatness to verify their performance based on international standards and design specifications. Second, plates with a thickness of 10 mm and 25 mm, a width of 4.8~5.0 m, and a length of 15 m were test fabricated by subjecting to pretreatment, beveling, and roll bending resulting in a final width of 4.5~4.8 m and a length of 14.8m with fabrication errors identical to conventional plates. Third, welded specimens obtained via shield metal arc welding used for vertical welding of inner tank shell and submerged arc welding used for horizontal welding were also tested for strength, toughness and ductility. Fourth, verification of shell plate material and fabrication was followed by test erection using two 25-mm-thick, 4.5-m-wide and 14.8-m-long 9%Ni steel plates. No undesirable welding failure or deformation was found. Finally, parametric design using wide and long 9%Ni steel plates was carried out, and a simplified design method to determine the plate thickness along the shell height was proposed. The cost analysis based on the parametric design resulted in about 2% increase of steel weight; however, the construction cost was reduced about 6% due to large reduction in welding work.

Design and Strength Verification of LNG Cargo Enclosure System FSP Type

The demand for natural gas in the world is increasing day by day. The efficient and flexible LNG becomes the preferred method for natural gas storage and transportation and has gradually entered people’s daily life. The enclosure system is the key core of LNG transport and storage vessels for storage of LNG at -163°C for isolation and thermal insulation. A new type of flat half-film prismatic LNG enclosure system has been developed for the shortcomings of the existing LNG cargo enclosure system. Through the breakthrough and mastery of key core technologies such as the overall layout and integration of the system, anti-leakage technology, liquid tank fixing technology, and large-scale friction stir welding (P-FSW) flat-line pipeline development technology, we’ll strive to fill the gap in the intelligent construction technology of large aluminum alloy tanks in China. The tank was subjected to water vapor test and numerical simulation. The results show that the structural strength of the FSP-LNG tank meets the strength check standard of IGC Code.

ЗАБЕЗПЕЧЕННЯ НАДІЙНОЇ ЕКСПЛУАТАЦІЇ НАФТОВИХ РЕЗЕРВУАРІВ У СКЛАДНИХ ГЕОТЕХНІЧНИХ УМОВАХ ПРИ СЕЙСМІЧНИХ ВПЛИВАХ

ЗАБЕЗПЕЧЕННЯ НАДІЙНОЇ ЕКСПЛУАТАЦІЇ НАФТОВИХ РЕЗЕРВУАРІВ У СКЛАДНИХ ГЕОТЕХНІЧНИХ УМОВАХ ПРИ СЕЙСМІЧНИХ ВПЛИВАХ

Static and Cryogenic Performance Evaluation of 2400 MPa PT Anchorage System for Applying LNG Storage Tank

In this paper, the static and cryogenic performance of the 2400 MPa PT anchorage system was evaluated in accordance with the ETAG013 standard in order to securely apply the 2400 MPa PS strand to the “I” LNG storage tank. The results of the static load test showed that the measured maximum load was 95.9% of the actual ultimate tensile load of the tendon, and the total elongation of the tendon at the maximum load was 2.36%. The cryogenic static load test results showed that the 2400 MPa PT anchorage system safely resists cyclic loading of the 80-100% characteristic yield load of the tendon in the cryogenic environment of -196 ℃, and the measured maximum load was 96.1% of the actual ultimate tensile load of the tendon. As a result, the static and cryogenic performance of the 2400 MPa PT anchorage system satisfied the ETAG013 standard. Keywords: Anchorage System, Post-tension, 2400MPa Prestressing Strand, Static Load Test, Cryogenic Static Load Test

Development of Construction Technique of LNG Storage Tank Wall Using Precast Concrete Panels

The conventional LNG storage tank wall has been constructed with cast-in-place (CIP) concrete method. However, CIP method is difficult for construction management because it is significantly affected by conditions of construction site, such as climate and material supply conditions. Therefore, this construction method consumes construction time and cost. Recently, to reduce the construction time, various construction methods, such as jump-form and slip-form method [1], are being applied to the LNG storage tank wall. But, There is a limit that construction of the inner tank has to be conducted after the construction of outer tank wall is completed. Meanwhile, precast concrete (PC) method has some different characteristics compared with that of CIP method. In the PC method, structural members are previously manufactured at a factory and transported to the construction site to be assembled. There are advantages which are reduction of construction time and cost and improvement on quality control and durability. The main objectives of this paper are to introduce a new construction technique for LNG storage tank wall using PC panels to overcome the existing limitations, and discuss the benefits of the technology. In addition, to verify the applicability of the new construction technique, a mock-up test was conducted considering PC panels.

A Study on Safety Assessment of Leakage of Small LNG Storage Facility Considering Numerical Simulation of Rollover Phenomena Using Vapor-Liquid Equilibrium at Cryogenic Fluid Interface

The share of natural gas as an energy source is gradually increasing, and natural gas has an important role as major energy source role that consumes more than 15% of the total energy consumption. In case of LNG, there is an increasing demand due to the advantage of cleanliness, convenience and economy of natural gas and also, demand for the small LNG storage facilities for fuel supplying LNG fuelled vessels, LNG cars and buses is increasing rapidly. In this study, we analyze the rollover case, which is the biggest LNG leakage accident in small LNG storage facility, by using Vapor- Liquid Equilibrium at the cryogenic fluid interface. Using this calculated results, we evaluate the accident impact by prediction and analysis of leakage damage in small LNG storage facility and examine the safety assessment for facilities to be constructed in the future.

Non-contact strain measurement for laterally loaded steel plate using LiDAR point cloud displacement data

Strain measurement in structures provides key information for structural health monitoring (SHM); therefore, researchers have developed various sensing methods for measuring strain in structures. Recently, light detection and ranging (LiDAR) has been studied as a non-contact strain measurement method (NCSMM). LiDAR is a technology for remotely acquiring high precision three-dimensional (3D) coordinate information for a terrain or a structure using a 3D laser scanning system. In recent years, LiDAR applications have expanded to include systems used to monitor structural behavior. Using this technology, structural behavior can be monitored without directly attaching sensors to the surfaces of target structures. It is advantageous to use non-contact 3D laser scanning measuring methods to obtain the 3D coordinates of a specific region or the shape of the target structures. LiDAR technology does not have some of the limitations associated with existing types of measuring sensors used for SHM. Therefore, in this study, we will present a method for estimating deformation and strains for a whole structure by measuring discretized 3D coordinate data of the target structure obtained from the LiDAR. The 3D coordinate data was revised using a regression analysis, and the strain was estimated by developing a finite element model based on the corrected 3D coordinate information. The experimental structural model is a steel plate, which is the primary material used for the outer wall construction of LNG storage tanks. The estimated strains will be compared to the measured values from real strain gauges, and the applicability of the proposed strain measurement method to structural behavior monitoring will be verified.

Determining the BTR by conducting a Trans-Varestraint test using a high-speed camera and two-color pyrometry

The Ni-Fe alloy consumable that applies to the welding of 9% nickel steel for LNG storage tanks is highly susceptible to solidification cracks. To evaluate susceptibilities such as the brittleness temperature range (BTR), a Trans-Varestraint test is generally conducted. However, it is difficult to evaluate the minimum strain value for the BTR and the real temperature at both ends of a solidification crack in a conventional Trans-Varestraint test because these values are measured indirectly. In this study, we propose determining the temperature range by conducting in-situ observations during a Trans-Varestraint test using a high-speed camera and two-color pyrometry so that the temperature range can be measured directly from the temperatures at both ends of the crack. Furthermore, we measured the augmented strain from the time elapsed since the initiation of bending. This method allowed us to successfully measure the augmented strain and the temperature range in the Trans-Varestraint test and to determine the BTR more accurately.

A design algorithm used for the roof frame and liner system of extra-large LNG storage tanks

The design of roof frame is one of the most important parts of LNG tank design. In China, however, the calculation of roof frame system of extra-large LNG tanks is currently faced with a series of problems. For example, there is no united yardstick on buckling characteristic value, the calculation is based on many assumptions, and the calculation is inconsistent with domestic specifications and stipulations. In view of these problems, the material non-linearity and structural non-linearity were introduced and the initial defect was taken into consideration. Then, the large non-linear finite element calculation software ABAQUS was adopted to carry out modeling on the roof frame and liner system of extra-large LNG tanks and calculate and analyze the force applied on them and their stability. Finally, a complete set of design algorithm for the roof frame and liner system of extra-large LNG tanks was established and applied to the design of a certain LNG tank (20 × 104 m3) in China. It is indicated that this design algorithm can simulate the actual situations accurately. This design algorithm is structurally composed of shell units and beam units, and it is connected in the pattern of common node. Besides, force calculation is conducted in 10 operational modes and the buckling calculation in 7 operational modes, including all operational modes in the construction process of roof frame and liner system of LNG tanks. It is also revealed that the maximum stress on the roof frame is 125.7 MPa, that on the liner is 101.4 MPa and the minimum safety coefficient used for buckling calculation is 2.57. Under this system, the force and stability of the roof frame of LNG tanks are satisfactory. The research results can be used as reference for relevant design and calculation.

Structural Health Monitoring of Offshore Buoyant Leg Storage and Regasification Platform: Experimental Investigations

Offshore platforms are of high strategic importance, whose preventive maintenance is on top priority. Buoyant Leg Storage and Regasification Platforms (BLSRP) are special of its kind as they handle LNG storage and processing, which are highly hazardous. Implementation of structural health monitoring (SHM) to offshore platforms ensures safe operability and structural integrity. Prospective damages on the offshore platforms under rare events can be readily identified by deploying dense array of sensors. A novel scheme of deploying wireless sensor network is experimentally investigated on an offshore BLSRP, including postulated failure modes that arise from tether failure. Response of the scaled model under wave loads is acquired by both wired and wireless sensors to validate the proposed scheme. Proposed wireless sensor network is used to trigger alert monitoring to communicate the unwarranted response of the deck and buoyant legs under the postulated failure modes. SHM triggers the alert mechanisms on exceedance of the measured data with that of the preset threshold values; alert mechanisms used in the present study include email alert and message pop-up to the validated user accounts. Presented study is a prima facie of SHM application to offshore platforms, successfully demonstrated in lab scale.

LNG bunkering pontoons on inland waters in China

LNG bunkering pontoons are presented to solve the fueling difficulty of LNG ships on inland waterways with a great variation of water height and channel width by seasonal change. First, the background of this concept was analyzed as well as the demand of LNG bunkering pontoons, and the involved idea of levels management. Then, from the safety barrier perspective, safety design principles were discussed, the safety principles and implement measures of LNG storage were provided, LNG tanks for the pontoon were analyzed in detail in terms of their types, design pressure, material selection and leakage protection principles. Also, the safety concerns of LNG supply and bunkering process were raised, and an improved handy bunkering arm & hose, lighter and more flexible than ever before, was introduced. Berthing and unberthing are related to the survival of the pontoon so that the key points of such design were highlighted. It is concluded that (1) based on the levels management, the pontoon equipped with IMO Type C tanks, with reasonable berthing/unberthing and safety designs adopted, is proved to be safe and reliable by practices; (2) by 2025, nearly 30 such improved LNG bunkering pontoons with a fueling capacity of 500 m3 each will be required on Yangtze and Pearl Rivers; and (3) the pontoon's safety and reliability has been verified by practices and its fourth generation has been developed.

Temperature change around a LNG storage predicted by a three-dimensional indirect BEM with a hybrid integration scheme

We employ a three-dimensional indirect boundary element method (BEM) to simulate temperature change around an underground liquefied natural gas storage cavern. The indirect BEM (IBEM) uses fictitious heat source strength on boundary elements as basic variables which are solved from equations of boundary conditions and then used to compute the temperature change at other points in the considered problem domain. The IBEM requires evaluation of singular integration for temperature change due to heat conduction from a constant heat source on a planar (triangular) region. The singularity can be eliminated by a semi-analytical integration scheme. However, it is found that the semi-analytical integration scheme yields sharp temperature gradient for points close to vertices of triangle. This affects the accuracy of heat flux, if they are evaluated by finite difference method at these points. This difficulty can be overcome by a combination of using a direct numerical integration for these points and the semi-analytical scheme for other points distance away from the vertices. The IBEM and the hybrid integration scheme have been verified with an analytic solution and then used to the application of the underground storage.

Fuzzy FMECA (failure mode effect and criticality analysis) of LNG storage facility

In high hazard industries like nuclear and chemical, a failure could lead to catastrophic events resulting in multiple fatalities, significant economic loss and reputation damage. Failure Mode and Effects Analysis (FMEA) is a safety and reliability analysis tool that systematically identifies the consequences of component failure on systems and determines the significance of each failure mode with regard to the system performance. FMEA uses a Risk Priority Number (RPN) for ranking the failure modes. RPN is commonly calculated as the product of the risk factors occurrence (O), severity (S) and non-detection (D) of the failure modes. When FMEA is used in criticality analysis of failure modes of components, it is also referred to as failure mode effect and criticality analysis (FMECA). Many researchers have pointed out the deficiencies of conventional risk priority number (RPN) used in FMEA. This paper describes a method for developing a fuzzy RPN (FRPN) that may rectify the limitations cited in the literature such as questionable nature of the mathematical formula for calculating RPN and the difficulties in prioritizing the RPN in the case of complex systems due to identical RPN values for different failure modes.The analysis was carried out by using fuzzy linguistic variables for occurrence, severity and non-detection and then using an if-then rule base to interconnect these variables to reach FRPN. The results obtained by using traditional FMECA and the fuzzy FMECA methods are compared. The difficulty in prioritizing the RPN in the case of complex systems such as LNG storage has been addressed in fuzzy FMECA.

A Study on the Cathodic Protection Design Optimization of Steel Piles for LNG Storage Tanks by Numerical Analysis

A Study on the Cathodic Protection Design Optimization of Steel Piles for LNG Storage Tanks by Numerical Analysis

Shock Response Analysis of a Large LNG Storage Tank Under Blast Loads

Ensuring the safe operation of large LNG storage tank projects under blast loads is very important. First, using LS-DYNA software, numerical simulations of air blast wave propagation are studied with the ALE algorithm and fluid-solid coupling theory. A new corrected formula for the peak overpressure is proposed based on the numerical results, and its accuracy is verified by comparing the numerical results with the empirical formula and test results. Then, a finite element model of a large LNG storage tank is built, assuming that the explosion source is located 10 m away from both the ground and the tank wall. This model is used to analyse the overpressure and dynamic response of the outer concrete tank and to predict the TNT equivalent quantity that the tank can withstand. The results show that the tank wall facing the burst loads is in a more dangerous state and that the principal tensile stress increases approximately linearly with increasing TNT equivalent quantity. When the TNT equivalent quantity reaches 2.5 t, concrete element failure occurs on the centre facing the explosions, and the outer tank structure is damaged. The conclusions can provide a reference for the blast-resistant design of large LNG storage tanks.

Dual Reutilization of LNG Cryogenic Energy and Thermal Waste Energy with Organic Rankine Cycle in Marine Applications

LNG is a promising alternative fuel at competitive price [1]. The LNG market is set to increase by 50% between 2017 and 2020. The worldwide fleet of LNG powered vessels is now expanding rapidly and the increasing number of LNG terminals are planned and constructed at major ports around the world. This study proposes a new Organic Rankine Cycle (ORC) with LNG Direct Expansion (DE) for the reutilization of the cryogenic energy within LNG storage tanks and potential waste thermal energy from various sources in the marine context. The proposed ORC system is designed in terms of the field testing data from a real marine application and analysed through dynamic simulation using Siemens LMS Imagine.Lab AMESim. Three optimal working fluids are examined on high vacuum and above atmospheric condensing pressures in the temperature range of -110˚C and 300˚C. The proposed ORC system is characterized by a significant improvement in thermal efficiency and power production in comparison of the existing ORC systems driven by waste thermal energy.

Selection of representative accident scenarios for major industrial accidents

Abstract This paper analyzes the problems with selecting representative accident scenarios, which are understood as the maximum credible accidents for major industrial accidents. The selection process is based on the risk ranking scheme, which is applicable to all potential accident scenarios identified during the process hazard analysis (PHA) for a major hazard plant. Unfortunately, the process implies a substantial level of uncertainty due to incomplete and vague information concerning the assessment of the frequency and severity of the categories required for the risk ranking matrix as well as the lack of data reflecting the impact of the layer of protection on those categories. In most cases, the uncertainty is caused by insufficient knowledge and experience of the PHA team. This uncertainty usually affects the credibility of the accident scenario identification process and, by the same token, results in underestimation or overestimation of the process risk level. To address all knowledge-based uncertainties, a new approach for the identification of representative accident scenarios is proposed. This approach consists of the inclusion of a semi-quantitative assessment of the safety performance of protection layers combined with a fuzzy logic approach to risk ranking assessment. The proposed methodology may be successfully used for any major hazard industry; a case study for the fictional model of LNG storage facilities is presented here. Preliminary tests confirmed that the final results of the risk index were determined in a more precise and realistic manner.

Research on maximum explosion overpressure in LNG storage tank areas

Maximum explosion overpressure is an important index in combustible gas explosions for safety managers and fire rescue commanders. The main factors affecting the maximum explosion overpressure in an LNG tank area were deduced by a series of reduced-scale tests. A correlation of maximum explosion overpressure in LNG tank area was developed based on the momentum conservation equation and the deduced factors in the explosion tests. The parameters in the correlation were fitted by FLACS simulations of explosions of different LNG storage tank areas. Compared with traditional methods such as the TNO Multi-Energy method and Baker-Strehlow method, this correlation is targeted to the scenario of LNG leaking from the joint of a pipeline and the tank top, which may be the most probable type of leak in LNG tank areas. The correlation was verified by five FLACS simulation cases of the LNG tank areas with tank radii of 10 m, 20 m, 30 m, 40 m and 50 m. Comparing the overpressures calculated with FLACS and the correlation, there are fewer relative deviations when the radii of tanks are larger. LNG tanks with a radius greater than 40 m have been widely developed in recent years, and the relative deviation of the correlation and FLACS greater than this size is less than 6.6%. The maximum overpressure of the test scale explosion obtained from the correlation is 326.09 Pa. It is close to 389 Pa, which is the maximum tested overpressure in this paper. This correlation can be used as a reference for LNG tank area safety managers, fire rescue commanders and researchers.