Demand for research on the use of hydrogen, an eco-friendly fuel, is rapidly increasing in accordance with global environmental problems and IMO environmental regulations in the shipbuilding and marine industry. In the case of hydrogen, similar to liquefied natural gas, it has a characteristic that its volume decreases hundreds of times during phase transformation from gas to liquid, so it must be stored in a tank in the form of liquefied hydrogen for transport efficiency. The material of the liquid hydrogen tank is selected in consideration of mechanical properties and hydrogen embrittlement at cryogenic temperatures. In this study, welding research was conducted on STS316L material, which was most commonly used in the space industry. In this study, flux cored arc welding was performed under 4 welding conditions to derive the optimal welding conditions for STS316L material, and then mechanical properties of the welded part were compared and analyzed.

Because of the International Maritime Organization(IMO)'s regulation to regulate emissions of ships, a change is taking place to replace ship fuels from Heavy Fule Oil(HFO) to Liquefied Natural Gas(LNG). In the case of LNG, it is a material obtained by liquefying Natural Gas(NG), and it is -163 degrees below zero, and the volume is reduced to 1/600 level. The material of the tank that can store LNG must be a material that can safely store LNG in a cryogenic environment, and the materials of the tank that can store LNG are limited in the International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk(IGC Code). Among the materials listed in the IGC Code, 9% nickel steel is used as a material for LNG fuel propulsion tanks that are recently ordered because of relatively high mechanical properties under cryogenic environments. In this study, the mechanical properties of butt welds were measured following the weld reliability evaluation of Flux Cored Arc Welding(FCAW) butt welds made of 9% nickel steel by PARTI. The measured mechanical properties are tensile strength, bending strength, hardness, and cryogenic impact test required by the classification for Welding Procedure Specification(WPS) approval.

Because of the International Maritime Organization(IMO)'s regulation to regulate emissions of ships, a change is taking place to replace ship fuels from Heavy Fule Oil(HFO) to Liquefied Natural Gas(LNG). In the case of LNG, it is a material obtained by liquefying Natural Gas(NG), and it is -163 degrees below zero, and the volume is reduced to 1/600 level. The material of the tank that can store LNG must be a material that can safely store LNG in a cryogenic environment, and the materials of the tank that can store LNG are limited in the International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk(IGC Code). Among the materials listed in the IGC Code, 9% nickel steel is used as a material for LNG fuel propulsion tanks that are recently ordered because of relatively high mechanical properties under cryogenic environments. In this study, butt welding was performed on a 9% nickel steel material using Flux Cored Arc Welding(FCAW), the most widely used welding method in shipyards. In PARTI, after securing the welding conditions, cross-sectional observation results analysis, liquid penetrating test, and radiographic test were performed to verify the reliability of the weld.

In this study, the correlation between microstructure and Charpy impact properties of FCAW(Flux cored arc welding) HAZ(Heat affected zone) of thick steel plates for offshore platforms was investigated. The 1/4 thickness(1/4t) location HAZ specimen had a higher volume fraction of bainite and finer grain size of acicular ferrite than those of the 1/2 thickness (1/2t) location HAZ specimen because of the post heat effect during the continuous FCAW process. The Charpy impact energy at -20 oC of the 1/4t location HAZ specimen was lower than that of the 1/2t location HAZ specimen because of the high volume fraction of coarse bainite. The Charpy impact energy at -40 and -60 oC of the 1/2t location HAZ specimen were higher than those of the 1/2t location HAZ specimen because the ductile fracture occurred in the fine acicular ferrite and martensite regions. In the ductile fracture mode, the deformed regions were observed in fine acicular ferrite and martensite regions. In the brittle fracture mode, long crack propagation path was observed in bainite regions.

In this study, we investigate the mechanical and metallurgical properties of the gas metal arc welding. According to flux cored arc welding parameters during welding ATOS80, improving the working conditions of the welding industry to use high strength steel ATOS80 we propose to. Weld test is the tensile strength, yield strength, elongation, hardness, brittleness, such as macro-structure check of the mechanical properties and the weld, the microstructure inspection, defects of the weld subjected to radio-graphic inspection and tissue after welding the test pieces according to the condition variable comparative analysis was investigated by the state.