Code No: 752
Video Running Time: 23 minutes
This training package deals with the hazardous subject of
handling shore supplied nitrogen on board ship, in the context of
tank purging, blanketing and cargo line clearing, when there is a
danger of tank over pressurisation.
The nitrogen is usually supplied at high pressure (16 bar) and
at high flow rate. Agreement on the procedure for handling the
nitrogen is paramount, and should be part of the pre-loading
checklist between ship and shore, with emphasis on firm parameters
for transfer rate and pressure.
Although the operation is an important stage in cargo handling,
it is also potentially hazardous. This is because tanks on chemical
tankers are not designed to withstand internal pressure, so the
structure could fail at less than 0.5 bar overpressure. The
associated risks of the operation need to be thoroughly
understood.
The video takes the viewer through the typical phases of
nitrogen and cargo control in a loading port and a discharge port.
It highlights the critical moments and how to ensure that these are
controlled safely in the Cargo Control Room, in the Terminal
Control Room and at the manifold.
Some of the topics included are communication between terminal
and ship, how to start the nitrogen supply, how to increase it to
agreed volume, how to slow down and stop the supply prior to
loading cargo. A similar process is illustrated with cargo loading,
including cargo line clearing. It is normally the terminal's
responsibility to control the pressure and volume of nitrogen and
line clearing is done towards the ship's tank and not the shore
tank. Pigging and line flushing are covered. In a discharge port,
it is assumed that the ullage space must be filled with nitrogen as
the cargo is being discharged.
In all cases it is established that if the tank atmosphere
contains cargo vapour which is prohibited from being vented into
the atmosphere, it must be returned to shore containers. In such
cases the flows into and out of the tank must be balanced by shore
control. The video is accompanied by a supporting booklet. It
supports the STCW Code, Chapter V, Section A-V/1.
