Page 127 - International safety guide for oil tankers and terminals

SHIPBOARD SYSTEMS

7.1.6.2 Loading Cargo or Ballast into Tanks in an Inert
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Condition
When loading cargo or ballast, the inert gas plant should be shut down
and the tanks vented through the appropriate venting system. On
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
completion of loading or ballasting, and when all ullaging is completed,
the tanks should be closed and the inert gas system restarted and
re-pressurised. The system should then be shut down and all safety
isolating valves secured.

Local regulations may prohibit venting after crude oil washing
(see Section 11.5.8).

7.1.6.3 Simultaneous Cargo or Ballast Operations
In the case of simultaneous loading and discharge operations involving
cargo or ballast, venting to the atmosphere can be minimised, or possibly
completely avoided, by interconnecting the tanks concerned through the
inert gas main. Depending on the relative pumping rates, pressure in the
tanks may be increased or a vacuum drawn, and it may therefore be
necessary to adjust the inert gas flow accordingly to maintain tank
pressures within normal limits.

7.1.6.4 Vapour Balancing During Ship-to-Ship Transfers
ึ
Vapour balancing is used to avoid the release of any gases to the
atmosphere through vents and to minimise the use of the inert gas
systems when transferring cargo from ship-to-ship. The inert gas mains of
the ships are connected using a flexible hose. As a minimum, the
following recommendations should be followed:

Before commencing cargo transfer:

Equipment should be provided on at least one of the vessels to enable
the oxygen content of the vapour stream to be monitored. This should
draw samples continuously from a location close to the vapour
manifold connection and should include the facility for audible and
visual alarms in the event that the oxygen content of the vapour
stream exceeds 8% by volume. The oxygen analyser and associated
alarms should be tested for proper function prior to each cargo
transfer operation.
The oxygen content of the vapour space of each tank connected to
the IG main of both ships should be checked and confirmed to be less
than 8% by volume.

The vapour transfer hose should be purged of air and inerted prior to
commencing transfer of vapours.
The vapour manifold valves should not be opened until the pressure in
the cargo system of the receiving vessel exceeds that of the ship
discharging cargo.

During the cargo transfer:

The inert gas system on the discharging ship should be kept
operational and on standby, with the inert gas main deck isolating
valve closed. The inert gas system should be used if the inert gas
pressure in the discharging vessel falls to a low level (300 mm WG).
The inert gas pressure on both ships should be monitored and each
ship advised of the other’s pressure on a regular basis.

© ICS/OCIMF/IAPH 2006 93