As the development of shale gas globally expands, the amount of natural gas is increased and thus expected to contribute to the stabilization of the increasing energy supply and price. Therefore, it is expected that the
demand for LNG carriers carrying natural gas will increases, which indicates that the demand for LNG Ship equipment also will increase. Especially, bellows for LNG carriers must have enough corrosion resistance in seawater environment and fatigue life to stand over 8,000
cycles of the repeated expansion and contraction which are caused by changing temperature from low temperature of -163 ℃ to high temperature of 150 ℃ under the pressure condition over Max. 10.0 bar. In order to make these properties in reality, it is inevitable to use low temperature special materials such as austenitic stainless steel, INCOLOY materials and thus required to develop forming procedure that makes original forms into bellows form. However, the components for bellows are imported currently. The domestic research doesn''t consider the extremely low temperature environment and it is difficult to find the result of investigating welded joints.
Therefore, the purpose of this thesis is developments of the optimized forming process on low temperature special materials such as STS316L and INCOLOY825, evaluations of mechanical properties and contribution to domestic production of bellows through reliability evaluation.
In this thesis that explores bellows for use in LNG carriers, therefore welding conditions best-fit to the product profile were extracted by performing welding to materials of STS316L and INCOLOY825 having features of high corrosion resistance and usability at low temperatures. In
addition, effort was made to secure the reliability of the prototype by analyzing the mechanical properties of the welded section. Moreover, fatigue testing was conducted to investigate the effect on shelf life of the product by analyzing the mechanical properties of those materials
depending on the forming method of bellows. The development of bellows taking advantage of the results of this study is expected not only to lead to the import substitution effect, but to contribute to the revitalization of
the domestic equipment industry for shipbuilding and marine plant sectors.