Safety of Liquid Chlorine Loading Arms
I. Equipment and Materials (Mandatory Requirements)
Materials: The loading arm, valves, flanges, and swivel joints must be constructed from 316L stainless steel or carbon steel lined with PTFE (Teflon), ensuring complete compatibility with liquid chlorine.
Prohibition of Flexible Hoses: National regulations strictly prohibit the use of standard flexible hoses for liquid chlorine transfer; rigid-pipe loading arms (universal transfer arms) are mandatory.
Safety Accessories (Mandatory Equipment)
Both the gas-phase and liquid-phase lines must be equipped with Emergency Shut-off Valves (operable remotely and locally).
The outlet of the loading arm must be fitted with an Emergency Breakaway Coupling (to prevent leakage in the event of accidental pull-away).
The enclosed section of the liquid-phase line must be equipped with a Safety Relief Device (connected to a chlorine gas absorption system).
Static grounding connections, pressure gauges, thermometers, and ammonia solution leak detection points must be provided.
II. Pre-Operation Checks (Mandatory)
Personnel Qualification: Operators must hold valid certifications; they must wear positive-pressure air-supplied respirators, chemical protective suits, cryogenic gloves, and safety goggles.
Vehicle Securing: The tank truck must be parked securely, with the handbrake engaged and wheel chocks in place; the static grounding clamp must be reliably connected (resistance < 4Ω).
Equipment Inspection
Check the loading arm, joints, and gaskets for cracks, deformation, or signs of aging.
Verify that all valves and emergency shut-off valves operate smoothly and freely.
Inspect all sealing surfaces using a low-concentration ammonia solution (the appearance of white fumes indicates a leak).
Environmental Assessment: Ensure forced ventilation is active; operations are strictly prohibited during thunderstorms, high winds, or periods of extreme heat.
III. Key Points for Loading and Unloading Operations
Connection: Dock the arm gently and carefully; strictly avoid any impact or forceful contact. Verify that the gas-phase and liquid-phase connectors are fully and securely locked in place.
Valve Operation: Open the gas-phase valve first, followed by the liquid-phase valve. Open valves slowly to prevent hydraulic shock (water hammer) and over-pressurization. Pressure Control
Differential Pressure Unloading: The tanker pressure must be 0.15–0.2 MPa higher than the storage tank pressure, with a maximum limit not exceeding 1.4 MPa.
Strictly Prohibited: Exceeding pressure, flow rate, or liquid level limits; an automatic interlock system for overfilling prevention must be installed.
Process Monitoring: Personnel must remain on duty throughout the entire operation to monitor pressure, temperature, and potential leaks; leaving one's post, using mobile phones, or performing hot work (work involving open flames/sparks) is strictly prohibited.
IV. Post-Unloading and Reset (Critical Steps)
Procedure: First close the tanker valve, then close the loading arm valve; dismantling components while under pressure is strictly prohibited.
Residual Liquid Handling: Purge residual chlorine from the loading arm using nitrogen gas, directing it into the chlorine absorption system; on-site venting/discharge is strictly prohibited.
Reset: Return the loading arm to its home position and secure it; clean up the work area; and complete all necessary records.
V. Maintenance and Inspection (Mandatory Schedule)
Semi-annually: Pressure testing (at 1.5 times the nominal pressure); thoroughly dry the equipment after testing to prevent corrosion.
Monthly: Inspect and lubricate rotary joints, seals, and emergency shut-off/breakaway valves.
Annually: Comprehensive wall thickness measurement, anti-corrosion treatment, and airtightness testing.
VI. Leak Emergency Response (Top Priority)
Immediate Action: Stop operations immediately, close the emergency shut-off valve, cut off the chlorine source, and evacuate personnel to an upwind location.
Personnel Protection: Personnel must wear positive-pressure SCBA (Self-Contained Breathing Apparatus) combined with a fully encapsulated chemical protective suit; take precautions to prevent frostbite.
Leak Mitigation Principles:
Minor Leaks: Tighten bolts or replace gaskets; use specialized chlorine leak-sealing tools.
Major Leaks: Activate the alkali absorption system (using NaOH or lime water) to neutralize the chlorine.
Strictly Prohibited: Directly spraying water onto the leak point (this will exacerbate vaporization, corrosion, and potential freeze-induced cracking).
Alarm/Reporting: Immediately notify the Fire Department (119), the Emergency Response Team, and Environmental Protection authorities; establish a designated cordon/exclusion zone.
VII. Absolute Prohibitions (Red Lines)
Prohibited: Using flexible hoses for loading or unloading liquid chlorine.
Prohibited: Dismantling, striking, or subjecting the loading arm to impact while it is under pressure.
Prohibited: Exceeding pressure limits, overfilling, or rapidly opening/closing valves.
Prohibited: Conducting operations without proper protective gear, continuous monitoring, or established emergency response measures.
Prohibited: Indiscriminately discharging residual liquid into the environment.
