Tetrahydrofuran is assigned UN2056, Class 3, Packing Group II under the IMDG Code, ADR, and 49 CFR. Typical shipments fall under UN packing instruction P001 for drums and the applicable UN IBC instruction for liquids. The liquid density at 20 °C is approximately 0.889 g/cm³; the closed-cup flash point is -14 °C, the normal boiling point is 66 °C, and the vapour pressure is 193 hPa at 20 °C. THF loading parameters: drums, IBCs and ISO tanks per container are therefore governed by two interacting constraints: the mechanical load capacity of the package and the requirement to preserve a stabilizer-effective ullage against peroxide formation. Commercial inhibited THF commonly contains butylated hydroxytoluene at 100–300 mg/kg. If the inhibitor is depleted, or if the product is unstabilized, oxygen ingress into an under-filled closure can generate tetrahydrofuran hydroperoxide, which changes storage interval and pre-shipment peroxide test requirements.

The package closure and gasket boundary is equally restrictive. THF swells or extracts plasticizers from natural rubber, EPDM, and many polychloroprene seals. Closed-head carbon steel drums are therefore specified with an interior phenolic or epoxy-phenolic coating. Composite IBC inner receivers are acceptable only when the manufacturer’s compatibility data cover THF at the intended voyage temperature. PTFE and flexible graphite are the usual gasket selections. Where IBC valves contain thin-wall polypropylene, terminal operators often restrict direct sunlight exposure by using insulated container liners; published data for long-term THF contact with polypropylene valve components above 35 °C is limited.

Why a 20 ft dry container is limited to 80 closed-head steel drums for THF

A standard 20 ft general-purpose dry container with a maximum payload near 28,230 kg and internal dimensions of 5,898 mm × 2,352 mm × 2,393 mm accepts 80 × 200 L closed-head steel drums in two layers. The typical drum outer diameter used for stowage planning is 584 mm. Four drums across the width occupy 2,336 mm, and ten drums along the length occupy 5,840 mm. The floor layer therefore contains 40 drums, and the second layer contains another 40, yielding 16,000 L of THF. Net product mass at 0.889 g/cm³ is 14,224 kg. Steel drum tare and dunnage add approximately 1,500–2,000 kg, keeping gross mass near 16,000–17,000 kg, below the payload limit.

The two-layer limit is not set by container volume alone. Each drum closure is subjected to the calculated vapour pressure at ambient temperature and to increased headspace pressure during tropical container service. Dock-level inspections of THF drum shipments have shown that loose-stowed three-high stacks increase capseal distortion and side-wall deflection; the observed failure mode is usually closure extrusion under longitudinal braking or transverse coupling, not drum shell rupture. Lashings are therefore arranged to resist the CTU Code acceleration values of 1.0 g longitudinal, 0.8 g transverse, and 0.2 g vertical. The coefficient of friction of steel drum bases on plywood is approximately 0.3–0.4. When condensation or spillage lowers that friction below 0.3, lashing tension must be increased or intermediate dunnage inserted; otherwise drums slide before the lashing reaches its yield point.

Composite IBC loading for THF is controlled by the approved 31HA1 package marking and the 1,200 mm × 1,000 mm base footprint. In the same 20 ft dry container, the floor layer is eight positions: four rows along the length, each holding two IBCs across the width. That layout consumes 4,800 mm of length and 2,000 mm of width. A ninth single-layer IBC cannot be placed without mixed-orientation packing, and published data for mixed-orientation THF IBC stowage is limited; standard terminal practice therefore uses the eight-base grid. If the IBC manufacturer has certified the cage for double-stacking under dynamic transport, the container carries 16 × 1,000 L, equivalent to 16,000 L and 14,224 kg net product. The lower IBC receives the upper filled unit’s gross mass, approximately 950 kg, and must have passed the stacking load test in the UN Manual of Tests and Criteria, Part 6.

Field inspections of caged IBCs in THF return service show stress-whitening at the lower outlet boss where lashing straps pass over the frame. The corrective control is a shaped bearing pad over the outlet area, not higher strap tension on the cage. Bottom discharge valves must be closed and locked before container entry; the valve outlet faces the container door for emergency access but is protected against door-swing impact. IBC inlets are fitted with sealed closures or pressure-vacuum relief only when the route involves substantial altitude changes. Because THF is hygroscopic, IBC inner bottles are not left open during loading when relative humidity exceeds 60 %.

When THF moves in 20 ft ISO tanks, ullage and pressure-relief sizing govern the fill ratio

ISO tank containers built to ISO 1496-3:2019 and approved under the applicable UN portable tank provisions carry THF as a single-shell load. Common 20 ft tank shells have capacities from 20,000 L to 24,000 L; the lower capacity yields 17,780 kg net product, and the upper capacity yields 21,336 kg at 0.889 g/cm³. Road and rail tank regulations for THF apply a maximum filling degree of 95 % at 50 °C, leaving a minimum vapour ullage of 5 %. The relief system is sized for fire engulfment under the recognized framework of ISO 4126-1 and the tank’s UN approval, with set pressure and flow capacity derived from shell wetted area and product vapour pressure.

Nitrogen blanketing at 10–20 kPa gauge is used for extended tank storage and long-sea-voyage shipments to preserve inhibitor concentration. Filling is stopped at the high-level shutoff trip; overfill beyond 95 % removes the vapour cushion needed for liquid thermal expansion. Terminal records attribute partial vent releases to overriding high-level interlocks during top-loading. Pressure-relief valves are routed away from personnel and are not blanked off for cleaning.

Tank shell compatibility requires an interior coating or passivated stainless steel rated for THF at 35–40 °C tropical deck temperatures. Older chlorosulphonated linings are generally unsuitable. The tank discharge valve and vapour-return line remain closed until the receiving line is connected and bonded. Electrostatic bonding is retained because THF may carry low-conductivity contaminants even though it is a polar solvent.

Before a container is released for shipment, the shipper verifies that the gross mass does not exceed the CSC plate payload, the CTU lashing plan covers all three axes, the UN package marking matches the consignment note, and the peroxide content of inhibited THF is within the certificate of analysis. Drums and IBCs are not intermingled in the same base layer; when mixed package loads are unavoidable, the heavier drum stack is placed against the front bulkhead and not over the container wheel pivot.