# The Evolution and Development Trends of LNG Loading and Unloading Arms
## 3 Development of Land-Used LNG Loading and Unloading Arms
### Overall Structure of the Land-Used Loading Arm
#### 3.1.2 Cryogenic Breakaway Valve  
The emergency disconnection device is an important part of the loading arm. It can quickly and safely disconnect the connection between the loading arm and the interface in case of an emergency. Most of its core components use emergency shut-off ball valves. The land-used LNG loading arm has a small diameter, and a cryogenic breakaway valve is usually used as the emergency disconnection device; the case is depicted in Figure 11. This can effectively prevent accidents and is widely used in the loading and unloading between  
Figure 11: Cryogenic breakaway coupling. Figure 12: Structure schematic diagram of rupture bolt breakaway coupling with protective components. 1—female valve component; 2—reset and protection component; 3—break-off bolt component; 4—male valve component; 5—signal generation component. loading spouts, fluid loading and unloading arms, vehicles, and ships. Its working principle is that when the pressure in the pipeline is greater than the predetermined pressure, the breakaway valve breaks in the middle, and the one-way valves at both ends automatically close, preventing the pipeline from being pulled apart and the medium from leaking, thus avoiding secondary disasters. It is generally installed in the middle of the vertical pipe of the loading spout. At present, there are mainly two structures for commonly used land-based ultra-low-temperature breakaway valves: the break-off bolt-type breakaway valve and the cable-disconnect-type breakaway valve. Among them, the break-off bolt-type breakaway valve is more widely used. This valve is equipped with check valves at both ends and is connected by break-off bolts. When the pulling force applied to the breakaway valve is greater than the set tensile value of the break-off bolt, the break-off bolt breaks instantly, and the check valves close instantly under the action of the spring to ensure that the breakaway valve does not leak. However, the break-off bolt-type breakaway valve has an obvious drawback, that is, it is difficult for the break-off bolt to meet the two requirements of \"stable connection during normal operation\" and \"easy breakage in case of an emergency\" simultaneously [59]. The critical fracture conditions for the fractured bolt are as follows:  
\[\sigma_{axial}=\frac{F_{applied}}{A_{bolt}} \tag{2}\]  
\[\tau=\frac{F_{applied}}{2\pi r_{neck}t_{neck}} \tag{3}\]  
When the axial stress is greater than the ultimate tensile strength of the bolt material or the shear stress in the necking area is greater than the shear strength of the material, the bolt will break. To solve the problem of the uncertain fracture of the break-off bolt, Lianyungang Ocean Fluid Loading and Unloading Equipment Co., Ltd. added a reset and protection component to the original structure of the breakaway valve; the case is depicted in Figure 12. The reset and protection component includes a reset protection bolt and a connecting device, which is installed at the joint surface of the female valve component and the male valve component and can be flexibly connected and separated. By rotating the reset protection bolt, the male valve component and the female valve component are docked to prevent the break-off bolt component from accidentally breaking during the pipeline connection and disconnection operation. After the operation is completed, this component is separated to enable the break-off bolt component to work normally, greatly improving the safety performance of the break-off bolt-type breakaway valve. After the breakaway valve is pulled apart, the breakaway valve can be manually reset through the reset and protection component and can be used for repeated break-off. Finding a balance between \"stable connection during normal operation\" and \"easy disconnection in case of an emergency\" will be the key focus in the future development of the break-off bolt-type breakaway valve.