An Experimental Study on Fatigue & Fracture Characteristics of IMO Type B CCS Materials at Cryogenic Temperature

초록

IMO type B CCS (cargo containment system) is considered for LNG FPSOs. For the three materials of SUS304, 9% Ni steel and Al 5083-O alloy regarded as possible candidates, extensive tensile, fatigue, fatigue crack growth rate and CTOD tests were carried out at room, intermediate low (− 100℃) and cryogenic (− 163℃) temperatures. All materials show a tendency for initial yield and tensile strengths to increase at low temperature, while change in elastic modulus is not as remarkable. In fatigue tests, it was shown that fatigue strengths increased at low temperature. Crack growth rate of each material was calculated with design criteria from yield stress and Paris exponent (m) & Paris constant (C) obtained from crack growth rate test. Analyzing these results, crack growth rates were generally improved at cryogenic temperature. Critical crack length obtained from CTOD shows different tendency for each material and weld type. In addition, tendency of changing material property at operation temperature of LNG tank which is based on test results were analyzed according to IGC code and rules of classifications. Perspectives of two kinds were used. First, each material compared with the others considering economic effects from design aspect. Second, material characteristics which were obtained from test results were analyzed in the viewpoint of safety aspect.