PSI - Issue 48

Haris Nubli et al. / Procedia Structural Integrity 48 (2023) 73–80 Nubli et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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2016;2018;2020;2022; Smaradhana et al., 2021; Ansori et al., 2022; Do et al., 2022; Carvalho et al., 2023; Faqih et al., 2023; Pratama et al., 2023). In terms of infrastructure, refuelling site is one of the important facilities, and among the modes available for replenishing LNG fuel, such as truck-to-ship (TTS), pipeline-to-ship (PTS), and ship-to-ship (STS), the last mode demonstrates better performance due to its large fuel quantity provision, operational flexibility, and lack of interference with cargo handling operations (EMSA, 2018; Fevre, 2018; Nubli et al., 2022a; Tam, 2020). Despite the advantages of STS replenishment, handling LNG fuel poses higher risks than conventional marine diesel fuel due to its volatility, low flashpoint, and cryogenic temperature (Nubli and Sohn, 2022). An accidental release of LNG could lead to damage to the ship's structure and subsequent structural collapse due to the brittle fracture of steel material (Park et al., 2021). Therefore, selecting high-strength and cryogenic temperature-resistant steel is crucial to mitigate the potential hazards associated with cryogenic temperatures subjected to an LNG carrying ship or LNG bunkering ship, which is related to the ductile to the brittle transition temperature (DBTT) of the steel material. The use of liquefied natural gas (LNG) as a fuel in the maritime industry requires special consideration due to the hazards associated with the cryogenic temperatures involved. At temperatures as low as -163°C, LNG must be stored and transported in specialized tanks, which pose a risk of brittle fracture due to DBTT of the steel used in the tank construction (Muttaqie et al., 2020; Nubli et al., 2022b). This hazard is particularly acute for ships carrying LNG or LNG bunkering ships, which are at risk of accidental gas leaks that can damage the ship's structure and result in a significant loss (Paik, 2020). To mitigate this risk, it is essential to develop high-strength or high-manganese steels, cryogenic temperature-resistant steel that can withstand prolonged exposure to LNG flow and maintain its ductile properties at low temperatures (Muttaqie et al., 2020). The IGC code provides detailed guidance on materials for ships carrying liquefied gases, including specifications for plate thickness, design temperature, and usage (International Maritime Organization, 2014). Of particular concern is the LNG storage tank, which must be constructed with materials capable of withstanding cryogenic temperatures as low as -165°C. Options for this application include 9% nickel steel, high manganese austenitic steel, and aluminum alloys, with the choice of material depending on the specific requirements of the Type-C independent tank (International Maritime Organization, 2014; Muttaqie et al., 2020). The IGC code specifies that these materials must be able to withstand a minimum absorbed energy of 41 J in the Charpy V-Notch test (International Maritime Organization, 2014). For example, high manganese austenitic steel exhibits an ultimate tensile stress of up to 1,500 MPa and a fracture strain of up to 0.45 mm/mm at -163°C. Careful selection of materials can be a key factor in mitigating the cryogenic hazards associated with these structures. In this paper, the utilization of steel in shipbuilding is examined, primarily addressing the potential hazards related to unintentional LNG discharge during transit and the behavior of steel when exposed to low temperatures. Drawing from available research, the analysis is structured around three main areas: experimental investigations performed at cryogenic temperatures encompassing tensile testing and Charpy V-notch impact testing, as well as material modeling employing finite element analysis. The paper outlines an approach and methodology concerning these subjects. 2. Hazard of the Liquefied Natural Gas The transport of liquefied natural gas (LNG) presents unique safety challenges compared to other cargo types due to its classification as a high-flammability material. LNG can be easily vaporized at normal pressure and room temperature and is capable of spontaneous ignition (Nubli et al., 2022b). The Electronic Major Accident Report System (eMARS) classifies accidents by material type, facility location, and activity type, with a focus on LNG bunkering incidents (European Commission, 2021). Bhardwaj et al. (2018) analyzed several gas release cases in offshore structures and classified them according to severity level, ranging from low to high. Hydrocarbon gas was found to have the highest number of releases, accounting for 50.5% of the 321 total cases in the FPSO's accident database. Moreover, fluid-release events frequently occur during normal operation, resulting in moderate severity (Bhardwaj et al., 2018). Potential hazards resulting from LNG releases include asphyxiation, cryogenic burns, structural damage, and fire, with catastrophic vapor cloud explosions (VCEs) possible when an ignition source and gas accumulation coincide (Park et al., 2018). An assessment of risk is essential to ensure the safe transportation and handling of liquefied natural gas (LNG) due to its high flammability and the potential hazards associated with cryogenic temperatures. One of the significant risks in the LNG transportation industry is generic accidents, which include collision, grounding, contact, fire/explosion, and accidents during loading/unloading. According to the SAFEDOR risk model, these accidents are the primary