Caisson Drainage Design_guide to the Selection_bp_rp44-11

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE June 1992

Copyright © The British Petroleum Company p.l.c.

Copyright © The British Petroleum Company p.l.c. All rights reserved. reserved. The information contained in this document is subject to the terms and conditions of the agreement or contract under which the document was supplied supplied to the recipient's organisation. None of the information contained in this document shall be disclosed outside the recipient's own organisation without the prior written permission of  Manager, Standards, BP Engineering, BP International Limited, unless the terms of such agreement or contract expressly allow.

BP GROUP RECOMMENDED PRACTICES AND SPECIFICATIONS FOR ENGINEERING

Issue Date Doc. No.

RP 44-11

June 1992

Latest Amendment Date

Document Title

GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE (Replaces BP Engineering Code of Practice CP 47)

APPLICABILITY

Regional Applicability: Business Applicability:

International All Businesses

SCOPE AND PURPOSE

This Recommended Practice gives guidelines for the selection, arrangement and specification of drainage systems within the topsides of offshore platforms. It includes recommendations for minimising drainage requirements in order to optimise platform weight and offshore drilling. While the principles herein are international in applicability, reference is made to certain British Standards that provide a standard that can be recommended.

AMENDMENTS Amd Date Page(s) Description ___________________________________________________________________

CUSTODIAN

Environmental Engineering Issued by:-

Engineering Practices Practices Group, BP International International Limited, Research & Engineering Engineering Centre Chertsey Road, Sunbury-on-Thames, Sunbury-on-Thames, Middlesex, TW16 7LN, UNITED KINGDOM Tel: +44 1932 76 4067

Fax: +44 1932 76 4077

Telex: 296041

CONTENTS

Section

Page

FOREWORD ............................................ ................................................................... .............................................. .............................................. ..........................iv ...iv 1. INTRODUCTIO INTRODUCTION N ......... .............. .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ......... ......... .......... .......... .......... .......... ..........1 .....1 1.1 Scope .............................................. ..................................................................... .............................................. .............................................. ......................... ..1 1 2. OVERALL OVERALL REQUIREMEN REQUIREMENTS TS .......... ............... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ......... ......... ....... ..2 2 2.1 General...................................... General............................................................. .............................................. .............................................. .................................2 ..........2 2.2 Safety 2 2.3 Piping Specification........................ Specification............................................... .............................................. .............................................. ........................... .... 3 2.3.1 General General..... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ........ ... 3 2.3.2 2.3.2 Open Drainage Drainage Systems Systems..... ......... ......... .......... ......... ......... .......... ......... ......... ......... ......... .......... ......... ......... ....... .. 3 2.3.3 Closed Closed Drainage Drainage Systems..... Systems.......... .......... .......... .......... .......... .......... .......... .......... ......... ......... .......... .......... ....... 4 2.3.4 2.3.4 Sanitary Sanitary Drainage Drainage Systems. Systems...... .......... ......... ......... ......... ......... .......... ......... ......... .......... ......... ......... ......... ...... .. 4 2.4 Catchment Areas............................... Areas...................................................... .............................................. .............................................. ......................... ..4 4 2.5 Drainage Gulleys .............................................. ..................................................................... .............................................. ................................ .........5 5 2.6 Collection System Maintenance ............................................. .................................................................... ................................. ..........5 5 2.7 Outfall Locations ............................................. .................................................................... .............................................. ................................. ..........6 6 3. GENERAL GENERAL DESIGN DESIGN REQUIREMEN REQUIREMENTS TS .......... ............... .......... .......... .......... .......... .......... .......... .......... .......... .......... ..........6 .....6 3.1 Topsides Structural Structural Design Considerations...................... Considerations............................................. .......................................6 ................6 3.2 Gravity Flow Requirements.................... Requirements........................................... .............................................. ..........................................7 ...................7 3.3 Hydraulic Design ............................................. .................................................................... .............................................. ................................. ..........8 8 3.3.1 General General..... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ........ ... 8 3.3.2 3.3.2 Open Drainage Drainage Systems Systems..... ......... ......... .......... ......... ......... .......... ......... ......... ......... ......... .......... ......... ......... ....... .. 8 3.3.2.1 Peak Flows ............................................. .................................................................... .......................................... ...................9 9 3.3.2.2 Minimum Flows/Sediment Transport Capability ............................ ............................9 9 3.3.2.3 Surcharging of Gulleys ................................. .................................................. ................................. ................10 10 3.3.2.4 Hydraulic Capacity and Line Sizing ................................. .............................................. .............10 10 3.3.2.5 Maintaining Liquid Levels Levels in Loop Seals/Seal Seals/Seal Pots Pots ...................... ...................... 11 3.3.3 Closed Closed Drainage Drainage Systems..... Systems.......... .......... .......... .......... .......... .......... .......... .......... ......... ......... .......... ......... ....11 11 3.3.4 3.3.4 Sanitary Sanitary Drainage Drainage Systems. Systems...... .......... ......... ......... ......... ......... .......... ......... ......... .......... ......... ......... .........11 ....11 3.4 Thermal Design ............................................. .................................................................... .............................................. ................................. ..........11 11 3.5 Weight Minimisation........................................ Minimisation............................................................... .............................................. .............................. .......11 11 3.6 Module Drainage Drainage Design and and Hookup Minimisation.......................... Minimisation............................................12 ..................12 3.7 Winterisation ............................................. .................................................................... .............................................. .....................................12 ..............12 3.8 Helidecks ............................................ ................................................................... .............................................. ............................................12 .....................12 3.9 Corrosion ............................................. .................................................................... .............................................. ...........................................12 ....................12 4. OIL-FREE OIL-FREE WATER DRAINAGE DRAINAGE .......... ............... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ..........13 .....13 4.1 General...................................... General............................................................. .............................................. .............................................. ............................... ........13 13 4.2 Equipment Requirements ............................................ ................................................................... ..........................................13 ...................13

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5. OILY WATER OPEN DRAINAGE DRAINAGE .......... ............... .......... .......... ......... ......... .......... .......... .......... .......... .......... .......... .......... ........14 ...14 5.1 General...................................... General............................................................. .............................................. .............................................. ............................... ........14 14 5.2 Oil/Water Separation Facilities .............................................. ..................................................................... ............................... ........15 15 5.3 Equipment Requirements ............................................ ................................................................... ..........................................16 ...................16 6. OILY WATER WATER CLOSED CLOSED DRAINAGE... DRAINAGE........ .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .........21 ....21 6.1 General...................................... General............................................................. .............................................. .............................................. ............................... ........21 21 6.2 Equipment Requirements ............................................ ................................................................... ..........................................24 ...................24 7. DRILLING DRILLING AREAS DRAINAGE.... DRAINAGE......... .......... .......... .......... .......... .......... ......... ......... .......... .......... .......... .......... .......... .......... ........26 ...26 8. FIREWATER FIREWATER OVERFLOW OVERFLOW DRAINAGE DRAINAGE .......... ............... .......... .......... .......... .......... .......... .......... .......... .......... .......... ....... 27 8.1 General...................................... General............................................................. .............................................. .............................................. ............................... ........27 27 8.2 Equipment Requirements ............................................ ................................................................... ..........................................28 ...................28 9. CHEMICAL CHEMICAL DRAINAGE DRAINAGE .......... ............... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... .......... ........29 ...29 9.1 General...................................... General............................................................. .............................................. .............................................. ............................... ........29 29 9.2 Equipment Requirements ............................................ ................................................................... ..........................................31 ...................31 9.2.1 Chemical Chemical Draina Drainage ge Piping Piping .......... ............... .......... .......... .......... .......... .......... .......... .......... .......... .......... ....... 31 10. SANITARY DRAINAGE................. DRAINAGE........................................ .............................................. .............................................. ........................... .... 31 10.1 General....................................... General.............................................................. .............................................. .............................................. ........................... .... 31 10.2 Equipment Requirements ............................................. .................................................................... ......................................31 ...............31 10.2.1 Sanitary Drainage Collection Piping.................................. Piping.............................................. ............31 31 10.2.2 Seals ............................................. .................................................................... .............................................. ........................... .... 32 10.2.3 Sewage Outfall Line.............................................. Line..................................................................... ......................... .. 32 33 FIGURE 1a....................................... 1a.............................................................. .............................................. .............................................. ..................................33 ...........33 SIMPLIFIED OVERALL DRAINAGE SYSTEM (DRAINAGE CAISSON SEPARATION PLUS OIL REMOVAL PACKAGE) PACKAGE) ................................ ................................................33 ................33 FIGURE 1b ............................................ ................................................................... .............................................. ............................................... ............................ ....34 34 SIMPLIFIED OVERALL DRAINAGE SYSTEM .......................... ....................................... ...........................34 ..............34 (PRIMARY OIL SEPARATION UPSTREAM OF DRAINAGE CAISSON) CAISSON) ...........34 FIGURE 2..................................... 2............................................................ .............................................. .............................................. ......................................35 ...............35 TYPICAL TOPSIDES DRAINAGE DRAINAGE ARRANGEMENT ................................. ...........................................35 ..........35 FIGURE 3..................................... 3............................................................ .............................................. .............................................. ......................................36 ...............36 OIL-FREE WATER DRAINAGE SYSTEM SCHEMATIC................. SCHEMATIC .................................. ..................... ....36 36 FIGURE 4a....................................... 4a.............................................................. .............................................. .............................................. ..................................37 ...........37 OILY WATER OPEN DRAINAGE SYSTEM SCHEMATIC......................... SCHEMATIC...................................37 ..........37 (DRAINAGE CAISSON CAISSON SEPARATION PLUS OIL REMOVAL REMOVAL PACKAGE) .......37 FIGURE 4b ............................................ ................................................................... .............................................. ............................................... ............................ ....38 38

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OILY WATER OPEN DRAINAGE SYSTEM SCHEMATIC......................... SCHEMATIC...................................38 ..........38 (PRIMARY OIL SEPARATION UPSTREAM OF DRAINAGE CAISSON) CAISSON) ...........38 FIGURE 5..................................... 5............................................................ .............................................. .............................................. ......................................39 ...............39 OILY WATER CLOSED CLOSED DRAINAGE SYSTEM SYSTEM SCHEMATIC .............................39 .............................39 FIGURE 6..................................... 6............................................................ .............................................. .............................................. ......................................40 ...............40 DRILLING AREAS DRAINAGE SYSTEM SCHEMATIC....................... SCHEMATIC.................................... ............... ..40 40 FIGURE 7..................................... 7............................................................ .............................................. .............................................. ......................................41 ...............41 FIREWATER OVERFLOW DRAINAGE SYSTEM SCHEMATIC......................... SCHEMATIC.........................41 41 FIGURE 8..................................... 8............................................................ .............................................. .............................................. ......................................42 ...............42 CHEMICAL DRAINAGE SYSTEM SCHEMATIC................. SCHEMATIC .................................. .................................42 ................42 FIGURE 9..................................... 9............................................................ .............................................. .............................................. ......................................43 ...............43 SANITARY DRAINAGE SYSTEM SYSTEM SCHEMATIC ................................. ..................................................43 .................43 APPENDIX A...................................... A............................................................. .............................................. .............................................. ............................... ........44 44 DEFINITIONS AND ABBREVIATIONS................. ABBREVIATIONS .................................. .................................. ................................44 ...............44 APPENDIX B ............................................ ................................................................... .............................................. .............................................. ......................... .. 45 LIST OF REFERENCED DOCUMENTS ................................... .................................................... ...............................45 ..............45 APPENDIX C...................................... C............................................................. .............................................. .............................................. ............................... ........46 46 SUPPLEMENTARY COMMENTARY ........................................... .................................................................. .......................... ... 46 C1 Scope............................... Scope...................................................... .............................................. ..............................................46 .......................46 C2 General....................... General .............................................. .............................................. ............................................... ............................ .... 46 C3 Gravity Flow Requirements ........................................... ................................................................. ......................47 47

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

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FOREWORD

Introducation to BP Group Recommended Practices and Specifications for Engineering

The Introductory volume contains a series of documents that provide an introduction to the BP Group Recommended Recommended Practices Practices and Specifications for Engineering Engineering (RPSEs). In particular, the 'General 'General Foreword' sets out out the philosophy of the RPSEs. Other documents in the Introductory volume provide general guidance on using the RPSEs and background information to Engineering Engineering Standards Standards in BP. There are also also recommendations recommendations for specific specific definitions and requirements. Value of this Recommended Practice

This document represents the accumulated knowledge of BP in offshore drainage from a variety of projects. projects. There are no comprehensive comprehensive external external documents documents addressing addressing this specialised area, area, other documents being being concerned with with onshore systems. systems. Provision of the required segregated drainage systems offshore has wide ranging safety and environmental implications which are addressed in this document to allow cost effective design to be achieved. Application

Text in italics is Commentary. Commentary. Commentary provides background background information which supports the requirements of the Recommended Recommended Practice, and may discuss alternative options. Contractors shall develop designs in accordance with the principles of this Recommended Practice. Designs will then be subject to general general discussion discussion and agreement agreement with BP. BP. For this reason, actions requiring approval or specification by BP are not individually identified in this document. This document may refer to certain local, national or international regulations but the responsibility to ensure compliance with legislation and any other statutory requirement lies with the user. The user should should adapt or supplement this document document to ensure compliance for the specific application. Principal Changes from Previous Edition

Safe and hazardous drainage systems are now totally independent.

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

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Feedback and Further Information

Users are invited to feed feed back any comments comments and to detail experiences in the application of  BP RPSEs, to assist in the process of their continuous improvement. For feedback and further information, please contact Standards Group, BP Engineering or the Custodian. See Quarterly Status Status List for contacts. contacts.

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

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1.

INTRODUCTION 1. 1

Scope

1.1.1

This Re Recommended Pra Pracctice ice pre pressents gu guide ideline ines fo for th the se selec lection ion, arrangement and specification of drainage systems within the topsides of offshore platforms. Particular attention attention is given to the specific specific points that require consideration during conceptual design development especially those concerned with safety. Recommendations for minimising drainage requirements in order to optimise platform weight and offshore hook-up are an integral part of  the document. See Appendix C1 for Commentary.

1.1.2 .1.2

This This docu ocument ment dea deals with with the the ana analysi lysiss of th the drain rainag agee requ requir irem emen ents ts on a fixed platform, and the selection of the appropriate system for the following:(a) (a) (b) (b) (c) (c) (d) (d) (e) (e) ( f) (g) (g)

1.1.3

Oil-f il-fre reee water ter dra draina inage system tem. Oily Oily wate waterr ope open n dra drain inag agee sys syste tem. m.(S (Saf afee and and Haza Hazard rdou ous) s) Oily Oily wate waterr clo close sed d dra drain inag agee sys syste tem. m.(S (Saf afee and and Haza Hazard rdou ous) s) Dril Drilli ling ng area reas drain rainaage syste ystem. m. Fire irewate waterr ove overf rflo low w dra drain inaage sy syste stem. Chemical drainage system. Sanitary drainage system.

This document does not cover:The treatment and handling of produced (formation) water, and discharges arising from the use of oil-based muds. All aspects of detailed design, although some important design points are included. It does not include manufacture, construction or commissioning. Requirements specific to floating production platforms, but reference should be made to the guidelines of this document when developing drainage philosophies for such installations. The collection and disposal of once-through seawater cooling water, although this may feature in the design of the platform effluent system.

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2.

OVERALL REQUIREMENTS 2. 1

General

2.1.1

At an an ea early stage of of de design, a drainage re requirement st study shall be carried out to identify every source of platform effluent, and the drainage systems that are required for their disposal.  Early evaluation will minimise conflict with with platform structural requirements. requirements.

The study shall consider the routing of the platform effluent into one or more of the segregated systems covered in Sections 4 to 10 inclusive. Consistent with the requirements for safe design, the number of  collection systems shall be kept to a minimum. This Recommended Practice assumes segregation of the produced water system from the oil-free and oily water drainage systems. systems. 2.1.2 .1.2

Con Consider ideraatio tion shou should ld be give iven to the the inte integ grati ration on of drain rainag agee into into the the process facilities wherever possible. If process conditions permit, this may allow savings in system extent and equipment duties. Any such such integration shall take full account of  the produced (formation) water treatment system. For example by using the LP flare drum as the closed drain collection drum. drum. The operational consequences of likely additional maintenance of the flare drum should  be evaluated. Flare systems are pressurised and the possibility possibility of back-flow into the drain system must be considered. Segregation of the produced water system is due to: (a) (a)

Comm Commin ingl glin ing g bei being ng detr detrim imen enta tall to to the the fina finall eff efflu luen ent  t 

(b) (b)

Risk Risk of bar bariu ium/ m/st stro ront ntiu ium m sc scale ale dep depos osit itio ion. n.

(c) (c)

Requ Requir irem emen entt to prev preven entt recy recycl clin ing g of det deter erge gent nt whic which h may may adve advers rsel elyy affe affect  ct   performance of the produced water package.

 It is necessary to recognise the use of detergents as part of an ongoing good  housekeeping policy. All effluent separators have limited performance performance when detergents are are extensively used. Therefore, with such equipment, BP operational  procedures should limit the use of detergents and make use of alternative cleaning  procedures (e.g. high pressure water jets) or, if no alternative, 'fast break'  detergents. See Appendix C2.

2. 2

Safety

The following general principles shall be applied to the design of all drainage systems:(a) (a)

Drai Draina nage ge syst system emss shal shalll be des desig igne ned d to pre preve vent nt pot poten entia tiall gas gas routes from one area to another through the drains.

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

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Particular attention should be given to avoidance of flow from hazardous to non-hazardous areas and also between hazardous areas.  An explosion which resulted from gas flowing from a hazardous area to a non-hazardous area, and subsequently being ignited, occurred on Shell Cormorant Alpha platform on 3rd March March 1983. Further details of this incident are given in document No. LL3/86 held by the Health, Safety and   Environmental Services Division of BP Exploration.

(b) (b)

The The des desig ign n sha shall ll not not per permi mitt pre press ssur ures es to buil build d up up ins insid idee drainage systems to the extent that flow of hazardous materials to non-hazardous areas could occur, e.g. because of blockage due to freezing. Oily water open drains from hazardous and non-hazardous areas shall be led separately separately to the oil/water separation facility. facility. (See Figure Figure 4a and and Figure 4b). Also, the closed drain drain drum discharge shall not be connected to an oily water separator associated with the oily water open drainage system.

(c) (c)

Haza Hazard rdou ouss and and nonnon-ha haza zard rdou ouss are areas as shal shalll be sepa separa rate ted d as as defined by the platform hazardous area drawings.

(d) (d)

Proce Procedu dure ress shal shalll be dev devel elop oped ed and and reg regul ular arly ly rev revie iewe wed d to avo avoid id pressure surges in common drain systems. For example, when blowing-down sight glasses or instrumentation. There may, in some circumstances, be a requirement for an intermediate pressure reduction stage, appropriately vented.  Attention to these basic points shall be given in order to prevent the known  possibility of gas being blown back through a liquid seal in the oily water  drainage system, and subsequently being ignited by welding operations or  other potential sources of ignition.

2. 3

Piping Specification

2.3.1

General The specification for the pipework of drainage systems should be compatible with the associated piping system.

2.3.2

Open Drainage Systems

2.3. 2.3.2. 2.1 1

For For ope open n (ve (vent nted ed-t -too-at atmo mosp sphe here re)) dra drain inag agee sy system stems, s, the the req requi uire reme ment ntss of  of  the piping specification for the relevant service may be relaxed. Relaxation should also be considered for drainage systems normally closed (spaded) and only used when the process system is depressurised. For example, to allow the use of socket welded fittings in sizes not greater than NPS  1 1/2 (DN 40) in place of butt-welded joints, and a possible reduction in testing.

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

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2.3.2.2

Where appropriate, welded sleeve joints may be considered. Welded sleeve joints may especially be considered for installation of spool pieces on offshore hook-up.

2.3.3

Closed Drainage Systems

2.3.3.1

The pressure rating of pipework and fittings on closed drainage systems (i.e. oily water closed drainage and chemical drainage systems) shall reflect the most severe upstream process temperature and pressure conditions which may be applied to the system if  blockage or overloading occurs.  Appropriate pressure rating is particularly important where auto-refrigeration auto- refrigeration may cause ice or hydrate formation, or where waxy or viscous materials are being blowndown. Trace heating and lagging may be required on some closed drainage pipework for  such duties.  It should be noted that corrosion can take place under lagging if water ingress occurs, e.g. from washdown.

2.3.3.2

Drain sources of different pressure (class) rating shall not be manifolded together. together. Drain headers headers of each each rating shall be routed directly and separately to the closed drain drum.

2.3.4

Sanitary Drainage Systems Piping specification shall comply with BS 5572 or equivalent.

2.4

Catchment Areas

Catchment areas shall be related to the process equipment which they surround. All areas must drain freely and away from other equipment. equipment. (see also 3.1).  Due allowance must be made for out-of-true alignment. under equipment where possible.

High points should be

2.5

Drainage Gulleys

2.5.1

Drainage channels recessed into the deck should be made as short as possible in hazardous areas, to minimise risk of spread of fire due to flammable liquids and vapours in the channels.

2.5.2

Gulleys shall be designed to slope towards the outlet, such that they do not remain permanently permanently liquid-filled. Use of weirs in gulleys gulleys generally should be avoided. Deck gulleys should be covered with grating. Unobstructed drainage will facilitate ease of cleaning, and reduce the risk of fire spreading in the event of a minor hydrocarbon spill.

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The grating should not present a trip hazard. The effect of partial partial blockage of the grating by debris such as rags or lagging should be considered.

2.5.3 .5.3

The The normal rmally ly-u -use sed d gulle ulley y outle utlett (i. (i.ee. not not the the fire firew wate ater ov overfl erflow ow gulle lley outlet) shall be fitted with a readily removable large-mesh strainer.

2. 6

Collection System Maintenance

2.6.1 .6.1

All All loo loop seal sealss shou hould be full fully y rodd roddab able le or flan flang ged to permi ermitt remo remov val in the event of a blockage.

2.6.2

All drainage pipe runs shall be fully roddable. The number and location of rodding-out points and removable flanged fittings shall be determined during detailed design, taking account of the rodding out procedure to be adopted and the ease of access. To facilitate access, swept rodding rodding eyes may be brought through decks.

2.6.3 .6.3

Acc Access to rodd roddin ing g poin points ts shall hall be cons consid ideered red in deta etail duri durin ng desi desig gn development. Branch connections to headers should be of the 'swept T' type to facilitate rodding operations. Particular consideration should be given to access to rodding points located on the underside of the platform lowest deck. An aim in design shall be to avoid running  piping below the lowest deck. Following the guidelines in this Recommended  Practice should enable such pipework (and possible associated heat tracing) to be minimised. The use of catch pots and pumps (fixed or portable) should be considered  if necessary and in preference to under-deck piping.

2.6.4 .6.4

Spa Spade isol isolat atio ion n shall hall be pro provide vided d to enabl nablee fac facilit ilitie iess to be iso isolate lated d where required during construction/commissioning, and for maintenance without complete shut down of the platform. The required number and location of spade isolation points shall be determined during detailed design. Spades shall be located located in accessible and prominent positions.

2.6.5 .6.5

Isola solati tio on spade ade poin points ts shall hall be pro provid vided with ith a valv alve on each side ide of  the spade, except where the spade is next to a vessel isolation valve, in which case, case, a downstream downstream valve only will be sufficient. If more than one production train is being provided, then the drains shall each be provided with spade isolation to allow one train to be maintained without shutdown shutdown of the process. There should should be be provision provision for separate draining connections on isolated sections of line, where breaking of flanged joints is not a practicable method of draining. These connections will allow purging prior to removal or reinstatement of a spade. The provision of drain connections will be influenced by the particular application. e.g., the nature of the fluid and the hold-up volume and location of the isolated line section. Thus, sections of small bore lines having a hold-up capacity of a few litres and whose contents would not represent a direct hazard to personnel or nearby operational equipment, would not require drain connections.

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

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2.6.6 .6.6

The The valve lves selec lected ted for for isol isolaation tion duty in dra draina inage colle ollect ctio ion n hea headers ders shall be full-bore to facilitate rodding, and to allow liquids and silt to be freely discharged. discharged. Where possible lightweight lightweight valve designs should be adopted.

2. 7

Outfall Locations

All drainage outfalls shall be positioned so that platform pump intakes (particularly those feeding the potable water plant) are at maximum distance and across across normal normal tidal tidal current direction. Outfalls would would typically be at different depth from any water intake. All overflows via deck plates shall be arranged to have discharge overboard away from equipment, personnel, escape routes and lifeboats on lower decks. 3.

GENERAL DE DESIGN RE REQUIREMENTS 3. 1

Topsides Structural Design Considerations

3.1.1

At an early stage, structur tural design shall take account of:(a)

Falls in Deck Areas  Deck areas should be sloped towards gulleys (or external edge if shedding oil-free water overboard although this method should be avoided if   possible) at a net gradient (allowing for possible out-of-level alignment  after installation) of not less than 1:80. Falls and gulley locations should  be arranged so that water is not shed from one side of the deck right across to the other side. Attention should be paid to possible possible implications of a sloping deck on the design of the supporting structure. structure. Due regard shall be given to deck plate settling under load and the stiffening action due to the use of box section gulleys.

(b) (b)

Pene Penetr trat atio ions ns thr throu ough gh Str Struc uctu tura rall Stee Steell Memb Member erss  In order to facilitate drain line falls, to avoid interference with other  systems and for ease of maintenance, gravity drainage systems should be kept as close to the underside of the platform decks as possible. In the case of the platform bottom deck drainage, platform underside piping should be avoided (see 2.6.3). These aims may often be achieved only if the structural steel members supporting the decks are appropriately designed for  drainage line penetrations.

(c) (c)

Location ion of Closed Drain Drum Structural design may be required to make space allowance between main deck beams for mounting a closed drain drum half below the lower deck  (see also 3.2).

(d) (d)

The The wei weigh ghtt load loadin ing g cau cause sed d by by tem tempo pora rary ry accu accumu mula latio tion n of  firewater during deluge.

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PAGE 6

3. 2

Gravity Flow Requirements

3.2.1 .2.1

Dra Draina inage systems tems sho should uld be des desig ign ned to to op operate rate,, wh where erever pra practic ticable ble, by gravity with a minimum net fall of 1:100. Where pumps are required, pumps with low turbulent energy dissipation should be used, and the resultant emulsification of oil in water accounted for in downstream separation facilities design. Pumping should be avoided wherever possible, especially on the oil/water drainage systems where the resultant emulsification of the oil in the water will impair the  performance of downstream separation separation facilities.

3.2.2

Pipes should be at su such le levels and gradients th that liq liqu uids ar are no not retained in any part of a drain system other than where designed to be so in the various traps.

3.2.3

Due ac account sh shall be ta taken of of th the lik likeeliho ihood of of mo modules les be being ou out of  of  level after construction and installation. The minimum design falls suggested in this Recommended Practice shall be considered as net falls, i.e. the fall that will be achieved if the modules are installed  with maximum out-of-level tolerance.  In the case of a fixed platform pla tform where a drain header requires a net fall of 1:100 and  the estimated maximum tolerance of module out-of-level after fabrication and  installation is 1/2 degree (i.e. 1:114), then the required slope of header relative to the module will be:1 1 1  +  =  i.e. 1:53 100 114 53  In some cases, the variation in the level of gravity drain lines is limited by the available vertical space under platform decks. decks. Judicious arrangement arrangement of falling gravity drain lines towards centrally placed collection points will make the best use of the variation in levels permitted by such limitations. See Appendix C3.

3.2.4 .2.4

Wher Wheree up-hil -hilll coll collec ecti tion on line liness are una unavoid voidaable, le, the there may may be a need for for gas pressure for blow-down of equipment and use of special operating procedures. For cases where effluent sources will be at a low level, it may be appropriate to consider the following arrangements in order to avoid up-hill closed drain collection lines which normally are not acceptable:(a)

Loca Locate te the the clos closed ed drai drain n dru drum m in or belo below w the the low lowes estt leve levell modu module le flo floor or..

(b)

Locate local closed drain catch pot(s) at appropriate points around the low-level modules, and feed the closed drain drum by means of low turbulent energy dissipation pumps (permanent or temporary).

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(c)

Locate the inlet nozzles of the closed drain drum at a lower level than the normal top mountings, but above the normal maximum operating level.

3. 3

Hydraulic Design

3.3.1

General Calculation of the hydraulic gradient within a drainage system shall be based on roughness factors appropriate to mature pipework. Consideration should be given to the use of hydraulic dampers on any large diameter lines to prevent flash flooding due to long vertical runs of pipe.

3.3.2

Open Drainage Systems The hydraulic design of open (vented-to-atmosphere) drainage systems involves detailed consideration of the following:(a)

Peak flows.

(b) (b)

Mini Minimu mum m flow flows/ s/se sedi dime ment nt tra trans nspo port rt cap capab abil ilit ity. y.

(c) (c)

Degr Degree ee of surc surcha harg rgee tha thatt can can be tole tolera rate ted. d.

(d) (d)

Hyd Hydrau raulic lic ca capac pacity ity and and lin line siz sizin ing g.

(e) (e)

Main Mainta tain inin ing g liqu liquid id lev level elss in loo loop p seal seals/ s/se seal al pot pots. s.

( f)

Provision of of ad adequate ve vents.

3.3.2.1

Peak Flows

3.3. 3.3.2. 2.1. 1.1 1

The The dra drain inag agee sy system stemss sha shall ll be be des desig igne ned d for for the the gre great ater er of of the the foll follow owin ing g three flows:(a) (a) (b) (b) (c) (c)

Rain ain-wa -water ter plu pluss proc rocess effl efflue uen nt. Wash Wa shdo down wn wate waterr plus plus proc proces esss effl efflue uent nt.. Fire Firewa wate terr plu pluss ass assoc ocia iate ted d pro proce cess ss leak leakag age. e.

The platform open drainage systems are required to carry process effluents, washdown water, water, rain-water and firewater. Note that in the case case of deck areas areas drained into the oily water open drainage system, this peak flow will be met by the oily water open drainage system (see Section 5) and the firewater overflow drainage system (see Section 8).

3.3. 3.3.2. 2.1. 1.2 2

The The des desig ign n rat ratee of of fir firew ewat ater er drai draina nage ge from from a pro proce cess ss area area shal shalll be be the the greater of:either

The rate of firew rewater deluge water applied to the area.

or

The rate of firewater applied to the area with the maximum number of fire hoses and fixed monitors in use.

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Specific flow rates for deluge water depend upon local statutory regulations. For  example, in example, in the case of platform designs that follow UK Statutory Instruments 1978  No. 611 (The offshore installations (fire-fighting equipment) regulations 1978), the rate of firewater applied can be calculated on the basis of 12.2 litres per minute over  each square metre of designated area (0.25 gallons/square foot/minute). There may be additional flows determined by the need to protect individual plant  components, firewalls and structures. Firewater flowrate employed should be the maximum output from all installed  nozzles not just the design output of the deluge system. The design rate of rain-water flow from open decks can be calculated from considering the design storm intensity on the exposed area. It will usually be very much less than that indicated above. Guidance regardin g calculation calculation methods, which include include consideration of vertical surfaces, is given in  BS 6367  and BP Group  RP 4-1. 4-1.

3.3.2.2

Minimum Flows/Sediment Transport Capability

3.3.2.2.1

Calculations shall be made to determine the minimum flow at which deposited solids are flushed out. This flow shall not exceed the hydraulic capacity of the drains.  Minimum flows arise when only process effluent is being discharged into the drainage system, or even if flow has completely completely stopped. In such cases, the flow velocities required for self cleansing (i.e. sediment transport) are seldom maintained.  As part of routine platform operating procedures, BP may establish a planned   programme for flushing open drainage systems. Flushing will also ensure that  liquid levels in loop seals and in seal pots on the open drain systems are maintained.  BP Group  RP 4-1 s pecifies a self cleansing velocity of 0.8 m/s, which shall be considered when calculating the required minimum flow.

3.3.2.2.2

The drilling drilli ng system deck drains should be segregated from other platform drains.Water flush and/or rodding should be provided at potential sludge build-up points.The cement handling area deck drains shall be provided with a permanent flush facility. Operational activities in the cement handling area can generate large amounts of  solids which will probably settle in the drains and form solid plugs.

3.3.2.3

Surcharging of Gulleys Surcharging of gulleys in open drainage shall be accommodated by provision of freeboard freeboard above the design flow rate rate level. This freeboard shall be not less than than 100mm. For gulleys gulleys provided with firewater overflows (see also 8.2.1), the freeboard shall be between the design flow rate level and the lip of the overflow tundish.

3.3.2.4

Hydraulic Capacity and Line Sizing

3.3.2.4.1

Calculation Calculati on of hydraulic capacity should be based on the ColebrookWhite formula.

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The hydraulic capacity of open drains depends on pipe size, allowances for entry, exit and fittings losses, gradient, condition, degree of surcharge that can be tolerated  and the nature of liquid to be carried.

3.3. 3.3.2. 2.4. 4.2 2

Drai Drain n line liness sho shoul uld d not not be be smal smalle lerr than than a cert certai ain n mini minimu mum m size size,, typically NPS NPS 1 1/2 (DN 40).  Avoidance of small lines will reduce the risk of blockage with corrosion products or  other debris such as lagging.

3.3. 3.3.2. 2.4. 4.3 3

A hy hydrau drauli licc che check ck on smal smalll-bo bore re pip pipin ing g sy system stemss sho shoul uld d be cons consid ider ered ed to ensure adequate flow capability, e.g. chemical drain lines.

3.3. 3.3.2. 2.4. 4.4 4

Air Air ent entra rain inme ment nt,, esp espec ecia iall lly y in down downco come mers rs,, sha shall ll be be ass asses esse sed d and and action taken to avoid vibration.  Air entrainment can, in some circumstances, lead to unstable flow conditions and  generate pipe vibration. vibration. Downcomers carrying carrying large quantities of liquid (as in a  firefighting situation) are the most susceptible. The problem occurs at Froude  Numbers greater than about 0.35. *G 1 *L 2 = liquid superficial velocity = pipe internal diameter  = acceleration due to gravity = liquid specific gravity = gas specific gravity

[

Froude No = V   L ÷ gd (*L where

V L  d g * L *G

]

(all units to be consistent to yield a dimensionless result)  Reference: 'Sizing Piping for Process Plants' L.L. Simpson, 'Chemical Engineering',  June 17th ,1968, pp 203-205. Three options are available to avoid the problem:(i) (i)

Adeq Adequa uate tely ly sup suppo port rt the the pip pipew ewor orkk and and tole tolera rate te the the uns unsta tabl blee flow flow,,

(ii) (ii)

Desi Design gn to ensu ensure re oper operat atio ion n at at Fro Froud udee Nos Nos belo below w 0.3 0.35 5

(iii) (iii)

Provid Providee drain drain entry entry boxes boxes with with integ integral ral vortex vortex breake breakers rs such such that that the the liqui liquid  d  depth will be sufficient to avoid entrainment. (There will be intermediate situations when flow rates will be low enough to give unstable conditions)

3.3.2.5

Maintaining Li Liquid Le Levels in in Lo Loop Se Seals/Seal Po Pots

3.3. 3.3.2. 2.5. 5.1 1

Pipi Piping ng desi design gn shal shalll prev preven entt the the pos possi sibi bilit lity y of of syph syphon onic ic empt empty ying ing of  of  loop seals.

3.3.3

Closed Drainage Systems The hydraulic design of closed drainage systems shall follow methods appropriate to flooded systems (i.e. lines fully liquid-filled). - see also 3.3.2.4.2

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3.3.4

Sanitary Drainage Systems The hydraulic hydraulic design of the sanitary drainage system shall follow BS 5572 or equivalent.

3.4

Thermal Design

Drainage piping system design shall accommodate thermal expansion/contraction of lines, resulting from the temperature range of  effluents. 3.5

Weight Minimisation

3.5.1

As open drainage piping systems are subject to negligible pressure, construction from lightweight material shall be considered in appropriate locations, e.g. thin wall carbon steel with adequate corrosion allowance (both inside and out) or GRP. Special consideration of support location may be necessary.

3.5.2

On small drain lines, e.g. instrument drain headers, compression fittings may be used where permitted by the piping specification (see 2.3).

3.6

Module Drainage Design and Hookup Minimisation

3.6.1

In order to minimise offshore hook-up time, drainage collection system pipework should be contained within the structure of the module and be included in the scope of the onshore fabricator. Access requirements and possible final out-of-alignment problems should be considered. See 3.2.3.

3.6.2

Drainage piping systems should preferably preferab ly not be exposed below platform floors. Where this is not practicable, practicable, heat tracing should be considered, to avoid freezing (see also 3.7).

3.6.3

Where possible, pipework of each system should be combined to a common header within each module before passing to the next, to reduce the number of inter-module connections.

3.6.4

Consistent with operational convenience convenience and efficiency, efficiency, washroom and toilet facilities should be centralised within a minimum number of  modules. Consideration should should be given given to providing both 'dirty' 'dirty' and 'clean' facilities within the accommodation module rather than providing separate facilities in adjacent modules.

3.7

Winterisation

Where applicable, drainage lines, loop seals, seal pots and head ers shall be protected for winterisation in accordance with BP Group RP 44-2.. 44-2

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3.8

Helidecks

Helidecks shall be surrounded by gulleys discharging directly to sea in cases where fuel loading does not take place. Where fuel loading l oading takes place the drains shall flow to the oily water open drainage collection system. Drains pipework shall be able to cope with burning fuel. See also 8.1. 3.9

Corrosion

3.9.1

The drains system design shall fully consider susceptibility to corrosion. Materials selected, fabrication procedures and layout shall be such as to ensure that corrosion damage remains within acceptable limits. Offshore drainage systems may suffer corrosion damage from aerated seawater and  water containing dissolved CO 2 or H 2S. Damage is usually severe in the transition  zones between wet and dry regions which, for example, feature in loop seals, dip  pipes, seal pots, pipework low points and where stagnant water can accumulate. Welding procedures and materials will influence the susceptibility to corrosion of the heat-affected-zones of the welds.

3.9.2

Corrosion monitoring procedures should be applied to those areas at most risk.  Refer to BP Group RP Group RP 6-1 f  6-1 f or or details of corrosion monitoring methods.

4.

OIL-FREE WATER DRAINAGE 4.1

General

4.1.1

This system shall be provided to deal with oil-free water drainage, for example potable water overflows, run-off (including firewater) from module roofs and open deck areas, other than those liable to be contaminated by oil or chemicals.

4.1.2

Intermittent oil-free water flows (e.g. rain-water and firewater) from topsides deck areas should be discharged overboard. This may be achieved by either of the following methods:(a)

Routing of run-off over the deck plates away from other plant areas and discharge overboard.

(b)

Collection of water in headers connected to an outboard discharge point below the platform topsides.

Method (a) is preferred as the lower-cost solution. Where Method (a) is not acceptable, a piped drainage system in accordance with Method (b) shall be provided, and have sufficient capacity to accommodate maximum firewater run-off. (See also Section 8)

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4.1.3

Contin tinuous oil-f l-free water dr drainage flow lows shall be be directed to to a seawater outfall caisson, independently of the oil-free water drainage system.

4. 2

Equipment Requirements

4.2.1

Gulleys Oil-free water drainage gulleys should be provided as shown in Figure 3 . (See also Section 8.2.1)

4.2.2

Drainage Headers and Sub-Headers Subject to module pressurisation requirements, the drainage headers and sub-headers should contain no loop seals or pockets, and should be designed to drain towards an outboard discharge point below the topsides bottom deck level.

4.2.3

Seals Modules that are designed to be pressurised shall be provided with loop seals to prevent air losses. losses. The depth of liquid required required in these seals will depend upon the pressure level chosen for the module, and likely pressure surges e.g. doors opening and closing.

5.

OILY WATER OPEN DRAINAGE 5. 1

General

5.1.1 .1.1

An open pen (i.e (i.e.. vente nted-to d-to-a -atm tmo osph sphere ere) system tem sha shall be prov rovide ided for for the the drainage of water contaminated by oil, such as may originate from the following sources:(a) (a)

Rain Rain-w -wat ater er,, wash washdo down wn wat water er and and fire firewa wate terr from from dec deck k area areass which are liable to be oil contaminated.

(b) (b)

Spill Spillag ages es and and leak leakss from from pro proce cess ss equi equipm pmen ent. t.

(c) (c)

Cool Coolin ing g wat water er fro from m wate water-c r-coo oole led d glan glands ds and and bea beari ring ngss of  equipment on hydrocarbon duty.

(d) (d)

Drai Draina nage ge fro from m samp sample le poi point nts, s, dra drain in coc cocks ks,, hydr hydroc ocar arbo bon n overflows and equipment fittings.

(e) (e)

Water fro from transforme rmer bays.

(f) (f)

Water fro from m la laborat ratory oi oil si sinks.

Figure 4a and Figure 4b are schematic diagrams for typical oily water open drainage systems. systems. Figure 4a is based on drainage caisson separation; Figure 4b is based on primary oil separation separation before the drainage caisson. caisson. These separation separation facilities are described described in 5.2.

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5.1.2

Oily water dr drainage fr from to topsides de deck ar areas sh should no normally be collected in headers, and flow by gravity to the applicable oil/water separation facility (see 5.2.1 or 5.2.2). Where an oily water separator is used, as indicated in Figure 4b, this should be located at a low enough level to permit the gravity inflow of  oily water effluent from the lowest deck. Under abnormal conditions of firewater surge flow, oily water drainage will be diverted from the headers - see Section 8.

5.1.3 .1.3

Oily Oily wate ater dra draina inage fro from non-h on-haazard zardo ous areas reas shall all be colle llected ted in headers separate separate from those for hazardous hazardous areas. It is essential essential that flammable vapour leakage through oily water drains to non-hazardous areas be prevented. prevented. The oily water water drain headers from non-hazardous non-hazardous areas shall be provided with a seal pot in addition to individual traps at inlet gulleys, etc.

5.1.4 .1.4

Whe Where bulk bulk stora torag ge is to be prov rovide ided for for helif elifue uel, l, lub lube oil and sea seal oil oil,, the handling areas shall be provided with kerbs and valved connections to the oily water open drainage system; the valves normally being closed. Valves to drain may be opened to to dispose of uncontaminated rain-water. If minor  contamination is present, adequate water flushing shall be available, and the area cleared via the drains.

5. 2

Oil/Water Separation Facilities

5.2.1

Primary Oil Separation in the Drainage Caisson

5.2. 5.2.1. 1.1 1

This This meth method od of sepa separa rati tion on is indi indica cate ted d in Figu Figure re 1a and and Fig Figure ure 4a. 4a. Oily water drainage shall be discharged directly to the drainage caisson.  A treatment loop is provided to allow the upper liquid layers in the drainage caisson to be recycled by a drainage caisson pump, under manual control, through an external oil removal package, e.g. an oil water filter coalescer. Sample points provided in the external pipework allow assessment of the degree of  oil contamination present. The recovered oil is passed under manual control directly to the process, e.g. to the main crude oil line downstream of the LP production separator outlet.  Note that the receiving process may be at a pressure which may present a risk of   flow-reversal in some failure situations. Water from the oil removal package is returned to the drainage caisson to a region near the sea outlet unless unless poor quality is demonstrated by sampling. In this case, the stream is diverted to the upper region of the caisson for further processing.

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The oil removal package should be integrated with with the drainage caisson caisson pump. The  feed to the package will be intermittent, and as most of the solids collected in the drainage system will have fallen out in the caisson, the necessity for pre-filters or  other means of sludge/solids removal in the feed line to the oil removal package should be evaluated. The feed to the oil removal package will be under manual control, unlike the feed to the oily water separator, and will be of known volume and pressure, thus permitting the selection of compact proprietary equipment.

5.2.2

Primary Oil Separation Upstream of Drainage Caisson

5.2. 5.2.2. 2.1 1

This This meth method od of sepa separa rati tion on is indi indica cate ted d in Figu Figure re 1b and and Figu Figure re 4b. 4b. It shall be used for Gulf of Mexico applications and should also be considered if discharge consent conditions cannot be met by separation within the caisson alone. Suspended oil is separated from water and collected in a separated oil compartment. Separated oil is pumped under manual control directly to the process, e.g. to the main crude oil line downstream of the LP production separator outlet.  Note that the receiving process may be at a pressure which may present a risk of   flow-reversal in some failure situations. The water fraction is led over a weir arrangement in the oily water separator, and  discharged to the drainage caisson.  A drainage caisson pump is provided as an additional facility, to allow any gross oil spillage into the drainage caisson to be returned to the closed drain drum. To check  whether oil is present in the drainage caisson, the pump shall be arranged to recycle oil/water back to the caisson caisson via a tundish. If a visual check of oil/water being collected by the tundish indicates the presence of a significant quantity of oil in the drainage caisson, then the pump discharge shall be arranged to be diverted to the closed drain drum. This operation should be supervised supervised throughout to minimise the risk of pumping 100% seawater subsequent to removal of oil. This will avoid the addition of excessive quantities of water to the closed drain drum.

5.2. 5.2.2. 2.2 2

Oily Oily wate waterr dra drain inag agee sha shall ll be disc discha harg rged ed into into an oily oily wate waterr sep separ arat ator or..  A bypass around the oily water separator is provided to allow maintenance, cleaning and inspection whilst the platform is on line.

5. 3

Equipment Requirements

5.3.1

Drainage Collection

5.3. 5.3.1. 1.1 1

Pipi Piping ng from from tund tundis ishe hes, s, equi equipm pmen entt dri drip p pans pans and and drai drain n gull gulley eyss shal shalll incorporate loop seals. The seal depth shall be consistent with module pressurisation requirements but not less than 300 mm.

5.3.2

Drainage Headers and Sub-Headers

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5.3.2.1

Other than at loop seals and seal pots, drainage headers and subheaders shall contain no pockets, and shall drain towards the applicable oil/water separation facility (see 3.1 and 3.2).

5.3.2.2

Separate drainage headers shall be run from the hazardous and nonhazardous areas to the applicable oil/water separation facility, to avoid the possibility of backflow from the t he hazardous to non-hazardous areas. areas.

5.3.3

Seal Pots

5.3.3.1

Where liquid seals are required on a drain header from a hazardous area, seal pots should be used in preference to piping loop seals.

5.3.3.2

The seal pots should have a seal depth at least twice the seal depth of  the loop seals at drainage collection points. The seal depth shall not be less than 600 mm.

5.3.3.3

Modules that are designed to be pressurised will require a seal depth suited to the level of pressurisation for the module.

5.3.3.4

Seal pots shall be connected to suitable vents or vent headers so that trapped gas is safely vented and pressure fluctuations in one drainage system cannot adversely affect another.

5.3.3.5

Seal pots should be provided with liquid-sealed overflow lines which discharge to sea at a safe location. l ocation.

5.3.3.6

Each seal pot shall be fitted with test cocks set at appropriate levels to allow the level of liquid seal in the pot to be proven.

5.3.3.7

The seal pot design and location should consider the need for routine seal level checking and cleaning.

5.3.3.8

Operating procedures should be developed which involve routine flushing, cleaning and inspection of seal pots.

5.3.4

Vents

5.3.4.1

Vents shall be provided in the oily water drainage system to maintain atmospheric pressure, and to release flammable vapours arising in the system. Lines shall drain back into the drainage system. Vents shall be in accordance with API RP 14C. 14C. Failure to provide vents can result in drainage systems being vapour locked as a result of vapour pressure. pressure. Such vapour locking will restrict drains drains flows or possibly even result in the blow-out of liquid seals.

5.3.4.2

Vent outlets shall be diverted away from sources of ignition.

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5.3. 5.3.4. 4.3 3

Flam Flamee aarr rres este ters rs shal shalll be be ffit itte ted d to to ven ventt out outle lets ts that that disc discha harg rgee int into o are areas as where an intermittent source of ignition is possible.

5.3.4 .3.4.4 .4

Ade Adequa quate acc access ess to flam flamee arre arrest steers sha shall be prov rovide ided.

5.3. 5.3.4. 4.5 5

Part Partic icul ular ar care care shal shalll be be take taken n to ensu ensure re the the saf safee loc locat atio ion n of vent ventss on platforms handling sour hydrocarbons. hydrocarbons.

5.3.5

Oily Water Separator

5.3. 5.3.5. 5.1 1

The The oily oily wate waterr sep separ arat ator or shal shalll rem remov ovee all all susp suspen ende ded d oil oil part partic icle less of of 50 50 microns and greater. Note that the suspended suspended oil content at the inlet to the separator separator is typically 0-2,000 mg/litre (normal), and 100,000 mg/litre (maximum).

5.3. 5.3.5. 5.2 2

Tras Trash h bask basket etss shal shalll be be fitt fitted ed at the the inle inlett to to the the sepa separa rato torr sys syste tem. m. Operational Procedures shall be developed to ensure routine inspection and cleaning of the trash baskets.

5.3. 5.3.5. 5.3 3

The The inl inlet et bay bay of plat platee-ty type pe sepa separa rato tors rs shal shalll be be arr arran ange ged d to to pro provi vide de for for preliminary oil separation, for deposition of solids in the form of  sludge, and to contain anticipated oil spills.  Deposition may be in the form of sludge caused by the presence of oil emulsifiers, which may cause blockage of the plates.  In some instances the oil-spill quantity quanti ty could be large, e.g. diesel di esel oil tank overflow.  If such a spillage cannot be routed to process or retained within a bund system, it  may be appropriate to supplement the separator with an upstream open drains collection tank which should be mounted in the module floor, with all pumps and  instruments top mounted.

5.3. 5.3.5. 5.4 4

Prov Provis isio ion n of of fil filte terr scr scree eens ns betw betwee een n the the sepa separa rato torr inl inlet et bay bay and and the the tilt tilted ed plate section should be considered.

5.3.5 .3.5.5 .5

The separa parato torr sha shall ll inc incorpo rporate rate a re recov covere ered oil oil compar mpartm tmeent.

5.3. 5.3.5. 5.6 6

The The sepa separa rato torr shal shalll be fitt fitted ed with with flus flushi hing ng faci facili liti ties es to faci facili lita tate te the the removal of sludge accumulations.

5.3.5 .3.5.7 .7

The sep separa arator tor sha shall ll have a pe perman rmaneent vent ent co conne nnectio ction n to to th the atmospheric vent header and the separator shall be continuously purged with nitrogen or fuel gas.

5.3. 5.3.5. 5.8 8

The The sepa separa rato torr sha shall ll be prov provid ided ed with with a liqu liquid id-s -sea eale led d over overfl flow ow to the the caisson to prevent gas backflow.

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5.3. 5.3.5. 5.9 9

The The sepa separa rate ted d oil oil pump pumpss and and sepa separa rato torr ins instr trum umen enta tati tion on may may be top top mounted to allow the separator to be located at low level, i.e. within or below platform lowest deck level.

5.3.6

Separated Oil Pumps

5.3. 5.3.6. 6.1 1

The The pump pumpss shal shalll take take suct suctio ion n from from the the sepa separa rate ted d oil oil comp compar artm tmen entt in in the oily water separator and discharge under level-switch control, typically to the main crude oil line, downstream of an LP production separator. Two sets of level level switches shall shall be fitted to the separated oil oil compartment for this purpose. Typically, two pumps should be installed, each capable of pumping 10% of the maximum normal liquid flow into the oily water separator. During normal operation, only one pump should be running, and shall be controlled using the lower  set of level switches. switches. However, if the drainage drainage into the separated oil compartment  compartment  exceeds the pump discharge rate, causing the level to rise, then the second pump shall be started automatically under control of the higher set of level switches. A selector switch shall be provided for selection of the leading pump.

5.3. 5.3.6. 6.2 2

Wher Wheree prac practi tica cabl ble, e, the the pump pumpss shou should ld be loca locate ted d exte extern rnal ally ly to the the separator to facilitate maintenance and to minimise gas release or air ingress to the separator.

5.3.7

Drainage Caisson

5.3. 5.3.7. 7.1 1

The The drai draina nage ge cais caisso son n shal shalll rece receiv ivee oily oily drai draina nage ge dire direct ctly ly or, or, alternatively, de-oiled water from an oily water separator (see Figure 4a and Figure 4b ).

5.3. 5.3.7. 7.2 2

The The wate waterr sha shall ll ente enterr the the cais caisso son n via via down downco come mers rs whic which h sha shall ll exte extend nd to be permanently submerged to provide a liquid seal and to minimise turbulence on entry. Consideration shall be given to the need for wave damping.

5.3. 5.3.7. 7.3 3

All All inco income mers rs from from nonnon-ha haza zard rdou ouss area areass sha shall ll disc discha harg rgee perm perman anen entl tly y below the caisson liquid level.

5.3. 5.3.7. 7.4 4

Mino Minor, r, inte interm rmit itte tent nt flow flowss from from haza hazard rdou ouss area areass may may disc discha harg rgee abov abovee the caisson water level, provided the design prevents back-flow of gas.  Note that the drainage caisson also receives manually controlled discharge of water   from the closed drain drum.

5.3.7 .3.7.5 .5

The dra draina inage ccaaiss isson sha shall ll exte exten nd we well belo elow LA LAT, and and sha shall be located in accordance with 2.7. The bottom of the caisson is typically at -50 m LAT in the Northern North Sea.

5.3. 5.3.7. 7.6 6

The The hold holdin ing g volu volume me of the the drai draina nage ge cais caisso son n sho shoul uld d be be pro propo port rtio ione ned d to to the largest vessel inventory.

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 A caisson having the typical internal diameter of 1.0 metre will provide only limited  damping of any vertical wave motion. Therefore, the use of a low level orifice or  slotted plate for damping should be considered if the platform is in an open-sea location. Consideration should be given to providing integral plates or using a proprietary caisson design to improve oil/water separation. Access for cleaning and  maintenance needs to be taken into account in such applications.

5.3. 5.3.7. 7.7 7

The The cais caisso son n desi design gn shou should ld incl includ udee a 150 150 mm mesh mesh or bars bars acro across ss the the exit, to prevent entry of divers.

5.3. 5.3.7. 7.8 8

The The cais caisso son n gas spac spacee shal shalll be be cont contin inuo uous usly ly purg purged ed with with nitr nitrog ogen en or fuel gas.

5.3.7 .3.7.9 .9

The cais caissson sha shall ll be pro prov vide ided wit with h a ven vent con conn necti ection on to the the atmospheric vent header.

5.3. 5.3.7. 7.10 10

The The cai caiss sson on shou should ld be desi design gned ed to acco accomm mmod odat atee a dra drain inag agee pum pump. p.

5.3.8

Drainage Caisson Pump

5.3. 5.3.8. 8.1 1

Desi Design gn temp temper erat atur uree of the the pump pumped ed flui fluid d shal shalll be be that that of the the ambi ambien entt seawater and the setting height of the pump suction shall reflect tidal variations.

5.3. 5.3.8. 8.2 2

The The pum pump p and and driv driver er shal shalll be be des desig igne ned d for for full fully y sub subme merg rged ed oper operat atio ion. n.

5.3. 5.3.8. 8.3 3

Pump Pump oper operat atio ion n sha shall ll be manu manual ally ly init initia iate ted d fro from m a loca locall con contr trol ol stat statio ion. n.

5.3.8 .3.8..4

Fac Facilit ilitie iess sh shall be pro prov vide ided to to ena enabl blee the the pump pump to be rem removed oved for for maintenance.

5.3. 5.3.8. 8.5 5

Disc Discha harg rgee pipe pipewo work rk asso associ ciat ated ed with with the the pump pump shal shalll be fitt fitted ed with with a non-return valve to prevent back-flow to the caisson.

5.3.8 .3.8..6

A man manua uall sa sample mple point int sha shall ll be pro provi vid ded on the the pum pump p dis disccharg arge pipework. See also 5.3.9

5.3. 5.3.8. 8.7 7

Wher Wheree the the pump pump is used used in conj conjun unct ctio ion n with with an oil oil remo remova vall pack packag agee (see Figure 4a ) the capacity of the pump should be sufficient to permit assessment of water quality through the depth of the drainage caisson.  Assuming, for example, the caisson diameter of 1.0 metre and extending 50 metre below LAT, a pump capacity of 20 m3/h would displace the volume of the caisson in about 2 hours, and be well within the capacity of the smallest oil removal package envisaged.

5.3. 5.3.8. 8.8 8

Wher Wheree the the pump pump is used used in conj conjun unct ctio ion n with with an oily oily wate waterr sep separ arat ator or (see Figure 4b) the following shall apply:-

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(a) (a)

The The pum pump p suc suctio tion n sho shoul uld d be be loc locat ated ed so as to mini minimi mise se the the induction of seawater, i.e. the pump will primarily perform the function of removing floating oil.

(b) (b)

The The pum pumpi ping ng capa capaci city ty shou should ld ty typica picall lly y be be 5% of the the nor norma mall maximum liquid flow from the oily water separator.  Assuming the caisson dimensions in 5.3.8.7 above, the pump capacity would be approximately 5 m3/h.

(c) (c)

5.3.9

The The wat water er cont conten entt of of the the oil oil rec recov over ered ed by the the pum pump p sho shoul uld d be be taken as 0 to 10% (normal), and 100% (peak).

Treated Water Monitoring Equipment To permit monitoring of the system, a manual sampling point shall be provided. Note that automatic automatic sampling might might be demanded demanded in future. Other sampling points should be available in the drainage and separator systems, to the extent necessary to permit checks in equipment performance.

6.

OILY WATER CLOSED DRAINAGE 6. 1

General

6.1.1

A clo clossed sy system (i. (i.ee. ve vented to to fl flare, no not to to at atmosphere) re) sh shall be provided for the drainage of potentially gaseous oil, or water which is normally heavily contaminated with oil from the following sources:(a) (a)

Prod Produc ucti tion on/u /uti tili lity ty equ equip ipme ment nt dra drain in-d -dow own n and and samp sample le poi point nts. s.

(b) (b)

Drai Drainn-do down wn poin points ts on cert certai ain n hy hydroc drocar arbo bon n liq liqui uid d line liness to to facilitate maintenance, e.g. wellhead ligaments, production manifolds, etc.  Drain down points include:(i) (ii) (iii) (iv) (v) (vi) (vii) (vii (viii) i) (ix)

(c) (c)

Production separators. Scrubbers. Crude oil pumps. Level gauges. Condensate pumps. Test separators. Knock-out drums. Comp Compre ress ssor or suct suctio ion n and and blo bloww-do down wn drum drums. s. Fuel oil tanks (including overflows).

Drai Draina nage ge cais caisso son n pump pump dis disch char arge ge,, when when an an oily oily wate waterr sepa separa rato torr is used for primary separation (see 5.2.2).

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6.1.2

Connectio tion of the sources referred to in 6.1.1 (a) and 6.1.1 (b) (b) to the oily water closed drainage system should be restricted to those where drain-down cannot be safely achieved by the following methods:(a) (a)

Using ex existin ting pr process ro routes.

(b) (b)

Conn Connec ecti tion on of drai drainn-do down wn poin points ts via via hose hosess to to oth other er equipment/hydrocarbon liquid lines capable of receipt of the drain-down liquid. Temporary connections shall not remain in place after draining operations are completed. Hoses shall be kept specifically specifically for the duty, be compatible with the fluids handled, be stored properly and be inspected and tested  regularly.

(c) (c)

Conn Connec ectio tion n of dra drain in-d -dow own n poin points ts,, via via hose hoses, s, to to a por porta tabl blee slop slopss drum (i.e. for small volumes of drain-down liquids). This system mainly applies to smaller platforms to avoid provision of oily water closed drains.

The use of portable pumps (hand operated, or powered) may be considered for the transfer of liquids by the methods of drain-down given in (a), (b) and (c).

6.1.3

The ha hazards as associat iated wit with h re release of of H2 H2S fro from m so sour hy hydrocarbo rbon liquids shall be given specific consideration.

6.1.4 .1.4

The The conte ontent ntss of the the oily oily wate waterr close losed d drain rainss syst systeem sho should uld be rou routed ted to fall by gravity, via oily water closed drain headers, to the closed drain drum (but see also 2.1.2).  Any layout which results in drain lines running 'uphill' in places, and thus requiring gas pressure pressure to assist assist drain-down, should be avoided. This may be achieved by  judicious location of the equipment, the closed drain drum and the interconnecting lines (see 3.1 and 3.2).

6.1.5

Closed dr drain lin lines fo for cco old/dr /dry service fr from NG NGL and co condensate vessels shall be kept separate from any wet oil drainage lines, to avoid blockage by hydrate and ice. A pre-heater shall be provided for the closed drain drum for such such service. Trace heating of the lines may also be required, with instrumentation to indicate blockages. Consideration should be given to increasing the drain diameter towards the drum to allow for gas breakout as pressure is reduced.

6.1.6 .1.6

Wher Wheree larg largee quan uantiti tities es of co cold liq liquids ids are to be dra drain ined ed,, co consid nsideerati ratio on should be given to provision of a separate closed drain drum. Provision for discharge of large quantities quantiti es should be via process routes. If discharge to the closed drain system is unavoidable, the outlet connections to downstream drainage equipment (including possible separate direct routing to the caisson) and  to the flare flare needs careful study. In particular, detailed procedures should be developed to ensure safe operation.

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6.1.7

Valved fl flushing point ints sh shall be pro prov vided on on cl closed dra draiin li lines on on cold/dry service to permit methanol flushing when hydrate formations require clearing. Particular care must be taken when methanol is being used, especially from temporary facilities as opposed to permanently installed injection points, because of  sudden release of pressure or when the system is sour.

6.1.8

The wa water co content of of th the li liquid fl flow fro from m th the cl closed dr drain system in into the closed drain drum should be taken as 0-10% (normal), and 100% (peak).

6.1.9 .1.9

Dep Depend ending ing on the the antic ticipa ipated ted duty uty for for the the clo closed dra drain drum rum a simp imple vessel only may be sufficient, with a pump sending all contents to an LP production separator. It may be necessary to achieve separation within the drum. See Commentary notes on flow reversal in 5.2.1 and 5.2.2 above. The requirement to achieve separation within the closed drain drum depends, for  example, upon the amount of seawater returned to the drum from the drainage caisson (see 5.2 of the essential requirements of this document), and the need to avoid commingling seawater with any produced water in the crude oil system.  If separation in the drum is necessary it should should be partitioned as follows:(a) (b) (c)

A centre (receiving) section. A recovered oil section. A de-oiled water section.

6.1. 6.1.10 10

For For larg larger er plat platfo form rms, s, with with a high higher er numb number er of pote potent ntia iall drai drain n sour source ces, s, a vessel suitable for primary oil separation should be provided.

6.1.1 .1.11 1

Oil Oil rec reco overe vered d fro from m th this prim primar ary y oil separ eparaatio tion ve vessel sel sh shall all be be pu pumpe mped to the LP production separator and its water content should be taken as 0-1% (normal), and 10% (peak). (peak). In normal normal operation, the contents contents of  the de-oiled water section shall be discharged, discharged, under manual control, to the drainage caisson (see 2.2 (b)). See Commentary notes on flow reversal in 5.2.1 and 5.2.2 above.

6.1.1 .1.12 2

Any Any flas flashe hed d vapou apourr fro from m nat natur uraal ga gas liq liqui uid ds or or dis disso solv lveed ga gases associated with drainage shall be free-vented directly to the LP flare header.

6.1.1 .1.13 3

Tho Those equip quipm ment ent dra drain inss whi whicch re requir quiree ob observ servaation tion durin uring g ope opera rati tio on shall be discharged to the open drains via an open tundish rather than by connection connection to the closed closed drain system. system. Sour water drains shall shall not be included in this category. Procedures and equipment shall be

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arranged so as to minimise release of flammable and/or toxic vapours in such applications. 6. 2

Equipment Requirements

6.2.1

General

6.2. 6.2.1. 1.1 1

The The des desig ign n of of the the drai draina nage ge syst system em shal shalll acc accom ommo moda date te the the req requi uire reme ment nt,, if necessary, to route small quantities of fluid from a vessel directly to the closed drainage system without first depressurising.  In some cases, where blowdown would lead to low temperatures, it may be appropriate to route the drains direct to the HP flare drum, which is often designed   for low temperatures. The flare drum will then 'catch' any liquids (e.g. blowdown  from the various compressor compressor suction drums).  Normally, hydrocarbon systems will be depressurised depressurised to flare prior to discharge into the drainage system.

6.2.1.2

Backflow fr from6.2.3

Closed Dr Drain Dr Drum. (S (See al also 2. 2.1.2).

6.2.3 .2.3..1

Sizi Sizin ng of of the the clos losed dra drain drum rum sh should ould be ba based sed on on the the foll follow owin ing g parameters:(a)

The largest item of equipment likely to be drained to the closed drain drum.

(b) (b)

The The con conte tent ntss of of the the inle inlett lin linee with with larg larges estt dia diame mete ter. r.

(c) (c)

Likel ikely y ov overflo rflow ws fro from m sto stora rag ge ta tanks. ks.

For very large vessels, there should be provision to reduce the inventory to a minimum using normal process outlets. The size of the drain drum can then be based  on the lowest lowest practical inventory of the vessel and piping. Consider supply supply operations and the likely overflow from storage tanks.

6.2. 6.2.3. 3.2 2

The The requ requir irem emen entt for for elec electr tric ic heat heater erss to main mainta tain in the the temp temper erat atur uree of the the liquid in the drum shall be considered. considered. Any such such heaters shall operate under temperature switch control. An extra-high-temperature switch shall be provided to switch off off the heaters in the event event of overheating.

6.2. 6.2.3. 3.3 3

If the the clos closed ed drai drain n dru drum m req requi uire ress des desan andi ding ng faci facili liti ties es,, the the spar sparge ge shal shalll be arranged so that the heating elements and bottom outlet nozzles as well as the vessel base are cleaned effectively. effective ly.

6.2. 6.2.3. 3.4 4

An extr extraa-hi hig gh-li h-liqu quid id-l -lev evel el swit switch ch shal shalll be prov provid ided ed in the the cent centre re section of the drum. Operation of this switch shall open an emergency dump valve discharging directly to the drainage caisson. Operation of the extra-high-liquid-level switch shall cause an emergency dump valve to open, allowing the drum contents to discharge directly to the drainage caisson. It 

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should be noted that the high-level control should be designed to avoid the risk of  liquid carry-over to the flare system.

6.2.3.5

In the case of closed drain vessels with a de-oiled water section, an extra-low level switch shall be provided on the de-oiled water section of the drum. Operation of this switch shall cause a valve on the deoiled water outlet line to close.  Note that for maintenance requiring complete emptying, the drum can be totally drained through a manhole by use of a portable pump.

6.2.3.6

The recovered oil pumps and closed drain drum instrumentation may be top mounted to allow the drum to be located at a low level, i.e. within or below platform lowest deck level.

6.2.4

Recovered Oil Pumps

6.2.4.1

Typically, Typically, two recovered oil pumps should be provided, each sized for 50% of the total design feed flow rate to the closed drain drum and suitable for the 'oil' properties. Frequently the oil will be light condensate, i.e. with a high vapour pressure.

6.2.4.2

The pumps shall discharge, under level-switch control, typically to the main crude oil line upstream of an LP production separator. The level switches should be arranged such that the pump-start frequency will not be greater than six times per hour. For partitioned drums, the pumps shall take suction  from the recovered oil section.

6.2.4.3

7.

Each recovered oil pump shall be fitted with with high and low  low   pressure switches on the discharge, in accordance accordance with API RP 14C. Operation of these switches shall initiate shutdown of the pumps.

DRILLING AREAS DRAINAGE

7.1

This Section applies only to the use of water-based drilling muds.  Note that, as stated in 1.1.3, the use of oil-based muds is outside the scope of this  Recommended Practice. These muds require specific provisions, i.e. total containment, or exemptions agreed with the regulating authority.

7.2

The drainage philosophy for the wellhead and drilling drilli ng areas should be generally as shown on Figure 6. The drainage systems systems in this area should be as follows:(a)

Segregated Segregated oil-free water drains for surface drainage from the mud handling handling area area and drilling floor. These drains drains should discharge to sea via the shale chute.

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(b) (b)

Oil-f Oil-fre reee wat water er deck deck drai drains ns for for sur surfa face ce drai draina nage ge from from the the piperack area (see Section 4).

(c) (c)

Clos Closed ed drai drains ns for for drai drainn-do down wn of lubr lubric icat ator ors, s, flowl flowlin ines es and and manifolds (see Section 6).

(d) (d)

Segr Segreg egat ated ed oiloil-fr free ee wat water er dra drain inss for for surf surfac acee drai draina nage ge fro from m the cement handling handling area. area. This drain should discharge discharge direct to sea.  As it is susceptible to blockage, this segregated drain from the cement  handling area shall be provided with a facility for permanent flushing.  Also, the lines shall be made from flanged sections of appropriate lengths  for easy dismantling.

7.3

An open oily water drainage system should not be necessary in this area. Disposal of lubricants, oil, sample point liquids, etc., can be more economically achieved by drumming.

7.4

The surface drainage of th the well deck and the BOP/impact de deck should be allowed to discharge direct to sea through the gaps between the BOP/impact deck plates and the open grating of the welldeck.  Note that the quantities of surface drainage flows on these decks will generally be limited by the collection system for deck drainage on the drilling floor above. This is because the drilling derrick/substructure derrick/substructure shields these decks.

8.

7.5

Gulleys should be provided under the BOP deck, to avoid leakage through gaps in the BOP/impact deck causing corrosion to equipment located beneath the BOP, e.g. corrosion under heat insulation on flowlines. Alternatively, the facilities facilities under under the BOP should should be be suitable for exposure to surface drainage from the deck above, or consideration may be given to the use of watertight hatches.

7.6

Rain-water cco ollected by by the dr drilling de derrick/substructure sh should be be directed overboard.

FIREWATER OV OVERFLOW DR DRAINAGE 8. 1

General

8.1.1

Firewater ov overflow dr drainage sh shall be be pr provided to to fu fulfil fil fo four ai aims:(i)

to mini minimi mise se the the sur surfa face ce area area of a poo pooll fire fire and and the there reby by redu reduce ce the fire size,

(ii) (ii)

duri during ng a fire fire,, to disp dispos osee of unwa unwant nted ed oil oil to to the the sea sea or to a caisson as quickly and safely as possible,

(iii (iii))

to prev preven entt the the spre spread ad of a fire fire,,

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(iv) (iv)

to min minim imis isee the the size size of of the the oily oily wat water er dra drain inag agee syst system em..

 Note that (i), (ii) and (iii) will only apply where a credible pool fire hazard exists. This excludes gas processing, high pressure condensate processing, high flash-point   fuels remote from other hazards, and process sections containing less than 1 tonne of low flash-point liquids after stabilisation or polar solvents.

These aims may be achieved by either:(a) (a)

Rout Routin ing g of of fir firew ewat ater er runrun-of offf ove overr the the dec deck k pla plate tess awa away y fro from m other plant areas, and discharge overboard. For environmental protection, local catchment trays may be necessary such as under pig trap doors. This is particularly important when the lower decks are of the open type. This method should be adopted on bottom decks and wellbays wherever   possible, as the large flows associated with the use use of firewater will result in the need for large diameter lines in a piped firewater overflow drainage collection system. If applied to other decks, overflow points at the edge of  the platform shall be identified and the consequences of the carry-over of  burning oil to lower decks assessed. This should consider the effect of wind, the location of escape routes and lifeboats as well as the proximity of  hydrocarbon equipment and structures which could be affected by fire.

(b) (b)

Colle Collect ctio ion n of fire firewa wate terr runrun-of offf in gul gulle ley ys asso associ ciat ated ed wit with h the the oily water open drainage system. The gulleys shall incorporate two offtakes; one at a low level leading to the oily water open drainage system, the other at a higher level leading to the firewater overflow drainage system. Where convenient, the individual firewater overflow drains should be piped directly overboard. Only if necessary should the firewater overflow drainage be collected in headers, the outlets of which shall discharge overboard. They should terminate at least 3.0 metre below the lowest equipment equipment and, wherever practicable, not above access ways.

(c)

Sub-di Sub-divid viding ing large large,, open open proces processs areas areas using using gulle gulleys ys,, gratin gratings gs or 'sleeping policemen'. Segregation according to process section is desirable. e.g Separator area and MOL pump area. Catchment areas should should be as small as reasonably  practical and should not exceed 600m 2  where there are large liquid  inventories.

These measures, plus solid floor edging at louvers shall be used to ensure that there is no overflow overflow into other areas.

8.1.2

The siz siziing of of th the fi firew rewater ov overfl rflow dr drainage sy system sh shall ta take no no credit for the capacity of the oily water open drainage system.

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The capacity of the system will be reduced if there are too many bends, dirt traps, etc. It may be improved by the inclusion of vortex breakers.

8.1.3 .1.3

The The hydr hydraaulic ulic desig esign n of th the fire firewa wate terr dra drain inaage system tem shall hall allo llow for for the maximum output (not just the design output) of the firewater system plus that of any portable equipment that may also be used. Where practicable, the design should be 110% of the maximum output so as to allow  for cross flow from other areas and pooling. An allowance for supercharging may also be made (see 8.2.1).

8. 2

Equipment Requirements

8.2.1

Gulleys Firewater overflow drainage gulleys should be provided as shown in Figure 7 (see also 3.3.2.3). Where practicable, practicable, the design should should ensure discharge of oil to the sea before the firewater.

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8.2.2

Divisions Upstands at louvered walls and 'sleeping policemen' should be 25 mm higher than that required for drainage control. Further allowance should be made for deck irregularities. When deciding on the position of a division, personnel movements and trip hazards shall be considered.

8.2.3

Firewater Drainage Piping

8.2. 8.2.3. 3.1 1

Drai Draina nag ge pipi piping ng shou should ld fall fall towa toward rdss the the disc discha harg rgee poi point nt (see (see 3.1 3.1 and and 3.2).

8.2. 8.2.3. 3.2 2

Fire Firewa wate terr dra drain inag agee from from safe safe area areass sha shall ll be kept kept phy physica sicall lly y sepa separa rate te from that from hazardous areas.

8.2.3 .2.3.3 .3

Loop sea seals ls should ould be pro prov vide ided on on fir firew ewat ateer ov overflo rflow w dra drain inss fro from m gulleys in hazardous areas and pressurised modules.

8.2. 8.2.3. 3.4 4

Subj Subjec ectt to pres pressu suri risa sati tion on requ requir irem emen ents ts loop loop seal sealss are are not not req requi uire red d below the lowest deck elevation. However, they may help in snuffing fires in the outflow.

8.2. 8.2.3. 3.5 5

Any Any form form of impe impedi dime ment nt to the the free free flow flow of surf surfac acee wate waterr to to the the dra drain inss should be avoided.

8.2. 8.2.3. 3.6 6

The The pos possi sibi bili lity ty of the the fir firew ewat ater er drai drain n fre freez ezin ing g bec becau ause se of spil spilla lage ge of  low temperature material during a fire should be considered.

8.2.4

Bunded Areas Firewater shall be prevented from overflowing from bunded areas, such as around tanks containing flammable or hazardous materials, during deluge. The use of overflow outlets leading to the firewater drainage system or provision of low-level manual drains to the oily drains system should be considered.

8.2.5

Helidecks Helidecks shall be provided with a gulley drain system which shall drain to a safe location (see 8.1.1 and 8.2.1).

9.

CHEMICAL DRAINAGE 9. 1

General

9.1.1

The pre prefferre rred me method of of di disposal of of sp spille lled ch chemicals is th that th they should be drummed for disposal ashore. ashore. Where this is not not feasible, and for most low toxicity chemicals, they may be diluted into the seawater discharge line, and discharged through the seawater outfall

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caisson, in accordance with the design and equipment guidelines below. 9.1.2 .1.2

Any Any haza hazard rdou ouss chemic emicaal disc ischarge rge into into lab laborato ratory ry drain rainss, sha shall be rendered non-hazardous, e.g. by manually flushing the drain immediately with a suitable neutralising solution.

9.1.3

At th the co commencement of of de design work, rk, BP BP wi will provide a list of of li likely chemical stock items, their properties and approximate quantities involved. This listing will also indicate:(a) (a)

Whether bu bulk st storage is in intended.

(b)

The The toxi toxici city ty ratin ratings gs and and cor corro rosi sivi vity ty of the the vari variou ouss item items. s.

(c) (c)

9.1.4 .1.4

Gene Genera rall haza hazard rd inf infor orma mati tion on,, e.g. e.g. som somee chem chemic ical alss are are inn innoc ocuou uouss on thei their  r  own but may react dangerously with others or with water. Chemical reactions may be highly exothermic or may release toxic of corrosive by products.

All All chemi hemiccal stora torag ge and hand andlin ling area reas and the their sub sub-div -divis isio ion ns, sh shall all be provided with kerbs and valved connections to chemical drains, the valves normally being closed. The layout shall be such that any significant sized spill can be collected and  drummed for disposal ashore. ashore. Valves to drain may be opened to dispose of  uncontaminated rain-water. If minor contamination is present adequate water   flushing shall be provided, and the area cleared via the chemical drain. Specific attention shall be given to ensure that the design of the containment is appropriate to the materials handled, and also to avoid risk to personnel, especially those working on lower platform levels.

9.1.5

Chemical dr drains ins sh should co connect to to se seawater he headers at po points where the headers are free-draining to the seawater outfall caisson. Connection of these drains to to free-draining headers will prevent the accumulation of chemicals should there be an interruption of seawater flow due to a platform shutdown.

9.1.6 .1.6

A hydra draulic lic check eck shall all be mad made on chem hemica ical drain rain lin lines and seawa eawate terr headers to ensure that there is adequate flow.

9.1.7

Removable in injec jection ion qu quill ills sh should be be pr provided wh wherever cch hemica ical drains are connected into the seawater headers.  A typical injection quill is shown on Figure 8. The quill design normally should  incorporate electrical insulation between the dissimilar metals of the chemical drain  piping and seawater header.

9.1.8

Reactions be between ch chemicals sh shall be be co considered. An Any necessary segregation shall be employed.

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

PAGE 29

10.

9.2

Equipment Requirements

9.2.1

Chemical Drainage Piping

9.2.1.1

Drainage piping should fall towards the discharge points. (see 3.1 and 3.2).

SANITARY DRAINAGE 10.1

General

10.1.1

A single sanitary drainage system shall be provided for domestic effluent, including drains from toilets, galley, internal internal floors, floors, laundry, etc., and shall be designed in accordance with BS 5572. A typical schematic diagram for a sanitary drainage system is given in Figure 9.

10.1.2

BP may specify special requirements requirement s for drainage from medical suites.

10.1.3

Reference shall be made to BP Group RP 4-1 for guidance in the calculation of maximum discharge rates into the drainage system.

10.1.4

A macerator is sufficient for the sanitary drainage system prior to drainage disposal in a gravity outfall line, unless statutory requirements specify additional facilities, such as a bio-treatment unit. A bypass for cleaning purposes shall be provided.

10.2

Equipment Requirements

10.2.1

Sanitary Drainage Collection Piping

10.2.1.1

Drainage piping should fall towards the discharge point. po int. The net slopes and line sizes shall be selected in accordance with BS 8301. 8301.

10.2.1.2

UPVC or other suitable pipe is acceptable where conditions permit. There are situations where plastic pipework is not suitable, for example in external situations or where there is a risk of damage from local operations or  equipment/material movements or in applications where high temperatures may be experienced.

10.2.2

Seals In cases where drains emanate from pressurised areas, e.g. accommodation modules, seals should be provided to minimise leakage of air.

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

PAGE 30

10.2.3

Sewage Outfall Line The sewage outfall line shall be extended to be submerged continuously continuous ly thereby preventing preventi ng blow back due to wave action. Its location shall be in accordance with 2.7.

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

PAGE 31

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I    O  C E  L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I   F   ,  N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

P  A  G E   3  2 

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I   E   O  C L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I    , F   N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

P  A  G E   3   3 

 S  I   M P  L  I   F  I    S  E  E  D P   O A  V R E  A T  R A I   L   O  N L  P  D L  R  U A  S   N I    O A I   L  G R E  E  S  MY  O  S  T   V E  A M L  (   P  D A R  C A K  N I   A A  G  G E   )   E   C A I    S   S   O  N

 (   P  R I   M A R Y  O  S  I   I   L  M  S  P  E  L  P  I   F  A I   R E  A D T  O I    O  V  N E  F  I    U R A  G P  L   S  L  U T  R R D E  E  R 1  A A B  M I    N  O A F   G D E  R  S  A Y I    S   N T  A E   G M E   C A I    S   S   O  N  )  

TO FLARE CRUDE OIL

GAS

) (

LP PRODUCTION SEPARATOR

PRODUCED WATER FLASH DRUM PRODUCED WATER TREATMENT PACKAGE

CRUDE OIL ) (

PRODUCED WATER

FROM HP SEPARATOR SCRUBBERS ETC.

F  I    G  U R E  1  A

(SECTION 10)

TREATMENT PACKAGE OIL PUMP

PRODUCED WATER

) (

OIL-FREE WATER DRAINAGE SYSTEM

DRILLING AREAS DRAINAGE SYSTEM

(SECTION 4)

(SECTION 7)

SANITARY DRAINAGE SYSTEM

PRODUCED WATER

) (

OILY WATER OPEN DRAINAGE SYSTEM (SECTION 5)

) (

OILY WATER CLOSED DRAINAGE SYSTEM (SECTION 6)

CHEMICAL DRAINAGE SYSTEM (SECTION 9)

FIREWATER OVERFLOW

FIREWATER OVERFLOW DRAINAGE SYSTEM

SEWAGE MACERATOR

(SECTION 8)

PRODUCED WATER OIL REMOVAL PACKAGE (OIL WATER FILTER COALESCER)

CLOSED DRAIN DRUM

) ( RECOVERED OIL PUMP

OVERBOARD

TREATED WATER

OVERBOARD

SEAWATER OUTFALL CAISSON

INPUTS TO BE BELOW LIQUID LEVEL AT ALL TIMES

SHALE SHUTE

SEA LEVEL

OVERBOARD

DRAINAGE CAISSON PUMP

SEWAGE OUTFALL LINE

DRAINAGE CAISSON

CRUDE OIL

TO FLARE

) (

GAS

LP PRODUCTION SEPARATOR PRODUCED WATER FLASH DRUM

CRUDE OIL PRODUCED WATER FROM HP SEPARATOR SCRUBBERS ETC.

SANITARY DRAINAGE SYSTEM (SECTION 10)

OIL-FREE WATER DRAINAGE SYSTEM (SECTION 4)

PRODUCED WATER TREATMENT PACKAGE

) ( PRODUCED WATER

SEPARATED OIL

TREATMENT PACKAGE OIL PUMP

PRODUCED WATER

) (

DRILLING AREAS ) DRAINAGE ( SYSTEM (SECTION 7)

OILY WATER OPEN DRAINAGE SYSTEM (SECTION 5)

) (

OILY WATER CLOSED DRAINAGE SYSTEM (SECTION 6)

CHEMICAL DRAINAGE SYSTEM (SECTION 9)

FIREWATER OVERFLOW

FIREWATER OVERFLOW DRAINAGE SYSTEM

SEWAGE MACERATOR

(SECTION 8)

SEPARATED OIL PUMP PRODUCED WATER CLOSED DRAIN DRUM

OILY WATER SEPARATOR

) (

SEAWATER

RECOVERED OIL PUMP OVERBOARD

TREATED WATER OVERBOARD SHALE SHUTE

SEWAGE OUTFALL LINE

SEAWATER OUTFALL CAISSON

INPUTS TO BE BELOW LIQUID LEVEL AT ALL TIMES

DRAINAGE CAISSON PUMP DRAINAGE CAISSON

SIMPLIFIED OVERALL DRAINAGE SYSTEM (PRIMARY OIL SEPARATION UPSTREAM OF DRAINAGE CAISSON)

SEA LEVEL

OVERBOARD

 (   P  R I   M A R Y  O  S  I   I   L  M  S  P  E  L  P  I   F  A I   R E  A D T  O I    V  O  N E  F  I    U R A  G P  L   U  S  L  R T  R D E  E  R 1  A A B  M I    N  O A F   G D E  R  S  A Y I    S   N T  A E   G M E   C A I    S   S   O  N  )  

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I    O  C E  L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I   F   ,  N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

P  A  G E   3   3 

 G  U I   D A E  N D T  S   O P  P  E T H L  C A E T I   F   S  F  I   E  O  C L R R A E P  M T  C 4  I   T D  O I   4  R  N  O 1  A  O  N 1  I    ,  N F  A A  O R  G F  R F  A E  S  H  N  O  G R E E M E  N T

P  A  G E   3   5 

T Y P  I    C A L T  O P   S  I   D E  S  D R A I    N A  G E A R R A  N  G E M E  N T

F  I    G  U R E 2 

CRUDE OIL

TO FLARE

) (

GAS

LP PRODUCTION SEPARATOR PRODUCED WATER FLASH DRUM

CRUDE OIL PRODUCED WATER FROM HP SEPARATOR SCRUBBERS ETC.

SANITARY DRAINAGE SYSTEM (SECTION 10)

OIL-FREE WATER DRAINAGE SYSTEM (SECTION 4)

PRODUCED WATER TREATMENT PACKAGE

) ( PRODUCED WATER

SEPARATED OIL

TREATMENT PACKAGE OIL PUMP

PRODUCED WATER

) (

DRILLING AREAS ) DRAINAGE ( SYSTEM (SECTION 7)

OILY WATER OPEN DRAINAGE SYSTEM (SECTION 5)

) (

OILY WATER CLOSED DRAINAGE SYSTEM (SECTION 6)

CHEMICAL DRAINAGE SYSTEM (SECTION 9)

FIREWATER OVERFLOW

FIREWATER OVERFLOW DRAINAGE SYSTEM

SEWAGE MACERATOR

(SECTION 8)

SEPARATED OIL PUMP PRODUCED WATER CLOSED DRAIN DRUM

OILY WATER SEPARATOR

) (

SEAWATER

RECOVERED OIL PUMP OVERBOARD

TREATED WATER OVERBOARD SHALE SHUTE

SEWAGE OUTFALL LINE

SEAWATER OUTFALL CAISSON

INPUTS TO BE BELOW LIQUID LEVEL AT ALL TIMES

DRAINAGE CAISSON PUMP DRAINAGE CAISSON

SIMPLIFIED OVERALL DRAINAGE SYSTEM (PRIMARY OIL SEPARATION UPSTREAM OF DRAINAGE CAISSON)

SEA LEVEL

OVERBOARD

 G  U I   D A E  N T D  S   O P  P  E T H L  C A E T I   F  F  I    S  E R  O  C L R A E P  M T  C 4  I   T D  O I   4  R  N  O 1  A  O  N 1  I   F   ,  N A A  O R  G F  R F  A E  S  H  N  O  G R E E M E  N T

T Y P  I    C A L T  O P   S  I   D E  S  D R A I    N A  G E A R R A  N  G E M E  N T

F  I    G  U R E 2 

P  A  G E   3   5 

 G  U I   D A E  N D T  S   O P  P  E T H L  C A E T I   F   S  F  I   E  O  C L R R A E P  M T  C 4  I   T D  O I   4  R  N  O 1  A  O  N 1  I    ,  N F  A A  O R  G F  R F  A E  S  H  N  O  G R E E M E  N T

P  A  G E   3   6 

 O I   L F  R E E  W A T E R D R F  A I   I    G  N A  U R  G E E  S   3  Y  S  T E M  S   C H E M A T I    C

 G  U I   D A E  N T D  S   O P  P  E T H L  C A E T I   F  F  I    S  E R  O  C L R A E P  M T  C 4  I   T D  O I   4  R  N  O 1  A  O  N 1  I   F   ,  N A A  O R  G F  R F  A E  S  H  N  O  G R E E M E  N T

 O I   L F  R E E  W A T E R D R F  A I   I    N  G A  U R  G E E  S   3  Y  S  T E M  S   C H E M A T I    C

P  A  G E   3   6 

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I   E   O  C L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I    , F   N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

P  A  G E   3   6 

 (   D R A I    N A  G E   C A I    S   S   O  N  S  E  P  A R A T  I    O  N P  L   U  S   O I   L  R E  M  O  V A L  P  A  C K A  G E   )  

OILY WATER DRAINS ( NON-HAZARDOUS AREAS ) VENT

OILY WATER DRAINS ( HAZARDOUS AREAS ) VENT

VENT

VENT GULLEY

 O I   L  Y  W A T  E  R  O P  E   N F  I   D  G R  U A R I   E   N A 4   G A E   S  Y  S  T  E  M  S   C H E  M A T  I    C

GULLEY

TUNDISH

TO CRUDE OIL OUTLET OF LP PRODUCTION FROM OTHER SEPARATOR DECK LEVELS

ATMOSPHERIC VENT RELIEF SYSTEM

TYPICAL CONNECTION (OTHER HAZARDOUS  AREAS)

TUNDISH 1:100 MIN

NET FALL

TYPICAL CONNECTION (OTHER NON-HAZARDOUS AREAS) NET FALL

1:100 MIN NET FALL RODDING POINT

1:100 MIN

NET FALL

1:100 MIN

DRAIN TANK OR CAISSON

LEGEND VALVE NORMALLY OPEN VALVE NORMALLY CLOSED

OIL REMOVAL PACKAGE (OIL WATER FILTER COALESCER)

SEAL LEVEL TEST COCKS

RELIEF VALVE REVERSIBLE  SPADE

REMOVABLE STRAINER

SAMPLING SYSTEM

FLAME ARRESTER

REMOVABLE GRATING

NITROGEN PURGE

DECK PLATE

DRAINAGE CAISSON PUMP SEA LEVEL

300mm

300mm

DRAINAGE CAISSON

FIREWATER OVERFLOW DRAINAGE SYSTEM

OILY WATER OPEN DRAINAGE SYSTEM TYPICAL OPEN DRAIN GULLEY WITH FIREWATER OVERFLOW

INPUTS TO BE BELOW LIQUID LEVEL AT ALL TIMES

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I    O  C E  L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I   F   ,  N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

P  A  G E   3   6 

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I   E   O  C L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I    , F   N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

P  A  G E   3   7 

 (   D R A I    N A  G E   C A I    S   S   O  N  S  E  P  A R A T  I    O  N P  L   U  S   O I   L  R E  M  O  V A L  P  A  C K A  G E   )  

 (   P  R I   M A R Y  O I   L   S  E  P  A R A T  I    O  N  U P   S  T  R E  A M  O F  D R A I    N A  G E   C A I    S   S   O  N  )  

OILY WATER DRAINS ( NON-HAZARDOUS AREAS ) VENT

OILY WATER DRAINS ( HAZARDOUS AREAS ) VENT

VENT

VENT GULLEY

 O I   L  Y  W A T  E  R  O P  E   N F  I   D  G R  U A R I   E   N A 4   G A E   S  Y  S  T  E  M  S   C H E  M A T  I    C

GULLEY

TO CRUDE OIL OUTLET OF LP PRODUCTION FROM OTHER SEPARATOR DECK LEVELS

TUNDISH

ATMOSPHERIC VENT RELIEF SYSTEM

TYPICAL CONNECTION (OTHER HAZARDOUS  AREAS)

TUNDISH 1:100 MIN

NET FALL

TYPICAL CONNECTION (OTHER NON-HAZARDOUS AREAS) NET FALL

1:100 MIN 1:100 MIN

NET FALL RODDING POINT

DRAIN TANK OR CAISSON

1:100 MIN

NET FALL

LEGEND VALVE NORMALLY OPEN VALVE NORMALLY CLOSED

OIL REMOVAL PACKAGE (OIL WATER FILTER COALESCER)

SEAL LEVEL TEST COCKS

RELIEF VALVE REVERSIBLE  SPADE

REMOVABLE STRAINER

SAMPLING SYSTEM

FLAME ARRESTER

REMOVABLE GRATING

NITROGEN PURGE

DECK PLATE

DRAINAGE CAISSON PUMP SEA LEVEL

300mm

300mm INPUTS TO BE BELOW LIQUID LEVEL AT ALL TIMES

DRAINAGE CAISSON

FIREWATER OVERFLOW DRAINAGE SYSTEM

OILY WATER OPEN DRAINAGE SYSTEM TYPICAL OPEN DRAIN GULLEY WITH FIREWATER OVERFLOW

 O I   L  Y  W A T  E  R  O P  E   N D R A I    N A  G E   S  Y  S  T  E  M  S   C H E  M A T  I    C

OILY WATER DRAINS ( NON-HAZARDOUS AREAS ) VENT

OILY WATER DRAINS ( HAZARDOUS AREAS )

VENT

VENT GULLEY

VENT TUNDISH

GULLEY

TO CRUDE OIL

FROM OTHER

OUTLET OF LP

DECK LEVELS

PRODUCTION SEPARATOR

TYPICAL CONNECTION

ATMOSPHERIC

TO CLOSED

DRAIN DRUM

VENT RELIEF SYSTEM

(OTHER HAZARDOUS AREAS)

TUNDISH NET FALL TYPICAL CONNECTION

1:100 MIN

(OTHER NON-HAZARDOUS AREAS)

NET FALL

1:100 MIN NET FALL

1:100 MIN

RODDING

POINT

F  I    G  U R E  4  B 

NET FALL

1:100 MIN DRAIN TANK OR CAISSON

BYPASS BYPASS

SEAL LEVEL TEST COCKS

LEGEND VALVE NORMALLY

OPEN

REMOVABLE

VALVE NORMALLY

FALL

STRAINER

CLOSED

REMOVABLE GRATING

RELIEF VALVE

FALL

REVERSIBLE

DECK PLATE

SPADE

NITROGEN

FLAME

PURGE

ARRESTER

NITROGEN PURGE 300mm

300mm

SEPARATED

OIL PUMP

OILY WATER

SEPARATOR

DRAINAGE CAISSON PUMP

OILY WATER OPEN DRAINAGE SYSTEM

SEA LEVEL

FIREWATER OVERFLOW

DRAINAGE SYSTEM

TYPICAL OPEN DRAIN GULLEY WITH FIREWATER OVERFLOW

INPUTS TO BE BELOW LIQUID DRAINAGE

CAISSON

LEVEL AT ALL TIMES

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I    O  C E  L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I   F   ,  N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

P  A  G E   3   7 

 (   P  R I   M A R Y  O I   L   S  E  P  A R A T  I    O  N  U P   S  T  R E  A M  O F  D R A I    N A  G E   C A I    S   S   O  N  )  

 O I   L  Y  W A T  E  R  O P  E   N D R A I    N A  G E   S  Y  S  T  E  M  S   C H E  M A T  I    C

OILY WATER DRAINS ( NON-HAZARDOUS AREAS ) VENT

OILY WATER DRAINS ( HAZARDOUS AREAS )

VENT

VENT GULLEY

VENT TUNDISH

TO CRUDE OIL

FROM OTHER

OUTLET OF LP

DECK LEVELS

PRODUCTION SEPARATOR

TYPICAL CONNECTION

GULLEY

ATMOSPHERIC

TO CLOSED

DRAIN DRUM

VENT RELIEF SYSTEM

(OTHER HAZARDOUS AREAS)

TUNDISH NET FALL TYPICAL CONNECTION

1:100 MIN

(OTHER NON-HAZARDOUS AREAS)

NET FALL

1:100 MIN NET FALL

1:100 MIN

RODDING

POINT

NET FALL

1:100 MIN DRAIN TANK OR CAISSON

F  I    G  U R E  4  B 

BYPASS BYPASS

SEAL LEVEL TEST COCKS

LEGEND VALVE NORMALLY

OPEN

REMOVABLE

VALVE NORMALLY

FALL

STRAINER

CLOSED

REMOVABLE GRATING

RELIEF VALVE

FALL

REVERSIBLE

DECK PLATE

SPADE

NITROGEN

FLAME

PURGE

ARRESTER

NITROGEN PURGE 300mm

300mm

SEPARATED

OIL PUMP

OILY WATER

SEPARATOR

DRAINAGE CAISSON PUMP

SEA LEVEL

FIREWATER OVERFLOW

OILY WATER

INPUTS TO BE BELOW LIQUID

DRAINAGE

OPEN DRAINAGE SYSTEM

LEVEL AT ALL TIMES

DRAINAGE

SYSTEM

CAISSON

TYPICAL OPEN DRAIN GULLEY WITH FIREWATER OVERFLOW

LEGEND VALVE NORMALLY OPEN

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I   E   O  C L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I    , F   N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

P  A  G E   3   8 

 O I   L  Y  W A T  E  R  C L   O  S  E  D D F  R I   A  G  U I    N R A E   G  5  E   S  Y  S  T  E  M  S   C H E  M A T  I    C

VALVE NORMALLY CLOSED RELIEF VALVE

ATMOSPHERIC VENT HEADER VESSEL AND TANK DRAINS

REVERSIBLE SPADE

LINE DRAINS (MANIFOLDS, HEADERS, ETC.)

TYPICAL CONNECTION

VENT TO  LP FLARE

TYPICAL AREA CONNECTION

RODDING POINT

NET FALL

FLUSHING POINT

RELIEF FLARE MANAGER

1:100 MIN

RODDING POINT FROM DRAINAGE CAISSON PUMP (SEE FIGURE 4b)

DRAINAGE FROM COLD, DRY VESSELS ETC. (NGL, GAS CONDENSATE ETC.) CARRIED IN SEPARATE COLLECTION HEADER.

NET FALL

1:100 MIN

( POSSIBLE TRACE HEATING)

NET FALL

1:100 MIN

INSTRUMENT PIPING SPECIFICATION PROCESS PIPING SPECIFICATION

TYPICAL MANIFOLDING OF INSTRUMENT DRAINS TO OILY WATER CLOSED DRAINAGE SYSTEM

OPTIONAL ENTRY TO VESSEL FROM LOWER SOURCES OF OILY WATER

OPTIONAL SPARGE (TREATED WATER)

EMERGENCY (HIGH-LEVEL) AUTOMATIC DUMP VALVE

OPTIONAL ELECTRIC HEATER CLOSED DRAIN DRUM

TO CRUDE OIL INLET OF LP PRODUCTION SEPARATOR

TO DRAINAGE CAISSON MANUAL DRAIN VALVE RECOVERED OIL PUMP

LEGEND VALVE NORMALLY OPEN

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I    O  C E  L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I   F   ,  N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

 O I   L  Y  W A T  E  R  C L   O  S  E  D D F  R I   A  G I    U  N R A E   G  5  E   S  Y  S  T  E  M  S   C H E  M A T  I    C

P  A  G E   3   8 

VALVE NORMALLY CLOSED RELIEF VALVE

ATMOSPHERIC VENT HEADER VESSEL AND TANK DRAINS

REVERSIBLE SPADE

LINE DRAINS (MANIFOLDS, HEADERS, ETC.)

TYPICAL CONNECTION

VENT TO  LP FLARE

TYPICAL AREA CONNECTION

RODDING POINT

NET FALL

FLUSHING POINT

1:100 MIN

RODDING POINT FROM DRAINAGE CAISSON PUMP (SEE FIGURE 4b)

DRAINAGE FROM COLD, DRY VESSELS ETC. (NGL, GAS CONDENSATE ETC.) CARRIED IN SEPARATE COLLECTION HEADER.

NET FALL

1:100 MIN

( POSSIBLE TRACE HEATING)

P  A  G E   3   9 

NET FALL

1:100 MIN

INSTRUMENT PIPING SPECIFICATION PROCESS PIPING SPECIFICATION

OPTIONAL ENTRY TO VESSEL FROM LOWER SOURCES OF OILY WATER

OPTIONAL SPARGE (TREATED WATER)

OPTIONAL ELECTRIC HEATER

EMERGENCY (HIGH-LEVEL) AUTOMATIC DUMP VALVE

TYPICAL MANIFOLDING OF INSTRUMENT DRAINS TO OILY WATER CLOSED DRAINAGE SYSTEM

TO CRUDE OIL INLET OF LP PRODUCTION SEPARATOR

CLOSED DRAIN DRUM

TO DRAINAGE CAISSON MANUAL DRAIN VALVE RECOVERED OIL PUMP

NOTES :

DRILLING FLOOR

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I   E   O  C L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I    , F   N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

RELIEF FLARE MANAGER

D R I   L  L  I    N  G A R E  A  S  F  D I   R  G A  U I   R  N A E   G  6  E   S  Y  S  T  E  M  S   C H E  M A T  I    C

1. NORMALLY, MINIMUM COST SOLUTION SHALL BE U SED.

PIPERACK AREA DECK

FIREWATER OVERFLOW TO SEA

IMPACT DECK

) (

) (

CEMENT AREA DECK WATER FLUSH

HOSE CONNECTION

) (

MUD MODULE DECK ) (

WELL COMPLETION FLOOR

) (

) (

) (

DRAINAGE THROUGH DECK PLATES TO FLOOR BELOW (SEE NOTE 1) FLANGED SECTIONS REQUIRED

HOSE CONNECTION

DRAINAGE OVERBOARD THROUGH OPEN MESH FLOOR

CLOSED OILY WATER DRAIN

SHALE CHUTE OVERBOARD

NOTES :

DRILLING FLOOR

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I    O  C E  L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I   F   ,  N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

P  A  G E   3   9 

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I   E   O  C L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I    , F   N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

P  A  G E  4   0 

D R I   L  L  I    N  G A R E  A  S  F  D I   R  G A  U I   R  N A E   G  6  E   S  Y  S  T  E  M  S   C H E  M A T  I    C

F  I   R E   W A T  E  R  O  V E  R F  L   O F  I    W  G  U D R R E  A I   7   N A  G E   S  Y  S  T  E  M  S   C H E  M A T  I    C

1. NORMALLY, MINIMUM COST SOLUTION SHALL BE U SED.

PIPERACK AREA DECK

FIREWATER OVERFLOW TO SEA

IMPACT DECK

) (

) (

CEMENT AREA DECK WATER FLUSH

HOSE CONNECTION

) (

MUD MODULE DECK ) (

WELL COMPLETION FLOOR

) (

) (

) (

DRAINAGE THROUGH DECK PLATES TO FLOOR BELOW (SEE NOTE 1) FLANGED SECTIONS REQUIRED

HOSE CONNECTION

DRAINAGE OVERBOARD THROUGH OPEN MESH FLOOR

CLOSED OILY WATER DRAIN

FIREWATER OVERFLOW DRAINAGE SYSTEM (HAZARDOUS AREAS)

SHALE CHUTE OVERBOARD

FIREWATER OVERFLOW DRAINAGE SYSTEM (NON-HAZARDOUS AREAS)

VENT

DECK PLATE

DECK PLATE

TYPICAL CONNECTION

TYPICAL CONNECTION

OPEN DRAIN GULLEY

OPEN DRAIN GULLEY

RODDING POINT

TYPICAL CONNECTION (PRESSURISED MODULE)

NET FALL

1:100 MIN

RODDING POINT

NET FALL

OVERBOARD

OVERBOARD

NOTES: REMOVABLE STRAINER

REMOVABLE GRATING 1. FIREWATER OVERFLOWS DO NOT REQUIRE LOOP SEALS IN NON-HAZARDOUS NON-HAZARDOUS AREAS, AREAS, UNLESS CONNECTED TO A HEADER.

DECK PLATE

2. FIREWATER OVERFLOWS DO NOT REQUIRE LOOP SEALS IN HAZARDOUS HAZARDOUS AREAS WHEN DISCHARGE IS DIRECT DIRECT TO SEA (i.e. NO COLLECTION HEADER). 300mm

300mm

SEE NOTE 1

OILY WATER OPEN DRAINAGE SYSTEM

TYPICAL OPEN DRAIN GULLEY WITH FIREWATER OVERFLOW

FIREWATER OVERFLOW DRAINAGE SYSTEM

1:100 MIN

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I    O  C E  L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I   F   ,  N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

P  A  G E  4   0 

F  I   R E   W A T  E  R  O  V E  R F  L   O F  I    W  G D  U R R E  A I   7   N A  G E   S  Y  S  T  E  M  S   C H E  M A T  I    C

FIREWATER OVERFLOW DRAINAGE SYSTEM (HAZARDOUS AREAS)

FIREWATER OVERFLOW DRAINAGE SYSTEM (NON-HAZARDOUS AREAS)

VENT

DECK PLATE

1:100 MIN

NET FALL

RODDING POINT

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I   E   O  C L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I    , F   N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

P  A  G E  4  1 

TYPICAL CONNECTION (PRESSURISED MODULE) TYPICAL CONNECTION

OPEN DRAIN GULLEY

OPEN DRAIN GULLEY

RODDING POINT

NET FALL

1:100 MIN OVERBOARD

OVERBOARD

NOTES: REMOVABLE STRAINER

REMOVABLE GRATING 1. FIREWATER OVERFLOWS DO NOT REQUIRE LOOP SEALS IN NON-HAZARDOUS NON-HAZARDOUS AREAS, AREAS, UNLESS CONNECTED TO A HEADER.

DECK PLATE

2. FIREWATER OVERFLOWS DO NOT REQUIRE LOOP SEALS IN HAZARDOUS HAZARDOUS AREAS WHEN DISCHARGE IS DIRECT DIRECT TO SEA (i.e. NO COLLECTION HEADER). 300mm

300mm

SEE NOTE 1

OILY WATER OPEN DRAINAGE SYSTEM

FIREWATER OVERFLOW DRAINAGE SYSTEM

TYPICAL OPEN DRAIN GULLEY WITH FIREWATER OVERFLOW

NOTES

LINE DRAINS (MANIFOLDS, HEADERS, ETC.)

VESSEL AND TANK DRAINS

 C H E  M I    C A L  D R A I    N F  A I    G  G E   U R  S  E  Y  S   8  T  E  M  S   C H E  M A T  I    C

DECK PLATE

TYPICAL CONNECTION

1. INJECTION QUILL REQUIRED TO DILUTE CHEMICALS IN SEAWATER STREAM. 2. HYDRAULIC CHECK SHOULD BE MADE ON CHEMICAL DRAIN LINE CONNECTIONS TO SEAWATER HEADER TO ENSURE HEAD IN SEAWATER HEADER ALLOWS FLOW IN CHEMICAL DRAINS TOWARDS HEADER.

TYPICAL CONNECTION

SEAWATER

3. ALL CHEMICAL DRAIN LINES SHOULD FALL TOWARDS INJECTION POINTS AT THE SEAWATER HEADER, NET FALL 1:100 MIN.

1:100 MIN

NET FALL

CHEMICAL DRAIN

LEGEND INSULATING GASKET AND BOLTING

VALVE NORMALLY OPEN VALVE NORMALLY CLOSED

CHEMICAL DRAIN PIPING SPECIFICATION SEAWATER PIPING SPECIFICATION

SEAWATER

TYPICAL DETAIL FOR CHEMICAL INJECTION QUILL (SEE NOTE 1)

REVERSIBLE SPADE SEAWATER OUTFALL CAISSON PIPING UNION

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I    O  C E  L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I   F   ,  N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

 C H E  M I    C A L  D R A I    N F  A I    G  G E   U R  S  E  Y  S   8  T  E  M  S   C H E  M A T  I    C

2. HYDRAULIC CHECK SHOULD BE MADE ON CHEMICAL DRAIN LINE CONNECTIONS TO SEAWATER HEADER TO ENSURE HEAD IN SEAWATER HEADER ALLOWS FLOW IN CHEMICAL DRAINS TOWARDS HEADER.

SEAWATER

3. ALL CHEMICAL DRAIN LINES SHOULD FALL TOWARDS INJECTION POINTS AT THE SEAWATER HEADER, NET FALL 1:100 MIN.

1:100 MIN

NET FALL

CHEMICAL DRAIN

LEGEND INSULATING GASKET AND BOLTING

VALVE NORMALLY OPEN VALVE NORMALLY CLOSED REVERSIBLE SPADE

CHEMICAL DRAIN PIPING SPECIFICATION

SEAWATER OUTFALL CAISSON

SEAWATER PIPING SPECIFICATION

PIPING UNION

SEAWATER

TYPICAL DETAIL FOR CHEMICAL INJECTION QUILL (SEE NOTE 1)

TYPICAL CONNECTIONS              )              (

P  A  G E  4  2 

1. INJECTION QUILL REQUIRED TO DILUTE CHEMICALS IN SEAWATER STREAM.

TYPICAL CONNECTION

P  A  G E  4  1 

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I   E   O  C L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I    , F   N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

NOTES

LINE DRAINS (MANIFOLDS, HEADERS, ETC.)

VESSEL AND TANK DRAINS

 S  A  N I   T  A R Y D R A F  I    G I    N A  U  G R E  E   S   9  Y  S  T  E  M  S   C H E  M A T  I    C

             )              (

NOTES :

             )  (

)              (

NET FALL

1.

EACH RODDING POINT SHALL BE FITTED WITH A STANDARD HOSE CONNECTION TO ENABLE LINES TO BE FLUSHED WITH SEA WATER.

2.

FALLS SHALL BE IN ACCORDANCE WITH 10.2.1.1 OF THIS CODE OF PRACTICE

3. SEALS TO BE PROVIDED ON DRAINS FROM PRESSURISED AREAS, SEE 10.2.2. LEGEND VALVE NORMALLY OPEN FLUSHING CONNECTION/  RODDING POINT (TYPICAL)

VALVE NORMALLY CLOSED SEWAGE MACERATOR

NET FALL

SEWAGE OUTFALL LINE

TYPICAL CONNECTIONS              )              (

 S  A  N I   T  A R Y D R A F  I    G I    N A  U  G R E  E   S   9  Y  S  T  E  M  S   C H E  M A T  I    C

 G  U I   A D  N E  D T   S   O P  T  P  E  L  C H A E  T  I   F   S  F  I    O  C E  L  R R A E  P  M T  C 4  I   T  4  D  O I   R  N  O 1  A  O  N 1  I   F   ,  N A A  O R  G F  R F  A E  S  H  N  O  G R E  E  M E   N T 

             )              (

NOTES :

             )  (

)              (

NET FALL

1.

EACH RODDING POINT SHALL BE FITTED WITH A STANDARD HOSE CONNECTION TO ENABLE LINES TO BE FLUSHED WITH SEA WATER.

2.

FALLS SHALL BE IN ACCORDANCE WITH 10.2.1.1 OF THIS CODE OF PRACTICE

3. SEALS TO BE PROVIDED ON DRAINS FROM PRESSURISED AREAS, SEE 10.2.2. LEGEND VALVE NORMALLY OPEN FLUSHING CONNECTION/  RODDING POINT (TYPICAL)

VALVE NORMALLY CLOSED SEWAGE MACERATOR

NET FALL

SEWAGE OUTFALL LINE

P  A  G E  4  2 

APPENDIX A

DEFINITIONS AND ABBREVIATIONS

Definitions

Standardised definitions may be found in the BP Group RPSEs Introductory volume. Abbreviations

ANSI API BOP BS DN GRP H2S LAT LP HP NGL NPS UPVC

American National St Standards Institute American Petroleum Institute Blowout preventer British Standard Nominal diameter Glass reinforced plastics Hydrogen sulphide Lowest astronomical tide Low pressure High pressure Natural gas liquids Nominal pipe size Unplasticized po polyvinyl ch chloride

APPENDIX A

DEFINITIONS AND ABBREVIATIONS

Definitions

Standardised definitions may be found in the BP Group RPSEs Introductory volume. Abbreviations

ANSI API BOP BS DN GRP H2S LAT LP HP NGL NPS UPVC

American National St Standards Institute American Petroleum Institute Blowout preventer British Standard Nominal diameter Glass reinforced plastics Hydrogen sulphide Lowest astronomical tide Low pressure High pressure Natural gas liquids Nominal pipe size Unplasticized po polyvinyl ch chloride

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

PAGE 43

APPENDIX B

LIST OF REFERENCED DOCUMENTS

A reference invokes the latest published issue or amendment unless stated otherwise. Referenced standards may be replaced by equivalent standards that are internationally or otherwise recognised provided that it can be shown to the satisfaction of the purchaser's professional engineer engineer that they meet or exceed the requirements of the referenced r eferenced standards. standards.

BS 5572

Code of practice for sanitary pipework.

 BS 6367 

Code of practice for drainage of roofs and paved areas.

BS 8301

Code of practice for building drainage.

API RP 14C

Recommended practice for analysis, analysis, design, installation and testing of basic surface safety systems for offshore production platforms.

BP Group RP 4-1

Drainage systems (was BP CP 5)

 BP Group RP Group RP 6-1

Corrosion Monitoring (was BP CP 50)

BP Group RP 44-2  44-2 

Winterisation (was BP CP 24)

BP Group GS 142-6

Piping Specifications (was BP Std 170)

SI 611

The offshore installations (firefighting equipment) regulations 1978

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

PAGE 44

APPENDIX C SUPPLEMENTARY COMMENTARY

C1

Scope

This Commentary relates to clause 1.1.  At the commencement of conceptual design, BP will provide an indication of regulatory restrictions which are expected to apply to discharge discharge from the platform. BP shall then be consulted with regard to the extent and type of waste water treatment facilities needed. The design concepts described in this document satisfy the following consent conditions and exemption levels currently applied by the UK Department of Energy to drainage systems on offshore North Sea installations: (a)Maximum oil content at point of discharge 100 mg/litre. (b)The drainage system to contain, so far as practicable, all spills, discharges and leaks of oil and  mixtures containing oil.  In other locations, particularly those close to shore or otherwise environmentally sensitive, other more stringent criteria criteria may be applied. These may require additional treatment equipment. Reference shall be made in all cases to the appropriate regulating authority to confirm requirements before design work commences.  Different and usually more stringent consent conditions are also applied to discharges of produced  water. Produced water is treated in separate systems and controlled by convention. It is not  considered in this Recommended Practice.  It is a legal requirement in UK waters, and frequently elsewhere, that no oil is discharged to sea.  However, for practical reasons, reasons, exemptions are given to offshore production production installations.  In the case of a major incident requiring the prolonged use of firewater, containment of all spills may not be practicable. This is acknowledged in 5.1.2 of the essential requirements of this document by the reference to the use of a firewater overflow system which effectively bypasses the oily water drainage systems.  However, except in the case of a major spill, as distinct from normal contamination of decks and  equipment, it is likely that the initial flow of firewater to the oil/water separation facility will clear a substantial proportion of contaminants from deck areas before firewater starts discharging to sea via the firewater overflow drainage system (see Section 8 of the essential requirements of this document).

C2

General

This Commentary relates to clause 2.1.2. Figure 1a includes a system in which primary separation of oil and water from the oily water open drainage system takes place in the drainage drainage caisson itself;. Figure 1b includes a system system in which  primary separation takes place in an oily water separator upstream of the drainage caisson. Local regulations will dictate which is the preferred system. These diagrams are representative only, and serve to illustrate typical effluent systems for an integrated platform supporting production, drilling and quarters facilities. In some cases, some

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

PAGE 45

sections would not be needed. For example, oily water may not be present present on the quarters platform of  a multi-platform complex.

C3

Gravity Flow Requirements

This Commentary relates to clause 3.2.3. Figure 2 shows typical locations of an oily water separator and closed drain drum on a platform topsides. These are placed centrally on the platform at levels which permit gravity flow from drainage  points, and gravity flow to the oily water separator. separator. Discharges of water from the oily water separator  and the closed drain drum are routed separately to the drainage caisson. These typical locations are appropriate for platforms on which the sources of effluent to the oily water  closed drainage system are generally elevated above the inlet nozzle of the closed drain drum, which is located on the platform's lowest deck level.

RP 44-11 GUIDE TO THE SELECTION, ARRANGEMENT AND SPECIFICATION OF OFFSHORE PLATFORM DRAINAGE

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