LNG (Liquefied Natural Gas) has an ultra-low boiling point of -162°C at atmospheric pressure, making its loading and unloading onto/from vehicles (e.g., LNG tank trucks, LNG-fueled heavy-duty vehicles) a high-risk operation with strict requirements for equipment. Cryogenic loading arms are specifically designed to address the unique challenges of LNG transfer, and their mandatory use stems from the following core reasons, which directly relate to operational safety, efficiency, and system reliability:
1. Adaptability to Ultra-Low-Temperature Environments
LNG’s extreme low temperature poses severe risks to conventional transfer equipment (e.g., ordinary hoses or non-cryogenic pipes):
Conventional materials (such as rubber hoses or carbon steel pipes) become brittle and prone to cracking or fracturing at -162°C, leading to catastrophic LNG leakage.
Cryogenic loading arms are constructed with cryogen-resistant materials (e.g., austenitic stainless steel 316L for the arm body, cryogenic-grade composite seals) that maintain mechanical toughness, structural integrity, and sealing performance even at ultra-low temperatures. This prevents material failure caused by cold brittleness, a critical safeguard against leakage.
2. Reliable Sealing to Prevent LNG Leakage and Vaporization Hazards
LNG is highly volatile—even a tiny leak can rapidly vaporize into natural gas (with a volume expansion ratio of about 625:1 at standard conditions), creating risks of fire, explosion, or oxygen depletion in confined spaces. Cryogenic loading arms ensure tight sealing through:
Specialized cryogenic sealing structures: Multi-layer seals (e.g., metal-to-metal primary seals + PTFE-based secondary seals) that resist cold shrinkage and maintain a tight fit between the loading arm and the vehicle’s tank interface, eliminating leakage points.
Stable connection under dynamic conditions: During loading/unloading, LNG vehicles may experience slight movements (e.g., ground settlement, tank thermal expansion). Cryogenic loading arms (especially those with flexible joints) can compensate for these displacements while keeping the seal intact—unlike rigid pipes that may loosen or break, or ordinary hoses that may kink and leak.
3. Structural Stability to Avoid Equipment Damage and Operational Disruptions
LNG vehicle loading/unloading involves repeated connection and disconnection, as well as exposure to external forces (e.g., wind, vehicle vibration). Cryogenic loading arms offer superior structural stability compared to alternative equipment:
Rigid yet flexible design: The arm body is supported by a sturdy frame and equipped with swivel joints (e.g., ball joints, sleeve joints) that allow smooth rotation and adjustment. This design avoids the risk of kinking (common with hoses) or bending (common with unstructured pipes), ensuring consistent flow and preventing blockages or pressure surges.
Resistance to mechanical stress: Unlike lightweight hoses that may be dragged or damaged by vehicle movement, cryogenic loading arms are fixed to a stable base and can withstand moderate external tension/compression, reducing the likelihood of accidental damage during operation.
4. Compliance with Industry Safety Standards and Regulations
Global LNG industry standards and local safety regulations (e.g., ISO 13628-6 for LNG transfer systems, GB 50156 for China’s LNG filling station design) explicitly mandate the use of cryogenic-specific equipment for LNG transfer operations involving vehicles. These standards are developed based on decades of operational experience and risk assessments, and they recognize cryogenic loading arms as the only equipment that meets the safety thresholds for:
Ultra-low-temperature resistance,
Leakage prevention,
Structural reliability,
And compatibility with LNG’s physical properties.
Using non-compliant equipment (e.g., repurposed industrial hoses) not only violates regulations but also exposes operations to unacceptably high safety risks, including fines, operational shutdowns, or accidents.
In conclusion, cryogenic loading arms are not just a "preferred" option but a mandatory safety critical component for LNG vehicle loading and unloading. They address the fundamental challenges of LNG’s ultra-low temperature and volatility, ensuring that transfer operations are safe, efficient, and compliant with industry norms—ultimately protecting personnel, equipment, and the surrounding environment from potential hazards.