12 SPB方式LNG船用アルミタンクの突合せ溶接の改善

概要

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Though two systems of LNG tank structure, membrane type combined with hull structure and MOSS type of independent tank, have widely been applied in LNG carrier in the world, Ishikawajima-Harima Heavy Industries, Co., Ltd. (IHI) originally developed the LNG carrier of SPB system (Self-supporting Prismatic type-B) having independent prismatic tank, which completely differs from these two systems. In SPB system, it must be guaranteed that the fatigue crack should not occur or be limited within the allowable length during ship service life. Therefore detail structural analysis and fatigue analysis for the tank have to be carried out, and also advanced quality control is necessary so that stress concentration around the welded joint is lesser. This paper focuses on the butt weld of aluminum alloy plates of the tank, and states the results of a series of study including some experiments to ensure the reliability of the joint, especially for the bead shape. The measuring device of weld beads and also flat bed structure with forced vacuum system to prevent the irregularity and angular distortion in the vicinity of weld bead are also reported.