Liquefied natural gas (LNG) is the cleanest fossil fuel available, producing less carbon emissions and fewer pollutants than other fossil fuels. Marine transportation is a key process in the LNG supply chain. The use of tank containers, which are portable equipment, can effectively facilitate multi-mode transportation. LNG evaporation causes pressurization, which is a safety concern during transportation. Ship motion and environmental temperature are the main factors affecting pressure variations. In this study, the effect of ship motion on pressurization and holding time was investigated through three types of experiments, namely, prototype, field, and self-pressurization experiments. The results showed that while increased boil-off gas was generated due to ship motion, this evaporation remained stable in dynamic cases. Higher evaporation rates were obtained under more severe dynamic conditions, and the holding time was shortened. The two different effects of ship motion on pressure development discussed here are the facilitation of pressurization due to the enhancement of heat transfer and the prevention of pressurization due to gas condensation at the vapor–liquid interface. These two effects show varied levels of predominance over the pressure variations depending on different stages of transportation. The holding time in the experiments was able to reach 87 days under the most severe condition, which is long enough for long-term shipping; the safety of transporting LNG in tank containers is further discussed based on the experimental results herein.

Flexible pipes are distinctive multi-layer structures that are designed to resist different loads when they are utilized in severe deep-water environments. However, they lack a special structural layer to withstand torsion. Tensile armors mainly resist torque although they are designed to bear only tension with the consideration of torque balance. Especially, when a flexible pipe is loaded out from the cargo vessel into the installation vessel, twist angle could be accumulated at high level so that some failure modes will occur due to the large torsion. However, the failure mechanism is very complicated owing to the interaction effect between the different layers. First, the interaction mechanism between the layers of flexible pipes is analyzed under large torsion, and a few potential failure modes are identified, such as the tensile armors strength failure and inner structural layers collapse failure. In addition, to offer a quantitative prediction of the maximum allowable twist angle for flexible pipes, a mechanical model is set up to analyze their torsion behavior. The theoretical descriptions of the involved failure behaviors are investigated, and the theoretical methodology of the failure criteria for predicting the torsion resistance capacity is proposed. Finally, a numerical model is established through experimental verification. The numerical results illustrate that the theoretical prediction methodology is conservative, which can be used to predict the torsion resistance capacity of flexible pipes and to guide their operation and installation in engineering.

Fiber-reinforced flexible pipes are subjected to large axial tension loads in deep-water applications, which may result in the excessive deformation of the pipes. Owing to the anisotropy of the composite materials, accurately describing the tensile behavior of these pipes is difficult. Theoretical, numerical, and experimental methods are employed in this study to investigate the mechanical characteristics of a glass fiber-reinforced unbonded flexible pipe under axial tensile loads. Based on the load–strain relationship of each pipe layer, analytical equations considering the effect of anisotropy and radial deformation are first proposed to calculate the axial tensile stiffness of the pipe. A detailed numerical model is established to simulate the tensile behavior of the pipe. A prototype test is performed on a 4500 mm long sample using a tensile testing machine. The leading roles of outer tensile reinforcement layers in axial tensile capacity are illustrated by the strain energy of the pipe layers obtained by the numerical model. Subsequently, a comparison analysis of the mean fiber direction strains of the selected sections are performed between numerical and experimental results, which validates the numerical model. Additionally, the stress distributions of different pipe layers are discussed based on the results of the numerical analysis. Finally, the comparison of axial tensile stiffness results validates the accuracy of the analytical model considering radial deformation. This study proposes effective theoretical and numerical models to predict the tensile behavior of a fiber-reinforced flexible pipe, which provides useful references for the design and structural analysis of these pipes.

With the increasing severity of climate change, Carbon Capture, Utilization, and Storage (CCUS) technology has become essential for reducing atmospheric CO₂. Marine carbon sequestration, which stores CO₂ in seabed geological structures, offers advantages such as large storage capacity and high stability. Cryogenic hoses are critical for the ship-to-ship transfer of liquid CO₂ from transportation vessels to offshore carbon sequestration platforms, but their design methods and mechanical analysis remain inadequately understood. This study reviews existing cryogenic hose designs, including reinforced corrugated hoses, vacuum-insulated hoses, and composite hoses, to assess their suitability for liquid CO₂ transfer. Based on CO₂’s physicochemical properties, a conceptual composite hose structure is proposed, featuring a double-spring-supported internal composite hose, thermal insulation layer, and outer sheath. Practical recommendations for material selection, corrosion prevention, and monitoring strategies are provided to improve flexibility, pressure resistance, and thermal insulation, enabling reliable long-distance tandem transfer. A mechanical analysis framework is developed to evaluate structural performance under conditions including mechanical loads, thermal stress, and dynamic responses. This manuscript includes an introduction to the background, the methodology for data collection, a review of existing designs, an analysis of CO₂ characteristics, the proposed design methods, the mechanical analysis framework, a discussion of challenges, and the conclusions.