Page 204 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

The possibility of exceeding 1 metre/second product velocity at
one tank inlet due to uneven distribution of product between
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the open tanks.

The following precautions should be taken to manage the risks
11.1.7.8สมุด ศูนย์ฝกพาณิชย์นาวี
associated with the spread loading of static accumulator cargoes:
The overall loading rate should be selected so as to ensure a
maximum product velocity of 1 metre/second into any one
tank, assuming even distribution of cargo between tanks.
Possible different flow distributions into different tanks should
be considered and best efforts should be made to ensure
equal flow distribution between cargo tanks.
Not more than four cargo tanks should be loaded at any one
time.
Tank inlet valves should not be used to control cargo flow in
the initial loading phase. Their use will reduce the
cross-sectional area of the inlet, resulting in increased tank
inlet velocity and greater turbulence and mist formation. If it is
necessary to throttle valves in order to control flow rate, this
should be done upstream of the tank valves.

The management of the risks inherent in spread loading will
require a risk assessment process to be followed. The risk
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assessment should consider:
The terminal’s piping configuration, including flow control
capability.

The ship’s piping configuration.
Ship’s cargo tank condition, for example previous cargo,
tank atmosphere and physical condition (such as the
integrity of heating coils).
The product to be loaded and the potential for generating a
flammable atmosphere.

Spread loading should only be carried out when the ship and the
terminal are both satisfied that the risks have been identified and
งานห้อง Limitation of Product Velocity (Loading Rates)
that appropriate risk response measures have been taken to
minimise, avoid or eliminate them.

After the Initial Filling Period (Bulk Loading)
After the initial filling period, electrostatic generating processes
such as mist formation and stirring up tank bottoms by turbulence
are suppressed by the rising liquid level, and the concern changes
to ensuring that excessive charge does not accumulate on the bulk
liquid. This is also done by controlling the flow rate, but the
maximum acceptable velocity is higher than for the initial filling
period, provided the product is ‘clean’ as defined in Section 3.2.1.

Two-phase flows (i.e. through oil and water) give higher
charging and may require that flow rate limitations have to be
imposed throughout loading (see Section 11.1.7.4).

When the tank bottom is covered, after all splashing and surface
turbulence has ceased and after all water has been cleared from
the line, the rate can be increased to the lesser of the ship or

170 © ICS/OCIMF/IAPH 2006