How Are Shipping Containers Made?
Jan 2020

How Are Shipping Containers Made?

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Shipping containers have become increasingly popular in the construction of homes, pop-up shops, and apartments, among other structures. And while innovative container designs make it possible to repurpose containers into livable, cost-effective, and sustainable structures, many people have no idea how shipping containers are made to withstand extreme weather conditions on land or at sea.

Containers Are Made of Corten Steel

While it’s expected that shipping containers are mostly made in Asia, what you may not know is that their fabrication is not completely automated. On the contrary, they are made from a rather labour intensive process whereby the primary material, Corten steel, has to be cut and assembled with other parts in a technical process.

Every component of a steel container, including the corrugated walls, frame, cross members, and cargo doors are made from Corten steel.

Corten steel is different from other types of steel because it comprises many steel alloys that were put together to eliminate the need for paintwork. This material possesses unique physical attributes that make it rust-resistant and weldable for easy assembly.

Rust-resistant implies that in the event that the paint chips, rust will only form on the surface but it won’t set in deeper into the material.

Components of Steel Containers

Every shipping container has several standard components, including:

  1. Beams or joints

    These cross members help to support the floor of the shipping container. They create space between the flooring and the ground, which prevents moisture from seeping from the ground and into the container.

    As such, cross members eliminate the need for a foundation because they lift your container home a safe distance from the ground, reducing the risk of damage from natural elements.

  2. Corner castings

    These refer to the reinforced corners of your shipping container. They are fitted with openings that allow for twist-lock connections with other containers or to anchors. These corner castings are incredibly strong and can be connected to a crane for lifting even when carrying cargo.

  3. Twist locks

    These are designed to help connect the shipping container to other containers or to secure the container to anchor points. The end piece of the lock can be fitted in the corner casting and then pivoted to a locked position through a lever.

  4. Forklift pockets

    Most containers are fitted with two reinforced slots along the bottom edge known as forklift pockets. Their design allows forklift tines to enter the opening when you want to lift or move the container.

    While it is largely safe to lift an empty shipping container this way, it may not be recommended for a modified container home due to the risk of excess weight, especially for 40-foot units.

Assembling the Components

Fabricating a shipping container begins with a big roll of Corten steel that is unrolled, cut into multiple sheets using advanced machinery systems, and then prepared for assembly. Here are the basic steps:

  1. Preparing the container wall panels

    The rolls of steel are unrolled and cut to pieces measuring 3 x 8 feet. The surface of the sheets is then prepared using sandblasting and priming to eliminate any dirt, rust, and other contaminants.

    Afterwards, the pieces are corrugated in order to enhance their overall strength and then joined together via welding to form the wall panels.

  2. Assembly of the floor frame

    Square tubing is welded on top of the wall panels, after which the frame for the floor is formed by assembling the floor panels. The floor frame comprises of I-beams, with the two longer ones joined perpendicularly.

    The other I-beams are then welded between them to form a base that resembles a slab. After finishing the welding process, the frame on the floor needs to be sanded using an appropriate grinder to remove any messy welding joints.

  3. Corner and doorposts

    The next step involves fabricating the container front and rear. The doors are made from corrugated steel, which is cut and surrounded with tubing made from square steel, and then sanded to remove the messy welding joints.

    Next, the posts making the corners are joined to I-beams so each door can be welded inside them. The corner post and door assembly are prepared separately.

  4. Giving shape to the container

    First, the frames of the door are placed on the frame of the floor before being welded down. Next, the panels forming the walls are installed and welded. Then the panel for the roof can be lowered down on top and welded to complete the box.

  5. Paint job

    After assembly, the finished container is moved to a painting workshop where the undercoat is sprayed to prepare the surface for the application of top paint layers so they adhere better.

    Priming also creates a protection layer on the container. Multiple layers are spray painted, one-at-a-time, to provide adequate protection against saltwater and other extreme conditions of sea transport.

  6. Floor installation

    Next, wooden flooring is applied to the finished floor frame. Manufacturers use panels made from six plywood, which are first coated with an appropriate protective layer to keep insects and pests away from the wood. When the panels dry, they are fixed to the floor beams using screws.

  7. Customization

    At this point, the container is branded with the manufacturer’s logo and other marketing material, which are usually in the form of adhesive stickers. Each unit is also labelled with a distinct identification code that is necessary to track it worldwide. The identification code consists of 11 alphanumeric characters with different meanings:

    • The first, second, and third letters represent the manufacturer
    • The fourth character can be one of three Product Group Coding: U for shipping container; or J for a power unit or other equipment that can be connected to the container; or Z indicating that a trailer is needed to transport it.
    • From the fifth to the tenth character comprise a unique serial number that the manufacturer can use to recognize their unit
    • The eleventh character — the Check Digit — is used for verifying the other characters
  8. Finishing touches

    After labelling, the door handles, as well as the locking systems are installed, and a rubber sealing is placed around the perimeter of the doors to make it watertight.

    Next, the container’s underside is sprayed with a waterproof sealant, after which it is immersed in water to inspect for any defects or leakage. If there’s no problem, the finished container can be sent off for cargo operations and other applications.

Manufacturing Shipping Containers

As with any other construction process, there are standards that must be followed. In this case, manufacturers follow the International Convention for Safe Containers (CSC), which consists of standards for shipping container design to eliminate the risk of structural failure and protect human life. Each container is inspected and certified before it can be used to transport cargo, and the CSC plate affixed to safe units.

To learn more about how shipping containers are made, call Sigma Containers at (855) 340-3342 or contact us here.