During international transports, the temperature is changing tremendously between day and night in the container. The high temperature air in the day is full of water-saturated, in contrast, the low temperature air at night just holds little water vapor. As a result, the air becomes supersaturated with water vapor, potentially leading to condensation on the surface of packing or on the wall of inside the container when the temperature falls down. This is why fungus, mould and mildew occurs, damaging the cargo. If the water condenses on the surface of metal products corrosion occurs.
(The similar situations also happen frequently in warehouse).
How to Prevent Condensation
Normally, the temperature is the external or uncontrollable factor except refrigerated container. Hence, drop the RH is the key to control the moisture and prevent condensation. Some moisture invariably becomes trapped either in airborne form (depending on the external ambient and relative humidity) or being present in timber packing or dunnage materials, the container floor or the cargo itself. This “invisible” captured water can amount to many litres when relative humidity is high and precipitated in tropical zones. It is by preventing this release as condensation that desiccants have proven effective on moisture protection and gained increased acceptance on the majority of the world’s container traders.