# The Evolution and Development Trends of LNG Loading and Unloading Arms
## 1 Introduction  
At present, economic development, population growth, industrialization, and urbanization are important reasons for the rapid growth in global energy consumption. The world population will increase by 22% in 2040. During the period from 2000 to 2013, worldwide energy consumption was raised nearly 2.4% per annum [1]. From 2012 to 2035, the global energy consumption is expected to increase by 41%. So far, oil remains the main source of global energy consumption. The combustion of oil and coal generates large amounts of sulfides, nitrogen oxides, and carbon dioxide, which have a serious impact on the global ecology and climate change. In parallel, renewable energy represented by solar and wind power is accelerating its displacement of conventional energy sources. For example, solar photovoltaic technology enables the widespread application of solar energy due to its advantages such as no toxic emissions, no noise, and ease of maintenance [2]. However, solar energy storage and utilization technologies remain immature, and solarenergy utilization faces unreliability risks due to natural constraints. Thus, natural gas is currently considered one of the cleanest energy sources. Liquefied natural gas (LNG for short), as a clean, environmentally friendly and high-quality energy source, is an important raw material for modern industry and plays an important role in the third energy transition [3]. In 2023, China imported 165.56 \(\times\) 108 m\({}^{3}\) of LNG, an increase of 14.76 \(\times\) 108 m\({}^{3}\) compared with 2022 [4]. China surpassed countries such as Japan to become the world's largest importer of liquefied natural gas. In the past two decades, the application technology of LNG has developed unprecedentedly. An LNG industry involving various links from liquefaction, storage, transportation, to end-use, as well as the manufacturing of supporting equipment, has been gradually established, which has become an important feature of the development of the LNG industry [5]. At present, the main transportation methods of natural gas globally are pipeline transportation and liquefied natural gas (LNG) transportation [6]. Pipeline transportation is suitable for long-distance and large-capacity transportation demands, while LNG transportation is applicable to ocean-going transportation [7]. It can break through environmental barriers, is more flexible and convenient, and better conforms to the trend of globalization. LNG transportation is the key to future development. The transportation methods of LNG include marine transportation and land transportation. Marine transportation uses LNG carriers to complete the long-distance transportation and storage of LNG [8], and land transportation uses LNG tank trucks to deliver LNG from large-scale receiving terminals or production points to specific consumption points. Whether it is maritime transportation or land transportation, the loading and unloading process of LNG is required, and this process requires a key piece of equipment, namely the LNG loading and unloading arm. With the rapid development of the application fields of LNG and the growth of LNG demand, higher requirements are put forward for the performance and technical level of LNG loading and unloading equipment, and the LNG loading and unloading equipment industry will also develop rapidly. This article conducts research on aspects such as the origin, development history, structural characteristics, principles and structures of key components, and key technologies of the loading and unloading arm. From dimensions such as structural lightweighting, intelligent control, and high-performance materials, it proposes the technical routes for future research. It not only systematically combs the development context of LNG loading and unloading arm technology but also conducts a quantitative analysis of the optimization of key technologies and indicators, providing experimental parameters and comparison benchmarks for subsequent research.