• Journal of Advanced Marine Engineering and Technology
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• v.21 no.1
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• pp.49-58
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• 1997

The membrane type LNG tank is non self-supporting tank which consists of both primary and secondary membrane supported through the insulation boxes by the adjacent hull struc¬ture. Although the membranes are not structural member. They are subject to periodical cyclic loads due to the thermal expansion and other expansions or contraction of membrane. At the design stage of the tank, an analytical and experimental approach on the fatigue strengths of membrane and its welds is necessary in order to assist the designer and the inpector. In this study the evaluation method of fatigue strength of membrane type LNG tank is pre¬sented with FEM analysis and fatigue test of lap welds and it contains the following:1) The fatigue tests and preparation of design S - N curve for lap welds 2) FEM analysis of test specimens 3) Estimation of cumulative damage factor of lap welds 4) Guideline for inspection of lap welds of membrane type LNG tank As the results of analytical and experimental approaches in this study, the evaluation method of fatigue strengths of membrane type LNG tank is proposed, which is expected to be useful for design and inspection of membrane type LNG tank.

• International Journal of Aerospace System Engineering
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• v.2 no.2
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• pp.34-39
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• 2015

Experimental studies were conducted on the liquid sloshing characteristics in a spherical tank covered with a flexible membrane. A spherical acrylic tank with 145.2 mm in radius was used as a test tank, and it was half-filled with water. Silicon membranes with 0.2 mm thickness were used as a test membrane with plane or hemispherical types. The test tank was harmonically excited in a vertical direction by an electro-dynamic exciter. In this case, a parametric instability vibration comes up when the excitation frequency is twice the natural frequency. Parametric instability regions of natural modes were measured for three cases, i.e. liquid surface is free, covered with plane membrane and hemi-spherical membrane.

• Journal of Ocean Engineering and Technology
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• v.31 no.2
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• pp.91-102
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• 2017

Recently, a new type of LNG membrane Tank called the "KC-1 membrane LNG Tank" was developed by KOGAS (Korean Gas Corporation). It is necessary to estimate the temperature distribution of the hull structure and insulation system for this new LNG tank, as well as the BOR (Boil-Off Rate) when exposed to outside temperature conditions to ensure the integrity of the tank structure and limit LNG evaporation, from a safety evaluation point of view. In this study, temperature distribution calculations for the hull structure and insulation system of the KC1 membrane tank were compared by employing four numerical approaches under the IGC condition. Approaches 1-3 studied 2D simulations and approach 4 used a 3D numerical simulation. Approach 1 was calculated by in-house Excel VBA codes and the three other approaches utilized ANSYS Fluent. The BOR of approach 4, the 3D simulation case, for the IGC condition was 0.0986%/day.

• Journal of the Korean Institute of Gas
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• v.13 no.1
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• pp.21-27
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• 2009

This paper presents the numerical study on the strength safety of the prestressed concrete outer tank for a LNG storage tank, which is manufactured by sets of membrane panels with special corrugations. This study for a finite element analysis assumes that the membrane panel of the inner tank was fractured and the liquefied natural gas stored in the inner membrane tank was leaked to the prestressed concrete outer tank. The stress and displacement of the outer tank have been analyzed for five different loadings, which are originated by a hydrostatic pressure and a weight of a LNG, a temperature difference, a weight of the prestressed concrete and a boil-off gas pressure. The computed FEM results indicate that the PC outer tank with a storage capacity of 200,000$m^3$ has a good strength safety for a leaked LNG from the membrane inner tank, but the increased cryogenic loadings in which are originated by a leaked LNG decreases the strength safety of the PC structure. This may lead to the collapse of the outer storage tank.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.10
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• pp.1644-1650
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• 2001

Mechanical properties of domestic 374 stainless steel have been evaluated fur membrane material used in LNG storage tank. LNG tank is operated around -162$^{\circ}C$. The temperature of membrane depends on LNG level. Accordingly, the membrane material is deteriorated by variation of liquid pressure and temperature. Tensile test and fatigue life test were performed at room temperature and -l62$^{\circ}C$ per code requirements. Especially the biaxial fatigue life test was conducted with shaped membrane sheet at a thermal strain of $\Delta$T=190$^{\circ}C$ The test results obtained with the domestic 304 stainless steel showed better properties compared to the values required by code.

• Journal of the Korean Institute of Gas
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• v.13 no.6
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• pp.9-14
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• 2009

In this study, the stress and deformation characteristics of corner protection in which is fabricated in an insulation area have been analyzed using a finite element method. The proposed corner protection may increase the strength and leakage safeties of conventional LNG storage system. The stress and deformation of LNG storage tank system are computed for an insulation panel box, membrane inner tank, and prestressed concrete outer tank. The FEM computed results indicate that the stress and displacement of new membrane LNG tank system with a corner protection between an inner tank and an outer tank are reduced in comparison to those of a conventional membrane LNG tank. This is explained that the strength safety of LNG membrane tank system may be increased due to a strength stiffness of a corner protection.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.6
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• pp.1203-1208
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• 2002

LNG demand has been rapidly increasing in Korea for a variety of reasons including stable supply, non-polluting, and high combustion efficiency characteristics. As a result the construction and expansion of LNG storage facilities have been continuing at a vigorous pace. Korea Gas Corp. (KOGAS) has developed the design technology of the LNG storage tank. One of the most important structural core element of the LNG storage tank is the membrane, made by stainless steel. The membrane to be applied inside of LNG storage tank is provided with corrugations to absorb thermal contraction and expansion caused by LNG temperature. Analytical results have been performed to investigate the strength of the membrane and the reaction farce at the anchor point. Experimental studies are performed to investigate the deformation and strength of the membrane which is designed by Kogas. All experiments are conducted on the basis of RPIS, and we found the results are fully satisfied with the RPIS.

• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.29-35
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• 1999

At the design of Mark III membrane type LNG tank, an analytical and experimental approach on the fatigue strengths of membrane and its welds are very important in order to assist designers and surveyors. In this study, fatigue tests of lap weld of Mark III membrane type LNG tank were carried out and cumulative damage factor was calculated in order to estimate the fatigue life by probability density function and rule methods. It contained the following tests and reviews : 1) The fatigue tests of lap weld of stainless steel according to statistical testing method recommended by JSME, 2)Preparation of S-N curve for lap welds considering the statistical properties of the results of fatigue tests. 3) Procedure for estimating the initiation life of fatigue crack of lap welds under variable loads by the rule lf classification society and probability density function, 4) Guideline for inspection of lap welds fo membrane type LNG tank.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.108-113
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• 2004

Korea Gas Corp. has developed the design technology of the LNG storage tank. The membrane to be applied inside of the LNG storage tank is provided with corrugations to absorb thermal contraction and expansion caused by LNG temperature changes. It is very important to measure their thermal strains under LNG temperatures by analytical and experimental stress analysis of the membrane. We have developed a stress measurement system using strain gages and measured the strain during cooldown and storing the LNG. We also analyzed the measured data by comparison with the FEM data. On the basis of these results, we could design and assure the application of the Kogas Membrane to large scale LNG storage.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.907-912
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• 2001

KOGAS had developed the Ring-knot membrane for LNG storage tank. But we found that some modifications were needed in using the Ring-knot membrane for the commercial LNG storage tanks. So, both analytical and experimental studies have been performed to investigate the strength of the new membrane and the reaction force at the anchor point. Using nonlinear FEM code and experiments, the stress analysis of the new corrugated membrane shapes subject to the cryogenic liquid pressure and thermal loading are performed to ensure the stability and fatigue strength of the new membrane. This paper reports on the results of investigations into this new type of membrane.