Container rust

Shipping containers are built to last and endure extreme environments. As they are made of steel, shipping container rust is, unfortunately, a possibility. Steps can be taken however to slow its onset and stop significant damage occurring from corrosion. Read below for some tips and information.

Rust is reddish brown compound which occurs when iron reacts with oxygen in the air, or chloride in water. Shipping containers are almost always constructed from steel, which is an alloy of iron, and are therefore susceptible to rust. Marine grade steel is used with anti-corrosive properties, but due to the harsh environments that containers encounter, rust will eventually, inevitably occur.

As metal rusts, it slowly corrodes and disintegrates. This can lead to what is known as structural rust on a container (i.e. rust which has begun to negatively affect the structural integrity of the container). Significant structural rust can render a container unusable. Non-structural rust (minimal surface level rust) is less of a concern, but it still can negatively affect the resale value of a container. It is can also give off a poor image for a freight forwarding company or similar business, to have visibly rusting containers.

Many shipping containers are made from COR-TEN steel, a.k.a. weathering steel (check the manufacturer’s plate on the container doors to verify). Commonly used in bridge and building construction, weathering steel forms a protective layer of surface level rust, which actually helps the steel to be more resistant to structural or severe rust. Weathering steel cannot, however, eliminate the risk of shipping container rust, it simply delays it. Humid subtropical climates have been known to stop weathering steel from functioning correctly as well.

Moisture drives the oxidation reaction leading to shipping container rust. Therefore, where possible containers should be dried, and all areas which collect water, drained. A common area is the bottom surface of the container doors as water collects in the area. If containers are laid on the ground as well, the bottom is likely to rust, encouraged by the ground moisture. A simple way to avoid this would be to store a container on ConFoot legs instead of on the ground.

Condensation, a.k.a. ‘container rain’ can also enhance the oxidation process. Click here for our guide on how to minimize the ammount of moisture forming in a container.

If purchasing a used container, inspect it carefully before purchase. Check for any signs of rust, especially on the base of the container, or anywhere water may have collected or been trapped. A container mounted on ConFoot legs is a great way to inspect the bottom of the steel structure for rust. Check for dents and deformations as well, because damage to the paint cover or metal structure can cause rust to occur more rapidly.

Applying a zinc paint coat can slow the process of shipping container rust significantly. By the process of ‘cathodic protection’ the zinc slows the process of the rusting of the underlying steel. Quality zinc paint should contain at least 90% dry zinc powder. Mounting a container on ConFoot legs would allow the bottom to be easily painted.

If you notice shipping container rust on a localized area, and it is not too severe, it can be treated. One method is to grind/ sand blast/ chip the rust down in the area. Once the surface has been ground down to the bare metal, paint it over with a primer and topcoat.

Although shipping containers are built to be very hard-wearing, they do have a limited lifespan. The conditions which they are exposed to greatly affect how long they will last. For example, a container exposed to sea salt and water will corrode faster than a container stored inland, in a warm and dry environment. Once they are displaying signs of significant rust or structural damage, they should be taken out of service.

If you notice signs of rust and corrosion on your container, contact the original dealer or certified professional as soon as possible to find out exactly what can be done.