ISO Tank: A Specialized Solution for Liquid

An ISO tank is a specialized container featuring a stainless steel tank mounted within a standard container frame, designed specifically for the safe transportation of liquid and gas cargo.

For sea transport of liquid and gas cargo, besides drummed goods, tank containers (ISO Tanks) are also commonly used for whole-tank shipment. This article provides a systematic explanation of tank specifications, applicable cargo, and key operation and cleaning points. Want to first learn about standard dry containers? SeeDry Container (20GP/40GP/40HQ) Guide; for organic and bulk cargo, refer toVentilated Container/Bulk Container Solutions; for more container type parameters, checkMain Parameter Table of Various Container Types.

1. Basic ISO Tank Specifications

Parameter	Standard 20ft Tank	Extended Tank	Gas Tank
Capacity	21,000–26,000 L	26,000–30,000 L	15,000–20,000 L
Max Payload	26,000–36,000 kg	24,000–30,000 kg	20,000–25,000 kg
Tank Material	316L Stainless Steel	316L Stainless Steel	Specialty Steel
Tank Thickness	4–6 mm	4–6 mm	8–12 mm
Design Pressure	4–10 bar	4–6 bar	10–25 bar
External Dimensions	6,058 × 2,438 × 2,591 mm	12,192 × 2,438 × 2,591 mm	6,058 × 2,438 × 2,591 mm
Tare Weight	3,500–5,000 kg	5,000–6,500 kg	5,000–7,000 kg
Insulation Layer	Optional (50–100 mm polyurethane)	Optional	Usually included

Data Source: ISO 1496-3 tank container standards + parameter sheets from major tank leasing companies (Exsif/Stolt/Seaco).

2. Suitable Cargo Types

2.1 Liquid Cargo Classification

Cargo Category	Specific Goods	Tank Requirements	Cleaning Requirements
Chemicals	Alcohols, ketones, acids, alkalis	316L stainless steel	Strict (deep cleaning required between different chemicals)
Food-Grade Liquids	Edible oils, fruit juices, syrups, alcohol	Food-grade 316L + polished interior	Extremely high (food-grade CIP cleaning)
Petroleum Products	Lubricants, base oils, additives	Standard stainless steel	Moderate
Liquefied Gases	Propane, butane, ammonia	High-pressure tank (10–25 bar)	Professional gas cleaning
Dangerous Liquids	Flammable liquids, corrosives	IMDG certification + hazard labels required	According to dangerous goods cleaning procedures

2.2 Liquids Unsuitable for Tank Containers

Liquid Type	Reason	Alternative Solution
High-viscosity liquids >10,000 cP	Difficult to discharge	Heated tank or drum packaging
Strong corrosives >98% sulfuric acid	Corrodes stainless steel	Specialized lined tank or drum packaging
Liquids with a pour point >40°C	Solidifies at ambient temperature	Insulated tank or heated container
Highly volatile and extremely toxic substances	High safety risk	Dedicated specialty tank

3. Tank Structure and Safety Devices

ISO Tank Structural Diagram (Cross-Section):
┌────────────────────────────────────────┐
│          ↕ Frame (Standard Container Frame)   │
│   ┌────────────────────────────┐       │
│   │   ↕ Tank (316L Stainless Steel)     │       │
│   │   ○ Top Manlid (Loading/Inspection Port) │       │
│   │   ○ Safety Valve (Pressure Protection)   │       │
│   │   ○ Vacuum Valve (Negative Pressure Protection) │       │
│   │   ○ Bottom Discharge Valve          │       │
│   └────────────────────────────┘       │
│          ↕ Insulation Layer (Optional)         │
└────────────────────────────────────────┘

Safety Device	Function	Inspection Frequency
Pressure Relief Valve	Automatic release of excess pressure	Before each use
Vacuum Relief Valve	Air intake protection during negative pressure	Before each use
Bottom Discharge Valve	Discharge interface	After each loading/unloading
Manlid	Loading and cleaning inspection port	Before each use
Sight Glass (if equipped)	Liquid level observation	After each loading
Thermometer / Pressure Gauge	Monitor internal conditions	Throughout the journey

4. Tank Operation Procedures

4.1 Pre-Loading Inspection Checklist

□ Tank cleanliness meets cargo requirements (see cleaning standards)
□ Safety valve and vacuum valve functioning properly
□ Manlid gasket intact (food-grade requires PTFE gasket)
□ Bottom discharge valve seals well
□ Tank exterior free of corrosion and dents
□ Frame and corner fittings intact
□ CSC plate and tank plate within validity (tank requires additional IMDG certification)
□ For dangerous goods tanks, also check hazard placards

4.2 Loading Operations

Step	Operation	Precautions
① Grounding	Ground the tank (static electricity prevention)	Especially important for flammable liquids
② Open Manlid	Inspect interior cleanliness	Residue can cause cross-contamination
③ Loading	Load via manlid or top interface	Loading speed ≤2,000 L/min
④ Leave Ullage	Leave ≥2%–5% space above liquid level	Prevents thermal expansion overflow
⑤ Close Manlid	Clean sealing surfaces + replace gasket + tighten bolts	Torque to standard (approx. 150–200 Nm)
⑥ Seal	Apply seals to manlid and discharge valve	Tamper-proofing
⑦ Labeling	Attach cargo label and hazard placards	Mandatory for dangerous goods

4.3 Ullage Space Calculation

Cargo expansion rate estimation:
For every 10°C temperature increase → liquid volume expands approximately 1%–2%

Example:
A 20,000 L tank loaded with 19,000 L of edible oil
During transport, temperature rises from 20°C to 40°C (+20°C)
Volume expansion: 19,000 × 2% = 380 L
Actual remaining space: 1,000 L (already reserved) → Safe ✅
Recommended minimum ullage: 5% of full load (must not be less than 2%)

5. Tank Cleaning Standards

Tank cleaning is one of the highest components of usage cost. Cleaning requirements vary significantly when switching between different cargoes.

Cleaning Level	Applicable Scenario	Cleaning Method
CIP Cleaning	Switching between similar cargo (e.g., Alcohol A → Alcohol B)	Hot water + chemical cleaning agent circulation
Food-Grade Cleaning	General cargo → Food-grade cargo	CIP + steam sterilization + testing
Deep Cleaning	High-purity chemical switching	CIP + acid wash + water rinse + drying + testing
Gas Tank Cleaning	Gas type switching	Professional gas cleaning + inert gas purging

Cost-Saving Tip: Keep tanks cycling within the same category whenever possible (chemicals → chemicals, food → food) to minimize deep cleaning frequency. Frequently changing cargo types adds significant cleaning costs.

6. Tank Leasing Models

Leasing Model	Suitable For	Min Lease Term
One-Way Lease	Single shipment	30 days min
Round-Trip Lease	Regular shipments on fixed routes	90 days min
Long-Term Lease	Stable cargo volume	1 year min
Tank Pool Service	Flexible return at multiple locations	None

7. Common Issues in Tank Transport

Problem	Cause	Consequence	Prevention
Cargo Contamination	Inadequate tank cleaning	Entire load scrapped	Conduct cleanliness test before loading
Discharge Difficulty	Viscosity increase due to low temperature	Incomplete unloading, 5%–10% loss	Use insulated tank or heated discharge
Leakage	Aged gasket / valve not fully closed	Safety + environmental incident	Inspect seals after each loading/unloading
Overweight	Overfilling / incorrect liquid density estimate	Fines + transport delays	Calculate load based on max payload
Safety Valve Leak	Valve malfunction / pressure exceeded	Cargo loss + environmental pollution	Regular PTI safety valve testing

Data Note: Tank parameters are cited from ISO 1496-3 standards. Cleaning and leasing costs are industry reference values; actual costs vary based on cargo type and route. Data current as of July 2026.

Shipping liquid cargo? One tank can replace 80 drums, significantly reducing per-shipment transport costs compared to drummed transport. Bofeng Logistics provides one-stop tank leasing, cleaning, and transport services.

Tank Transport Consultation: info@zhbfwl.com

Tank Container Frequently Asked Questions (FAQ)

Q: For liquid cargo, should it be transported in tank containers or drums?

A: When the shipment volume is large (usually above 15,000L), the liquid viscosity is moderate, and the cargo type is stable, tank containers have more obvious advantages—fast loading/unloading, no need for a large number of drums and pallets, and reusable after cleaning as needed. For small batches or multiple product types consolidated, drummed transport is more flexible. You can consult your freight forwarder based on the cargo nature and shipping route before choosing.

Q: Can ISO tanks carry dangerous liquid goods?

A: Yes, but the tank container must have IMDG certification and dangerous goods markings. Before loading, documents such as MSDS and dangerous goods packaging certificate must be provided, and the shipping company should be confirmed as to whether they accept this type of dangerous goods booking. Declaration and container loading must be carried out in accordance with dangerous goods transport regulations.

Disclaimer: This article was compiled and written by the Bofeng Logistics team, with content verified in September 2026. Container specifications and tank container usage fees may vary due to shipping company, tank container leasing market, and route changes; please refer to the information confirmed at the time of booking.