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 extensively used to connect seabed and floating production systems for the development of deep-water oil and gas. In the top connection area, end fitting (EF) is the connector between the flexible pipe and floating platform, as a critical component for structural failure. To address this issue, a combined numerical and experimental prediction method is proposed in this paper to investigate the failure behavior of flexible pipes EF considering tensile armor and epoxy resin debonding. In order to analyze the stress distribution of the tensile armor and the damage state of the bonding interface as the tensile load increases, a finite element model of the EF anchorage system is established based on the cohesive zone model (CZM). Additionally, the effects of the epoxy resin shear strength (ss) and the steel wire yield strength (ys) on the structural load-bearing capacity are discussed in detail. The results indicate that wire strength and interface bonding have a substantial effect on the anchorage system’s failure behavior, and the low-strength wire anchorage system has a three-stage failure behavior with wire yielding as the predominant failure mode, while the high-strength wire anchorage system has a two-stage failure behavior with interface debonding as the predominant failure mode.

Flexible risers are subjected to significant tensile loads during manufacturing, installation, and in-service phases, and they experience multiple cyclic tensile loads throughout their entire service life. Whether the armour wires can achieve shakedown under cyclic tensile loads remains an open question to be investigated. In this study, first, the winding process of the tensile armour layers was explored, and the residual stress distribution in the cross-section of the armour wires after the winding process was obtained. Subsequently, a numerical simulation model of the flexible riser that considers residual stress was established based on the ABAQUS 2021 software to study the shakedown behaviour of the flexible riser under cyclic tensile loads. The results show that, during the initial loading–unloading process of the example pipe, the stress in the armour wire cross-section undergoes obvious redistribution. When cyclic loading is applied with a tensile force range of 0–16.1 kN, the armour wire cross-section tends to reach a shakedown state as the number of loading cycles increases. However, when cyclic loading is applied with a tensile force range of 0–30.2 kN, the strain of the armour wire cross-section gradually increases with each loading–unloading cycle, thus exhibiting a ratcheting effect. The cyclic tensile shakedown prediction model proposed in this study can provide a reference for the design of armour layers in deepwater flexible risers.

With the increasing application of flexible pipes in deep-sea operations, higher processing accuracy is required for the individual metal layers of these pipes to withstand greater service loads. In the helical winding production of tensile armor layer, the accuracy of tension control greatly affects the uniformity of steel strip after winding. To ensure tension stability during armored steel strip processing, a tension model for the manufacturing process is proposed. The model predicts the magnitude and trend of tension fluctuations caused by the unwinding device, facilitating the design of a steel strip constant tension control system based on integral separation fuzzy PID algorithm, which can achieve fast convergence of tension when tension fluctuation is large. The effectiveness of the system is verified by steel strip winding experiments. The experimental results confirm the accuracy of the prediction model and the reliability and effectiveness of the designed tension control system. With this control system, the tension fluctuation range is reduced by nearly 40% and the average value of standard deviation of spacing after steel strip winding is reduced by 0.21 mm, demonstrating its potential in improving the manufacturing quality of flexible tube tensile armor layer.