Fatigue and Fracture Performance of Insulation System in LNG Carriers

Abstract

With the increase of the size of LNG (Liquefied Natural Gas) carriers, LNG cargo containment systems are exposed to more frequent severe sloshing impact actions. In design and construction of LNG carriers, dynamic failure of LNG cargo containment system (CCS) under repeated sloshing impact actions is a very important issue [1]. While the importance of dynamic strength characteristics of LNG cargo containment system is well recognized, no consideration with regard to the fatigue and fracture performance of insulation system toward the cryogenic environment is readily available. In this respect, a systematic experimental research is carried out for the assessment of fatigue and fracture strength of LNG insulation system at both ambient and cryogenic environments. This study begins with the fatigue test of LNG insulation system. In particular, the fatigue characteristic at the secondary barrier is explicitly considered. The effect of the density of R-PUF (Reinforced Poly-Urethane Foam) with respect to fatigue performance is investigated. In the later section, the fracture toughness of LNG Insulation system is characterized in terms of the critical strain energy release rate (GIC) in the context of linear elastic fracture mechanics (LEFM). The specimen geometries used in this study are the center-cracked and double-edge-cracked tension specimen according to ASTM standard [2]. Fracture toughness tests have been carried out for structural components of MARK III type LNG insulation system such as Reinforced Poly-Urethane Foam (Insulation material) and SUS 304L (Primary barrier) under ambient and cryogenic temperature.