Crude Oil Washing System 16c3r

CRUDE OIL WASHING SYSTEMS including amendments adopted by the MEPC at its forty-third session (28 June to 2 July 1999) and by the Assembly at its twenty-first session (15 to 26 November 1999)

B

International Maritime Organization London, 2000

First published in 1980 by the INTERNATIONAL MARITIME ORGANIZATION 4 Albert Embankment, London SE1 7SR Second edition 1982 Third edition 1983 Fourth edition 2000 Printed by the International Maritime Organization, London 2 4 6 8 10 9 7 5 3

ISBN 92-801-5094-4

IMO PUBLICATION Sales number: IMO-617E

Copyright # IMO 2000 All rights reserved. No part of this publication may, for sales purposes, be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, electrostatic, magnetic tape, mechanical, photocopying or otherwise, without prior permission in writing from the International Maritime Organization.

FOREWORD This publication contains: . Revised Specifications for the design, operation and control of crude oil washing systems (resolution A.446(XI), as amended by resolutions A.497(XII) and A.897(21)); . standard format for the Crude Oil Washing Operations and Equipment Manual (resolution MEPC.3(XII), as amended by resolution MEPC.81(43)); . examples of Crude Oil Washing Operations and Equipment Manuals; . Guidelines for in-port inspection of crude oil washing procedures. REVISED SPECIFICATIONS The International Conference on Tanker Safety and Pollution Prevention (TSPP Conference) convened by the International Maritime Organization (IMO) in February 1978 adopted, inter alia, the Protocol of 1978 relating to the International Convention for the Prevention of Pollution from Ships, 1973, which modified the 1973 Convention.* MARPOL 73/78 (regulation 13 of Annex I) requires certain ships to operate with a cargo tank cleaning system using crude oil washing. The crude oil washing installation, associated equipment and arrangements must meet the requirements established by the istration based on the Specifications for the design, operation and control of crude oil washing systems adopted by the Conference in resolution 15 and as may be revised by the Organization (regulation 13B of Annex I of MARPOL 73/78). The Conference requested the Organization to review and revise the Specifications, as necessary, in order that the Revised Specifications would reflect the latest technology and practices which might be developed by the time of entry into force of MARPOL 73/78. The task of reviewing and revising the Specifications was carried out by the Marine Environment Protection Committee (MEPC) of the Organization at its 10th and 11th sessions as a matter of urgency. In the course of its work, the MEPC found that there was a need, not only to revise certain provisions of the Specifications, but also to agree on interpretations of some of the provisions. The IMO Assembly, at its 11th session (November 1979), received and examined the recommendations made by the MEPC on this matter and adopted, by resolution A.446(XI), the Revised Specifications for the design, operation and control of crude oil washing systems, together with agreed interpretations of certain of the provisions of the Revised Specifications. As stated in the resolution, the Revised Specifications supersede the Specifications contained in the annex to resolution 15 of the TSPP Conference. Since the 11th session of the Assembly, the MEPC has kept the Revised Specifications under review and recommended certain amendments and additions both to the Revised Specifications and to the agreed interpretations; these were adopted by the Assembly at its 12th session (November 1981) by resolution A.497(XII), and at its 21st session (November 1999) by resolution A.897(21). The attention of Governments is drawn to the fact that the Assembly urged them to establish, in time for the entry into force of MARPOL 73/78, requirements for crude oil washing installations and associated equipment and arrangements based on the Revised Specifications, and urged further that such requirements should not impose requirements over and above those laid down in the Revised Specifications.

* The 1973 Convention, as modified by its 1978 Protocol, is referred to throughout this publication as MARPOL 73/78.

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Crude oil washing systems CRUDE OIL WASHING OPERATIONS AND EQUIPMENT MANUAL Every tanker which operates with crude oil washing, in accordance with regulation 13, must be provided with an Operations and Equipment Manual approved by the istration. The Manual must detail the system and equipment and specify operational procedures (regulation 13B of Annex I of MARPOL 73/78). As the purpose of the Operations and Equipment Manual is not only to provide guidance to the crew of the ship on the proper operation of the system but also to provide information on the system and its operational procedures for inspectors going on board for inspection in ports, the MEPC decided to develop a standard format for the Manual. This was adopted by the MEPC at its 12th session by resolution MEPC.3(XII). The MEPC adopted revisions to the standard format at its 43rd session by resolution MEPC.81(43). It is hoped that the standard format will help shipowners in preparing the Manuals for their ships and istrations in approving them. The standard format contains: . standardized wording for the introduction of the Manual; . index of the Manual; . eighteen sections, detailing the information or operational instructions to be provided under each section as required by the Revised Specifications for the design, operation and control of crude oil washing systems, including the revised section 9 (resolution MEPC.81(43)). istrations may require information and operational instructions to be included in the Manual in addition to those specified in the standard format. Such information should be included in part 2 of the Manual. If no such information or operational instructions are required, the Manual will consist of one part only. This publication also contains two examples of the Manual, developed by tanker owners in accordance with the standard format, for two actual tankers, one of which is a conventional pipeline tanker of about 315,000 tons deadweight and the other a full free flow tanker of about 270,000 tons deadweight. As will be seen from these two examples, the information and operational instructions under the corresponding sections vary considerably in their wording and presentation. It should be noted in this connection that: . what is standardized is the type of information to be included in the Manual under each section and not its presentation; . the two examples show how the Manuals may be presented. Although some sections may be generally applicable to all ships, these are merely examples and should be treated as such. The attention of Governments is drawn to the recommendation made by the MEPC, inviting them to use the standard format when approving the Manual and to ensure that, if the language of the Manual is neither English nor French, the Manual includes a translation into one of those languages.

GUIDELINES FOR IN-PORT INSPECTION By resolution 7 the TSPP Conference recommended that the Organization take urgent action to develop guidelines for the performance of in-port inspections of the results of cargo tank cleaning using crude oil washing, which should be implemented by Governments as soon as they are adopted by the Organization. iv

Foreword The Conference recognized that in order to implement effectively the requirements of regulations 13 and 13B of Annex I of MARPOL 73/78, continuing strong emphasis should be placed on the effective operation of crude oil washing procedures, and also that uniform guidelines for the extent and particulars of in-port inspections of the results of cargo tank cleaning are a prerequisite for ensuring that crude oil tankers using crude oil washing systems comply at all times with the provisions of MARPOL 73/78. The MEPC at its 12th session adopted the Guidelines for in-port inspection of crude oil washing procedures and requested the Secretariat to circulate them to Governments. Governments were invited, by an MEPC circular, to take note of the Guidelines for implementation.

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CONTENTS I

Revised Specifications for the design, operation and control of crude oil washing systems Resolution A.446(XI), as amended by resolutions A.497(XII) and A.897(21) Appendix I –

II

List of changes when applying the specifications to new crude oil tankers of 20,000 tons deadweight and above . . . . . . . . . . . . . . .

13

Appendix II – Training for persons intended to assume overall charge of crude oil washing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

15

Appendix III – Agreed interpretations of certain of the provisions of the Revised Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17

Standard format for the Crude Oil Washing Operations and Equipment Manual Resolution MEPC.3(XII) as amended by MEPC.81(43)

III

IV

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

23

Index of sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

24

Sections 1 to 18 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

25

Examples of Crude Oil Washing Operations and Equipment Manuals Explanatory note . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

31

Example 1 – Conventional pipeline tanker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

33

Example 2 – Full free-flow tanker. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

57

Guidelines for in-port inspection of crude oil washing procedures . . . . . . . . . . . . . . . . .

85

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I REVISED SPECIFICATIONS FOR THE DESIGN, OPERATION AND CONTROL OF CRUDE OIL WASHING SYSTEMS

Crude oil washing systems

Index Page 1

Purpose

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3

2

Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

3

General provisions 3.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Initial survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 3

Design criteria 4.1 Piping . . . . . . . . . . . . . 4.2 Tank washing machines 4.3 Pumps . . . . . . . . . . . . . 4.4 Stripping system . . . . . . 4.5 Ballast lines . . . . . . . . .

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3 4 7 8 9

5

Qualification of personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

6

Operation 6.1 Tankage to be crude oil washed . . . . . . . . . . . . . 6.2 Drainage and discharge ashore of cargo lines . . . . 6.3 Filling of departure ballast tanks . . . . . . . . . . . . . . 6.4 Crude oil washing at sea . . . . . . . . . . . . . . . . . . . 6.5 Discharge of oily water effluents on ballast voyage 6.6 Use and control of inert gas . . . . . . . . . . . . . . . . . 6.7 Precautions against electrostatic generation . . . . . 6.8 Vapour emission . . . . . . . . . . . . . . . . . . . . . . . . .

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9 10 10 10 10 10 10 10

Operations and Equipment Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11

Appendix I – List of changes when applying the Specifications to new crude oil tankers of 20,000 tons deadweight and above . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13

Appendix II – Training of persons intended to assume overall charge of crude oil washing.

15

Appendix III – Agreed interpretations of certain of the provisions of the Revised Specifications

17

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Note: The Revised Specifications comprise the annex to resolution A.446(XI), as amended by resolutions A.497(XII) and A.897(21).

2

Revised Specifications 1

Purpose

The purpose of these Specifications is to provide specific design criteria, operational requirements and control and enforcement procedures for the crude oil washing of cargo tanks of crude oil carriers as specified in section 2. 2

Application

2.1

These Specifications apply to: (a) existing crude oil tankers of 40,000 tons deadweight and above in accordance with regulation 13(8) of Annex I of MARPOL 73/78; and (b) new crude oil tankers of 20,000 tons deadweight and above in accordance with regulation 13(6) of Annex I of MARPOL 73/78, with the changes listed in appendix I.

Compliance of these ships with these Specifications shall be shown on the International Oil Pollution Prevention Certificate as modified by MARPOL 73/78. 2.2 If a crude oil that is not suitable for crude oil washing is intended to be carried as cargo in a ship that is provided with only a crude oil washing system, then that ship must comply with segregated ballast tank requirements in accordance with regulation 13(7) or dedicated clean ballast tank requirements in accordance with regulation 13(9) of Annex I of MARPOL 73/78. 3

General provisions

3.1

Definitions

For the purpose of these Specifications: 3.1.1 Arrival ballast means clean ballast as defined in regulation 1(16) of Annex I of MARPOL 73/78. 3.1.2 Departure ballast means ballast other than arrival ballast. 3.2

Initial survey

The initial survey referred to in regulation 4 of Annex I of MARPOL 73/78 shall include a complete inspection of the crude oil washing equipment and arrangements and shall include, except for the cases specified in 4.2.11, an examination of the tanks after they have been crude oil washed and the additional controls as specified in 4.2.10 to ensure that the washing system efficiency is in accordance with these Specifications. 4

Design criteria

4.1

Piping

4.1.1 The crude oil washing pipes and all valves incorporated in the supply piping system shall be of steel or other equivalent material and shall be of adequate strength having regard to the pressure to which they may be subjected, and shall be properly ted and ed. 4.1.2 The crude oil washing system shall consist of permanent pipework and shall be independent of the fire mains and of any system other than for tank washing except that sections of the ship’s cargo system may be incorporated in the crude oil washing system provided that they meet the requirements applicable to crude oil pipework. Notwithstanding the above requirements, in combination carriers the arrangements may allow: 3

Crude oil washing systems (a) the removal of the equipment, if necessary, when carrying cargoes other than crude oil, provided that, when reinstated, the system is as originally fitted and tested for oil tightness; (b) the use of flexible hosepipes to connect the crude oil washing system to tank washing machines if it is necessary to locate these machines in a cargo tank hatch cover. Such flexible hosepipes must be provided with flanged connections and be manufactured and tested in accordance with standards acceptable to the istration and be consistent with the duties the hoses are required to perform. The length of these hoses shall be no greater than necessary to connect the tank washing machines to an adjacent point just outside the hatch coaming. These hoses shall be removed to suitably prepared and protected stowage when not in use and be pressuretested by an authority acceptable to the istration at intervals of not more than two and a half years. 4.1.3 Provision shall be made to prevent overpressure in the tank washing supply piping. Any relief device fitted to prevent overpressure shall discharge into the suction side of the supply pump. Alternative methods to the satisfaction of the istration may be accepted provided an equivalent degree of safety and environmental protection is provided. 4.1.4 Where hydrant valves are fitted for water washing purposes on tank washing lines, all such valves shall be of adequate strength and provision shall be made for such connections to be blanked off by blank flanges when washing lines may contain crude oil. Alternatively, hydrant valves shall be isolated from the crude oil washing system by spade blanks. 4.1.5 All connections for pressure gauges or other instruments shall be provided with isolating valves adjacent to the lines unless the fitting is of the sealed type. 4.1.6 No part of the crude oil washing system shall enter the machinery spaces. Where the tank washing system is fitted with a steam heater for use when water washing, the heater must be effectively isolated during crude oil washing by double shut-off valves or by clearly identifiable blanks. 4.1.7 Where a combined crude oil–water washing supply piping is provided the piping shall be so designed that it can be drained so far as is practicable of crude oil, before water washing is commenced, into spaces designated in the Crude Oil Washing Operations and Equipment Manual. These spaces may be the slop tank or other cargo spaces. 4.1.8 The piping system shall be of such diameter that the greatest number of tank cleaning machines required, as specified in the Operations and Equipment Manual, can be operated simultaneously at the designed pressure and throughput. The arrangement of the piping shall be such that the required number of tank cleaning machines to each cargo compartment, as specified in the Operations and Equipment Manual referred to in these Specifications, can be operated simultaneously. 4.1.9 The piping system shall be tested to one and one half times the working pressure after it has been installed on the ship. 4.1.10 The crude oil washing supply shall be anchored (firmly attached) to the ship’s structure at appropriate locations, and means shall be provided to permit freedom of movement elsewhere to accommodate thermal expansion and flexing of the ship. The anchoring shall be such that any hydraulic shock can be absorbed without undue movement of the supply piping. The anchors should normally be situated at the ends furthest from the entry of the crude oil supply piping. If tank washing machines are used to anchor the ends of branch pipes then special arrangements are necessary to anchor these sections when the machines are removed for any reason. 4.2

Tank washing machines

4.2.1 The tank washing machines for crude oil washing shall be permanently mounted and shall be of a design acceptable to the istration. 4

Revised Specifications 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 cleaning 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 shall be to the satisfaction of the istration. 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 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 deckmounted 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 istration. 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 , the total area shielded from direct impingement by deck or bottom transverses, main girders, stringers or similar large primary structural shall not exceed 10% of the total horizontal area of tank bottom, the upper surface of stringers and other large primary structural . (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 shall not exceed 15% of the total area of the tank’s sides. (c) For existing crude oil tankers, the istration may permit the percentages required in (a) and (b) above to be exceed for tanks having complicated internal structural provided that the percentages calculated over all the cargo tanks do not exceed 10% for horizontal areas and 15% 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 istration 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. 5

Crude oil washing systems 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 istration. (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 istration 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 Operations and Equipment Manual. An istration may require an internal examination as described in subparagraph (b)(i) of this section, or by an alternative method acceptable to the istration, 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 istration 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 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 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 istration. 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 shorebased laboratory is also acceptable. (c) During all crude oil washing system surveys, internal visual inspections of the tanks by inspectors should not be considered a mandatory requirement. When an istration considers that there is a possible failure of the crude oil washing system indicated by other crude oil 6

Revised Specifications washing survey requirements, the istration 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 istration. 4.2.11 Where an istration 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 istration 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 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. 4.3

Pumps

4.3.1 The pumps supplying crude oil to the tank cleaning machines shall be either the cargo pumps or pumps specifically provided for the purpose. 4.3.2 The capacity of the pumps shall be sufficient to provide the necessary throughput at the required pressure for the maximum number of tank cleaning machines required to be operated simultaneously as specified in the Operations and Equipment Manual. In addition to the above requirement, the pumps shall, if an eductor system is fitted for tank stripping, be capable of supplying the eductor driving fluid to meet the requirements of 4.4.2. 4.3.3 The capacity of the pumps shall be such that the requirements of 4.3.2 can be met with any one pump inoperative. The pumping and piping arrangements shall be such that the crude oil washing system can be effectively operated with any one pump out of use. 4.3.4 The carriage of more than one grade of cargo shall not prevent crude oil washing of tanks. 4.3.5 To permit crude oil washing to be effectively carried out where the back pressure presented by the shore terminal is below the pressure required for crude oil washing, provision shall be made that such an adequate pressure to the washing machines can be maintained in accordance with 4.3.2. This requirement shall be met with any one cargo pump out of action. The minimum supply pressure required for crude oil washing shall be specified in the Operations and Equipment Manual. Should this minimum supply pressure not be obtainable, crude oil washing operations shall not be carried out. 7

Crude oil washing systems 4.4

Stripping system

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 istration. 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 connection 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% of that of a main cargo discharge line. Where such a line is already fitted on an existing tanker, a crosssectional area of not more than 25% of that of a main cargo discharge line may be accepted. 4.4.6 The means of 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 istration. 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 connections 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. 8

Revised Specifications 4.5

Ballast lines

4.5.1 Where a separate ballast water system for ballasting cargo tanks is not provided, the arrangement shall be such that the cargo pump, manifolds and pipes used for ballasting can be safely and effectively drained of oil before ballasting. 5

Qualification of personnel

5.1 The training requirements of ships’ personnel engaged in the crude oil washing of tankers shall be to the satisfaction of the istration. 5.2 Where a person such as the master, the chief officer or the cargo control officer assumes overall charge of a crude oil wash he shall: (a) have at least one year’s experience on oil tankers where his duties have included the discharge of cargo and associated crude washing. Where his duties have not included crude oil washing operations, he shall have completed a training programme in crude oil washing in accordance with appendix II to these Specifications and satisfactory to the istration; (b) have participated at least twice in crude oil wash programmes one of which shall be on the particular ship for which he is required to undertake the responsibility of cargo discharge. Alternatively, this latter participation may be acceptable if undertaken on a ship that is similar in all relevant respects; and (c) be fully knowledgeable of the contents of the Operations and Equipment Manual. 5.3 Where other nominated persons are intended to have particular responsibilities as defined in the Operations and Equipment Manual, they shall have at least six months’ experience on oil tankers where, in the course of their duties, they should have been involved in the cargo discharge operation. In addition, they should have been instructed in the crude oil washing operation in the particular ship for which they are required to undertake this responsibility and be fully knowledgeable of the contents of the Operations and Equipment Manual. Appendix II to these Specifications should be used as guidance in establishing the content of such instruction. 6

Operation

6.1

Tankage to be crude oil washed

Before departure on a ballast voyage, after the complete discharge of cargo, sufficient tanks shall have been crude oil washed in accordance with the procedures specified in the Operations and Equipment Manual to ensure that: (a) as a minimum, sufficient tanks have been washed to permit compliance with the draught and trim requirements of regulation 13(2)(a), (b) and (c) of Annex I of MARPOL 73/78 during all phases of the ballast voyage; and (b) is taken of the ship’s trading pattern and the expected weather conditions so that additional ballast water is not put into tanks which have not been crude oil washed. In addition to the tanks referred to in (a) above, approximately one quarter of all remaining tanks shall be crude oil washed for sludge control on a rotational basis, but these additional tanks may include the tanks referred to in (b) above. However, for sludge control purposes, no tank need be crude oil washed more than once in every four months. Crude oil washing shall not be conducted between the final discharge and loading ports; that is to say, no crude oil washing shall be undertaken during the ballast voyage. Ballast water shall not be put into tanks that have not been crude oil washed. Water that is put into a tank which has been crude oil washed but not water rinsed shall be regarded as dirty ballast. 9


Drainage and discharge ashore of cargo lines

At the end of cargo discharge all cargo mains and stripping lines shall be drained and stripped and the drainings and strippings discharged ashore via the special small-diameter line required by 4.4.5. In addition all cargo tanks are to be stripped before the ship leaves its final port of discharge. 6.3

Filling of departure ballast tanks

Care shall be taken at the completion of crude oil washing of any departure ballast tank to strip the tank as completely as possible. Where departure ballast is loaded through cargo lines and pumps, these must be drained and stripped of oil using the means required by 4.4.5 before ballast is loaded. 6.4

Crude oil washing at sea

All crude oil washing must be completed before the ship leaves its final port of discharge. Where any tank is crude oil washed while the ship is at sea between multiple discharge ports, the tank shall be left empty and available for inspection at the next discharge port before commencing the next ballast voyage. This inspection may consist of multiple sounding/dipping of the bottom of the tank when the tank is empty. Departure ballast tanks shall be ballasted prior to departure from port so that examination of the surface of the ballast water can be made. In the latter case the guidance given in 4.2.10(b) is relevant to the inspection. 6.5

Discharge of oily water effluents on ballast voyage

The discharge of departure ballast and any other water effluent discharged during the ballast voyage shall comply with the requirements of regulation 9 of Annex I of MARPOL 73/78. 6.6

Use and control of inert gas

On ships to which these Specifications apply, no tank shall be crude oil washed unless the inert gas system required by regulation 13B(3) of Annex I of MARPOL 73/78 is in proper operation. Before each tank is crude oil washed, the oxygen level shall be determined at a point 1 m from the deck and at the middle region of the ullage space and neither of these determinations shall exceed 8% by volume. Where tanks have complete or partial wash bulkheads, the determinations should be taken from similar levels in each section of the tank. The oxygen level of the inert gas being delivered during the washing process shall be continuously monitored. If during crude oil washing: (a) the oxygen level of the inert gas being delivered exceeds 8% by volume; or (b) the pressure of the atmosphere at the tanks is no longer positive then the washing must be stopped until satisfactory conditions are restored. 6.7

Precautions against electrostatic generation

To avoid excessive electrostatic generation in the washing process due to the presence of water in the crude oil washing fluid, the contents of any tank to be used as a source of crude oil washing fluid must first be discharged by at least 1 m before being so used. Any tank used as a slop tank on the previous ballast voyage shall be completely discharged and refilled with dry crude oil if that tank is to be used as a source of washing fluid. 6.8

Vapour emission

On ships to which these Specifications apply there shall be means to avoid vapour emission during the filling of departure ballast wherever local conditions require it. The method of preventing the emission of hydrocarbon vapour into the atmosphere shall be: 10

Revised Specifications (a) by the use of permanent ballast tanks wherever these are sufficient to provide the minimum departure draught; or (b) by containment of vapour in empty cargo tanks by simultaneous ballasting and cargo discharge. Alternative methods to the satisfaction of the istrations may be accepted provided an equivalent degree of environmental protection is provided.

7

Operations and Equipment Manual

The Operations and Equipment Manual must be to the satisfaction of the istration and shall contain the following information and operational instructions: (a) The complete text of the Revised Specifications for the design, operation and control of crude oil washing systems. (b) A line drawing of the crude oil washing system showing the respective position of pumps, lines and washing machines which relate to the crude oil washing system. (c) A description of the system and a listing of procedures for checking that equipment is working properly during crude oil washing operations. This shall include a listing of the system and equipment parameters to be monitored, such as line pressure, oxygen level, machine revolutions, duration of cycles, etc. The established values for these parameters shall be included. The results of the tests carried out in accordance with 4.2.10 and the values of all parameters monitored during such tests shall also be included. (d) Details of the requirements of section 6 of these Specifications together with advice and instructions, where appropriate, in meeting these requirements such as: (i)

recommended methods and programmes of crude oil washing in order to accord with all foreseeable circumstances of cargo discharge restraints and to obtain maximum trim during the completion of washing and draining of each tank;

(ii) the procedure on ships to avoid vapour emission in accordance with 6.8; (iii) the method of draining tanks which shall include information on optimum trim conditions as required by 4.4.10; (iv) the method of draining cargo pumps, cargo lines, crude oil washing lines and stripping lines, the identification of spaces into which they may be drained and procedures for discharge ashore of drainings and strippings via the small-diameter discharge line on completion of cargo discharge; (v) typical washing programmes under various conditions of loading specifying: (1) the tanks to be washed in accordance with 6.1; (2) the method for washing each tank, that is, single- or multi-stage; (3) the number of tank washing machines to be used simultaneously; (4) the duration of the crude oil wash and water rinse where the latter is appropriate; 11

Crude oil washing systems (5) the volume of water used for water rinse, which shall be at least equal to that used in the water rinse prior to the inspection required by 3.2 and 4.2.10; and (6) the preferred order in which the tanks are to be washed; (vi) the procedure for draining and stripping, where appropriate, cargo lines and pumps before being used for the loading of departure ballast; (vii) the procedure for water washing lines before discharge of departure ballast and the loading and final discharge of arrival ballast; (viii) the procedure for ing by sound patterns that bottom-mounted machines are operating shall be carried out towards the end of the wash cycle for each tank. When carrying out such verification all other machines shall be shut down if necessary; (ix) precise details of procedure to ensure compliance with regulation 9 of Annex I of MARPOL 73/78 in the discharge of departure ballast, the water flushing of lines and the decanting of the slop tanks at sea. (e) The dangers of leakage from the crude oil washing system and the precautions necessary to prevent leakage and the action to be taken in the event of a leakage. Guidance shall be given on how the crude oil washing system is to be operationally tested for leakage before each discharge. (f)

The method of preventing the entry of oil to the engine room through steam heaters as required by 4.1.6.

(g) The personnel required at all times to conduct the dual operation of discharging cargo and crude oil washing. The numbers of such personnel shall include: (i)

the person meeting the requirements of 5.2 who will have overall control of the crude oil washing process;

(ii) those persons meeting the requirements of 5.3 who will be expected to undertake the actual operation; and (iii) at least one person on deck at all times during washing to keep watch for leaks and malfunctioning of equipment, to test the oxygen content of tanks before washing, to check tank atmosphere pressure, to sound tank bottoms if required, to lift ullage floats if necessary and to change drive units when this is necessary; The duties of such persons are not necessarily mutually exclusive. (h) An effective means of communication between the watchkeeper on deck and the cargo control position so that in the event of a leak in, or malfunctioning of, the crude oil washing system the washing may be stopped as soon as possible. (i)

The typical procedures for ballasting.

(j)

A pre-crude oil wash operational checklist for the use of the crew at each discharge which shall include the checking and calibration of all instruments.

(k) The recommended intervals for on-board inspection and maintenance of crude oil washing equipment in addition to statutory surveys. Reference should be made to technical manuals supplied by the manufacturers of the equipment. (l) 12

A list of crude oils unsuitable for the crude oil washing process and their origin.

Revised Specifications: Appendix I

Appendix I

List of changes when applying the Specifications to new crude oil tankers of 20,000 tons deadweight and above Paragraph number

List of changes

4.2.10 Subparagraph (c) is not applicable. 6.1

Replace by the following: 6.1

Tankage to be crude oil washed

6.1.1 Before departure on a ballast voyage: (a) approximately one quarter of the cargo tanks shall be crude oil washed for sludge control purposes on a rotational basis in accordance with the procedures specified in the Operations and Equipment Manual. However, for these purposes, no tank need be crude oil washed more than once in every four months; and (b) if it is considered that additional ballast in a cargo tank or tanks may be required during the ballast voyage under the conditions and provisions specified in regulation 13(3) of Annex I of MARPOL 73/78, the tank or tanks which may be used for this ballast shall be crude oil washed in accordance with the procedures specified in the Operations and Equipment Manual. 6.1.2 Ballast water shall not be put into cargo tanks that have not been crude oil washed. Water that is put into a tank which has been crude oil washed but not water rinsed shall be regarded as dirty ballast. 6.1.3 Crude oil washing shall not be conducted between the final discharge and loading ports; that is to say, no crude oil washing shall be undertaken during the ballast voyage. 6.3


Ballasting of cargo tanks

Care shall be taken at the completion of crude oil washing of any cargo tank that might contain ballast to strip the tank as completely as possible. Where this ballast is filled through cargo lines and pumps, these must be drained and stripped of oil using the means required by 4.4.5. 6.4

The last two sentences are not applicable.

6.5


Discharge of oil water effluents on ballast voyage

The discharge of additional ballast from cargo tanks and any other water effluent discharged during the ballast voyage shall comply with the requirements of regulation 9 of Annex I of MARPOL 73/78. 6.8

This paragraph is not applicable.

7(d)

Replace by the following: 7(d)

Details of the requirements of section 6 of these Specifications together with advice and instructions, where appropriate, in meeting these requirements such as: 13

Crude oil washing systems (i)

recommended methods and programmes of crude oil washing in order to accord with all foreseeable circumstances of cargo discharge restraints and to obtain maximum trim during the completion of washing and draining of each tank;

(ii) the method of draining tanks which shall include information on optimum trim conditions as required by 4.4.10; (iii) the method of draining cargo pumps, cargo lines, crude oil washing lines and stripping lines, and spaces into which they may be drained, together with the final discharge ashore via the small discharge line on completion of discharge; (vi) typical washing programmes under various conditions of loading specifying: (1) the tanks to be washed in accordance with 6.1; (2) the method for washing each tank, that is, single- or multi-stage; (3) the number of tank washing machines to be used simultaneously; (4) the duration of the crude oil wash and water rinse where the latter is appropriate; (v) The procedure for ing by sound patterns that bottom-mounted machines are operating shall be carried out towards the end of the wash cycle for each tank. When carrying out such verification all other machines shall be shut down if necessary.

14

Revised Specifications: Appendix II

Appendix II

Training for persons intended to assume overall charge of crude oil washing Introduction Any required training shall be supervised instruction, conducted in a shore-based facility or aboard a suitably equipped ship having training facilities and instructors for this purpose, dealing with the principles involved and the application of these principles to ship operation. In drawing up an istration-approved syllabus of training, the Revised Specifications for the design, operation and control of crude oil washing systems of tankers shall be taken into . Such training shall include but not necessarily be limited to: (a)

An introduction to the principles of crude oil washing which shall include: – the characteristics of crude oil as a washing fluid and its contrast with water washing; – top washing; – bottom washing; – trim requirements; – methods of bleeding off from the cargo discharge; – maintenance of required washing fluid pressure; – washing at sea between discharge ports; – recirculatory washing; – relative priorities and requirements for the departure ballast tanks, arrival ballast tanks and cargo-only tanks.

(b)

Equipment and design (i)

location of washing machines;

(ii) washing machines, deck-mounted and submerged: – types; – characteristics; – features of construction; – operating parameters; (iii) drive units; (iv) washing fluid supply and distribution systems; (v) stripping systems; (vi) means of sounding tanks; (vii) inert gas requirements. (c)

Generalized crude oil washing procedures (i)

traditional pipeline ship/free-flow ship/partial free-flow ship;

(ii) single-/multi-parcel cargoes; (iii) optimization of washing procedure in order to minimize extra berth time; 15

Crude oil washing systems (iv) ballasting for departure with various ship and pipeline configurations; (v) procedure for washing at sea between discharge ports. (d)

Associated procedure (i)

means for minimizing residues on board – stripping of cargo tanks; – draining and stripping of cargo lines; – final discharge of cargo ashore;

(ii) water rinsing of arrival ballast tanks; (iii) filling and ultimate discharge of arrival ballast; (iv) discharge of departure ballast; (v) build-up and decanting of residues in slop tank; (vi) requirements of regulation 9 of Annex I of MARPOL 73/78; (vii) avoidance of venting in port during ballasting operation. (e)

Safety (i)

inert gas procedure;

(ii) maintenance and monitoring of inert gas quality and pressure; (iii) stopping of washing/discharge under abnormal inert gas conditions; (iv) electrostatic generation and the precautions required to avoid it; (v) pipework integrity; (vi) avoidance of surge pressures; (vii) spillage. (f)

Checklists (i)

before entering port;

(ii) before commencing crude oil washing; (iii) after crude oil washing; (iv) after sailing. (g)

Regulatory enforcement procedures (i)

Operations and Equipment Manual;

(ii) Oil Record Book; (iii) sounding of tanks; (iv) measurement of oil on surface of departure ballast. (h)

Maintenance of plant and equipment (i)

maintenance of equipment in accordance with manufacturers’ instructions;

(ii) additional maintenance items. istrations shall ensure that the training facility issues an appropriate document to those qualified in accordance with this appendix to serve as officers primarily responsible for crude oil washing. 16

Revised Specifications: Appendix III

Appendix III

Agreed interpretations of certain of the provisions of the Revised Specifications 4.1.1

This paragraph requires pipes and valves to be of steel or other equivalent material. As classification societies permit grey cast iron for cargo piping with a maximum permissible working oil pressure of 16 kg/cm2, grey cast iron may be permitted in the supply system for crude oil washing systems when complying with nationally approved standards.

4.1.3

The requirements of this paragraph allow alternative arrangements. One such alternative is that where the system is served only by centrifugal pumps so designed that the pressure derived cannot exceed that for which the piping is designed, a temperature sensing device located in the pump casing is required to stop the pump in the case of overheating.

4.1.6

On new oil tankers the steam heater referred to shall be located outside the machinery spaces. However, on an existing oil tanker with an existing steam heater located in the machinery spaces, no more additional isolation will be required other than that which isolates the crude oil washing system from the machinery spaces.

4.2.4

This paragraph requires each machine to be capable of being isolated by means of stop valves in the supply line. Where more than one submerged machine is connected to the same supply line a single isolating stop valve in the supply line may be acceptable provided the rotation of the submerged machines can be verified in accordance with paragraph 4.2.13(a) or (c) of the Revised Specifications for the design, operation and control of crude oil washing systems.

4.2.8

With regard to the application of this paragraph a slop tank is considered as a cargo tank.

4.2.9

Guidelines for the assessment of shadow diagrams (a) Shadow diagrams (to be prepared in accordance with 4.2.9) must be on drawings the scale of which must be at least: (i)

1:100 for tankers of less than 100,000 tons deadweight;

(ii) 1:200 for tankers of 100,000 tons deadweight and above. (b)

The drawings must provide at least a plan view, a profile view and an end elevation for each tank, or for tanks considered to be similar.

(c) Sufficient detailed drawings of the vessel must be provided to check that all large primary structural have been included. (d)

The term large primary structural is to be construed as those components of a tank structure which contribute significant strength to the ship, such as web frames and girders. It is intended that smaller components such as those that contribute to plate stiffening be excluded. In general the following lists, in conjunction with the diagram showing structural components of cargo tanks, may be used to amplify this interpretation. (See diagram on page 20.) Include (i) web frames (ii) girders (iii) stringers (iv) webs (v) main bracket

Disregard (i) longitudinals (ii) brackets (iii) stiffeners (iv) ladders (v) pipe work

17

Crude oil washing systems Include (vi) transverses (vii) crossties in transverse web frames, unless it can be verified by tank inspection that their presence does not affect the cleanliness of the tank. However, for the purpose of making an initial assessment, where there are no more than two crossties and each is less than 1/15 of the total depth of the tank they may be ignored.

Disregard (vi) corrugations on corrugated bulkheads (vii) face plates

(e) Shadows cast upon the underside of decks, web frames, centre and side girders can be ignored. (f)

Calculations must be provided either on the drawing or separately to show how the percentages required by 4.2.8 have been arrived at. The calculations should be itemized so that it is possible to relate each item with a particular shadow area.

(g) Where a curved surface is presented to jets it is not necessary to provide exact geometric projections to determine the resultant shadow. A reasonable estimate is acceptable.

4.2.10

(h)

For the purpose of determining the bottom area of wing tanks, the breadth of the tank is to be taken as the horizontal distance measured across the top of the bottom longitudinal frames to the inside of the shell plating, midway between the tank bulkheads.

(i)

A swash bulkhead may be taken as a tank boundary. However, in this event the bulkhead must be assumed to have no openings in it.

Water rinse means the water washing process carried out in connection with tank cleaning after crude oil washing and is not intended to be construed as limiting the amount of water needed in the process.

4.2.10(c) (a) The oil monitoring system referred to in this paragraph means any approved system, including laboratory tests, which verifies that the oil content of the effluent does not exceed the stated level. If laboratory tests are to be conducted, standards contained in resolution A.393(X) should be used as guidance. Oil tankers engaging in a trade where discharge of cargo takes place in one port State and cargo loading in another port State create a special problem with respect to verification. Two alternatives available to confirm the tanker’s capability are: (i)

the tanker could be required to conduct the entire crude oil washing operations at the discharge port, taking inspectors to sea if necessary to observe water washing, handling of departure ballast and discharge of arrival ballast;

(ii) co-ordination between the flag State istration and port States to obtain the required documentation. However the test is performed, it should be decided on a case-by-case basis taking into the service of the tanker and the availability of surveyors. 18

Revised Specifications: Appendix III (b)

The expression totally discharged to the loading port harbour which is used in this paragraph shall be so construed as to mean the total quantity of arrival ballast except that quantity which is to be retained on board as specified in section 15 of the Operations and Equipment Manual.

4.4.3

During bottom washing the stripping capacity shall be at least 1.25 times the total throughput of all the machines that may be simultaneously in use according to paragraph 4.4.3. This does not mean that all machines in a tank have to be operated simultaneously during bottom washing but the bottom washing may be carried out in steps according to detailed procedures laid down in the Operations and Equipment Manual. The stripping capability should be at least 1.25 times the throughput of all machines that are in operation simultaneously during any stage of the bottom washing.

4.4.5

In crude oil tankers having individual cargo pumps in each tank, each pump having an individual piping system, dispensation from the required special small-diameter line may be given in cases where the combined amount of oil left in the tank after stripping and the volume of oil in the piping system from the manifold to the tank is less than 0.00085 times the volume of the cargo tank. If a deepwell cargo pump system is provided with an evacuating system for retained oil, the above consideration should also apply.

5.2(b)

This paragraph requires that officers who assume overall charge of a crude oil washing operation must have participated in a crude oil washing operation on the ship for which they are required to undertake the responsibility for cargo discharge, or on a similar ship. However, for new ships, for ships changing for the first time to the carriage of crude oil, for ships new to a particular owner, or for ships which are changing registry in which it may not be possible to acquire the particular experience, the istration may accept as an alternative: (i)

a person such as a shore-based senior officer appointed by the company (additional to the ship’s complement) who is experienced in the operation of crude oil washing and is present to advise the ship’s personnel; or

(ii)

a senior member of the crew such as the master, chief officer or cargo control officer who has participated in at least four crude oil washing operations and is on board the ship;

provided that an Operations and Equipment Manual, in a language readily understood by the ship’s officers, is available on the ship.

19

20 Bottom girder

Bottom transverse

Main bracket

Web (on bulkhead)

Stringer

Transverse bulkhead

Main bracket

Stiffener

Deck girder

Upper deck

Longitudinal

Keel plate

Bottom girder

Longitudinal

Longitudinal bulkhead Longitudinal Web frame

Bottom shell

Main bracket

Crosstie

Longitudinal

Stiffener

Side shell

Web frame

Main bracket

Longitudinal

Deck girder

Deck transverse

Crude oil washing systems Diagram showing structural components of cargo tanks

00057

II STANDARD FORMAT FOR THE CRUDE OIL WASHING OPERATIONS AND EQUIPMENT MANUAL

Standard format for the COW Manual

STANDARD FORMAT FOR THE CRUDE OIL WASHING OPERATIONS AND EQUIPMENT MANUAL (The standard format consists of a standardized text of an introduction and of an index, and 17 or 18 sections depending on the type of tanker)

INTRODUCTION 1 This Manual is written in accordance with the requirements of regulation 13B of the Protocol of 1978 relating to the International Convention for the Prevention of Pollution from Ships, 1973 (MARPOL 73/78). 2 The purpose of the Manual is to meet the requirements for crude oil washing in accordance with the Revised Specifications for the design, operation and control of crude oil washing systems (Assembly resolution A.446(XI) as amended by resolutions A.497(XII) and A.897(21)). It provides standard operational guidance in planning and performing a crude oil washing programme and describes a safe procedure to be followed. 3 Part 1 of the Manual contains all the information and operational instructions required by the Revised Specifications. Part 2 of the Manual contains additional information and operational instructions required or accepted by the istration.* 4 This Manual has been approved by the istration and no alteration or revision shall be made to any part of it without the prior approval of the istration.

Note: The standard format comprises the annex to resolution MEPC.3(XII), as amended by resolution MEPC.81(43).

* If the istration requires or accepts information and operational instructions in addition to those provided for by the Specifications, they should be included in part 2 of the Manual. If no such additional information or operating instructions are required or accepted by the istration, the Manual will consist of one part only, and paragraph 3 should read: ‘‘This Manual contains all the information and operational instructions required by the revised Specifications.’’

23


Index of sections

Page

Relevant paragraph(s) of the Revised Specifications

Part 1 1

Text of the Revised Specifications . . . . . . . . . . . . . . . . . . . . .

[25]

7(a)

2

Drawings of the crude oil washing system . . . . . . . . . . . . . .

[25]

7(b)

3

Description of the crude oil washing system and operational and equipment parameters . . . . . . . . . . . . . . . . . . . . . . . . .

[25]

7(c), 7(d)(viii) and 7(f)

4

Dangers of and precautions against oil leakage . . . . . . . . . .

[25]

7(e)

5

Use and control of inert gas . . . . . . . . . . . . . . . . . . . . . . . . .

[25]

6.6

6

Precautions against electrostatic hazards . . . . . . . . . . . . . . .

[26]

6.7

7

Personnel requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[26]

7(g)

8

Methods of communication . . . . . . . . . . . . . . . . . . . . . . . . .

[26]

7(h)

9

Determination of the suitability of a crude oil for use in crude oil washing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[26]

7(l)

10

Crude oil washing checklists . . . . . . . . . . . . . . . . . . . . . . . . .

[29]

7(j)

11

Approved methods and programmes for crude oil washing .

[29]

7(d)(i)

12

Typical crude oil washing programmes . . . . . . . . . . . . . . . . .

[30]

7(d)(v)

13

The method of draining cargo tanks . . . . . . . . . . . . . . . . . . .

[30]

7(d)(iii)

14

The method and procedures for draining cargo pumps and lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[30]

7(d)(iv) and (vi)

Typical procedures for ballasting and the method of preventing hydrocarbon emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[30]

7(d)(ii), 7(i)

15 16

Compliance procedures for regulation 9 of Annex I of MARPOL 73/78 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[30]

7(d)(vi), (vii) and (ix)

17

Inspections and maintenance of equipment . . . . . . . . . . . . .

[30]

7(k)

18

Procedure for changing from crude oil trade to product trade*

[30]

—

Part 2 (Additional information and operational instructions required or accepted by the istration, if any)

* Section 18 is included in the Manual for a particular tanker only if applicable.

24


Contents of sections 1 to 18 SECTION 1: TEXT OF THE REVISED SPECIFICATIONS This section contains the complete text of the Revised Specifications for the design, operation and control of crude oil washing systems and the agreed interpretations of certain of the provisions of the Revised Specifications (Assembly resolution A.447(XI) as amended by resolutions A.497(XII) and A.897(21)). SECTION 2: DRAWINGS OF THE CRUDE OIL WASHING SYSTEM This section contains line drawings showing: (1) crude oil washing lines and valves; (2) cargo pumps, lines and valves; (3) ballast systems (where fitted); (4) stripping systems; (5) position of tank washing machines; (6) position of holes for hand dipping and tank gauges; (7) inert gas deck distribution system. SECTION 3: DESCRIPTION OF THE CRUDE OIL WASHING SYSTEM AND OPERATION AND EQUIPMENT PARAMETERS This section contains a description of the cargo, ballast, washing and stripping systems and in addition specifies: (1) types of tank washing machines and their standpipe length inside the tanks; (2) revolutions of the machines; (3) methods of checking the operation of tank washing machines; (4) minimum operation pressure for crude oil washing; (5) maximum permitted oxygen level in cargo tanks; (6) duration of tank washing machine cycles; (7) results of the tests performed in accordance with paragraph 4.2.10(b) of the Revised Specifications and the method of computation; (8) method of preventing entry of oil into the engine room. SECTION 4: DANGERS OF AND PRECAUTIONS AGAINST OIL LEAKAGE This section contains information on the dangers of leakage from the crude oil washing system, the precautions necessary to prevent leakage and the action to be taken in the event of leakage. SECTION 5: USE AND CONTROL OF INERT GAS This section contains information on the inert gas requirements and the instructions to cover those periods when the inert gas pressure is released for reasons of cargo operation. In addition it indicates the method and procedures to be used for taking samples of the tank atmosphere. 25

Crude oil washing systems SECTION 6: PRECAUTIONS AGAINST ELECTROSTATIC HAZARDS This section contains details of the procedures for minimizing electrostatic generation. SECTION 7: PERSONNEL REQUIREMENTS This section specifies the numbers of persons to be associated with the crude oil washing process and their necessary qualifications. Their names and ranks may be provided on separate documents. SECTION 8: METHODS OF COMMUNICATION This section gives the details of communication between the watchkeeper on deck and the cargo control position so that, in the event of a leak or malfunctioning of the crude oil washing system, the washing may be stopped as soon as possible. SECTION 9: DETERMINATION OF THE SUITABILITY OF A CRUDE OIL FOR USE IN CRUDE OIL WASHING This section contains guidance in determining the suitability of a crude oil for use in crude oil washing. In lieu of a list of crude oils unsuitable for carriage and crude oil washing to be inserted in the Operations and Equipment Manual the following standard text may be used: (1)

For a tanker not fitted with heating coils This tanker is not fitted with heating coils in the cargo tanks and should not carry cargoes which will require to be heated either to obtain pumpability criteria or to avoid excessive sludging of both the designated clean ballast tanks and the vessel’s tanks to be washed for sludge control. Notes and definitions: – Pumpability criterion is determined by the oil’s kinematic viscosity at the observed temperature of the cargo prior to its discharge. In order to attain optimum efficiency for discharge this viscosity should not exceed 250 centistokes and never in excess of 600 centistokes. – Excessive sludging criterion is determined primarily by the crude oil’s temperature throughout its transportation and storage. If the cargo’s temperature is likely to drop below the crude oil cargo’s cloud point temperature then sludging of cargo tanks is to be expected. The cloud point temperature is the temperature at which the crude oil’s wax and associated oil phase separates from the bulk liquid phase of the cargo.

(2)

For a tanker fitted with heating coils in slop tank(s) This tanker is fitted with heating coils only in her slop tank(s) and should not carry cargoes which will require to be heated for pumpability. Notes: If sludge deposition is suspected or determined in the main cargo tanks then an alternative crude oil washing programme should be utilized. Recommendations regarding this programme and procedure are to be found in section 11 of this Manual.

(3)

For a tanker fitted with heating coils This tanker is fitted with heating coils in all the cargo tanks and, subject to the limitations of the cargo heating system, can carry cargoes which require heating for either pumpability or sludge deposition/control.

26

Standard format for the COW Manual General guidance Attention is drawn to the difficulties which may be encountered with certain crude oils. During the discharge of crude oils that exhibit the necessary criteria that would create either pumpability problems or sludge deposition, crude oil washing of each tank scheduled for such an operation should be carried out concurrently with the discharging of the particular tank in order to minimize the effect on the crude oil residues for cooling. Cooling will increase both the kinematic and dynamic viscosities* of the tank residues and therefore affect the efficiency of the crude oil washing programme. As a general guidance to the suitability of an oil for crude oil washing on board this tanker, the following criteria should be used: For aromatic crude oils whose kinematic viscosity is the temperature controlling characteristic, the kinematic viscosity of the oil used for crude oil washing should not exceed 60 centistokes at the oil wash medium temperature; or For paraffinic crude oils whose pour point temperature is the controlling characteristic, the temperature of the cargo to be used for crude oil washing should exceed its cloud point temperature by at least 108C if excessive sludging is present and should only be used once in a ‘‘closed cycle’’ washing programme. The approximate cloud point temperature of an oil may be calculated by use of the following formula where the pour point temperature (x) of the crude oil is known: Cloud point temperature (8C) = 20.2 (100.00708x

– 0.1157714

)+8

Worked example: Assume the pour point temperature is + 18C. Then: = = = = =

20.2 6 (10(0.00708 6 1) – 0.1157714) + 8 20.2 6 (100.00708 – 0.1157714) + 8 20.2 6 (10–0.1086914) + 8 (20.2 6 0.7785896) + 8 15.72 + 8

Answer: approx. cloud point = 248C or Consult the accompanying graph (fig. 1), where if the pour point is known then the cloud point can be extracted. or If the pour point exceeds approximately 258C then the Bondi test procedure could be used to determine this temperature.

* Definitions: kinematic viscosity is the measure of resistance to flow with gravitation under its own mass force. This is normally reported in centistokes (cSt) or mm2/s. Dynamic viscosity is the measure of resistance to flow with an induced shear stress or at a known rate of shear. This is determined from the equation of shear stress (in pascals (Pa)) divided by rate of shear (inverse seconds (s–1)). The unit of dynamic viscosity is either the centipoise (s) or the millipascal second (mPa.s).

27


&ORXGSRLQWWHPSHUDWXUH’&

x

x

3RXUSRLQWWHPSHUDWXUH’&

Figure 1: Graph to determine cloud point temperature Bondi test procedure (see fig. 2) This method will obtain the cloud point temperature of high pour point type crude oils. Equipment and procedure (1) Obtain a representative sample of the cargo. Do not allow the cargo sample to cool before commencing the test procedure. (2) Obtain a glass container (preferably nearly spherical) that is made of heat/temperature-resistant glass and fill the container with the sample. (3) Insert a thermometer into the centre of the sample volume and heat the sample to a temperature of at least 308C above the pour point temperature of the crude oil in a hot water bath. Do not tightly stopper the container during this process. (4) Prepare an alternative bath with water whose temperature is at least 158C below the sample’s pour point temperature. Have a clock or watch available with a second hand. (5) Immerse the heated sample container into the cold bath and record at very regular intervals (at least every 30 s) the temperature of the sample. (6) Graphically plot the sample temperature against time elapsed from the start of the test. Determine the temperatures at which there was no loss of temperature with time elapsed. The first such instance detected will be the approximate cloud point temperature and the second instance, if testing time is extended to the required period, will be the approximate pour point temperature of the crude oil. 28


80

75

Temperature (oC)

70

65

Cloud point temperature

60

55

50 Pour point temperature

45 00059

40 0

1

2

3

4

5

6

7

8

9

Time (minutes)

Figure 2: Example Bondi test plot SECTION 10: CRUDE OIL WASHING CHECKLISTS This section contains operational checklists for the use of the crew at each discharge which shall include the checking and calibration of all instruments.

SECTION 11: APPROVED METHODS AND PROGRAMMES FOR CRUDE OIL WASHING This section contains those details which form the basis of crude oil washing in the tanker and which are necessary to formulate a washing programme which will accord with all foreseeable circumstances of cargo discharge restraints. It includes information on: (1) the minimum number of tanks to be washed in accordance with paragraph 6.1 of the Revised Specifications; (2) the method of washing each tank, i.e., single- or multi-stage; (3) the number of tank washing machines to be used simultaneously; (4) the crude oil washing pressure and means to maintain the required pressure; (5) the duration of the crude oil wash; (6) the preferred order in which tanks are to be washed; (7) the minimum trim during completion of washing and draining tanks; (8) when draining and stripping of tanks is to commence. 29

Crude oil washing systems SECTION 12: TYPICAL CRUDE OIL WASHING PROGRAMMES This section contains details of some typical washing programmes under various conditions of discharge such as single- or multi-port discharge and single- and multi-grade cargoes. SECTION 13: THE METHOD OF DRAINING CARGO TANKS This section contains a description of the method of draining cargo tanks and should include the parameters which indicate when the tank is dry and which will be at least all of those required by paragraph 4.4.8 of the Revised Specifications. The minimum trim conditions must be stated. SECTION 14: THE METHOD AND PROCEDURES FOR DRAINING CARGO PUMPS AND LINES This section contains a description of the method and procedures for draining cargo pumps, cargo lines, crude oil washing lines and stripping lines and includes information on the use of the small-diameter line. SECTION 15: TYPICAL PROCEDURES FOR BALLASTING AND THE METHOD OF PREVENTING HYDROCARBON EMISSION This section contains a description of typical procedures for ballasting and includes: (1) the procedure for draining and stripping before loading ballast; (2) the procedures for preventing hydrocarbon emission into the atmosphere. SECTION 16: COMPLIANCE PROCEDURES FOR REGULATION 9 OF ANNEX I OF MARPOL 73/78 This section contains information and procedures for water washing tanks and lines, discharge of departure ballast and the decanting of slops at sea to ensure compliance with regulation 9. SECTION 17: INSPECTIONS AND MAINTENANCE OF EQUIPMENT This section contains information on procedures to be followed at recommended intervals for on-board inpections and maintenance of crude oil washing equipment. SECTION 18: PROCEDURES FOR CHANGING FROM CRUDE OIL TRADE TO PRODUCT TRADE* This section contains operational procedures for changing from crude oil trade to product trade for a tanker which is fitted with separate independent pumping and piping arrangements for ballasting dedicated clean ballast tanks and which has been issued with two IOPP Certificates running concurrently with one Certificate certifying the tanker to be a crude oil tanker and the other certifying it to be a product carrier.

* Section 18 is included in the Manual for a particular tanker only if applicable.

30

III EXAMPLES OF CRUDE OIL WASHING OPERATIONS AND EQUIPMENT MANUALS

Explanatory note The following specimen Manuals were originally prepared by tanker owners for particular tankers which they wished to be certified as COW tankers under MARPOL 73/78. The texts of the Manuals have been reviewed in order to ensure conformity with the standard format but editing has been kept to a minimum to show possible variations in the language and in the manner of presentation of the required information. As the flag istration of these tankers does not require the inclusion of any information or operational instructions in addition to those provided for by the Revised Specifications, the specimen Manuals consist of one part only as explained in the introduction to the standard format.*

* See page 23 of this publication.

Example 1: Conventional pipeline tanker

Example 1 Conventional pipeline tanker

CRUDE OIL WASHING OPERATIONS AND EQUIPMENT MANUAL

Name of ship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Distinctive number or letters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Port of registry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deadweight tonnage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

33

Crude oil washing systems INTRODUCTION 1 This Manual is written in accordance with the requirements of regulation 13B of the Protocol of 1978 relating to the International Convention for the Prevention of Pollution from Ships, 1973 (MARPOL 73/78). 2 The purpose of the Manual is to meet the requirements for crude oil washing in accordance with the Revised Specifications for the design, operation and control of crude oil washing systems (Assembly resolution A.446(XI) as amended by resolutions A.497(XII) and A.897(21)). It provides standard operational guidance in planning and performing a crude oil washing programme and describes a safe procedure to be followed. 3 This Manual contains all the information and operational instructions required by the Revised Specifications. 4 This Manual has been approved by the istration and no alteration or revision shall be made to any part of it without the prior approval of the istration.

34


Index of sections Page

Relevant paragraph(s) of the revised Specifications

Part 1 1


[36]

7(a)

2


[37]

7(b)

3


[40]

7(c), 7(d) (viii) and 7(f)

4


[43]

7(e)

5


[43]

6.6

6


[43]

6.7

7


[44]

7(g)

8


[44]

7(h)

9

List of crude oils unsuitable for crude oil washing . . . . . . . . .

[44]

7(l)

10


[45]

7(j)

11


[46]

7(d)(i)

12


[48]

7(d)(v)

13


[51]

7(d)(iii)

14

The method and procedures for draining cargo pumps and lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[52]

7(d)(iv) and (vi)


[52]

7(d)(ii), 7(i)

15 16

Compliance procedures for regulation 9 of Annex I of MARPOL 73/78 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[53]


17


[54]

7(k)

18

Procedures for changing from crude oil trade to product trade*

[54]

—

* This specimen Manual as originally prepared by the tanker owner for a particular tanker did not include a section 18 as the procedures for changing from crude oil trade to product trade were not applicable. This section has been added as an example of how the information might be presented if required in a particular case.

35

Crude oil washing systems SECTION 1: TEXT OF THE REVISED SPECIFICATIONS This section contains the complete text of the Revised Specifications for the design, operation and control of crude oil washing systems and the agreed interpretations of certain of the provisions of the Revised Specifications (Assembly resolution A.446(XI) as amended by resolutions A.497(XII) and A.897(21)). (Text of the Revised Specifications to be inserted) SECTION 2: DRAWINGS OF THE CRUDE OIL WASHING SYSTEM This section contains line drawings showing: (1)

crude oil washing lines and valves;

(2)

cargo pumps, lines and valves;

(3)

ballast systems (where fitted);

(4)

stripping systems;

(5)

position of tank washing machines;

(6)

position of holes for hand dipping and tank gauges;

(7)

inert gas deck distribution system.

(See following pages for drawings)

36


Figure1: Cargo pumps, lines and valves, ballast and stripping systems

Butterfly valve, hydraulic

Direct loading

Gate valve, hydraulic & manual, locally operated

Cascade in slop tanks Port slop tank

Gate valve, manual

1 Blank

Butterfly bulkhead valve, hydraulic Non-return valve To tank cleaning line and heater

Eductor

To vacuum tank

Stripping pump

Sea chest

rt po k To p tan slo rt po nk To p ta slo

Sea chest

Sea chest

s

ng

3 To

wi

00060

37


Figure 2: Crude oil washing lines and valves and position of tank washing machines

PORT SLOP TANK

No 6 PORT WING CARGO TANK




TO ‘K’ TYPE M/C 4m OVER TANK BOTTOM


CENTRE SLOP TANK

PI

TT

TI

MP2 19

TI

TANK CLEANING LINE TO FORWARD SECTION

CENTRE SLOP TANK

MP2 22

HEATER 1.4.2 TI


MP2 22 PT

TI

CARGO AND STRIPPING LINES (PUMP ROOM) 5.2.1(2)

STARBOARD SLOP TANK

164

No 7 STARBOARD WING CARGO TANK

196

187

179

172

167




AFT SECTION


No 3 PORT WING WATER BALLAST TANK


KEY DIAPHRAGM VALVE HOSE VALVE BUTTERFLY VALVE

TANK CLEANING LINE FROM AFT SECTION

FIXED TANK CLEANING MACHINE

00061

218 No 3 STARBOARD WING WATER BALLAST TANK

196

210

FORWARD SECTION

38



202

Sounding point

PV/ breaker

High-velocity pressurerelease valve, manually operated

Purge/Sounding pipe

Inert gas tank inlet

Sounding point

High-velocity P/V valve with line valve

Non-return valve

Remote-operated butterfly valve Manually operated butterfly valve

Water seal and I.G. supply


Figure 3: Inert gas tank distribution system and sounding points

00079

39

Crude oil washing systems SECTION 3: DESCRIPTION OF THE CRUDE OIL WASHING SYSTEM AND OPERATIONAL AND EQUIPMENT PARAMETERS This section contains a description of the cargo, ballast, washing and stripping systems and in addition specifies: (1) types of tank washing machines and their standpipe length inside the tanks; (2) revolutions of the machines; (3) methods of checking the operation of tank washing machines; (4) minimum operation pressure for crude oil washing; (5) maximum permitted oxygen level in cargo tanks; (6) duration of tank washing machine cycles; (7) results of the tests performed in accordance with paragraph 4.2.10(b) of the Revised Specifications and the method of computation; (8) method of preventing entry of oil into the engine room. Cargo system The tank system of this vessel consists of eight centre tanks and eight pairs of wings, but with No. 3 wings reserved for permanent ballast and not connected into the cargo piping. The aftermost set of tanks, No. 8 across, forms a triple slop tank arrangement. No. 8 port is the dirty slop tank with first separation across to No. 8 starboard and thence a second separation into No. 8 centre. The total capacity of the three slop tanks is 20,000 m3. Cargo is handled by four main cargo pumps each of rated capacity of 4,500 m3/h. Each pump has a 700 mm suction line running the full length up to No. 1 across. No. 1 and No. 4 pumps are used to discharge the wing tanks and No. 2 and No. 3 pumps to discharge the centre tanks. There are crossover lines between the pump suctions which permits a variation on the normal practice. Stripping system The pumps are of the VAC-STRIP type which enables them to drain tanks right out. Thus there is no stripping line but in each tank a small stripping suction bell-mouth, separately valved, is taken off the appropriate main line. For water washing and occasional use during the closing stages of crude oil washing, two eductors are fitted, each of rated capacity 900 m3/h, which are normally powered by either No. 2 or No. 3 cargo pump. These eductors can be put on to any of the four main suction lines, and thus drain any tank. They discharge directly into the dirty slop tank, No. 8 port. One Duplex steam reciprocating pump of 350 m3/h is fitted for the purpose of line draining. It has suction connections to the four main suction lines, the four cargo pumps, the discharge lines, the sea line and the crude oil washing line. It can discharge to the slop tank, the oil/water separator, the main discharge lines, overboard or through a special 250 mm line which runs along the deck and terminates outboard of the manifold gate valves. This latter 250 mm line should always be used for final line draining ashore. Ballast system Permanent ballast is carried in No. 3 wings and is handled by a separate pump of capacity 4,250 m3/h. The pump and tanks are not connected into the cargo pumps or lines and have their own separate sea suction and discharge. The permanent ballast pump also has the capability of ballasting No. 1, No. 4 and No. 6 centres over the top. Once the cargo is discharged from No. 1, No. 4 and No. 6 centres, these tanks should be ballasted over the top concurrently with discharge of cargo from other tanks. They then form the departure ballast. On the subsequent ballast age, No. 2, No. 5 and No. 7 centres should be washed and 40

Example 1: Conventional pipeline tanker then used as the clean arrival ballast. Cargo tank ballast is discharged by No. 2 and No. 3 cargo pumps through the pump-room high overboard discharge. Variations on the ballast arrangement are permissible to permit inspection and maintenance except that ballast should not normally be carried in wing tanks. Washing system The tank washing line, either crude oil or water, is fed from either No. 2 or No. 3 cargo pump or alternatively the line may be fed from a cross-connection from the midships manifold. In the latter case, any cargo pump or pumps could feed the washing line. When water washing, No. 2 or No. 3 pump should be used drawing from the clean slop tank, No. 8 centre, and the dirty washings from the tank being washed drained back with an eductor which discharges into the dirty slop tank, No. 8 port. One cargo pump operating in this closed cycle method is capable of driving both eductors fitted and operates 10 tank washing machines while maintaining a back pressure of 10 kg/cm2. For crude oil washing, it is preferable to feed the washing line from the manifold as long as possible as it is not then necessary to take one cargo pump completely out of the discharge programme, and recirculation of ‘‘dirty’’ oil is avoided. Crude oil must never be ed through the Butterworth heater which is situated in the pump-room. Apart from fouling the heater, there is the chance of a ruptured or leaking tube allowing crude oil to back into the engine room via the steam system. Two spade blanks are fitted, one on the inlet side and one on the outlet side of the heater, and these must always be in position when crude oil washing. For all types of washing machines, the desired pressure on the wash line on deck is 10 kg/cm2. If the pressure on the deck line falls below 8 kg/cm2, then crude oil washing should be stopped until such time as the pressure has been restored. The complete crude oil washing system has been inspected and approved by the istration, and no alterations may be made to the system or any part of the system without the approval of the istration. Cargo tanks were inspected after crude oil washing in accordance with the requirements of paragraph 4.2.10(a) of the Revised Specifications and met the required standards of cleanliness, being essentially free of oil clingage and deposits. The surface of the departure ballast was examined in accordance with the requirements of paragraph 4.2.10(b) of the Revised Specifications and was found to be satisfactory. The procedure for computing the ratio of the volume of oil on top of the total departure ballast water to the volume of tanks that contain this water is described below: Tank number

Port, starboard or centre

X

Total

Tank volume (m3)

Ullage space in tank (measured to top of oil layer) (m)

Oil thickness (mm)

Volume of oil (m3)

Vx

Ux

tx

vx

Total

v

V

41

Crude oil washing systems 1.

Determine the thickness of the oil layer on the ballast water (tx).

2.

Using the tank capacity tables: .1

determine the aggregate volume (100%) of all tanks that contain departure ballast (V);

.2

determine the volume of the ballast water and oil layer in each tank from the ullage (U)x;

.3

determine the volume of ballast water in each tank from the ullage plus the thickness of the oil layer (Ux + tx).

3.

Subtract the value obtained in 2.3 from that obtained in 2.2 for each tank and add the resultant values together to obtain the total volume of oil (v).

4.

The ratio of the volume of oil on top of the total departure ballast water to the total volume of tanks containing departure ballast water = Vv :

Washing machines This vessel is fitted with 77 deck-mounted Butterworth Lavomatic machines, 13 bottom-mounted Butterworth MP machines and 3 fixed bottom-mounted Butterworth K machines. Deck-mounted machines Lavomatic S.A. single-nozzle. Those fitted in the centre tanks have a standpipe length of 4.8 m with a natural frequency of 6.19 Hz and those fitted in the wings have a standpipe length of 4.0 m and a natural frequency of 7.166 Hz. The propeller-induced frequency for this vessel at full speed is 5.666 Hz. All machines have selective arc heads which enable their angular programme to be varied as required. The time taken to complete one full cycle is 67 min when operating at a pressure of 10 kg/cm2 and the output at this pressure is 140 m3/h. The full cycle consists of an arc from 08 to 1208 to 08 to –308 to 08. The operation of these machines can be verified by observing the gearbox where both rotation and elevation are mechanically displayed. Submerged machines, MP, single-nozzle Thirteen of these machines are fitted; one at the forward end of No. 2, No. 4, No. 5, No. 6 and No. 7 wings and, additionally, one at the after end of No. 7 wings and No. 7 centre. They are positioned on the centreline of the tank on level with the third stringer down. They are piped and valved separately from the deck-mounted machines. Their programme is fixed and covers an arc of 2408 which at an operating pressure of 10 kg/cm2 takes 1 h to complete. The output at this pressure is 100 m3/h. To the operation of these machines, all other machines in the tank and in any adjacent tank should be shut off, and the movement of the machine identified by its sound pattern. Submerged machines, ‘‘K’’, twin-nozzle One of these is fitted underneath the bottom stringer at the aft end of each of No. 7 wings and one ‘‘Super K’’ is fitted at the bottom of the dirty slop tank No. 8 port. They are valved and lined separately from any other machines. Their capacity is 30 m3/h (60 m3/h for the ‘‘Super K’’) and the time for one full cycle is 40 min. A full cycle consists of one full revolution (3608) of the machine. 42

Example 1: Conventional pipeline tanker It is not possible to their operation by sound pattern and therefore after six usages or at intervals of not more than 12 months these machines must be sighted and seen to be working, using water. SECTION 4: DANGERS OF AND PRECAUTIONS AGAINST OIL LEAKAGE This section contains information on the dangers of leakage from the crude oil washing system, the precautions necessary to prevent leakage and the action to be taken in the event of leakage. Leakage of crude oil from the system can be a potential fire and pollution hazard. Before arrival at the discharge port, the tank washing system should be pressure-tested and examined for leaks. Any leaks found should be made good and the resultant oil cleaned up. During the pressure test, special attention should be given to inspection and tightening of valve glands and of flanges and couplings on lines to prevent any leakage. During the course of oil washing, the system must be kept under continuous observation and on completion of washing it must be completely drained of oil. If it is necessary for the system to be cleaned out, it should be flushed through with water into appropriate tanks; if the system is required to be gas-free it should be ventilated in the same way as cargo lines. The crude oil washing must be stopped when any sign of leakage or fault in the tank wash system is discovered, either on deck or in the pump-room. SECTION 5: USE AND CONTROL OF INERT GAS This section contains information on the inert gas requirements and the instructions to cover those periods when the inert gas pressure is released for reasons of cargo operation. In addition it indicates the method and procedures to be used for taking samples of the tank atmosphere. The ship should arrive at the discharge port with all cargo tanks pressurized with good quality inert gas. Pressure may be released for ullaging, sampling and water dips before discharge and at this stage the oxygen level in tanks should be checked to ensure that it is below 8% by volume. The supply of inert gas must be commenced immediately before the commencement of cargo discharge to avoid a vacuum in tanks. By this means a safe condition will be maintained throughout discharge. Apart from this initial release of pressure the pressure in the cargo tanks should always be above atmospheric pressure. Under no circumstances should air be allowed to enter any tank which is to be crude oil washed. Before each tank is washed, the oxygen content should be checked with the portable oxygen analyser to ensure that it does not exceed 8% by volume. The sample should be taken at a point 1 m below the deck and at the middle region of the ullage space well clear of the inert gas inlet point. (See section 2 of this Manual for the position of the sampling points.) The crude oil washing must be stopped if there is a failure of the inert gas plant or if the oxygen content of the delivered inert gas exceeds 8% by volume or if the pressure of the atmosphere in the cargo tanks falls below atmospheric pressure. SECTION 6: PRECAUTIONS AGAINST ELECTROSTATIC HAZARDS This section contains details of the procedures for minimizing electrostatic generation. Mixtures of oil and water can produce an electrically charged mist during tank washing. The use of dry crude is therefore important. To overcome the possibiity of developing such an electrically charged mist, 43

Crude oil washing systems before crude oil washing is commenced any tank containing crude oil which is to be used as the crude oil washing fluid is to be partially discharged to remove any water which has settled out during the voyage. To ensure adequate safety a minimum of 1 m depth of cargo is to be discharged in this way. For the same reason, as the slop tank will invariably contain a mixture of retained oil residues and cargo, the whole content of the slop tank should be discharged ashore before crude oil washing commences and then be refilled with fresh crude from the cargo discharge deck line, if the slop tank is to be used as a source of washing fluid. It must be ed that this refilling will take place after the discharge of the bottom 1 m depth of cargo from other tanks, referred to above, has been completed.

SECTION 7: PERSONNEL REQUIREMENTS This section specifies the numbers of persons to be associated with the crude oil washing process and their necessary qualifications. Their names and rank may be provided on separate documents. The following personnel are required to be on board to carry out the dual operation of discharging cargo and crude oil washing: 1.

The master or chief officer who will have overall responsibility for the operation. He must meet the requirements of paragraph 5.2 of the Revised Specifications. (See section 1 of this Manual.)

2.

The officer who will undertake the actual operation. He must meet the requirements of paragraph 5.3 of the Revised Specifications. (See section 1 of this Manual.)

3.

A minimum of one petty officer or rating who is to be on deck at all times during washing to keep watch for leaks and malfunction of equipment, to test the oxygen content of tanks before washing, to check tank atmosphere pressure, to sound tank bottoms when required and to lift ullage floats.

The duties of the persons referred to above are not necessarily mutually exclusive.

SECTION 8: METHODS OF COMMUNICATION This section gives the details of communication between the watchkeeper on deck and the cargo control position so that, in the event of a leak or malfunctioning of the crude oil washing system, the washing may be stopped as soon as possible. This ship is equipped with hand-held walkie-talkie radios which are certified intrinsically safe. While crude oil washing is being carried out, the man patrolling the deck for the purpose of monitoring machines and checking against any oil leakage from the system must carry one of these walkie-talkies. Additionally, in or in the immediate vicinity of the cargo control room, there must be a second man similarly equipped with a walkie-talkie. The provision of two sets for crude oil washing purposes has priority over any other requirements for walkie-talkie. No valves should be opened or closed on the crude oil washing system without the one party informing the other as to the action he is taking.

SECTION 9: LIST OF CRUDE OILS UNSUITABLE FOR CRUDE OIL WASHING This section contains a list of crude oils unsuitable for crude oil washing. This vessel is not fitted with heating coils in the cargo tanks and it should not carry cargoes which will require to be heated for pumpability. 44

Example 1: Conventional pipeline tanker SECTION 10: CRUDE OIL WASHING CHECKLISTS This section contains operational checklists for the use of the crew at each discharge which shall include the checking and calibration of all instruments. PRE-ARRIVAL CHECKS AT DISCHARGE PORT No.

ITEM

1. 2. 3. 4. 5. 6. 7. 8.

Has terminal been notified? Is oxygen analysing equipment tested and working satisfactorily? Is tank washing pipeline system isolated from water heater and engine room? Are all hydrant valves on tank washing line blanked? Are all valves to fixed tank washing machines shut? Have tank cleaning lines been pressurized and leakages made good? Have portable drive units for fixed tank-washing machines been tested? Have pressure gauges on top discharge line, manifold and tank cleaning main been checked? Has the stripping system monitoring equipment been checked? Has the communications system been checked and tested? Has the organization plan been drawn up and posted with duties and responsibilities defined? Have the discharge/crude oil wash operation plans been drawn up and posted? In cases where the terminal has a standard radio checklist, has this been completed and transmitted?

9. 10. 11. 12. 13.

CHECKLIST FOR USE BEFORE, DURING AND AFTER CRUDE OIL WASH OPERATION No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

ITEM A – Before crude oil wash operation Are all pre-arrival checks and conditions in order? Has discharge/crude oil wash operation been discussed with both ship and shore staff and is agreed plan readily available for easy reference? Has communication link between deck/control station and control station/shore been set up and is it working properly? Have crude oil wash abort condition and procedures been discussed and agreed by both ship and shore staff? Have fixed and portable oxygen analysers been checked and are they working properly? Is inert gas system working properly and is the oxygen content of inert gas being delivered below 5% by volume? Is oxygen content of tank(s) to be crude oil washed below 8% by volume? Have all cargo tanks positive inert gas pressure? Has a resonsible person been assigned to check all deck lines for leaks as soon as washing starts? Are the fixed machines set for the required washing method and are portable drive units, if fitted, mounted and set? Have valves and lines both in pump-room and on deck been checked?

45


No.

ITEM B – During crude oil wash operation Is quality of inert gas being delivered frequently checked and recorded? Are all deck lines and machines being frequently checked for leaks? Is crude oil washing in progress in designated cargo tanks only? Is the pressure in the tank wash line as specified in this Manual? Are cycle times of tank washing machines as specified in this Manual? Are the washing machines in operation, together with their drive units if applicable, frequently checked and are they working properly? Is a responsible person stationed continuously on deck? Will trim be satisfactory when bottom washing is in progress as specified in this Manual? Will recommended tank draining method be followed? Have ullage gauge floats been raised and housed in tanks being crude oil washed? Is level in holding tank for tank washings frequently checked to prevent any possibility of an overflow?

12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

C – After crude oil wash operation Are all valves between discharge line and tank wash line closed? Has tank wash line been drained of crude oil? Are all valves to washing machines closed? Are cargo pumps, tanks and pipelines properly drained as specified in this Manual?

23. 24. 25. 26.

SECTION 11: APPROVED METHODS AND PROGRAMMES FOR CRUDE OIL WASHING This section contains those details which form the basis of crude oil washing in the tanker and which are necessary to formulate a washing programme which will accord with all foreseeable circumstances of cargo discharge restraints. It includes information on: (1)

the minimum number of tanks to be washed in accordance with paragraph 6.1 of the Revised Specifications;

(2)

the method of washing each tank, i.e., single- or multi-stage;

(3)

the number of tank washing machines to be used simultaneously;

(4)

the crude oil washing pressure and means to maintain the required pressure;

(5)

the duration of the crude oil wash;

(6)

the preferred order in which tanks are to be washed;

(7)

the minimum trim during completion of washing and draining tanks;

(8)

when draining and stripping of tanks is to commence.

Before departure on a ballast voyage, both the departure and arrival ballast tanks must have been crude oil washed. These are No. 1, No. 4 and No. 6 centres and No. 2, No. 5 and No. 7 centres, respectively. If for any operational or maintenance reason, there is the likelihood or intention to put ballast in any other tanks during the voyage, then these tanks must also be crude oil washed. Additionally, one quarter of the remaining tanks must be crude oil washed for sludge control, but any exceptional ballast tanks as mentioned above may be included in the additional quarter required to be washed for sludge control. 46

Example 1: Conventional pipeline tanker In complying with the above policy and reconciling the objectives of ship safety, cargo out-turn, and minimum ship delay, the following principles should be applied. Discharge of wet oil Because of the electrostatic hazards involved, oil which may contain water should not be used for crude oil washing. All tanks to be discharged should therefore be debottomed by 1 m before any crude oil washing is started. In particular, oil in slop tanks which have been used for load-on-top purposes must not be used. If it is required to use slop tanks for the supply of wash oil, they should be discharged first, and then refilled with dry oil from another tank. Sequence of tank washing Priority should be given to crude oil washing departure ballast tanks first so that they are ready for ballasting if freeboard problems arise and so that over-the-top ballasting can be concurrent with discharge, thereby avoiding the venting of tank gases to atmosphere within port areas. Multi-stage washing Each tank should be washed in two stages, the side wash and the bottom wash, in order to minimize ship delay. During bottom washing the oil depth should not be allowed to increase over 1 m and towards the end of the washing, the bottom should be kept well drained to achieve the best results. Extent of washing In each tank being crude oil washed, all guns must be used. The programme of the deck-mounted machines shall be as follows: Side wash: two es, 308–max–308 (to be started when ullage reaches approximately 23 m) Bottom wash: three es, 408–08–308–08 The bottom guns in the wing tanks and No. 7 centre are to be used in the bottom wash together with the deck-mounted guns. Their cycle time is 1 h and they should be started when there is a depth of 1 m remaining in the tank. It is at this point that the draining of the tank should be considered to be started and the trim of the ship should be not less than 4 m by the stern. Multi-tank washing To minimize ship delay it is desirable to crude oil wash several tanks simultaneously, provided that: 1.

the maximum number of guns on any one centre tank, or pair of wing tanks, are in use at one time;

2.

pressure on the deck wash line does not fall below 8 kg/cm2; and

3.

the normal maximum number of guns that can be operated at one time is 12 due to a maximum permissible flow rate through the line of 5.5 m3/s; however, if more than 12 guns are required to be operated simultaneously, then it will be necessary to shut the block valve situated on the wash line main amidships and feed the forward section of the line from the manifold bleed-off and the after section from the pump-room. In this way up to 24 guns may be operated at one time;

4.

during the bottom washing the output of the guns does not exceed the available stripping capacity. 47

Crude oil washing systems Supply of wash oil The traditional method of tank washing using closed cycle recirculation via the slop tanks and eductors is not suited to routing crude oil washing as it causes unnecessary delay. It also increases risk of ing sediment through the machines and of using oil which has lost much of its solvent effect. The wash oil therefore should be bled off from a cargo pump discharge or from the manifold crossover. To retain the required pressure using the bleed-off method, it may be necessary to reduce the number of machines being used, to ask the shore to increase back pressure or to fully close one of the ship’s manifold valves. Under no circumstances should butterfly manifold valves be throttled in order to control the tank wash line pressure, but it is possible to control the pressure by throttling in the discharge valve of the cargo pump used to supply the wash oil. Alternatively, it may be necessary to dedicate one main cargo pump to supplying the wash oil and accept the reduction in the rate of discharge. Discharge of tank washings In order to maintain as consistent a quality in out-turn as possible, recovered residues should be co-mingled with the main cargo discharge. During multi-stage washing of the tank sides this co-mingling occurs automatically. During bottom washing, it is preferable to use the self-priming cargo pump to discharge the washing oil and recovered residues direct with the cargo. Overheating of these pumps may be avoided by draining several tanks simultaneously. When discharge directly ashore is not possible, residues should be stripped into some convenient holding tank, taking care to avoid any over-filling before the tank is periodically discharged to shore. Recirculation of cargo, that is dedicating the same tank both for supplying the washing oil and for receiving the recovered residues, should be avoided as long as possible. However this method does have to be used when crude oil washing at sea between two discharge ports and on occasion towards the end of a parcel discharge when more than one grade is being carried. SECTION 12: TYPICAL CRUDE OIL WASHING PROGRAMMES This section contains details of some typical washing programmes under various conditions of discharge such as single- or multi-port discharge and single- and multi-grade cargoes. See following pages for typical programmes in bar diagram form.

48


00080

49

00081


50

Example 1: Conventional pipeline tanker SECTION 13: THE METHOD OF DRAINING CARGO TANKS This section contains a description of the method of draining cargo tanks and should include the parameters which indicate when the tank is dry and which will be at least all of those required by paragraph 4.4.8 of the Revised Specifications. The minimum trim conditions must be stated. This vessel is fitted with a self-priming ‘‘Vac-Strip’’ system where it is possible to drain tanks dry with the main cargo pumps. As a tank or tanks approach draining level the system is manually set in operation and thereafter vacuum pumps automatically draw off excess gases and the pump discharge valve closes as flow decreases. The optimum method to use is as follows: With a number of tanks approaching draining level, i.e., approximately 1 m sounding, the system should be set in operation and then when the first tank reaches 0.5 m the main suction(s) should be shut and the process should be repeated for each tank until the last tank is reached. When the level in that tank reaches 0.5 m the pump should be slowed to 800 rpm, the stripping suction(s) opened and the main suction shut slowly. The tank will then drain until the area around the strum is oil free. This is indicated by the following: 1.

Whessoe gauge at maximum ullage (gauge should be housed while crude oil washing);

2.

flow trace absolutely zero with no fluctuation;

3.

separator virtually empty;

4.

discharge valve closed;

5.

pump nozzle steam pressure falling;

6.

vacuum on suction trace falls away;

7.

pump casing temperature rising;

8.

dips showing empty.

Thereafter the process should again be repeated for each tank back along the deck. On occasions, for example at sea between discharge ports, it may prove necessary to employ the closedcycle system already described in this Manual. However, where a different grade may be contained in the centre slop tank it is possible to use No. 2 main cargo pump drawing from the port slop tank via No. 1 bottom line across the bottom pump-room crossover, and thence to the tank cleaning line and eductors. When draining tanks using eductors, a good indication that a tank is empty is when the vacuum showing on the remote eductor suction gauge in the cargo control room drops completely away. Again hand dipping must be carried out as described when using the Vac-Strip system. Should for any reason the eductor drive pressure fall away below 6 kg/cm2 then it is imperative that the eductor suction valves should be shut immediately to prevent the contents of the slop tank running back through the eductors to the washing tank. When bottom crude oil washing of any tank nears completion, using either method of draining, the tank washing machines in that tank should be shut off one at a time and when all washing is complete sufficient time should be given to complete the draining. It is important that when draining tanks, also using either system, the vessel is trimmed by the stern sufficiently to enable the cargo to run aft to the tank suction. The trim should be as much as possible with due regard to berth security and tank stresses but should not be less than 4 m. 51

Crude oil washing systems SECTION 14: THE METHOD AND PROCEDURES FOR DRAINING CARGO PUMPS AND LINES This section contains a description of the method and procedures for draining cargo pumps, cargo lines, crude oil washing lines and stripping lines and includes information on the use of the smalldiameter line. On completion of discharge, all top and bottom lines should be dropped back to either wing slop tank via the direct loading drops and bottom pump-room crossovers. The port deck line can be dropped via the port drip and No. 1 line to the port slop tank, and the starboard deck line via the starboard drop, No. 4 line, and to the starboard slop tank via the stripping suction. The shore staff should be asked to vent their loading arms to permit the oil to drop back. At the same time the small by line on each cargo pump should be opened and the stripping pump set to drain the remains of each line individually to the port slop tank. The tank wash line should be drained by the stripping pump. If the eductor suction valves E2 and D2 are opened together with valves E3 and H3 then it will be possible for the stripping pump to drain the entire tank wash line to the port slop tank. A tank cleaning machine should be opened in one of the forward tanks to facilitate the line dropping back. When all lines are drained and cargo tanks dipped manually, the stripping pump can be set to discharge the line drainings in each wing slop tank via the direct stripping suctions discharging through the special 250 mm diameter line to the manifold and thence to the shore.

SECTION 15: TYPICAL PROCEDURES FOR BALLASTING AND THE METHOD OF PREVENTING HYDROCARBON EMISSION This section contains a description of typical procedures for ballasting and includes: (1)

the procedure for draining and stripping before loading ballast;

(2)

the procedures for preventing hydrocarbon emission into the atmosphere.

The departure ballast tanks for this vessel are No. 1 centre, No. 3 wings, No. 4 centre, and No. 6 centre tanks. No. 3 wing tanks are for permanent ballast only and are supplied by a dedicated ballast pump of 4,250 m3/h capacity with its own pipeline. No. 1 centre, No. 4 centre and No. 6 centre are cargo tanks but can be supplied with ballast using the dedicated ballast pump via a separated discharge line over the upper deck and by direct drops to these tanks. The typical method of ballasting No. 1 centre, No. 4 centre and No. 6 centre is to plan the discharge so that they are discharged as early as possible. They must be crude oil washed and good care must be taken while bottom washing, with frequent monitoring of soundings to ensure the tank bottoms are well cleared. Once the tanks are empty to the satisfaction of the chief officer, with the main suction and stripping valve controls lashed in the closed position together with all Lavomatic stop valves on those tanks checked shut, then ballasting to No. 1 centre, No. 4 centre and No. 6 centre can be commenced as soon as required. During cargo discharge there is no hydrocarbon emission to atmosphere, with the vacant cargo space being replaced by inert gas. Also, when ballasting No. 1, No. 4, and No. 6 centres concurrently with the discharge of other tanks, again there should be no hydrocarbon emission as the rate of supply of inert gas is reduced automatically to maintain the normal overpressure. However, if for any reason, cargo discharge is stopped or slowed sufficiently so that the deck I.G. pressure increases due to the displacement of the incoming ballast then once 1,000 mm WG is reached further ballasting should be postponed until the deck pressure is reduced by the resumption of cargo discharge. 52

Example 1: Conventional pipeline tanker SECTION 16: COMPLIANCE PROCEDURES FOR REGULATION 9 OF ANNEX I OF MARPOL 73/78 This section contains information and procedures for water washing tanks and lines, discharge of departure ballast and the decanting of slops at sea to ensure compliance with regulation 9. Departure ballast is taken in No. 1, No. 4 and No. 6 centres using the permanent ballast pump and the ‘‘over the top’’ line. On the ballast voyage, it will be necessary to wash the arrival ballast tanks, No. 2, No. 5 and No. 7 centres, fill them with clean ballast and then discharge No. 1, No. 4 and No. 6 centres. In order to wash the arrival ballast tanks, it is first necessary to charge the slop tanks with sea water. The opportunity should be taken at this time to give an initial wash of top and bottom lines to the dirty slop tank. The arrival ballast tanks should be washed with cold water on the closed-cycle system. Each tank must receive not less than the following wash: One full cycle and one hour on bottom cycle 08 to 308. All guns must be used including the bottommounted machine in No. 7 centre. On completion of the tank washing the vessel is then ready to receive clean ballast. Initially the pumps and lines to be used should be cleared to the dirty slop tank and thereafter clean ballast loaded to the required ullage in No. 2, No. 5 and No. 7 centres. Before discharging the dirty ballast it will be necessary to discharge a sufficient quantity of water from the slop tanks to create sufficient ullage for the expected dirty ballast drainings. An interface of the three slop tanks should therefore be taken to establish the limits to which discharge of slops can be taken without discharge of oil. On commencement of slop tank discharge, both No. 2 and No. 3 main cargo pumps should be cleared, pumping from No. 8 centre through the eductors to the dirty slop tank, and thereafter to sea via the high overboard discharge. Pumping from No. 8 centre should then be continued with the balance valves and lines open until sufficient ullage is obtained. Once the water has been discharged from the slop tanks, the suction can be changed to No. 1 centre, No. 4 centre and No. 6 centre, the pumps again cleared to the port slop tank via the eductor discharges and thereafter to sea via the high overboard discharge. Close visual attention must be paid to the overboard discharge throughout, but particularly when the levels in each tank approach draining level. However, when 2.5 m sounding in the first tank is reached, both main cargo pumps should be slowed to 800 rpm, and at 1.5 m one cargo pump should be stopped. At 1 m sounding or at the first sight of any oil in the outgoing stream, discharge should be stopped and the system set up for educting the remainder of the dirty ballast back to the slop tanks. On completion the lines should again be washed to the slop tanks. Once all tank washing and the ballast operations are complete the slop tank contents can be discharged. Preferably 24 h should be given for oil/water separation; this may have to be reduced, however, on short voyages, and then interface readings taken of each slop tank to establish the oil quantities in each tank. The free water can then be discharged, the centre and starboard tanks to 1 m from the oil layer, the port slop tank to 2 m from the oil layer. Again, very close attention must be paid to the overboard discharge. Thereafter the quantities remaining in the centre and starboard slop tanks should be transferred to the port slop tank using the stripping pump. Again, preferably 24 h should be allowed for separation and after an interface establishing the oil layer has been taken, the free water can be discharged overside with the stripping pump to 1 m from the oil level and thereafter to the oil/water separator on deck at a slow rate (maximum 100 m3/h) until no further water can be discharged. 53

Crude oil washing systems SECTION 17: INSPECTIONS AND MAINTENANCE OF EQUIPMENT This section contains information on procedures to be followed at recommended intervals for onboard inspections and maintenance of crude oil washing equipment. Deck-mounted machines It is not intended that these machines be removed from the tanks unless there has been an actual mechanical failure. However, in the event of such a failure, a lifting tripod, chain block and tools are provided and must be kept in good order. Normal maintenance will therefore consist of ensuring that the gearbox is topped up with lubricating oil, the filter is clear, the stop valve is tight and the machine is carrying out its programme. During periodic dry dock, the opportunity shall be taken to confirm that the nozzles are clear. This may be done by observing the water jet. Bottom-mounted machines Maintenance of these machines shall consist of ensuring that the filter is clear and the stop valve is tight. The correct operation of the machine, lube oil level and nozzle jet can be confirmed by observation whenever a tank is in a gas-free condition, but inspections should be made after not more than six usages or at intervals of 12 months, whichever is the more frequent. SECTION 18: PROCEDURES FOR CHANGING FROM CRUDE OIL TRADE TO PRODUCT TRADE This section contains operational procedures for changing from crude oil trade to product trade for a tanker which is fitted with separate independent pumping and piping arrangements for ballasting dedicated clean ballast tanks and which has been issued with two IOPP Certificates running concurrently with one certificate certifying the tanker to be a crude oil tanker and the other certifying it to be a product carrier. Note: This section was not included in the Manual as originally prepared by the tanker owner as it was not applicable to the particular tanker concerned. It has been added to this specimen Manual as an example of how the information relating to section 18 might be presented if required in a particular case. This oil tanker is equipped with a COW system for the crude oil trade and also has a CBT system for the product trade with separate independent pumping and piping arrangements for ballasting the dedicated clean ballast tanks; it may therefore change from the crude oil trade to the product trade without undergoing a survey. When making this change from the crude oil trade operating with a COW system to the product trade operating with dedicated clean ballast tanks, the following procedures shall be followed: 1.

During the discharge of the crude oil cargo, the tanks that are to be used as dedicated clean ballast tanks when the vessel is in the product trade should be crude oil washed in accordance with the approved methods and programmes contained in section 11 of this Manual. These tanks are to be crude oil washed in addition to those that are required to be crude oil washed by section 11.

2.

To remove any oily water mixtures that might remain in the separate independent pumping and piping arrangements, this separate system should be flushed by pumping sea water through the system into the tanks before water washing commences. This flushing water should be discharged to the slop tank through the cargo piping connection to the tanks.

54

Example 1: Conventional pipeline tanker 3.

After discharging all flushing water from these tanks through the cargo piping connections, all valves in the cargo piping lines that are connected to the tanks that are to be used as dedicated clean ballast tanks should be closed and secured.

4.

The tanks that are to be used as dedicated clean ballast tanks should be water washed in accordance with the procedures used for preparing arrival ballast tanks contained in section 16 of this Manual prior to the loading of the next cargo.

5.

After completion of water washing of these tanks, all wash water should be discharged to the slop tank.

6.

At the loading port, product cargo can be loaded on the vessel, but it may not be loaded into the tanks that are designated as dedicated clean ballast tanks while the vessel is in the product trade.

7.

The vessel should now operate as a product carrier with a CBT system and the Dedicated Clean Ballast Tank Operation Manual should be used while the vessel is in this trade.

55

Example 2: Full free-flow tanker

Example 2 Full free-flow tanker

CRUDE OIL WASHING OPERATIONS AND EQUIPMENT MANUAL

Name of ship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Port of registry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Distinctive number or letters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deadweight tonnage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

57

Crude oil washing systems INTRODUCTION 1 This Manual is written in accordance with the requirements of regulation 13B of the Protocol of 1978 relating to the International Convention for the Prevention of Pollution from Ships, 1973 (MARPOL 73/78). 2 The purpose of the Manual is to meet the requirements for crude oil washing in accordance with the Revised Specifications for the design, operation and control of crude oil washing systems (Assembly resolution A.446(XI) as amended by resolutions A.497(XII) and A.897(21)). It provides standard operational guidance in planning and performing a crude oil washing programme and describes a safe procedure to be followed. 3 This Manual contains all the information and operational instructions required by the Revised Specifications. 4 This Manual has been approved by the istration and no alteration or revision shall be made to any part of it without the prior approval of the istration.

58


Index of sections Page

Relevant paragraph(s) of the revised Specifications

Part 1 1


[60]

7(a)

2


[61]

7(b)

3


[67]

7(c), 7(d)(viii) and 7(f)

4


[71]

7(e)

5


[71]

6.6

6


[71]

6.7

7


[72]

7(g)

8


[72]

7(h)

9

List of crude oils unsuitable for crude oil washing . . . . . . . . .

[72]

7(l)

10


[72]

7(j)

11


[74]

7(d)(i)

12


[76]

7(d)(v)

13


[78]

7(d)(iii)

14

The method and procedures for draining cargo pumps and lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[78]

7(d)(iv) and (vi)


[79]

7(d)(ii), 7(i)

15 16

Compliance procedures for regulation 9 of Annex I of MARPOL 73/78 . . . . . . . . . . . . . . . . . . . . . . .

[80]


17


[81]

7(k)

59

Crude oil washing systems SECTION 1: TEXT OF THE REVISED SPECIFICATIONS This section contains the complete text of the Revised Specifications for the design, operation and control of crude oil washing systems and the agreed interpretations of certain of the provisions of the Revised Specifications (Assembly resolution A.446 (XI) as amended by resolutions A.497(XII) and A.897(21). (Text of the Revised Specifications to be inserted) SECTION 2: DRAWINGS OF THE CRUDE OIL WASHING SYSTEM This section contains line drawings showing: (1)

crude oil washing lines and valves;

(2)

cargo pumps, lines and valves;

(3)

ballast systems (where fitted);

(4)

stripping systems;

(5)

position of tank washing machines;

(6)

position of holes for hand dipping and tank gauges;

(7)

inert gas deck distribution system.

(See following pages for drawings)

60


Figure 1: Crude oil washing lines and valves

G.P. pump

Tank cleaning heater

No. 5 slop centre & side tanks

No. 4 cargo oil centre and side tanks




Fuel oil deep tank

Forepeak tank

Boss and thermometer centre line

Boss and pressure gauge

Tank washing ringmain 00082

61


Figure 2: Cargo pumps, lines and valves

S slop tank

P slop tank

C slop tank

Overboard discharge Tank cleaning line

No. 4 starboard outer C.O. pump

No. 3 starboard inner C.O. pump

No. 2 port outer C.O. pump

No. 1 port outer C.O. pump

G.P. pump

Tank cleaning heater

Separation tank 6 P.W.B. tank

Slop tank

No. 1 C.P. Suction

No. 2 C.P. Suction No. 1 C.P. Suction No. 2 C.P. Suction

Forward F.O. tank

No. 3 C.P. Suction No. 4 C.P. Suction

Forepeak tank

No. 3 C.P. Suction

No. 4 C.P. Suction

62

Slop tank

00083

6 P.W.B. tank


Figure 3: Ballast pumps, lines and valves

00084

63


Figure 4: Stripping pumps, lines and valves

oily water separator S. slop tank C. slop tank

P. slop tank

Stripping and bilge pump

6 P.W.B tank

Slop tank

Pump-room bilge suction

Forward F.O. tank

6 P.W.B tank

Forepeak tank

Slop tank 00085

64


Figure 5: Position of tank washing machines

No. 5 slop centre and side tanks





Fuel oil deep tank

Forepeak tank

00088

Figure 6: Position of holes for hand dipping and tank gauges






Fuel oil deep tank

Forepeak tank

00086

65


Figure 7: Inert gas deck distribution system


To pressure Emergency control unit inerting of pump-room From cargo machinery control console From deck seal From cargo pumps





Fuel oil deep tank

Forepeak tank

Mast. riser Liquid-filled P/V breather

From G.P. pump

No. 1 control stand Mast. riser vent valve

Boss and plug for pressure cock

00087

66

Example 2: Full free-flow tanker SECTION 3: DESCRIPTION OF THE CRUDE OIL WASHING SYSTEM AND OPERATIONAL AND EQUIPMENT PARAMETERS This section contains a description of the cargo, ballast, washing and stripping systems and in addition specifies: (1)

types of tank washing machines and their standpipe length inside the tanks;

(2)

revolutions of the machines;

(3)

methods of checking the operation of tank washing machines;

(4)

minimum operation pressure for crude oil washing;

(5)

maximum permitted oxygen level in cargo tanks;

(6)

duration of tank washing machine cycles;

(7)

results of the tests performed in accordance with paragraph 4.2.10(b) of the Revised Specifications and the method of computation;

(8)

method of preventing entry of oil into the engine room.

The cargo system consists of 12 cargo tanks and three slop tanks. Details of layout are shown diagrammatically in section 2. The system is so designed that cargo is discharged from cargo tanks entirely by free flow. Discharge from slop tanks is by special suctions in each tank. Cargo (or ballast) loading is achieved by individual drop lines to each of the cargo tanks and slop tanks. Ballast can also be free-flowed into wing tanks by gravity using two sea inlets. The centre tanks and wing tanks are completely separated. This permits two grades of cargo to be carried and also permits multi-port loadings and discharges. In addition to ballast carried in cargo tanks, permanent ballast tanks are located in the forepeak and No. 6 wings. Details are shown diagrammatically in section 2. These tanks have their own independent loading and discharging systems. The normal cargo loading procedure is for arrival ballast to be discharged from centre tanks concurrently with the loading of cargo in wing tanks. On completion of the loading of wing tanks, the deballasted centre tanks are then loaded. The normal cargo discharge procedure is for the wing tanks to be discharged first and then ballasted with the departure ballast concurrently with the cargo discharge from the centre tanks. During the ballast age, necessary water washing is carried out and the arrival ballast loaded into centre tanks and departure ballast discharged from wing tanks. The slop tank arrangement provides a three-stage separation system consisting of a centre slop tank and port and starboard wing slop tanks which are interconnected by levelling lines and valves. All three tanks are filled with clean sea water to predetermined levels prior to commencing water washing using a recirculatory system. The tank washings are discharged into the centre slop tank and then decanted into the starboard wing slop tank and, from there, decanted into the port wing slop tank. This provides efficient separation since, at each stage of decanting, the slops are discharged at low velocity in an upward direction into the oil scum near the surface of the liquid in the tanks. The centre slop tank may be used on its own as a single separator, or the wing slop tanks may be used in tandem as double-stage separation units. Four cargo pumps are provided. All four pumps may take direct suction from No. 4 centre tank. No. 1 and No. 2 pumps may take suction from No. 4 port wing tank, and No. 3 and No. 4 pumps may take suction from No. 4 starboard wing tank. The cargo pumps discharge to the manifold through two deck lines; the 67

Crude oil washing systems inner pumps, No. 2 and No. 3, discharge through the port line and the outer pumps, No. 1 and No. 4, discharge through the starboard line. Cross-over lines at the pump suctions and discharge permit flexibility in the selection of cargo pumps. One general-purpose pump is provided and this is primarily used for crude oil washing, educting and stripping duties. It is also used to discharge the slop tank on completion of the main cargo discharge. The pump is self-priming through connection with an automatic stripping system. Two eductors are provided. The motive power for the eductors is normally taken from the discharge of the general-purpose pump. No. 1 and No. 2 cargo pumps may also be used to supply motive power to the eductors. Both eductors discharge into the centre or starboard slop tanks or in the case of clean ballast may discharge overboard. The eductors may take direct suction from No. 4 centre tank or from the stripping ring main. The stripping ring main is connected to all cargo tanks, with the exception of No. 4 centre tank. Eductors can be connected to the bilge system via interconnections with the stripping pump line. A reciprocating stripping pump is provided. This takes direct suction from the centre slop tank or the stripping suction cross-over line or the outboard side of the manifold valves, port and starboard. The pump discharges directly to the oil/water separator of the cargo pump cross-over line or the outboard side of the manifold valves, port and starboard. The stripping pump is used for the stripping of pipelines and cargo pumps to the centre slop tank and then the final stripping of that tank ashore. Two sea inlets are provided. These enable any of the four cargo pumps, the general-purpose pump and the stripping pump to draw from the sea. The inlets can also be used for shipping ballast into the wing tanks by gravity. There are two high overboard discharges provided, port and starboard, for the discharge of ballast overboard. These are taken from the cargo pump discharge cross-over. The cargo control room provides the focal point for all cargo handling, ballasting and tank cleaning operations. Facilities are provided within the control room for remote control of the pumping equipment and remote operation of the hydraulically operated valves situated in the pump-room. The inert gas system performance is monitored and the operation of the deck main isolating valve is controlled from the cargo control room. The bulkhead valves in the tank space and hydraulically operated valves on the upper deck are operated from five local control stations on the upper deck. The inert gas system mast riser vent is operated from the forward local control station. Draught gauge indicators are fitted in the cargo control room. The indicator system indicates the ship’s draught at four positions; forward, aft, and midships port and starboard. A water heater is fitted in the cargo pump-room for use when hot water tank washing is required. During crude oil washing the heater is isolated from the tank cleaning system by means of the spectacle blanks provided. A Loaster computer is provided and is fitted in the cargo office adjacent to the cargo control room. In addition to the standard ullage fittings, each cargo tank and each slop tank is fitted with a Whessoe gauge giving visual ullage readings at the upper deck level. Additional gauges are fitted in the after ends of No. 4 centre and No. 4 wing tanks, the forward fuel oil tank and No. 7 fuel oil bunker tanks. A remote-reading tank level gauge for the centre slop tank is installed in the cargo control room.

68

Example 2: Full free-flow tanker PUMP PARTICULARS Service

No.

Type

Drive

Capacity and pressure/head at the pump

Cargo oil pumps

4

Horizontal centrifugal volute

Single-stage impulse steam turbine

4700 m3/h oil (sp. gr. 0.85) at 140 m head Pump speed: 1000 rpm

Cargo oil stripping pump

1

Vertical duplex double-acting reciprocating

Steam reciprocating

350 m3/h oil (sp. gr. 0.85) at 130 m head Pump speed: 31 strokes/min

Generalpurpose pump

1

Horizontal centrifugal volute

Single-stage impulse steam turbine

2000 m3/h oil (sp. gr. 0.85) at 140 m head Pump speed: 1650 rpm

EDUCTOR PARTICULARS Service

No.

Type

Drive

Capacity

Cargo oil stripping eductors

2

Golar

Discharge from No. 1 or No. 2 cargo pump or generalpurpose pump

Approximately 400 m3/h sea water Driving fluid needed: 800 m3/h

No. 6 tank permanent water ballast eductors

2

Golar

Discharge from fire, bilge and generalservice pumps


Forepeak tank permanent water ballast eductor

1

Golar

Discharge from fire, bilge and generalservice pumps


3.1 The cargo tanks and slop tanks are fitted with VP-Matic and VP-Monomatic fixed tank washing machines. These are manufactured by Victor Pyrate Limited. The machines have 2.6 m standpipes and are fitted with either 32 mm or 38 mm single nozzles. Natural vibration frequency of the machines is 10.83 Hz (650 cycles/min) which is well in excess of the maximum frequency that the propeller can induce. The layout and distribution of the machines are shown in diagrammatic form in section 2. 3.2 The machine nozzles rotate through 3608 in the horizontal plane and through 1408 in the vertical plane. Each complete horizontal revolution moves the nozzle through 2.38 vertically. The combination of horizontal and vertical movement produces a close spiral cleaning path within the tank. 3.3 A total of 24 control boxes are provided for mounting onto the turbine housing of the VP-Matic machines. This is a sufficient number for all wing tank VP-Matics to be fitted at the same time. The control boxes provide the means for actuating the position of the nozzles during the tank cleaning cycle. When they are fitted, the machines will automatically operate when the crude oil supply valve is opened. VPMonomatic machines are fitted with permanent integral control units. The controls are fitted with upper and lower stops which can be adjusted to give a wash over a selected arc. On reaching a stop the mechanism trips and the nozzle then proceeds on the return arc. The controls, settings and movements are visible externally and can be visually checked at any stage. 69


The minimum line pressure for crude oil washing is 8 bars. Normal working pressure is 10 bars.

3.5 Crude oil washing must only be carried out when the oxygen level in the tank is less than 8%. This is the maximum permitted level. 3.6

The duration of the tank washing cycles at 10 bars line pressure for various arcs is as follows:

Limit of cycle

1208

1008

808

608

408

Time

2 h 7 min

1 h 46 min

1 h 24 min

1 h 4 min

42 min

A cycle consists of two complete es of the nozzle through the designated vertical arc. A maximum of 18 tank washing machines can be operated simultaneously. 3.7 During tests, the amount of oil floating on the departure ballast did not exceed the permitted ratio given in paragraph 4.2.10(b) of the Revised Specifications. 3.8 The procedure for computing the ratio of the volume of oil on top of the total departure ballast water to the volume of tanks that contain this water is described below: Tank number

Port, starboard or centre

Tank volume (m3)

Ullage space in tank (measured to top of oil layer) (m)

Oil thickness (mm)

Volume of oil (m3)

Vx

Ux

tx

vx

Total

v

X

Total

V

3.8.1 Determine the thickness of the oil layer on the ballast water (tx). 3.8.2 Using the tank capacity tables: .1

determine the aggregate volume (100%) of all tanks that contain departure ballast (V);

.2

determine the volume of the ballast water and oil layer in each tank from the ullage (Ux);

.3

determine the volume of ballast water in each tank from the ullage plus the thickness of the oil layer (Ux + tx).

3.8.3 Subtract the value obtained in 3.8.2.3 from that obtained in 3.8.2.2 for each tank and add the resultant values together to obtain the total volume of oil (v). 3.8.4 The ratio of the volume of oil on top of the total departure ballast water to the total volume of tanks containing departure ballast water = Vv : 3.9 There is no part of the crude oil washing system in the machinery spaces other than the pump-room. Spectacle blanks are fitted to isolate the pump-room–sited heater from the system. On completion of a crude oil wash programme, the crude oil washing piping is drained into the centre slop tank. 70

Example 2: Full free-flow tanker SECTION 4: DANGERS OF AND PRECAUTIONS AGAINST OIL LEAKAGE This section contains information on the dangers of leakage from the crude oil washing system, the precautions necessary to prevent leakage and the action to be taken in the event of leakage. Leakage of crude oil from the system can be a potential fire and pollution hazard. Before arrival at the discharge port, the tank washing system should be pressure-tested and examined for leaks. Any leaks found should be made good and the resultant oil cleaned up. During the pressure test, special attention should be given to the inspection and tightening of valve glands and of flanges and couplings on lines to prevent any leakage. During the course of oil washing the system must be kept under continuous observation and on completion of washing it must be completely drained of oil. If it is necessary for the system to be cleaned out, it should be flushed through with water into appropriate tanks; if the system is required to be gas-free it should be ventilated in the same way as cargo lines. The crude oil washing must be stopped when any sign of leakage or fault in the tank wash system is discovered, either on deck or in the pump-room. SECTION 5: USE AND CONTROL OF INERT GAS This section contains information on the inert gas requirements and the instructions to cover those periods when the inert gas pressure is released for reasons of cargo operation. In addition it indicates the method and procedures to be used for taking samples of the tank atmosphere. The ship should arrive at the discharge port with all cargo tanks pressurized with good-quality inert gas. Pressure may be released for ullaging, sampling and water dips before discharge and at this stage the oxygen level in tanks should be checked to ensure that it is below 8% by volume. The supply of inert gas must be commenced immediately before the commencement of cargo discharge so as to avoid a vacuum in the tanks. By this means a safe condition will be maintained throughout discharge. Apart from this initial release of pressure the pressure in the cargo tanks should always be above atmospheric pressure. Under no circumstances should air be allowed to enter any tank which is to be crude oil washed. Before each tank is washed, the oxygen content should be checked with the portable oxygen analyser to ensure that it does not exceed 8% by volume. Samples should be taken at a point 1 m below the deck and at the middle region of the ullage space well clear of the inert gas inlet point. (See section 2 of this Manual for the position of the sampling points.) The crude oil washing must be stopped if there is a failure of the inert gas plant or if the oxygen content of the delivered inert gas exceeds 8% by volume or if the pressure of the tank atmosphere in the cargo tanks falls below atmospheric pressure. SECTION 6: PRECAUTIONS AGAINST ELECTROSTATIC HAZARDS This section contains details of the procedures for minimizing electrostatic generation Mixtures of oil and water can produce an electrically charged mist during tank washing. The use of dry crude is therefore important. To prevent the possibility of developing such an electrically charged mist, before crude oil washing is commenced any tank containing crude oil which is to be used as the crude oil washing fluid is to be partially discharged to remove any water which has settled out during the voyage. To ensure adequate safety, a minimum of 1 m depth of cargo is to be discharged in this way. 71

Crude oil washing systems For the same reason, as the slop tank will invariably contain a mixture of retained oil residues and cargo, the whole content of the slop tank should be discharged ashore before crude oil washing commences and then be refilled with fresh crude from the cargo discharge deck line, if the slop tank is to be used as a source of washing fluid. It must be ed that this refilling will take place after the discharge of the bottom 1 m depth of cargo from other tanks, referred to above, has been completed.

SECTION 7: PERSONNEL REQUIREMENTS This section specifies the numbers of persons to be associated with the crude oil washing process and their necessary qualifications. Their names and rank may be provided on separate documents. The following personnel are required to be on board to carry out the dual operation of discharging cargo and crude oil washing: 1.

the master or chief officer who will have overall responsibility for the operation. He must meet the requirements of paragraph 5.2 of the Revised Specifications; (see section 1 of this Manual)

2.

the officer who will undertake the actual operation. He must meet the requirements of paragraph 5.3 of the Revised Specifications; (see section 1 of this Manual)

3.

a minimum of one petty officer or rating who is to be on deck at all times during washing to keep watch for leaks and malfunction of equipment, to test the oxygen conent of tanks before washing, to check tank atmosphere pressure, to sound tank bottoms when required, and to lift ullage floats and to assist with changing drive units when this is necessary.

The duties of the persons referred to above are not necessarily mutually exclusive.

SECTION 8: METHODS OF COMMUNICATION This section gives the details of communication between the watchkeeper on deck and the cargo control position so that, in the event of a leak or malfunctioning of the crude oil washing system, the washing may be stopped as soon as possible. The ship is provided with portable VHF sets which operate on two frequencies. A set must be used by the person at the cargo controls and another by the person supervising crude oil washing on deck.

SECTION 9: LIST OF CRUDE OILS UNSUITABLE FOR CRUDE OIL WASHING This section contains a list of crude oils unsuitable for crude oil washing. This vessel is not fitted with heating coils in the cargo tanks and it should not carry cargoes which will require to be heated for pumpability.

SECTION 10: CRUDE OIL WASHING CHECKLISTS This section contains operational checklists for the use of the crew at each discharge which shall include the checking and calibration of all instruments.

72

Example 2: Full free-flow tanker PRE-ARRIVAL CHECKS AT DISCHARGE PORT No.

ITEM

1. 2. 3. 4. 5. 6. 7. 8.

Has terminal been notified? Is oxygen analysing equipment tested and working satisfactorily? Is tank washing pipeline system isolated from water heater and engine room? Are all hydrant valves on tank washing line blanked? Are all valves to fixed tank washing machines shut? Have tank cleaning lines been pressurized and leakages made good? Have portable drive units for fixed tank washing machines been tested? Have pressure gauges on the top discharge line, manifold and tank cleaning main been checked? Has the stripping system monitoring equipment been checked? Has the communications system been checked and tested? Has the organization plan been drawn up and posted with duties and responsibilities defined? Have the discharge/crude wash operation plans been drawn up and posted? In cases where the terminal has a standard radio checklist, has this been completed and transmitted?

9. 10. 11. 12. 13.

CHECKLIST FOR USE BEFORE, DURING AND AFTER CRUDE OIL WASH OPERATION No.

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

ITEM A – Before crude oil wash operation Are all the pre-arrival checks and conditions in order? Has discharge/crude oil wash operation been discussed with both ship and shore staff and is the agreed plan readily available for easy reference? Has communication link between the deck/control station and control station/shore been set up and is it working properly? Have the crude oil wash abort condition and procedures been discussed and agreed by both ship and shore staff? Have fixed and portable oxygen analysers been checked and are they working properly? Is inert gas system working properly and is the oxygen content of the inert gas being delivered below 8% by volume? Is oxygen content of tank(s) to be crude oil washed below 8% by volume? Have all cargo tanks positive inert gas pressure? Has a responsible person been assigned to check all deck lines for leaks as soon as washing starts? Are the fixed machines set for the required washing method and are portable drive units, if fitted, mounted and set? Have valves and lines both in pump-room and on deck been checked?

73


No.

ITEM B – During crude oil wash operation Is quality of inert gas being delivered frequently checked and recorded? Are all deck lines and machines being frequently checked for leaks? Is crude oil washing in progress in designated cargo tanks only? Is the pressure in the tank wash line 8 bars or above? Are cycle times of tank washing machines as specified in this Manual? Are the washing machines in operation, together with their drive units if applicable, frequently checked and working properly? Is a responsible person stationed continuously on deck? Will trim be satisfactory when bottom washing is in progress as specified in this Manual? Will recommended tank draining method be followed? Have ullage gauge floats been raised and housed in tanks being crude oil washed? Is level in holding tank for tank washings frequently checked to prevent any possibility of an overflow? C – After crude oil wash operation Are all valves between discharge line and tank wash line closed? Has tank wash line been drained of crude oil? Are all valves to washing machines closed? Are cargo pumps, tanks and pipelines properly drained as specified in this Manual?

12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

23. 24. 25. 26.

SECTION 11: APPROVED METHODS AND PROGRAMMES FOR CRUDE OIL WASHING This section contains those details which form the basis of crude oil washing in the tanker and which are necessary to formulate a washing programme which will accord with all foreseeable circumstances of cargo discharge restraints. It includes information on: (1)

the minimum number of tanks to be washed in accordance with paragraph 6.1 of the Revised Specifications;

(2)

the method of washing each tank, i.e., single- or multi-stage;

(3)

the number of tank washing machines to be used simultaneously;

(4)

the crude oil washing pressure and means to maintain the required pressure;

(5)

the duration of the crude oil wash;

(6)

the preferred order in which tanks are to be washed;

(7)

the minimum trim during completion of washing and draining tanks;

(8)

when draining and stripping of tanks is to commence.

The cargo system comprises four centre tanks, four pairs of wing tanks, a centre slop tank within No. 4 centre and a pair of wing slop tanks abaft No. 4 wing tanks. The system is served by four cargo pumps, one general-purpose (GP) pump, two eductors and one stripping pump. The slop tanks form part of the main cargo system, with cargo being loaded on top of oily residues which remain from previous cargoes. 74

Example 2: Full free-flow tanker Cargo pump capacities Main cargo pump – 4700 m3/h GP pump – 2000 m3/hV Eductor – 400 m3/h Stripping pump – 350 m3/h Discharge from main cargo tanks is by free flow through bulkhead sluice valves to No. 4 centre and No. 4 wings, from which the main cargo pumps take suction. The slop tanks are discharged by direct suctions serving individual compartments. The GP pump is used to provide the fluid for washing machines and eductors. Eductors are used for cargo stripping. In the event of a GP pump failure either No. 1 or No. 2 main cargo pump can be used instead. The stripping pump is used for the final stripping of pumps and lines. A bottom ring main is provided, which serves tanks 1 to 3, principally to facilitate stripping in water washing. The standard procedure is to crude oil wash and discharge all wing cargo tanks first and, after stripping them and draining the associated pipelines, to load departure ballast in the wings concurrently with the discharge of cargo and crude oil washing of centre tanks and wing slop tanks. Deck lines are drained into the centre slop tank and manifold lines; pump-room lines and pumps are drained via the stripping pump to the centre slop tank. Finally, the centre slop tank is pumped ashore through the special 150 mm diameter line. This procedure is not materially affected if different grades are loaded in wings and centres, nor if the wings are discharged at one port and centre tanks at a second port. However, if it is required to discharge centre tanks at one port and wing tanks at a second port it will be necessary to transfer cargo from the wing tanks to the centre tanks to enable ballasting procedures to be carried out. The procedure may be materially affected if more than one grade is loaded in the centre tanks or in the wing tanks. In this case, it will be necessary to discharge the first grade on the ring main using the GP pump. 11.1 In this ship, all wing cargo tanks are used for departure ballast and all centre cargo tanks for arrival ballast. The slop tanks do not carry ballast. Therefore, to comply with the requirements of paragraph 6.1 of the Revised Specifications, all cargo tanks and one of the slop tanks must be crude oil washed prior to sailing on a ballast voyage. However, a slop tank need not be washed more than once every four months except that it is recommended that the centre slop tank be washed each time. 11.2 Tanks are crude oil washed by the multi-stage method. That is, they are washed in three stages (1208–708: 708–408: 408–08). Each stage is given one and a half cycles (i.e., three es of the machine nozzle). During the final stage – the bottom wash – the first of the nozzle should commence with about 1 m of cargo remaining in the tank. During the second , the tank should be emptied and during the final the tank bottom should be dry. 11.3 The ship is fitted with 43 VP-Matic machines and 10 VP-Monomatic machines. There are 24 control boxes provided for actuating VP-Matic machines. This allows all tanks required to be washed with only one move of the control boxes. A total of 18 machines can be operated simultaneously. 11.4

During washing, the optimum line pressure is 10 bars. The minimum permissible pressure is 8 bars.

11.5 Crude oil washing will continue throughout the cargo discharge programme. It will commence approximately 2 h after the commencement of discharge and be completed prior to the final discharge of the centre slop tank. At 10 bars pressure, the time taken to wash each tank is: Top wash: Middle wash: Bottom wash:

1208–708: 708–408: 408–08 : Total

1 h 19 min 48 min 1 h 3 min 3 h 10 min

11.6 As the ship is designed to discharge by the free-flow method, the tanks at the forward end of the ship empty in advance of those aft because of the natural trim of the ship. The normal procedure therefore is to 75

Crude oil washing systems begin with the first stage (top wash) in No. 1 and No. 2 wing tanks and follow this with the first stage (top wash) in No. 3 and No. 4 wings. The sequence is then for the second stage (middle wash) and third stage (bottom wash) in those tanks in the same alternating orders. The bottom stage must not be commenced until the depth of oil is about 1 m. On completion of the bottom washing of wing tanks, control boxes are moved to the centre tanks and a washing sequence similar to that of the wing tanks carried out. 11.7

During the bottom washing and draining of tanks, the trim must be not less than 4 m.

11.8 As the ship is free flow, the draining of No. 1, No. 2 and No. 3 wings and centres is concurrent with cargo discharge. The draining of No. 4 wings and centre is to commence during the second of the tank cleaning machine nozzle during the bottom washing stage. SECTION 12: TYPICAL CRUDE OIL WASHING PROGRAMMES This section contains details of some typical washing programmes under various conditions of discharge such as single- or multi-port discharge and single- and multi-grade cargoes. Crude oil washing sequence in relation to cargo discharge The following sequence is the basic programme and is easily adapted to all conditions of cargoes and ports. Sequence

Cargo operation

Pump

COW operation

Pump

1

Commence discharge of centre slop tank

No. 1

2

Commence discharge of Nos. 1, 2, 3 & 4 wing tanks

Nos. 1, 2, 3&4

3

Wash centre slop tank

No. 1

4

8 m ullage Wash Nos. 1 & 2 wings 112 cycles 1208–708

GP on No. 4 wings

5

76

Refill centre slop tank with dry crude

6

Wash Nos. 3 & 4 wings 112 cycles 1208–708

7


8


9



Sequence

Cargo operation

Pump

COW operation

10

Commence discharge of Nos. 1, 2, 3 & 4 centre tanks

Nos. 2 & 3


11

Strip No. 4 wings using eductors. Discharge Nos. 1, 2, 3 & 4 centre tanks

GP Nos. 1, 2, 3&4

12

Pump

Check dips in wing tanks less than 25 mm

13

Strip all wing tanks and lines to centre slop tank

14

Commence flooding ballast into wing tanks

15

Discharge wing slop tanks

Stripping pump

No. 1

16

Wash requisite wing slop tank

GP on No. 4 centre

17

9 m ullage Wash Nos. 1, 2, 3 centre tanks 112 cycles 1008–708

GP on No. 4 centre

18

Wash No. 4 centre tank 112 cycles 1008–708

19

17 m ullage Wash Nos. 1, 2, 3 centre tanks 112 cycles 708–408

20

Stop Nos. 1 & 4 pumps. Drain pumps and lines to centre slop tank

21

Commence pumping ballast to wing tanks

Nos. 1 & 4

22


23

24 m ullage Wash Nos. 1, 2 & 3 centre tanks 112 cycles 408–08

24


GP on centre slop tank

77


Sequence

Cargo operation

Pump

25

26

COW operation

Pump

Check dips in Nos. 1, 2 & 3 centre tanks and wing slop tanks less than 25 mm Stop discharge while bottom washing and stripping No. 4 centre

27

Check dip in No. 4 centre tank

28

Discharge centre slop tank

29

Strip Nos. 2 & 3 and GP pumps and lines and manifolds to centre slop tank

30

Discharge centre slop tank via special 150 mm line

GP

SECTION 13: THE METHOD OF DRAINING CARGO TANKS This section contains a description of the method of draining cargo tanks and should include the parameters which indicate when the tank is dry and which will be at least all of those required by paragraph 4.4.8 of the Revised Specifications. The minimum trim conditions must be stated. Draining of No. 1 , No. 2 and No. 3 centre and wing tanks is by free flow into No. 4 centre and wings. No. 4 centre and wings are drained by eductors which are powered by the GP pump, although No. 1 or No. 2 main cargo pump can be used if the need arises. The wing slop tanks are also drained by the eductors. Final draining of the centre slop tank is by a steam reciprocating pump which discharges directly ashore through the special stripping line. It can be verified that a tank is empty by fully extending the Whessoe gauge, which is housed during crude oil washing, and by hand dipping. To monitor the stripping system efficiency, cargo pump revolution indicators and eductor and stripping pump suction and discharge gauges are displayed in the cargo control room. The minimum trim condition for draining tanks is 4 m by the stern.

SECTION 14: THE METHOD AND PROCEDURES FOR DRAINING CARGO PUMPS AND LINES This section contains a description of the method and procedures for draining cargo pumps, cargo lines, crude oil washing lines and stripping lines and includes information on the use of the smalldiameter line. 14.1

Deck lines

14.1.1 The starboard deck line is drained through the direct load lines into the wing slop tanks. This is prior to the ballasting operation. 78

Example 2: Full free-flow tanker 14.1.2 Direct load lines are drained into their individual cargo wing tanks. On completion, cargo wing tanks are given a final strip using the stripping pump. This is prior to the ballasting operation. 14.1.3 The port deck line and manifold lines are drained through the direct loading line into the centre slop tank. Manifold pressure compensation valves are opened during this operation. 14.1.4 Direct load lines are drained into their individual cargo centre tanks. On completion, cargo centre tanks are given a final strip using the stripping pump. 14.1.5 Manifold outboard areas are drained to the centre slop tank via the stripping pump and special stripping line. 14.1.6 The crude oil washing line is drained to the centre slop tank via the fixed tank washing machine. To equalize the pressure, the forward machine in No. 1 centre is opened. 14.2

Stripping line crossover and by lines

There is a stripping line crossover connecting the stripping pump suction to each of the cargo pumps and GP pump strainers. There are by lines with manual valves fitted around the non-return valves in each cargo pump and GP pump discharge line. 14.2.1 Prior to pumping ballast, the by lines around No. 1 and No. 4 pump non-return valves are opened and the pumps plus associated pipelines drained via the stripping pump to the centre slop tank. 14.2.2 On completion of cargo discharge, all pump-room and cargo tank lines that contain oil are stripped into the centre slop tank using the stripping pump. To equalize the pressure, No. 1 centre tank suction should be open. On completion of the pumps and lines stripping programme, check that all valves are closed. 14.3

Special stripping line

This line has the dual purpose of draining the outboard manifold lines to the centre slop tank and the final draining of the centre slop tank to shore. In this latter operation, the stripping line is set so that the stripping pump takes suction from the centre slop tank and discharges to shore via the connection to the outboard side of one of the manifold valves. When the tank is drained, the pump is left running for approximately 10 minutes to allow air to be pumped up the line. SECTION 15: TYPICAL PROCEDURES FOR BALLASTING AND THE METHOD OF PREVENTING HYDROCARBON EMISSION This section contains a description of typical procedures for ballasting and includes: (1)

the procedure for draining and stripping before loading ballast;

(2)

the procedures for preventing hydrocarbon emission into the atmosphere.

15.1 At the completion of discharge of wing cargo tanks, No. 4 wings are drained using the eductors. Dips are taken in all wing cargo tanks to ensure that they are dry. Ballast is loaded by gravity for the first two hours and then it is pumped using No. 1 and No. 4 cargo pumps. Before the gravity loading commences, the starboard deck line must be drained and the tanks given the final stripping in accordance with section 14.1. Prior to pumping ballast, No. 1 and No. 4 pumps must be stopped and the pumps plus associated pipelines drained in accordance with section 14.2. 79

Crude oil washing systems 15.2 Inert gas supply must be regulated to obtain a slight positive pressure in tanks during discharge, but this must be below a level where emission to atmosphere occurs. When wing tanks are being ballasted, the displacement tank atmosphere is to be contained within the centre tanks which are being discharged. The inert gas supply must be reduced so that the slight positive pressure is maintained in the system. SECTION 16: COMPLIANCE PROCEDURES FOR REGULATION 9 OF ANNEX I OF MARPOL 73/78 This section contains information and procedures for water washing tanks and lines, discharge of departure ballast and the decanting of slops at sea to ensure compliance with regulation 9. 16.1

Pump and line washing

The GP pump and lines are washed by taking suction from the sea and discharging round the manifold to the centre slop tank. The stripping pump and special stripping line are washed by taking suction from No. 3 cargo wing tanks (using the stripping ring main) and discharging back to the same tanks via the manifold drain lines. No. 1 and No. 4 pumps and lines will have been washed during the loading of ballast during the cargo discharge operation. No. 2 and No. 3 pumps and lines are washed during the loading of additional ballast in cargo wing tanks. Suction is taken from the sea and ballast discharged to wing tanks via the port and starboard deck lines and direct loading lines. The direct loading lines to cargo centre tanks are also to be washed at this time. Manifold lines are washed concurrently with the shipping of additional ballast. The manifold drain valves to No. 3 wing cargo tanks and manifold crossover valves are opened. The drain line valves must remain open until ballasting is completed so as to ensure adequate washing of the whole deck line system. 16.2

Water washing of tanks

Water washing is carried out by the recirculatory system using all three slop tanks. Therefore, before the loading of the additional ballast is completed, each slop tank is to be partially filled through its respective direct load lines. On completion of the ballasting, pumps and deck lines are to be drained and all centre tanks purged with inert gas to remove hydrocarbon gases. The centre tanks are then to be washed. The GP pump takes suction from the port slop tank and supplies water to the tank washing line and to the eductors. Tank washing machines are set to wash one full cycle followed by a bottom wash. That is, 08–1008–08–408–08. Tanks are to be washed sequentially and the eductors used to strip the washings. The eductors discharge to the centre slop tank. Levelling valves between the centre and starboard slop tanks and the starboard and port slop tanks are to be open during this operation. 16.3

Discharge of departure ballast

Departure ballast is initially discharged overboard using either No. 1 or No. 4 pump on the free-flow system. When the ullage in No. 4 wing tanks is 22 m, the pump is to be slowed down and the discharge closely monitored. When the first traces of discoloration are observed, the discharge overboard is to stop and the balance discharged to the slop tanks. The eductors are used to drain No. 4 wing cargo tanks. The arrival ballast is loaded into the centre tanks via their direct load lines using either No. 2 or No. 3 pump concurrently with the discharge of the departure ballast. 80

Example 2: Full free-flow tanker On completion of the discharge of departure ballast, all wing cargo tanks are to be purged with inert gas to remove hydrocarbon gas. Any necessary water washing can then be done. 16.4

Decanting of slop tanks

After completing the ballast transfer and tank washing programmes, the oil/water interfaces in the three slop tanks are to be measured. The water contents of these tanks are to be discharged overboard using the stripping pump. The oil and oil/water mixture in the wing slop tanks is to be transferred to the centre slop tank via the deck oil/water separator. Finally, the cargo pumps and GP pump are to be flushed through to ensure that they are clean. After a settling period, the stripping pump is used to discharge the centre slop tank contents through the oil/ water separator until the water bottom has been decanted. SECTION 17: INSPECTIONS AND MAINTENANCE OF EQUIPMENT This section contains information on procedures to be followed at recommended intervals for onboard inspections and maintenance of crude oil washing equipment. The inspection and maintenance procedures for the crude oil washing equipment are contained in the planned maintenance programme. These are to be carried out regularly to ensure that the equipment is maintained in good working condition.

81

IV GUIDELINES FOR IN-PORT INSPECTION OF CRUDE OIL WASHING PROCEDURES

Guidelines for in-port inspection

GUIDELINES FOR IN-PORT INSPECTION OF CRUDE OIL WASHING PROCEDURES 1

INTRODUCTION

1.1 Guidelines for the in-port inspection of crude oil washing procedures as called for by resolution 7 of the International Conference on Tanker Safety and Pollution Prevention, 1978, are required to provide a uniform and effective control of crude oil washing to ensure compliance of ships at all times with the provisions of the Protocol of 1978 relating to the International Convention for the Prevention of Pollution from Ships, 1973 (MARPOL 73/78). 1.2 The design of the crude oil washing installation is subject to the approval of the istration of the flag State. However, although the operational aspect of crude oil washing is also subject to the approval of the same istration it might be necessary for the authority of a port State to see to it that continuing compliance with agreed procedures and parameters is ensured. 1.3 The Operations and Equipment Manual contains all the necessary information relating to the operation of crude oil washing on a particular tanker. The objectives of the inspection are therefore to ensure that the provisions of the Manual dealing with safety proceures and with pollution prevention are being strictly adhered to. 1.4 The method of the inspection is at the discretion of the authority of the port State and the actual inspection may cover the entire crude oil washing operation or only those parts of the operation which occur when the inspector is on board. 1.5

Inspection will be governed by articles 5 and 6 of MARPOL 73/78.

2

INSPECTIONS

2.1 A port State should make the appropriate arrangements so as to ensure compliance with requirements governing the crude oil washing of tankers. This is not, however, to be construed as relieving terminal operators and shipowners of their obligations to ensure that the operation is undertaken in accordance with the regulations. 2.2 The inspection may cover the entire operation of crude oil washing or only certain aspects of it. It is thus in the interest of all concerned that the ship’s records with regard to the crude oil washing operations are maintained at all times so that an inspector may those operations undertaken prior to his inspection. 3

SHIP’S PERSONNEL

3.1 The person in charge and the other nominated persons who have responsibilities in respect of the crude oil washing operation should be identified. They must, if required, be able to show that their qualifications meet the requirements as appropriate of paragraphs 5.2 and 5.3 of the Revised Specifications for the design, operation and control of crude oil washing systems as adopted by IMO. 3.2 The verification may be accomplished by reference to the individual’s discharge papers, testimonials issued by the ship’s operator or by certificates issued by a training centre approved by an istration. The numbers of such personnel should be at least as stated in the Manual. 4

DOCUMENTATION

4.1

The following documents will be available for inspection: 85

Crude oil washing systems 4.1.1 the International Oil Pollution Prevention Certificate, to determine: .1

whether the vessel is fitted with a crude oil washing system as required in regulation 13(6) or (8) of Annex I of MARPOL 73/78; and

.2

whether the crude oil washing system is according to and complying with the requirements of regulation 13(B) of Annex I of MARPOL 73%78;

.3

the identification of the Operations and Equipment Manual;

.4

the validity of the Certificate;

4.1.2 the approved Operations and Equipment Manual; 4.1.3 the Oil Record Book and attached Supplement; 4.1.4 the Cargo Ship Safety Equipment Certificate to confirm that the inert gas system conforms to regulations contained in chapter II-2 of the International Convention for the Safety of Life at Sea, 1974, as modified and added to by the Protocol of 1978.

5

INERT GAS SYSTEM

5.1 Regulations covering inert gas systems require that instrumentation shall be fitted for continuously indicating and permanently recording the pressure and oxygen content of the gas in the inert gas supply main at all times when inert gas is being supplied. The permanent recorder should indicate if the system has been operating in a satisfactory manner before and during the cargo discharge. 5.2 If conditions specified in the Operations and Equipment Manual are not being met the washing must be stopped until satisfactory conditions are restored. 5.3 As a further precautionary measure, the oxygen level in each tank to be washed is to be determined at the tank. The meters used should be calibrated and inspected to ensure that they are in good working order. Readings from tanks already washed in port prior to inspection should be available for checking. Spot checks on readings may be instituted.

6

ELECTROSTATIC GENERATION

6.1 It should be confirmed, either from the cargo log or by questioning the person in charge, that presence of water in the crude oil is being minimized as required by paragraph 6.7 of the Revised Specifications.

7

COMMUNICATION

7.1 It should be established that effective means of communication exist between the person in charge and the other persons concerned with the crude oil washing operation.

8

LEAKAGE ON DECK

8.1 Inspectors should ensure that the crude oil washing piping system has been operationally tested for leakage before cargo discharge and that the fact has been noted in the ship’s Oil Record Book. 86

Guidelines for in-port inspection 9

EXCLUSION OF OIL FROM ENGINE ROOM

9.1 It should be ascertained that the method of excluding cargo oil from the machinery space is being maintained by inspecting the isolating arrangements of the tank washing heater (if fitted) or of any part of the tank washing system which enters the machinery space. 10

SUITABILITY OF THE CRUDE OIL

10.1 The types of crude oil being carried should not be on the list provided in the Operations and Equipment Manual as being unsuitable. 11

CHECKLIST

11.1 It should be determined from the ship’s records that the checks in the pre-crude wash operational checklist were carried out and that all instruments functioned correctly. Spot checks on certain items may be instituted. 12

WASH PROGRAMMES

12.1 Where the tanker is engaged in a multiple-port discharge the Oil Record Book should indicate if tanks were crude oil washed at previous discharge ports or at sea. It should be determined that all tanks which will be, or may be, used to contain ballast on the forthcoming voyage will be crude oil washed before the ship leaves the port. There is no obligation to wash any tank other than ballast tanks at a discharge port except that each of these other tanks must be washed at least in accordance with paragraph 6.1 of the Revised Specifications. The Oil Record Book should be inspected to check that this is being complied with. 12.2

All crude oil washing must be completed before a ship leaves its final port of discharge.

12.3 If tanks are not being washed in one of the preferred orders given in the Manual, the inspector should satisfy himself that the reason for this and the proposed order of tank washing are acceptable. 12.4 For each tank being washed it should be ensured that the operation is in accordance with the Operations and Equipment Manual in that:

13

.1

the operation of deck-mounted machines and submerged machines is verified by reference either to indicators, or to the sound patterns of the machines, or by other approved methods;

.2

the deck-mounted machines, where applicable, are programmed as stated;

.3

the duration of the wash is as required;

.4

the number of tank washing machines being used simultaneously does not exceed that specified.

STRIPPING OF TANKS

13.1 The minimum trim conditions and the parameters of the stripping operations are to be as stated in the Operations and Equipment Manual. 13.2 All tanks which have been crude oil washed are to be stripped. The adequacy of the stripping is to be checked by hand dipping at least in the aftermost hand dipping location in each tank or by such other means as are provided and described in the Manual. It should be ascertained that the adequacy of stripping has been checked or will be checked before the ship leaves its final port of discharge. 87

Crude oil washing systems 14

BALLASTING

14.1 Tanks that were crude oil washed at sea will be recorded in the Oil Record Book. These tanks must be left empty between discharge ports for inspection at the next discharge port. Where these tanks are the designated departure ballast tanks they may be required to be ballasted at a very early stage of the discharge. This is for operational reasons and also because they must be ballasted during cargo discharge if hydrocarbon emission is to be contained on the ship. If these tanks are to be inspected when empty, this must be done shortly after the tanker berths. If an inspector arrives after the tanks have begun accepting ballast, the sounding of the tank bottom will not be available to him. However, an examination of the surface of the ballast water is then possible. The thickness of the oil film should not be greater than that specified in paragraph 4.2.10(b) of the Revised Specifications. 14.2 The tanks that are designated ballast tanks will be listed in the Manual. It is, however, left to the discretion of the master or responsible officer to decide which tanks may be used for ballast on the forthcoming voyage. It should be determined from the Oil Record Book that all such tanks have been washed before the tanker leaves its last discharge port. It should be noted that where a tanker back-loads a cargo of crude oil at an intermediate port into tanks designated for ballast then it should not be required to wash those tanks at that particular port but at a subsequent port. 14.3 It should be determined from the Oil Record Book that additional ballast water has not been put into tanks which had not been crude oil washed during previous voyages. 14.4 It should be seen that the departure ballast tanks are stripped as completely as possible. Where departure ballast is filled through cargo lines and pumps, these must be stripped either into another cargo tank or ashore by the special small-diameter line provided for this purpose. 14.5 The methods of avoiding vapour emission where locally required will be specified in the Manual and they must be adhered to. The inspector should ensure that this is being complied with. 14.6 The typical procedures for ballasting listed in the Operations and Equipment Manual must be observed. The inspector should ensure this is being complied with. 14.7 When departure ballast is to be shifted, the discharge into the sea must be in compliance with regulation 9 of Annex I of MARPOL 73/78. The Oil Record Book should be inspected to ensure that the vessel is complying with this.

88

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