How Absorgel Help to Solve Moisture Problems

How Absorgel Help to Solve Moisture Problems

Insurers estimate that 12% of all container shipment damage is moisture related, which translates to substantial product wastage and a hit to the bottom line.

Moisture forms within shipping containers as a result of two factors:

  • the relative humidity of the loading location. Increased moisture in tropical climates such as Australia is trapped and held within the container creating condensation.
  • Temperature changes en route. The amount of moisture the air can hold doubles for every 10 degrees Celsius over normal temperatures. Considering the changing weather conditions, day and night time extremes and the distance goods have travelled, there can be significant fluctuations to the relative humidity within a container.

Container rain, or “sweat” is the condensation that takes place within a sealed shipping container. Similar to a cold drink left in the sunshine, the water accumulates on the coldest parts, which in the case of a shipping container is typically the walls and ceiling of the container, hence the prospect of container rain.

Absorgel Hanging provides a high moisture absorption solution with no liquid water residue.  Using calcium chloride it aggressively extracts the water from the air binding it into a gel so no liquid water can leak.

It is easy to use and is designed to occupy minimal container space. A single-use unit, the calcium chloride and gelling agent are non-toxic and the outer materials are recyclable.

The Absorgel Hanging starts working as soon as it is removed from its sealed packaging and can hang within the corrugated recess of container side panels or horizontally above the cargo.

Calcium chloride absorbs moisture from the surrounding air as it passes through its outer breathable packaging material.  The Absorgels adhesive gel ensures absorbed moisture stays trapped within the product. It is secured in place with a hook and adhesive pad.

Absorgel Hanging can be used for any type of cargo that only requires 25mm between the cargo and the absorption unit. It is well suited to tightly loaded containers and effectively protects items such as:

  • Agricultural products
  • Metal products and machinery
  • Furniture and handicrafts
  • Textiles and leather
  • Consumer products

How many hanging units are required depends on shipment time, climatic conditions en route, air volume in the container, cargo type, packaging type and so on. An approximate guide is:

Container sizeDry cargoWet cargo
20 ft4-68-10
40 ft8-1216-20

We can assist you to calculate the precise number of units to fit your unique circumstances.

So don’t risk your precious cargo, protect your investment with Absorgel Hanging units.

Moisture Damage Checklist

Sea Containers is an economical and safe way of shipping almost any kind of cargo. But putting a cargo into a closed strong box also entails a constant risk of moisture damage for every kind of cargo on every voyage, which you can check for using this helpful moisture damage checklist.

– 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 Absortech 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 dollars.

Moisture Control in Shipping Containers

Whoever has opened a shipping container only to find his valuable cargo rusted, moldy and dripping with water can readily appreciate the dangers of moisture in container transports. Most cases of moisture damage are far less severe – peeling labels, spotted surfaces or soggy packaging-, but are nonetheless unacceptable. Every year thousands of shipments arrive damaged, causing losses of millions of dollars from lower quality as well as additional costs for handling and administration. And in most cases such damage is not even covered by the insurance.

The root cause of moisture damage in container transport is the simple fact that warm air can hold more moisture than cold air. Take the dewy grass in the morning after a cool summer night as an example. Moisture gets into the air in the container from the outside or by evaporation from the cargo. When the temperature in the container changes or there is a difference in temperature between different parts of the cargo, damaging moisture conditions arise

Moisture is great for chocolate cake, but not for Sea Containers!

Moisture damage happens even where there is no condensation. Many grades of steel will start to corrode at a relative humidity of about 70%. Mould growth could begin after even a short period over 80%.

The only remedy is to keep the air inside the container dry. The first thing to do is to ensure that the cargo and all the packaging are as dry as possible. A wet container floor or some pallets stored in the rain may be enough to ruin a cargo.

No container is airtight whatever you do; – it will “breathe” as a result of temperature cycles. When the air inside the container cools, the pressure drops. Air – and moisture – moves in from the outside to equalize the pressure. The opposite happen when the air inside the container heats up, but it is easy to show how a repeating cycle of breathing can cause a buildup of moisture inside he container, especially if there is absorbing packing materials. Using a container with good seals and vents taped shut will slow down, but not stop- the “container breathing”.

Substances that remove moisture from the air are called “Desiccants”. The most widely used desiccants are probably “Silica Gel”, a kind of porous glassy substance that adsorbs moisture well under the right conditions. When used in containers they are fatally flawed in that they work best at room temperature, and not at all at the much higher temperatures often found in containers. Other widely used desiccants based on Clay work to a little higher temperature, but then similarly fail in an even more dramatic way.

The worst case is when the desiccant is already fully charged and then meet high temperature, followed by low temperature, e.g. as a result of a day and night cycle when the container is on the quayside. Much of the moisture absorbed is then first re-evaporated and then rained out. Sometimes the container will look as someone threw a bucket of water inside the container, and wet moldy desiccant bags are a common sight.

Desiccants based on Calcium Chloride, have a vigorous absorption over a large temperature range. Desiccants based on a mixture of clay and calcium chloride or Tyvec pouches with calcium chloride are very good absorbers, but easily “over saturate”. If an “over-saturated” absorbent meet dry conditions, e.g. as a result of a sudden increase in temperature, it will re-evaporate the moisture already absorbed in a very destructive way. Only calcium chloride absorbers that sequester the absorbed moisture to keep it from contact with the air are free of this problem.

The important thing to remember is that there is always a risk of moisture damage in the next shipment, and one needs to implement a moisture protection program that will prevent the build up of moisture in the air to levels where it may cause damage.To design an efficient moisture protection requires finding the most economic balance between packaging, container desiccants and in-packaging desiccants, taking into account not only the individual package, but how it is stuffed and combined throughout the logistic chain.

Why You Need a Moisture Absorber

Every year thousands of cargoes suffer damage by moisture. Metal cargoes arrive rusted or oxidized, cartons soft and moldy. Wooden crates are found covered by smelly black mold. Containers of coffee, cocoa, nuts and beans arrive dripping with damp, moldy and inedible. The losses amount to millions of dollars.

Most of this damage can be prevented by the appropriate use of moisture absorbing products like Absorpole desiccants for shipping containers. They will not only help to prevent and limit moisture condensation in the container, but will also work all the time to help to prevent serious cargo damage caused by prolonged periods of elevated humidity.

Moisture damage often seems unpredictable. After five containers with no problem, there may be one that is a disaster. This is not due to any mysterious causes, but is a consequence of the exponential character of most of the underlying processes. This means that a small change in conditions can have a great effect on the outcome.

Moisture damage is caused by temperature differences

The ultimate cause of all moisture damage in cargo shipments is a difference in temperature. It may be a change in temperature, eg when a container cools down after a hot day in the sun. Or it may be a difference in temperature between different parts of a cargo, eg when a cargo loaded at a cool temperature and then shipped across the equator.

There is a maximum amount of moisture that air at a particular temperature can hold. Any excess moisture beyond this amount will be condensed as a fog of small droplets floating in the air or as dew on a nearby cold surface.

Warm air can hold more moisture than cold air. When warm air cool down it becomes more humid, even though there is no change in the amount of moisture the air contains. If the temperature drops enough condensation will occur.

How humid the air is depends on its Relative Humidity (RH). This is quite simply the percentage of moisture held in the air out of the maximum that air of that temperature could hold. Entirely dry air has RH 0. Maximally humid air has an RH of 100.

There is rarely any moisture damage if RH is less than 60-70%.

As a rough rule of thumb the amount of moisture the air can hold doubles for every 10 C over “normal” temperatures. If for instance air of 20 C and RH 50% is cooled to 10 C, the RH will reach 100%. Any further cooling would cause immediate condensation. If the air was then heated, the RH would drop below 100% and any condensation that had happened would over time re-evaporate back into the air.

Condensation and Container Sweat

The most visible kind of moisture problems happens as a result of falling temperature outside the container. The container wall or ceiling becomes colder than the air and moisture condenses as a thin film on the coldest surface. Eventually droplets of water may form and drip onto the cargo or run down the walls. Container sweat is a result of a temperature change.

Container sweat is common before and after the sea voyage, when the container suffers daily temperature cycles as it is exposed during overland transport or waiting on the dock. Unless the container is loaded on top of the ship, container sweat is less common during sea transport. However, as a result of temperature differences within the cargo, container sweat is for instance commonly observed during the last few days of shipments from tropical regions arriving in northern destinations during winter.

Cargo Sweat

Cargo sweat happens when warm air rapidly cools over a cold cargo. Such condensation onto the cargo is often invisible. The moisture is absorbed into the carton, goods or wood before there are ever any visible droplets of water. Moisture absorption by the cargo in fact happens as a result of high levels of humidity, even if the point of condensation is not reached.

Warm and humid air can usually be formed within a container only when there is a difference in temperature between different parts of a cargo that contain a source of moisture. In a container warming up after a cold night the outer part of the cargo may warm up first and cause warm moist air to diffuse into the centre.

Cargo sweat commonly occurs during sea voyages between different climate zones. It may take weeks for temperatures to become equal within a cargo. During this time warm moist air from one part of the cargo will move into the cooler part and create prolonged periods of cargo sweating or elevated levels of humidity.

Dry Cargoes

In a container with a completely dry cargo, moisture is a limited problem. Typically all the air in a 20 ft container will hold less than a liter of moisture. The exchange of air and moisture with the surroundings is very limited during the voyage when the container is in a good condition. A small number of Absorpole desiccants will absorb the moisture in the air and prevent any moisture problems.

However, few cargoes are entirely dry. Container floors, pallets, crates, cartons and other packaging materials will certainly contain moisture that may be released into the air and cause problems. Yet if the cargo and packaging materials are reasonably dry, the amount of moisture released will still be within the absorption capacity of a reasonable number of Absorpoles. This will not completely guarantee that condensation does not occur, but the Absorpoles will limit and dry up any condensation in such a way that damage to the cargo is unlikely.

Moist Cargoes

The problem is quite different when the container holds a cargo that contains tons of water, such as a cargo of wood, agricultural products or paper. If any significant proportion of this moisture were released into the air, any desiccants would be overwhelmed. The trick is of course to try to make sure that the moisture stays in the cargo.

It is not possible to really control the moisture within a container loaded with a moist cargo, but from a good understanding of the interaction between the cargo, the air and the Absorpole desiccants it is possible to manage conditions in a way to prevent damage.

If any moisture containing cargo is put into an enclosed space and left at a constant temperature for a length of time, water will evaporate or be absorbed by the cargo until an equilibrium is established at a characteristic RH level. This level depends on the particular cargo, its moisture content and the temperature. So long as there is any amount of liquid water in the container, the RH will essentially stay at 100%. For many agricultural products at normal moisture content such as peanuts, the equilibrium RH is typically 70-80%.

If the air should be somehow circulated and conditioned to a level of RH that is below the equilibrium level, the cargo will dry out. If the air one the other hand is made more humid than the equilibrium RH, the cargo will absorb moisture and its moisture content will increase.

Warm relatively dry air from a warmer part of the cargo, cools down and become more moist (RH increases) as it flows into a cooler section of the cargo. This results in a section of the cargo having an elevated RH, often high enough that mould will grow (>RH 80%). As the cargo absorbs moisture at high RH, the net effect is to create a migration of moisture from one part of the cargo to another part.

The moisture processes in the air happen very quickly. The interaction between the air and the cargo happen more slowly, over a period of time. How quickly a cargo evaporates or absorbs moisture depends strongly on how far the air RH is from the equilibrium RH and on the temperature. In fact this dependence has an exponential character.

The Absorpole Desiccant

Absorpole desiccants, absorb moisture out of the air in a very aggressive way. They start to absorb at about RH 30 % and have a greater rate of absorption the higher the RH. In fact the absorption rate increases exponentially to reach a maximum on the order of 20 g per hour at RH 100%.

Protecting the cargo from condensation damage

If the cargo is reasonably dry, it will have a fairly low equilibrium RH (< 80%) and will evaporate moisture only slowly into the surrounding air. Under constant temperature conditions there is little or no risk of damage to the cargo.

If, however, there should be a rapid fall in temperature, the RH in the air will immediately increase, perhaps to 100%, and condensation will occur. In a container the condensation will happen on the coolest available surface, which is often the ceiling. It will take some time for the thin film of condensation to coalesce into droplets and drip onto the cargo. The condensation might indeed dry up before any damage is caused. Absorpoles would help prevent damage from condensation, both by limiting the amount of condensation and by helping to dry it up before it could drip on the cargo. During a condensation event RH is at or near 100%, and the Absorpoles are absorbing at their maximum rate.

To gain an idea of the magnitudes, it may be noted that there is typically 10-15 m2 of air in a loaded 20 ft container. If the temperature should suddenly drop from 30C to 20C something less than half a Kg of water could condense on the ceiling. Some portion of this may eventually drip onto the cargo. The time frame is on the order of hours. If the container is equipped with say 6 Absorpoles, these will absorb on the order of 100g per hour, and it is clear that they will have a real effect on limiting the damage from condensation.

Tests where the cargo has been covered with clean sheets of cardboard (a drop of condensation will leave a discoloration even after it has dried up), shows that clear condensation events as detected by data-loggers do not necessarily result in much dripping in the presence of Absorpoles.

Protecting the cargo from extended periods of high RH

Cargo damage from condensation is somehow obvious. Yet much, or even most cargo damage, happen as a result of prolonged periods of RH above 80%, without any condensation. This can happen throughout a cargo with a high moisture content, or it can happen in a portion of a cargo as a result of temperature gradients. A container of agricultural products may contain tons of moisture. It is obvious that no reasonable number of absorber can handle more than a small fraction of this amount, were it to be released. Fortunately this is not necessary.

As previously mentioned the cargo will evaporate moisture very slowly when the RH in the air is near the equilibrium level of the cargo. To maintain a level of RH that is a little below the equilibrium level, requires only that the slow rate of evaporation from the cargo is matched by absorption in the Absorpoles. Since the Absorpoles are very effective absorbers at typical cargo equilibrium levels, it requires only a small number of Absorpoles to do this.

Were we on the other hand to attempt to lower the RH in the air more substantially, the evaporation rate from the cargo would quickly increase and the number of poles required to match it would soon become impractical. In fact we would soon come to a point where adding additional poles has no effect but to increase the flow of moisture from the cargo to the Absorpoles, without any significant reduction of the RH.

While it is thus relatively easy to use Absorpoles to lower the RH in the air in a container of say agricultural products by say 10 percentage points, it may be virtually impossible to lower it by say 20 percentage points. Yet it will often make all the difference to the cargo if the RH is kept at 75-80% instead of being allowed to rise to say 85%. The exponential character of the relevant processes, makes it possible to manage the moisture condition of tons of cargo with a few kilos of Absorpole desiccants.

How To Protect Your Cargo from Moisture Damage

Shipping in containers is an economical and safe way of shipping most types of cargo. But putting cargo into a enclosed steel box also entails a constant risk of moisture damage for almost every kind of cargo on every voyage.

  • Metals corrode, discolor and lose their shine
  •  Cargo and packaging get moldy, soft, crumbled and discolored
  • Bad odor
  • Physical damage from water, ice, caking etc

Not every shipment suffers moisture damage. But when damage occurs it may result in substantial losses and costs. In fact, a considerable amount of moisture damage remains unrecognized, because it is considered “normal”. There may be aspects of moisture related issues that they do not know completely about.

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 four perfectly safe shipments and the fifth may be a disaster. This means that there is always a risk of moisture damage in the next shipment, even if the last one arrived ok.

Rust and discoloration can affect metals during long-term transport and storage. Absortech products offer effective moisture protection to avoid these problems.

Mold and fungus are two types of moisture damage, which can affect almost any organic product including food products, textiles, leather etc

Moisture Damage can be Prevented

All containers contain moisture from the time of loading. No container is completely airtight. Moisture will move in and out of the container during the course of the voyage known as “Container Breathing”. The objective of a moisture protection program is to prevent the buildup 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 “Humidity Absorbers” to remove moisture from the air.

Is the Container Airtight?

A minimum requirement is that the container should be watertight without any risk of rain and spray.

– This should be checked for every container before loading. Especially the doors as they are vulnerable to damage that may not easily be noticed.
– Check the seals. Certainly no container is airtight, but a container in good condition only allows air and moisture to move in and out of the container slowly.
– This 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 may in certain circumstances be better to leave the ventilation 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 a lot of water. In particular, attention must be paid to the container floor.

  • The humidity of the wood should not be above 15%.
  • All pallets and other wooden dunnage must be dry.
  • Preferably the moisture content should not above 15% and certainly not above 20%.
  • It is easy to check the moisture content of the wood with a handheld moisture reading device.