Page 128 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

No air should be allowed to enter the cargo tanks of the discharging
ship.
---ใช้เพื่อการศึกษาเท่านั้น---
Transfer operations should be suspended if the oxygen content of the
vapour stream exceeds 8% by volume and should only be resumed
once the oxygen content has been reduced to 8% or less by volume.
commencement of discharge.ูนย์ฝกพาณิชย์นาวี
The cargo transfer rate must not exceed the design rate for the vapour
balancing hose.

7.1.6.5 Loaded Passage
A positive pressure of inert gas should be maintained in the ullage space
at all times during the loaded passage in order to prevent the possible
ingress of air (see also Section 7.1.5.3). If the pressure falls below the
low pressure alarm level, it will be necessary to start the inert gas plant to
restore an adequate pressure in the system.

Loss of pressure is normally associated with leakages from tank
openings and falling air and sea temperatures. In the latter cases, it is all
the more important to ensure that the tanks are gas tight. Gas leaks are
usually easily detected by their noise and every effort must be made to
eliminate leaks at tank hatches, ullage lids, tank washing machine
openings, valves etc.

ึ
Leaks that cannot be eliminated should be marked and recorded for
sealing during the next ballast passage or at another suitable opportunity.
Certain oil products, principally aviation turbine kerosenes and diesel oil,
can absorb oxygen during the refining and storage process. This oxygen
can later be liberated into an oxygen deficient atmosphere such as the
งานห้องสมุด ศ
ullage space of an inerted cargo tank. Although the recorded incidence of
oxygen liberation is low, cargo tank oxygen levels should be monitored so
that any necessary precautionary measures can be taken prior to the

7.1.6.6 Discharge of Cargo or Ballast from Tanks in an Inert
Condition
The inert gas supply must be maintained throughout cargo or ballast
discharge operations to prevent air entering the tanks. If a satisfactory
positive inert gas pressure can be safely maintained without a continuous
supply of inert gas then it is acceptable to re-circulate or stop the supply
of inert gas provided that the inert gas plant is kept ready for immediate
operation.

If on arrival in port the inert gas has to be de-pressurised in order to
measure or sample the cargo, it may be difficult, because of the low
boiler load, to re-pressurise with inert gas having sufficiently low oxygen
content. In this event, it may be necessary to create a load on the boiler
by using the main cargo pumps to circulate the cargo around the ship’s
pipelines until the inert gas quality is satisfactory. Great care is necessary
to ensure that the pumping arrangements used for circulating cargo do
not give rise to an overflow.

Throughout the discharge of cargo, particularly when the boiler load is
low or fluctuating, the oxygen content of the inert gas supply must be
carefully monitored. Additionally, both the oxygen content and pressure of
the inert gas main should be continuously recorded during discharge. For

94 © ICS/OCIMF/IAPH 2006