A Comparative Evaluation of Fatigue and Fracture Characteristics of Structural Components of Liquefied Natural Gas Carrier Insulation System

This study examined the fatigue strength and fracture toughness of the structural components of membrane type liquefied natural gas carrier (LNGC) insulation systems, such as reinforced poly-urethane foam (R-PUF, insulation material) and 304 L stainless steel (STS 304 L, Primary barrier membrane), at both ambient and cryogenic temperatures. The fatigue strength of the LNGC insulation system was compared with that of low density R-PUF (130 kg/m³) and high density R-PUF (210 kg/m³). The fracture toughness of R-PUF and STS 304 L was investigated in terms of the density effect of R-PUF and the difference in the nickel composition of STS 304 L, STS 304 L (10.2%Ni) versus STS 304 L (9.4%Ni) at both ambient and cryogenic temperatures. In this study, the high density R-PUF (210 kg/m³) and STS 304 L (9.4%Ni) were proposed to improve the structural strength of the LNGC insulation system and reduce the cost. The fracture toughness was characterized in terms of the critical strain energy release rate (GIC) in the context of linear elastic fracture mechanics (LEFM). The geometries of the fracture toughness test used were the center-cracked tension (CCT) and double-edge-cracked tension (DECT) specimens according to ASTM STP381 standard.