해양구조용 고강도강의 구속도의 영향에 따른 용접부 잔류응력특성 평가에 관한 연구

Abstract

Recently, due to the depletion of marine resources, interest in the extraction of marine energy from deep and deep seas has increased, and the installation environment for offshore structures is moving to extreme areas. In addition, as oil field development expands to about 1000mm in deep sea, the installation environment for offshore structures is getting worse. In order to properly install offshore structures in the use environment, it is necessary to develop high-tensile steel for offshore structures and to develop appropriate welding technology. Since steel materials for offshore structures are different from ships and installation environments, they are mostly of a fixed type and require stricter quality. Welding is a core technology that must be used inevitably in the manufacture of offshore structures, and deformation and residual stress occurring during welding are well known as major factors causing various problems. In welding technology applied to various industrial sites, control of deformation and residual stress is a very important issue, and it is a task given to all structures where welding is used. In particular, since residual welding stress adversely affects fatigue fracture and fracture toughness, efforts are being made to control residual stress. In this study, the residual stress generated during welding of high-tensile steel applied to offshore structures was quantitatively identified through destructive, non-destructive, and numerical analysis. To investigate the effect, the residual stress distributions were evaluated under various restraints. First, butt weld joints were fabricated under different welding constraint conditions in order to understand the characteristics of the welding residual stress distribution according to the influence of the constraint conditions by varying the constraint conditions of high tensile steel for offshore structures. Second, the welding residual force characteristics of fully constrained and unconstrained specimens were evaluated. The destructive and non-destructive methods were applied to evaluate the welding residual stress. As the fracture method, the most widely known cutting method was applied, and a relatively recently applied contour method was applied for mutual comparison. By applying the neutron diffraction method using Hanaro as a non-destructive method, the welding residual stress in the thickness direction as well as the surface was measured. the FEM method was established by comparing the experimental results of the welding residual stress distribution according to the influence of the constraint conditions through FEM. Finally, it is judged that the distribution characteristics of the welding residual stress according to the influence of the constraint conditions can be grasped through the analysis technique.