Page 235 - International safety guide for oil tankers and terminals

SHIPBOARD OPERATIONS

The system should be drained down after testing to avoid the risk of leaks
due to thermal expansion.
---ใช้เพื่อการศึกษาเท่านั้น---
Any leaks found should be made good, after which the system should be
re-tested and proved leak free.
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
During crude oil washing, the system must be kept under constant
observation so that any leak can be detected immediately and action
taken to deal with it.

When tanks for crude oil washing are being changed over, the pressure in
the COW line should be reduced to a minimum before any valves on the
system are opened or closed, thereby minimising the potential for
damage due to surge pressure.

11.5.6 Avoidance of Oil and Water Mixtures

Mixtures of crude oil and water can produce an electrically charged mist
during washing with an electrical potential considerably in excess of that
produced by ‘dry’ crude oil. The use of ‘dry’ crude oil is therefore
important. Before washing begins, any tank that is to be used as a source
of crude oil for washing should be partly discharged to remove any water
that has settled out during the voyage. The discharge of a layer at least
one metre in depth is necessary for this purpose.
ึ

For the same reason, if the slop tank is to be used as a source of oil for
washing, it should first be completely discharged ashore and refilled with
‘dry’ crude oil.

11.5.7 Isolation of the Tank Cleaning Heater

If the tank washing water heater is fitted outside the engine room, it must
be blanked off during crude oil washing to prevent oil from flowing
through it.

11.5.8 Control of Vapour Emissions

During crude oil washing, hydrocarbon gas is generated within the cargo
tanks beyond normally existing levels. Subsequent ballasting of such
cargo tanks could lead to considerable hydrocarbon gas being expelled to
the atmosphere. Some port authorities prohibit such discharges. The
emission of hydrocarbon gas from ballasted cargo tanks can be avoided
in one of four ways:

a) By the use of permanent ballast tanks of sufficient capacity to provide
the minimum departure draught.
b) By containing gas in empty cargo tanks by simultaneous ballasting
and cargo discharge, where the ullage spaces of the tanks being
ballasted are directly connected to those of the tanks being
discharged.
c) By the gas compression method. This requires that, on completion of
the discharge, the tank pressure is at a minimum and all cargo tanks
are made common via the inert gas line. While ballasting, the gases
from the ballasted cargo tanks are transferred through the inert gas
lines into all available cargo tank spaces and, with all vent valves,
ullage ports etc closed, the gases are compressed within the vessel
up to a safe margin below pressure/vacuum valve and breaker

© ICS/OCIMF/IAPH 2006 201