Used containers
Corten Steel & Build Quality: What Makes a Used Container Last
How shipping containers are built, why Corten weathering steel resists rust, which parts carry the load, and what that means when you buy a used container.
A shipping container is built to survive years of salt spray, storms and rough handling at sea, all while stacked many high on a rolling ship. That's why a used one can still give years of service on land. Understanding how containers are built helps you judge which used ones still have plenty of life left.
Here's what containers are made of, which parts do the work, and what to check before you buy used cargo shipping containers. When you're ready, browse our graded units to buy used cargo shipping containers.
Corten steel: why containers resist rust
Most container walls, roofs and doors are made from Corten, a type of weathering steel. When it's exposed to weather, it forms a tight layer of surface rust, called a patina, that slows further corrosion.
Combined with marine paint, this is why a container can spend years at sea and still be sound. It's also why surface rust is normal on a used container and not a reason to reject it.
Weathering steel isn't rust-proof, though. Where water sits for long periods, such as in roof dents or against wet ground, corrosion can keep going until it eats through. That's what to look for.
The parts that carry the load
A container's strength comes from its frame, not its walls:
Corner posts
Four vertical steel posts carry the weight of the container and anything stacked on it. They need to be straight and uncracked.
Corner castings
Cast steel blocks at all eight corners are used for lifting, stacking and locking containers together. They must be intact.
Top and bottom rails
Steel rails run along the top and bottom edges of each side. The bottom rails are close to the ground and the most prone to rust.
Cross members
Steel beams run across the base under the floor, supporting it and the load. They should be solid, without heavy, flaking rust.
Corrugated walls
The walls are corrugated steel panels. The corrugations add stiffness, helping the walls resist bending.
The floor
The floor is usually thick marine plywood or hardwood planks, laid over the cross members and screwed down from underneath. It's built to carry forklifts and heavy cargo. Many floors are treated with pesticides to meet quarantine rules for international shipping.
The doors
Container doors are heavy steel, hung on strong hinges and closed with locking bars that turn into cam keepers top and bottom. Rubber gaskets around the edges seal out water. The doors take constant use, so check hinges, bars and gaskets on any used container.
What wears and what lasts
| Part | How it ages | What to check |
|---|---|---|
| Corrugated walls | Dents and surface rust; very durable | Holes, poor patches |
| Roof | Dents can hold water and rust through | Holes, deep dents, heavy rust |
| Corner posts | Very strong; can be bent by impacts | Straightness, cracks |
| Bottom rails | Rust if left on wet ground | Scaling rust, holes |
| Cross members | Rust from underneath | Flaking, holes |
| Floor | Wears near the doors | Soft spots, delamination |
| Door gaskets | Harden and crack | Flexibility, gaps |
| Locking gear | Stiffens without grease | Smooth operation |
Build quality differences
Containers are built to international standards, so they're broadly similar. Differences you might notice:
- Paint quality and thickness, which affects how long the finish lasts
- Floor type, plywood or hardwood
- Door hardware, including lock box designs
- Steel thickness in some parts, such as the floor cross members
For storage, these differences rarely matter as much as the container's current condition.
Buying used with build quality in mind
- Focus on the structure: corner posts, rails and cross members.
- Check the roof for holes and deep dents.
- Walk the floor for soft spots.
- Test the doors and look at the gaskets.
- Ignore cosmetics such as dents in the walls and faded paint.
See the grades on our used conex containers page.
Making it last on land
- Set it on a level base, off the ground
- Keep the roof clear of water, leaves and snow
- Touch up rust spots and scratches every year
- Grease hinges and locking bars
- Replace hardened door gaskets
- Ventilate to reduce condensation inside
FAQ
What steel are shipping containers made of?
Most are built from Corten, a weathering steel that forms a protective surface rust and resists deeper corrosion.
Is rust on a used container a problem?
Surface rust is normal. Flaking, layered rust or rust that has eaten through is the problem to look for.
Which part of a container is strongest?
The corner posts and corner castings, which carry the container's weight and anything stacked on it.
Do containers rust from the inside?
They can, from condensation. Ventilation and keeping the floor dry help prevent it.
Are all shipping containers built the same?
They follow international standards, so they're broadly similar, with small differences in paint, floors and hardware.
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