Drying of Cargo Tanks

Cargo tanks that have been opened, contain humid air and will therefore need to be dried. This is done to: 

• Prevent the formation of corrosive agents, occurring when the humidity combines with sulfur or nitrogen oxides which are available in the tank from the inert gas.
• To ensure that the tanks are ready for the next cargo.

As was noted before, humidity causes water droplets in the air which will contaminate the cargo or cause an unwanted reaction, if not taken care of.   

The drying operation is carried out in the same way as an inerting operation, therefore, by supplying dry inert gas, this operation can be achieved. It is of paramount importance to note that during such operations, special attention is required for the delivery temperature of nitrogen, in order to prevent condensation of humid air inside the tank. As mentioned in the previous lesson, nitrogen has a dew point of -40° celsius, and therefore it can be used as a drying gas. Prior to and during such an operation, the following will take place:

• The cargo tanks are thoroughly inspected for cleanliness, any liquid residues of previous cargo, or any loose objects and fittings.
• Once the inspection is completed, the cargo tank will be securely closed, and the drying operation will commence by flowing nitrogen into the tank.
• During the operation, a measure of the atmosphere must be taken at different intervals and different levels.
• When the dew point of the cargo tank reaches the planned temperature, the drying operation is deemed to be complete.