Flexitank

What Is a Flexitank?

A flexitank is a flexible, multi-layer polyethylene liquid transport bladder installed inside the internal volume of a standard 20ft sea container. It turns the container into a temporary bulk liquid tank without requiring any special equipment or tank investment, allowing significantly more liquid to be carried in the same container volume compared to drums, IBC tanks, or palletized jerry cans.

Preparing the Container

Because a flexitank applies direct pressure to the container walls, a wooden or metal support panel (bulkhead) must be installed against the front wall (opposite the doors) before installation. As the bladder fills, this panel distributes the load across the container structure and prevents the walls from bulging outward. These bracing systems and the door barrier — both counted among flexitank accessories — can, if installed incorrectly, cause the bladder to place excessive pressure on the doors and leak.

How Much Liquid Does It Carry?

A standard 20ft container flexitank can carry approximately 24,000–26,000 liters of bulk liquid, with allowance left for thermal expansion during loading and movement during transport. The exact capacity depends on the container's internal volume, the amount of headspace left, and the density of the liquid being carried. Filling the container completely is not recommended, since liquid expanding with rising temperature can then place excessive pressure on the bladder.

Which Liquids Can Be Carried?

Flexitanks are manufactured in two main classes: food-grade and industrial-grade. Food-grade flexitanks are used to carry liquids suitable for direct or indirect food contact, such as vegetable oil, olive oil, wine, fruit juice, and glucose/syrup, while industrial-grade flexitanks are preferred for non-food products such as chemical liquids, base oil, glycerin, and liquid fertilizer. The difference between the two types lies in whether the bladder's inner surface is made from a food-contact-grade raw material; choosing the wrong type for the liquid being carried creates a risk of both product contamination and chemical degradation of the bladder.

Why Is It Single-Use?

Flexitanks are designed for single use and are disposed of after discharge; they are not reused. The main reason is the risk of residue or chemical reaction on the bladder's inner surface when switching from one liquid to another — in food-grade bladders in particular, even trace residue left from the previous load can count as contamination. Cleaning and recertifying a flexible bladder at an industrial scale can also cost more than a new bladder, making reuse uneconomical as well.

Loading and Discharge Configurations

Flexitanks can be manufactured with different valve configurations, such as top loading/top discharge or top loading/bottom discharge. Top loading is done with a pump through a valve near the top of the bladder, close to the container doors, while bottom discharge uses a valve at the front bottom corner of the bladder to allow gravity discharge, shortening unloading time. The right configuration should be chosen based on the equipment available at the loading and unloading site (pump, hose connection height); this is covered in detail on the valve and filling system product page.

Advantages

• High capacity: Carries a greater liquid volume in the same container than drums or IBC tanks.
• No return-load cost: There's no need to ship empty IBC tanks or drums back; the flexitank is disposed of at destination.
• Fast installation: With the right bracing equipment, a standard container is ready for bulk liquid transport in a short time.

Common Mistakes

• Insufficient bracing: A missing or poorly installed support panel can let the bladder press against the doors under transport vibration and tear.
• Overfilling: Filling without leaving room for expansion increases the risk of the bladder bursting when temperatures rise.
• Choosing the wrong type: Using an industrial-grade flexitank to carry a food product creates a serious contamination risk.

Container Selection and Previous Cargo Suitability

The interior surface of a container intended for flexitank use must be sound, free of holes or sharp protrusions; even a small metal burr or weld seam can wear through the bladder over time. For food-grade flexitank use, it's important that the container's previous cargo was not incompatible with food or liable to leave residue; suppliers therefore generally recommend checking the container's most recent cargo history.

Use With Other Products

For temperature-sensitive liquids (certain food oils, wines), using a thermal pallet cover or an in-container thermal liner alongside the flexitank can be considered to reduce temperature fluctuation inside the container. For liquid shipments too small in volume to justify a flexitank, bag-in-box or liquid transport bags are a more suitable solution.