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Shipping Container Home Rust and Corrosion: Identifying, Preventing and Treating

Posted By: January 24, 2017 In How To

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Unfortunately many people are under the false belief that shipping containers are “bullet-proof” and rust proof.

Whilst many general purpose shipping containers are made from Cor-ten steel this does not mean that they are rust proof.

Failing to protect your shipping containers from rust can spell big trouble when using them to build a shipping container home.

In this article we’re going to look at: what causes shipping containers to rust, how to prevent this rust and how to treat rust if it occurs.

What Are Shipping Containers Made From?

Shipping Container

To understand why shipping containers can rust we first need to understand what material shipping containers are made from.

Once we know this we can look into how to prevent rust and how to treat rust if it occurs.

Whilst shipping containers can be made from a variety of steels, general purpose shipping containers such as the 20ft and 40ft regular height and high cube containers are made from Cor-ten steel (also known as Weathering steel).

Cor-ten steel was developed by United States Steel Corporation back in 1930 and the name was shortened from [cor]rosion resistance” and [ten]sile strength”.

Cor-ten steel was created using a group of steel alloys with the aim being to create corrosion resistant steel.

Whilst in the right environment, Cor-ten steel can display a high resistance to corrosion, however it isn’t entirely corrosion proof- meaning it can still rust and corrode.

What Causes Shipping Containers to Rust?

As mentioned above, whilst Cor-ten steel has a high level of corrosion resistance, it is not entirely rust proof. Cor-ten steel only slows corrosion it doesn’t eliminate it.

Cor-ten steel has an enhanced corrosion resistance due to “the development of a protective oxide film on the metals surface which slows down further corrosion”.

However, for this oxide film to develop it requires interchanging wet and dry cycles.

The wet causes the corrosion process but the dry cycle creates the oxide layer and the container gains its nonporous state.

The more wet/dry cycles the container is exposed to the greater the oxide layer is.

This is why one of the key factors of rust is the climate which the container is placed in.

As we know, for containers to rust they need to come into contact with both water and oxygen.

When the containers come into contact with both oxygen and water an oxidation reaction occurs.

This reaction between the steel, water and oxygen causes hydrated iron(III) oxide to form which we can visibly see as rust.

A container which is constantly exposed to sea air full of salt will rust much faster than one in a climate with alternating wet and dry cycles. This is because it’s speeding up the oxidation reaction and also restricting the growth of the oxide film.

Worst of all for rusting is when the containers have surface water lying on them.

Other climates which should be avoided for container homes include “areas that have salt laden air, high rainfall, humidity, or persistent fog”.

An ideal climate for a shipping container is one which has alternating wet and dry cycles as this promotes the growth of the oxide film which restricts corrosion.

However, a dry climate is also suitable but clearly isn’t ‘ideal’ as you’ll lack to wet cycle.

Another way shipping containers rust is through them getting damaged during transit and movement.

When they get damaged it removes any protective coating on the containers and allows the oxidation reaction to occur.

When purchasing a used container you should check the container thoroughly for rust and pay attention to any points of contact during transportation, for instance the: sides, top and bottom when they are stacked together.

You should also check areas that are heavily used such as the doors- pay special attention to the underneath of the doors and corners.

The underside of the doors can rust away because they sometimes allow water to collect underneath them for long periods of time.

I won’t go into much more detail here, because I have a complete guide to buying used containers here. However, I will just reemphasize the importance of following my checklist and to never purchase a container without inspecting it first.

Types of Shipping Container Rust

There are two types of rust on shipping containers which you need to be aware of: structural and non-structural.

Non-structural rust can be easily treated and whilst it’s ugly to look at isn’t too much of a concern.

The real concern for shipping container home owners is structural rust. This is rust which has gone beneath the surface level and can actually reduce the container’s structural integrity.

In some cases the rust can be so devastating that it’s best to cut your losses, discard the container and start again. However to reiterate, this is only in the most extreme circumstances.

How to Prevent Shipping Container Rust

As we all know “Prevention is better than cure” so the majority of your efforts (and money) should be spent preventing rust from occurring on your shipping containers, rather than waiting for rust to occur before you do anything about it.

There are three key ways which you can prevent rust from building up on your shipping container: pre-construction, maintenance and location.

Let’s go through each one step by step.

Pre-Construction Rust Prevention

One of the best ways to prevent rust from forming on your containers is to design your shipping container home properly.

This means that you should ensure your shipping containers aren’t exposed to the direction which the weather blows in from.

For instance if you lived to the east of a mountain range and the weather blew in from over the mountains, you’d want to protect the east side of your containers.

If you have enough time you could plant trees or other large vegetation around your container home to block much of the rain and weather from hitting the containers.

Failing this you can clad the exposed sides of your shipping containers to prevent the Cor-ten steel from being exposed.

Maintenance Rust Prevention

Another great way to prevent rust from forming on your container home is to regularly inspect it.

Maintaining the external shell of your shipping containers is a great way to prevent rust from forming.

Rust will typically form when the containers have been knocked or damaged.

So during your maintenance you should walk around the perimeter of your containers and check to see if anything has fallen on your containers and damaged the protective coating.

In addition to this, during the visual inspection you also need to look for any standing water. The most common place for this will be on the roof.

When inspecting the roof pay special attention to any dents. Dents can collect rain water and this speeds up the corrosion process- not ideal. Make sure to repair all the dents to prevent the roof from corroding.

Location Rust Prevention

As previously mentioned “areas that have salt laden air, high rainfall, humidity, or persistent fog” don’t make ideal locations for shipping container homes.

This isn’t to say you can’t build in these areas using shipping containers.

But rather, in extreme cases of these types of locations you shouldn’t build using shipping container homes without applying addition protection to the containers- more on that later.

So you can prevent a lot of rust from building on your containers just by selecting the right location to build in.

Shipping Container Rust Treatment

Sometimes you haven’t been able to stop the rust from forming on your shipping containers.

This could be for a number of reasons.

Maybe you’ve just purchased the containers used and they’re already rusty.

Whatever the reason though, you need to remove the rust and re-protect the containers to prevent the rust from moving from non-structural to structural.

One of the best but most expensive choices is to sandblast the rust away and then seal and paint the container.

To ensure you’ve removed the rust you need to go down to bare metal where you can no longer see the rust anymore. Again once you’ve removed the rust you need seal and paint the container.

Most of the time sandblasting and completely refurbishing the container is excessive.

Instead you can remove the patch(es) of rust using a wire brush and sand paper.

You need to start by removing the rusted areas with the wire brush first then use the sand paper to tidy it up.

Once the rust has been removed use vinegar and rub this gently on the cleaned areas and leave to dry.

Once the vinegar has dried you need to use marine grade DTM (direct to metal) paint and cover the cleaned area. For a 20ft container you will need 4 gallons to cover it and 8 gallons to cover a 40ft container.

Summary

Whilst shipping containers are made from Cor-ten steel, they aren’t corrosion/rust proof.

Cor-ten steel only restricts the rate at which the rust can form at.

The best way to maintain your shipping containers is to prevent rust from forming on your containers in the first place.

This can be largely achieved through maintenance and regular checks.

However, if you do find patches of rust on your container you can use the technique outlined above to remove these patches.


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