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얇은판의 용접변형이 압축 최종 강도에 미치는 영향 검토
이명수(Myung-Su Yi),박주신(Joo-Shin Park) 대한용접·접합학회 2024 대한용접·접합학회지 Vol.42 No.1
As ships become larger and faster, attempts are being made to reduce weight by optimally arranging structures and expanding the application of high-strength steel. From the shipyard’s perspective, this reduces construction costs, and from the shipping company’s perspective, fuel efficiency increases. As weight is reduced, the use of thinner plates increases, resulting in excessive deformation even with the same welding heat, resulting in significant loss of time and cost during correction work. In particular, ship accommodations are structures that use the highest percentage of thin plates, so the time and cost involved in corrections are often an issue. In this study, we analyzed the standards for welding deformation for representative plates subjected to compressive loads in ship accommodations, and analyzed the reasonable initial deflection size for buckling strength design. Longitudinal and lateral compressive loads were selected as the main load components, and nonlinear finite element analysis was performed to summarize the strength pattern according to plate thickness. Through various considerations, the intermediate initial imperfection amount proposed by Smith’s equation was found to be the most physically feasible as it could take into account changes in plate width, yield strength, and thickness. The main contents discussed in this study are expected to be used as important data to predict changes in buckling strength due to welding deformation of thin plates.
종 방향 버트 용접으로 제작된 고망간강 라이저 파이프의 잔류응력 연구 (2) : 파라메트릭 스터디 통한 잔류응력 예측식 도출
이명수(Myung-Su Yi),서정관(Jung-Kwan Seo) 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.2
In recent years, the deep and ultra-deep seas are recognized as the last remaining regions on the planet where oil and natural gas resources are discovered and produced. In order to develop such natural resources in an environmentally safe and cost-effective method, various engineering systems and technologies are being developed. In keeping with this direction of development, there is significant worldwide interest among major offshore structural and system operators in examining the possibility of using high-strength steel for long-distance gas transmission pipelines and risers. In particular, riser pipes using high manganese steel are often made by longitudinal butt welding, but studies related to the prediction of residual stresses for this are insufficient. In general, it is known that in a cylindrical structure such as steel catenary risers (Hereafter, ‘SCRs’), residual stress in the through-thickness direction can be decomposed into a membrane component and a bending component. In this paper, a parametric study through nonlinear finite element analysis was performed to predict the residual stress for each direction of a longitudinal butt-welded riser by considering the main parameters (r/t) of the pipe that can affect the actual residual stress. A new predicting equation for estimating the residual stress profile was proposed using the results of a number of parametric precision numerical analysis derived through this process.
종 방향 버트 용접으로 제작된 고망간강 라이저 파이프의 잔류응력 연구 (1) : 잔류응력 계측 및 수치해석
이명수(Myung-Su Yi),서정관(Jung-Kwan Seo) 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.2
In recent years, the deep and ultra-deep seas are recognized as the last remaining regions on the planet where oil and natural gas resources are discovered and produced. In order to develop such natural resources in an environmentally safe and cost-effective method, various engineering systems and technologies are being developed. In keeping with this direction of development, there is significant worldwide interest among major offshore structural and system operators in examining the possibility of using high-strength steel for long-distance gas transmission pipelines and risers. In particular, riser pipes using high manganese steel are often made by longitudinal butt welding, In order to make a riser, which is a large pipe structure, it is necessary to do pipework to bend the plate. At this time, welding is required in the longitudinal direction of the riser, and this welding is the longitudinal butt welding. But studies related to the prediction of residual stresses for this are insufficient. In this paper, the residual stress values of longitudinal butt welding of high manganese steel using the hold drilling method were measured. Furthermore, the residual stresses in various directions were calculated using a precise thermal-elastic analysis technique, and comparative verification with the measured values was conducted to see if this method is valid as a residual stress prediction method.
현충민,이명수,조시훈,장태원,Hyun, Chung Min,Yi, Myung Su,Cho, Si Hoon,Jang, Tae Won 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.1
Due to of high intensity, lower noise and easy controllability of the heat, induction heating system became well known. Induction heating method has been suggested as substitute for the gas heat source and adopted in the automation of curved hull forming system. In this study, an investigation was accomplished to find the effects on the change of material properties when the induction heating was applied on the mild steel plate. Plates were heated using weaving method to get sufficiently heat affected zone and then cooled with water or in the air. The mechanical properties of the heated plate were evaluated. As results, the tensile test, impact test and microstructures satisfied the class rule.
하윤석,양진혁,원석희,이명수,Ha, Yun-Sok,Yang, Jin-Hyuk,Won, Seok-Hee,Yi, Myung-Su 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.3
As ships become to be larger than ever, the thicker plate and the higher tensile steel plate are used in naval shipyard. Though special chemical composition is needed for high-tensile steels, recent high-tensile steels are made by the TMCP(Thermo-Mechanical control process) skill. The increase of yield stress and tensile stress of TMCP steels is induced from bainite phase which is transformed from austenite, but that increased yield stress can be vanished by another additional thermal cycle like welding and heating. As thermal deformations are deeply related by yield stress of material, the study for prediction of plate deformation by heating should reflect principle of TMCP steels. This study developed an algorithm which can calculate inherent strain. In this algorithm, not only the mechanical principles of thermal deformations, but also the predicting of the portion of initial bainite is considered when calculating inherent strain. The simulations of plate deformation by these values showed good agreements with experimental results of normalizing steels and TMCP steels in welding and heating. Finally we made an inherent strain database of steels used in Class rule.
용접배관 절단 및 원주용접을 고려한 잔류응력 재분포 특성 연구
노지선(Ji-Sun Roh),이명수(Myung-Su Yi),박중구(Jung-Goo Park),김명현(Myung-Hyun Kim) 대한용접·접합학회 2024 대한용접·접합학회지 Vol.42 No.1
Seam pipes are easier to manufacture and cheaper than seamless pipes, and are widely used in the manufacture of pipe spools for marine plant facilities. The manufacturing and assembly of seam pipes involve welding and cutting. The localized heating and cooling that occur during these processes may change the existing residual stress and cause deformation. Uncontrolled deformation can accumulate as assembly errors at the next step, potentially delaying the entire process and causing economic losses. Therefore, characteristics of residual stress redistribution caused by cutting and girth welding of seam pipes need to be studied further. In this study, we performed thermo-mechanical analysis of the manufacturing, cutting, and girth welding processes of seam pipes using the commercial finite element analysis (FEA) software MSC Marc and analyzed the characteristics of residual stress. Furthermore, we measured the residual stress in each process using the hole drilling method, analyzed the characteristics of redistributed residual stress, and ensured reliability. Based on the results of FEA and measured residual stress redistribution, we can provide a basis for reasonable mitigation when performing structural integrity evaluation if there is a defect in the weld of the pipe.