1. General guidelines for CBT operation procedures
(section 4 of Manual)
1.1 CBT operation requires full appreciation of the
procedures and thorough understanding of what is going on at all times.
Frequent checks are essential to ensure that contamination or pollution does
not occur. These checks include visual observation of the ballast tanks, the
piping and valve system, etc. and a general awareness of the possibilities
of leakages that may permit oil to enter the ballast system. The items in
the procedure which emphasize safety must therefore be followed in full.
1.2 The cargo discharging and ballast handling sequence
should be clearly illustrated in a programme worked out by the key personnel
involved. The programme should clearly identify the responsibility of all
persons involved and should specify in a time-related manner essential
facts, such as:
- the procedure and the timing for taking the necessary quantity of piping
flush water into the ballast tanks;
- the cargo discharging sequence, specifying pumps and lines to be used at
each point in the sequence and the projected timetable;
- the procedure and the timing for flushing the ballast piping and taking
on ballast: if this is done before the cargo is fully discharged great
attention must be paid to the details of the programme so that safe
segregation is maintained;
- the procedure for stripping and draining of the cargo tanks, and
particularly the cargo pipes, after completion of the discharge.
1.3 The above cargo discharge and ballast handling
programme together with the checklist (see section 5 of Manual) and other
relevant information should be displayed in the cargo control room or other
appropriate place easily accessible to all persons involved.
1.4 During any part of the CBT operation, when quick and
reliable communication is required between activities taking place some
distance apart, adequate and approved portable radio equipment should be
1.5 The tanker should be loaded bearing in mind the
requirements of a cargo discharge sequence compatible with the CBT
1.6 When loading cargo that will be unloaded at two or
more discharge ports it is important to ensure that this can be done
following the CBT procedures and while maintaining safe trim and stress
1.7 Prior to arrival at loading port, the clean ballast
may be reduced to berthing condition, using a pump and pipe that have been
cleaned or kept clean during the ballast voyage.
1.8 The ballast may be discharged prior to loading or
after some cargo has been loaded, depending on the ship and terminal
limiting requirements. If cargo has to be loaded prior to deballasting, this
must only be done through piping that can be kept separated from the
dedicated clean ballast tanks and associated piping.
1.9 Ballast water carried in dedicated clean ballast tanks
should be visually checked prior to and during discharge for presence of any
oil. If any doubt about the cleanliness of the water during discharge
exists, the discharge should be stopped and the remainder retained in the
ballast tank or transferred to the slop tank for later discharge to the
reception facility or at sea in compliance with Regulation 9 of Annex I of
1.10 Normal line flushing must be carried out by drawing
water from the dedicated clean ballast tanks and discharging to a slop tank.
Flush water must never be discharged into a dedicated clean ballast tank.
The related method for making flush water available to the ballast tanks for
line flushing depends on the piping system and influences the entire CBT
procedure for the tanker.
1.11 If the tanker has a separate pump and deck line for
water washing of cargo tanks, isolated from the cargo system, this may be
used for transferring the necessary amount of flush water to the ballast
tanks at any time. Tank washing hoses are used as required between the deck
line and the individual tanks. This method can be adopted by most tankers
(which have not been built to use fixed, high capacity washing machines) and
it offers the most flexible and convenient arrangement. Alternatively, the
fire pump and the fire main and hoses or other deck service lines may be
used for this purpose, subject to approval by the Administration of the use
of the firefighting system. The operation can normally be carried out
completely independently of the cargo tank activities. The amount of water
transferred to the ballast tanks prior to line flushing should always be at
least ten times the volume of the pipes to be flushed. There is, however, no
disadvantage in taking in more: what is not used for line flushing simply
remains in the ballast tanks, becoming part of the departure ballast.
1.12 In vessels which do not have a water supply system
suitable for transfer of flush water over deck, flush water must be
transferred to the ballast tanks through the cargo piping during the
operational stages when the piping is clean. This means that a quantity of
flush water has to be left in the ballast tanks at deballasting and
subsequently is used for line flushing after the loading of cargo. Similarly
a quantity of flush water has to be taken in through the clean piping
towards the end of the loaded voyage in order to be used for line flushing
after the cargo discharge. A part of the cargo piping thus has to remain
flushed and clean during the loaded passage. This procedure requires more
control and more careful planning than that described in paragraph 1.11
above which is therefore the procedure to be followed whenever possible.
1.13 For tankers in short haul trades operating on the
principle outlined in 1.12 above it may be preferable to leave the necessary
quantity of flush water in the ballast tanks throughout the loaded passage.
In this case some part of the ballast water is simply left in the tanks at
deballasting and used for line flushing after the following cargo discharge.
Since a CBT tanker always has unused deadweight capacity, this. small
dead-freight will normally be of no importance. The effect on tank corrosion
should be considered and necessary preventive measures taken.
1.14 When carrying out pipe flushing, water must always be
routed from a ballast tank to a slop tank. In addition, in tankers where the
piping can be connected as a ring line it is possihle to pump water from the
sea or from a slop tank through the pipe system and back to a slop tank but
water which has passed through an oily pipe section must never be passed to
a dedicated clean ballast tank. The amount of pipe flushing water used
should be at least ten times the volume of the piping system to be flushed.
1.15 When flushing from ballast tanks containing the
prescribed minimum amount of flush water it is important that the line has
first been thoroughly drained of oil. Flushing should normally start from
the tank farthest from the pump. After the line has been primed and suction
established, the pumping is stopped and the valves are closed for a period
of about half an hour to allow the oil from the pipe walls to separate out.
Pumping is then resumed at a moderate speed, with throttling of the output
at the pump delivery side.
1.16 When a ring line can be arranged, water is first
drawn from the individual tanks to clear the branch pipes and as the tanks
become empty and are closed off from the main line, the inlet to the ring is
opened from a slop tank to permit continued closed loop flushing. Towards
the end, the inlet should be switched to clean seawater.
1.17 Towards the end of the loaded passage, a normal
amount of pipe flushing water is transferred to the CBT tanks, either by use
of a clean deck line and related pump or via the cargo piping that has been
left clean during the voyage. During short voyages and provided the CBT
tanks have adequate corrosion protection, the pipe flushing water left in
the tanks prior to loading may be retained in the tanks. This procedure
eliminates the need for flushing the cargo piping during the loaded passage.
In either alternative, the tanker should have the nominal quantity of pipe
flushing water in the CBT tanks when entering the discharge port.
1.18 Before any CBT tank is ballasted a check should be
made for any presence of hydrocarbon gases as a result of leakage. This
check is also important from the safety point of view. Ballast water must
never be loaded into a ballast tank containing hydrocarbon gases in a higher
concentration than 20 per cent of the lower explosive limit in such a way
that splashing or free fall of water can occur.
1.19 During unloading, the tanks which are served by the
pump and piping used for ballast handling should be discharged first. At the
point when ballast has to be taken on, the affected piping is first flushed
using the procedure in paragraphs 1.14-1.16 whereupon the CRT tanks are
ballasted to the extent required. Thereafter the ballast handling piping
should be kept clean to permit any additional handling of ballast that may
1.20 During the bailast voyage the piping is kept clean as
a preparation for deballasting. Should any part become contaminated, for
instance by its use during tank cleaning of cargo tanks, it is again flushed
using ballast water, whereupon the ballast quantity may again be