How shipping containers are made

A shipping container is a steel box whose corrugated walls do most of the work of holding up a stack of its neighbors.

stations: 8
things upstream: 77
raw sources: 23
steps from the ground: 10

The short version

A shipping container is built from rolled weathering steel and a plywood floor. Corrugated side and roof panels are welded to a rigid frame with strong corner fittings. Doors, rubber seals and locking bars are added, the box is sprayed with paint, and each unit gets a code painted on the outside.

Roll the weathering steel

Container steel is a weathering grade, usually called CorTen, that builds a protective rust layer instead of eating itself away. It is rolled thin and cut into panels.

Goes in
Steel
Corrugate the panels

Rollers and presses fold the sheets into waves. Corrugating adds much of the rigidity and stacking strength to the thin walls.

Goes in
Sheet steel
Weld the frame and corners

Steel rails and posts are welded into a rectangular frame. Strong corner castings give the container its twistlock points, which hold a stack together on a ship.
Weld on the panels

Wall, roof and end panels are welded to the frame so every seam is sealed against water.
Lay the plywood floor

Marine plywood boards are fitted to steel cross-members and fastened down. Forklifts will drive over this floor for years.

Goes in
Plywood
Hang the doors

Double doors with locking bars go on one end, sealed with rubber gaskets that keep rain and spray out.

Goes in
Vulcanized rubber
Paint and mark

The box is sprayed with paint, and an identification code is stenciled on the outside. Every container carries its own unique code.

Goes in
Paint
Check the box

Inspectors test the doors and look for leaks and weak welds. Boxes have to carry 20 to 25 tonnes of cargo.

End of the lineShipping container

Worth repeating

Most containers are 8 feet wide and either 20 or 40 feet long, under the ISO 668 standard.
The 1948 US Army Transporter was a corrugated steel container with double doors that carried 9,000 pounds.