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Offshore Safety and Survival Centre

Crude Oil Washing

STUDENT HANDBOOK

Be ready for the challenge.

School of Maritime Studies Student Handbook 2005

Crude Oil Washing

Except as provided by legislation governing the use of materials for educational purposes, no part of this publication may be reproduced, stored in a database or a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior written permission from the Marine Institute of Memorial University. Care has been taken to ensure that ownership of any copyright material contained in this publication is being traced and permission for its use obtained. The Marine Institute would welcome any information that would correct any errors or omissions in assigning appropriate credit or reference in future editions.

Crude Oil Washing

Table of Contents Course Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.0

National and International Legislation and Regulations . . . . . . . . . . . . 3 1.1 Canada Shipping Act and Regulation . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 IMO Conventions and Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.0

Introduction to Crude Oil Washing . . . . . . . . . . . . . . . . . . . . . . . 9 2.1 Principles of Crude Oil Washing . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2 Benefits of Crude Oil Washing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.3 Principles of Effective use of Slop Tanks and Oil Discharge Monitors. . . . . . . . 15

3.0

Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.1 3.2 3.3 3.4 3.5

4.0

Tank Washing Machine . . . . . . . . . . . Piping Arrangement for Crude Oil Washing Driving Medium . . . . . . . . . . . . . . . Stripping Systems . . . . . . . . . . . . . . Pumps and Eductors . . . . . . . . . . . . .

. . . . .

22 23 24 24 25

Operational Procedures and Processes. . . . . . . . . . . . . . . . . . . . . . 27 4.1 Operational Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 4.2 Effectiveness of Crude Oil Washing . . . . . . . . . . . . . . . . . . . . . . . . . 33

5.0

Safety Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 5.1 Inert Gas System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 5.2 Electrostatic Charges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

6.0

Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 6.1 Maintenance of Plant and Equipment . . . . . . . . . . . . . . . . . . . . . . . . . 46

APPENDIX A - References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 APPENDIX B - Course Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

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School of Maritime Studies Offshore Safety and Survival Centre

Crude Oil Washing

CRUDE OIL WASHING TYPE AND PURPOSE:

The course is intended to provide students with a thorough understanding of the use of crude oil as a washing medium in vessels carrying crude oil in bulk as well as the precautions and safeguards necessary for it to be used to assist in the discharge of the maximum possible amount of oil, thus reducing the amount of oil discharged into the environment.

CALENDAR ENTRY:

National and International Legislation and Regulations; Introduction to Crude Oil Washing; Equipment; Operational Procedures and Processes; Safety Aspects; and Maintenance of Plant and Equipment

CLASS SIZE:

Maximum 8

CERTIFICATE AWARDED:

Certificate of Achievement

PREREQUISITES:

- Certificate of Competency as Watchkeeping Mate or 4th Class Engineer with Level 1 Endorsement or Watchkeeping rating with minimum of three months sea service on tankers - Successful completion of INERT GAS SYSTEMS Course - First aid certificate.

SCHEDULE:

1.5 days (11hrs.)

COURSE AIMS:

To help students understand the operation of a Crude Oil Washing installation and the use of crude oil as a washing medium.

To enable students to become familiar with relevant regulations and associated safety requirements for Crude Oil Washing.

To help students understand the importance that routine maintenance, inspection, and testing play in the safe and efficient operation of Crude Oil Washing systems.

To help students recognize that an efficient crude oil washing system, correctly operated, contributes greatly to the prevention of pollution in the marine environment.

MAJOR TOPICS:

1.0 National and International Legislation and Regulations 2.0 Introduction to Crude Oil Washing 3.0 Equipment 4.0 Operational Procedures and Processes 5.0 Safety Aspects 6.0 Maintenance of Plant and Equipment

EVALUATION:

25 multiple-choice question examination 60% rating required to pass 100% attendance required to pass

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Crude Oil Washing

~NOTES~

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Crude Oil Washing - 1.0 National and International Legislation and Regulations

1.0 NATIONAL AND INTERNATIONAL LEGISLATION AND REGULATIONS

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Crude Oil Washing - 1.0 National and International Legislation and Regulations

Crude Oil Washing Introduction The main research and development pertaining to Crude Oil Washing (COW) began in the early 1970s aboard the British Scientist and the British Prospector. This led to the realization that the use of Crude Oil Washing as a standard procedure on Very Large Crude Carriers (VLCCs) could significantly reduce the time spent on water washing tanks for clean ballast. This led to greatly reduced quantities of retained oil on board as part of the load-on-top operation and eliminated the problems of sludge build-up in tanks. Crude Oil Washing was adopted in 1978 by the Tanker Safety and Pollution Prevention Conference as an alternative to segregated ballast tanks in existing tankers. This preserves deadweight capacity. Although there are some disadvantages with COW; these are greatly outweighed by the advantages.

1.1

Canada Shipping Act and Regulations

Applications to Tankers and Inert Gas (a)

Oil Pollution Prevention Act and Regulations

Figure 1 - Regulations and Guidelines

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Crude Oil Washing - 1.0 National and International Legislation and Regulations

The Oil Pollution Prevention Act and Regulations govern the prevention of the pollution of water by oil discharged from ships and from loading and unloading facilities for ships. These regulations include standards for construction, equipment, operations, and inspections. They • apply to any Canadian ship operating outside of waters under Canadian jurisdiction; • apply to any ship operating in waters under Canadian jurisdiction; and • do not apply to warships or ships used in government non-commercial service. Construction Plans and specifications for the following must be submitted to the Steamship Board for approval:

• • • •

slop tank arrangement - Regulation 15(2), Annex 1, MARPOL; inert gas system referred to in Regulation 13B(3) of Annex 1, MARPOL; crude oil tankers of 20,000 dwt or more; and product carriers of 30,000 dwt or more.

Equipment Inert gas systems are required to meet the standards specified in Regulation 62, Chapter 11-12 SOLAS. Equipment regulations for Crude Oil Washing are specified in Resolution A446(XI). Operation Manuals The owner or master of every crude oil tanker of 20,000 dwt or more, shall submit to the board four copies of these operating manuals for the tanker’s.

• inert gas system; and • Crude Oil Washing system. Inspections Inspections are required by the Steamship Board under the Canada Shipping Act to verify that a tanker’s construction, equipment fittings and installations and systems are in accordance with the oil pollution regulations. These inspections are to be carried out before a ship is put into service or issued its first Canadian Oil Pollution Prevention Certificate. An Oil Pollution Prevention Certificate is valid for a period of 5 years. (b)

Occupational Health and Safety Act and Regulations

These regulations provide standards such that people working in the marine environment can do so in a safe and healthy manner. They specify the standard, or condition of a ship, that the employer must provide for its employees: for example, a shower for every 10 employees on all ships other than a day ship. Other areas subject to these safety and health regulations include the following: 1.

Training Every employer, in consultation with the safety and health committee, must develop an employee education program for hazard prevention and control of the workplace (WHMIS).

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Crude Oil Washing - 1.0 National and International Legislation and Regulations

Confined Space Entry Entry into a confined space is not allowed without prior testing of that space by a qualified person. The O2 in the confined space atmosphere must not be less than 19.5% nor more than 23% by volume.

1.2

IMO Conventions and Guidelines

Applications to Installation and Operation International Codes and Regulations:

The Crude Oil Washing installation, associated equipment and arrangements must comply with the requirements established by the government of the state under whose authority the ship is operating. These requirements should contain at least all the provisions of the specifications for the design, operation and control of Crude Oil Washing systems adopted by the International Conference on Tanker Safety Pollution Prevention 1978, in Resolution 15, notwithstanding the revised specifications by International Maritime Organization (IMO). The IMO publication Crude Oil Washing Systems (revised edition, 1983) provides a summary of the various IMO Conventions and Resolutions affecting the implementation of COW operations. The COW installation on tankers must undergo a design review and a practical demonstration test before certification is given. A properly maintained and operated Crude Oil Washing system should be capable of delivering the performance required by IMO Resolution A. 446 (XI). Every oil tanker required to be fitted with a COW system, must have: • A Crude Oil Washing Operations and Equipment Manual; and • trained personnel to take overall charge of Crude Oil Washing operations. The training standards for COW operations for officers and ratings are required by Resolution 10 of the International Convention on Standards of Training and Certification for Watchkeepers 1978/95 Amendments (STCW CODE). The requirements can also be found in Appendix II of IMO, Resolution A.446 (XI), revised specification for design, operation and control of Crude Oil Washing Systems. (a)

MARPOL 73/78, Amendments to Annex I Regulation 9: Control of discharge of oil Paragraph (1) (a) (iv): the instantaneous rate of discharge of oil content does not exceed 30 litres per nautical mile Paragraph (1) (b) (iii): the oil content of the effluent without dilution does not exceed 15 parts per million Regulation 10: Methods for the prevention of oil pollution from ships while operating in special areas Paragraph (2) (a) Any discharge into the sea of oil or oily mixture from any oil tanker and any ship of 400 tons gross tonnage and above other than an oil tanker shall be prohibited while in a special area. In respect to the Antarctic

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Crude Oil Washing - 1.0 National and International Legislation and Regulations

area, any discharge into the sea of oil or oily mixture from any ship shall be prohibited. Regulation 16: Oil discharge monitoring and control system and oil filtering equipment (b)

SOLAS Regulations Part A Application, definitions, etc. Regulation 1: Application SOLAS regulations apply to ships on international voyages. Each chapter specifies the class of ship to which the regulations apply. Regulation 4: Exemptions Regulation 4 deals with vessels that can be exempt from compliance to SOLAS regulations; for example, a vessel not normally engaged in international voyages, but is required to undertake a single voyage, may be exempt from any of the regulations, provided it complies with satisfactory safety requirements. Part B Surveys and Certificates Regulation 13: Issue of certificates by another Government This regulation deals with the issue of a certificate by another government. A Contracting Government may, at the request of the flag State, cause a ship to be surveyed and, upon completion, issue a certificate, which will have the same force as a regular issued certificate.

(c)

Oil Record Book: Mandatory use: All oil tankers of 150 dwt and larger are required by Regulation 20 of MARPOL 73/78 to carry and maintain Parts I and II of the Oil Record Book. Part I is designed for recording machinery space operations. Part II is designed for recording cargo or ballast operations on oil tankers. All entries made in the Oil Record Book must be signed by the officer or officers in charge. Each completed page shall be signed by the master of the ship. Entries in the Oil Record Book should be arranged according to a letter and a code and are inserted in columns in a chronological order. Great care should be taken when making entries, so that they are made correctly and reflect accurately the action taken to avoid pollution. All entries in the oil record book should be made without delay. The book should be readily available for inspection and should be kept on board for a period of 3 years after the last entry.

NOTE The master should obtain a receipt of any discharge to shore reception facilities, including date and time of transfer and attach such receipts to the Oil Record Book.

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Crude Oil Washing - 1.0 National and International Legislation and Regulations

(d)

Operations and Equipment Manual Mandatory Use Regulation 13B: Marpol 73/78 requires every oil tanker operating with Crude Oil Washing systems to be provided with an Operation and Equipment Manual which details the system and equipment and specifies operational procedures. If any alteration affecting the Crude Oil Washing system is made, the Operation and Equipment Manual shall be revised accordingly. A specific section (D) on Crude Oil Washing (COW tankers only) is to be completed in the Oil Record Book, when the requirements of the Operations and Equipment Manual cannot be followed.

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Crude Oil Washing - 2.0 Introduction to Crude Oil Washing

2.0 INTRODUCTION TO CRUDE OIL WASHING

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Crude Oil Washing - 2.0 Introduction to Crude Oil Washing

2.1

Principles of Crude Oil Washing

Characteristics of Crude Oil as a Washing Medium to Remove Crude Oil Residue from Cargo Tanks Most crude oils contain relatively heavy components of waxy and asphaltic substances. During a voyage, these components settle out as sludge which builds up on the horizontal members of a tank’s structure. After the oil is discharged, the sludge remains and, unless it is removed, will build up over several voyages to eventually impede tank drainage. If the sludge is allowed to build up it will greatly reduce the carrying capacity of a ship. Crude Oil Washing (COW) is a tank-cleaning technique that has been adopted for use on crude oil carriers. It reduces the amount of slop water accumulated on a ship. The tanks are washed with a crude oil spray taken from the ship's cargo and delivered to a tank using fixed tank-cleaning machines. A COW system takes advantage of the solvent properties of crude oil. These properties are greatly augmented when delivered in a high pressure spray. Advantages of Crude Oil Washing versus Water Washing COW reduces the amount of slop water accumulated on a ship and is more economical than water washing, especially when hot water is used (water washing is time and labour intensive). COW is also very effective against the build-up of sludge on tank surfaces and reduces the need for manual mucking. Water is not the best medium for tank cleaning for the following reasons: • water contributes to the corrosion of tank structures; • sludge remains on board after water washing when operating Load-On-Top; • water washing introduces salt water to oil refineries; • water washing leads to large quantities of oil/water slops which require careful decanting; and

• water is incompatible with oil. Suitability of all Types of Crude Oil as a Washing Medium Not all crude oils are suitable for Crude Oil Washing; therefore, the type of crude on board must be taken into account. Section 9 of a vessel’s Operations and Equipment Manual lists crude oils that are not suitable for this purpose. Before Crude Oil Washing begins, the crude oil tank to be used as the source for driving the tank-cleaning machines must first be debottomed by at least one metre to eliminate residual water. This precaution is important because, when used for tank cleaning, oil/water mixtures generate large electrostatic charges. If a tank is particularly complicated the effectiveness of the tank-washing machine coverage is to be established by building a model of the tank and then shining pinpoint lights from the positions where tank-washing machines are located.

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Crude Oil Washing - 2.0 Introduction to Crude Oil Washing

Method of Producing “Dry” Washing Fluid Due to the hazard of electrostatic charges being generated by the movement of oil/water mixtures, only “dry” crude oil should be used for Crude Oil Washing. To ensure this, all tanks to be discharged should be debottomed by one metre before any Crude Oil Washing is started. Any oil in the slop tanks which has been used for Load-On-Top purposes must not be used. If the slop tanks are to be used they should first be discharged to shore and refilled with dry crude (after debottoming is completed). Maintaining Pressure in the Washing Medium The optimum pressure for Crude Oil Washing is 8.5 to 10.5 bar. This pressure is obtained by bleeding off from a main cargo pump discharge line into the Crude Oil Washing line, or by using special pumps that are fitted for COW and stripping duties only. If a low shore back-pressure or the loss of the hydrostatic head, during discharge, results in the line pressure being too low, the pressure must be increased by closing down an isolator valve on the discharge line. During Crude Oil Washing the quality of the inert gas must be frequently checked by a portable analyzer and the pressure and oxygen content must be continually recorded. The tank-washing-line pressure should be frequently monitored and the cycles of the machines carefully watched. Near the completion of the discharge, the line pressure will become low and washing must be carried out by re-circulation. The pump takes suction directly from the slop tanks and delivers into the tank-cleaning line to supply the machines and power the eductors. These eductors draw from the tanks being washed into the slop tank. This maintains the oil level in the slop tank. Crude Oil Washing and Ballasting in Double-Hull Tankers There are two major concerns in working with double-hull tankers during Crude Oil Washing and ballasting: Question: Depending on the degree of cleanliness, what cycles are required?

The cooling of the crude oil on the final wash during COW (i.e. crude oil temperature approximately 45°C and sea water about -1°C): The cooling of crude oil can occur when the vessel is discharging cargo and loading ballast. As the cold ballast water cools the steel tanks and warmer cargo the crude oil is cooled to the point of solidification. This condition makes pumping impossible and the remaining cargo creates many problems.

Ballasting - double-hull tankers: In single-hull tankers, the metacentric height is usually such that these vessels are generally stable in all conditions of loading and ballasting. However, the introduction of double hulls in tanker design is likely to change this situation. The main problem to be encountered would probably be free-liquid-surface in the cargo and double-bottom tanks.

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Crude Oil Washing - 4.0 Operational Procedures and Processes

Stripping System

The stripping system must be capable of removing oil at the rate of 1.25 times the total throughput of all tank-cleaning machines that are operated simultaneously when washing the bottom of the cargo tanks. Level gauges, hand dipping and stripping-system-performance gauges must be provided for checking that the bottom of every cargo tank is dry after Crude Oil Washing. Equipment must be provided for monitoring the efficiency of the stripping system. The equipment should have remote read-outs located in the cargo control room.

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Crude Oil Washing - 5.0 Safety Aspects

5.0 Safety Aspects

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Crude Oil Washing - 5.0 Safety Aspects

5.1

Inert Gas System

Essential Requirement for Crude Oil Washing Inert gas (IG) is an essential requirement for Crude Oil Washing. Research has shown that water washing can generate huge levels of electrostatic charge. An electrical charge of sufficient magnitude acts as an ignition source and is all that is needed to set off an explosion in a flammable atmosphere. This very situation caused three explosions on VLCCs off the coast of Africa in 1969. The three explosions had several common features: • the ships had the same type of fixed tank-washing machines; • all were water washing centre tanks at the time; • two of the ships were using bottom-blowing systems to ventilate tanks before and during tank washing; and all explosions occurred in the tropics.

• Eventually it was concluded that an electrostatic charges were the cause of the explosions. A number of experiments were conducted on the British Surveyor, which was fitted with an IG system. The objective of these experiments was to take electrostatic measurements in cargo tanks during: 1.

cold washing with oil/water mixtures containing from 90% to 5% oil;

normal cold washing for clean ballast;

hot washing at two temperatures with a mixture containing 95% water and 5% oil; and

hot washing with tank cleaning chemicals.

The tests were carried out on centre tanks when doing cold re-circulatory washing with oil/water mixtures and hot washing at temperatures of 110°F and 150°F with a minimum of oil in the mixture. The results of the tests were that: • the least amount of electrostatic charge was generated when 100% crude oil or 100% water •

was used as the washing medium; and the highest readings were obtained when using mixtures of about 95% crude and 25% crude. Zero readings occurred for mixtures containing 60% crude and 20% crude

During these tests, the hydrocarbon vapour generation in the cargo tanks during Crude Oil Washing was measured. The findings were that despite high vapour generation during Crude Oil Washing, it was impossible to keep the vapour concentration above the flammable limit throughout the tank at all times. Without inert gas, large flammable regions could exist anywhere in a tank during COW. MARPOL 73/78 now makes it mandatory for crude oil tankers of 20,000 dwt and above and product carriers of 30,000 dwt and above to carry inert gas systems.

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Crude Oil Washing - 5.0 Safety Aspects

Figure 8 - Charge Densities Created by Oil/Seawate Mixtures

Measurement Requirements and the Testing of Ballast Samples To obtain a Crude Oil Washing notation on its International Oil Pollution Prevention Certificate, a ship needs to go through a stringent inspection and survey by its national administration officials. This process involves the following three areas: 1.

An inspection of tanks after they have been washed with crude oil;

An inspection of the Crude Oil Washing installation; and

The measurement of ballast samples.

Inert Gas on Deck Vented gases from the mast risers or other sources, possibly due to wind conditions, may fall around the deck area. These gases may be oxygen deficient and harmful to crew personnel. Checks should also be made for H2S and, if the TLV of 10 ppm is detected, only personnel wearing respiratory protection equipment should be allowed on deck. Before tank entry, to ensure the dilution of the toxic components of inert gas to below TLV, gas freeing should continue until tests with an oxygen analyzer show an oxygen level of at least 21% by volume, a flammable gas level of not more than 1% LFL and that the pressure level of toxic components is below TLV or zero.

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Crude Oil Washing - 5.0 Safety Aspects

Pyrophoric Ignition in Cargo Tanks Question: What is pyrophoric ignition?

The requirement to carry IG systems on crude carriers has probably increased the possibility of pyrophoric deposits. Sulphide gas reacts with rusted surfaces in the absence of oxygen and may cause such deposits to be present in the cargo tanks. These deposits can heat to incandescence when they come into contact with air. A failed inert gas system must be repaired and then restarted, or an alternative source of inert gas provided, before any discharge of cargo or ballast. As long as the cargo tanks remain inerted there is no danger of pyrophoric ignition. Critical Oxygen Content of Inert Gas On older crude oil tankers of 40,000 dwt or greater and new tankers of 20,000 dwt or greater, no tank is to be crude oil washed unless the inert gas system, as required by MARPOL 73/78, is in proper operation. Before a tank is crude oil washed the oxygen level is to be determined at a point one metre below the deck and at the middle region of the ullage space. Neither of these determinations should show that the oxygen level exceeds 8% by volume. Maintaining and Monitoring of Inert Gas Quality and Pressure Crude Oil Washing should not be carried out unless the inert gas system is working properly. The atmosphere in the tank must be maintained correctly; hence, it is important that the IG supply be of good quality and kept at the required pressure. Instrumentation should be fitted for continuously indicating and permanently recording the IG pressure when the IG is being supplied, showing: • the pressure of the IG supply mains forward of the non-return devices (low gas pressure •

alarm when IG is below 100 mm w.g.; there is also a gas alarm when the pressure in the IG main is high); and the high oxygen content of the IG in the supply main on the discharge side of the blowers (a high content of O2 in the IG main should activate an alarm when 8% by volume is exceeded).

Interruption of IG Supply of Good Quality Gas The IG supply is interrupted if the IG plant fails to supply inert gas with an O2 content of less than 8% by volume, or if there is loss of positive pressure in the cargo tanks, or if the IG plant fails to function properly. If pyrophoric ignition occurs, immediate action must be taken to prevent the ingress of air into the tanks (due to a vacuum suction). All Crude Oil Washing operations and any operation with the potential of causing pyrophoric ignition (i.e. all cargo operations) should stop and the IG deck-isolating valve should be closed. Tank-cleaning procedures should not commence or continue until the operation of the IG system has been restored or an alternative source of inert gas has been provided.

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Crude Oil Washing - 5.0 Safety Aspects

Masters are reminded that national and local regulations may require that the failure of the IG system be reported to: • harbour authorities; • the terminal operator; and/or • the port and flag state administrations. Provisions to Enable Tank Bottoms to be Sounded Question: When is a cargo tank considered to be dry?

To check that the bottom of every cargo tank is dry after Crude Oil Washing, level gauges, level-dipping and/or stripping-system-performance gauges should be provided. 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. Equipment and Procedures for Assessing Atmosphere in Inerted Tanks During Crude Oil Washing, tank atmospheres must be monitored frequently. The following instruments should be available to do this: • portable oxygen analyzers to measure the oxygen content of the tank atmosphere; • combustible gas indicators for testing the cargo tank atmosphere (this should be an •

instrument suitable for operation in inerted spaces. A catalytic combustion instrument is not suitable for use in inerted spaces); and before each tank is Crude Oil Washed the oxygen level should be determined at a point one metre below the deck and at the middle region of the ullage space and neither should show a level that exceeds 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. Safety Concerns Regarding Toxicity Levels in Inert Gas Tanker personnel should take every precaution to avoid the inhalation of, or contact with, inert gas vapours. Caution should be exercised when ullaging or sampling cargo, especially on ships not equipped with vapour locks. The low oxygen content of inert gas can rapidly cause asphyxiation. Care should be taken to avoid standing in the path of vented gas during measuring and sampling. The main hazard with inert gas is its low oxygen level; however, it also contains traces of hazardous toxic material. Some of its toxic components are nitrogen dioxide (i.e. NO2 with a TLV of 3 ppm), sulphide dioxide (i.e. SO2 with a TLV of 2 ppm) and carbon monoxide (i.e. CO with a TLV of 25 ppm). Sulphide dioxide causes irritation of the eyes, nose and throat and may cause breathing difficulties in some people. Carbon monoxide restricts oxygen uptake by the blood, causing a chemically induced form of asphyxiation.

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Crude Oil Washing - 5.0 Safety Aspects

5.2

Electrostatic Charges

Electrostatic charges present fire and explosion hazards during the handling of petroleum. Certain operations can give rise to accumulations of electric charges which may be released suddenly and with sufficient energy to ignite flammable hydrocarbon gas/air mixtures; there is, of course, no risk of ignition unless a flammable mixture is present. There are three basic stages leading up to such a hazard: 1

Charge separation;

Charge accumulation; and

Electrostatic discharge.

All three of these are necessary for electrostatic ignition. 1.

Charge Separation

Charge separation occurs at the interface between two dissimilar materials. The interface may be between two solids, between a solid and a liquid or between two immiscible liquids. At the interface, a charge of one sign (e.g. positive) moves from material A to material B so that materials A and B become negatively and positively charged, respectively. While the materials stay in contact and are, relative to each other, the charges are extremely close together. The voltage difference between these charges of opposite sign is then very small and no hazard exists. The charges can be widely separated by many processes such as: • the flow of liquids (e.g. petroleum or mixtures of petroleum and water) through pipes or • • •

fine filters; the settling of a solid or an immiscible liquid through a liquid (e.g., rust or water through petroleum); the ejection of particles or droplets from a nozzle (e.g. steaming operations); the splashing or agitation of a liquid against a solid surface (e.g. water washing operations or the initial stages of filling a tank with oil); and the vigorous rubbing together and subsequent separation of certain synthetic polymers.

• When charges are separated, a large voltage difference develops between them. Also, a voltage distribution, known as an electrostatic field, is set up throughout the neighbouring space. For example, a charged petroleum liquid in a tank produces an electrostatic field throughout the tank both in the liquid and in the ullage space. The charge on a water mist, created by tank washing, produces a field throughout the tank.

If an uncharged conductor is present in an electrostatic field it has approximately the same voltage as the region in which it is located. Furthermore, the field causes a movement of charge within the conductor; a charge of one sign is attracted by the field to one end of the conductor and an equal charge of opposite sign is left at the opposite end. Charges separated in this way are known as induced charges and as long as they are separated by the presence of the field are capable of contributing to an electrostatic charge.

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Crude Oil Washing - 5.0 Safety Aspects

Charge Accumulation

Charges which have been separated attempt to recombine and neutralize each other. This process is known as charge relaxation. If one or both of the separated materials carrying a charge is a poor electrical conductor, recombination is impeded and the material retains or accumulates a charge. The period of time during which the charge is retained is characterized by the relaxation time of the material and is related to the material’s conductive characteristics: the lower the degree of conductivity the greater the relaxation time. If a material has a comparatively high degree of conductivity, the recombination of charge is rapid and can counteract the separation process. Consequently little or no electrostatic charge would accumulate. A highly conductive material can only retain or accumulate charge if it is insulated, by means of a poor conductor; the rate of loss of charge then depends on the relaxation time of the insulating material. The important factors governing relaxation therefore relate to the electrical conductive properties of the separated materials and the conductive properties of any interposing materials. 3.

Electrostatic Discharges

Electrostatic breakdown, between two points, giving rise to a discharge depends on the strength of the associated electrostatic field. This field strength, or voltage gradient, is found approximately by dividing the difference in voltage between the points by their distance apart. A field strength of about 3000 kilovolts per metre is sufficient to cause breakdown of air or petroleum bases. The field strength near protrusions is greater than the overall field strength; therefore, discharges generally occur at points of protrusion. A discharge may occur between a protrusion and the space in its vicinity without reaching another object. These single electrode discharges are rarely incendive in the context of normal tanker operations. Sometimes there is a discharge between two adjacent electrodes. For example: • between sampling apparatus lowered into a tank and the surface of a charged petroleum liquid; and

• between an ungrounded object floating on the surface of a charged liquid and the adjacent tank structure.

Two-electrode discharges may be incendive if various requirements are met. These include: • the discharge gap is short enough to allow the discharge to take place, with the present voltage difference, but not so short that any resulting flame is quenched; there is sufficient electrical energy to initiate combustion; and the release of this energy into the discharge gap is nearly instantaneous.

• • Certain oils, which offer a high resistance to current flow, are known to accumulate and store electrical charges. Other oils are non-accumulators and may be loaded without precaution as they readily conduct electricity and do not build up an electric charge.

ãMarine Institute

School of Maritime Studies Offshore Safety and Survival Centre Revised - Dec/2003

Crude Oil Washing - 5.0 Safety Aspects

Clean oils such as the following are known to be accumulators: • natural gasolines; • motor and aviation gasolines; • kerosene; • white spirits; • jet fuels; • naphtha; • heating oils; • heavy gas oils; • clean diesel oils; and • lubricating oils. However, a clean oil containing an antistatic additive may be handled as a non-accumulator provided its rate of conductivity is known to be greater than 100 picosiemens per metre. Some examples of non-accumulators are: • crude oils; • bitumens; • black diesel oils; and • residual fuels. The most important countermeasure in preventing an electrostatic hazard is to bond all metal objects together. Bonding eliminates the risk of dangerous discharges. To avoid discharges from conductors to a ground, it is normal practice to include ground bonding. On a ship, grounding is effectively accomplished by making a connection to the metal structure of the ship, which is naturally grounded by the sea. Some examples of objects which might be electrically insulated in hazardous situations and which must therefore be grounded are: • Ship/shore hose couplings and flanges if one or more lengths of non-conductivehose or • • •

pipe are used in a string; Portable tank cleaning machines; Conductive manual ullaging and sampling equipment; and The float of a permanently fitted ullage device if it lacks a grounding path through the metal tape.

The most effective method of grounding is by means of a metallic connection between conductors. This method should be used whenever possible, although for electrostatic purposes an adequate ground can be made using a material of intermediate conductivity. Certain objects may be insulated from the hull during tanker operations. For example: • a metal object such as a can floating in an electrostatic-accumulating liquid; and • a loose metal object while it is falling in a tank during washing operations. Every effort should be made to ensure that such objects are removed from a tank since there is no possibility of deliberately grounding them. This necessitates careful inspection of tanks particularly after repairs. ãMarine Institute

School of Maritime Studies Offshore Safety and Survival Centre Revised - Dec/2003

Crude Oil Washing - 5.0 Safety Aspects

Some other sources of electrostatic hazards are: • the free fall of oil in tanks; • sprayed water mists; • steam mist clouds; • inert gas; • the discharge of carbon monoxide; • clothing and footwear; • synthetic materials; and • lightning. During Crude Oil Washing operations the cargo tanks are inerted. This means that the oxygen content in the cargo tanks is below that which is required for combustion. Therefore, in the event of an electrostatic discharge no explosion would occur. The inert gas system must be operational during Crude Oil Washing. In the event of a breakdown of this system, Crude Oil Washing must be halted.

ãMarine Institute

School of Maritime Studies Offshore Safety and Survival Centre Revised - Dec/2003

Crude Oil Washing - 5.0 Safety Aspects

~NOTES~

達Marine Institute

School of Maritime Studies Offshore Safety and Survival Centre Revised - Dec/2003

Crude Oil Washing - 6.0 Maintenance

6.0 Maintenance

達Marine Institute

School of Maritime Studies Offshore Safety and Survival Centre Revised - Dec/2003

Crude Oil Washing - 6.0 Maintenance

6.1

Maintenance of Plant and Equipment

The objective of any maintenance program on board a vessel is to maintain the integrity and reliability of the ship’s structure and all its components. The two basic types of maintenance are mandatory maintenance and voluntary maintenance. Mandatory maintenance is performed to comply with all regulations imposed by regulatory bodies of the country of registry or by classification societies. Voluntary maintenance has the backing of the owner and the crew and is performed to minimize maintenance costs, to extend the service life of a ship and to increase the safety of a ship and crew. The Crude Oil Washing system requires regular maintenance and inspections to ensure reliability and to minimize vessel downtime. The system pipelines require pressure testing with maximum discharge pressure before each arrival at a port where Crude Oil Washing is to take place. All pipes and connections should be inspected for signs of leaks and corrosion. All support brackets and flanges should be checked for damage. Any deficiencies should be corrected and an appropriate record kept of all repairs. All mechanical equipment should be operated and checked according to the manufacturer’s recommendations. The manufacturer’s recommendations and schedules may sometimes have to be adjusted if equipment use and conditions dictate. All tankers should have Operations and Equipment Manuals that contain inspection and test procedures. It is important that these procedures be followed as they have been designed for that particular vessel and will provide the most effective means of maintaining a safe and efficient ship. Presently, all tankers have a planned maintenance system in place. Some vessels have computerized maintenance and inventory systems. Whatever the system, it is important that it be adhered to and that all repairs, tests and inspections be duly recorded.

ãMarine Institute

School of Maritime Studies Offshore Safety and Survival Centre Revised - Dec/2003

Crude Oil Washing - Appendix A- References

APPENDIX A - REFERENCES

達Marine Institute

School of Maritime Studies Offshore Safety and Survival Centre NPC Approved - Rev. Dec/2003

Crude Oil Washing - Appendix A- References

REFERENCES: Boughton, R. COW Technology for the 1990s. Paper for the Institute of Marine Engineers Transactions, Volume 104, Part 3. ISSN 03093948. Marine Management (Holdings) Ltd., London: 1992. Canada Shipping Act and Regulations. ISBN 0 660 55696 0. Ministry of Supply and Services, Ottawa: 1990. International Maritime Organization, Inert Gas Systems. ISBN 92 801 12627. London: 1990. International Maritime Organization, Model Course 1.02: Advanced Training Program on Oil Tanker Operations. London: 1988. International Maritime Organization, MARPOL 73/78 Consolidated Edition. ISBN 92 801 1280 5. London: 1992. International Maritime Organization, International Conference on Training and Certification of Seafarers, 1978. ISBN 92 801 1085 3. London: 1978. Reprinted 1982. International Maritime Organization, Crude Oil Washing Systems. ISBN 92 801 1133 7. Revised Ed. 1983. London: 1984. International Chamber of Shipping OCIMF, and International Association of Ports and Harbors, International Safety Guide for the Operation of Oil Tankers and Terminals. ISBN 0 900886 88 9. Fourth Edition. Witherby & Co. Ltd., London: 1994. Marton, G.S. Tanker Operations. ISBN 0 87033 240 6. Cornell Maritime Press, Inc., Centreville, Md.: 1978. OCIMF, Clean Seas Guide for Oil Tankers. ISBN 0 948691 158. London: 1989. Polytech International, Ships Operational Safety Manual. ISBN 0906 314 09 7. 1979.

達Marine Institute

School of Maritime Studies Offshore Safety and Survival Centre NPC Approved - Rev. Dec/2003

Crude Oil Washing - Appendix B- Course Description

APPENDIX B - COURSE DESCRIPTION

達Marine Institute

School of Maritime Studies Offshore Safety and Survival Centre NPC Approved - Rev. Dec/2003

Crude Oil Washing - Appendix B- Course Description

COURSE OUTLINE: 1.0 National and International Legislation and Regulations 1.1

Canada Shipping Act and Regulations

1.2

IMO Conventions and Guidelines

2.0 Introduction to Crude Oil Washing 2.1

Principles of Crude Oil Washing

2.2

Benefits of Crude Oil Washing

2.3

Principles of Effective Use of Slop Tanks and Oil Discharge Monitors

3.0 Equipment 3.1

Tank Washing Machines

3.2

Piping Arrangements for Crude Oil Washing Systems

3.3

Driving Medium

3.4

Stripping Systems

3.5

Pumps and Eductors

4.0 Operational Procedures and Processes 4.1

Operational Procedures

4.2

Effectiveness of Crude Oil Washing

5.0 Safety Aspects 5.1

Inert Gas System

5.2

Electrostatic Charges

6.0 Maintenance of Plant and Equipment

達Marine Institute

School of Maritime Studies Offshore Safety and Survival Centre NPC Approved - Rev. Dec/2003

Crude Oil Washing - Appendix B- Course Description

LEARNING OBJECTIVES: THE EXPECTED LEARNING OUTCOME IS THAT THE STUDENT WILL BE ABLE TO: 1.0 National and International Legislation and Regulations 1.1

Canada Shipping Act and Regulations

– Discuss how the Oil Pollution Prevention Act and Regulations applies to Crude Oil Washing.

– Discuss how the Occupational Health and Safety Act and Regulations applies to Crude Oil Washing. 1.2

IMO Conventions and Guidelines

– Discuss the International codes and regulations as they apply to the installation and operation of Crude Oil Washing systems.

– Discuss how MARPOL 73/78, SOLAS Regulations Chapter 2, Oil Record Book and Operations and Equipment Manual apply to washing with crude oil: 2.0 Introduction to Crude Oil Washing 2.1

Principles of Crude Oil Washing

– Describe the characteristics of crude oil as a washing medium to remove crude oil residue from cargo tanks.

– List the advantages of Crude Oil Washing as compared to water washing. – Explain why every type of crude oil is not suitable for use as a washing medium. – Define the requirements for tank coverage for a Crude Oil Washing system to be acceptable for certification.

– – – – – – 2.2

Outline the methods of producing a “dry” washing fluid. Explain how to maintain the required pressure in the washing medium. Discuss Crude Oil Washing and ballasting in double-hulled tankers. Discuss Crude Oil Washing between ports in a multiple discharge cargo. Identify the priorities for the washing of cargo tanks. Define “clean” and “dirty” ballast.

Benefits of Crude Oil Washing

– Outline the principles behind the Retention On Board (ROB) and Load-On-Top (LOT) systems of oil pollution reduction.

– – – –

Discuss the effects of Crude Oil Washing on the quantities of oil involved. Explain why Crude Oil Washing increases effective cargo carrying capacity. Explain why Crude Oil Washing improves cargo out-turn. Describe the reduction in oil pollution attributable to the use of Crude Oil Washing techniques.

– Describe how Crude Oil Washing reduces the contamination of cargo by salt water. – Explain why Crude Oil Washing reduces tank corrosion. 2.3

Principles of Effective Use of Slop Tanks and Oil Discharge Monitors

– Outline the limitations on the discharge of oil into the sea. – Describe a modern slop tank system. – Discuss the build-up and decanting of residues in the slop tanks.

ãMarine Institute

School of Maritime Studies Offshore Safety and Survival Centre NPC Approved - Rev. Dec/2003

Crude Oil Washing - Appendix B- Course Description

– Describe the operation of an Oil Discharge Monitor. – Explain how to use a modern slop tank system when: Crude Oil Washing in general, Crude Oil Washing the last tank, completing discharge of cargo, deballasting, and tank washing. 3.0 Equipment 3.1

Tank Washing Machines

– Describe the characteristics, features of construction and operating parameters of deck-mounted and submerged washing machines.

– State the number and location of washing machines required in each tank. – Indicate the number of machines encountered in modern VLCCs and the parameters for this decision.

– Indicate the minimum number of portable drivers which must be carried if a vessel is designed with a modern VLCC system.

– Explain the terms “top wash”, “bottom wash”, and “wash cycle”. – Describe how the operation of each washing machine is verified. 3.2

Piping Arrangements for Crude Oil Washing Systems

– Explain why all piping must be of sufficient strength to withstand the pressures to which it is subjected.

– State why each cargo tank must have a separate and independent branch of the distribution system.

– Explain why the piping is permanent, suitably jointed, and independent of the fire mains. – Explain why portions of the cargo system may be incorporated into the washing system. – Explain why the piping system may also serve to water wash and/or ballast the cargo tanks.

– Explain why no section of the piping may go through the vessel’s accommodation spaces. – Describe the means for isolating each of the cargo tanks. 3.3

Driving Medium

– Explain why the driving medium is outgoing cargo which is bled from the discharge side of the pumps.

– State the minimum and maximum pressure permitted in the system. – State the maximum throughput to any one tank. – Describe direct and re-circulatory drive systems. 3.4

Stripping Systems

– Explain why an efficient stripping system must have the capacity to remove 125% of the oil used for washing.

– Explain why the system must be designed to keep the bottom of the tank free from oil and sediment during the last stages of stripping the tank.

– Explain how a tank is verified as being “dry”. – Detail the provisions made for cargo lines and crude oil wash lines and pumps to be drained and stripped. 3.5

Pumps And Eductors

– State why the stripping suction must be provided by a positive displacement pump, self-priming centrifugal pump, or an eductor.

– Differentiate between the operating principles and the characteristics of positive displacement pumps, self-priming centrifugal pumps, and eductors.

– Describe how individual tanks are isolated from a common stripping line. ãMarine Institute

School of Maritime Studies Offshore Safety and Survival Centre NPC Approved - Rev. Dec/2003

Crude Oil Washing - Appendix B- Course Description

– State why the carriage of more than one grade of cargo does not preclude the Crude Oil Washing of the tanks.

– Describe how the efficiency of the stripping system is measured. – State why the tank structure must facilitate oil drainage to the stripping suction. – Describe the trim under which tank stripping best functions. 4.0 Operational Procedures and Processes 4.1

Operational Procedures

– Explain the need for good communications and co-operation among those responsible for conducting a crude oil wash.

– Describe the information which must be contained in the Operations and Equipment Manuals.

– Discuss the use of checklists. – Describe the setting up, testing, and checking of Crude Oil Washing equipment. – Prepare Crude Oil Washing schedules for discharging a free-flow vessel, a pipeline vessel, and a partial free-flow vessel, taking into consideration the trim requirements for stripping and departure and cargo/ballast distribution for maintaining stress within limitations.

– – – – – – –

Design a Crude Oil Washing program, which minimizes extra berth time. Justify the precautions, which must be taken during a crude oil wash operation. Discuss ballasting for departure, using various pipeline configurations. Describe the water rinsing of departure ballast tanks after Crude Oil Washing. Discuss the requirement to measure the oil layer on top of the departure ballast. Explain how the thickness of the oil layer is measured. Describe how to avoid the venting of cargo tank vapours to the outside atmosphere during ballasting.

– Discuss the typical operations conducted on Crude Oil Washing equipment during a ballast passage. 4.2

Effectiveness of Crude Oil Washing

– Discuss how the effectiveness of the Crude Oil Washing system and its equipment is monitored. 5.0 Safety Aspects 5.1

Inert Gas System

– – – –

State why an inert gas system is an essential requirement for Crude Oil Washing. Explain the critical oxygen content of inert gas. Describe the maintenance and monitoring of inert gas quality and pressure. Outline the procedures to be followed in the event of an interruption to the supply of good quality inert gas.

– Explain “Pyrophoric Ignition”. – Describe the provisions made to enable tank bottoms to be sounded. – List the equipment and the procedures needed for assessing the atmosphere of an inerted cargo tank.

– Identify the safety concerns regarding the toxicity levels of inert gas.

ãMarine Institute

School of Maritime Studies Offshore Safety and Survival Centre NPC Approved - Rev. Dec/2003

Crude Oil Washing - Appendix B- Course Description

5.2

Electrostatic Charges

– Describe the generation of an electrostatic charge and the procedures adopted to minimize any potential differences.

– State the precautions which must be taken to avoid any uncontrolled incendive discharge of an electrostatic field. 6.0 Maintenance of Plant and Equipment

– State the necessity of and requirements for maintaining the integrity of the crude oil wash system pipelines on deck.

– Discuss the importance of following the manufacturer’s suggested maintenance guidelines and schedule.

– Explain the importance of following the testing procedures laid down in the Operations and Equipment Manuals.

ãMarine Institute

School of Maritime Studies Offshore Safety and Survival Centre NPC Approved - Rev. Dec/2003

Crude Oil Washing - Appendix B- Course Description

~NOTES~

達Marine Institute

School of Maritime Studies Offshore Safety and Survival Centre NPC Approved - Rev. Dec/2003