PREVENT MOISTURE DAMAGE - A CHECKLIST
Sea Containers is an economical and safe way of shipping almost any kind of cargo. But putting cargo into a closed steel box also entails a constant risk of moisture damage for every kind of cargo on every voyage.
- Metals corrode, discolor and loose their shine
- Cargo and packaging get moldy, soft, crumbled and discolored.
- Bad smell
- Physical damage from water, ice, things gluing together, caking etc
Such damage may result in substantial losses and costs. Yet obviously not every shipment suffers moisture damage, and most of those that do, suffer only limited damage. In fact, lots of moisture damage remains unrecognized, because it is considered “normal”. Very few shippers have a good system of feedback from the receivers of their goods. There may be lots of things they don’t know.
The pattern of moisture damage may seem random. The moisture processes are examples of strongly non-linear physics. That means that very small differences in the cargo and voyage conditions can have a huge effect of the outcome. That is why you may have 4 perfectly safe shipments and the 5th may be a disaster. This means that there is always a risk of moisture damage in the next shipment, even if the last one was ok.
Moisture Damage can be Prevented
All containers contain moisture from the time of loading and in the cargo. No container is airtight. Moisture will move in and out of the container during the course of the voyage – “Container Breathing”.The objective of a moisture protection program is to prevent the build up of moisture in the air to levels where it may cause damage. This is done by reducing the amount of the moisture entering the container and by using “Absorbers” to remove moisture from the air.
We like to present the Absorbopak moisture protection program as a kind of checklist of things that should be arranged as well as possible. And it is to be noted that many of the items on the list can be influenced only to a degree. Yet even small changes can result in big improvements. In some cases a few tens of grams of water in the wrong place is enough to cause significant damage.
Storing pallets inside or outside is often enough to make the difference between no damage and “disaster”. Simply adjusting the temperature of the cargo at loading can prevent damage. Thus it is well worth to make what improvements are at all practical, and the balance will then have to be taken up by the packaging and the absorbers.
Is the Container Tight?
A minimum requirement is of curse that the container is watertight against rain and spray. That is usually the case, but especially the bottom side and the doors are vulnerable to damage that may not be noticed.
Check the seals. Certainly no container is airtight, but a container in good condition allows air (and moisture) to move in and out of the container only slowly, over hours perhaps. That significantly reduces the amount of moisture moving into the container under common circumstances. (Container Breathing)
Tape the vent holes if you are shipping a dry cargo. For a moist cargo, such as
agricultural commodities, it is usually better to leave the vent holes open.
Is the Container Dry?
A container that has been washed before loading, brought in from outside into a warm loading area or stored in a humid place, may contain lots of water. In particular, attention must be paid to the container floor. The humidity of the wood should not be above 18%.
All pallets and other wooden dunnage must be dry. Preferably the moisture content should not above 18% and certainly not above 20%. It is easy to check the humidity with a small handheld device commonly used in the construction industry and costing a couple of hundred euros.
Is the Cargo Dry?
Some cargoes are entirely dry and don’t contain any moisture, eg pure metal products without corrosion protection or surface treatment.
But most cargoes contain moisture, if only in the packaging that usually include wood, cartons, paper etc. Most of this moisture is bound in the material and is not easily released, but even a small percentage can cause problems. Even if the product appears dry at loading is no guarantee against things going wrong in a container where temperatures may later on reach 60-70C.
Some cargoes unavoidably contain a large mounts of moisture, even after having been made as dry as practical. They require a more sophisticated moisture protection installation.
Is the Loading Dry?
You can easily destroy all the other precautions you have taken by loading the container under the wrong conditions.
Particular attention should be given to the storage of containers, pallets and dunnage. Not to speak of the cargo. Even under a tarpaulin dry pallets or crates stored outside, can quickly absorb significant moisture.
Wet or snowy tarpaulins, truck wheels or even shoes may introduce a lot of water into the container. Again beware of wood, including the container floor, that may look dry but in reality be very moist.
A more subtle consideration is to make the cargo have the same temperature as the container during and after loading. It is especially dangerous to load a cool cargo under warm and moist conditions. A moisture containing warm cargo loaded into a cold container, eg a reefer, is also a problem.
As the doors on the container are closed a certain amount of air is enclosed. Under normal conditions the amount of moisture contained in the air is usually insignificant in comparison with that which will be exchanged with the outside and the cargo during the voyage. But when loading under tropical conditions the amounts of moisture involved may be greater by a factor 10 or more, and special consideration will then need to be taken to quickly absorb the surplus moisture.
Is the Cargo well packaged and stuffed?
Even a completely sealed package may suffer moisture problems as a result of
Most packaging materials let moisture though and moisture will move both into and out of the packages during the voyage. This can be advantageous in a dry container, where the cargo will dry out into the container air. But it is f course a danger if there are moisture problems in the container.
A properly designed moisture protection considers the entire logistic chain and may
involve a combination of absorbers placed within the cargo as well in the container and several layers of barriers with different properties chosen so that the net effect of the moisture migration is positive. To stop the moisture migration through using sealed alufoil bags is usually too expensive.
It is usually an advantage if the cargo is closely stuffed and there is as little free air as possible in the container. The pallet wrapping should have openings at least on the bottom. If mold or condensation is observed on the inside of the wrapping it is to tight.
Use Absorbers correctly
There are different types of absorbers with different properties. Calcium Chloride based absorbers are by far best suited for use in the container. For several reasons, perhaps most importantly because they do not risk re-evaporation of already absorbed moisture, the Absorbopak absorbers are by far the best and safest of the Calcium Chloride absorbers.
Other types of absorbers, so called “desiccants”, are more suitable for use inside
packages. Whether one should have absorbers both in the container and within the
packages, and in which proportions, depend on many considerations. Most importantly one must consider the entire logistic chain, and the need of protection before and after the container transport.
Generally, however, the container transport is the worst part of the logistic chain. It
usually makes economic sense to provide as much of the moisture protection as possible in the packages. Using standard formulas to calculate the amounts otherwise required within the packages often lead to very large amounts of desiccants.
How may Absorpoles are required depends on the cargo, how long the voyage is and what risk of damage is acceptable. For a dry cargo 3-6 Absorpoles are often sufficient in a 20 ft container.
Systematic Follow Up
Every transport is in some sense unique. The best way to optimize the moisture
protection is to gather systematic feedback on all shipments. Please refer to our
Absorbopak Standard Feedback Form. Some things to note are:
- Is the container dry. Are there any signs, eg discolored carboard, bad smell, mold or insects, that indicate that the container at some point has been wet?
- Is there any moisture damage on the packaging? N the cargo? In that case is there a pattern o damage –only on top, only in the centre of the cargo etc?
- How much waer has collected in the Absorpoles? Is the amount about the same in all the Absorpoles or does it differ according to placement?
- Temperature/weather at arriva.
To get much more information on what has happened during the voyage, it is possible to put an electronic logger in the container that records temperature and humidity throughout the voyage.
More regularly one can use the so called Alfasensor moisture indicators. They are a pair of simple stickers that can be put anywhere in the container, eg on an Absorpole or somewhere in the cargo. They will indicate how long the humidity has been above a certain set level giving much information about the voyage.