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The learning objective of this section
is to ensure relevant personnel are
acquainted with
the purpose of crude oil washing
the property of crude oil
the dissolving effect in crude oil
applicability of the requirements
advantages and disadvantages with crude
oil washing
disadvantages with water washing
marpole 7378 recognizes that crude oil
washing provides a means of reducing the
contact between oil and water washing
cargo tanks with crude oil reduces the
amount of water washing needed for those
tanks required for ballast and eliminate
it for sledge control purposes
virtually all crude oil contains
relatively heavy components of waxy and
asphaltic substances during a tank is
loaded passage these components settle
out and horizontal members of Tanks
structures require substantial coatings
of sludge deposits
after the oil is discharged from tanks
the majority of this sludge will remain
unless it is removed it will build up
over several voyages and eventually
impede the efficient drainage of the
tanks this will effectively reduce the
cargo carrying capacity of the ship
crude oil has the property of being able
to dissolve its own residues dispense
and suspend the sediments in the cargo
and this restore the cargo to the
original condition when loaded this
property is the basis of crude oil
washing cow which as a description
implies involves the cleaning or washing
of cargo tanks with high-pressure Jets
of crude oil part of the cargo is
circulated through fixed piping and
washing machines doing Carlo discharge
cleaning with water gives reasonable
good results only when water jets with
sufficient impact force directly hitting
the surface within a tank
accordingly the cleaning effect is
almost non-existent as far as reflected
jets and drainages are concerned when
using crude oil a surprisingly good
cleaning result is obtained even from
drainages and reflected Jets of crude
oil the so-called splashback effect
the superiority of crude oil to water as
a tank cleaning fluid is exclusively
dependent upon the dissolving property
of crude oil it is not possible to
dissolve sediments from crude oil
cargoes with water
by 1977 crude oil washing have been
widely adopted by a large number of
major oil companies and independent
tanker owners as a means of sediment
control it was offered as an alternative
to the fitting of segregated ballast
tanks SBT
the international conference on tanker
safety and pollution prevention convened
in London during februari 1978 resulted
in protocols amending those of the
International Convention for the safety
of life at sea 1974 so last and the
International Convention for the
prevention of pollution from ships
marpol 7378
briefly existing crude oil carriers must
be fitted with SBT systems if they are
40,000 deadweight tons or above but as
an alternative crude oil washing cow or
a clean ballast tank system cbt may be
allowed in the case of cbt the ship
owner declares certain cargo tanks as
dedicated clean ballast tanks and these
are not allowed to carry cargo a cbt
system is similar to an SBT system
except that the pumps and lines serving
the cbt tanks may also be used for cargo
operations
advantages with crude oil washing
considerable reduction in pollution
potential since less oil remains on
board after discharge and less soil
contaminated water is handed during the
ballast passage
reduction in time and cost of tank
cleaning
d sludging by hand obviated
reduced tank cleaning time at sea
increased out turn of cargo
reduced dead freight as less oil water
and slops I retained on board
less salt water discharged to refineries
tank corrosion due to water washing is
reduced
disadvantages with crude oil washing
increased workload during discharging
prolonged time for discharging
costs for extra personnel
costs the crude oil washing equipment
potential safety in pollution risk
more equipment higher demand for
maintenance
disadvantages with water washing
longer time for washing each tank
resulting in increased bunker costs
handling larger amounts of water is
costly and causes increased pollution of
the sea since the water is contaminated
with oil even when load on top procedure
is used
increased corrosion due to extensive
water washing
reduced cargo capacity due to largest
slop quantity
discharge of more salt water with slops
to refineries
longer period of time needed to prepare
tanks are dry dock or intermediate cold
or hot work tank inspection included
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