Solidifying cargo

Solidifying cargoes have been the cause for many over and under pressurization of cargo tanks with severe subsequent consequences.

When loading solidifying cargoes, it is possible that cargo vapours will settle in the venting system subsequent reducing the diameter and worse case blocking the same. This can be identified by slowly increasing pressure in the cargo tank when monitoring the pressure.

It should be remembered that the same is applicable when a vapour return line is connected to the vapour return system.

During transit it is also possible that solidifying cargo will enter venting system at the tank dome connection due to movement of the vessel and the cargo.

Therefore, it is essential that the vapour line system and P/V valves are checked during loading and prior arrival at the discharge port.

Prior discharging the entire vapour system should be rechecked if the system is operational. Note: a cargo tank is much more sensitive to under pressurization than for over-pressurization.

One way is to knock on the venting system with a metal object whereby the sound will indicate if the pipework is free or not.

The following picture shows solidified slack wax in a venting line: