# The Evolution and Development Trends of LNG Loading and Unloading Arms
## 5 Conclusions  
This study comprehensively and thoroughly explores the evolution and future trends of liquefied natural gas (LNG) loading and unloading arms. Firstly, it introduces the background of the LNG industry and the significance of loading and unloading arms. Subsequently, it delves into two application scenarios, namely marine and land:  
* In the field of marine loading and unloading arms, it systematically analyzes the design of full-balance/rotary-balance/double-balance structures, the multi-sealing coordination mechanism of cryogenic swivel joints, the rapid-response principle of emergency disconnection devices, and the intelligent docking technology based on vision-multi-sensor fusion;
* In the field of land-based loading and unloading arms, it focuses on the mechanical optimization model of the spring cylinder balance system, the sealing materials of cryogenic butterfly valves, the automated control strategies for multi-vehicle parallel loading and unloading, and the unmanned docking technology based on trajectory planning algorithms. The research also reveals the challenges faced by key technologies such as material failure at low temperatures, control accuracy under dynamic loads, and sealing reliability in complex environments. It proposes technical paths for future research from dimensions such as structural lightweighting, control intelligence, and material high-performance-ization. (1) Innovative Contributions  
The research content of this paper is interdisciplinary, breaking through the single-perspective of traditional mechanical engineering. It combines fluid mechanics, materials science, control engineering, and intelligent algorithms to construct a four-in-one technical analysis framework of \"structural design-sealing mechanism-intelligent control- safety protection\". For example, in the research on swivel joint sealing, it for the first time expounds on the coupling model between material shrinkage rate and sealing pre-tightening force in a low-temperature environment, as well as the innovative solution of \"dynamic compensation of the main seal + redundant protection of the secondary seal + collaborative nitrogen purging\", providing a method to solve the elastic failure problem of the traditional double-sealing structure at \(-162\)\({}^{\circ}\)C. By comparing and analyzing the equipment data of international mainstream manufacturers such as FMC, SVT, and Kanon, and combining with the engineering practices of domestic LNG receiving stations, it elaborates on the optimized formula for the anti-overturning moment of loading arms suitable for complex sea conditions (such as the moment of inertia distribution model of the double-balance system) and verifies the flange interface recognition algorithm based on the YOLOv8 deep-learning model. This algorithm maintains a docking accuracy of \(\pm 1\) mm under \(\pm 30^{\circ}\) pitch angles and sea state 6 conditions, filling the research gap in intelligent docking technology in dynamic environments in China. Aiming at the current situation of domestic LNG loading and unloading equipment relying on imports, it sorts out the differences between domestic and international standards such as ISO 20519 [81] and GB/T 44412 [82]. Combining with accident cases from LNG terminals in Lianyungang, Tangshan, etc., it proposes material selection standards suitable for the high-humidity and salt-fog corrosion environment along China's coast (such as low-temperature toughness indicators for nickel-based alloys and cold-flow rate control parameters for polytetrafluoroethylene sealing rings), providing a key basis for the standardized design of domestic equipment. (2) Scientific Research Contributions  
This paper expounds on the multi-field coupling model of the mechanical structure-sealing system-control system of loading arms in a low-temperature environment, revealing the influence of temperature gradients on the contact stress of swivel joints, the viscous resistance of hydraulic systems, and the signal transmission of sensors.