Classification and Application of Fluid Loading and Unloading Arms
Fluid loading and unloading arms-often referred to as "crane pipes" (or loading arms)-serve as alternatives to rubber hoses for transferring liquids or cryogenic media between tank trucks, ships, and storage tanks. They are categorized based on five key dimensions-carrier type, loading/unloading method, medium characteristics, drive mechanism, and material-and are selected to match specific operating conditions. I. By Loading/Unloading Medium/Carrier (Mainstream Industry Classification)
1. Truck Loading/Unloading Arms (Road-based oil depots / Chemical plant loading racks)
Top-loading arms for trucks Bottom-loading arms for trucks
Structure: Arm length 2–3m; lightweight and compact; single-operator; small turning radius
Diameter: Primarily DN80/DN100; moderate flow rate
Applications: Gasoline, diesel, methanol, ethanol, common chemical solvents; gas stations, private oil depots, small-scale chemical loading racks
Sub-types: Truss-style automatic truck loading arms (3D movement, automated loading; standard for large refined oil depots)
2. Railcar Loading/Unloading Arms (Railway tank car loading racks)
Top-loading enclosed arms for railcars
Structure: Arm length 3–6m; heavy-duty balancing mechanism; long reach; large diameter (DN150/DN200); high flow rate
Features: Compatible with long trains of tank cars; capable of long-distance alignment across multiple cars; supports continuous loading/unloading without uncoupling
Applications: Crude oil, aviation kerosene, diesel, liquefied hydrocarbons, bulk chemical raw materials; refinery railway spurs, railway freight oil depots
3. Marine Loading/Unloading Arms (Terminal/Port-specific arms)
Structure: Extra-long multi-section swivel arms; equipped with wave compensation and emergency release systems; resistant to marine corrosion
Sub-types: Oil tanker arms, LNG cryogenic arms, chemical tanker arms
Applications: Coastal/inland river ports; loading/unloading of crude oil, refined oil, LNG, and liquid chemicals (standard equipment for oil/chemical terminals such as Dar es Salaam and Port of Shanghai)
4. Aircraft Refueling Arms
Small, telescopic, enclosed arms; dedicated to aviation kerosene; transfers fuel from airport depots to aircraft wing inlets
II. By Loading/Unloading Interface Method (Key distinction for environmental and safety regulations)
1. Top-Loading Arms (Single liquid phase / Enclosed gas-liquid dual-phase)
Coaxial gas-liquid enclosed top-loading arms
1) Standard single-pipe top-loading arms Drop pipe extends into the tank opening; no vapor recovery; low cost and simple structure. Suitable for: diesel, heavy oil, lubricating oil, asphalt, low-volatility products, and older, small-scale storage depots. 2) Gas-liquid dual-phase sealed top-loading arm (V-type coaxial loading arm): Liquid enters while vapors are simultaneously recovered; meets VOC emission standards. Suitable for: gasoline, methanol, benzene, and volatile toxic media; mandatory for new standardized oil depots.
2. Bottom-loading arm (API standard bottom loading; mainstream choice for environmental compliance)
Structure: Connects to the API dry-break quick-connect coupling at the bottom of the tanker; fully sealed process with no splashing; features integrated vapor recovery and emergency shut-off.
Advantages: Extremely low volatility, no static-inducing splashing, highest safety rating.
Applications: Gasoline, ethanol, naphtha, hazardous light oils; standard equipment for large domestic refined oil depots and hazardous chemical industrial parks.
III. Classification by conveyed medium & special functions
1. Standard loading arm for ambient-temperature oils (carbon steel)
Media: Gasoline, diesel, kerosene, crude oil, lubricating oil; temperature range: 0–80°C.
2. Corrosion-resistant chemical loading arm
1) PTFE-lined loading arm: Carbon steel with PTFE lining; resistant to strong acids and alkalis (hydrochloric acid, dilute sulfuric acid, liquid caustic soda, acetone, acetic acid); cost-effective. 2) All-stainless steel (304/316L) loading arm: Mirror-polished finish, no dead zones; 304 suitable for neutral/mildly corrosive media; 316L resistant to chloride ions, suitable for fine chemicals, food-grade liquids, and pharmaceuticals.
3. Cryogenic loading arm (TBD type)
LNG cryogenic loading arm
Resistant to -196°C cryogenic temperatures; features pipeline insulation, nitrogen purging to prevent icing, and specialized cryogenic seals.
Media: LNG, liquid ammonia, liquid oxygen, liquid ethylene, LPG.
4. Jacketed heat-tracing loading arm (full-jacket type)
Double-walled jacketed pipeline circulates steam or hot water for thermal insulation to prevent medium solidification. Media: Asphalt, residual oil, molten sulfur, high-viscosity resin, heavy oil prone to solidification in winter
5. Specialized loading arms for liquefied hydrocarbons
Dry-break couplings, explosion-proof seals, emergency release systems; Media: LPG, liquid ammonia, propylene, butane
IV. By drive/operation method
1. Manual loading arm: Spring-cylinder counterweight balancing, manual push-pull operation; for low-volume loading, small depots, and low-frequency scenarios
2. Pneumatic loading arm: Compressed air cylinder drives lifting and rotation; for large oil depots and high-frequency loading; labor-saving
3. Electric/Hydraulic fully automatic loading arm: Remote PLC control, truss-mounted movement; for smart depots, large refining/chemical plants, and automated port terminals
V. By main pipeline material
1. 20# Carbon steel loading arm: General petroleum products; lowest cost
2. 304 Stainless steel: Food products, mildly corrosive chemicals, low-temperature light media
3. 316L Stainless steel: Chloride-containing media, strong acids, fine chemicals
4. PTFE-lined carbon steel: Highly corrosive acids/alkalis, organic solvents
5. Lightweight aluminum alloy: Aircraft refueling, small-scale loading/unloading of light media
VI. Summary of typical industry applications
1. Petroleum refining / Finished oil depots: Closed-loop bottom-loading arms for trucks, large-bore top-loading arms with vapor recovery for railcars, marine loading arms for terminals; Media: Gasoline, diesel, aviation kerosene, crude oil
2. Fine chemical parks: PTFE-lined loading arms, 316L stainless steel closed-loop loading arms; Media: Methanol, acids/alkalis, benzene derivatives, various organic solvents
3. LNG / Gas storage and transport stations: Cryogenic loading arms, specialized liquefied hydrocarbon loading arms; Media: LNG, LPG, liquid ammonia
4. Asphalt / Heavy oil storage: Steam-jacketed/heat-traced loading arms; Media: Asphalt, residual oil, high-viscosity heat transfer oil
5. Port terminals for foreign trade (e.g., Shanghai, Dar es Salaam): Marine loading arms, high-flow railcar loading arms, compatible with international standard steel piping Loading and Unloading at Petroleum Export Tank Farms: Key Selection Criteria
1. Road-based tanker trucks (small-scale/scattered) → Sealed bottom-loading loading arms (gasoline/methanol); simple top-loading arms are acceptable for standard diesel.
2. Rail-based bulk transfer → Heavy-duty, large-diameter top-loading arms with dual vapor return lines.
3. Strong acids and corrosive chemicals → PTFE-lined loading arms.
4. LNG / Cryogenic liquefied gases → Specialized cryogenic loading arms with thermal insulation.
5. Marine/Ocean-going vessel loading/unloading → Marine loading arms (equipped with wave compensation and emergency release systems).
6. High-viscosity, easily solidifying media → Jacketed (heat-traced) loading arms.
