Drain System for Offshore Installation

DEP SPECIFICATION

DRAIN SYSTEMS FOR OFFSHORE INSTALLATIONS

DEP 37.14.10.10-Gen. February 2011

DESIGN AND ENGINEERING PRACTICE

DEM1

© 2011 Shell Group of companies All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, published or transmitted, in any form or by any means, without the prior written permission of the copyright owner or Shell Global Solutions International BV.

DEP 37.14.10.10-Gen. February 2011 Page 2

PREFACE DEP (Design and Engineering Practice) publications reflect the views, at the time of publication, of Shell Global Solutions International B.V. (Shell GSI) and, in some cases, of other Shell Companies. These views are based on the experience acquired during involvement with the design, construction, operation and maintenance of processing units and facilities. Where deemed appropriate DEPs are based on, or reference international, regional, national and industry standards. The objective is to set the recommended standard for good design and engineering practice to be applied by Shell companies in oil and gas production, oil refining, gas handling, gasification, chemical processing, or any other such facility, and thereby to help achieve maximum technical and economic benefit from standardization. The information set forth in these publications is provided to Shell companies for their consideration and decision to implement. This is of particular importance where DEPs may not cover every requirement or diversity of condition at each locality. The system of DEPs is expected to be sufficiently flexible to allow individual Operating Units to adapt the information set forth in DEPs to their own environment and requirements. When Contractors or Manufacturers/Suppliers use DEPs, they shall be solely responsible for such use, including the quality of their work and the attainment of the required design and engineering standards. In particular, for those requirements not specifically covered, the Principal will typically expect them to follow those design and engineering practices that will achieve at least the same level of integrity as reflected in the DEPs. If in doubt, the Contractor or Manufacturer/Supplierr shall, without detracting from his own responsibility, consult the Principal. Manufacturer/Supplie The right to obtain and to use DEPs is restricted, and is typically granted by Shell GSI (and in some cases by other Shell Companies) under a Service Agreement or a License Agreement. This right is granted primarily to Shell companies and other companies receiving technical advice and services from Shell GSI or another Shell Company. Consequently, three categories of users of DEPs can be distinguished: 1)

Operating Units having a Service Agreement with Shell GSI or another Shell Company. The use of DEPs by these Operating Units is subject in all respects to the terms and conditions of the relevant Service Agreement.

2)

Other parties who are authorised to use DEPs subject to appropriate contractual arrangements (whether as part of a Service Agreement or otherwise).

3)

Contractors/subcontractors Contractors/subcontrac tors and Manufacturers/Suppli Manufacturers/Suppliers ers under a contract with users referred to under 1) or 2) which requires that tenders for projects, materials supplied or - generally - work performed on behalf of the said users comply with the relevant standards.

Subject to any particular terms and conditions as may be set forth in specific agreements with users, Shell GSI disclaims any liability of whatsoever nature for any damage (including injury or death) suffered by any company or person whomsoever as a result of or in connection with the use, application or implementation of any DEP, combination of DEPs or any part thereof, even if it is wholly or partly caused by negligence on the part of Shell GSI or other Shell Company. The benefit of this disclaimer shall inure in all respects to Shell GSI and/or any Shell Company, or companies affiliated to these companies, that may issue DEPs or advise or require the use of DEPs. Without prejudice to any specific terms in respect of confidentiality under relevant contractual arrangements, DEPs shall not, without the prior written consent of Shell GSI, be disclosed by users to any company or person whomsoever and the DEPs shall be used exclusively for the purpose for which they have been provided to the user. They shall be returned after use, including any copies which shall only be made by users with the express prior written consent of Shell GSI. The copyright of DEPs vests in Shell Group of companies. Users shall arrange for DEPs to be held in safe custody and Shell GSI may at any time require information satisfactory to them in order to ascertain how users implement this requirement. All administrative administrative queries should should be directed to the DEP Administrator in Shell Shell GSI.

DEP 37.14.10.10-Gen. February 2011 Page 3 TABLE OF CONTENTS 1. 1.1 1.2 1.3 1.4 1.5 1.6

INTRODUCTION ........................................................................................................4 SCOPE........................................................................................................................4 DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS .........4 DEFINITIONS .............................................................................................................5 CROSS-REFERENCES .............................................................................................6 SUMMARY OF MAIN CHANGES...............................................................................6 COMMENTS ON THIS DEP .......................................................................................6

2. 2.1 2.2 2.3

DRAIN SYSTEMS PHILOSOPHY..............................................................................7 PURPOSE AND FUNCTION OF FACILITY DRAIN SYSTEMS.................................7 REGULATORY REQUIREMENTS.............................................................................7 DRAIN SYSTEM CLASSIFICATIONS........................................................................8

3. 3.1 3.2 3.3 3.4 3.5 3.6

DRAIN SYSTEMS DESIGN REQUIREMENTS .......................................................10 SOURCES AND DESTINATIONS OF DRAIN SYSTEM LIQUIDS ..........................10 OPEN NON-HAZARDOUS AREA DRAIN SYSTEM................................................ 12 OPEN HAZARDOUS AREA DRAIN SYSTEM .........................................................12 INSTRUMENT DRAINS............................................................................................12 HELIDECK DRAINS .................................................................................................13 FIREWATER DRAINS ..............................................................................................13

4. 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14

GENERAL DESIGN REQUIREMENTS ...................................................................15 SIZING DRAIN SYSTEMS........................................................................................15 SELECTION AND SIZING OF COLLECTION AND SKIMMING VESSELS ............15 PIPING SYSTEMS....................................................................................................17 PROCESS SAND AND SOLIDS ..............................................................................19 TOXIC FLUIDS .........................................................................................................19 FACILITY SOLID WASTES ......................................................................................19 BACKFLOW PROTECTION .....................................................................................19 FLOOR DRAINS .......................................................................................................19 DRIP PANS...............................................................................................................20 TUNDISHES .............................................................................................................20 VENTS ......................................................................................................................20 CHEMICAL TREATMENTS ......................................................................................21 SAMPLING OF EFFLUENT......................................................................................21 DISPOSAL TO SEA..................................................................................................21

5.

REFERENCES .........................................................................................................22 APPENDICES

APPENDIX 1

FIGURES.........................................................................................................23

APPENDIX 2

LIST OF CHANGES ........................................................................................25

DEP 37.14.10.10-Gen. February 2011 Page 4 1.

INTRODUCTION

1.1

SCOPE This DEP specifies requirements and gives recommendations for the design of drain systems for offshore oil and gas production facilities. This DEP covers the following: a)

Rainwater and wash-down water from deck drains in non-hazardous / utility areas (2.3.1);

b)

Rainwater and wash-down water from deck drains in hazardous / process areas (2.3.2);

c)

Process drains (2.3.4);

d)

Specialty fluid recovery and disposal systems (2.3.5);

e)

Instrument drains (2.3.6);

f)

Helideck drains (2.3.7);

g)

Firewater drains (2.3.8);

h)

Laboratory drains (2.3.9).

This DEP does not cover the drainage of domestic waste water and sewage streams, or drainage from drilling units. Generic closed maintenance drains of the type described in previous DEPs are no longer supported, however hard piped drain systems to support specific process or utility systems are included under Process drains (2.3.4). Specifics for deck drainage in environments with long periods of freezing temperatures or requirements for winterizing of facilities in colder climates are not included. This DEP contains mandatory requirements to mitigate process safety risks in accordance with Design Engineering Manual DEM 1 – Application of Technical Standards. This is a revision of the DEP with the same number dated January 2010; see (1.5) regarding the changes. 1.2

DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS Unless otherwise authorised by Shell GSI, the distribution of this DEP is confined to Shell companies and, where necessary, to Contractors and Manufacturers/Suppliers nominated by them. Any authorised access to DEPs does not for that reason constitute an authorization to any documents, data or information to which the DEPs may refer. This DEP is intended for use in facilities related to offshore oil and gas production facilities but may also be applied to onshore facilities located in bodies of water, i.e. in lakes and swamps. This DEP may also be applied in other similar facilities. When DEPs are applied, a Management of Change (MOC) process should be implemented; this is of particular importance when existing facilities are to be modified. If national and/or local regulations exist in which some of the requirements could be more stringent than in this DEP, the Contractor shall determine by careful scrutiny which of the requirements are the more stringent and which combination of requirements will be acceptable with regards to the safety, environmental, economic and legal aspects. In all cases the Contractor shall inform the Principal of any deviation from the requirements of this DEP which is considered to be necessary in order to comply with national and/or local regulations. The Principal may then negotiate with the Authorities concerned, the objective being to obtain agreement to follow this DEP as closely as possible.

DEP 37.14.10.10-Gen. February 2011 Page 5 1.3

DEFINITIONS

1.3.1

General defini tio ns The Contractor is the party that carries out all or part of the design, engineering, procurement, construction, commissioning or management of a project or operation of a facility. The Principal may undertake all or part of the duties of the Contractor. The Manufacturer/Supplier is the party that manufactures or supplies equipment and services to perform the duties specified by the Contractor. The Principal is the party that initiates the project and ultimately pays for it. The Principal may also include an agent or consultant authorised to act for, and on behalf of, the Principal. The word shall indicates a requirement. The capitalised term SHALL [PS] indicates a process safety requirement. The word should indicates a recommendation.

1.3.2

Specific defini tion s Term

Definition

Hazardous Ar ea

An area in which flammable gases or vapours can be present in quantities sufficient to produce explosive or ignitable mixtures in the atmosphere. In European and most other world countries it is identified as Zone 0 - An area in which an explosive gas atmosphere is present continuously, or is present for long periods; or Zone 1 - An area in which an explosive gas atmosphere is likely to occur in normal operation.

NonHazardous Ar ea

An area in which flammable gases or vapours are not likely to occur in quantities sufficient to produce explosive or ignitable mixtures in the atmosphere. In European and most other world countries it is identified as Zone 2 - An area in which an explosive gas atmosphere is not likely to occur in normal operation and if it does occur it will exist for a short period only. Note: Area classification is a technical HSSE concept and shown on the hazardous area classification drawings. Refer to DEP 80.00.10.10-Gen. for details.

Very tox ic (substances)

substances that are very hazardous for the environment or human health

Segregated

Typically the complete physical separation (with no connections between) of the collection piping, vessels and water disposal routes of different drainage systems. Alternative means of segregation using intrinsically secure methods shall be subject to approval by the Principal. Potential corrosion or other degradation of drainage system components (e.g. dip legs, seal loops, etc.) shall be taken into account. Enclosed modules present particular hazards in this respect due to potential differences between module atmospheric pressures dependent on HVAC design and operation.

Note:

The classification of the toxicity of substances is a very complex matter and one should refer to DEP 01.00.01.30-Gen. (which also identifies "toxic" substances by reference to chemical substances databases) for more details. In general the process fluids on oil and gas production facilities will not be classified as very toxic unless that there are substantial levels of hydrogen sulphide. With regard to the chemicals used for treatment of the process fluids, their material safety data sheets shall be consulted for their toxicity classification.

DEP 37.14.10.10-Gen. February 2011 Page 6 1.3.3

1.4

Abbreviations FPSO

Floating Production System Offshore (most commonly used when referring to a tanker shaped vessel)

HVAC

Heating, Ventilation and Air Conditioning

OHD

Open Hazardous area Drains

ONHD

Open Non-Hazardous area Drains

TLP

Tension Leg Platform

CROSS-REFERENCES Where cross-references to other parts of this DEP are made, the referenced section number is shown in brackets. Other documents referenced by this DEP are listed in (5).

1.5

SUMMARY OF MAIN CHANGES This DEP is a revision of the DEP of the same number dated January 2010. The changes to this DEP are extensive and the main non-editorial changes are listed in (Appendix 2). For this revision a companion document called a “DEP Informative” has been created containing background information and which is accessible from the Shell Standards web page.

1.6

COMMENTS ON THIS DEP Comments on this DEP may be sent to the Administrator at [email protected], using the DEP Feedback Form. The DEP Feedback Form can be found on the main page of “DEPs on the Web”, available through the Global Technical Standards web portal http://sww.shell.com/standards and on the main page of the DEPs DVD-ROM.


DRAIN SYSTEMS PHILOSOPHY

2.1

PURPOSE AND FUNCTION OF FACILITY DRAIN SYSTEMS The purposes of the drain systems considered in this DEP are: 1) To collect and convey facility drained liquids to an appropriate treating and / or disposal system in such a way as to protect personnel, equipment; and 2) to avoid environmental pollution. It is written in the context of oil and gas production facilities where pollution due to the discharge of hydrocarbons or other hazardous liquids to the sea is a significant environmental risk. Drain systems provide the means of safely removing rainwater run-off and wash-down liquids from drip pans, plated and curbed areas and flooring together with residual process hydrocarbons drained from vessels, piping, and instruments, resulting either from operational activities or from preparation prior to carrying out maintenance work. The liquids collected in a recovery system with the water are disposed of in a safe and environmentally acceptable fashion. Any accompanying solids shall be collected and transported to an onshore site for disposal. A fundamental safety consideration is that a drain system must not provide a route for migration of a fire, flammable liquids or vapours from one hazardous area to another, or to non-hazardous areas. For this reason, drain systems SHALL [PS] be segregated into specific systems, each designed for a particular type of stream, with no interconnection between the systems. Further to this, when appropriate, features such as seal loops and air gaps shall be used to segregate areas served by the same drain system. Other factors affecting the safety and environmental acceptability of a drain system include: a) Its effectiveness in separating oil from water before discharge overboard; b) Its ability to block the discharge of oil overboard during upset conditions; c)

Its ability to handle solids and prevention of flow blockages;

d) Its resistance to degradation from corrosion; e) A design that reduces the risk of accidental misuse; f)

A design that prevents release of very toxic substances to the atmosphere and contact with personnel;

g) The selection of the proper materials of construction; h) Its ability to be cleaned and maintained. Specific safety and environmental considerations for open drain systems shall apply to refrigerated hydrocarbons, cryogenic liquids (e.g. LNG) or other fluids which are otherwise vapour at ambient conditions. These systems merit specific considerations based on fluid behaviour, safety considerations and environmental impacts if discharged to the deck or sea. For example, where a hydrocarbon will completely evaporate on contact with sea (e.g. LNG) it is normal not to attempt to collect an accidental spill, but to allow the fluids to be released overboard for safety reasons. 2.2

REGULATORY REQUIREMENTS All operating locations should have mandated discharge limits in accordance with national and international regulations, as well as company policy, for pollutants as part of their environmental management plan. It is the reponsibility of the designer to ensure the system proposed can be operated in compliance with these limits, and seek clarification as necessary from the Principal.


DRAIN SYSTEM CLASSIFICATIONS The types of drain systems found on typical offshore facilities are classified as follows:

2.3.1

Open non -hazardous area drai n system (ONHD) This system provides drainage from those areas of the facility which have been designated non-hazardous. These generally include storage areas for utility liquid consumables such as diesel fuel and lubricating oils. This type of drain system handles fluids collected from floors, drip pans and tundishes in non-hazardous areas and operates at atmospheric pressure. Open non-hazardous drain systems SHALL [PS] be completely segregated from all other drain systems to eliminate the possibility of flammable vapour transmission through the drains from other areas to the non-hazardous area.

2.3.2

Open hazardou s area drain system (OHD) This system provides drainage from those areas which are designated hazardous. These generally include all process areas and other locations in the facility where process hydrocarbons may be present. Open hazardous drain systems handle liquids collected from plated decks, drip pans and tundishes in hazardous areas. Open hazardous drain systems are only used for draining residual hydrocarbon liquids from vessels and equipment after the majority of the liquid hydrocarbons from those vessels or equipment have been transferred to other process systems or to storage, e.g. by operational procedure rather than design.

2.3.3

Closed maintenance drain In the previous version of this DEP, this was defined as a fully contained (hard-piped) system to route drains from process vessels and equipment to a common collection system. This relied to a significant degree on maintenance preparation procedures to avoid hazardous events such as overpressure and inadvertent communication between systems. Closed maintenance drain systems SHALL [PS] not be installed in new facilities or as a modification to existing systems. Where by virtue of fluid characteristics (e.g, volatility, toxicity, impact on water treatment systems, temperature, value) it is desired to fully contain, segregate or recover fluids, these systems SHALL [PS] be designed as part of the overall process system as a process drain (2.3.4), with suitable engineered barriers against hazards. Equipment and piping shall be of a consistent standard with the standards for the installation. NOTE:

2.3.4

Closed maintenance drains are not considered further in this DEP.

Process drains Some operations and equipment in the process facilities require periodic and partial draining during operation to keep them working at peak efficiency. This drainage often occurs when the connected system may still be operational rather than a maintenance activity. Hence they SHALL [PS] be designed as part of the overall process system with engineered barriers against hazards and appropriate standards for vessels, tanks, piping and overpressure protection. Streams drained typically include, but are not limited to the following: emulsion layers in freewater knockouts and oil dehydration vessels, condensate layers in glycol contactors and glycol surge tanks, refrigerant heavy ends blowdown, compressor scrubber drains where no continuous liquids are present. These systems may route fluids from one part of the process to another rather than to a dedicated system. In some cases for fluids under pressure, drainage to the flare system may be appropriate. NOTE:

Process drains are not considered further in this DEP.


Specialty fluid recovery and disposal systems Certain liquids such as: a) lube oils; b) diesel fuel; c)

aviation fuel;

d) hydraulic oils; e) methanol; f)

glycol;

g) amines and refrigerants; require segregation and disposal separately from the open drain systems during maintenance activities. This may be because of environmental considerations, impact on the process or water treatment (if recycled to the process), value or hazard control. An example of this is collection of lube oil from machinery maintenance activities. Heat transfer fluids as defined in DEP 20.05.50.10-Gen. normally require a dedicated hardpiped collection system. DEP 20.05.50.10-Gen. shall be referred to for specific requirements. On oil production facilities, it may be permissible via suitably engineered systems to dispose of some of these liquids via the oil export pipeline. These systems are typically used for maintenance activities. Rainwater, wash water and minor spillages into drip pans can flow into the relevant open drain system. 2.3.6

Instr ument drains Refer to Section 3.4.1.

2.3.7

Helideck drains Refer to Section 3.5.

2.3.8

Firewater drains Refer to Section 3.6.

2.3.9

Laboratory drains Laboratory drains are used for the disposal of hydrocarbon samples, chemicals and solvents. The normal disposal route would be to an open hazardous area drain via a water sealed drain pipe and / or a drain with an air gap into an OHD gully outside the laboratory wall. Since the laboratory is typically in an enclosed area, the drain SHALL [PS] not be hardpiped to the OHD to avoid the possibility of back-flow of flammable vapours. Only hydrocarbon and water samples may be disposed of into the laboratory drain system. All other liquids shall be collected in drums for removal from the platform. If the only convenient drain is an open non-hazardous drain, then all liquids including hydrocarbons shall be collected in containers for onshore disposal.


DRAIN SYSTEMS DESIGN REQUIREMENTS

3.1

SOURCES AND DESTINATIONS OF DRAIN SYSTEM LIQUIDS (Table 1) lists the most commonly encountered drain liquid sources, their expected contents, the type of drain system to which liquids would normally be routed and the probable classification of the area in which the source is located. The type of drain system that each source ties into shall be given careful consideration to avoid the introduction of additional hazards. The forms of hydrocarbon pollutants encountered on an offshore facility typically include: a)

Free oil, which typically accompanies rainwater run-off; it is the easiest to remove since it will rise to the surface of the water in the collection and skimming equipment given adequate time.

b)

Oil coated solids, which typically accompany the cleaning of a process vessel; solids should be removed from the facility to an onshore site for disposal. These pollutants will settle to the bottom of a piping system and collection vessel.

c)

Mechanical dispersions are fine oil droplets that spread throughout the water. These typically accompany high pressure washing of oil in drip pans, floors and process equipment. Their creation should be avoided as they are difficult to separate from the water by gravity separation.

d)

Emulsions are tightly bound mixtures of oil and water in which the components are sometimes indistinguishable from each other. Emulsions most often occur in process equipment resulting from oil and water passing thru a control valve at high velocity. Some may be created by the use of surfactants when cleaning. Emulsions cannot typically be broken by gravity separation.

e)

Dissolved oil is no longer in droplet form so that physical removal by gravity separation is impossible. Dissolved oil is not typically found in rainwater runoff. It is typically present in negligible volumes and is not subject to overboard discharge regulations. Table 1 Sources and destinations of drain liquids

Item

Drain fluid source

Expected contents

Suitable destination

Probable area classification

1

Drains on process equipment and piping containing hydrocarbons

Oil, condensate, some gas, produced water, sand, wash water

OHD (See Note 2)

Hazardous

2

Process vessels Drip pans under process equipment and piping (flanged components)

Onshore disposal site OHD

Hazardous

3

Sand and solids Oil, rainwater, wash water

4

Drip pans under aviation fuel storage tanks, filters, hose reels, etc.

Aviation fuel, rainwater, wash water

ONHD or OHD (See Note 1)

Non-hazardous or Hazardous

5

Drip pans under diesel fuel storage tanks, filters, diesel engines, hose reels, etc.

Diesel fuel, rainwater, wash water

ONHD or OHD (See Note1)

Non-hazardous or Hazardous

Hazardous


Suitable destination

Probable area classification

Spilled chemicals, wash water, rainwater


Non-hazardous or hazardous

Hazardous modules / areas floor drains

Spilled oil, wash water, rainwater

OHD

Hazardous

8

Non-hazardous modules / areas floor drains

Spilled lube oil, wash water, rainwater

ONHD

Non-hazardous

9

Overflows on diesel fuel tanks

Diesel fuel

(See Note 3)


10

Drains on compressor seal oil tanks, etc.

Seal oil and gas condensate

Specialty fluid recovery and disposal system (2.3.5)

Hazardous

11

Lube oil drains on turbines, reciprocating engines, compressors, filters, storage tanks, etc.

Lubricating oil



12

Drains on diesel, aviation fuel, hydraulic oils, glycol, etc. storage tanks, filters and handling equipment

Diesel, Aviation Fuel, Hydraulic Oils, Glycol



13

Drains on equipment not in hydrocarbon service

Freshwater, seawater



14

Firewater deluge drains

Firewater

Overboard


15

Hydrocarbon liquid free roof and deck drains

Rain water

Overboard

Non-hazardous

16

Helideck drains

Rain water, spilled fuel

Rainwater Overboard (via fire trap)

Non-hazardous

17

Instrument drains (if not collected locally)

Oil, water, chemicals



18

Sample point drains (if not collected locally)


OHND or OHD (See Note 1)


19

Laboratory drains


ONHD, OHD, collection drums (2.2.9)


Item

Drain fluid source

6

Drip pans under chemical storage tanks, filters, pumps, piping etc.

7

NOTE :

Expected contents

1

Drain disposition is driven by the hazardous or non hazardous area classification of the area in which equipment is located. May be driven by surrounding equipment as well as the fluids contained in the equipment to be drained.

2

Process vessels, equipment and piping shall not be drained into the open drain systems until the appropriate maintenance procedures have been executed to remove as much of the process hydrocarbons as practical.

3: When feasible, the overflow from diesel tanks shall be routed back to the primary storage tank. Otherwise the overflow shall be contained in an open drain system which provides adequate separation equipment.


OPEN NON-HAZARDOUS AREA DRAIN SYSTEM Drainage from non-hazardous areas SHALL [PS] be completely segregated from any other drainage system to eliminate the risk of hydrocarbon vapour transmission to non hazardous areas. Discharge into the system shall be by open gullies for the drip pans and floor drains and a tundish for instrument drains. (Figure 1) shows a typical gully seal design. In order to prevent possible vapour communication between areas through the nonhazardous open drains system, all enclosed modules SHALL [PS] have liquid seal traps in the drain headers. The preferred seal type is an inverted cap design that can be easily inspected (see Figure 1). The liquid seals in the traps may evaporate, especially in enclosed modules containing equipment operating at relatively warm temperatures., In these cases, a maintenance procedure SHALL [PS] be developed to periodically inspect and replenish the liquid seals. Alternatively, provisions for a continuous trickle flow of water through the drain gullies to maintain seal levels avoid the need for frequent checks. Account must be taken of possible pressure differences between modules resulting from the operation of HVAC systems.

3.3

OPEN HAZARDOUS AREA DRAIN SYSTEM Drainage from hazardous areas SHALL [PS] be completely segregated from any other drainage system to eliminate the risk of hydrocarbon vapour transmission to other areas. Drainage from hazardous areas containing liquids such as crude oil, which pose an environmental threat upon overboard discharge, shall be routed to a hydrocarbon recovery system to remove and recycle the oil before allowing the water to be discharged overboard. Liquid seal traps SHALL [PS] be provided in the open hazardous drain system to prevent the transmission of hydrocarbon vapours between modules/areas. Liquid seal traps SHALL [PS] be corrosion resistant to avoid loss of liquid seal due to corrosion leaks. Plated deck areas under equipment or flanged piping handling hydrocarbon liquids shall be provided with a local curbed area to prevent spillage of hydrocarbons directly into the sea or spreading through facility. Care must be taken to keep the curbed area size to a practical minimum to reduce the load on the drain system during periods of heavy rain. On facilities with segregated hazardous areas, the open drains from each area SHALL [PS] be routed to separate drain headers and segregated from each other by liquid seals. The open hazardous area drain stream shall be collected and routed to a suitable collection, oil skimming and disposal system, i.e. one which conforms to the local regulatory and operating unit requirements.

3.4

INSTRUMENT DRAINS

3.4.1

General Instrument drains SHALL [PS] be accounted for in hazardous area classification. It is typically not practical to provide a dedicated drain system for instruments, therefore the handling of instrument drains shall be on a case by case basis, with guidance as noted below. In all cases, the instrument drain piping (or tubing) shall be arranged so that the draining liquid is visible to the operator when the instrument is being drained.

3.4.2

Process servic es Liquids whose vapours are lighter than air will typically disperse on open deck facilities. These liquids may be drained into a tundish or open drain, provided the volume of flashing vapour will not create a flammable or explosive mixture. In that case the instrument SHALL [PS] be drained into a process or flare system operating at lower pressure.

DEP 37.14.10.10-Gen. February 2011 Page 13 Liquids whose vapours are heavier than air may be collected in low spaces and thus pose a fire hazard. In closed modules, these services SHALL [PS] be identified on the PEFS and their drains hard piped into a process or flare system operating at lower pressure. Open deck facilities shall be reviewed on a case-by-case basis. 3.4.3

Utili ty servic es Instruments in non-hydrocarbon services, e.g. potable water, compressed air, nitrogen, etc., shall be drained into a container or to the ONHD via tundish or open drain gully.

3.5

HELIDECK DRAINS A helideck SHALL [PS] have its perimeter contained within a curb and rainwater shall be collected in gullies and drained overboard. The helideck drains SHALL [PS] be fitted with fire traps so that burning fuel cannot pass directly overboard. Aviation fuel filters, hose reels and miscellaneous equipment mounted adjacent to the helideck shall be surrounded by a curb to prevent the spread of any fuel spillage. The curbed area shall be drained via the ONHD. Though aviation fuel may be classified as non hazardous, since its vapours do not meet the hazardous criteria (similar to diesel fuel), it should be drained into a system that provides adequate retention time for separation of the fuel from water to avoid discharge of fuel to sea. The design should take into account the drainage of spilt aviation fuel with the purpose of removing any spillage quickly from the vicinity of the aircraft. Minor aviation fuel spills on the helideck should be dealt with by evaporation in warm climates or absorbent materials. Compliance with national and applicable international regulations for landing areas shall be ensured with clarification sought as necessary from the Principal.

3.6

FIREWATER DRAINS

3.6.1

General The quantities of water used in fire-fighting could be much greater than other drainage quantities. It would generally be uneconomic to design a water collection system to allow the passage of these quantities. Inadequate firewater drainage could cause a fire to spread within the facility and may overload the support structure. The drain system should therefore be designed to minimise fire spread while also preventing overload of structural members. The design requirements for handling firewater and fire suppressing foams in the drainage collections systems could vary greatly between fully enclosed modules and open deck facilities. For this reason, options for these configurations are presented below.

3.6.2

Enclos ed modul es Fully enclosed modules are typically provided with a flooring system that encloses the space and thus prevents the over flow of firewater collecting in the floor and drip pans. Where deluge systems and / or monitors are installed for fire fighting, a direct overflow into the sea SHALL [PS] be provided. Deluge water within any enclosed module SHALL [PS] be collected in open drain gullies and discharged directly overboard via downcomers which are sized to serve several drain outlets. Any manifolding SHALL [PS] maintain area segregations and discharges SHALL [PS] be to a safe location. In pressurised areas, seal legs SHALL [PS] be required. The take-off point for deluge water from the drain gully shall be above that for the normal open drain so that the deluge water effectively overflows. When a deluge system is activated, pool fires could form if the drains were under-sized, which would increase the chance of a fire spreading. To prevent excessive back-up of

DEP 37.14.10.10-Gen. February 2011 Page 14 water in the modules, the deluge drain lines SHALL [PS] be sized for the full deluge system discharge capacity in each area plus an additional 50% to allow for extra fire-fighting equipment. Some of the deluge water in hazardous areas will travel via the normal OHD system and if a drains collection tank is employed, this shall be considered when sizing the overflow line. 3.6.3

Open decks Open decks typically have grated and open areas which drain directly to the sea and may not have the drainage problems associated with an enclosed module. The drain systems on open deck facilities SHALL [PS] be designed to prevent the spread of fire via the drain systems and the overload of structural members.


GENERAL DESIGN REQUIREMENTS

4.1

SIZING DRAIN SYSTEMS The flow rate of liquids into a facility’s drain systems can vary widely. The design flow rate for sizing the system components will be specific to each case and some of the main factors to be taken into account are: •

•

•

•

The deck area and the duration and rate of rainwater falling on areas that are collected in the drainage system. The deck area and the duration and rate for wash down water from hand-held hoses that are collected in the drainage system. Firewater rates from fixed fire monitors, deluge systems and portable fire-fighting equipment that overflow directly to the sea or are collected in the drainage system. Draining the contents of process equipment during their cleaning. The capacity of the drain system should allow this to be carried out within a reasonable time.

4.2

SELECTION AND SIZING OF COLLECTION AND SKIMMING VESSELS

4.2.1

Selection The selection of the type of collection and skimming vessels typically depends upon the type of structure supporting the facility. Factors that could affect the selection of the collection and skimming vessels include: •

•

Weight and size constraints, e.g. generally a TLP will have greater constraints than an FPSO. Height constraints since the vessels will have to be at a low point on the facility.

The vessel shall be located to prevent the continuous accumulation of water in the inlet piping. Vessels, caissons, sumps and tanks shall be designed to an appropriate and recognised mechanical design standard or code consistent with the standards applied for the facility as a whole and subject to approval by the Principal. 4.2.2

Sizing The sizing criteria for collection and skimming vessels shall be consistent with the intended operations and maintenance procedures. The overall capacity of each of the chosen collection systems shall be sufficient to collect and treat: •

•

•

The largest volume of water expected from the open drains during the design rain; The largest volume of oily water that is expected from the draining/maintenance operations; The handling of solids.

Note: Sizing criteria omitted from the previous edition of this DEP include: •

•

The risk of a vessel rupture or pipework failure shall be considered negligible and therefore the sizing of a collection vessel for the largest expected volume of spilled hydrocarbons is not a necessary sizing criteria. The sizing of a collection vessel to handle the volume of water during an emergency deluge is not required since overflow provisions are provided for enclosed modules.

It may not be practical to predict droplet size distribution in drain systems because of the different hydrocarbons and hydrocarbon sources that may be present. Therefore the settling time criterion used in sizing other oil-water gravity separation equipment may not be applicable.

DEP 37.14.10.10-Gen. February 2011 Page 16 In the event that a droplet size distribution can be approximated, Stokes’ Law may be used for vessel sizing. 4.2.3

Design pressur e The design pressure for these vessels shall be adequate for the back pressure created in the vessel from the vent system. Protection for the vessel from failure due to a vacuum shall be provided.

4.2.4

Materials selectio n Carbons steels are most commonly used because of their strength, though fibreglass may be considered because of its corrosion resistance and light weight. Whether a fire-resistant material is required or not may be subjected to the local operating unit’s requirements. The inventory of hydrocarbons in these vessels is typically low and firewater deluge is not typically required.

4.2.5

Vessel int ernals The inlet piping from the drain headers SHALL [PS] enter the collection vessels via a liquid seal to prevent possible backflow of vapour and to avoid static hazards. The liquid seal can be: •

in the form of the entrance below the minimum water level; or

•

an external piping seal loop; or

•

a dip pipe inside the vessel.

The external piping liquid seal requires regular checking to ensure its integrity and accessibility aspects shall therefore be considered during detailed piping design. Dip pipes SHALL [PS] be provided if a caisson is used for the OHD systems even though it might appear that they are not strictly required where non-hazardous and hazardous area drainage systems, including collection caissons, are totally segregated from one another. However, they are useful in minimising vapour release into the modules in the event of backflow or other system upset conditions by creating an extra water seal between the process and the drainage systems. 4.2.6

Vessel appurtenances An adequate number of manways shall be provided to allow for the periodic inspection and cleaning of the vessel. These shall also be provided with the consideration of ventilation to comply with the requirements for confined space entry. An adequate number of drain connections shall be provided to facilitate cleaning and entry into the vessel. An adequate number of sample connections shall be provided on the vessel for sampling the water section and the skimmed oil section.

4.2.7

Corrosi on prot ection Carbon steel vessels shall be internally coated and provided with sacrificial anodes and an anode test port due to corrosive nature of the water in the drain systems. Inert gas blanketing may also be considered to reduce the internal corrosion. Blanketing with hydrocarbon vapour SHALL [PS] not be provided due to the hazard of vapour entering the drain headers.

4.2.8

Dispos al caisso ns Drainage from an open non-hazardous drain system SHALL [PS] be discharged into a dedicated non-hazardous caisson, separate from the one installed on the OHD system.

DEP 37.14.10.10-Gen. February 2011 Page 17 Alternatively, separate ONHD and OHD collection vessels may be considered. The advantages and disadvantages of caissons and vessels are described in (Table 3). Caissons shall be provided with a means to determine the elevation of the oil-water interface within the caisson to ensure that hydrocarbons do not underflow into the sea. When a large amount of hydrocarbons has entered the caisson, operational procedures should ensure that it will be pumped out immediately. Drain piping within caissons shall be made of Monel or glass-fibre reinforced plastic (GRE/GRP) to avoid corrosion. Sea wave motion will cause fluctuations of the levels in a caisson and this shall be accounted for in the design. Table 3 Caissons (vertical)

Caissons versus collection vessels

Ad vantages 1. Easy to achieve low point drainage and large holding volumes for hydrocarbon fluids. 2. Less affected by solid materials in drained fluids. 3. Little or no water recycled back to the process system. 4. Tolerant of upset conditions. Disadvantages 1.

Less effective in oil and water separation.

2.

Should not be used for the discharge of oil contaminated solids.

3.

Access for inspection and return pump maintenance needs careful consideration during facility design.

4.

Likely to be more expensive than collection vessels and to entail higher maintenance costs.

5.

Difficult to confirm that there is no underflow of hydrocarbons and hence there is a greater environmental risk.

6.

Wave motion causes fluctuations in internal pressure and levels.

7.

Level control instrumentation not easily accessible and failure may lead to hydrocarbon underflow.

Collection vessels

Ad vantages

(horizontal)

1. 2. 3. 4.

Likely to be less costly than caissons. Easy access and maintainability. Possible to measure discharge water quality/flow. More effective in oil and water separation.

Disadvantages 1. 2. 3. 4.3

Must be installed at a low point in the facility requiring special provisions in the structural framework. Susceptible to accumulation of solids in both the vessels. Limited capacity for hydrocarbon holding volumes.

PIPING SYSTEMS Piping systems for drain shall be specified against a recognised standard or code and facility piping class consistent with the overall facility design standard and subject to approval by the Principal.


Sizing Drain piping shall be sized for the maximum expected flow, including 70% of the firewater deluge system rate where applicable or the maximum expected flow during heavy rain, whichever is the higher. A minimum DN 100 pipe size shall be used in drain headers when and where sand or other solids might collect. Once the largest size for the drain header is selected, that size shall be used to the collection vessel because any reduction in line size provides a location where the drain header could be plugged by debris.

4.3.2

Layouts The piping shall be self-draining with horizontal sections sloped downwards towards collection vessels with a slope of not less than 1:100. For floating production systems such as FPSOs, specific attention should be paid to drain system gradients to ensure the drains function correctly over the normal operating range of vessel trim and movements. Liquid seal loops and air gaps shall be considered for use to segregate segments of the piping systems to help prevent vapour migration in the piping system. Seal loops shall be accessible for clean-out. A vacuum breaker is sometimes required to prevent loss of the seal loop. The checking, cleaning and filling of the seal loop shall be a part of the facility’s maintenance procedures. Air gaps can consist of the drain pipe discharging into an open drain trough or into an expander two pipe size larger than the drain pipe. Attention should also be given to the piping layouts between different elevations in the piping system to prevent backflow of liquids at lower levels. Pump suction piping on collection vessels shall be above the vessel bottom to account for the accumulation of solids on the vessel bottom. Removable pipe spools or spectacle blinds shall be provided on the vessel piping tie-ins for use when positive isolation is required for confined space entry.

4.3.3

Design pressur e If operated at atmospheric pressure, the design pressure of the piping shall be a minimum of 1000 kPa based on the requirement to allow the connection and use of fire hoses for flushing and cleaning.

4.3.4

Material selectio n Drain piping should preferably be a corrosion resistant material, due to the presence of seawater in the effluent. Fibreglass (GRP or GRE) is the most commonly used material and provides the added advantage of weight savings on floating systems. When fibreglass piping is selected, an electrically conductive version conforming to IMO Resolution A.753(18), Section 2.2.5 electrical conductivity SHALL [PS] be used in electrically classified hazardous areas. The flange facing on fibreglass flanges are typically flat faced and steel flanges bolted to fibreglass flanges shall be flat faced. In the event a fire resistant material is required for the drain piping, hot dip galvanized steel piping should be considered.

4.3.5

Basket str ainers Baskets strainers may be used in the inlet piping to the collection and skimming vessels to collect solids before they enter the vessel. When basket strainers are installed, a means shall be provided to prevent the drain system from backing up into the drain headers in the event the basket strainers become clogged. This could be in the form of an overflow pipe around the strainers and to the collection vessel.

DEP 37.14.10.10-Gen. February 2011 Page 19 No block valves shall be included in drain system piping which could completely block the drainage routeunless locked open. Valves used in the piping system shall be the full opening type with full sized ports and lockable. 4.4

PROCESS SAND AND SOLIDS Oil contaminated sand and solids from process vessels shall not be allowed to enter the open drain system. The gravity separation mechanism in the collection vessel will not be adequate to “wash” the oil from the sand.

4.5

TOXIC FLUIDS Fluids classified as toxic SHALL [PS] be identified on the PEFS. The design of systems handling toxic fluids SHALL [PS] prevent the contact of those fluids with personnel, e.g. drains shall be hard piped into a process system operating at lower pressure.

4.6

FACILITY SOLID WASTES Solid wastes from the facility are likely to enter the drain systems and will include plastics, paper, drink cans, electrical wire and their jacketing, welding rods, nylon wraps, etc. Provisions for handling these solid wastes shall include: a) Adequate line sizes, e.g. a minimum DN 100 line size shall be used. b) Minimize the number of changes in direction and flanges, as these are areas where the solids tend to collect. c)

o

o

Use of 45 bends in lieu of 90 bends to help facilitate “rodding” of the drain line.

d) Provide an adequate number of cleanouts. Clean-outs for drain lines that are not readily accessible shall be routed to accessible location to allow access without the use of scaffolding. These cleanouts shall not present tripping hazards and may be located below a removable grating panel. e) Seal traps shall be located in accessible locations to allow for periodic cleaning. f)

Baskets strainers may be used on the inlet to collection vessels to capture these wastes before entering the collection vessel.

Solid wastes may cause further problems in the collection tank due to the potential build-up of material in the tank and the blockage of pump filters and suction lines. Entry into the pump suction line shall be above the base of the tank to allow for the presence of solids in the collection vessel. 4.7

BACKFLOW PROTECTION Hydrocarbons liquids separated in collection vessels and caissons will in most cases be pumped back to the process for recovery (unless discharged to a marine vessel). A tie-in is therefore required between the process and the drain system, but this has the risk of hydrocarbons backflowing from the process to the drain system. In order to minimise this possibility, the pumps SHALL [PS] discharge to the lowest practical pressure level in the process. A reliable non-return system SHALL [PS] be employed which, in addition to a nonreturn valve, SHALL [PS] consist of another system to positively prevent backflow such as an actuated valve tied into the pump start/stop logic. A positive-displacement pump will also help to prevent backflow. Hydrocarbon liquids from ONHD systems SHALL [PS] normally be routed to OHD hydrocarbon collection systems or a dedicated disposal route not connected to the process or flare system as an additional segregation barrier.

4.8

FLOOR DRAINS Where there is no risk of environmentally damaging hydrocarbon spillage, the drain system may be discharged directly overboard, thereby reducing the volume of uncontaminated water which would otherwise be collected through the drains system.

DEP 37.14.10.10-Gen. February 2011 Page 20 When structurally feasible, plate decks and floors shall be adequately sloped to promote flow to drainage system gullies, thus minimising the formation of liquid pools and limiting the spread of spills. On facilities with segregated hazardous areas, the open drains from each area SHALL [PS] be routed to separate drain headers, segregated from each other by liquid seals. 4.9

DRIP PANS Drip pans shall be installed under process equipment and flanged piping, where spillage of hydrocarbons is possible. Drip pans shall slope to a collection trough and shall be free of areas where liquids can accumulate. Seal welding to structural members shall be used to reduce corrosion. Strainers shall be installed over the drip pan drains to prevent solid contaminants from entering the piping system. The flange facings on drip pans drain connections shall be flat faced when bolted to fibreglass flanges.

4.10

TUNDISHES All tundishes shall be fitted with covers when not in use to prevent debris entering the pipework. These covers will also help to restrict the backflow of vapours. The use of valves in pipework below the tundishes to restrict backflow is not recommended due to operability and cost disadvantages. The height of all tundishes should be kept as low as possible and they should be installed at an approximately equal elevation to minimise the possibility of liquid backflow. The end of a drain line shall terminate inside a tundish, not above it, to avoid splashing and spread of the drained fluid. Tundishes beneath sampling points shall have a side-entry slot to allow insertion of sample bottles. The piping from the tundish should preferably be routed to a drip pan’s drain outlet to minimize hydrocarbons from collecting in the drip pan. When piped to a drain header, the connection should be via a liquid seal and be flanged. This allows the tundish connection to be blinded off for pressure testing the drain piping and also provides a flushing connection for clean-out.

4.11

VENTS Vents act to both relieve positive pressure as well as potential negative pressure relative to atmospheric pressure. The atmospheric vents from the collection vessels and caissons SHALL [PS] not be interconnected with vents containing hydrocarbons. The discharge piping from the vents SHALL [PS] be designed and positioned so that ignition by static electricity (or other ignition source) is precluded. The top of the vent pipe SHALL [PS] be sharp-edged to prevent brush discharges. Consideration should be given to placing the vent within the protective "umbrella" of the facility’s lightning conductor system or inside the Faraday cage formed by part of a structure, such as the flare boom. When sizing the vents backpressure or partial vacuum in the worst cases SHALL [PS] not interfere with safety critical liquid seals required for segregation or as vapour barriers. The vents SHALL [PS] be sited away from air compressor and HVAC inlets.

DEP 37.14.10.10-Gen. February 2011 Page 21 If flame arrestors or detonation arrestors are fitted, they: •

SHALL [PS] be constructed of corrosion resistant materials;

•

located at a sufficient elevation to avoid contact with liquids;

•

•

•

installed in the vertical when feasible to prevent liquid accumulation or fitted with drain valves when installed in the horizontal; installed in a location accessible for periodic inspection; and piping routed to prevent the accumulation of liquids.

Refer to DEP 80.45.10.10-Gen. for additional requirements regarding detonation and flame arrestor installation in vents. The installation of arrestors (flame or detonation) arrestor shall be justified and approved by Principal taking into account local regulations. The location of the arrestor shall also consider the manufacturer’s recommendation with regard to the maximum number of pipe diameter lengths from the vent outlet. Where detonation or flame arrestors are fitted, engineered safeguards (e.g, vacuum breaker, adequate design pressure) against potential underpressure (vacuum) or overpressure that may occur due to blockage SHALL [PS] be installed as required based on system analysis in compliance with DEP 80.45.10.11-Gen., taking into account requirements to maintain liquid seals in the system. Regular inspection of the arrestor SHALL [PS] not be relied upon as the sole safeguard. The nature of an open drain system with vessels/tanks fitted with overflows usually means that the potential for overpressure is limited. However the safeguards SHALL [PS] ensure that integrity and operation of safety critical liquid seals required for segregation remains intact. 4.12

CHEMICAL TREATMENTS Periodic treatment of the collection and skimming vessel with a biocide may be considered to reduce or eliminate biological growth in the system. A means to mix the water in the vessel should be provided to disperse the biocide for greatest effectiveness. The use and discharge overboard of any biocide may be subject to discharge regulations.

4.13

SAMPLING OF EFFLUENT Refer to Section 2.2 Where collection vessels are used, sampling points with convenient access shall be provided to monitor the quality of the water discharged from the drains vessels. In the event periodic sampling of the effluent from a disposal caisson is required, an eductor system at the outlet of the caisson may be a feasible solution.

4.14

DISPOSAL TO SEA Adequate separation between the overboard water disposal locations and the seawater lift facilities shall be maintained to prevent the possibility of hydrocarbons being lifted with the seawater. The respective locations of seawater intakes and drain caissons should be determined with account being taken of tidal currents, winds and the type of platform substructure design.


REFERENCES In this DEP reference is made to the following publications: NOTES:

1. Unless specifically designated by date, the latest edition of each publication shall be used, together with any amendments/supplements/revisions thereto. 2. The DEPs and most referenced external standards are available to Shell staff on the SWW (Shell Wide Web) at http://sww.shell.com/standards/.

SHELL STANDARDS Definition of temperature, pressure and toxicity levels

DEP 01.00.01.30-Gen.

Heat transfer fluid (HTF) systems

DEP 20.05.50.10-Gen.

Area classification (amendments / supplements to IP 15)

DEP 80.00.10.10-Gen.

Design of pressure relief, flare and vent systems

DEP 80.45.10.10-Gen.

Overpressure and underpressure - Prevention and protection

DEP 80.45.10.11-Gen.

INTERNATIONAL STANDARDS IMO Resolution A.753(18) (adopted on 4 November 1993) Guidelines for the Application of Plastic Pipes on Ships Issued by: International Maritime Organisation www.imo.org

DEP 37.14.10.10-Gen. February 2011 Page 23 APPENDIX 1

FIGURES Figure 1

Typical seal-trap arrangement

DEP 37.14.10.10-Gen. February 2011 Page 24 Figure 2

Typical Schematic – drainage sys tem

Typical disposal route

Note Not Used


LIST OF CHANGES Appendix 2 – Lis t of c hang es

Section General 1.1 1.1 1.1 1.1 1.1 1.1 1.3.2 1.3.2 1.3.2 1.3.3 2.1 2.1 2.1

Change Replaced “bunded area” with “curbed area” and reference to “fluids” with “liquids” when appropriate st Simplified the 1 paragraph to refer solely offshore oil and gas production facilities Added paragraph referring to DEP 37.14.10.10 Informative Expanded the listing of drain systems covered by the DEP Reworded paragraph excluding domestic waste water and draining from drilling rigs Added paragraph excluding closed maintenance drain systems Added paragraph excluding drain systems and winterizing of drains systems in low temperature climates Definitions: Added definitions for Hazardous Area and Non Hazardous Area Definitions: Added clarifying note to Very Toxic Definitions: Added definition for Segregated Abbreviations: Deleted Closed Drain and added FPSO and TLP Purpose and Function of Facility Drain Systems: Deleted the reference to the MARPOL Convention (added reference in new Section 2.2) Added sentence regarding the transport and disposal of solids at an onshore site Added sentence regarding the use of seal loops and air g aps to segregate drains in the same drain system Expanded the listing of factors affecting the safety and environmental acceptability


LIST OF CHANGES Appendix 2 – Lis t of c hang es

Section General 1.1 1.1 1.1 1.1 1.1 1.1 1.3.2 1.3.2 1.3.2 1.3.3 2.1 2.1 2.1 2.1 2.1 2.1 2.2 2.3 2.3.1 2.3.2 2.3.3 2.3.4 2.3.5 2.3.6 2.3.7 2.3.8 2.3.9 Formerly 2.2.8 Formerly 2.2.10 3 3.1 3.1

Change Replaced “bunded area” with “curbed area” and reference to “fluids” with “liquids” when appropriate st Simplified the 1 paragraph to refer solely offshore oil and gas production facilities Added paragraph referring to DEP 37.14.10.10 Informative Expanded the listing of drain systems covered by the DEP Reworded paragraph excluding domestic waste water and draining from drilling rigs Added paragraph excluding closed maintenance drain systems Added paragraph excluding drain systems and winterizing of drains systems in low temperature climates Definitions: Added definitions for Hazardous Area and Non Hazardous Area Definitions: Added clarifying note to Very Toxic Definitions: Added definition for Segregated Abbreviations: Deleted Closed Drain and added FPSO and TLP Purpose and Function of Facility Drain Systems: Deleted the reference to the MARPOL Convention (added reference in new Section 2.2) Added sentence regarding the transport and disposal of solids at an onshore site Added sentence regarding the use of seal loops and air g aps to segregate drains in the same drain system Expanded the listing of factors affecting the safety and environmental acceptability of drain systems. Deleted the paragraph regarding modifications to existing drain systems Added final paragraph regarding requirements for cryogenic fluids Reworded to direct designer to specific operating unit or location requirements. Drain Systems Classifications: renumbered from 2.2 to 2.3 Open non-hazardous area drain system: Added the last paragraph regarding segregation of drain systems Open hazardous area drain system: Added reference to the majority of liquid hydrocarbons being transferred to other process systems or storage Closed maintenance drains: Modified this section to exclude the use of these types of “hard piped” process drain systems Process drains: Modified this section to clarify the handling of process drains Speciality fluid recovery and disposal systems: Added this section Instrument drains: Referred to Section 3 to avoid duplicate information Helideck drains: Referred to Section 3 to avoid duplicate information Firewater drains: Referred to Section 3 to avoid duplicate information Laboratory drains: Minor modifications to wording. Deleted SHALL [PS] process safety requirement. Living quarters drain system: Deleted this section as it was excluded in Section 1.1 Scope Drilling module drain system – Deleted this section as it was excluded in Section 1.1 Scope Changed title from ‘Guidelines’ to ‘Requirements’ Sources and Destinations of Drain Systems Liquids: Added the descriptions of the types of hydrocarbon pollutants encountered on an offshore facility Table 1: Moved Notes to the top of the table


Appendix 2 – Lis t of c hang es Section 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.2 3.2 3.3 3.3 3.3 3.3 Formerly 3.4 Formerly 3.5 3.4 3.5 3.6 3.6.1 3.6.2 3.6.3 4 4.1 Formerly 4.2

Change Table 1: Added a column for Item No. (can be used for reference purposes) Table 1, Item 1: Added note regarding the removal of hydrocarbons before draining a vessel into the OHD and deleted the reference to CD if very toxic fluids Table 1, Item 2: Added this item reading the handling of sands and solids Table 1: Deleted Process drains from process vessels Table 1, Item 3: Added reference to piping (flanged components) Table 1, Item 4: Replaced reference to Drains from with Drip pans under Table 1, Item 5: Added this item for drip pans at diesel fuel handling equipment Table 1, Item 6: Added reference to filters, pumps, piping etc. Table 1, Item 9: Deleted the reference to Drains and added note regarding the routing the overflow from a diesel tank to the primary storage tank Table 1, Item 11: Revised the destination of lube oil drains to the specialty fluid recovery and disposal system Table 1, Item 12: Added this section regarding the equipment drains for diesel, aviation fuel, hydraulic oils, glycol, etc. being routed to the specialty fluid recovery and disposal system Table 1, Item 13: Replaced hazardous with hydrocarbon Table 1, Item 18: Deleted reference to CD if very toxic fluids Table 1: Deleted Drilling rig mud drains Open Non-Hazardous Area Drain System: Deleted the sentence “Open modules do not require seal traps.” Open Non-Hazardous Area Drain System: Deleted the paragraph regarding disposal options Open Hazardous Area Drain System: Added “for enclosed module only” as a clarification in the third paragraph. Open Hazardous Area Drain System: Reworded the final paragraph to include a reference to the regulatory and operating unit requirements Open Hazardous Area Drain System: Deleted the paragraph referring to older facilities Open Hazardous Area Drain System: Deleted the paragraph referring to the closed drains Closed (Maintenance) Drain System: Deleted this section Process Drain System: Deleted this section Instrument Drains: Renumbered from 3.6 to 3.4 and reorganized this section. 3.4.1: Deleted SHALL [PS] process safety requirement. rd Helideck Drains: Renumbered from 3.7 to 3.5 and added the 3 paragraph. Deleted SHALL [PS] process safety requirement in para 2. Firewater Drains: Renumbered from 3.8 to 3.6 rd General: Added 3 paragraph regarding designs for fully enclosed modules and open deck designs. st Enclosed modules: added the 1 paragraph regarding the use of this section for enclosed modules Open decks: Added this section regarding firewater drains on open deck facilities Changed title from ‘Considerations’ to ‘Requirements’ Sizing Drain Systems: Added the duration and rate as criteria affecting the sizing of the drain systems Drain System Levels: Deleted this section as its contents was moved to the section on Piping Systems


Appendix 2 – Lis t of c hang es Section Formerly 4.2 Formerly 4.3 4.2 4.2.1 4.2.1 4.2.2 4.2.2 4.2.3 4.2.4 4.2.5 4.2.5 4.2.6 4.2.7 4.2.8 4.3 4.3.1 4.3.1 4.3.1 4.3.2 4.3.3 4.3.3 4.3.4 4.3.5 4.4 4.5 4.6 4.7 Formerly 4.8 4.8 4.8 4.8 4.9 4.9 4.9

Change Drain System Levels: Deleted the process safety requirement that “Separate drain headers from each level to the receiving systems SHALL [PS] be used to overcome this problem.” Drain System Gradients: Deleted this section as its contents was moved to the section on Piping Systems Selection and Sizing of Collection and Skimming Vessels: Renumbered from 4.4 to 4.2 and replaced “Caissons and Drains” with “Collection and Skimming Vessels” in the title Selection: Added this section with general selection criteria Added text on codes and standards for vessels and tanks Sizing: Deleted vessel rupture and deluge volumes from the sizing criteria. Deleted SHALL [PS] process safety reuirement. Sizing: Added a reference to Stoke’s Law for sizing in the vent a droplet size distribution can be approximated. Design pressure: Added this section. Deleted SHALL [PS] process safety requirement (2x). Material selection: Added this section Vessel internals: Added this section Vessel internals: Deleted the section regarding hydrocarbons from a ONHD caisson being routed to a OHD caisson Vessel appurtenances: Added this section Corrosion protection: Added this section Disposal caissons: Added this section Piping Systems: Renumbered from 4.5 to 4.3 Sizing: Added this section Added sentence on codes, standards and piping class Sizing: Deleted the 0.8 m/s maximum fluid velocity Layouts: Added this section. Deleted SHALL [PS] process safety requirement. Design pressure: Added this section Design pressure: Deleted the process safety requirement that “The design pressure of collection vessels SHALL [PS] be 350 kPa minimum.” Material selection: Added this section Basket strainers: Added this section Process Sand and Solids: Added this section Toxic Fluids: Added this section Facility Solid Wastes: Added this section Backflow Prevention: Added the recommendation that the hydrocarbon liquids from an ONHD system be routed to the OHD collection system as an additional segregation barrier. Liquid Seals and Dip Pipes: Deleted this section as its contents was moved to the section on the Collection Vessels and Piping Systems Floor Drains: Renumbered from 4.9 to 4.8 Floor Drains: Replaced negligible with no risk of hydrocarbon spillage Floor Drains: Added “When structurally feasible,” regarding the sloping of plate decks and floors. Deleted [PS[ requirement, replaced with ‘shall’ Drip Pans: Renumbered from 4.10 to 4.9 Drip Pans: Deleted the reference to drip pans are likely to form a hazardous zone Drip Pans: Added requirement to install strainers over the drip pan drains


Appendix 2 – Lis t of c hang es Section 4.10 4.10 4.11 4.11

4.11 4.11 4.11 4.12 4.13 4.14 5 5 5. 5. 5. 5. 5.

Appendix 1 Appendix 2

Change Tundishes: Renumbered from 4.11 to 4.10 Tundishes: Deleted the references to funnels. Replaced SHALL [PS] with shall. Vents: Renumbered from 4.12 to 4.11 Rewrote section on vents and added reference to DEPs 80.45.10.10 and 80.45.10.11. Fitment of a flame or detonation arrestor in an open drain system vent is considered permissible, Vents: Reworded the first paragraph to exclude connecting the vents to vents containing hydrocarbons and removed the process safety requirement that the vents not be interconnected Vents: Added air compressor inlets regarding the location of the vents Vents: Added paragraph clarifying the use of flame arrestors Chemical Treatments: Added this section Sampling of Effluent: Added this section. Deleted SHALL [PS] process safety requirement. Disposal at Sea: Relocated the final paragraph to Section 4.13 Sampling of Effluent. Deleted SHALL [PS] process safety requirement. Added reference to DEPs 80.45.10.10 and 80.45.10.11 Deleted MARPOL 1973 reference References: Replaced the reference to SWW (Shell Wide Web) with Shell Technical Standards Portal References: Added DEP 20.05.50.10-Gen., Heat transfer fluid (HTF) systems References: Added DEP 80.00.10.10-Gen., Area classification (amendments / supplements to IP 15) References: Added IMO Resolution A.753(18) (adopted on 4 November 1993) Guidelines for the Application of Plastic Pipes on Ships References: Replaced the addresses of international organisations with their web address Figure 3, Schematic – drainage system with closed drains – Deleted this Figure because generic closed drain designs are no longer supported in this DEP List of changes - Added this appendix

Drain System for Offshore Installation

Recommend Documents