Hydrochloric acid (HCl) is commercially transported as an aqueous solution containing 28 wt% to 36 wt% hydrogen chloride, with density at 20 °C ranging from 1.139 kg/L at 28 wt% to 1.179 kg/L at 36 wt%. Under UN 1789, concentrated grades are Class 8 corrosive liquids assigned to Packing Group II, while dilute grades fall to Packing Group III. Anhydrous hydrogen chloride is excluded from these liquid-acid volumes because it is transported as a compressed liquefied gas under different tank requirements. The liquid capacity question is not a single shell volume; it is a function of maximum gross mass, tare mass, filling degree, acid concentration, and the distinction between an ISO tank container and a general-purpose 20 ft dry freight container.

How Much HCl Fits in an ISO Tank or a 20ft Container?

An ISO tank container for hydrochloric acid is built and tested under ISO 1496-3:2019. The nominal shell volume is typically between 21,000 L and 26,000 L, with 24,000 L and 25,000 L among the most common configurations. The permitted cargo volume is not the nominal shell volume. For liquid dangerous goods, the maximum filling degree is normally 95 % at 15 °C under ADR 4.3.2.2 and the corresponding IMDG Code tank provisions. Therefore, a 24,000 L tank has an effective liquid volume of 22,800 L, and a 25,000 L tank has an effective liquid volume of 23,750 L.

Whether these masses can be loaded is governed by the maximum gross mass rating of the tank container. Intermodal liquid tank containers are produced with maximum gross mass ratings such as 24,000 kg, 30,480 kg, 34,000 kg, and 36,000 kg. Tare mass ranges from approximately 3,500 kg to 4,800 kg depending on lining, frame engineering, insulation, and valve arrangement. For a representative 30,480 kg maximum gross mass rating and 3,800 kg tare mass, the allowable product payload is 26,680 kg. A 32 wt% HCl load at 22,800 L has a mass of 26,425 kg, yielding a total road mass of 30,225 kg and a payload margin of 255 kg. The same concentration in a 25,000 L nominal tank at 95 % fill has a mass of 27,526 kg; with the same tare, the total mass reaches 31,326 kg, which exceeds a 30,480 kg rating by 846 kg but is permissible in a 36,000 kg rated tank. At 36 wt%, the 22,800 L load mass is 26,881 kg; total mass becomes 30,681 kg, exceeding 30,480 kg by 201 kg. For that concentration and rating, the payload-limited volume is approximately 22,630 L, equivalent to 94.3 % of a 24,000 L nominal shell, so the filling-degree limit is not the controlling constraint.

Regulatory Fill Limits and Tank Lining Compatibility

The 95 % filling ceiling under ADR 4.3.2.2 is applied to the actual shell volume and provides ullage space for thermal expansion. Hydrochloric acid solutions expand with increasing temperature; without adequate ullage, a liquid-filled tank can develop hydraulic pressure sufficient to deform the shell or lift relief valves. Many tank operators impose a surface temperature limit near 40 °C for concentrated HCl service to limit vapour pressure, lining stress, and expansion. The density values at 20 °C are used for practical payload calculation, while terminals may correct to 15 °C reference density tables for custody transfer.

Concentrated hydrochloric acid cannot be carried in unlined carbon steel or unlined 316L stainless steel tanks. Chloride ions initiate pitting and stress corrosion cracking in stainless steel, while carbon steel is attacked rapidly with hydrogen evolution and iron chloride formation. Lined ISO tanks for HCl service typically use rubber, ebonite, or high-density polyethylene linings selected for the concentration range and maximum operating temperature. Failure experience on lined tanks shows that breaches at manway gaskets, outlet flanges, or vapour-return nozzles allow acid to reach the shell beneath the lining, producing local wall loss that may be detected only by ultrasonic thickness inspection at scheduled intervals.

Vapour-phase corrosion is also a constraint. Pressure-relief valves and vapour-line components must resist wet HCl vapour. Valve trim is commonly specified in PTFE or PVDF with Hastelloy C-276 metallic parts, while unlined stainless steel relief springs and guide rods are unsuitable for continuous exposure. Closed-loop transfer with vapour return is used at loading racks to reduce moisture ingress and vapour release. Hydrochloric acid must be segregated from cyanide-bearing materials, hypochlorite solutions, and strong alkalis under the applicable IMDG segregation tables; contact with sodium hypochlorite liberates chlorine gas, and contact with cyanides liberates hydrogen cyanide.

When a 20 ft General-Purpose Container Carries Packaged Hydrochloric Acid

A general-purpose 20 ft dry freight container conforming to ISO 668 has internal dimensions of approximately 5.898 m length, 2.352 m width, and 2.393 m height, giving an internal volume of about 33.2 m³. It does not carry bulk liquid HCl. The governing limits are package count, stacking capability, package certification, and the container payload. For a maximum gross mass of 30,480 kg and a tare mass of 2,180 kg, the available payload is 28,300 kg.

For 200 L UN 1H1 high-density polyethylene drums containing 32 wt% hydrochloric acid, each drum holds 231.8 kg of product. Non-palletised drums with a diameter of 580 mm can theoretically be arranged ten drums along the length and four across the width, giving 40 drums per layer. If the drum certification permits two-high stacking, the internal height allows two layers, producing 80 drums, 16,000 L of acid, and 18,544 kg product mass. Package tare and securing materials must be added to the container payload calculation. Palletised loading significantly reduces the drum count because four drums per 1.2 m × 1.0 m pallet and ten pallets per single tier yield only 40 drums, equivalent to 8,000 L and 9,272 kg product.

A common packaged alternative is the 1,000 L UN 31H1 high-density polyethylene intermediate bulk container. With a footprint of approximately 1.219 m × 1.016 m, four IBCs fit along the container length and two across, giving 8 IBCs per single tier. This configuration provides 8,000 L and 9,272 kg of 32 wt% acid, far below the container payload but limited by floor dimensions. Stacking of IBCs is not assumed unless the specific IBC design and approval permit superimposed load.

The volume breakpoint for packaged acid is therefore package geometry rather than container volume. A 20 ft general-purpose container loaded with double-stacked drums carries more acid than an IBC configuration, but the drum arrangement requires verified stacking limits, robust blocking and bracing, and compatible pallet or dunnage material. Spill containment and acid-resistant floor protection are required because hydrochloric acid attacks standard steel container floors and may generate corrosive vapour inside the enclosed space. Package-level certification to UN 1H1 or UN 31H1 is mandatory, and closures must be vented only where the design permits pressure equalisation without releasing liquid.

Operational boundaries include the exclusion of aluminium, zinc, and galvanised components from the liquid and vapour path. Loading hoses for ISO tank transfer are normally specified with PTFE or polypropylene liners and Hastelloy C-276 metallic trim, while unlined stainless steel is unsuitable for concentrated acid service. These constraints, rather than the bare shell volume, determine how much hydrochloric acid is placed on board.