As you probably already know, all the shipping containers are built from cor-ten steel and lots of layers of rust proof paint, and maybe that’s why most of the people believe that they are tougher than they really are, unbreakable, bullet proof or rust and corrosion proof which is not necessarily true.
We strongly recommend to power wash and paint your shipping container after delivery. Failing to protect it from rust, can trigger a big problem when used for long term storage or use them to build housing.
First of all, to understand why shipping containers rust, we first need to understand what materials are used in making the steel of a shipping container. Shipping containers can be manufactured from a variety of steels. General purpose shipping containers, such as the 20-foot and 40-foot, standard 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. In the right environment, Cor-ten steel can display a high resistance to corrosion, however, it isn’t entirely corrosion proof. It can still rust and corrode.
Cor-ten steel has a high level of corrosion resistance, but only slows corrosion. It doesn’t eliminate corrosion completely. Cor-ten steel has an enhanced corrosion resistance due to the development of a protective oxide film on it’s surface which slows down corrosion.
However, for this oxide film to develop, it requires interchanging wet and dry cycles. The wet cycle causes the corrosion process to begin. The dry cycle creates the oxide layer which gives the container its nonporous state. This is why one of the key factors of rust, is the climate in which the container is sitting.
This reaction between the steel, the 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 that is full of salt, will rust 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 climates, which should be avoided for building container homes, include areas that have salt laden air, high rainfall, humidity, or persistent fog. The 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 limits corrosion.
Trying to prevent the shipping containers to rust or to stop the rust it’s as easy as it sounds but also you have to understand the importance of protecting your shipping container, because it’s not indestructible.
If you live to the east of a mountain range and the weather blew in from over the mountains, you’d want to protect the side of your container that will be hit the hardest. You could plant some large vegetation around your container home to block much of the rain and weather from hitting the containers. Another option would be to clad the exposed sides of your shipping containers to prevent the Cor-ten steel from being exposed.
We recommend that you notice problem areas early as a way to prevent extensive rust corrosion. Regularly walk around your container home to inspect it.
During this visual inspection, notice whether anything has fallen on your container and damaged the protective coating. Look for any standing water. The most common place for standing water will be on the roof. When inspecting the roof, pay special attention to any dents or scuffs. Unless repaired, dents can collect rain water which will speed up the corrosion process.
When you buy a used shipping container, don’t expect it to be indestructible and have no flaws, so that’s why is important to see and acknowledge them and understand that they are like that, no company will bring a used shipping container that will not have any surface rust, some dings or dents or some wear and tear because that’s why they are called used, they have the marks of many overseas trips. It doesn’t affect their price when bough, because they are bought in bulks and only the personnel at the yard does inspection on them to categorize them. When you receive it, you should make sure you understand you have to take care of the box otherwise will depreciate and start leaking.
If you received a rusty unit or your units started to rust, then the rust should be removed. The container then needs to be protected again to prevent further damage that could change the issue from a non-structural problem to a structural problem.
One of the best, but expensive choice, is to sandblast the rust away, seal and paint the container. To ensure that you’ve removed the rust, you need to go down to bare metal where you can no longer see the rust. Once the rust is removed, it is essential that the container needs to be sealed and painted.
Most common rust spots you can remove them by using a wire brush and sand paper. Start by removing the rusted areas with the wire brush first. Use some sand paper to finish. Once the rust has been removed, use vinegar and rub this gently on the cleaned areas and leave to dry. After the vinegar has dried, use marine grade DTM (direct to metal) paint and cover the cleaned area.
Some advice to help you if you want to paint your shipping container, is that for a 20-foot container you will need 4 ( four ) gallons of paint to cover it and about 8 ( eight ) gallons to cover a 40-foot container.
If you have any stories or dealt with these issues before, and you fixed them, please share with us your story so we can better understand how to prevent and fix them.
