Oil Storage

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SHELL NIGERIA EXPLORATION AND PRODUCTION

COMPANY

COMPANY Ltd

Ltd

Bonga FPSO Bonga FPSO Bonga FPSO Bonga FPSO

Plant Operating Procedures Manual Plant Operating Procedures ManualPlant Operating Procedures Manual Plant Operating Procedures Manual

Volume 4 Volume 4 Volume 4 Volume 4

OIL STORAGE, HANDLING AND BALLAST SYSTEMS OIL STORAGE, HANDLING AND BALLAST SYSTEMS OIL STORAGE, HANDLING AND BALLAST SYSTEMS OIL STORAGE, HANDLING AND BALLAST SYSTEMS

OPRM OPRM OPRM

OPRM----200320032003-2003--0304-030403040304

Version: 1.2

This document is not confidential.

The Copyright of this document is vested in Shell Nigeria Exploration and Production Company Limited. All rights reserved. Neither the whole nor any part of this document may be reproduced, stored in any retrieval system or transmitted in any form or by any means (electronic, mechanical, reprographic, recording or otherwise) without the prior written consent of the copyright owner.

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Document Status Information

1.0. DOCUMENT CONTRO

1.0. DOCUMENT CONTROL

L

1.1. Change History 1.1. Change History1.1. Change History 1.1. Change History

Date Date Date

Date VersionVersionVersionVersion AuthorAuthor AuthorAuthor Ref Ref Ref Ref Indicator Indicator Indicator

Indicator Change DescriptChange DescriptionChange DescriptChange Descriptionion ion

01/03/04 1.0 ODL – Issue of document for

signature.

31/08/05 1.1 ODL – Amendment to Part 1

Section 2 Paragraphs 2.2 and 2.3, and Section 5 Paragraphs 2.1 and 4. Part 2 Section 1 Procedure No 1/001 Valve Checklist 1 restructured; Valve Checklist 2 and its

procedure updated; Valve Checklist 3 restructured. Part 2 Section 2 Procedure No 2/003 Danger notices and Step 4 altered.

Part 2 Section 3 Procedure No 3/001 Step 10 altered; Procedure No 3/002 Introduction altered; Procedure No 3/004 Preamble and Step 22.

30/04/06 1.2 ODL/SNEPCO – Amended throughout to

address outstanding HOLDs and to reflect the latest PFS (Rev 00). Amendments to Part 1 Section 5 Tables 5.2 and 5.3.

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2.0 2.02.0

2.0 PURPOSEPURPOSE PURPOSEPURPOSE

The purpose of this document is to provide guidance on the safe, efficient and environmentally aware operation of the Oil Storage, Handling and Ballast Systems.

It is one Volume within an overall suite of Volumes, which comprise the Bonga FPSO Plant Operating Procedures Manual (POPM). The full listing of Volumes is as follows:

Volume 1 Field and Facilities Overview Volume 2A Subsea Production System Volume 2B Subsea Waterflood System Volume 2C Subsea Control System Volume 2D Flow Assurance Guidelines Volume 3 Oil Separation and Treatment Volume 4

Volume 4Volume 4

Volume 4 Oil Storage, Handling and Ballast SystemsOil Storage, Handling and Ballast SystemsOil Storage, Handling and Ballast SystemsOil Storage, Handling and Ballast Systems Volume 5 Oil Metering and Export System

Volume 6 Vapour Recovery Compression System Volume 7 Field Gas Compression System

Volume 8 Gas Dehydration/Glycol Regeneration Systems Volume 9 Gas Export/Import/Lift Systems

Volume 10 Flare and Vent Systems

Volume 11 Produced Water Treatment Systems Volume 12 Waterflood System

Volume 13 Chemical Injection and Methanol Injection System Volume 14 Fuel Gas System

Volume 15 Heating Medium System Volume 16 Drainage Systems

Volume 17 Sewage Treatment Systems

Volume 18 Bilge and Oily Water Separation Systems Volume 19 Inert Gas System

Volume 20 Nitrogen Generation System Volume 21 Seawater System

Volume 22 Fresh and Potable Water Systems Volume 23 Diesel Fuel System and Incinerator Volume 24 Aviation Fuel System

Volume 25 Instrument and Utility Air System Volume 26 Deck Hydraulic Systems

Volume 27 Fire Protection Systems and Equipment Volume 28 Safety and Lifesaving Equipment

Volume 29 PSCS and ESS

Volume 30 Power Generation and Distribution Systems Volume 31 Black Start Procedures

Volume 32 HVAC Systems

Volume 33 Deck Machinery and Mechanical Handling Systems (Cranes, etc) Volume 34 Telecommunications

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3.0 3.03.0

3.0 SCOPESCOPE SCOPESCOPE

This document provides a detailed description of the plant and equipment, which comprise the Oil Storage, Handling and Ballast Systems, and includes step-by-step guidance on the operation of the system and its equipment, under both normal and abnormal operation.

4.0 4.04.0

4.0 TARGET READERSHIPTARGET READERSHIP TARGET READERSHIPTARGET READERSHIP

All SNEPCO staff, contractors and other third-party personnel who may be involved in the operation of the Oil Storage, Handling and Ballast Systems onboard the Bonga FPSO.

5.0 5.05.0

5.0 SPECIAL NOTESPECIAL NOTE SPECIAL NOTESPECIAL NOTE Not applicable.

6.0 6.06.0

6.0 ABBREVIATIONSABBREVIATIONS ABBREVIATIONSABBREVIATIONS

The abbreviations used within this document are listed at the end of these introductory pages.

7.0 7.07.0

7.0 REFERENCE INFORMATION/SUPPORTING DOCUMENTATIONREFERENCE INFORMATION/SUPPORTING DOCUMENTATION REFERENCE INFORMATION/SUPPORTING DOCUMENTATIONREFERENCE INFORMATION/SUPPORTING DOCUMENTATION

The primary reference/supporting documents, which have been either used or referred to in the development of this document, are listed at the end of these introductory pages. These are part of the available Operational Documentation which SNEPCO Offshore Operations (OO) has in place to support its day-to-day operations. These and many other documents are available within the SNEPCO Livelink System. Where appropriate, these documents have been cross-referenced within this document.

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Abbreviations

AC Alternating Current

ANSI American National Standards Institute API American Petroleum Institute

APWBT Aft Peak Water Ballast Tank

BA Breathing Apparatus

bara Bar Absolute

barg Bar Gauge

BASEEFA British Approvals Service for Electrical Equipment in Flammable Atmospheres

BBL Barrel

BOPD Barrel of Oil per Day

BPD Barrels per Day

BS&W Base Sediment and Water BWPD Barrel of Water per Day

CCR Central Control Room

CI Chemical Injection

CIGM Clean Inert Gas Main

CIV Chemical Injection Valve

COT Crude Oil Tank

COW Crude Oil Washing

CV Production Choke Valve

DC Direct Current

DCS Distributed Control System

DE Drive End

DIGM Dirty Inert Gas Main

ESD Emergency Shutdown

ESR 1 Process Shutdown

ESR 2 Surface Process Shutdown

ESR 3 Total FPSO Shutdown

ESS Emergency Support System

F&G Fire and Gas

FBHP Flowing Bottomhole Pressure

FC Fail Closed Valve

FCV Flow Control Valve

FG Flow Indicating Gauge

FIC Flow Indicating Controller

FLA First Line Ashore

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FPSO Floating Production, Storage and Offloading FPWBT Forward Peak Water Ballast Tank

FT Flow Transmitter

FTP Flowing Tubing Pressure

GA General Alarm

GOR Gas/Oil Ratio

H High Alarm

HH High Trip

HCU Hydraulic Control Unit

HCV Hand Control Valve

HMI Human Machine Interface

HOV Hand-operated Valve

HP High Pressure

HPI High Performance Insulation

HPU Hydraulic Power Unit

HSE Health, Safety and Environment

HVAC Heating, Ventilation and Air Conditioning

Hz Hertz (Frequency)

ID Internal Diameter

IG Inert Gas

IGF Induced Gas Flotation

IMO International Maritime Organisation

IP Intermediate Pressure

IS Intrinsically Safe

ISO International Standards Organisation

kW Kilowatt

L Low Alarm

LAT Lowest Astronomical Tide

LC Locked Closed

LCV Level Control Valve

LEL Lower Explosive Limit

LG Level Gauge

LIC Level Indicating Controller

LL Low Trip

LNG Liquefied Natural Gas

LO Locked Open

LOS Line of Sight

LP Low Pressure

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LT Level Transmitter

LU Level Unit

m3 _{Cubic Metres}

MAC Manual Alarm Callpoint

MCC Motor Control Centre

MEG Mono Ethylene Glycol

MIV Methanol Injection Valve

MMSCFD Millions of Standard Cubic Feet per Day

MOV Motor Operated Valve

m/s Metre per Second

MSDS Material Safety Datasheets

MW Megawatt

NB Nominal Bore

NC Normally Closed

NDE Non-drive End

NDT Non-destructive Testing

NGL Natural Gas Liquid

NO Normally Open

NPSHA Net Positive Suction Head Available

NRV Non-return Valve

OD Outside Diameter

ODMS Oil Discharge Monitoring System

OLI On-line Inspection

P&ID Piping and Instrument Diagram

PCV Pressure Control Valve

PDR Pressure Difference Ratio

PDS Differential Pressure Switch PDT Differential Pressure Transmitter

PFD Process Flow Diagram

PG Pressure Gauge

PIC Pressure Indicator Controller

PIL Process Interlocks

PIV Pigging Isolation Valve

PM Production Manifold

PMV Production Master Valve

ppm v/v Part per Million by Volume ppm wt/wt Parts per Million by Weight

PT Pressure Transmitter

PTW Permit to Work

RTJ Ring Type Joint

RV Relief Valve

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Abbreviations (cont’ d)

SCSSV Surface Controlled Subsea Safety Valve

SCU Subsea Control Unit

SDV Shutdown Valve

SI Statutory Instrument

SIL Shutdown Interlocks

Sm3_/hr _{Standard Cubic Metres per Hour}

SSDS Safety Shutdown System

STIL Startup Interlocks

SWL Safe Working Load

SWP Safe Working Pressure

SWV Sacrificial Wing Valve

TC Tank Cleaning

TCV Temperature Control Valve

TEG Tri-ethylene Glycol

TG Temperature Gauge

TIC Temperature Indicating Controller T/T Tangent to Tangent (Vessel Length)

TT Temperature Transmitter

TVP True Vapour Pressure

UEL Upper Explosive Limit

UPS Uninterruptible Power Supply

UV Ultraviolet

VDU Visual Display Unit

VRU Vapour Recovery Unit

WBT Water Ballast Tank

WI Water Injection

WSV Well Switching Valve

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Reference Information/Supporting Documentation

Project Data Project DataProject Data Project Data

Document No/R Document No/R Document No/R

Document No/Refefefef Document TitleDocument TitleDocument TitleDocument Title BON-AME-3GN-J-15658-005 Rev

A03

Ballast Tanks – PFS

BON-AME-3GN-J-15626-007 Rev A01

Cargo Storage and Handling – PFS (NAPA)

BON-AME-3GN-J-15626-013 Rev A01

PFS Cargo Storage and Handling

BON-SHI-P-00002-001/002/003-00

Ballast System (Sheets 1, 2 and 3)

BON-SHI-P-00002-004/005-00 Air Sounding System (Sheets 1 and 2) BON-SHI-P-00002-007-00 Position of Tank Gauging

BON-SHI-P-00002-008-00 Crude Oil Headers

BON-SHI-P-00002-009 to 016-00 Storage Compartments (1 to 8)

BON-SHI-P-00002-017-00 Storage Compartments 8 (Tank Utilities) BON-SHI-P-00002-08-00 Tank Cleaning and Nitrogen Headers BON-SHI-P-00002-019 to 024-00 Storage Compartments 1 to 7 (Utilities)

Vendor Data Vendor DataVendor Data Vendor Data

Vendor Vendor Vendor

Vendor Document NumberDocument Number Document NumberDocument Number Document TitleDocument TitleDocument TitleDocument Title

FRAMO FRAMO doc 1008 dated

2/7/2002/TS

Service Manual for Cargo Pumping System

SAAB BON/1DA2617/SAAB/000001 Load Computer

FRANK MOHN

BON/1JA0980/FRANK/000003 Ballast Pump

NIASCO BON/1YA1151/NIASCO/000001 Valve Remote Control System Ballast Valves

SAAB BON/1DA2177/SAAB/000002 COT Level Gauging System

CONSILIUM BON/1DA2160/CONSILIUM/0000 01

Remote Sounding System (Ballast, FO)

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GUNCLEAN BON/1FA1108/GUNCLEAN/0000 01

Fixed Tank Cleaning Machine

FRANK MOHN

BON/1JA0980/FRANK/000001 Cargo Oil Pump

SEIL BON/1SA1043/SEIL/000001 Oil Disch Monitoring System

SAAB BON/1DA2177/SAAB/000002 COT Level Gauging System

CONSILIUM BON/1DA2160/CONSILIUM/0000 01

Remote Sounding System (Ballast, FO)

HEMP Actions HEMP ActionsHEMP Actions HEMP Actions

No NoNo

No DescriptionDescription DescriptionDescription Control MeasureControl Measure Control MeasureControl Measure ODL ActODL ActODL ActODL Actionionion ion

1 Portable Cargo Pump (Part 2 Section 2 Procedure No 2/004).

Steps for hooking up the hoses need to give details about the minimum requirements such as pressure ratings, connection types, material of construction etc. Caution added to Part 2 Section 2 Procedure No 2/004.

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Main Table of Contents

Document Status Information

Abbreviations

Reference Information/Supporting Documentation

Part 1

Part 1 Part 1 –

––

– Technical Description

Technical Description

Section 1 Section 1Section 1

Section 1 System OverviewSystem OverviewSystem OverviewSystem Overview Section 2

Section 2Section 2

Section 2 Detailed Description Detailed Description Detailed Description Detailed Description –––– Cargo Loading Cargo Loading Cargo Loading Cargo Loading Sec

SecSec

Section 3tion 3tion 3tion 3 Detailed Description Detailed Description Detailed Description Detailed Description –––– Ballast System Ballast System Ballast System Ballast System Section 4

Section 4Section 4

Section 4 Detailed Description Detailed Description Detailed Description Detailed Description –––– Crude Oil Washing Crude Oil Washing Crude Oil Washing Crude Oil Washing Section 5

Section 5Section 5

Section 5 Detailed Description Detailed Description Detailed Description Detailed Description –––– Slops System Slops System Slops System Slops System

Part 2

Part 2 Part 2 –

––

– Operating Procedures

Operating Procedures

Section 1 Section 1Section 1

Section 1 System Operating ProceduresSystem Operating ProceduresSystem Operating ProceduresSystem Operating Procedures Section 2

Section 2Section 2

Section 2 Equipment Operating ProceduresEquipment Operating ProceduresEquipment Operating ProceduresEquipment Operating Procedures Secti

SectiSecti

Section 3on 3on 3 on 3 Supplementary Operating ProceduresSupplementary Operating ProceduresSupplementary Operating ProceduresSupplementary Operating Procedures

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PART 1 TECHNICAL DESCRIPTION

Section 1 System Overview

Section 2 Detailed Description – Cargo Loading

Section 3 Detailed Description – Ballast System

Section 4 Detailed Description – Crude Oil Washing

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Part 1 Technical Description

Section 1 System Overview

1.0 INTRODUCTION

Bonga FPSO is a spread moored barge shaped vessel at the Bonga field offshore Nigeria. It is moored with a 12-anchor spread in 1000m water depth and produces from a network of remote subsea wells connected to Bonga FPSO by a system of seabed pipelines and risers. Well fluids are treated in the topside processing facilities and dry crude oil is stored in the hull cargo tanks. Associated gas is exported by pipeline to the Liquefied Natural Gas (LNG) terminal at Bonny and any produced water is treated before being disposed of overboard. Treated seawater is pumped into the reservoir to maintain reservoir pressure and thus enhance oil recovery.

The Cargo and Ballast System can be broken down into the following five sub-sections:

• Crude Oil Loading and Storage • Ballast System

• Crude Oil Washing • Crude Oil Slops System • Crude Oil Offtake

These systems are primarily concerned with the safe storage of crude onboard Bonga FPSO, and counter-action of the effects of the crude on the vessel stability and structural integrity.

2.0 PROCESS

DESCRIPTION

Refer to Figure 1.1.

2.1 Crude Oil Loading and Storage

The crude oil, recovered from the well fluids, is stabilised before passing through the crude coolers to storage. The coolers reduce the temperature of the crude product to below 43.3°C. Isolation valves are fitted to the crude outlet line from the coolers upstream of the tie-in point of the produced oil line to provide topside isolation from storage.

Stabilised crude oil at a maximum flowrate of 1450m3_{/hr from the oil processing} facilities can be loaded through a loading header and drop lines, fitted with hydraulically operated isolation valves, into selected Cargo Tanks as required in accordance with the pre-calculated loading plan. Each tank spur feeds the port centre and/or starboard cargo tank through a manual isolation and a hydraulically operated valve.

Loading into the cargo tanks is carried out on a continuous basis from the topsides processing module through the loading header and into the selected cargo tanks, normally the reception tank COT 3C. In the reception tank, some separation will take place to further reduce the water content.

From COT 3C the oil overflows a standpipe and the crude oil is cascaded by gravity to COT 2C and COT 4C from where it can be transferred via bottom transfer valves into adjacent tanks, or pumped to any other tank via the crude oil transfer header in

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Crude capacity of the 15 Crude Oil Tanks is 2,039,200 barrels (324,233m3_), however it is unlikely that all tanks will be completely filled as the crude is offloaded prior to reaching this point. If there is any delay in offloading due to problems with the tanker or offloading facilities it may be necessary to reduce and, in extreme cases, stop oil production.

A submerged, hydraulically driven, Cargo Oil Pump is provided in each COT to deliver crude from the associated tank to the discharge header for export (refer to Volume 5 Oil Metering and Export System (OPRM-2003-0305)) or to the transfer header when being decanted to another COT.

The Framo hydraulic system is designed for simultaneous operation of five submerged cargo pumps and two water ballast pumps.

The cargo piping system is configured to permit loading of crude oil into the cargo tanks and simultaneously offloading to the export tanker, using a combination of manual and remote hydraulically operated valves.

Each cargo tank and the two slop tanks are provided with a Saab radar tank level gauge, a Metritape backup level gauge, pressure sensors and temperature sensors that provide information to the DCS System and the Load Computer. In addition to these sensors, oil-water interface level sensors are provided in the slop tanks and the reception tank COT 3C.

Manual sounding points are also provided for each tank. These allow the operator to monitor the filling or emptying of each tank through tank dips as planned in a manually controlled loading or offloading programme in order to meet the design operational and safety requirements of Bonga FPSO.

Export of crude oil to the offtake tanker is normally via the offloading cargo system and the topsides SPM booster pumps to the calm buoy, or via the stern offloading facility if the calm buoy is unavailable.

Stripping facilities are provided on the cargo pumps to permit the operation of the cargo pumps when pumping from a tank when the level is very low, such as during the removal of any residual fluids from the tank prior to tank cleaning.

During the stripping process the submerged pump is operated under local control from the Framo control panel. Compressed nitrogen is injected at the base of the pump discharge column to lift the oil up through the column. Stripping ensures that the tank can be totally emptied prior to, and during, cleaning operations. It is not envisaged that the tanks will be stripped on the completion of every discharge, as Bonga FPSO storage capacity is much greater than the anticipated offloaded parcel size.

Oily water mixtures from the topsides equipment are normally routed to the port (dirty) slop tank but can, if required, be routed to the primary reception tank, COT 3C. Generally the liquid to these tanks is from drains or overflows in the process systems. When the produced water quality is such that it cannot be disposed of directly overboard, it is directed to one of these tanks.

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Gravity separation of the liquid phases in the port slop tank occurs allowing the oil and emulsion to be drawn off and returned to storage using the skimming pump. Clean water is then passed to the starboard slop tank, where it is polished prior to disposal overboard. The oil content of water to overboard disposal from the starboard slop tank is continually monitored to ensure it is below the maximum oil-in-water content.

Note: No transfer of crude oil, ballast or other significant weight transfer should be performed without first simulating the weight transfer on the loading computer, in compliance with the Cargo Planning Procedure.

2.2 Ballast

System

Refer to Figure 1.2.

A segregated Ballast System, in compliance with MARPOL 73/78, is used to adjust draft, trim and list of the hull to control transverse stability and structural loading. Ballast water is stored in 12 Water Ballast Tanks (WBTs), six down each side of the vessel outside of the crude oil tanks. A ballast main runs through each set of six wing tanks, allowing the distribution of ballast to and from each tank.

Two further ballast tanks, the fore peak tank and the aft peak tank, can also be used to take ballast if required. The arrangement of the ballast wing tanks and crude oil tanks provides protection to the crude tanks in the event of a rupture of the ship’s hull.

A certain amount of ballasting and de-ballasting can be carried out under gravity using the draught differential to fill or empty the tanks, although normally adjustment of ballast is carried out using the two ballast pumps located in BWT 4 Port and BWT 4 Starboard.

Level monitoring in the ballast tanks uses a Metritape System as primary and RF Admittance Probe type for backup and independent high-level indication, which provides level indication to the DCS and the Load Computer.

The Ballast System can also be used to supply seawater to the Tank Cleaning System when water washing is to be carried out.

An emergency inert gas connection to the Ballast System allows the ballast mains and tanks to be purged and inerted with inert gas should hydrocarbons leak into the tanks.

Seawater for ballasting is taken onboard via the port and starboard sea chests. The sea chests are manually treated with sodium hypochlorite for the control of marine growth.

Ballasting and de-ballasting operations are carried out from the DCS.

2.3 Tank Cleaning Systems

Crude oil washing is carried out to ensure the vessel is operated in accordance with the requirements of Regulation 13B of the Protocol of 1978 to the International Convention for the Prevention of Pollution from Ships 1973 (MARPOL 73/78).

Crude Oil Washing Systems should be operated in accordance with the IMCO Revised Specifications for the Design, Operation and Control of Crude Oil Washing

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Bonga FPSO is equipped with fixed tank cleaning machines served by fixed piping that can be used with either crude oil or seawater as a washing medium.

Although it is possible to crude oil wash several tanks simultaneously, the normal practice is to clean one cargo oil tank at a time. Normal tanker practice is to crude oil wash during discharge; on Bonga FPSO, crude oil washing will be performed between offtakes, thus avoiding reducing the pumping rate to the export tanker. The deck-mounted programmable washing machines can be selected to do a full clean or a bottom clean. If bottom clean is selected, the nozzle of the machine is elevated to no higher than 30° so that only the lower section of the walls and base of the tank are cleaned. A crude oil tank containing dry crude is used to supply the washing media to clean an empty tank.

The standard washing cycle is one full cycle followed by one bottom cycle on the programmable machines, while at the same time running the bottom-mounted machines. The time required for a full-cycle wash is approximately 60 minutes and the time duration of a tank bottom wash is approximately 30 minutes.

The residues and any sediment from the cargo oil tank being washed is pumped out using the submerged cargo pump of that tank discharging into the transfer header. From the transfer header it can be routed back to any cargo tank but normally to the tank which is supplying the wash fluid. It must never be routed to the slop tanks. The contents of the supply tank are then exported at the next offtake.

The manual isolation valves fitted on the individual feed lines to the cleaning machines should not be throttled to control the pressure of the crude oil supply to the machines.

Tank cleaning is normally followed by water washing if entry to the cargo tank is required.

Crude oil washing has the major benefit that cargo residues, which mainly consist of settled-out waxy and asphaltic substances, are dissolved and subsequently discharged with the rest of the cargo. This substantially reduces the amount of residues left in the cargo tanks. Crude oil washing can only be practised on vessels fitted with an Inert Gas System.

Tank cleaning, by cold or hot seawater washing, is normally only carried out on a tank when access is required for inspection or repair. The tank will normally be cleaned using the same fixed tank cleaning machines that are used for crude oil washing. Movement of water at high velocity can generate static electricity, therefore water washing is always performed in an inert atmosphere.

IT IS ESSENTIAL THAT THE OXYGEN LEVEL IN THE VAPOUR SPACE OF THE TANK IS MAINTAINED BELOW 5% (VOLUME) AT ALL TIMES

DURING TANK WASHING. FOR THIS REASON

THE INERT GAS SYSTEM MUST BE AVAILABLE PRIOR TO THE COMMENCEMENT OF TANK WASHING.

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During seawater washing operations, a closed or open cycle method may be used. In either case, tank washings are returned to the dirty slop tank for separation prior to disposing overboard via the Slop Tank System.

Seawater for tank washing is supplied to the tank cleaning header either from the clean slop tank or from the tank cleaning pump which is supplied from one of the starboard ballast pumps.

2.3.1 Closed Cycle Wash

If the slop tanks are to be used, before seawater washing operations commence, the port and starboard slop tanks are charged with seawater to an ullage of approximately 15m, sufficient to cover the outlet from the decant line in the clean slop tank.

The Slop Pump P-2605A submerged in the starboard slop tank is then started and utilised to pump clean seawater from the slop tank to the COW/TC header and thence to the tank cleaning machines on the tank to be washed.

At the same time, the submerged cargo pump located in the cargo oil tank being washed, strips the tank and returns the oily water from the tank to the port slop tank for separation. Following separation in the port slop tank, the recovered crude oil can be directed to a cargo tank using the skimmer pump.

The cleaned wash water from the port slop tank is decanted to the starboard slop tank then pumped overboard, monitored by the Oil Discharge Monitoring System (ODMS).

2.3.2 Open Cycle Wash

Open cycle washing is normally only used where there is insufficient clean seawater in the slop tanks, the starboard slop pump is not available or when washing the slop tanks.

During an open cycle wash, clean seawater is supplied by one of the starboard Ballast Pumps P-5804C/D from the starboard sea chest to the Tank Cleaning Pump P-2604 (refer to Part 1 Section 3).

There is a Filter P-2604-S-01 fitted with a differential pressure alarm on the suction side of the tank cleaning pump. A removable spool is fitted on the discharge side of the pump that must be fitted before the line is used.

As this is a hydrocarbon/non-hydrocarbon system interface it is important that this spool is removed when not in use to avoid the possibility of contaminating the ballast system.

The tank cleaning pump discharges into the COW/TC header. The procedure for stripping the tank being washed back to the port slop tank and subsequent treatment of the washings is the same as for a closed cycle wash.

The slop tanks can only be water washed using the open cycle method. The clean slop tank can be washed and the washings pumped to the port slop tank via the transfer main. The port (dirty) slop tank can be similarly washed to the starboard (clean) slop tank, however, in order to avoid contaminating the starboard slop tank it is preferable to direct the port slop tank washings via the transfer main to the cargo reception tank, 3C.

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The minimum operating parameters for any system during seawater washing are as follows:

• Seawater pressure at cleaning machine – 8barg • Flowrate deck-mounted machines – 87m3_/hour • Flowrate bottom-mounted machines – 39m3_/hour

A suitable number of closed ullage stations are provided for each cargo oil tank and slops tank to check the tank before and after cleaning. Two stands fitted with a vapour seal valve for use with appropriate 2in portable measuring instrument are provided for each cargo oil tank and slop tank. Two stands fitted with a vapour seal valve for use with appropriate 1in portable measuring instrument are provided for each cargo oil tank and one in each slop tank.

Tank washings are returned to the dirty slop tank for disposal whether open or closed cycle washing is employed.

2.4 Slop Tank System

The slop tanks are designed to treat mixtures of water and entrained oil from crude oil processing, cargo handling, cargo tank washings, open and closed drains and bilge systems. The port (dirty) Slop Tank T-2603 receives the mixtures to allow time for settling out before transfer of the water to the starboard (clean) Slop Tank T-2602.

Oil is removed from the upper part of the dirty slops tank by a Dirty Slops Tank Oil Skim Pump P-2603 which delivers the wet oil to a selected cargo tank, normally the reception tank 3C. Water is decanted to the starboard slop tank to allow further separation of oil before being pumped overboard.

The hydraulically driven skimming pump has a capacity of 100m3_{/hour. The suction} of the pump is set approximately 10m from the top of the tank.

Both slop tanks have a hydraulically driven slop pump installed in a similar manner to the cargo pumps. The pumps each have a capacity of 400m3_{/hour and can} discharge to either the transfer header or tank-cleaning header.

After confirmation by sampling that the oil-in-water content of the starboard clean slop tank is below 29ppm, water can be discharged overboard by the clean water overboard pump. The overboard discharge is monitored for quality by the ODMS and, if oil content is above specification, the flow is directed to the dirty slop tank. If a significant amount of oil collects on the surface of the clean starboard slop tank it can be skimmed from the surface by filling the tank with water. When the oil/water interface level is above the upper oil skim pipe inlet (70% tank height) the top level can be run off back into the port tank by hydrostatic head via the Remote-operated Valves 26-ZCV-108 and 26-ZCV-109.

There are also facilities to isolate the flow to the transfer header and pump to the Flare Scrubber V-4640 for disposal to the LP Separator V-2340A via the Flare Scrubber Pumps P-4640A/B/C.

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2.5 Crude

Oil

Offtake

The Offtake System is designed to offload the crude cargo from the vessel to an export tanker safely and efficiently, whilst also maintaining loading into the storage tanks from the production facilities. The export of crude oil from Bonga FPSO to the offtake tanker can be either via the SPM buoy or via the stern discharge system. A cargo pump is located in each of the cargo tanks and can be lined up to the discharge header or to the transfer header. The cargo pumps are powered by variable speed hydraulic motors and have their suction 100mm above the base of the tank. Each pump can deliver crude to the discharge header at 1500m3_/hour. The design export rate is 7500m3_{/hour, requiring up to five cargo tanks to be} pumped out simultaneously.

Nitrogen is injected at the base of the pump discharge column, this then lifts the oil in the column on a pocket of gas during stripping. Stripping ensures that the tank can be totally emptied prior to and during cleaning operations.

It is not envisaged that the tanks will be stripped on the completion of every discharge, as Bonga FPSO storage capacity is larger than the anticipated offloaded parcel size.

From the discharge header, the oil flows through the LACT metering package (fiscal meter) topsides before being directed to the topsides CALM booster pumps or to the stern discharge system.

Note: For details and operation of the Cargo Offloading and LACT Metering Systems reference should be made to Volume 5 Oil Metering and Export System.

3.0 HEALTH, SAFETY AND ENVIRONMENT (HSE)

3.1 General

The Cargo and Ballast System is located mostly in the vessel hull with some pipework on the vessel topsides, which is part of the main topside operating area. All personnel in the areas must have received training in, and be fully conversant with, the following:

• Location and use of fire and safety equipment in the area

• Recognition and response to all the vessel’s visual and audible alarms • Muster and evacuation procedures

• Escape routes

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3.2 Specific

Hazards

The Cargo and Ballast System handles crude oil and separated water at relatively low temperature (below 43°C) and pressure. Hazards are therefore low compared with other processing systems. The oil storage tanks are inert gas blanketed.

However, it is incorrect to assume that no hazards exist. Potential hazards include the following:

• If storage tank levels containing water/crude oil mix are left static for a period of time there is a real danger of large quantities of H2S being generated when the tanks are disturbed

• Most of the pumps and actuated valves used in operation of the system are driven from a high-pressure hydraulic system

• The cargo tanks are inerted using inert gas supplied from the inert gas system. The inert gas is an asphyxiant and may contain toxic gases such as carbon dioxide and carbon monoxide

• The Cargo and Ballast System employs various items of rotating equipment which must have all moving parts securely guarded at all times

• Excessive list, trim and hull stress causing structural integrity concerns • Oil pollution/spills to ballast tanks or to outside directly

All personnel must wear the appropriate protective clothing (overalls, safety helmet, gloves, goggles etc) when in the area, and wear hearing protection if noise levels in the area are high.

3.3 Environmental

Issues

3.3.1 Overboard Discharge

Since the Cargo, Slops and Ballast System discharges effluent overboard, environmental issues could arise if the discharge fails to meet the target requirement of less than 29ppm monthly average, with a maximum single occurrence of 40ppm. The water effluent is continuously monitored for oil at the discharge point and if its quality deteriorates below the acceptable value, the off-specification water is automatically diverted to the dirty slops tank for further treatment.

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DERIVED FROM PFD BON-AME-3GN-B-21192-006-C02 AC91003_VOL_004_001.ai FC FC FI PC PC PC PC PC FC TO FLARE SCRUBBER FROM CRUDE COOLER TO PRODUCTION FLARE HEADER FORWARD HEADER DRAIN TRANFER HEADER CRUDE OIL LOADING HEADER

A-5401 CARGO PUMP HPU A TO F L/C FROM OIL DEGASSING TANK FROM PRODUCTION SUMP AND COLLECTION TANKS TO SUBSEA FLOWLINE WARMUP PIGGING EXCHANGE REMOVABLE SPOOL REMOVABLE SPOOL STERN OFFLOADING ESD ESD ESD ESD TO SUBSEA FLOWLINE WARMUP PIGGING EXCHANGE CRUDE OIL WASH AND TANK CLEANING HEADER

BACKFLUSH/METER PROVING HEADER

DRAIN TANK

FROM FLARE SCRUBBER FROM INDUCED GAS FLOTATION SEPARATOR P-2604 TANK CLEANING BOOSTER PUMP FROM BALLAST SYSTEM (FOR TANK CLEANING)

INERT GAS FROM OIL DEGASSING TANK AFT CARGO HOSE CLEANING MANIFOLD AFT HEADER DRAIN T-2603 DIRTY SLOP TANK

T-2603 CLEAN SLOP TANK

TANK T-2601 M(5S) TANK T-2601 J(4S) TANK T-2601 G(3S)

SEAL LOOPS SEAL LOOPS

TANK T-2601 E(2S) TANK T-2601 A(1S) P-2605A SLOP TANK PUMP TANK T-2601 O(5P) P-2061O CARGO PUMP P-2061N CARGO PUMP P-2061L CARGO PUMP P-2061I CARGO PUMP P-2061F CARGO PUMP P-2061C CARGO PUMP P-2061C P-2061B P-2061A TANK T-2601 L(4P) TANK T-2601 F(2P) TANK T-2601 C(1P)

SEE NOTE 1

NOTE 1: ACTUAL ARRANGEMENT (TYPICAL FOR ALL CARGO PUMPS) FROM I/G FLOTATION SEPARATOR FROM PRODUCED WATER TANK DISCHARGE HEADER TRANSFER HEADER OVERBOARD VIA ODME P-2741A SPM BOOSTER PUMP A-0821A SPM BUOY LAUNCHER RECIVERS A-2740 LACT METER A-2741 METER PROVER A-2742 LACT SAMPLE CABINET A-0821B SPM BUOY LAUNCHER RECIVERS A-0821C SPM BUOY LAUNCHER RECIVERS P-2741B SPM BOOSTER PUMP P-2741C SPM BOOSTER PUMP P-0821A CIRCULATION PUMP P-0821B CIRCULATION PUMP DISCHARGE HEADER P-2605B SLOP TANK PUMP P-2603 SLOP OIL SKIMMING PUMP P-2602 CLEAN WATER DISCHARGE PUMP T-2601 N(5C) BACK-UP RECEPTION TANK T-2601 H(3C) BACK-UP RECEPTION TANK T-2601 K(4C) TANK T-2601 D(2C) TANK T-2601 B(1C) TANK TANK T-2601 I(3P) P-2061M CARGO PUMP P-2061J CARGO PUMP P-2061G CARGO

PUMP P-2061ECARGO PUMP P-2061A CARGO PUMP P-2061B CARGO PUMP P-2061D CARGO PUMP P-2061K CARGO PUMP P-2061H CARGO PUMP

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Figure 1.2 – Ballast Facilities Overview

A.P.T T-6501(P) No 6 WBT (P&S) T-5801(P) T-5801(S) No 5 WBT (P&S) T-5801(P) T-5801(S) No 4 WBT (P&S) T-5801(P) T-5801(S) No 3 WBT (P&S) T-5801F(P) T-5801G(S) No 2 WBT (P&S) T-5801D(P) T-5801E(S) No 1 WBT (P&S) T-5801B(P) T-5801C(S) FPT T-5801A SLOP OIL TANK (P) P-5804A/B SUBMERGED BALLAST PUMPS

P-5804C/D SUBMERGED BALLAST PUMPS LOAD WATER

LINE

FROM

SEA CHEST CHLORINE DOSING TO ATMOSPHERE UPPER DECK SLOP OIL TANK (S) FROM SEA CHEST FROM CLEAN

INERT GAS SYSTEM

FROM CLEAN INERT GAS SYSTEM TO CARGO TRANSFER HEADER TO TANK CLEANING PUMP CHLORINE DOSING LOAD WATER LINE

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Part 1 Technical Description

Section 2 Detailed Description – Cargo Loading

Table of Contents (cont’d)

FIGURES

Figure 2.1 – Graphical Interface – Cargo Headers ... 20 Figure 2.2 – Graphical Interface – Cargo Storage ... 21 Figure 2.3 – Hull Tanks – Level System Schematic... 22

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1.0 INTRODUCTION

The purpose of the Cargo Loading System is to allow, in conjunction with the ballast system, crude oil cargo to be distributed to the cargo oil tanks to maintain the vessel’s stability within the specified design envelope to avoid causing excessive stresses or bending moments in the hull. The cargo storage tanks are used to store the treated and stabilised crude oil production for regular offloading, approximately every 5 days, to the tankers via the single point buoy mooring system or the Stern Discharge System (when the single point mooring buoy is not available).

The cargo loading facilities consists of the following pieces of equipment: • Loading Header

• Cargo Storage Tanks • Transfer Headers

Loading into the cargo tanks is carried out on a continuous basis from the topsides processing module through the loading (rundown) header and into the selected cargo tanks.

Refer to the following P&IDs:

• BON-AME-3SP-B-21425-001 Crude Cooler • BON-SHI-008-P-00002-008 Crude Oil Headers • BON-SHI-008-P-00002-011 Storage Compartment 3 • BON-SHI-008-P-00002-012 Storage Compartment 4 • BON-SHI-008-P-00002-013 Storage Compartment 5 • BON-SHI-008-P-00002-014 Storage Compartment 6 • BON-SHI-008-P-00002-015 Storage Compartment 7

• BON-SHI-008-P-00001-012 Position of Tank Gauging and Hand Dipping System

2.0 EQUIPMENT

DETAILS

2.1 Loading

Facilities

Refer to Figure 1.1 or P&IDs BON-SHI-008-P-00002-011 Storage Compartment 3, BON-SHI-008-P-00002-008 Crude Oil Headers and BON-AME-3SP-B-21425-001 Crude Cooler.

Equipment Description

Processed oil from the crude oil coolers flows down the rundown line through the Isolation Valve 25-MOV-401 into the 20in (500mm) loading header. The loading header runs the length of the main deck to allow oil to be distributed to the 15 cargo tanks as required.

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There are five sets of cargo tanks numbered one to five from the forward end of the vessel. Above each set of tanks there is a 20in (500mm) (Nos 1 and 2 Tanks are 14in (350mm)) transverse manifold running, connected to the loading header through a remotely operated, hydraulically actuated butterfly valve. The manifold delivers oil to each of the three tanks in each set, Port, Centre and Starboard, through a drop line that extends almost to the bottom of each tank. The drop line is isolated from the manifold by a manual butterfly valve and a remotely operated, hydraulically actuated butterfly valve.

Each drop line has a removable spool to provide positive isolation of the tank from processed crude.

Each of the five manifolds also have a connection to the transfer header, described in the following paragraphs, complete with a remotely operated, hydraulically actuated butterfly valve.

2.2 Cargo Oil Storage Tank T-2601C (Typical)

Equipment Details Tag Number: T-2601C Capacity: 18,740m3 Maximum Operating Pressure: 1400mm WG (1.4barg) Minimum Operating Pressure: 400mm WG (0.4barg)

Refer to Figure 1.1 and P&IDs BON-SHI-008-P-00002-015 Storage Compartment 7, and BON-SHI-008-P-00002-024 Storage Compartment 7 Tank Cleaning and Utilities.

The following paragraphs describe Crude Oil Tank T-2601C (COT 1P). The other crude oil storage tanks have similar facilities.

Crude enters the tank via a 14in (350mm) nominal bore drop line from the loading header/manifold. The tank drop line incorporates Valve 26-ZCV-011 on the main deck.The valve is hydraulically actuated controlled from the DCS. Open and closed position signals are provided to the DCS by position switches.

In normal operation the tank is connected to the dirty inert gas header through Three-way Valve 55-SV-001 to maintain a positive pressure in the tank under all conditions. Pressure in the dirty inert gas header is controlled by Pressure Control Valve 55-PCV-104, set at 800mm WG (0.8barg), that relieves pressure to the vent riser. During offloading operations, pressure in the dirty inert gas header is maintained by operation of the inert gas generators.

Alternatively, during inerting and gas freeing operations Three-way Valve 55-SV-001 is used to connect the tank to the clean inert gas header. Venting in this operation is provided through a 10in (250mm) line which extends down to the bottom of the tank and connects to the crude oil purge main. Isolation of this line is provided by a manual Butterfly Valve 55-BUV-003. Refer to POPM Volume 19 Inert Gas System (OPRM-2003-0319).

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The tank is protected against over-pressurisation or vacuum conditions through Pressure/Vacuum Valve 55-RV-003 located on the 10in (250mm) connection to the vent main. This valve has two settings, 1600mm WG (1.6barg) to relieve over pressure conditions and -200mm WG (-0.2barg) to relieve vacuum conditions. Pressure relief is to the crude vent header.

For tank isolation, a spectacle blind is provided in the connection to the clean and dirty inert gas headers and the crude oil purge main. A removable spool is provided below the Relief Valve 55-RV-003 and on the oil loading line.

Communication with tanks in the next set is provided through the lower transfer valves, for example COT 1P can be connected to COT 2P by opening 26-ZCV-071 located in COT 1P and 26-ZCV-070 in COT Number 2P.

The valves can be used to transfer oil in either direction between tanks when filling tanks or to allow both tanks to be offloaded using one pump if the other is out of service.

The valves are operated from the DCS and position of the valves is indicated on the DCS by measuring the flow of hydraulic oil to the valve actuator.

In the cargo oil tank Sets 2 and 4, lower transfer valves are provided for transfer fore and aft, and between adjacent tanks in the set.

Offloading from the tank is carried out using the dedicated Cargo Pump P-2601C which takes suction from the bottom and towards the aft end of the tank. The pump is a hydraulically driven submersible Framo pump controlled from the DCS. In exceptional circumstances it can be controlled locally from the Framo panel. The pump discharges into the common manifold for the No 1 cargo tanks and on into either the discharge or transfer headers. Each pump has a discharge capacity of 1500m3_{/hr, at 150nlc. Refer to POPM Volume 5 Oil Metering and Export System} (OPRM-2003-0305).

As a backup there is one portable cargo pump which can be inserted into the tank through a Butterworth hatch in the tank top. A tie-in to the hydraulic supply is provided at each cargo tank to drive the pump. The portable pump discharges through a flexible hose to a 6in (150mm) connection at each cargo pump discharge valve.

This is an abnormal operation and the risks involved should be assessed via the PTW System. For details of the operation refer to Part 2 Section 2 Procedure No 2/005.

Level in each tank is measured by a SAAB radar type level measuring transmitter 26-LIT-002 installed in the top of the tank. The transmitter also measures tank pressure and temperature at three levels within the tank. A second system, 26-LZT-001, using Metritape provides an alternative level measurement. The second system also provides a shutdown capability.

Three fixed tank washing machines are fitted to the roof of the tank allowing it to be washed with either crude oil or water. The washing machines are isolated from the crude oil washing header by manual Isolation Valves 26-GTV-001/002/035.

In the centre tanks there are additional washing machines, located on the tank bottom, to provide additional cover in areas not accessible to the main machines.

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Facilities are provided to allow manual tank dips to be performed using the closed tank portable gauging system. The portable instrument can be mounted on 2 x 2in and 2 x 1in valves at deck level so that access is gained without venting the tank. This portable system can measure the oil level, the oil/water interface level and temperature at any point over the depth of the tank.

The cargo tanks are coated with coal tar epoxy for the top 2m and the bottom 3m, plus the upper side of all horizontal stringers. The remainder of the tank is uncoated. Sacrificial anodes are fitted based on the assumption that the bottom 1m of the tank being in contact with water 100% of the time.

COT No 100% Capacity _(m3₎ 98% Capacity _(m3₎ Pump Dry _(m3₎

1P&S: T-2601C&A 18,740.2 18,365.4 0.5 1C: T-2601B 23,771.1 23,295.7 0.5 2P&S: T-2601F&E 21,086.4 20,664.7 0.5 2C: T-2601D 14,862.0 14,564.8 0.5 3P&S: T-2601I&G 21,086.4 20,664.7 0.5 3C: T-2601H 26,751.6 26,216.6 0.5 4P&S: T-2601L&J 21,086.4 20,664.7 0.5 4C: T-2601K 26,751.6 26,216.6 0.5 5P&S: T-2601O&M 21,082.7 20,661.0 0.5 5C: T-2601N 28,742.7 28,167.8 0.5

Table 2.1 – Crude Oil Tank Capacities

2.3 Cargo Reception Tank T-2601H (COT 3C)

Equipment Details Tag Number: T-2601H Capacity: 26,751.6m3 Max Operating Pressure: 1400mm WG (1.4barg) Minimum Operating Pressure: 400mm WG (0.4barg)

Refer to Figure 1.1, P&IDs BON-SHI-008-P-00002-013 Storage Compartment 5 and BON-SHI-008-P-00002-022 Storage Compartment 5 Tank Cleaning and Utilities.

Two cargo reception tanks are provided, T-2601H (COT 3C) nominated as the primary and T-2601N (COT 5C) nominated as the backup if T-2601H is out of service.

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The tanks have all the same equipment as the cargo tanks described above in addition to facilities required to perform reception duties.

Oil is loaded through the 20in (500mm) drop line which deposits the freshly processed oil in the bottom of the tank.

Oil leaves the tank to adjacent tanks (COT 2C and 4C in the case of primary reception, and COT 5P and 5S in the case of backup reception) through a 20in (500mm) cascade line which is 70% (24m) of the height of the tank. The cascade line has a remotely operated Butterfly Valve 26-ZCV-101 controlled through the DCS. The valve position is indicated on the DCS.

The two centre tanks either side of the primary reception tank have lower transfer valves that will permit the free flow of crude oil from either centre tank into the adjacent wing tanks. It is intended that such an arrangement permit the ‘free flow’ loading of crude and can minimise deep well pumping.

Process drains and overflow lines can flow to either the dirty slop tank or to the reception tank. Initially these will be routed such that the drains will be routed to the dirty slop tank and the overflow routed to the reception tank. During later field life when produced water rates increase it is likely that they will both be routed to 3C as the ability of the dirty slop tank to handle them diminishes.

In the reception tank the process drains and overflow lines terminate at the bottom of the tank in seal pots 3m and 10m high respectively.

Separated water from the reception tanks is pumped by the Cargo Oil Pump P-2601H directly into the dirty slop tank via a dedicated oily water transfer line, for eventual disposal overboard.

In the event of a reception tank cargo oil pump failure, drain/free-flow transfer valves 26-ZCV-086/087 connected to the bottom transfer header are used to free flow the reception tank crude into an adjacent tank. The bottom header is kept as low as possible to facilitate this transfer.

The primary reception tank is fully coated with pure epoxy. Sacrificial anodes are fitted based on the bottom 3m of the tank being in contact with water 100% of the time.

Number 5 COT centre tank is designated as the ‘backup’ reception tank with similar piping and valve arrangements, coating and anodes.

2.4 Cargo Transfer Header

Oil from the crude oil pumps can be diverted from the transverse discharge manifold for a set of tanks through an isolation valve into the 20in (500mm) transfer header. The transfer header runs the length of the main deck to allow oil to be transferred between any tanks during loading and tank cleaning operations.

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3.0 CONTROL AND INSTRUMENTATION

3.1 Control

Overview

Refer to Figures 2.2 to 2.4, and P&IDs BON-SHI-008-P-00001-012 Position of Tank Gauging and Hand Dipping System, and BON-SHI-008-P-00001-024 Storage Compartment 7 Tank Cleaning and Utilities.

Cargo loading and associated de-ballasting operations are carried out in several stages. For loading and offtake, the Trim and Stability Book places the cargo tanks in two groups. Group A comprises Crude Oil Tanks 2 and 4, and Group B comprises Crude Oil Tanks 1, 3 and 5. However, any combination of tanks can be used as dictated by operational requirements, provided trim and stress requirements are met.

The loading sequence for the FPSO is dictated by the maximum available production rate of crude oil and the expected offloading schedule from the FPSO to the offtake tanker.

Following offtake, the cargo tanks are not normally completely stripped empty and will have a remaining level of around 1%. Cargo Offtake takes place when at least 75% of the one million barrel (159,000m3_{) parcel is available.}

Variation in the weight of consumables, such as diesel and freshwater, stored at the aft end of the vessel, also affect the trim and to a lesser extent stability of the vessel. Changes to the weight of consumables is balanced by adjusting the weight and distribution of ballast.

Tank loading valves are remotely controlled from the Central Control Room (CCR) with the tank levels monitored by the SAAB radar system. Tanks should normally be loaded with the production initially going to the reception tank and the oil then being distributed to the other tanks either by pumping or through a network of inter-tank sluice valves.

Prior to each loading/unloading operation, a loading or unloading plan will be issued by the Marine Supervisor.

The cargo oil tanks are provided with SAAB radar level gauges fitted to the main deck in the respective tanks. The analogue signals from the radar beams reflecting off the liquid within the cargo tanks are passed from the local instrumentation to the DCS and NAPA System in the control room.

The cargo tanks are additionally provided with deck-mounted temperature transmitters. The temperature transmitters consist of three temperature probes of lengths corresponding to lower, middle and upper levels of each cargo tank. A pressure transmitter is incorporated within the SAAB unit, giving a read out of the pressure within the individual tanks.

The temperature and pressure transmitter signals are linked with the radar ullage signals from each cargo tank and pass jointly back to the DCS System.

It is essential that cargo loading and de-ballasting is accomplished in the correct sequence to maintain vessel stability and provide for acceptable bending moments and shear forces on the FPSO.

The loading computer interfaces with the DCS to ensure that the cargo loading program or discharge program is monitored safely and will alarm if the actual operation differs significantly from the plan.

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In general, the cargo tanks will be loaded to a maximum 95% capacity but in exceptional circumstances this can be increased to 98%, in which case it must be carefully monitored.

3.2 Tank Level Gauging

The cargo, slop, chemical and diesel tanks are provided with SAAB tank radar level gauge system as the ‘primary’ level sensing system. This integral system consists of radar level transmitter, IG pressure transmitter and three sets of temperature sensors for each tank (eg 26-LIT-002, 26-PT-001 and 26-TT-001-003 for COT 1P). These signals are interfaced to the DCS via a serial link and used for monitoring/alarming.

The tank radar is an intrinsically safe system with a narrow beam parabolic antenna located on the tank top, which measures the ullage distance from the transmitter to the liquid surface.

It is hardwired to the central Level Unit (LU), which is located in the CER and communicates via a serial interface connection to the DCS. The LU serial link transmits level, pressure and temperature data to the DCS, as well as the status of the equipment for alarm purposes.

Using the SAAB radar transmitters, the level in the storage tanks is measured as ullage, which is the distance from the top of the tank to the top of the liquid measured in metres.

All tank levels will be displayed in ullage on the tank monitoring screens. The same data is also to be used to display the level (0 to 100%) on the process screens. Level is the measured linear value as a percentage of the measured range ie 0 to 100%.

The SAAB system provides a high level alarm when the tank level exceeds 95% and a low level alarm when the tank level falls below 5%.

The Pt100 Temperature Detectors are installed in a stainless steel guide pipe. To provide accurate data, three separate temperature elements are installed per guide pipe. Each tank therefore has three temperature readouts: at the top (27.3m), middle (16.8m) and bottom (5.8m). All cargo and slop tank temperatures are displayed on the DCS.

A pressure transmitter is fitted on the top of each cargo tank and both slop tanks to monitor the operating pressure of the tanks. All individual cargo and slop tank pressure readouts can be displayed on the DCS though normally the common system pressure only will be displayed.

A Metritape liquid level sensor (eg 26-LZT-001 for COT 1P) is fitted, mounted in a tube with the termination on the top of the tank. The system uses a pressure sensitive tape that varies in resistance according to submerged length.

The resistance signal provides a level indication which gives a high level alarm when the tank level exceeds 95% and a high-high level (safety) alarm when the tank level exceeds 98% of capacity. This system is totally independent of the radar gauges and is connected directly to the SSDS.

Signals from the level transmitter are also fed to the load computer which calculates volume and makes corrections for list and trim.

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When the tank level reaches 98%, a high level alarm is initiated in the DCS and the tank loading valve will close to prevent further loading into the tank. The valve cannot be re-opened until the level is below 94%.

Reception tank COT 3C is equipped with a Halla Oil/Water Interface Level Transmitter 26-LZT-037. This provides interface level indication and a high level alarm on the DCS to an accuracy of +/-0.5%.

Instrument Tag Number

Low Low

Trip Low Alarm High Alarm

High High Trip

Controller Set Point

Cargo Tank No 1 Port

26-LIT-002 4% 96%

26-PT-001 -100mmwg 1200mmwg

26-LZT-001 95% 98%

Cargo Tank No 1 Centre

26-LIT-004 4% 96%

26-PT-002 -100mmwg 1200mmwg

26-LZT-003 95% 98%

Cargo Tank No 1 Starboard

26-LIT-006 4% 96%

26-PT-003 -100mmwg 1200mmwg

26-LZT-005 95% 98%

26-LIT-008 4% 96%

26-PT-004 -100mmwg 1200mmwg

26-LZT-007 95% 98%

26-LIT-010 4% 96%

26-PT-005 -100mmwg 1200mmwg

26-LZT-009 95% 98%

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Low Low

26-LIT-012 4% 96%

26-PT-006 -100mmwg 1200mmwg

26-LZT-011 95% 98%

26-LIT-014 4% 96%

26-PT-007 -100mmwg 1200mmwg

26-LZT-013 95% 98%

26-LIT-016 4% 96%

26-PT-008 -100mmwg 1200mmwg

26-LZT-015 95% 98%

26-LIT-018 4% 96%

26-PT-009 -100mmwg 1200mmwg

26-LZT-017 95% 98%

26-LIT-020 4% 96%

26-PT-010 -100mmwg 1200mmwg

26-LZT-019 95% 98%

26-LIT-022 4% 96%

26-PT-011 -100mmwg 1200mmwg

26-LZT-021 95% 98%

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Low Low

26-LIT-024 4% 96%

26-PT-012 -100mmwg 1200mmwg

26-LZT-023 95% 98%

26-LIT-026 4% 96%

26-PT-013 -100mmwg 1200mmwg

26-LZT-025 95% 98%

26-LIT-028 4% 96%

26-PT-014 -100mmwg 1200mmwg

26-LZT-027 95% 98%

26-LIT-030 4% 96%

26-PT-015 -100mmwg 1200mmwg

26-LZT-029 95% 98%

Table 2.2 – Cargo Tank Alarm and Trip Settings (cont’d)

3.3 NAPA Loading Computer

Refer to P&ID BON/1DA2617/SAAB/000001 Load Computer.

The ‘Onboard NAPA’ software allows loading and unloading plans to be developed by the Marine Supervisor. The plans detail the magnitude of liquid volumes and sequencing transfer to and from the tanks, eg loading from the topsides process and unloading to the offtake tanker with concurrent ballasting/de-ballasting as required. Onboard NAPA is run in two separate locations; on a standalone PC situated in the Marine Supervisor’s office and on an identical online PC located in the CCR. The NAPA software does not perform control functions and is only used for monitoring, alarm generation and reporting. The same software version is loaded in both PCs and in the event of failure of the CCR PC it can be replaced by the other one.

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The loading and unloading plans are developed on the standalone copy of the software and transferred, by disk, to the DCS server mounted in the CCR engineering console.

The ‘Onboard NAPA’ program in the CCR PC monitors the vessel draft, the levels, pressures and temperatures in the cargo, ballast, clean and dirty slops, methanol, chemical, diesel and freshwater storage tanks. The vessel dimensions, lightweight values and capacities of all of the tanks are built into the loading computer software. The software uses these values as inputs to a vessel model and calculates the various stability and stress values for the ship at all times. It is essential that the operator maintains each of these parameters within safe limits at all times.

The ‘Onboard NAPA’ is a computerised version of the Class Approved Stability and Strength Manuals and is always consulted prior to moving cargo or ballast volumes. The ‘Onboard NAPA’ is frequently referred to during the execution of these operations to ensure that the operation is going to plan with respect to structural limitations and stability.

The Trim and Stability Book provides calculation data and methodology for manual calculation of the data, which the loading computer provides. The booklet also contains a number of standard conditions, which Bonga FPSO will often load and must always be referred to in the event of non-availability of the loading computer. Although the same software configuration runs on both machines, the NAPA generated alarms from the online system in the CCR are displayed on the CCR PC only. The standalone PC in the Marine Supervisor’s office is updated every 30 minutes from the CCR PC.

The measured tank level data is provided over a serial link from the SAAB tank gauging system; the SAAB unit also sends the tank level data to the DCS via a separate data link. Alarms generated within NAPA are routed via the SAAB unit to the DCS for annunciation and logging.

Although tank level measurements are normally online inputs, it is possible to input tank levels manually in the event of a communication or equipment failure. For this purpose manual dips can be taken on deck through the closed hand dipping system using a portable tank gauging tape.

The aft MMC 2in dipping point on each cargo tank is designated as the tank datum point, and all SAAB and Metritape readings are corrected to this datum. Values obtained in this way can then be entered manually into the load computer.

Note: Prior to commencing the loading sequence, all crude oil loading and discharging operations must be fully simulated on the loading computer. A safe loading plan must be drawn up, agreed and fully understood by all personnel involved in loading operations. The cargo loading operation is carried out from the control room.

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3.3.1 NAPA Operator Interface

The NAPA PC located on the operator console in the CCR is the primary operator interface for the loading computer and allows access to all NAPA displays provided including the following:

NAPA controls on the PC: • Develop Loading Plan • Initiate Stability Calculations • Start Loading Plan Monitoring

• Access Menus for Tank Loading, 3D model etc Indication from NAPA on the PC:

• Load Tanks • Load Stores • Draft Survey • GM Required • Grade Database

The DCS replicates the displays used in the SAAB cargo monitoring system which includes:

• Tank ullage, corrected for trim and list • Tank temperatures, top, middle and bottom • Ship trim and list

The following NAPA vessel monitoring alarms are available: • GM

• Bending Moment • Shear Force • Trim

• Mean Draft

Reports generated in the NAPA software package are available for printing on the report printer on the LAN. The following reports are available from the package: • Tank Report

• Stability Report

• Longitudinal Strength Report • Cargo History Report

• Tank Inspection Report • Damage Case Report

All displays provided with the NAPA package are available for viewing via the server interface to the DCS.