An ISO tank is a pressure-rated tank, usually stainless steel, held inside a 20-foot steel frame with the same corner fittings as a standard container. It carries bulk liquids, including many chemicals, and moves by ship, rail and truck like any container.
Between loads, the tank is cleaned at a specialist depot, using a method chosen for the previous cargo and the next one. The depot issues a cleaning certificate before the tank goes to the filling site.
When an ISO tank makes sense
- Volumes are large enough to fill a tank, commonly in the range of about 20,000 to 26,000 litres depending on the tank.
- You want to avoid the cost and waste of drums or IBCs and the labour of filling them.
- The product is a liquid, or can be kept liquid with heating coils during transport.
- Your site can receive a bulk delivery, with a suitable discharge point and storage tank.
- The product is dangerous goods and a suitable tank type is permitted for it under the IMDG Code.
Filling rules
ISO tanks must not travel partly filled. A half-empty tank lets the liquid surge, which can damage the tank and unbalance trucks. Most operators require filling to at least about 80% of capacity while leaving space at the top for expansion. The exact limits depend on the product and the rules, so confirm them with the tank operator.
For dangerous goods, the IMDG Code sets which portable tank types may be used for each UN number, through tank instructions coded T1 to T22. The tank operator checks this before releasing a tank.
How cleaning works
The depot chooses a cleaning method based on the last cargo. Common steps are draining, rinsing with water, washing with hot water and detergent, steaming, solvent washing for products that do not dissolve in water, and drying. Gaskets and valves are checked and replaced where needed.
In Europe, many depots issue the European Cleaning Document, a standard format promoted by the industry federation EFTCO. Elsewhere, depots issue their own certificates. Either way, ask for the certificate and the tank's last three cargoes before filling.
Contamination risks
- Residue from a previous cargo can contaminate yours, especially if that cargo was incompatible.
- Some sensitive products, such as food or high-purity grades, need tanks dedicated to compatible cargo, or a stricter clean.
- Water left after cleaning can spoil moisture-sensitive products.
- Damaged gaskets or valves can leak or contaminate the load.
What to agree with your supplier
Specify acceptable previous cargoes, cleaning standard, and who inspects the tank before filling. Ask for photos of the tank interior, the cleaning certificate and a sample taken from the tank after filling. For larger bulk loads, read about a loading survey for bulk chemicals. Compare tanks with other packaging in drums, IBCs or ISO tanks.
Next step
We inspect tank documents, check cleanliness before filling where access allows, and witness sampling. To start, book a free sourcing review.