Avoiding Freezing of Liquid Ammonia Loading Arms in Low-Temperature Environments
Liquid ammonia has a boiling point of -33.5℃. In low-temperature environments (especially outdoor operations or winter), the surface of the loading arm is prone to frosting due to heat absorption from liquid ammonia evaporation. Accumulated frost and freezing can cause swivel joints to jam, valves to fail, and even pipe blockages. Freezing not only interrupts loading and unloading operations but may also cause equipment damage from forced operation, indirectly increasing leakage risks. Thus, preventing freezing is fundamental to ensuring stable operation of the loading arm under low-temperature conditions.
Specific measures
1. Install heat tracing and insulation devices：Wrap electric heat tracing cables around the loading arm pipes and valves, combined with insulation layers (e.g., polyurethane foam) to maintain the pipe temperature above -30℃, preventing local condensation and freezing of liquid ammonia. The heat tracing system should be equipped with temperature sensors to automatically power off when overheating.
2. Regular defrosting and cleaning：Remove surface frost with non-flame heat sources (e.g., heat guns) before operation, avoiding hard objects to prevent pipe damage; check insulation layer integrity daily and repair damaged areas promptly to prevent heat loss.
3. Optimize operation procedures：Before loading/unloading, slowly open valves for "pipe warming" to preheat the pipeline with a small flow of liquid ammonia; keep a small amount of medium circulating during intervals to avoid stagnation and freezing; thoroughly drain residual liquid ammonia after operation and purge the pipeline with dry nitrogen.
4. Use low-temperature resistant materials and structures：Adopt cold-resistant designs for moving parts like swivel joints, with seals made of materials that do not harden at low temperatures; avoid right-angle designs at pipe elbows to reduce medium retention dead corners and lower freezing risks.
