How Are Shipping Containers Made?

A shipping container has to survive years at sea, stack several units high, and be lifted, dropped and hauled around the world, all while keeping its contents dry. That toughness is designed and built in from the very start. So how are shipping containers made?

This guide walks through how a container is built, from the raw steel to the finished box, and explains why each stage matters.

What Are Shipping Containers Made Of?

Shipping containers are made mainly from Corten steel, also known as weathering steel. It is a type of steel that forms a tight, protective layer of surface rust when exposed to the weather, and that layer then slows down any further corrosion. This is what allows a container to spend years outdoors and at sea without rusting through.

The main part that is not steel is the floor, which is usually heavy duty marine plywood, chosen because it is strong enough to take the weight of a loaded forklift. The door seals are rubber, and the corner fittings are solid cast steel.

Cutting and Shaping the Steel

Container manufacture starts with large coils and sheets of Corten steel. These are cleaned and cut to size, then pressed into the familiar corrugated profile. The corrugations, those repeating ridges you see along the walls and roof, are not decorative. They make thin steel panels far stronger and stiffer than a flat sheet, which is how a container can be light enough to transport but strong enough to stack.

Separate panels are formed for the side walls, the roof and the front end wall, ready to be assembled into the shell.

Building the Frame

The strength of a container comes from its frame, which is built up from several heavy steel parts:

• Corner castings are the solid steel blocks at each of the eight corners. Every crane lift, twist lock and lashing point connects here.
• Corner posts are the vertical columns that join the top and bottom castings. They carry the weight of every container stacked above, which is why the corner posts, and not the roof, bear the stacking load.
• Top and bottom rails run the length of the container and tie the frame together.

Underneath, a set of cross members is welded between the bottom rails to support the floor. You can see how all these parts fit together in our guide to the parts of a shipping container.

Assembling the Container

With the parts ready, the container is assembled in stages. The floor frame and cross members are joined to the corner castings and posts to create the steel skeleton. The corrugated side walls, roof and end wall are then welded into place, turning the frame into a sealed box.

The double doors are hung on heavy hinges at one end, fitted with the locking bars that hold them shut and the rubber gaskets that keep wind and water out. Once the shell is complete, the marine plywood floor is laid and fixed down onto the cross members.

Painting, Marking and Testing

The finished steel is cleaned and given protective coats of paint, which add a further barrier against corrosion on top of the weathering steel itself. Each container is then stencilled with its owner code, serial number and size and type code, all set by the same ISO standards that govern its dimensions. A CSC plate is fitted to confirm it is certified for shipping.

Before it leaves the factory, a container is checked for watertightness so that it will keep its cargo dry. Built to ISO standards, it can then join the global pool of containers and be handled anywhere in the world.

New-Build and One-Trip Containers

Most new containers are manufactured overseas and then put straight to work. A one-trip container is a brand-new unit that carries cargo for a single voyage before being sold, which is why it arrives in near-new condition. It is the closest thing to a factory-fresh container without buying in bulk from the production line.

We supply both new-build and used containers across the North East of England and Scotland. Because we hold our own stock, we can send you photographs of the actual unit before you buy. If you would like help choosing, get in touch with our team.

Frequently Asked Questions

How are shipping containers made?

Shipping containers are made by cutting and corrugating Corten steel panels, welding them onto a frame of corner castings, posts and rails, fitting a marine plywood floor and steel doors, then painting, marking and testing the finished unit for watertightness. They are built to ISO standards.

What are shipping containers made of?

Shipping containers are made mostly from Corten steel, also called weathering steel, which resists corrosion by forming a protective surface layer. The floor is usually heavy duty marine plywood, the door seals are rubber, and the corner castings are solid cast steel.

Why are shipping containers corrugated?

The corrugations, or ridges, in the walls and roof make thin steel panels much stronger and stiffer than flat sheets would be. This lets a container stay light enough to transport while being strong enough to stack and to withstand years of handling at sea.

Where are shipping containers made?

Most shipping containers are manufactured overseas, historically in large volumes in China, before entering the global shipping pool. Many arrive in the UK as one-trip units, having carried cargo on a single voyage from the factory.

What holds a shipping container together?

A container is welded together around a frame of corner castings, corner posts and top and bottom rails, with cross members supporting the floor. The corner castings and posts carry the structural and stacking loads, while the welded steel panels form a rigid, sealed shell.