An ISO Tank Container is a stainless-steel or alloy-steel cylindrical pressure vessel mounted in a 20-foot ISO 1496-3 container frame, designed for the transport of bulk liquids, gases, and powders. Capacities are typically 18-26 cubic metres, equating to 16-25 MT depending on cargo density. UN portable tanks are classified by T-code in IMDG Code Chapter 6.7, with each code specifying minimum test pressure, minimum shell thickness in reference steel, bottom-outlet permission, and pressure-relief regime. ISO tanks carry the bulk of the world’s hazardous liquid chemical trade, competing with parcel tanker chemistry shipping for the same cargoes at different scales.
ISO tank type codes
T-codes are UN Portable Tank Instructions per IMDG Code Chapter 6.7. The system splits into four families.
| Family | Codes | Cargo class |
|---|---|---|
| T1 to T22 | 22 codes | Liquids and solids of Class 1 and Classes 3 to 9 |
| T23 | 1 code | Class 4.1 self-reactive substances and Class 5.2 organic peroxides |
| T50 | 1 code | Non-refrigerated liquefied gases (LPG, ammonia, chlorine, ethylene oxide, refrigerants) |
| T75 | 1 code | Refrigerated cryogenic liquefied gases (LIN, LOX, LAR, LCO2, LNG, LH2) |
Common codes seen on China to Australia chemical lanes:
| Code | Min test pressure | MAWP | Bottom outlet | Pressure relief | Typical cargo |
|---|---|---|---|---|---|
| T1 | 1.5 bar | 1.0 bar | Allowed | Normal PRV | Wine, juice, glycerin, water |
| T6 | 4 bar | 2.65 bar | Allowed | Normal PRV | Class 3 PG II flammables: methanol, ethanol, acetone, MEK, toluene |
| T11 | 6 bar | 4 bar | Allowed | Normal PRV | The workhorse: ~1,000 UN-numbered chemicals plus food and water |
| T14 | 6 bar | 4 bar | Not allowed | Frangible disc plus tell-tale gauge | PG I corrosives, Class 6.1 PG I/II: 98% sulphuric acid, oleum, fuming nitric, hydrofluoric, sodium hypochlorite |
| T20 | 10 bar | 4 bar | Not allowed | Frangible disc | Bromine (UN 1744), titanium tetrachloride, trichlorosilane |
| T22 | 10 bar | 4 bar | Not allowed | Frangible disc | Highest-hazard organometallics and fluorinations |
| T50 | Per gas (5 to 34.4 bar) | Per gas | Per gas | Various, often frangible | Liquefied compressed gases |
| T75 | Vacuum-jacketed | 10 to 24 bar | Not allowed | Dual relief plus vapour vent | Cryogenic liquefied gases |
For routine chemical buyers, T11 is the workhorse and T14 covers the high-hazard corrosives and toxics that cannot ride in T11. A substance assigned a specific T-code may also be carried in any stronger code: a T11 cargo may go in T11 through T22, a T6 cargo in T6 through T22.
A common point of confusion is shell thickness. The IMDG values (typically 6 mm minimum) are quoted in “reference steel” with Rm 370 N/mm2. The actual wall thickness in 316L stainless steel is calculated through the Lloyd’s formula in IMDG 6.7.2.4 and works out at about 4.18 mm for the 6 mm reference. A 316L tank quoted as “T11 / 6 mm reference” is not 6 mm of stainless on the wall.
Standard ISO tank dimensions and capacity
Most ISO tanks share standard dimensions to fit container handling:
| Dimension | Standard |
|---|---|
| Length | 6058 mm (20-foot ISO frame) |
| Width | 2438 mm |
| Height | 2591 mm |
| Empty mass | 3,500-4,500 kg |
| Maximum gross mass | 30,480 kg (standard for road and rail) |
| Net cargo capacity | 16-25 MT depending on density |
For caustic soda solution at SG 1.5, a 24,000-litre T11 tank holds 36 MT brimful but is typically loaded to ~26 MT (at 73% fill, allowing 27% ullage for thermal expansion). For methanol at SG 0.79, the same tank holds 18-20 MT.
Lining options
The internal lining is the critical specification for chemical compatibility. Common lining-cargo pairings:
| Lining | Compatible cargoes | Incompatible cargoes |
|---|---|---|
| Stainless steel (316L) bare | Most acids (sulphuric, nitric at >70%), most non-aggressive chemicals | Strong reducing acids (concentrated HCl); chloride-containing solutions for long contact |
| Stainless steel with electropolish | Pharma and food-grade chemicals where ultra-clean surface matters | n/a (polish is additive) |
| HDPE-lined | Caustic soda, sodium hypochlorite, dilute acids, sodium silicate | Strong oxidisers; high-temperature cargoes |
| PFA-lined (PTFE / fluoropolymer) | Hydrofluoric acid, very pure pharma chemistry, aggressive halogenated chemistry | High mechanical-stress cargoes (lining is mechanically fragile) |
| Rubber-lined | Some sulphuric acid grades, certain mineral acids | Solvents that swell rubber |
The lining is built into the tank specification at manufacture. Tank operators maintain dedicated fleets of lined tanks for specific cargo categories. Re-lining is expensive and rarely done; tanks are typically retired and replaced when lining wears.
For a chemical buyer specifying ISO tank shipping, the lining must be confirmed at booking. A buyer ordering caustic in an unlined stainless tank receives iron-contaminated cargo that may fail downstream specs, the SS interior reacts with caustic over the voyage time.
When ISO tank is the right packaging
ISO tank is the right choice for:
- Liquid chemical volumes above ~15-20 MT per shipment, the volumetric efficiency vs IBCs or drums is significant
- Long-term supply where the ISO tank fleet provides cargo control, buyer-owned or buyer-leased tanks rotate predictably
- Buyer with destination tank-storage capability, discharging to a buyer-side storage tank vs decanting to drums
- Cargo where contamination sensitivity drives packaging quality, a clean dedicated ISO tank carries less contamination risk than a barrel-cleaned drum fleet
When ISO tank is the wrong packaging
ISO tank is wrong for:
- Smaller parcels under ~10 MT. IBC or drum format is more economical
- Specialty cargoes where dedicated tanks are not available, operators cannot economically maintain dedicated fleets for low-volume chemistries
- Buyers without destination unloading infrastructure. ISO tank discharge requires pumps, hoses, and personnel rated for the cargo type
- Routes where ISO tank repositioning costs are prohibitive, laden one-way to a low-backhaul market drives the round-trip equivalent rate up
ISO tank repositioning economics
The freight rate on an ISO tank is dominated by repositioning. A laden tank from Shanghai to Houston ships at the laden rate. The empty repositioning back to China is the trickier economics:
| Backhaul scenario | Effect on per-tonne rate |
|---|---|
| Strong demand backhaul (the same operator finds a Houston-China laden cargo) | Lowest rate; the tank is fully utilised in both directions |
| Weak backhaul (the operator runs the empty tank back at low priority) | Higher rate; the buyer effectively pays for half the empty leg |
| No backhaul (one-way pricing) | Highest rate; the buyer pays the full round-trip equivalent |
For volume buyers running stable-volume chemical lanes, negotiating backhaul-utilised pricing with major ISO tank operators (Stolt-Nielsen, Hoyer, Bertschi, Bulkhaul) can save USD 300-600 per tonne vs spot pricing. The negotiation hinges on the operator’s fleet utilisation in your specific lane.
ISO tank operators in Chinese chemical export
Major operators with significant Chinese-origin business:
- Stolt-Nielsen (especially STX-led joint ventures in China)
- Hoyer (strong on caustic and methanol from northern Chinese ports)
- Bertschi (specialty chemicals from Shanghai and Tianjin)
- Bulkhaul (UK-based with strong China presence)
- Newport Tank (specialty chemistry)
- Several Chinese-domiciled operators (HOLT, Tianjin Bohai)
Each operator has stronger or weaker fleet positioning in specific cargo categories. For a long-term supply line, choosing the operator that has natural laden-flow alignment with your lane saves repositioning cost.
Operator note: the tank cleaning cost
After discharge, ISO tanks must be cleaned before the next loading. Cleaning costs vary by cargo:
- Routine non-DG / low-DG cargo cleanings: USD 200-600 per tank
- Standard DG cleanings (most Class 8, Class 3): USD 600-1,500 per tank
- Specialty cleanings (between incompatible cargoes, or after pharma-grade cargo): USD 1,500-4,000 per tank
The cleaning cost is built into the per-shipment leasing cost in most operating models. For spot bookings it can show as a separate line. For high-frequency shipments of the same cargo, dedicated tank fleets with no cleaning between shipments achieve the lowest per-tonne economics.
Full ISO tank reference
For the complete catalogue covering every UN portable tank instruction (T1 through T22 plus T23, T50, T75), every design and build variant (food-grade, lined, heated, reefer, baffled, swap-body, offshore, powder-silo), and every frame size (10ft, 20ft, 30ft, 40ft, 45ft), see the ISO Tank Container Reference. Each type page carries the full dimensional spec, permitted UN cargoes, manufacturers, operators, and indicative pricing.
The most commonly used tank types: T11 stainless (the global workhorse, ~1,000 UN cargoes), T14 stainless (high-haz corrosives like 98% sulphuric, oleum, fuming nitric), T11 PE-lined (the China-Australia chemical-lane workhorse for HCl 35%, NaOH 50%, sodium hypochlorite), T50 LPG / ammonia (non-refrigerated liquefied gases), T75 cryogenic (LIN, LOX, LAR, LCO2, LNG, LH2). Use the ISO Tank Loading Calculator to compute maximum loadable mass for any tank build under the IMDG 4.2.1.9 fill rules.
Related terms
IBC is the smaller-scale alternative (1 MT vs 25 MT). Drum is the smallest-scale parcel format (200-220 kg). IMDG Class 8 corrosives are heavy ISO-tank users. MARPOL Annex II governs the bulk-liquid pollution category that applies to ISO-tank shipping. Twenty-foot container is the standard ISO frame an ISO tank fits.