InterDry Power Desiccant – Frequently Asked Questions:

1. How does InterDry Power Desiccant help solve moisture problems?

This unique product absorbs moisture by extracting water vapor present in the air, thus preventing the humidity inside the container from reaching dew point and condensing. The desiccant then starts to turn into a gel as it continues to absorb moisture. The water absorbed is retained due to the presence of a special binding agent, thus preventing it from leaking. Lower relative humidity InterDry controls the humidity inside containers by preventing the air from reaching dew point and condensing, thus protecting your precious cargo.

2. What is Relative Humidity (RH)?

Relative humidity measures the amount of moisture in the air. It is expressed in a percentage of how much moisture the air could possibly hold. The wetter or damper the air is, the higher the relative humidity. The drier the air feels, the lower the relative humidity. Thus, 100% humidity is actually rain.

3. What are the most common problems caused by moisture?

Moisture in containers causes problems such as mold, fungus, mildew, rust decay, lumping, caking, agglomeration, and decomposition. Moisture can also cause electronics to malfunction.

4. Is moisture damage always instantly visible when handling the cargo?

Unfortunately not. Though common forms of moisture problems such as corrosion, mold, or fungus are visible on the cartons, surfaces etc there are some kinds of damage that is not visible.
Mostly these damages are internal and visible only when the customer opens the shipments. In the case of devices, they often cease to function the way they should.

5. I fumigate my containers; do I still need to put in desiccants?

Fumigation and using desiccants have two different purposes and are not alternatives to protect your goods against moisture damage. Fumigation is primarily to eliminate insects and eggs in the container and in the goods. It has no influence on the humidity inside a container. Desiccants will not influence the effects of fumigation and can easily be put in before or after fumigation.

6. If I use InterDry, will I have any more moisture problems?

InterDry Prevents Moisture damage by controlling the Relative humidity and indeed prevents those problems. However, the ventilation holes in the container need to be closed and the number of units to be put in a container needs to be adjusted to the situation.

7. I load my container under dry conditions and it is very tightly sealed. How come I still experience moisture problems?

If there are still moisture problems, we can easily say that the number of units per containers currently is not sufficient and it is advisable to increase the units per container. There are many factors for bigger amounts of moisture inside the container.

Examples of those factors are:

  • Container Floor: Recent studies carried out by R&D department, proved that the moisture content of the wooden floors is higher than they used to be. That is partly because of the quality of the wood that is being used nowadays and partly because the floors are being cleaned with water and they are not dried out enough before being used.
  • Packaging: Wooden pallets always contain more than 20 % moisture, which always causes problems whichever products are put on the pallets. The packaging, often being cartons, contains a lot of moisture in itself, which will spread into the cargo or vaporizes into the air.
  • Products: The biggest factor of moisture inside a container is the products itself. The MC varies roughly spoken between 10% and 35%. When the MC reach the 25%, the cargo is in the danger zone.
  • Journey and climate factors: When all the above mentioned factors are controlled and there is still a problem, they surely are the conditions during transport. The first point of consideration is the transport time. It depends on the destination and more importantly the climate during shipment and final destination.
  • Basically, the changes in temperature and automatically the relative humidity is the cause of condensation. If long transits cannot be avoided, again our advice is to add more units to absorb the extra water molecules.

8. I ship consumer goods in tubes/cans/jars etc that contain no moisture, yet I still have problems.

As said before the moisture comes from the container floor, pallets, open ventilations, weather change during journey. And it will condense on the tubes/cans/jars that cause corrosion and labels to fall off.

9. Each container of my cargo of peanuts/coffee/cocoa contains tons of moisture. What difference does it make if InterDry absorbs a few liters moisture during a voyage?

InterDry absorbs the exceeding water molecules in the air and reduces the Relative Humidity inside the container, so that it will not reach the dew point.

10. Does it make a lot of difference that my cocoa beans have a moisture content of 8% instead of 7%?

One percent more or less doesn’t make a difference, especially not when the MC is on the lower side.

11. My cargo of peanuts had suffered damage in the centre even though the outside of the cargo looked fine and there were no signs of condensation. Why?

Condensation on the surface of your cargos can evaporate quickly, but it takes more time for the moisture which gets
trapped deeper. Before it evaporates back to the air, mold and fungus would have already grown.

12. How does Silica gel works?

Silica gel is the most common type of desiccant in use today. It is porous sand and can absorb moisture in the air. However, silica gel absorbs moisture best in small, confined spaces and often ends up getting saturated in a very short time span, making them unsuitable for container shipments. Beware that some silica gel – the blue contains cobalt – is toxic, and cannot be disposed of any which way.

13. Do I still need to use silica gel in my boxes?

It is definitely not a bad idea to use sachets of silica where the air is tight, and moisture is trapped, like in boxes and items packed in plastics.

14. My Cargo was damaged even though I used a lot of silica gel and there was no condensation. Would it help to switch to InterDry?

Perhaps there was not enough Silica Gel put inside the container. You need about 40Kg Silica Gel for a 20″ container. I can assure you a better result with InterDry Power Desiccants. Silica works pretty well in smaller closed spaces, like shoeboxes. It absorbs very quickly and is often already saturated before the container is moved.

15. What is so great about InterDry anyway?

We have superb products that actually reduce the RH inside the container. When it absorbs moisture, the powder base will change into a gel. It is more efficient and safe in use. Even when the product gets damaged, it will not spill any water on the goods. It is easy, safe, and inexpensive solution for the problems with moisture damage.

16. How many units must be put in one container?

That depends on many things. The container size, the cargo, moisture of cargo, moisture of container’s floor, moisture of pallets, length of journey, and weather during journey and so on.
An example: a 20 feet container with KD (Kiln Dried) furniture needs 4 units, while 20″ air dried furniture needs 6 units. We generally offer expert advice regarding optimum usage of the desiccants for best results.

17. Do I need to line my container with Kraft paper?

Sweat or Kraft paper is a commonly used method of containing “rainfall” that occurs inside a container. Normally it is installed under the ceiling to absorb the moisture that may occur due to container rain. It is most useful while shipping goods that have very high moisture condensation, but it cannot replace a desiccant that soaks up the humidity before it even turns into rain.

18. My containers are stuffed till the top. Can InterDry still be useful?

It seems that there is almost no free air in the container, while there is actually a lot of free air between the products, and InterDry absorbs the moisture in that air and prevents condensation.

19. I have problems with mold growth inside my shrink-wrapped pallets. Will InterDry help?

No, unless you make holes so the water molecules won’t get trapped.

20. My shipment of steel/galvanized components, aluminum, machinery etc. arrives corroded, stained or discolored, despite heavy packaging. Will InterDry help?

Yes, as long as you put enough units per containers and do not wrap the items in plastic.

21. Can I re-use my InterDry Power Desiccants?

InterDry Power Desiccants are one-time usable, environmental neutral and disposable as normal waste.

22. My cargoes are outdoor furniture with brass parts on it. When the goods arrive at the destination, the wooden part is in perfect condition but the brass part has slight stains on it. What should I do to avoid this? Should I use more units of InterDry?

In some cases, it can happen. I can suggest adding one or two more units and wrapping it properly with only single face carton.

23. I notice that two kinds of containers available in the market right now, which are steel and aluminum types. If I shipped the same commodity inside of steel and aluminum containers should I used same numbers of InterDry or not?

There is not much difference between those containers, so you don’t have to adjust the number of units.

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Formation of condensation in container due to temperature changes by sunlight

By: Pakarada Premtitikul
General Manager
InterDry (Thailand) Co., Ltd.

Formation of condensation in container due to temperature changes by sunlight

Hygroscopic goods collected in an airtight container will lead to condensation in sunny weather.

During the day the container walls and ceiling heat up. In the evening they cool off leads to accumulation of condensation in the container.

During heating of the container walls and the internal air, the relative humidity drops. The container floor and the cargo will now dissipate condensation by which the absolute humidity in the air rises.

The water from the cargo comes from the upper layers of the load. This reduces the vapour pressure of the liquid inside the cargo which then migrates from the underlying layers of the cargo to the outer layers.

Figure 1: Warming of a container through radiation. The left figure depicts the start of condensation. The right figure, the condensation builds up for the coming days.

If the container warming has reached its peak, the temperature will drop with the result that the relative humidity increases. Part of the moisture will condense on the cooler container walls when their temperature gets below the dew point of the internal air. During the heating that occurs over the following days, the condensation of the vertical walls evaporate into the air so that the cargo needs to evaporate less condensation to achieve balance.

The condensation on the ceiling does not get into thermal contact with the circulating air, but will diffuse to lower drier air. This process is slower than the evaporation of condensation on the vertical walls by dry air. The condensation on the ceiling does not dry despite the heat. So day after day there is more and more because of moisture condensation from the cargo goods.

When the limit is reached, the condensation begins to drip. The right drawing in Figure 1 shows that the majority of the condensation is formed on the ceiling . This is important because condensation on the vertical walls do not directly cause damage but condensation from the ceiling drips into the goods.

The figure below shows the forming of condensation inside a container that was heated during the day. The moment the temperature of the container wall goes below the dew point of air inside the container, condensation forms in the container.


Figure 2: The daily temperature variations in a container: The temperature, relative humidity and the dew point of air, the temperature of the cargo and the container walls.

Climate in the container and climatic influencing factors

The significance of interfaces for the cryptoclimate in the container

An examination of published incidents of loss due to climatic factors involving container cargoes reveals that such incidents affect the entire range of products with no particular class of product being disproportionately represented. On the basis of the published examples, losses caused by sweating are clearly the most striking. Sweating includes both that which occurs on the cargo itself (cargo sweat) and that which drips down onto the cargo from the upper surfaces of the container (container sweat). All classes of goods are affected by this type of loss. For example, reported losses range from nonhygroscopic goods, such as steel and steel products, canned foods, to hygroscopic goods, such as cocoa, coffee, millet, dried fruit, sago, pepper, milk powder, furs, textiles and rattan furniture.

In addition to the preponderance of losses due to sweat, a second problem is particularly noticeable, namely the care which is required to adapt the goods, loaded under the climatic conditions of the place of departure, to the climatic conditions of the destination while in transit, without causing damage to the goods or making such damage inevitable due to inadequate adaptation. The theoretical basis on which these issues are addressed resides in "interfacial" physics, which take account of the differences in heat and water vapour transfer at interfaces. The most important basic requirement in this connection is to prevent condensation of the water vapour present in the air at an interface, whether on the container wall boundaries, on the surface of the cargo, in air layers in the vicinity of interfaces or within cargo blocks, if the temperature of the interface falls below the dew point temperature of the surrounding body of air. This requirement in turn makes it necessary to adapt the temperature of the cargo to the anticipated air temperature at the destination. Abrupt changes in temperature or humidity or both occur at these interfaces.

The following types of interface in container transport may be distinguished on the basis of their thermal and hygroscopic properties:

  1. Container parts as 1st order interfaces

    These include interfaces which exhibit good heat transfer, are impermeable to water vapour and on which relatively large variations in temperature occur on exposure:

    • container walls and ceilings
  2. Container parts as 2nd order interfaces

    These include interfaces which, in addition to exhibiting good heat transfer, are also permeable to water vapour or actively interact with the water vapour in the container:

    • wooden dunnage
    • dunnage
  3. Cargo surfaces as 1st order interfaces

    Hygroscopic goods which release heat and water vapour into the container air. These include:

    • actively respiring goods of vegetable origin
    • goods of vegetable or animal origin or chemical products which, as a result of ongoing biological or chemical processes, have a tendency to undergo self-heating and are capable of exchanging water vapour with the air
  4. Cargo surfaces as 2nd order interfaces

    nonhygroscopic goods with surfaces having good thermal conductivity and a relatively large heat capacity of the individual package or stack:

    • unpackaged metallic surfaces
    • hygroscopic and nonhygroscopic goods packaged in metallic containers or metal foils as the surface
  5. Cargo surfaces as 3rd order interfaces

    Surfaces of hygroscopic goods capable of heat transfer and permeable to water vapour which exchange heat and water vapour with the container air without actively generating heat or requiring this exchange in order to retain service properties:

    • salt and fertilizer
    • sugar
    • hygroscopic minerals, ores and rock
    • lumber, furniture
    • general cargo packaged in wooden cases

Storage temperatures in the container

If the correct decision as to the suitability of a container for transporting a product without causing damage is to be made, it is essential to have sufficient information about the anticipated climatic conditions in the container. Fig. 9 shows factors which have an influence on the cryptoclimate in the container.

Factors influencing container cryptoclimate

Figure 9: Factors influencing container cryptoclimate

The four decisive influencing factors are:

  • weather conditions during the voyage
  • the type of cargo with which the container is packed
  • the type of container
  • the container stowage space

Clarifying the complex thermodynamic processes occurring in containers, especially in containers exposed to radiation, was the objective of the hold meteorology study group at the Warnemünde-Wustrow University of Seafaring (Fig. 10), where cryptoclimate was investigated in two containers, both on a test rig and on board commercial vessels. The investigations were carried out on two standard containers, each of which was equipped with an air lock to prevent disturbing the cryptoclimate when monitoring and making measurements and a weather station. The containers were packed with hygroscopic goods, in particular sawdust in one case and packets of sugar wrapped in paper in the other.

Climatic conditions during the voyage are determined by the route, season and current weather events. Consequently, it is not entirely straightforwardly possible to transfer the experience gained from one voyage or one route to another as the stresses vary between the different routes and individual voyages. Solar radiation, air temperature and wind are of significance to thermal stress.

The temperatures encountered in containers are primarily determined by heat exchange across the steel boundary surfaces, with inward and outward radiant transfers predominating.

Hold meteorology study group of Warnemünde-Wustrow University of Seafaring

Figure 10: Hold meteorology study group of Warnemünde-Wustrow University of Seafaring, 1970:
container with air lock and weather station; Svenson

Good heat-transfer properties, especially through the metal walls, and the relatively large ratio of container surface area to container volume have a favourable impact in this respect (20′ container, approx. 1.80 m²/m³).

Influence of solar radiation on daily variation in container temperature – radiation classes

The average air temperature in the container and also the temperature of the cargo surface are, on a daily average, higher than that of the external air.

The daily variation in the individual temperatures is of great significance to maintaining quality.

In addition to radiant conditions, external air temperatures, wind and precipitation also have an impact upon temperatures. The great daily variation in overall radiation results in a marked variation in temperature within the container. This variation primarily affects the temperatures of the container air and in particular of the bodies of air in those areas exposed to radiation (e.g. under the container ceiling).

Overheating of the air inside the container, i.e. heating to above the external air temperature, may be considerable even under normal conditions.

For example, daily overheating on sunny summer days amounts on average to 20°C even in temperate latitudes and is still higher in the subtropics. This means that temperatures of > 50°C, to which the surfaces of the cargo are exposed, may occur in the upper part of the container.

Four radiation classes were defined to describe radiation conditions, the classes being calculated on the basis of the measured duration of sunshine and solar altitude for 10 day measurement periods. The classes may be described in words as follows:

Class A:

Little or no effect of solar radiation. Average maximum overheating is 2.0°C (less than three hours of sunshine per day with low solar altitude, no radiant input on several days of the 10 day measurement period).

Class B:

Weak effect of solar radiation. Average maximum overheating is 5.2°C (four to eight hours of sunshine per day, but without sunshine on each individual day of the measurement decade).

Class C:

Moderate effect of solar radiation. Average maximum overheating is 11.5°C (up to twelve hours of sunshine per day, but without sunshine on each individual day of the measurement decade).

Class D:

Strong effect of solar radiation. Average maximum overheating is 17.3°C (more than twelve hours of sunshine per day, in general on all days).

Class A primarily occurs in Central Europe during the autumn and winter months, class B in the autumn and spring, class C in the summer and class D in periods of radiation weather in high summer which are similar to subtropical conditions.

Fig. 11 shows air overheating at an upper measurement point in a stationary container. The values were plotted by radiation class. It should be noted that the overheating values shown in Fig. 11 are averages. Overheating of 20 – 25°C was measured at an upper measurement point in the container in

0.0% of class A,

0.8% of class B,

5.4% of class C,

25.5% of class D,

as a proportion of all measurements, with overheating in class D being in the 15 – 25°C range in 83.6% of all cases. At an external air temperature of 25 – 30°C, air temperatures within the container may accordingly rise as high as 50 – 55°C.

Average daily variation in overheating of the air inside a container
Figure 11: Average daily variation in overheating of the air inside a container,
plotted by radiation class; Svenson

Depth of penetration of temperatures

The influence of temperature variations of the container walls and of the air in the container on the temperature of the goods is a significant factor in storage.

Fig. 12 shows the daily amplitude in goods temperatures measured within the stack of a container packed with sugar on a sunny day in June: the daily amplitude in the interior of the stack is only 1.2°C, while that for the superficial layer is 6.3°C (see Fig. 12).

emperature differences over 24 hours within the stack of a container packed with sugar in sales packaging

Figure 12: Temperature differences over 24 hours within the stack of a container
packed with sugar in sales packaging; U. Scharnow

This means that the temperature in the interior of a stack of cargo adapts to changing external temperatures only very slowly. It is clear from these measurements how far the interior temperature of the goods lags behind changes in external air temperature caused by changes in weather conditions (see Fig. 13).

Measured air and goods temperatures at different times of day in a container packed with 16 metric tons of white sugar on a sunny day in June a) at 06:00, b) at 14:00 and c) at 18:00

Figure 13: Measured air and goods temperatures at different times of day in a container packed with 16 metric tons of white sugar on a sunny day in June a) at 06:00, b) at 14:00 and c) at 18:00; U. Scharnow

The exposure of the goods to thermal stresses is determined by the size of the stack and its internal compactness. Stacks which are so dense that the ambient air cannot freely circulate within the stack do not readily adjust to external temperatures and water vapour also cannot be dissipated. Considerable delays may be observed even with this comparatively small stack in the container. The daily variation in temperature of a packed cargo is less marked. Although none of the cargo is more than 1 m away from a boundary surface of the cargo stack, the daily variations in air temperature in the container have, as can be seen, only a very gradual impact on the daily variation in goods temperature in the interior of the stack.

A different temperature regime is to be anticipated in a container which is completely filled with goods than in an empty or partially filled container.

Fig. 15 shows, for example, the frequency distribution of overheating in two differently loaded containers. While M 11 was obtained in a container packed with 16 metric tons of sugar (see Figs. 12 and 13), M 2 was simultaneously obtained in a container packed with 1.75 metric tons of bagged sawdust (see Fig. 15) which occupied approx. 30% of the container volume. The differences in humidity were still more extreme. While the sugar container did indeed also constantly exhibit comparatively high relative humidities of 70 – 80%, no appreciable sweating occurred and, after 6 months’ storage, the sugar was unpacked again in perfect condition, whereas severe sweating was constantly observed in the sawdust container.

Frequency distribution of overheating in two differently loaded containers

Figure 15: Frequency distribution of overheating in two differently loaded containers; U.Scharnow/Svenson

Water vapour in the container

Water vapour conditions in the container are primarily determined by internal factors, i.e. the water vapour conditions are largely determined by the hygroscopic properties of the cargo inside. The quantity of water vapour contained in the air is small and does not generally result in sweat damage. However, it may lead to other damage, e.g corrosion of metal goods.

Relatively large quantities of sweat in closed containers are always attributable to the cargo or its packaging (and/or the container floor if wooden). Sweat is thus actually possible only if water enters the container with the cargo. High air temperatures in the container and the associated low relative humidity drive water vapour out of the hygroscopic cargo. This water vapour condenses on the container walls and ceiling which is cooled by nocturnal radiation. Investigations reveal among other things that, starting with a dry container ceiling and side walls, sweat coverage increases in stages and reaches a maximum after a few days.

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