Cryogenic Liquid Unloading Arm

Cryogenic liquid unloading arms are high-efficiency loading/unloading devices specifically designed for ultra-low-temperature media such as liquefied natural gas (LNG), liquid hydrogen, and liquid oxygen. Widely used in the energy, chemical, and aerospace industries, they enable safe fluid transfer between storage tanks, tank trucks, ships, and receiving stations. The following introduction covers technical characteristics, structural design, application scenarios, safety protection, and industry trends:

I. Core Functions and Technical Characteristics

Ultra-Low-Temperature Adaptability

Adopting a double-layer vacuum insulation structure, the inner pipe conveys ultra-low-temperature media ranging from -196℃ to -253℃, while the outer pipe forms a vacuum interlayer to minimize heat conduction and prevent frosting and leakage. For example, LNG unloading arms typically have a design temperature range of -196℃ to +200℃, a nominal diameter of DN50, and a working pressure of 0.6MPa, capable of withstanding dynamic loads from tank truck displacement and ship sway.

3D Flexible Operation

Equipped with multiple sets of swivel joints (e.g., double-raceway structure) and a spring balancing system, the arm supports free movement in 3D space to adapt to different loading/unloading positions. For instance, LNG marine loading/unloading arms can achieve automatic ship-to-shore docking through multi-axis linkage, with a precision of millimeters.

High-Efficiency Sealing and Reliability

Swivel joints are made of austenitic stainless steel or aluminum alloy, paired with PTEE seals or metal sealing surfaces to ensure long-term leak-free operation at low temperatures. Some products incorporate cold compensation technology, maintaining stable sealing performance within the range of -196℃ to +65℃, with a service life of over 15 years.

II. Structural Composition and Key Components

Basic Structure

It includes a column, liquid-phase arm, gas-phase recovery arm, balancing device, and control system. The column is fixed to the loading/unloading platform via bolts; the liquid-phase and gas-phase arms are independently designed to handle medium transportation and gas recovery, respectively.

Key Components

Swivel Joint: Precisely machined with a double-raceway structure, supporting 360° rotation. Some models enable smooth operation without nitrogen purging.

Emergency Release System (ERS): Automatically separates in case of accidental pulling to prevent medium leakage, with both ends sealing quickly after separation.

Intelligent Sensors: Integrate monitoring modules for temperature, pressure, displacement, and vacuum degree to provide real-time operation status feedback and support IoT-based remote monitoring.

Balancing System: Utilizes a spring cylinder or counterweight design to keep the arm balanced at any position, reducing the operating force to below 150N.

Materials and Manufacturing Processes

The inner pipe is made of 304/316L stainless steel, while the outer pipe can be aluminum alloy or carbon steel. TIG argon arc welding is used for welding, with weld flaw detection meeting Grade Ⅱ standards. Some products adopt a topology-optimized structure, reducing self-weight by over 20% while ensuring strength.

III. Application Scenarios and Industry Cases

Energy Sector

LNG Receiving Terminals: Used for rapid docking between transport ships and onshore terminals, with a single unloading capacity of up to 170,000 cubic meters and support for continuous operation.

Hydrogen Refueling Stations: Adapt to the ultra-low temperature (-253℃) and high-pressure environment of liquid hydrogen, enabling efficient refueling of hydrogen fuel cell vehicles.

Cryogenic Storage Tanks: Connect tank trucks and storage tanks to complete loading/unloading of industrial gases such as liquid nitrogen and liquid oxygen.

Chemical and Aerospace Industries

Cryogenic Ethylene Transportation: Realize sealed loading/unloading of cryogenic ethylene in petrochemical plants to avoid medium volatilization.

Rocket Fuel Refueling: Provide high-precision and high-safety fuel delivery for liquid oxygen/liquid hydrogen rocket engines.

IV. Safety Protection and Operation Specifications

Multiple Safety Mechanisms

Leakage Early Warning: Built-in high-sensitivity sensors monitor vacuum degree and medium pressure in real time; abnormal conditions trigger automatic alarms and valve shutdown.

Static Electricity Discharge: The all-metal structure is connected to tank trucks via grounding wires to ensure safe static discharge.

Emergency Shutdown: The ERS is typically set with a triggering force of 1.5-3 tons, a separation time of <0.5 seconds, and a leakage volume of <50 milliliters.

Maintenance and Inspection

Daily Maintenance: Monthly checks of hydraulic oil******, wire rope wear, and swivel joint lubrication; annual air tightness tests and pressure tests.

Overhaul Cycle: Comprehensive disassembly and inspection every 5-8 years, replacement of seals, hydraulic oil, and worn parts, and testing of vacuum degree and movement precision.

V. Industry Trends and Technological Innovation

Intelligent Upgrading

Integration of AI visual recognition, Internet of Things (IoT), and digital twin technology to achieve fully automatic control and remote operation of the loading/unloading process. For example, intelligent unloading arms can automatically identify tank truck interface positions via laser scanning, with an error of <2 millimeters.

Lightweight Design and Composite Materials

Adoption of carbon fiber-reinforced composite materials or topology-optimized aluminum alloy structures to reduce self-weight while maintaining strength, minimizing loads on supporting structures.

Hydrogen Energy and Deep-Sea Applications

Development of new sealing technologies for the ultra-low temperature characteristics of liquid hydrogen, while exploring high-pressure-resistant designs for deep-sea LNG ship unloading arms to adapt to future offshore energy development needs.