Sources of Moisture

  Cargo Sweat

  Container Sweat

  Heat Radiation

 Definitions

The risk of condensation damage during a voyage is very real, especially in general purpose containers. in serious cases this leads to huge losses and resultant claims.

The following section highlights the problems associated with condensation and also identifies the main sources of condensation during a voyage.

Overview

Condensation causes corrosion, rust, mould, mildew, fungus, swelling and spoiling of product integrity.

The diagram below represents a packed 20ft shipping container and highlights the main sources of moisture. The cargo has been stacked on pallets.

1. Containers are fitted with ventilation holes, normally 6 for a 20ft container . This allows moisture to enter/exit the container. ideally these holes should be sealed for better control when desiccants are used.
2. Cargo takes up free space in the container. This will decrease the volume of atmospheric moisture entering the container.
3. The volume of a 20ft container is 33m³. At 20ºC and 80% relative humidity this equates to almost 850ml of airborne moisture.
4. Cargo and packaging materials such as paper, board and cardboard are a source of moisture.
5. in containers with wooden floors, the floors themselves are a major source of moisture. Wooden floor areas allow for faster moisture release than that of wooden pallets. Careful consideration should be given to managing this risk.
6. Wooden pallets are one of the major contributors of moisture. Wood tends to have a moisture content that is in equilibrium with atmospheric conditions. A pallet with 20% moisture content could release as much as 3.5 litres of moisture inside a container.

Factors Affecting Condensation

1. The weather during the voyage
2. The duration of the voyage
3. Type of goods, commodities or materials in the container
4. The condition of the container
5. The sensitivity of the goods
6. The moisture content of the floor and/or wooden pallets and/or packaging material