The fire safety assessment procedure of ships and offshore structures can be briefly described as a procedure for assessing safety by defining fire loads according to accident scenarios and analyzing their effects on the structure. In general, safety is reviewed via the temperature criteria of the structures under fire loads, and it is assessed in more detail via thermal-structural analysis, which combines fire simulation-heat transfer analysis with structural analysis in the design stage. Therefore, the accuracy of the thermal-structural analysis is crucial for reliable fire safety assessment, and the most applied method for validating the accuracy is to compare with the experimental results.Although fire experiments have been conducted by many researchers to analyze the characteristics of flames and heat transfer of steel members, constructing the temperature-dependent material property data, verifying the fire resistance performance of the structure itself, developing and validating numerical models, including other experiments have been conducted from the perspective of fluids with a primary focus on measuring gas and steel surface temperatures. On the other hand, fire experiments from the perspective of structure, which measure the displacement of a structure under fire load, were conducted mainly in limited environments such as inside a furnace because it was difficult to measure displacement in a high-temperature environment with a mixture of flames and smoke, as well as controlling the heat of the fire source. In addition, fire experiments conducted in open space have been seldom carried out. The British Steel Corporation (BSC) has summarized standard fire experiment results for structures such as steel beams and columns (Wainman and Kirby, 1988;Wainman et al., 1990). Cong conducted a furnace fire experiment on an I-beam, which is widely used as structural members for offshore structures, under mechanical loads to measure the steel surface temperature and vertical displacement. The vertical displacement was then measured by linear variable differential transformers (LVDTs) installed on top of the specimen exposed to the exterior parts of the furnace (Cong et al., 2005). The results obtained from this experiment have been widely used by other researchers to develop numerical analysis techniques (Kim, 2014;Kim et al., 2017).In addition to steel, fire experiments have also been conducted on sandwich panel structures made of fiber-reinforced plastic (FRP)

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MOERI-KORDI (Maritime and Ocean Engineering Research Institute-Korea Ocean Research and Development Institute)has conducted the development of an unmanned underwater vehicle (UUV) for 6000 m deep-sea exploration, which was completed in 2006. Several pressure vessels were mounted on the UUV frame for loading electric and electronic equipment. The pressure vessels were constructed with titanium alloy Ti-6Al-4V for two main cylindrical canisters and with aluminium alloy Al6061-T6 for several hemispherical housings of electric motor drivers, respectively. This article presents the design process of the pressure vessels and experimental results acquired by high-pressure tests, which were conducted with the cooperation between MOERI-KRISO and Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The pressure vessels were designed on the basis of the buckling analysis as well as structural yielding analysis, and checked the safety by the finite-element analysis (FEA) and analytical (empirical) formula. Moreover, by structural reliability analysis, the cylindrical part and the end plates of the main pressure vessels made of Ti-6Al-4V were designed with a safety of 99.98% under circumstance of 75 MPa. The pressure housings made of Al6061-T6 were also designed by the same procedure. Pressure test was performed with the large high-pressure environment simulation unit of JAMSTEC. The pressure vessels made of the titanium-aluminium alloy were safe even when they were under pressure of 75.46 MPa. Test results show that there are less than 5% difference between the FEA and the high-pressure tests. In this research, the pressure test was conducted up to 75 MPa, which corresponds with a safety factor of 1.25. Even though this is lower than the usual safety factor of 1.5-2.5, this study shows that the pressure vessels are safe if we consider the reliability analysis.

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