• Journal of the Korean Institute of Gas
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• v.25 no.6
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• pp.14-21
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• 2021

Inner shell material of LNG storage tanks that store ultra-low temperature LNG at -162℃ requires structural integrity assessment of a crack-like defect. From the viewpoint of conventional fracture mechanics, the assessment has mainly performed by single parameter using stress intensity factor K, J-integral and CTOD. However, the stresses in a material of crack tip are not unique caused by constraint loss due to size and geometry of the structure. Various attempts have been made to complement a single parameter fracture mechanics, typically with Q-stress. In this paper, we have performed a two-parameter approach by deriving the Q-stress coupling with J-integral suitable for the evaluation of the crack tip stress field in the non-linear elastic region. A quantitative evaluation of the constraint effect has performed by using the J-Q approach. It was evaluated that the SENB type specimen had a crack ratio of 0.1 to 0.7 and the wide type specimen had a crack ratio of 0.2 to 0.6.

• Journal of the Korean Institute of Gas
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• v.14 no.5
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• pp.13-18
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• 2010

This paper presents the development of an integrated control and safety management system for 9% nickel steel LNG storage tank. The new system added the measuring equipment of pressure, displacement and force compared to the conventional measurement and control system. The measured data has simultaneously been processed by integrating and analyzing with new control equipments and safety management systems. The integrated control and safety management system, which may increase a safety and efficiency of a super-large full containment LNG storage tank, added additional pressure gauges and new displacement/force sensors at the outer side wall and a welding zone of a stiffener and top girder of an inner tank, and the inner side wall of a corner protection tank. The displacement and force sensors may provide failure clues of 9% nickel steel structures such as an inner tank and a corner protection, and a LNG leakage from the inner tank. The conventional leak sensor may not provide proper information on 9% nickel steel tank fracture even though LNG is leaked until the leak detector, which is placed at the insulation area between an inner tank and a corner protection tank, sends a warning signal. Thus, the new integrated control and safety management system is to collect and analyze the temperature, pressure, displacement, force, and LNG density, which are related to the tank system safety and leakage control from the inner tank. The digital data are also measured from control systems such as displacement and force of 9% nickel steel tank safety, LNG level and density, cool-down process, leakage, and pressure controls.

• Journal of Power System Engineering
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• v.16 no.2
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• pp.54-59
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• 2012

In the present study, process optimization for thermal-sprayed Ni-based alloy coating has been performed using Taguchi method and analysis of variance(ANOVA). Ni-based alloy coatings were fabricated by flame spray process on steel substrate, and the hardness test and wear test were performed. Experiments were designed as per Taguchi's L9 orthogonal array and tests were conducted with different Oxygen gas flow, Acetylene gas flow, Powder feed rate and Spray distance. Multi response signal to noise ratio (MRSN) was calculated for the response variables and the optimum combination level of factors was obtained simultaneously using Taguchi's parametric design.

• Journal of Welding and Joining
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• v.9 no.3
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• pp.18-25
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• 1991

The purpose of this paper was to investigate the effect of deposition configuration on the mechanical properties of the flame sprayed titania ceramic coating. The sprayed deposition configuration was made in different five types with titania ceramic and Ni-base alloy on the mild steel substrate. The composite coating exhibited superior mechanical properties such as hardness, adhesive strength, thermal shock resistance and corrosion resistance, whereas the mixed coating proved to be more resistant to erosion. Especially graded coating, which consist of Ni-base alloy undercost, intermediate grade coat and titania ceramic overcost, showed excellent mechanical properties.

• Journal of Powder Materials
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• v.23 no.3
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• pp.207-212
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• 2016

In this study, Fe-Cu-Ni-Mo-C low alloy steel powder is consolidated by spark plasma sintering (SPS) process. The internal structure and the surface fracture behavior are studied using field-emission scanning electron microscopy and optical microscopy techniques. The bulk samples are polished and etched in order to observe the internal structure. The sample sintered at $900^{\circ}C$ with holding time of 10 minutes achieves nearly full density of 98.9% while the density of the as-received conventionally sintered product is 90.3%. The fracture microstructures indicate that the sample prepared at $900^{\circ}C$ by the SPS process is hard to break out because of the presence of both grain boundaries and internal particle fractures. Moreover, the lamellar pearlite structure is also observed in this sample. The samples sintered at 1000 and $1100^{\circ}C$ exhibit a large number of tiny particles and pores due to the melting of Cu and aggregation of the alloy elements during the SPS process. The highest hardness value of 296.52 HV is observed for the sample sintered at $900^{\circ}C$ with holding time of 10 minutes.

• Journal of Magnetics
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• v.7 no.2
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• pp.29-39
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• 2002

The initial NiCuZn synthetic ferrite were acquired from thermally decomposing the metal nitrates $Fe(NO_3)_39H_2O, Zn(NO_3)_26H_2O, Ni(NO_3)_26H_2O, and Cu(NO_3)_23H_2O$ at $150^circ{C}$ for 24 hours, and then we calcined the synthetic powder at $500^circ{C}$, pulverized each of those for 3, 6, 9, 12, and 15 hours in a steel ball mill, sintered each at $700^circ{C}$ to $1,000^circ{C}$ for 1 hour, and thus studied their microstructures and electromagnetic properties. We could make the initial specimens chemically bonded in liquidity at a low-temperature $150^circ{C}$, by using the low melting points less than $200^circ{C}$ of the metal nitrates instead of the mechanical ball-mill pulverization, then narrow a distance between the particles into a molecular one, and thus lower the reaction point of sintering by at least $200^circ{C}$ to $300^circ{C}$. Their initial permeability was 50 to 400 and their maximum magnetic induction density and coercive force, 2,400 G and 0.3 Oe to 0.5 Oe respectively, which was similar to those of NiZnCu ferrite synthesized in the conventional process. In the graph of initial permeability by frequencies, a $180^circ{C}$ rotation of the magnetic domains which appears in a broad band of micro-wave before and after the resonance frequency, could be perceived.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.3
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• pp.246-253
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• 2014

Liquid natural gas is stored and transported inside cargo tank which is made of specially designed cryogenic materials such as 9% Ni steel, Al5083-O alloy and SUS304 and so on. The materials have to keep excellent ductile characteristics under the cryogenic environment, down to -163oC, in order to avoid the catastrophic sudden brittle fracture during the operation condition. High manganese steel is considered to be the promising alternative material that can replace the commonly used materials mentioned above owing to its cost effectiveness. In line with this industrial need, the mechanical properties of the high manganese steel under both room and cryogenic environment were investigated in this study focused on its tensile and fatigue behavior. In terms of the tensile strength, the ultimate tensile strength of the base material of the high manganese steel was comparable to the existing cryogenic materials, but it turned out to be undermatched one when welding is involved in. The fatigue strength of the high manganese steel under room temperature was as good as other cryogenic materials, but under cryogenic environment, slightly less than others though better than Al 5083-O alloy.

• Journal of Welding and Joining
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• v.35 no.3
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• pp.82-87
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• 2017

Recent trends in shipbuilding and offshore industries are a huge increase in the ship size and the exploration and production of oil and natural gas in the arctic offshore region. High performance steel plates are required by these industrial trends. Also in IMO(International Maritime Organization) has begun to regulate of fuel of ship to environmental protection, therefore it is little bit difficult to use bunker-C oil to working ship. As the problem of environmental change such as global warming is emerged, the operation of the ship is considered to be involved in the environmental change problem, and the regulation of environmental pollution is gradually strengthened. As these environmental regulations are strengthened demand for LNG fuel ships is rapidly increasing. Currently, cryogenic steels used in LNG tanks include aluminum alloy, SUS 304, and 9%-Ni steel. Those steels are has high cost to construction of large LNG carrier. The new materials were suggested several steel mills to decrease construction cost and easy construction. The new cryogenic steel should be evaluate safety to applied real structure include LNG ship. Therefore, in this study, fracture toughness of weld joints were investigated with cryogenic steel for application of LNG tank.

• Journal of Welding and Joining
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• v.9 no.4
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• pp.28-39
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• 1991

The change of microstructure in the bonded interlayer and mechanical properties of the joints were investigated during Transient Liquid Phase Diffusion Bonding(TLP bonding) of STS304/SM17C and STS304/SM45C couples using Ni base amorphous alloys added boron and prepared alloy as insert metal. Main experimental results obtained in this study are as follows: 1) Isothermal solidification process was completed much faster than theoretically expected time, 14ks at 1473K temperature. Its completion times were 3.6ks at 1423K, 2.5ks at 1473K and 1.6ks at 1523K respectively. 2) As the concentration of boron in the insert metal increased, the more borides were precipitated near bonded interlayer and grain boundary of STS304 side during isothermal solidification process, its products were $M_{23}P(C,B)_6}_3)$ The formation of grain boundary during isothermal solidification process was completed at structural carbon steel after starting the solidfication at STS304 stainless steel. 4) The highest value of hardness was obtained at bonded interface of STS304 side. The desirable tensile properties were obtained from STS304/SM17C, STS304/SM45C using MBF50 and experimentally prepared insert metal with low boron concentration.

• Resources Recycling
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• v.12 no.6
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• pp.13-18
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• 2003

The initial NiCuZn synthetic ferrite were acquired from thermally decomposing the metal nitrates Fe($NO_3$)$_3$ㆍ$9H_2$O, Zn($NO_3$)$_2$ㆍ$6H_2$O, Ni($NO_3$3)$_2$ㆍ $6H_2$O and Cu(NO$_3$)$_2$ㆍ $3H_2$O at 1$50^{\circ}C$ for 24 hours and was calcined at $500^{\circ}C$. Each of those was pulverized for 3 and 9 hours in a steel ball mill and was sintered between $700^{\circ}C$ and $1,000^{\circ}C$ for 1 hour, and then their microstructures and magnetic properties were examined. We could make the initial specimens chemically bonded in liquid at the temperature as low as $150 ^{\circ}C$, by using the melting points less than $ 200^{\circ}C$ of the metal nitrates instead of the mechanical ball milling, then narrowed a distance between the particles into a molecular level, and thus lowed sintering temperature by at least $200 ^{\circ}C$ to $300^{\circ}C$ Their initial permeability was 50 to 490 and their saturation magnetic induction density and coercive force 2,400G and 0.3 Oe to 1.2 Oe each, which were similar to those of NiCuZn ferrite synthesized in the conventional process.