4.4.1 The design of the system for stripping crude
oil from the bottom of every cargo tank shall be to the satisfaction
of the Administration.
4.4.2 The design and capacity of the tank stripping
system shall be such that the bottom of the tank being cleaned is
kept free of accumulations of oil and sediment towards completion
of the tank washing process.
4.4.3 The stripping system shall be capable of
removing oil at a rate of 1.25 times the total throughput of all the
tank cleaning machines to be operated simultaneously when washing
the bottom of the cargo tanks as described in the ship's Operations
and Equipment Manual.
4.4.4 Means such as level gauges, hand dipping
and stripping system performance gauges as referred to in 4.4.8 shall be provided for checking that
the bottom of every cargo tank is dry after crude oil washing. Suitable
arrangements for hand dipping must be provided at the aftermost portion
of a cargo tank and in three other suitable locations unless other
approved means are fitted for efficiently ascertaining that the bottom
of every cargo tank is dry. For the purpose of this paragraph, the
cargo tank bottom shall be considered “dry” if there is
no more than a small quantity of oil near the stripping suction with
no accumulation of oil elsewhere in the tank.
4.4.5 Means shall be provided to drain all cargo
pumps and lines at the completion of cargo discharge, where necessary,
by connexion to a stripping device. The line and pump draining shall
be capable of being discharged both to a cargo tank and ashore. For
discharge ashore a special small diameter line shall be provided for
that purpose and connected outboard of the ship's manifold valve.
For new oil tankers or existing oil tankers not already fitted with
such a line the cross-sectional area of this line shall not exceed
10 per cent of that of a main cargo discharge line. Where such a line
is already fitted on an existing tanker, a cross-sectional area of
not more than 25 per cent of that of a main cargo discharge line may
be accepted.
4.4.6 The means for stripping oil from the cargo
tanks shall be by positive displacement pump, self-priming centrifugal
pump or eductor or other methods to the satisfaction of the Administration.
Where a stripping line is connected to a number of tanks, means shall
be provided for isolating each tank not being stripped at that particular
time.
4.4.7 The carriage of more than one grade of cargo
shall not prevent crude oil washing of tanks.
4.4.8 Equipment shall be provided for monitoring
the efficiency of the stripping system. All such equipment shall have
remote read-out facilities in the cargo control room or in some other
safe and convenient place easily accessible to the officer in charge
of cargo and crude oil washing operations. Where a stripping pump
is provided, the monitoring equipment shall include, as appropriate,
a flow indicator, or a stroke counter or a revolution counter, and
pressure gauges at the inlet and discharge connexions of the pump
or equivalent. Where eductors are provided, the monitoring equipment
shall include pressure gauges at the driving fluid intake and at the
discharge and a pressure/vacuum gauge at the suction intake.
4.4.9 The internal structure of the tank shall
be such that drainage of oil to the tank suctions of the stripping
system is adequate to meet the requirements of 4.4.2 and 4.4.4. Care shall be taken
that both longitudinal and transverse drainage are satisfactory and
shall be verified during the inspection required by 3.2 and 4.2.10.
4.4.10 The trim conditions for crude oil washing
given in the Operations and Equipment Manual shall be adhered to.
In general, trim by the stern is only important during the final stages
of tank discharge and shall be the maximum possible compatible with
operational constraints but in no case less than that recorded during
the crude oil washing prior to the inspection required by 3.2 and 4.2.10.