4.2.1 The tank washing machines for crude oil
washing shall be permanently mounted and shall be of a design acceptable
to the Administration.
4.2.2 The performance characteristic of a tank
washing machine is governed by nozzle diameter, working pressure and
the movement pattern and timing. Each tank cleaning machine fitted
shall have a characteristic such that the sections of the cargo tank
covered by that machine will be effectively cleaned within the time
specified in the Operations and Equipment Manual.
4.2.3 Tank washing machines shall be mounted in
each cargo tank and the method of support shall be to the satisfaction
of the Administration. Where the tank washing machines are positioned
well below the deck level to cater for protuberances in the tank,
consideration may need to be given to additional support for the machines
and their supply piping.
4.2.4 Each machine shall be capable of being isolated
by means of stop valves in the supply line. If a deck mounted tank
washing machine is removed for any reason, provision shall be made
to blank off the oil supply line to the machine for the period the
machine is removed. Similarly, provision shall be made to close the
tank opening with a plate or equivalent means.
4.2.5 Where the drive units for the tank cleaning
machines are not integral with the tank cleaning machine, sufficient
drive units shall be provided to ensure that no drive unit need be
moved more than twice from its original position during cargo discharge
to accomplish the washing programme as specified in the Operations
and Equipment Manual.
4.2.6 The number and location of the tank washing
machines shall be to the satisfaction of the Administration.
4.2.7 The location of the machines is dependent
upon the characteristics detailed in 4.2.2 and upon the configuration
of the internal structure of the tank.
4.2.8 The number and location of the machines
in each cargo tank shall be such that all horizontal and vertical
areas are washed by direct impingement or effectively by deflection
or splashing of the impinging jet. In assessing an acceptable degree
of jet deflection and splashing, particular attention shall be paid
to the washing of upward facing horizontal areas and the following
parameters shall be used:
-
(a) For horizontal areas of a tank bottom and
the upper surfaces of a tank's stringers and other large primary structural
members, the total area shielded from direct impingement by deck or
bottom transverses, main girders, stringers or similar large primary
structural members shall not exceed 10 per cent of the total horizontal
area of tank bottom, the upper surface of stringers, and other large
primary structural members.
-
(b) For vertical areas of the sides of a tank,
the total area of the tank's sides shielded from direct impingement
by deck or bottom transverses, main girders, stringers or similar
large primary structural members shall not exceed 15 per cent of the
total area of the tank's sides.
-
(c) For existing crude oil tankers, the Administration
may permit the percentages required in (a) and (b) above to be exceeded
for tanks having complicated internal structural members provided
that the percentages calculated over all the cargo tanks do not exceed
10 per cent for horizontal areas and 15 per cent for vertical areas.
In some installations it may be necessary to consider the fitting
of more than one type of tank washing machine in order to effect adequate
coverage.
4.2.9 At the design stage the following minimum
procedures shall be used to determine the area of the tank surface
covered by direct impingement:
-
(a) Using suitable structural plans, lines are
set out from the tips of each machine to those parts of the tank within
the range of the jets.
-
(b) Where the configuration of the tanks is considered
by the Administration to be complicated, a pinpoint of light simulating
the tip of the tank washing machine in a scale model of the tank shall
be used.
4.2.10 To confirm the effectiveness of the crude
oil washing system and stripping system, the crude oil washing operation
should be witnessed to the satisfaction of the Administration.
-
(a) For ships that comply with regulation 13F(3), the crude oil
washing operations are to be carried out using the approved crude
oil washing equipment and as specified in the approved Operations
and Equipment Manual. For at least one tank of a group of tanks of
similar configuration, the Administration should:
-
(i) Confirm the operation of the stripping system
by observing the monitoring devices and monitoring the oil level (by
dipping or other means) during bottom washing.
-
(ii) Monitor the proper operation of the washing
machines with particular reference to supply pressure, cycle times
and machine function.
On completion of washing and
final draining, the tanks are to be hand dipped, as close as practical
to the forward end, centre and aft end in each tank and a record of
these dips should be made in the COW Manual. An Administration may
require an internal examination as described in subparagraph (b)(i)
of this section, or by an alternative method acceptable to the Administration,
if deemed necessary.
-
(b) For ships other than those complying with regulation 13F(3), where fitted
with cargo tanks intended to be used in certain circumstances as ballast
tanks, the following requirements apply in addition to those specified
in paragraph (a) of this section:
-
(i) To ensure that the tank is essentially free
of clingage and deposits, the Administration may require that the
cleanliness of the tank be confirmed by a visual inspection made by
entering the tanks after a crude oil washing but prior to any water
rinse which may be specified in the Operations and Equipment Manual.
If the tanks cannot be gas freed for safe entry of the surveyor, an
internal examination should not be conducted and the stripping test
specified in paragraph 4.2.10(b)(ii) will be acceptable.
In
this case, the bottom of the tank to be inspected may be flushed with
water and stripped in order to remove any wedge of liquid crude oil
remaining on the tank bottom before gas-freeing for entry. If the
flushing procedure is adopted, a similar but unflushed tank must be
used for the test specified in (ii) below.
-
(ii) To verify the effectiveness of the stripping
and drainage arrangements, a measurement should be made of the amount
of oil floating on top of the departure ballast. The ratio of the
volume of oil on top of the total departure ballast water to the volume
of tanks that contain this water should not exceed 0.00085. This test
should be carried out after crude oil washing and stripping in a tank
similar in all relevant respects to the tank examined in accordance
with (b)(i) above, which has not been subjected to a water rinse or
to the intervening water flushing permissible in (b)(i) above.
-
(iii) To verify the design, installation and operation
of the system, the arrival ballast, after a typical ballast voyage
before which the arrival ballast tanks have been crude oil washed
and during which the tanks have been water rinsed in accordance with
the programme set out in the Operations and Equipment Manual, should
be totally discharged to the loading port harbour through an Oil Discharged
Monitoring and Control (ODM) system approved by the Administration.
The oil content of the effluent in this test should not exceed 15
ppm. Alternatively, the option of taking ballast water samples to
be analysed in a shore-based laboratory is also acceptable.
-
(c) During all COW system surveys, internal visual
inspections of the tanks by inspectors should not be considered a
mandatory requirement. When an Administration considers that there
is a possible failure of the COW system indicated by other COW survey
requirements, the Administration may require an internal examination
of the tanks involved. Internal examinations may be completed using
alternative methods, e.g., video survey or other new technology, as
accepted by the Administration.
4.2.11 Where an Administration is satisfied that
ships are similar in all relevant respects, the requirements of 4.2.10 need only be applied to one such ship.
Furthermore, where a ship has a series of tanks that are similar in
all relevant respects then, for that series of tanks, the requirements
of 4.2.10(a) need only be applied to
one tank of that series.
4.2.12 The design of the deck mounted tank washing
machines shall be such that means are provided, external to the cargo
tanks, which, when crude oil washing is in progress, would indicate
the rotation and arc of the movement of the machine. Where the deck
mounted machine is of the non-programmable, dual nozzle type, alternative
methods to the satisfaction of the Administration may be accepted
provided an equivalent degree of verification is attained.
4.2.13 Where submerged machines are required,
they should be non-programmable and, in order to comply with the requirements
of 4.2.8, it must be possible to verify
their rotation by one of the following methods:
-
(a) By indicators external to the tank;
-
(b) By checking the characteristic sound pattern
of the machine, in which case the operation of the machine shall be
verified towards the end of each wash cycle. Where two or more submerged
machines are installed on the same supply line, valves shall be provided
and arranged so that operation of each machine can be verified independently
of the other machines on the same supply line;
-
(c) By gas freeing the tank and checking the operation
of the machine with water during ballast voyages. In this case the
check shall take place after a maximum of six usages of the machine
but the interval between checks shall not exceed 12 months. Each verification
shall be recorded in Supplement 2 to the Oil Record Book.
The method of verification shall be stated in the Operations
and Equipment Manual.