Page 274 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

14.2.2 Product Limitations
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The Master should be provided with the correct cargo specification and
full carriage and handling details in the form of an MSDS. The
specification should indicate the cargo quality and, where relevant, the
potential to leave residues and/or the effect on cargo tank steelwork.
Pre-Loading Preparationsย์ฝกพาณิชย์นาวี
The specification should give details on colour, specific gravity, olefins,
residues, lead, Methyl Tertiary Butyl Ether (MTBE) contents, copper strip
corrosion test and final boiling point.

Naphtha derivatives can have a severe corrosion effect on synthetic
flexible hoses used in gas freeing operations. For this reason, designated
metal spool pieces should be used in areas where such corrosion can
occur.

Petroleum product vapour, mixed with impurities from inert gas, can
corrode the synthetic internals of tank safety valves, causing them to
open due to broken or seized seals. Unless proper precautions are taken,
cargo tank safety valves could lift at quite low pressures once the ship
has reverted to LPG carriage, with potentially serious implications in
terms of safety. Therefore, extreme vigilance and regular inspections are
required to ensure that the integrity of tank safety valve components has
not been compromised.
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Products such as low density pentane derivatives can penetrate some
gaskets. On changeover to LPG, these gaskets can freeze and
subsequently will fail under pressure. Only gaskets compatible with the
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product should be used.

14.2.3

The stripping system should be carefully inspected before loading and,
where portable pumps have to be fitted, these should be tested using
fresh water prior to installation. Portable pumps, if made from aluminium,
should be lowered into cargo tanks inside canvas bags to prevent
‘aluminium grazing’ on the steelwork structures (see Section 4.6).
To protect the diaphragms of air-driven portable pumps, a positive
pressure should always be maintained on the ‘drive’ side of the pump
throughout the period of cargo carriage. This can be achieved with air or
nitrogen.

The cargo compressor room should be totally isolated from the cargo
system. Some ships may require the use of a compressor for inert gas
cooling and, if so, additional measures must be taken in order to ensure
safe operation in the vicinity of the petroleum products.

Inert gas should be dry enough to prevent water residues. This is
especially important with pentane derivatives, where water mixed with the
product will create a noxious liquid.

Means of preventing hydrocarbon vapour passing back to the engine
room or inert gas plant must be in place. This can take the form of a deck
seal or similar arrangement. It should be cleaned and all alarms and
associated shutdowns tested. The setting of the cargo tank safety valve
must be such as to ensure that it lifts before the deck seal arrangement
safety valve.

240 © ICS/OCIMF/IAPH 2006