Exploration & Production
GENERAL SPECIFICATION
SAFETY
GS EP SAF 228
Liquid drainage
Main Instructor for Derogation: ECP (Process)
03
10/2009
Complete revision
02
10/2005
Addition of EP root to document identification, plus modified
section 4.5 and checked for internal consistencies
01
10/2003
Change of Group name and logo
00
04/2001
Old TotalFina SP SEC 228
Rev.
Date
Notes
This document is the property of Total. It must not be stored, reproduced or disclosed to others without written authorisation from the Company.
Exploration & Production
Date: 10/2009
General Specification
Rev: 03
GS EP SAF 228
Contents
1. Scope .......................................................................................................................4
1.1
Purpose of the specification...............................................................................................4
1.2
Applicability........................................................................................................................4
2. Reference documents.............................................................................................5
3. Terminology and definitions ..................................................................................7
4. Design principles for liquid drainage (closed and open drains) ....................... 10
4.1
The different liquid drainage systems ..............................................................................10
4.2
Effluent categories in open drains ...................................................................................11
4.3
Segregation .....................................................................................................................14
4.4
Drainage piping: diameters, gradients, miscellaneous ....................................................16
4.5
Drainage piping: connections to closed drains and to OD 1 or OD 2 headers ................17
4.6
Drainage piping: material and rating................................................................................17
4.7
Underground facilities (onshore)......................................................................................18
4.8
Toxic service....................................................................................................................18
4.9
Winterisation ....................................................................................................................18
4.10
Accidental spillage ...........................................................................................................19
5. Design of closed drains........................................................................................19
5.1
Maintenance and operation drains ..................................................................................19
5.2
Piping...............................................................................................................................20
5.3
Closed drain drum ...........................................................................................................24
5.4
Standard design...............................................................................................................25
5.5
Minimum installations ......................................................................................................25
5.6
LPG and LNG units closed drain system.........................................................................26
6. Design principles for open drains .......................................................................26
6.1
General ............................................................................................................................26
6.2
Design flows ....................................................................................................................27
6.3
Flow velocities .................................................................................................................28
6.4
Pipe minimum diameters and gradients ..........................................................................29
6.5
Drainage piping: washing/clearing...................................................................................29
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6.6
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Gas migration and fire spreading.....................................................................................29
7. Design of onshore open drains ...........................................................................30
7.1
Oily water onshore drains typicals ...................................................................................30
7.2
Infiltration .........................................................................................................................31
7.3
Open ditches and channels .............................................................................................32
7.4
The collection of the drainage effluent in process and utility areas .................................32
7.5
Liquid hydrocarbon storage tanks....................................................................................32
7.6
Off-sites ...........................................................................................................................33
7.7
Buildings ..........................................................................................................................33
8. Design of offshore open drains ...........................................................................33
8.1
Configuration of offshore open drains..............................................................................34
8.2
Detailed design of collection system................................................................................35
8.3
Helidecks .........................................................................................................................35
8.4
Buildings ..........................................................................................................................35
8.5
Sump tank and disposal tube ..........................................................................................36
8.6
Minimum installations ......................................................................................................37
9. High volatility hydrocarbon liquids .....................................................................38
9.1
Containment of accidental spillage ..................................................................................38
9.2
Onshore process areas: paving and impounding basins.................................................38
Appendix 1
Accidental spillage flow rate calculation.............................................................41
Appendix 2
Run-off water rates (onshore) (Informative).......................................................42
Appendix 3
Liquid drainage (informative) .............................................................................43
Appendix 4
The collection of the drainage effluent in onshore process and utility areas
(prescriptive) ......................................................................................................................52
Appendix 5
The collection of the drainage effluent in offshore process and utility areas
(prescriptive) ......................................................................................................................60
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GS EP SAF 228
Rev: 03
1. Scope
1.1 Purpose of the specification
GS EP SAF 228 defines the safety requirements for liquid drainage facilities in the petroleum
installations of the upstream segment of COMPANY’s activities in order to minimise
uncontrolled spillage and risk of hydrocarbon ignition and subsequent fire escalation.
The design of oil-contaminated drains, open drains and closed drains, from process, storage
and utility areas is the main subject of this GS EP SAF 228. These drains are designed to
handle liquid wastes produced in normal operation, any degraded operating modes foreseen
during design, and maintenance.
GS EP SAF 228 also addresses the collection and containment of accidental spillage from
facilities processing hydrocarbon liquids.
GS EP SAF 228 also aims to minimise direct discharge of polluted streams to the environment
by channelling them to appropriated treatment units, in line with COMPANY Environmental
requirements as per GS EP ENV 001.
1.2 Applicability
New installations designed by or on behalf of COMPANY shall comply with this specification.
Modifications and extensions of existing installations should also comply with this specification,
unless it is demonstrated and documented that it results in inconsistencies that are detrimental
to the overall safety of the installation.
GS EP SAF 228:
• Is not retroactive, but it is used as a reference during the design and operability reviews of
the existing oil and gas installations operated by COMPANY affiliates.
• Applies to all onshore and offshore fixed installations handling hydrocarbon liquids in the
upstream segment of COMPANY activities, including those handling liquefied gases.
GS EP SAF 228 does not cover:
• Hydrocarbon gases and vapours disposal facilities (covered by GS EP SAF 262)
• Treatment of production water (i.e. water from reservoir) and utility waters (e.g. cooling
water, desalting water)
• Containment of accidental spillage from onshore storage facilities (covered by
GS EP SAF 341)
• Detailed design of oily water treatment facilities to achieve the specification set for
disposal of oily water to the environment
• Design of the facilities treating the effluents not compatible with oily water, such as
chemicals, drilling cuttings, solids, domestic sewage
• Collection of LPG/LNG spillage offshore (on deck or on boat)
• Detailed design of the instrument drains (addressed in GS EP INS 900).
• The mobile marine facilities covered by the codes issued by the IMO (International
Maritime Organisation)
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• The petroleum installations of the COMPANY downstream segment i.e. refinery,
marketing and petrochemicals.
The design features that are specific to F(P)SO installations (Floating, (Production) Storage and
Offloading) are addressed in GS EP STR 651, and only addressed in this document where
additional clarification is necessary.
The drawings and figures contained in this specification are illustrative only and should not be
regarded as detailed engineering documents. They illustrate some of the points made in the
specification and should be used as a basis for the preparation of detailed engineering
drawings.
2. Reference documents
The reference documents listed below form an integral part of this General Specification. Unless
otherwise stipulated, the applicable version of these documents, including relevant appendices
and supplements, is the latest revision published at the EFFECTIVE DATE of the CONTRACT.
Standards
Reference
Title
Not applicable
Professional Documents
Reference
Title
ISO 10418 / API RP 14C
Petroleum and natural gas industries Offshore production
installations Basic surface process
ISO 13703 / API RP 14E
Petroleum and Natural Gas Industries - Design and Installation of
Piping Systems on Offshore Production Platforms
ISO 17776 / API RP 14J
Petroleum and Natural Gas Industries - Offshore Production
Installations - Guidelines on Tools and Techniques for Hazard
Identification and Risk Assessment
ISO 14620
Space Systems - Safety Requirements
API RP 55
Recommended Practice for Oil and Gas Producing and Gas
Processing Plant Operations Involving Hydrogen Sulfide
ISO 23251 / API RP 521
Petroleum, petrochemical and natural gas industries Pressurerelieving and depressuring systems
Regulations
Reference
NFPA 59A
Title
Standard for the Production, Storage, and Handling of Liquefied
Natural Gas (LNG)
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Codes
Reference
IP Code, Part 15
Title
Area classification code for petroleum for installations, part 15 of
the Institute of Petroleum Model Code of Safe practice (March
1990)
Other documents
Reference
Title
Statement Of Requirements (SOR)
Safety Concept
Operating Philosophy
Total General Specifications
Reference
Title
GS EP CIV 202
Drainage and underground networks
GS EP ECP 103
Process sizing criteria
GS EP ENV 001
Environmental Requirements for Projects Design and E&P
Activities
GS EP ENV 270
Deep well disposal
GS EP INS 900
Instrument hook-up diagrams
GS EP PVV 112
Piping material classes
GS EP SAF 216
Area classification
GS EP SAF 253
Impacted area, restricted area and fire zones
GS EP SAF 261
Emergency Shut-Down and Emergency De-Pressurisation (ESD &
EDP)
GS EP SAF 262
Pressure protection relief and hydrocarbon disposal systems
GS EP SAF 321
Fire pump stations and fire water mains
GS EP SAF 341
Location and protection of onshore hydrocarbon storage
GS EP STR 651
General principles for a F(P)SO Design
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3. Terminology and definitions
There are five types of statements in this specification, the “shall”, “should”, “may”, “can” and
“must” statements. They are to be understood as follows:
Is to be understood as mandatory. Deviating from a “shall”
Shall
statement requires derogation approved by COMPANY.
Should
Is to be understood as strongly recommended to comply with the
requirements of the specification. Alternatives shall provide a similar
level of protection and this shall be documented.
May
Is to be understood as permission.
Can
Is to be understood as a physical possibility.
Must
Expresses a regulatory obligation
Note that “will” is not to be understood as a statement. Its use is to be avoided, unless it is
necessary to describe a sequence of events.
For the purpose of this specification, the following definitions shall apply:
Gravity-differential type oil-water separator and auxiliaries designed
API separator
according to API recommendations. This is an open pit used
onshore in the primary treatment of waste water.
Bunded areas
Bunded areas are areas surrounded by embankments and/or
bundwalls at or above grade level that are designed for the
containment of major accidental spillage and are connected to the
open drains via a normally closed valve. "Bund" has the same
meaning as the American wording "dike". Not to be confused with
drip pans and impounding basins.
Catch basin
Catch basins are onshore recessed, grated drainage collection
points within a drainage curbed area to channel the surface liquids
to the open drain system.
Classified/Unclassified
open drains
Classified open drains collect waste oily water from hazardous area
(i.e. hydrocarbon liquid production and process areas). Unclassified
open drains collect waste oily water from non hazardous area.
Closed drains
Closed drains are fully contained drains, hard piped from the
equipment to be drained to the treatment facilities.
Cold Flare
A cold flare system collects and disposes of cold/dry effluents which
are not compatible with warm/wet effluents.
Disposal tube
Facility installed in offshore oil and gas installations as the last oil
trap before disposal of oily water to sea.
Drip pans
Drip pans (or trays) designed to collect, contain and send to the
installation drains the oily drips (hydrocarbons, oils, greases) likely
to occur underneath process equipment and machines in normal
operation. They are permanently connected and lined up to the
installation open drain systems. Not to be confused with bunded
areas and impounding basins.
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Fire break / gas seal
U-shaped siphon whose low point is normally filled with liquids,
aimed at preventing fire and gas propagation between two different
segments of an open drains piping system
GRP
To designate the Glass Reinforced Plastics used in the fabrication
of piping.
Hazardous area
A three-dimensional area in which a flammable atmosphere may be
expected to be present at such frequencies as to require special
precautions for the control of potential ignition sources (COMPANY
from IP Code, Part 15).
High volatility
hydrocarbon liquids
Those hydrocarbon liquids which are referred to as Category A
petroleum fluids. The criteria for categorising flammable liquids “A”
as per the IP code are given in GS EP SAF 216.
Basically all liquefied methane and ethane (LNG), all liquefied
propane and butanes (LPG), and the more volatile of the rest of
Natural Gas Liquids (NGL) belong to this category.
HP flare or HP vent
A HP flare or HP vent is a disposal system where the back pressure
can be higher than that what is admissible in the LP relief system.
The HP flare collects the high flowrate sources which cannot be
routed to the LP flare disposal system because they would create
excessive back pressure.
Impounding basins are basins below grade level that are designed
for the containment of major accidental spillage. They can be
equipped with an uplift pump for rainwater removal, but this pump is
not intended to transfer hydrocarbon liquids. The impounding basins
stand-by are located adjacent to the process equipment, not
underneath. Not to be confused with drip pans and bunded areas.
Impounding basins
LP flare or LP vent
Maintenance drains
A LP flare or LP vent is a disposal system where the back pressure
must be maintained low (maximum 3.5 barg) even at maximum
relief flowrate.
Closed system which collects liquid drains from depressurised
equipment and piping. The system is used for maintenance purpose
only.
Minimum installations
Installations handling oil and gas for production or transport
purposes, with no processing facilities. Offshore, they are the
wellhead and/or manifold platforms which are not bridged to a
process installation. Onshore they are the wellhead clusters and/or
production manifolds. A minimum installation may include helideck,
(dry) firewater network, electrical cabin, etc. Test separators and pig
traps are not considered as processing facilities. Well-Head
Platforms or clusters with FWKO drums and water degassing drums
are not considered as minimum installations.
Observation basin
Facility installed in onshore oil and gas installations as the last oil
trap before disposal of oily water to public waters. It is an open pit
designed as to retain the drainage effluent for a certain time.
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(OD1) Permanently oilcontaminated drains
Waste water open drains contaminated in normal operation by
significant quantities of liquid hydrocarbons.
(OD2) Accidentally oilcontaminated drains
Waste water open drains :
(OD3) Oil-free drains
• either (1) contaminated in normal operation or during other
routine operations foreseen during design (e.g. maintenance)
by very small volumes of hydrocarbons so that it is acceptable
environmental-wise to route directly the effluents directly to an
observation basin or a disposal tube without first separation
in API separator or sump tank.
• or (2) normally clean and for which contamination with
hydrocarbons can only result from an accidental leak (e.g.
piping weld puncture) or a rare event (e.g. storm flooding and
cross-contaminating normally clean areas).
Waste water open drains in areas where the risk for contamination
by hydrocarbons is minimal and can be disregarded.
Oil trap
Facility designed to retain and allow recovery of floating liquid
hydrocarbons only. Disposal tubes are offshore final oil traps and
observation basins are onshore final oil traps.
Oily water or oilcontaminated water
Waste water generated during the industrial process and which
contains oil, emulsified oil, or other hydrocarbons.
Oily water treatment
Facilities designed for the treatment (primary, secondary) of oily
water to meet a given specification (maximum oil in water content)
for its disposal to sea or to public waters.
Open drains
They are basically atmospheric drains: their intakes (entry points)
are permanently vented to atmosphere.
Operational drains
Closed system which collects liquid drains from process equipment
and piping whilst the process unit is live and the process equipment
and piping is at normal operating pressure.
Paved areas
Refers to paving, concrete slabs and other liquid tight surfaces
required underneath and around the onshore hydrocarbon process
equipment to prevent infiltration into the soil of hydrocarbon liquids
(and other pollutants likely to spill).
Gravity-differential separation of oil from waste waters: API
separator onshore, or sump tank offshore.
Primary treatment
Secondary treatment
Facilities designed for the treatment of oily water by means other
than gravity-differential separation to meet a given specification
(maximum oil content in water) for its disposal to sea or public
waters: e.g.: filtration, flotation, chemical flocculation and biological
treatment.
Seals, sealed
The “seals” are in this specification hydraulic seals. Drains are
“sealed” if they are provided with a hydraulic seal to prevent fire
spreading and gas migration. This can be implemented either in the
piping (siphon) or by entering a capacity below the liquid level.
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Self-contained
equipment
Equipment provided with a bund designed for containment of a
major accidental leak, this bund is connected to the open drains
system via a normally closed valve.
Sump tank
Atmospheric tank designed as a gravity-differential oil-water
separator to treat offshore oil and gas installations oily water drains
from the hydrocarbon production and process areas.
Toxic fluids
The characteristics of a chemical substance to produce injury once
it reaches a susceptible site in or on the body. The effects may be
acute
or
chronic,
local
or
systemic
(OGP).
The criteria to define a substance as a toxic fluid are set in
applicable local regulations and in GS EP SAF 253.
4. Design principles for liquid drainage (closed and open drains)
This chapter addresses the basic COMPANY requirements for the design of liquid drainage
systems.
4.1 The different liquid drainage systems
Drainage systems are networks of pipes collecting liquid wastes from numerous intake points in
catchment areas, and transferring these liquids to treatment facilities before safe and controlled
disposal (or recycling these liquids into the processing plant).
4.1.1 The different types of effluents
In oil and gas production/treatment installations, there are four types of effluents concerned with
drainage:
• Waste waters
-
run-off water (rainfall, fire-fighting and deck/slab washings) polluted or not
-
equipment cleaning water (“jetting”, line and vessel cleaning)
-
storage water (settling)
• Hydrocarbons
-
drips and spillage from hydrocarbon process equipment, wireline and other well
servicing activity, and other facilities containing oils and greases
sampling, draining of process equipment before maintenance
• Chemicals
-
from the laboratory and other analyses houses
-
chemicals used in oil and gas processes
• Sewage
-
Waste waters from domestic areas (galley, laundry, accommodation and sanitary
facilities).
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4.1.2 The different configurations of drainage networks
4.1.2.1 Closed drains
Any facility containing hazardous liquids which need to be drained for operational reasons and
may not be drained directly to atmosphere without undue risk to personnel, environment or
assets from release of flammable or toxic vapours, shall be connected to a closed drain
system. In particular:
• Hydrocarbon process equipment and/or piping operated under pressure
• Equipment containing toxic fluids as defined in section 4.8
• Equipment containing high volatility hydrocarbon liquids which require draining for
maintenance / inspection purposes.
The design of closed drains is detailed in chapter 5.
4.1.2.2 Open drains
They are basically atmospheric drains collecting the surface waste liquids: all their intakes (entry
points) are permanently vented to atmosphere.
For safety reasons the facilities containing hydrocarbon flashing fluids under pressure, toxic
fluids or high volatility hydrocarbon liquids shall not be drained to an open drain system.
4.1.3 Particular cases
4.1.3.1 Instrument drains
The design features that are specific to instrument drains are addressed in GS EP INS 900.
The nominal size of instrument drains is normally much smaller than vessel and piping drains.
All instrument drains shall however comply with the basic principles laid down in sections 4.2
and 4.3.
Note that vessel standpipe drains shall be regarded as vessel/piping drains and therefore shall
comply with this specification, whereas level glass should be regarded as instrument drains.
4.1.3.2 Sampling
For each new project or major revamping, sampling typicals should be developed. As a
minimum the Operating Philosophy and/or Safety Concept documents should list the different
types of sampling facilities to be implemented. Sampling typicals shall be approved by Company
representative and shown on a dedicated P&ID.
Samples from a facility containing hydrocarbon flashing fluids under pressure, toxic fluids shall
not be connected to the open drain system. They shall be collected in a closed, sealed
container rated to match the facility maximum operating pressure, or if necessary connected to
the closed drain system or to a lower pressure process system.
4.2 Effluent categories in open drains
4.2.1 Open drains, permanently oil-contaminated (OD1)
OD1 drains are found in hydrocarbon liquid production, process and storage areas.
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OD1 waters shall be treated in a purposely designed oily water treatment unit containing a
primary treatment unit as a minimum, and if necessary a secondary treatment before
disposal.
OD1 sources include :
• Liquid collected underneath the oil or gas/condensate process equipment likely to produce
drips in routine operation (e.g. pumps, compressors, vessels, HC wellheads, manifolds,
sampling devices and generally all the equipment with a concentration of non-welded
fittings). Such liquid shall be collected in a drip pan.
• Liquid collected underneath oil loading areas including loading arms, hose handling areas
at jetties and filling points
• Water draw-off from oil storage tank bottoms
• Water from oil laboratory and analyser houses (they require an independent collection
system, see section 4.2.4)
• Drainage from oil sample points (not of fluid cat. A)
4.2.2 Open drains, accidentally oil-contaminated (OD2)
They are waste water open drains.
Before disposal to the environment, OD2 waters shall be treated and, as a minimum, floating oil
recovered in an oil trap (offshore: an oily water disposal tube designed as per section 8.5.2,
onshore: an observation basin designed as per section 7.1.1).
OD2 sources include :
• In plants processing hydrocarbons liquids: waste waters collected in the vicinity of process
units i.e. (i) offshore: the deck drains, (ii) onshore: the paved areas.
• In plants not handling hydrocarbon liquids: waste waters collected in areas polluted with
lube oils and greases from machines such as power generation, water injection pumps or
other equipment (e.g. transformer using insulating oil), subject to segregation
requirements set in section 4.2.4.8.
• Oil and condensate storage tank bunds waste waters
• Cooling waters that may be polluted with oil
4.2.3 Open drains, oil-free (OD3)
OD3 water may be discharged directly into the environment (offshore through an outfall pipe
discharging directly to sea, onshore through a pipe or a ditch discharging directly to public
waters)
OD3 sources include :
• Offshore: the “clean” decks e.g. lay-down areas, peripheral areas away from the process
equipment (e.g. outside process and utility modules), and the rooves of modules and
shelters
• Onshore: the green belt, undeveloped areas, building rooves (buildings outside the
process area).
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4.2.4 Effluents not compatible with OD1, OD2 and OD3 sources
This section lists the main types of wastes encountered in oil and gas production and treatment
facilities that shall not be mixed with waste waters collected in the installation open drains
without prior adequate treatment.
The effluents which are toxic for health or the environment and cannot be treated on site, shall
be stored in adequate sealed containers, and then transported to appropriate treatment
facilities outside the installation.
4.2.4.1 Domestic sewage
A dedicated collecting network and specific treatment units (e.g. degreaser) are required to
handle wastes from living quarters, kitchen and sanitary facilities. Domestic waste waters shall
not be mixed with other drainage effluents or disposed of before appropriate treatment.
4.2.4.2 Laboratories
Laboratory sink drains handle oily products but also chemically polluted effluents, which shall
not be sent directly to the installation open drain system. The laboratory drains shall be piped
independently from other drains to a dedicated, vented atmospheric tank.
These wastes must be processed in one of the following ways:
• Treated (secondary treatment like neutralisation), or
• Stored before transport to an appropriate treatment facility.
The solution should be selected depending on the regulatory requirements and plant design.
The selected design shall be approved by COMPANY.
4.2.4.3 Chemical storage
Permanent storage containing hazardous chemicals incompatible with water shall be provided
with bunds to safely contain minor spillage and major accidental leaks. The contained spillage
should then be treated (e.g. using one of the methods defined in section 4.2.4.2). The method
selected shall be approved by COMPANY.
4.2.4.4 Sour water/Chemically polluted streams
Sour Water streams (e.g. containing H2S or NH3) shall be stripped in a sour water stripper,
unless otherwise specified by COMPANY. Further treatment may be necessary before they can
be discharged to the main oily water treatment system.
Units handling:
• Methanol, glycol, amines
More generally any chemical that cannot be separated by gravity from wastewaters, shall not be
drained to the installation open drain system. Their wastewaters and drips shall be collected
and stored independently for further handling (e.g. recycling to the process, dedicated
secondary treatment).
4.2.4.5 Water contaminated with acids
Such waters shall be neutralised, as near as possible to the source.
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4.2.4.6 Water containing agents that can impair gravity separation
Streams that can impair gravity separation, such as streams containing solids, emulsifying
agents and/or contaminants that tend to flocculate upon dilution shall:
• Not be mixed with oily water
• Be treated and/or disposed of separately, as specified by COMPANY.
Falling in this category are the “jetting” waters which are used to clean vessel internals to
prevent accumulation of sands and sediments. A specific collecting network, independent from
the other open drains, shall be provided. Jetting waters shall be washed and filtered before
allowing them to drain in the installation OD2 drains.
4.2.4.7 Cold drains
Drainage of cold effluents which, mixed with wastewater at ambient temperature, may lead to
icing shall be collected in dedicated piping. Treatment, de-oiling, should also be performed in
dedicated facilities, unless it is demonstrated that mixing cannot lead to icing in the equipment
shared by the cold and humid effluents.
4.2.4.8 Machinery space
Many regulations and best practices require that, for environmental purposes, oily waters from
machinery spaces, involving lube oils with metallic contents, are handled separately from other
oils. This segregation shall be addressed in the Safety Concept.
4.2.5 High volatility hydrocarbon liquids
High volatility hydrocarbon liquids shall not be drained to an open drain system. For the
containment of accidental spills from facilities containing such liquids refer to chapter 9.
4.3 Segregation
As shown in section 4.2, drainage systems carry a large number of different effluents. Improper
segregation of drainage systems is one of the main causes of accidents in oil and gas
installations. Segregation must therefore be incorporated as early as possible in the design of
drainage systems.
4.3.1 Segregation: Closed drains/Open drains
Closed drains shall always be segregated from open drains in order to prevent pressuredriven gas from the closed drains coming back up into the plant via the open drains system.
The piping networks collecting closed drains and open drains shall be independent (no interconnections at all, even for maintenance purposes).
The closed drain drum shall receive no effluents from the open drains collection network. The
closed drain drum shall not discharge into an atmospheric enclosure (tank, drum) receiving
open drain effluents.
4.3.2 Segregation: Hazardous/Non hazardous areas
The risk of sending hydrocarbons from areas categorised “hazardous” (as per GS EP SAF 216)
to areas categorised “non-hazardous” shall be minimised by segregation of the systems
draining these areas.
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The piping networks collecting open drains from hazardous areas and from non-hazardous
areas shall be independent (no inter-connections at all, even for maintenance purposes). This
principle applies to all open drains, including the instrument open drains.
Drain headers from hazardous and non-hazardous areas may all discharge into a common oil
trap or primary treatment facility provided both conditions below are met:
• Headers from hazardous areas are not connected to headers from non-hazardous areas
and each header enters the common treatment facility via its own dedicated inlet nozzle.
• Hydraulic seals are provided at the oil trap/primary treatment facility by means of an
inlet pipe discharging below the liquid level in the facility (the drain header from nonhazardous areas shall be sealed at entry with 1 m water depth minimum).
4.3.3 The segregation requirement for drip pans
A drip pan shall be provided underneath every process and utility facility likely to pollute waste
water during routine operation.
Generally catchment areas should be arranged in order to prevent mixing of effluents that
require different treatment methods.
Open drainage systems shall be arranged and sized to prevent flooding of the drip pans and
the spread of fire and flammable liquids from one catchment area to another. There shall be no
carry-over:
• From the drip pans to the adjacent deck (offshore) or grade (onshore)
• From one deck to the deck located below (offshore).
To achieve this, the open drain systems shall be capable of handling the design flows which
are defined in section 6.2.
The arrangements of OD1, OD2, OD3 drains are detailed in chapter 7 for onshore installations
and chapter 8 for offshore installations.
4.3.4 The segregation requirement for paved areas
In onshore installations, paved areas shall be provided in process areas in order to:
• Prevent infiltration of oily effluents into the soil
• Minimise the evaporation rate of hydrocarbons liquids and thus the extent of the
flammable gas cloud.
Paved areas shall be split into spillage catchment areas :
• Spillage catchment areas should be arranged in order to prevent mixing of effluents that
require different treatment methods.
• Spillage catchment areas shall be arranged in order to prevent mixing of effluents that
require non compatible methods for vapours control and fire-fighting.
• The location, size and shape of the spillage catchment areas shall be such that the effects
of a pool fire of the size of one spillage catchment area can be controlled. The fixed and
mobile active fire-fighting systems, and the passive fire protection of equipment and
structures shall be defined accordingly.
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Open drainage systems shall be arranged and sized to prevent flooding of the spillage
catchment areas and the spread of fire and flammable liquids from one catchment area to
another. There shall be no carry-over:
• From one spillage catchment area to the adjacent spillage catchment areas
• From paved to unpaved areas
4.3.5 The segregation of cold / wet effluents
The collection and treatment of drains shall be segregated such that icing may not occur: cold
drains (handling LNG, refrigerated LPG or NLG) shall not be mixed with wet drains.
4.4 Drainage piping: diameters, gradients, miscellaneous
The design of the drainage systems should minimise the presence of stagnant hydrocarbon
mixtures (liquids, emulsions, and solid residues) on surfaces and inside the collection system.
Evacuation of drainage effluents shall be by gravity. Drainage headers are normally laid
horizontally with sizes and gradients in order to ensure proper evacuation. The open drain
systems shall be capable of handling the design flows defined in section 6.2.
Maximum capacity of open drain horizontal headers shall be in accordance with
GS EP CIV 202.
The system shall be designed to prevent any flooding of paved areas, floors or decks around
control rooms, technical rooms (containing instrument or electrical equipment) and furnaces.
Restrictions, fittings and generally piping routings with a high resistance to flow should be
avoided (special rules apply to closed drains, see chapter 5).
Other than siphons and seal pots (or manholes onshore), drainage headers shall contain no
pockets and slope continuously towards the primary treatment, oil trap or sump tank.
4.4.1 Piping diameter
Piping diameters depend on service (see chapter 5 for closed drains piping diameter and
chapter 6 for design velocities in open drains piping).
The nominal diameter of drainage headers, open and closed, in onshore and offshore
installations shall not be less than 3”.
Onshore the minimum nominal diameter of oily water open drain headers shall be in
accordance with GS EP CIV 202, 4” for branches less than 15 m and for headers collecting a
maximum of 4 drains, otherwise it shall be 6” minimum. A minimum of 8” is required for drainage
sewer between manholes (sub headers).
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4.4.2 Piping gradients
The minimum gradients of the horizontal piping are specified below for fixed installations (for
gravity-type drains, non-flooded pipes):
Type of installation
Line size
Minimum gradient
Ø ≥ 18”
18” > Ø ≥ 6”
6” > Ø ≥ 3”
0.2%
0.4%
1.25%
Offshore pre-fabricated module
Ø ≥ 3”
1% + hook-up tolerances
Offshore
Ø ≥ 3”
1%
Onshore
Note that F(P)SO may require higher gradients to make up for vessel movements.
4.5 Drainage piping: connections to closed drains and to OD1 or OD2 headers
The level of risk of plugging of the open and closed drain headers by solids (sand etc.),
deposits (wax etc.) or high viscosity fluids shall be identified where credible in the Safety
Concept.
Based on this, the type of connection from drain branches or sub headers to drain headers can
be made either:
• At 90 degrees, but in this case rodding points shall be provided for each header at risk
• At an angle of 45 or 60 degrees.
4.6 Drainage piping: material and rating
Drainage piping material and rating shall be selected as per specification GS EP PVV 112.
4.6.1 Closed drains
The piping material shall be steel, either carbon or alloy depending on service.
GRP (Glass Reinforced Plastics) shall not be used for this service. For pressure ratings refer to
chapter 5.
4.6.2 Open drains
Piping shall be class 150# ANSI.
Oil-contaminated water OD1 and OD2 drains piping material should be either steel or GRP
depending on service.
Oil free water OD3 drains piping material should be either GRP, concrete or steel.
Oil-free water may be collected in open channels/ditches.
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4.7 Underground facilities (onshore)
Tanks and vessels handling hydrocarbon liquids shall not be installed in excavated pits.
When installation underground or below grade level is necessary, the gap between the facility
and the pit shall be filled with dry sand, and suitable protection against rain shall be provided.
Burying those tanks and vessels may be an acceptable alternative only if :
• They are of a double containment fabrication type to minimise the risk of an unnoticed
leak to the environment
and if
• They are provided with suitable protection to avoid rainwater percolation.
4.8 Toxic service
Substances regarded as toxic shall not be exposed to personnel without due precaution being
taken.
Process streams containing hydrogen sulphide (H2S) are regarded as toxic and shall not be
released intentionally to atmosphere if any one of the following conditions is met:
• The concentration of H2S in the gas on release (1) is 100 ppm (2) or more,
• In inadequately ventilated
ppm (4) or more.
(3)
areas the concentration of H2S in the gas on release is 5
A similar approach shall be adopted for other toxic material (e.g. SO2, CO, CO2, Cl2, disulfides,
mercaptans, BTEX, refer to GS EP SAF 253), for which concentration in the gas on release
shall be validated by COMPANY.
• Facilities handling such toxic streams shall:
• Not be drained to an open drain system
Be drained to a closed drain system.
(1): The “gas on release” is the gas flashing from the process liquid at atmospheric and ambient temperature.
(2): Corresponding to the IDHL of H2S (Refer to GS EP SAF 253).
(3): With regards to H2S concentration, an area is defined as inadequately ventilated when the ventilation (natural or artificial) is
not sufficient to prevent the accumulation of significant quantities of H2S-Air mixtures in excess of 10 ppm (definition from
API RP 55). For example areas with 100% plain walls and either 100% plain ceiling or 100% plain floor shall be regarded as
inadequately ventilated. Typical examples are pits and depressions. For further guidance on areas inadequately ventilated refer to
GS EP SAF 216.
(4): Corresponding to the TLV TWA of H2S (refer to GS EP SAF 253)
4.9 Winterisation
Where applicable, drainage lines, seal pots and headers shall be winterised against freezing by
heat tracing or alternate solutions.
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4.10 Accidental spillage
Provisions for mitigating the effects of an accidental spillage should be considered below and
around any facilities containing combustible, flammable liquids.
These provisions are widely dependent on the type of the liquid, the type of the facilities, their
size and inventory, and their location. It is not the purpose of this present document to give
detailed solutions for all cases.
The specific case of onshore facilities handling highly volatile hydrocarbons is further addressed
in chapter 9. The specific case of hydrocarbon storage is addressed in GS EP SAF 341. Toxic
and environmentally harmful liquids are addressed in section 4.2.4. For others fluids the general
principles are:
• A kerb of minimum 150 mm high should be provided around the area under the equipment
where potential leakage could occur. This kerbing area could encompass more than one
vessel, depending on the layout of the plant. The area contained within the kerbing shall
take into account the estimated flow-rate and volume of the liquid lost during a credible
event
• In a consistent manner with GS EP SAF 253, the credible leak should be based on a
20mm hole size and a release duration of 10 minutes (see section 6.2.5)
• Onshore the liquids caught in the kerbed area should preferably be routed to a dedicated
impounding basin via open ditches and by gravity flow. Alternatively these liquids can be
connected to the open drain system.
• Offshore the liquids caught in the kerbed area shall be routed to the open drain sump
tank as shown in Appendix 3, Figure 3C.
• Finger-type slug catchers shall be provided with a paved area underneath their liquid
bottle sections. This paved area shall slope to an impounding basin whose capacity
shall accommodate the maximum liquid volume of the slug catcher, and which is not
located underneath the slug catcher.
5. Design of closed drains
5.1 Maintenance and operation drains
Closed drains shall be designed as per the requirements set out in chapters 4 and 5.
Closed drain systems are principally designed for the collection of maintenance drains, but
can be designed for operational drains with the provisions given below.
5.1.1 Maintenance drains
The closed drain system connects drains used for maintenance purposes, i.e. to drain a facility
after it has been isolated and depressurised (the residual pressure before drainage shall not
exceed 3.5 barg).
These closed drains shall be referred to as maintenance drains.
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5.1.2 Operation drains
Liquids from process equipment are routed to other process units.
It may be accepted to route liquids from process equipment to the closed drains system only
where transferring these liquids to process facilities is impractical e.g.:
• Facilities which would produce small liquid volumes at very low pressure in remote
locations (e.g. vent and flare piping low points on some onshore installations)
• Facilities which would release very small liquid volumes infrequently (e.g. compressor
casing drains to sweep liquids out before starting, fuel-gas filters).
Automatic transfer of liquids from a flare KO drum to the closed drain drum may be accepted if
gas blow-by and high level in the closed drain drum safeguards are in place. A dedicated
nozzle should be provided on the closed drain drum.
These closed drains shall be referred to as operation drains.
Manual operation drains (i.e. that can be operated only manually) shall be justified by Project
in an auditable document.
Automatic operation drains (i.e. that can be operated without operator manual intervention)
shall require a derogation to this specification duly approved by COMPANY.
All operation drains shall be highlighted on the P&ID and in the project OPERATING
PHILOSOPHY: a note shall state their design intent.
The above rules related to operational drains shall also be applied to VENDOR packages.
5.2 Piping
The lines collecting closed drain effluents are referred to as piping in this chapter.
5.2.1 General
Closed drain piping shall comply with COMPANY hydrocarbon piping specifications (refer to
GS EP PVV 112), in particular buried sections shall be all-welded (no flanges).
Closed drain lines shall slope continuously down to the closed drain drum (see section 5.3).
There shall be no low points in the piping.
All the consequences of a gas blow-by scenario (effect on drain line design temperature and
pressure, and effect on flare/vent line diameter from the closed drain drum, and safety
distances around flare/vent) shall be considered in the design of closed drains not positively
isolated from the process equipment to which they are connected.
• Positive isolation can be a spectacle blind (in closed position), a blind flange or a
removable spool piece.
Care shall be taken that back pressure from high pressure drains cannot impair low pressure
drains and their connected equipment.
The closed drains not fitted with positive isolation should be carefully considered; these are :
• The operation drains
• Some of the maintenance drains (see section 5.2.5 and Figure 1).
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5.2.2 Diameter
The nominal diameter of headers shall not be less than 3”. When determining the diameter of
the piping, possible occurrence of multi-phase flow shall be considered.
For more details on the design of the branches connecting drain points to the headers, see
sections 5.2.5 and 5.2.6.
5.2.3 Design pressure
The piping upstream of the closed drain drum shall be rated to match the highest design
pressure of the process facilities to which it is connected. This rule applies to all types of closed
drains, including those fitted with a spectacle blind for positive isolation from the process
equipment.
Mixing LNG with warmer, high volatility liquids (e.g. LPG or NGL) may result in serious
vacuums with a potential for piping collapse. LNG shall not be mixed with such liquids, unless
piping and vessels are designed to withstand the resulting vacuum.
The closed drain collection piping may be segregated into sub-systems of different piping
classes; in that case, each sub-system shall be provided with an independent header connected
to the closed drain drum via a dedicated nozzle.
In the case of modification to an existing facility, preference is given to the upgrade of the whole
closed drain system to match the highest design pressure of the process facilities to which it is
connected.
The derogation process remains appropriate for any brown field modification where the aspect
of the SAF 228 cannot be achieved, e.g. to connect new HP (typically 600 or 900#) closed
drain individual lines to an existing LP (typically 150#) closed drain header and subsequent
existing closed drain drum.
The derogation dossier shall address at least:
• Existing LP network blockage (e.g. by hydrates, solids, sands, paraffin, asphaltenes)
• Presence of valves on existing LP drain network
• Existing LP closed drain network over-pressurisation
• Assessment of existing individual closed drain lines design and arrangement against the
requirements of GS EP SAF 228
• Gas blow by to the existing closed drain drum
• Existing closed drain drum over-pressurisation
• Existing closed drain drum overfilling.
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5.2.4 Design temperature
For closed drains that are positively isolated from the process equipment, the lowest
temperature resulting from (mal operation) drainage under full process pressure shall be
considered. The piping material shall be selected to withstand this temperature at the
atmospheric pressure only (refer to GS EP ECP 103).
For closed drains that are not positively isolated from the process equipment, the
simultaneous occurrence of the lowest temperatures and the highest process pressure shall be
considered (see section 5.2.1).
It should be noted that LPG stored under pressure at ambient temperature is prone to contain
free water. This water may freeze after the LPG flashes in the drain system. Piping and vessels
in LPG drainage systems prone to contain water shall be protected against the risk of icing e.g.
with heat tracing.
5.2.5 Maintenance drains connections
The connection of a maintenance drain to a process facility shall be designed as per the
drawings of Figure 1, and the requirements of the present section.
Branches connecting the process facilities (e.g. hydrocarbon piping and vessels) to closed
drain headers shall be :
• Of a 2” nominal diameter, as a minimum
• Fitted with a full bore ball (or gate) valve located as close as practicable to the facility to
which it is connected.
• Fitted with a spectacle blind, associated with a bleed to vent gas that could be trapped
between the ball valve and the spectacle blind. This bleed shall discharge into an open
drain intake for all facilities provided with a drip pan. For the other facilities such as
piping header this is recommended but not mandatory.
• Fitted with a globe valve located downstream of the spectacle blind. The diameter of the
globe valve may be reduced to decrease the flow in case of gas blow-by scenario.
• Fitted with a check valve located between the spectacle bind and the globe valve to
prevent gas return when spectacle blind is opened.
To optimise the number of valves and flanges (sources of leaks) multiple drain connections from
the same equipment or unit to a single drain connection is acceptable provided that all above
principles are followed.
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GS EP SAF 228
FLAMMABLE (CAT. B OR C)
CAT. A (LNG, LPG, NGL)
& NON TOXIC
OR TOXIC
(2)
(2)
2"
Process liquids
(3)
(4)
LC or CSC
Process liquids
600mm mini
(1)
2"
600mm mini
(1)
LC
(5)
3" x 2"
3" x 2"
OD
CD
CD
FLAMMABLE (CAT. B OR C)
& NON TOXIC
CLEAN SERVICE (6)
NON FLAMMABLE & NON TOXIC
(3)
Process liquids
(2)
2"
LC (3)
Process liquids
2"
600mm mini (1)
OD
(3)
(4)
OD
CD
Legend :
FLAMMABLE, CAT., LNG, LPG
TOXIC relate to the materials handled by the equipment
CD : Closed Drains System
OD : Open Drains System
LC : Locked Closed
CSC : Car Seal Close
full bore block valve
globe valve
Figure 1 - Maintenance drains connections
Notes:
Important note: The drawings and figures contained in this specification are illustrative only
and should not be regarded as detailed engineering documents. They illustrate some of the
points made in the specification and should be used as a basis for the preparation of detailed
engineering drawings.
General note: Figure 1 is to be used in conjunction with section 4.8; 2” and 3” are minimum
nominal diameters.
(1):
Minimum distance required if icing is a possibility during drainage.
(2): First block valve (ball or gate) as close as possible to equipment, straight line, no elbow
from equipment to last valve to open drains.
(3): Valve to open drains shall be blanked off with a blind flange (valve can be used to bleed
pressure before turning the spectacle blind).
(4): If the close drain connection is from a line rather than an equipment item, a dedicated
connection to the open drains is not mandatory.
(5): A spacer or a spectacle blind normally in open position is necessary to ensure that
positive isolation means are readily available for the maintenance/inspection activities.
(6): For vertical and or horizontal vessels in clean service, it is acceptable that the drain
connection is on the process liquid outlet line, upstream or downstream of the liquid outlet
automatic isolation valve if any.
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Figure 1 assumes that all process equipment, including lines, are provided with adequate
depressurisation facilities. If an item of equipment is designed to be depressurised via a remote
facility connected to flare or vent (e.g. flow-line depressurisation via a test separator to a flare)
this shall be noted on the P&ID for clarification purposes. Typically dedicated cleaning/flushing
nozzles (inlet and outlet) are provided and not shown on this sketch.
5.2.6 Operation drains connections
The design of operation drains connections shall be studied on a case by case basis and shall
be approved by COMPANY. As for all process facilities a safety analysis shall be performed (as
per ISO 10418 / API RP 14C and GS EP SAF 261) and appropriate shutdown devices
incorporated in the design. The gas blow-by scenario shall be considered for the design of
closed drain facilities collecting operation drains.
The minimum nominal diameter of piping and block valves shall be 2” to prevent blockage. To
decrease the flow in the event of a gas blow-by the nominal diameter of throttling or control
valves may be reduced.
5.3 Closed drain drum
5.3.1 Purpose
Closed drains shall discharge first into a flash drum, referred to as the closed drain drum. The
closed drain drum shall be designed as a flash drum for the closed drain effluents, and shall
have no other function.
5.3.2 Venting
The closed drain drum should be connected to the LP (Low Pressure) flare. It may be
connected to a LP vent, if there is no LP flare on the installation. It shall not be connected to a
HP (High Pressure) flare or vent which may cause undue back-pressures in the closed drain
network.
The closed drain drum and its gas relief outlet piping shall accommodate the largest flow
resulting from the largest gas blow-by occurring in one single drain not isolated from the process
equipment by a positive isolation (see section 5.2.1).
5.3.3 Design pressure
The design pressure of the closed drain drum shall be 3.5 barg or LP flare design pressure
which may be governed by internal explosion resistance, refer to GS EP SAF 262.
All facilities connected to a closed drain drum shall be designed at no less than the design
pressure of the closed drain drum.
Design shall ensure that all risks of vacuum or air entry are properly addressed.
Purging requirements: refer to GS EP SAF 262.
5.3.4 Design temperature
The same rules shall apply for the closed drain drum as for the drainage collection piping (refer
to section 5.2.4).
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5.3.5 Design capacity
The capacity of the closed drain drum depends on the drainage philosophy which shall be
defined in the Operating Philosophy. As an absolute minimum, the closed drain drum shall be
capable to handle the maximum liquid inventory from a single vessel at LSLL. Specific cases
shall be addressed in the Operating Philosophy.
5.3.6 Miscellaneous
The closed drain drum shall have no connection for liquid transfer directly to mobile facilities
(e.g. offshore: to a boat). Such transfer, if necessary, shall be done from a dedicated
downstream atmospheric tank or pit.
In case of operational drainage, a LSHH shall be installed to shut off all operational drains
lines. In case of manual maintenance drainage, a LAH and visible and audible alarms in the
workplace shall be provided as a minimum.
For the automatic shutdown actions in case of LSHH, refer to GS EP SAF 261.
5.4 Standard design
Appendix 3, Figure 3C illustrates the application of chapter 5 for an offshore platform.
The standard design shall apply to all COMPANY installations which are not regarded as
“minimum installations” (defined in chapter 3).
Closed drain drum liquids should be returned (pumped back) directly to the LP process.
If sending closed drain drum liquids back to the process is not practicable (e.g. onshore if the
drum is located far from the process), the closed drain drum liquids can be sent to oily water
treatment. Closed/open drains segregation rules defined in section 4.3 shall be followed.
In particular:
• Offshore: No open drain headers shall be connected to a tank or vessel receiving the
closed drain drum liquids. Another tank shall be dedicated to collect open drains.
• Onshore: An API separator or other open pit may receive closed drain drum liquids and
oily water from the open drains. Liquid seals shall be provided at the inlet to counter balance
the maximum anticipated back pressure from the closed drains side (the open drain header
inlet shall be submerged at no less than 1 meter under the liquid level).
5.5 Minimum installations
A simpler design may be adopted for the minimum installations.
Appendix 3, Figure 3D illustrates the application of section 5.5 for an offshore minimum
installation platform.
Appendix 3, Figure 3I
installation.
illustrates the application of section 5.5 for an onshore minimum
A single vessel may be designed and used as both LP flare/vent KO drum and closed drain
drum, if this vessel complies with the requirements of section 5.3 and if both conditions below
are met:
• There is a LP flare/vent network, which is independent from the HP flare and low
temperature flare network, and whose operation back pressure cannot exceed 3.5 barg
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• The drain headers tie directly into the LP flare/vent KO drum via dedicated nozzles, and
are not connected to the LP flare/vent piping/header.
Combining LP flare/vent KO drum and closed drain drum shall be accepted only if the
Operating Philosophy clearly states that any maintenance drainage or liquid disposal to mobile
facility is made after the installation is shut-down in such a manner that LP flare/vent receives
no more flow. If installation shutdown is not the selected option, liquids offloading to mobile
facilities shall be made via a dedicated downstream atmospheric tank or pit.
This design is acceptable if all the requirements listed below are met (otherwise the standard
design of section 5.4 shall be adopted):
• The combined LP flare and closed drain drum is permanently vented through a flare
stack or vent designed in accordance with GS EP SAF 262. In the case of a vent both
systems (LP vent system and closed drain system) are designed for internal explosion.
• The drain headers inlets to the combined LP flare/vent and closed drain drum are made
with dip pipes with a minimum liquid seal of 300 mm in order to prevent gas return flow
when turning the closed drain spectacle blind.
• No operation drains are connected to the closed drain drum
• The closed drain drum is not connected to another process facility nor to a HP vent
whose back-pressure can exceed 3.5 barg.
• The closed drain drum receives no effluents from the open drain system.
• The closed drain drum liquids are sent back to the process by pumps.
Liquids offloading to mobile facilities, if any, shall be made via a dedicated downstream
atmospheric tank or pit.
5.6 LPG and LNG units closed drain system
For requirements specific to category A fluids (LNG and LPG), refer to section 9.
LNG and LPG closed drains may discharge directly into the KO drum of a LP cold flare. LNG
and LPG drains shall not be mixed with other drains until they enter the flare drum. Also LPG
and LNG drain and flare systems shall be segregated, because of the vacuum hazard (see
section 5.2.3)
6. Design principles for open drains
6.1 General
Open drains shall be designed as per the requirements set out in chapters 4 and 6. Further
requirements are developed in chapter 7 for onshore open drains and in chapter 8 for offshore
open drains.
This section is not applicable to the units handling high volatility hydrocarbon liquids which
shall not be provided with open drainage systems for normal operation (refer to chapter 9).
The open drainage systems should be kept as simple as possible in terms of construction,
operation and maintenance.
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For onshore installations: open, gravity-based drainage systems shall be used for the drainage
of waste water, unless they are prohibited by local regulations. Alternatives to gravity-based
drainage systems (e.g. flooded systems) shall require COMPANY’s approval.
6.2 Design flows
The loading on a drainage system consists mainly of:
• Rainwater (Qr)
• Fire-fighting water (Qf)
• Washdown water (Qw)
• Effluent (Qe)
• Accidental spillage (Qa)
Drainage system shall be designed for the greatest of the following cases:
• Firewater case = Qf + Qe
• Rainwater case = Qr + Qe
• Washdown case = Qw + Qe
• Accidental spillage case = Qr + Qa
These flows are described in details below.
6.2.1 Rainwater
Peak rainfall data over a selected return period should be used where available and justified.
Onshore, 95% of the paved areas surface should be used to estimate the rainfall drainage to
the open drains system. The contribution of run-off from unpaved areas should be considered
on a case by case basis using the guidance given in Appendix 2.
Offshore, a minimum rainwater rate of 0.05 l/s.m2 shall be used, if not exceeded by rainfall
records over the reference return period. The surface to be taken into account is:
• On the highest deck (referred to as weather deck), the total surface
• On lower decks, strips with a width equal to the elevation between two consecutive decks
(based on rainfall at an angle of 45°)
6.2.2 Fire-fighting water
The calculation of the quantity of fire-fighting water to be discharged through the drainage
system shall be based on the assumption that:
• Only one fire zone (definition in GS EP SAF 253) is subject to a fire at any one time
• Fire water used for the protection of “self-contained” equipment is contained in the
bund.
The most demanding fire scenario, excluding fires in “self-contained” equipment, shall be
selected.
Unless detailed hydraulic calculations are available, the fire water flow to be evacuated shall be
taken as the fire water demand, as calculated by GS EP SAF 321, multiplied by a factor of 1.25.
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No credit shall be taken for loss of sprayed firewater through evaporation, etc
6.2.3 Washdown water
A rate of no less than 50 m3/hr (washdown hose capacity plus some contingency) shall be
considered.
6.2.4 Effluent
All the flows other than mentioned in sections 6.2.1 through 6.2.3. Mainly: the water draw-off
from hydrocarbon storage tanks, the effluent volumes from the final draining/emptying of the
process facilities that cannot be sent to the closed drains. This flow is usually marginal
compared to firewater and rainwater flows, with the exception of bottom tank water from the
onshore large hydrocarbon storage tanks.
In the absence of any specific figure, a value of 30 m3/h can be used.
6.2.5 Accidental spillage
The accidental spillage flow-rate and volume design shall be defined as the lesser of:
• The total liquid lost in 600 seconds through a 20mm diameter hole from any equipment of
a kerbing area (see section 4.10) or,
• The normal liquid volume of the biggest vessel of the kerbing area.
The accidental spillage flow-rate should be calculated with the formula in Appendix 1.
6.3 Flow velocities
Velocities shall be kept within a range that allows self-cleansing, prevents emulsification and
damage to the pipe and fittings (erosion).
6.3.1 Minimum
The introduction of solids into drain pipes cannot be avoided and this is prone to produce silting
in the pipes.
A minimum velocity of 0.8 m/s, either from process effluent flows alone, or from combined
process and rainwater flows shall be attained a minimum of six times per year to achieve
periodic cleansing of the drains. If it cannot be obtained though process or rainwater flows,
flushing facilities shall be provided to meet the requirement in each pipe run of the system.
In drain pipes where heavy amount of sand or other solids may be present 1.2 m/s shall be the
minimum velocity.
6.3.2 Maximum
In oily water (OD1 and OD2) and domestic sewage drain pipes, velocities attained should not
regularly exceed 2.0 m/s to prevent emulsification.
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GS EP SAF 228
6.3.3 Flow velocities in piped drains
Drainage system
OD 3
OD 1, OD 2
Minimum (1)
Maximum (2)
0.8 m/s (3)
3 m/s
0.8 m/s
2.0 m/s (4)
(1): Minimum frequency of 6 times a year
(2): Regular occurrence, however no restrictions apply to firewater peak flows
(3): 1.2 m/s for heavy amount of sand or other particles present
(4): Velocity limit to prevent emulsification.
6.4 Pipe minimum diameters and gradients
Refer to section 4.4.
6.5 Drainage piping: washing/clearing
Offshore, all drainage pipe runs shall be fully roddable.
Onshore, all drainage pipe runs shall be fully sweepable, and manholes shall serve as
sweeping entry points.
Connections to drainage headers shall be provided as follows:
• Rodding-out of offshore headers: flanged connections to allow vertical and horizontal
clearing (one flanged connection at each end of horizontal headers). Flanges shall be
accessible for routine clearing.
• Washing/inerting of offshore headers: utility connections at strategic locations of the
network to allow clearing/inerting with high-pressure water, steam, N2 or CO2.
• Sweeping of onshore headers: manholes or accessible flanged connections of a diameter
of 4” or more, in particular near diversions. In straight portions of headers, there should
not be more than 60 m between two such manholes or connections.
6.6 Gas migration and fire spreading
Open drain systems are essentially atmospheric systems connecting all areas of an oil and gas
installation. Fire breaks and seals shall be installed within the drain systems as barriers against
gas migration and fire spreading: e.g. hydraulic seals, vents, flame arresters. Location and
types of seals are detailed in chapters 7 and 8.
Flame arresters shall be fitted to all degassing vent outlets that discharge into areas where a
source of ignition may be present.
Drainage piping crossing two independent fire zones should be avoided.
Where a same drainage system serves different fire zones, fire beaks/gas seals shall be
installed at the limit in between two fire zones.
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7. Design of onshore open drains
Open drains in COMPANY onshore installations shall be designed as per the requirements set
out in chapters 4, 6 and 7.
There are three types of wastewaters that are encountered in all onshore oil and gas
installations:
• The oil-contaminated also called oily waters (OD1 and OD2)
• The oil-free also called clean waters (OD3)
• The domestic sewage also called sanitary waters.
Domestic sewage shall be collected and treated independently from the other drains before
mixing with the installation wastewaters. The details of such systems are outside the scope of
this specification.
7.1 Oily water onshore drains typicals
7.1.1 Onshore installations provided with primary treatment
The points made in this section are illustrated in Appendix 3, Figure 3B.
This section sets out the minimum COMPANY requirements. Local regulations that require
further treatment before disposal shall be adhered to.
This section applies to all the installations provided with primary treatment. All onshore
installations producing or processing crude oils, and most of the onshore installations handling
gas condensates shall be provided with a primary treatment.
As a minimum, oily water primary treatment consists of an API separator.
Tank bottom waters may content contaminants such as salts, heavy metals, radionuclides,
BTEX…
When their discharge has a potential impact to the receiving body (public waters or land) of
open drains, these waters should not be routed directly to the OD1. Alternative solutions
should be implemented and approved by COMPANY, such as reinjection into the reservoir,
injection into a disposal well (as for produced waters) – see GS EP ENV 270, complementary
treatment…
In addition to the OD1 drains, the same API separator may receive closed drain drum liquids,
provided they come in independent headers, sealed at entry (minimum water seal depth for the
open drain header: 1 meter).
OD2 waste waters open drains and water from primary treatment shall be sent to an
observation basin. They may be collected together with the drains from the drip pans (OD1)
and sent to the primary treatment if this makes the construction of the piping collection network
much simpler.
The sizing of the observation basin shall be based on the time of concentration required for
rainwater or firewater to flush the accidentally oil contaminated areas, and to be collected to the
observation basin. After this time of concentration, it may be assumed that the waters arriving
to the observation basin are clean and can be discharged directly to public waters. In absence
of evaluation of this time of concentration, the absolute minimum for the retention time of
observation basin shall be 20 minutes and 6 hours for rainwater and firewater respectively.
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The sizing of the observation basin shall take into account the volume of accidental spillage
(see section 6.2.5) to ensure retention and recovery by environmental spill response plan.
In regions where severe storms can occur, the design, location and elevation of the facility shall
prevent flooding of the API separator and observation basin that would spread hydrocarbons
over the adjacent areas. Storm waters should be diverted to public water before they enter the
observation basin.
7.1.2 Installations that do not require primary treatment
The onshore installations that may not be provided with primary treatment unit are:
• The gas plant handling hydrocarbon liquids in insignificant quantities, i.e. in quantities that
cannot pollute significantly waste waters.
• The minimum installation drainage effluents may be collected and stored in a dedicated
open drain drum which is periodically offloaded to a suitable external facility.
No drains from this installation are categorised OD1 and all oil-contaminated drains are OD2.
All oil-contaminated wastewaters shall be sent to an observation basin (same design as in
section 7.1.1) before disposal to public waters.
This minimum requirement may be exceeded by local regulations, which shall then take
precedence
7.1.3 Oil-free water drains in all plants (OD3)
Rainwater falling on unpaved, uncontaminated ground within an installation should normally be
disposed of by natural percolation into the sub-soil and evaporation.
Where the land is not sufficiently permeable for this to be effective without undue ponding, the
surface should be preferably graded to catch basins (see Appendix 4) discharging to a piped
system. When this is not practicable, land drains (channels) should be provided.
Where severe storms can occur (e.g. tropical areas), storm waters may have to be collected in
unpaved areas to:
• Prevent the flooding of oil-contaminated or inhabited areas
• Minimise soil erosion (slopes).
Oil-free drains discharge directly to public waters
7.1.4 Rain water collection
As a general rule rain water collection shall be minimised onshore. Paved areas shall be
installed only where there is a risk of pollution. Elsewhere, water shall be allowed to infiltrate the
soil (see also section 7.1.3).
Hydrocarbon storage tanks and some other very large liquid hydrocarbon inventories (such as a
big slug catcher) require containment systems (bunded areas, impounding basins) designed
to contain large, accidental leaks, see section 4.10.
7.2 Infiltration
Infiltration into the soil of hydrocarbons and other pollutants likely to spill from the process
equipment shall be prevented.
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7.2.1 Hydrocarbon process plant
Areas designed to prevent infiltration are referred to as “paved areas”. They shall be made of a
material such as to prevent infiltration rates of more than 10 -6 m/s. Reinforced concrete is
recommended. Care shall be taken that joints are properly sealed.
7.2.2 Hydrocarbons storage
Refer to GS EP SAF 341. Bunds installed around hydrocarbon storage tanks shall be liquid-tight
with a maximum infiltration rate of 10 -8 m/s.
The bund shall normally be made of an adequate (tested) material (e.g. reinforced concrete).
If the soil of the installation site is deemed adequate or is thought to be made adequate with
additional layers of compacted natural material (e.g. clay type), this shall be demonstrated by
permeability tests performed in situ.
7.2.3 Roads and other access ways
Roads and other access ways should be designed to prevent an infiltration rate of more than
10 -8 m/s.
Where roads are water-tight (asphalt or else), the rainwater collected shall be routed to OD2.
7.3 Open ditches and channels
Open ditches and channels shall generally not be used to collect or convey drainage effluents.
There are two exceptions to this rule:
• Drainage systems liable to collect oil-free water only
• The collection and containment of accidental spillage from units processing high volatility
hydrocarbon liquids (as per chapter 9).
The maximum effluent velocity in concrete lined open ditch shall be 4.0 m/s, and the minimum
effluent velocity shall be 0.8 m/s.
7.4 The collection of the drainage effluent in process and utility areas
For the detailed design of the facilities required to collect the drainage effluent in onshore
process and utility areas refer to Appendix 4 which is part of this specification.
7.5 Liquid hydrocarbon storage tanks
Water draw-off from oil storage tanks shall be regarded as permanently oil-contaminated (OD1).
The arrangement for draining this water shall be designed as per Appendix 3 Figure 3A.
Permanent storage tanks shall be provided with bunds designed for retention of an accidental
leak (refer to GS EP SAF 341).
The storage tank bunds shall be provided with suitable drainage facilities for rainwater and
firewater. In locations within the bunded area which can be contaminated with oil (e.g. under
valves and manifolds), water shall be regarded as accidentally oil-contaminated (OD2). Such
water shall drain by gravity to a gully, which shall be located in a low point within the bund, as
far as practicable from the tank. The connection to the drain system shall be valved outside the
bund. This valve shall remain normally closed. In areas with severe storms, a diversion to a
storm water system should be provided to handle the large clean water run-off rates.
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Waster water drainage in the bund as described above does not apply to LNG and LPG storage
facilities, which shall not be connected to oily water drains.
7.6 Off-sites
This section concerns the hydrocarbon units installed far from the main process area such as:
wells, flare drum and pumps, gas pipeline pig traps, loading/unloading areas, pipeline valve
stations.
Their open drains shall be collected as in the main plant. When connection of their oily water
drains to the main plant oily water drain system is not practicable, oily waters shall be sent to
a dedicated, vented, atmospheric tank or collection pit closed with a gas-tight cover. Mobile
means shall be provided to transport the collected effluents to the main primary treatment
facility.
7.7 Buildings
“Technical buildings or rooms” designed to house primarily electrical and instrument systems
shall not be connected to an open drain system (oily water or domestic). They shall not
contain potential leak sources of hydrocarbons.
Enclosures in general shall not contain equipment processing hydrocarbons. Some buildings
however, classified as non-hazardous areas, may contain mechanical equipment that need to
be connected to the oil-contaminated open drains because they are sources of pollution such
as lube oils and greases. Examples of those buildings are: shelters for utility pumps and
compressors (not handling hydrocarbon streams), diesel engines, workshops. These buildings
are referred to as “industrial buildings”.
The industrial buildings require floor drains, which shall be regarded as accidentally oilcontaminated (OD2). Tundishes and gullies shall be used which should be equipped with
siphons (minimum seal depth: 150 mm) and shall be connected to vented manholes sealed at
entry (minimum seal depth: 300 mm).
Special care shall be taken so as to prevent flammable gases from entering an industrial
building (classified non-hazardous) via the drainage system. As a minimum, their floor drainage
effluents shall be routed to treatment separately from hazardous areas drains (refer to section
4.3).
Laboratory drains prone to be polluted by chemicals shall be disposed in accordance with
section 4.2.4.
Rainwater from building rooves can be considered as OD3 unless a particular risk of
contamination has been identified.
8. Design of offshore open drains
Open drains in COMPANY offshore installations shall be designed as per the requirements set
out in chapters 4, 6 and 8.
The case of offshore “minimum installations” is addressed specifically in section 8.6 because
the design of open drains on these installations may be simpler than on the other installations.
This chapter sets out the minimum COMPANY requirements. Local regulations may require
further treatment of oily water based on other then gravity mechanisms (secondary treatment)
to bring the oil content on specification before disposal of wastewater.
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8.1 Configuration of offshore open drains
The main types of wastewaters that are encountered on offshore installations are:
• The oil-contaminated waters also called oily waters (OD1 and OD2)
• The oil-free waters also called clean waters (OD3)
• The domestic sewage also called “sanitary” drains.
Domestic sewage shall be collected and treated independently from the other drains before
mixing with the installation wastewaters. The details of such systems are outside the scope of
this specification.
Deck skirting: All open decks shall be delineated with plates (they are usually referred to as
deck plates or sometimes “kick plates”) which should be 100 mm high as a minimum. As an
exception to this rule single deck platform may not require deck skirting.
The drain fluid flows in pipes, laid to suitable gradients between the entry points, seal pots (see
Appendix 5) and treatment facilities.
On production, process and utility platforms, plant drainage shall normally be configured as
follows (refer to the typicals of Appendix 3, Figures 3C, 3E and 3F):
8.1.1 Classified open drains
The classified open drains include:
• The drains from the equipment drip pans and hydrocarbon producing wellheads (OD1)
• The surface drains from the adjacent deck areas (deck washings, OD2).
To make the design of platform drains simple these drains shall be collected together in the
same headers and sent into an atmospheric tank designed for oil-water separation (referred to
as sump tank). Seals pots shall receive the effluents from each drain sub-header to allow any
gases dissolved to vent away from ignition sources. The main collection header(s) shall be
sealed into the sump tank on entry.
An overflow feature shall be provided at each entry point of classified open drains to divert
excess fire/rainwater from classified open drains to OD3. See Appendix 5, Figure 5A "high
capacity gully" as example.
Open drains of each given system (classified, unclassified, OD1 and OD2) should be
collected within each module or at each deck level, in one sub-header that ties-in to the main
collection header (vertical). This is to reduce the number of inter-module/deck connections.
For all open drains (OD1 and OD2), siphons shall be fitted in the outlet piping of every entry
point to prevent the unwanted migration of gases. U-shaped siphons are recommended. The
minimum seal depth of these siphons shall be 300 mm. They shall be easily accessible and
flanged to allow easy retrieval (see Appendix 5).
8.1.2 Unclassified open drains
They collect the oily water drains from the non-hazardous areas, where equipment not
handling hydrocarbons is still likely to pollute wastewaters:
• The drains from the equipment drip pans (e.g. machine skids and transformers)
• The surface drains from their adjacent deck areas (deck washings).
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OD2 may be "unclassified" where contaminant is not a flammable product (e.g. lube oil,
transformer oil, workshop, etc.). See Appendix 3, Figure 3C as an example.
These drains are OD2, they shall be collected and piped into an oily water disposal tube. The
main collection header(s) to the disposal tube shall be sealed by discharging permanently
below the caisson liquid level.
Open drains of each given system (classified, unclassified, OD1 and OD2) should be
collected within each module or at each deck level, in one sub-header that ties-in to the main
collection header (vertical). This is to reduce the number of inter-module/deck connections.
For all open drains (OD1 and OD2), siphons shall be fitted in the outlet piping of every entry
point to prevent the unwanted migration of gases. U-shaped siphons are recommended. The
minimum seal depth of these siphons shall be 300 mm. F(P)SO may require greater seal depth
to make up for vessel movement. They shall be easily accessible and flanged to allow easy
retrieval (see Appendix 5).
8.1.3 Clean water drains
They shall be collected and piped directly to sea. The outfalls shall be open ended below the
level of the lowest, routinely accessible deck (where access is granted without special
precautions (but life vest) or work permit, referred to as “cellar deck”). As an exception to this
rule, single deck platforms may discharge their fire and rain water directly overboard (to sea or
to river).
They collect oil-free water from clean surfaces (OD3):
• From module roofs
• From open deck areas other than those liable to be contaminated (e.g. lay-down areas
such as on weather decks, deck peripheral areas outside equipment modules or far from
machinery and process equipment)
• Firewater/rainwater overflows from the classified drains.
8.2 Detailed design of collection system
For the detailed design of the facilities required to collect the drainage effluent in offshore
process and utility areas refer to Appendix 5.
8.3 Helidecks
Helidecks shall be provided with gullies (see Appendix 5). On helidecks where fuel loading does
not take place, gullies shall be connected to the clean water drains. On helidecks where fuel
loading takes place, gullies in areas prone to collect accidental fuel leaks should be connected
to the unclassified OD2.
Helifuel storage and handling facilities shall be located away from the helideck and drained into
the platform classified drains.
8.4 Buildings
Same requirements as for onshore installations (see section 7.7).
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8.5 Sump tank and disposal tube
This chapter is illustrated in Appendix 3, Figure 3G.
8.5.1 Sump tank
Sump tank shall be an atmospheric tank designed as a gravity-differential oil-water separator to
treat the open drains from hazardous areas (the classified drains). It shall not receive liquids
from the closed drain drum (refer to chapter 5).
Sump tank vent shall discharge to atmosphere via a degassing vent fitted with a flame arrestor.
The sump tank should normally be sized based on the washdown case (refer to section 6.2),
provided that rain and firewater surge flows are diverted away from the classified open drains
and discharged to sea via the clean water drains.
The sump tank should normally be located on the cellar deck.
Cellar deck wastewater should bypass the sump tank and tie into the sump tank water
discharge line running into the oily water disposal tube. If however some cellar deck
wastewaters are heavily contaminated, oil shall be separated from this water before discharging
to the oily-water disposal tube.
The drain header(s) shall be sealed at the inlet to the sump tank, i.e. submerged in the entry
compartment. The minimum seal depth shall be 1 m.
If the open drain fluids (typically rainwater, oils and greases) are compatible with the process
fluids (effluent and additives), the oil skimmed from the sump tank should be pumped back to
the closed drain drum. Chemical treatment shall be considered, in particular to avoid corrosion
from bacteria. If open drain and process fluids are incompatible, the skimming from the sump
tank should be recovered and disposed of with no harm to the environment (it may be burnt in
an incinerator).
The water from the sump tank shall flow to and be sealed into the oily water disposal tube
i.e. be permanently submerged in the caisson. There shall also be an overflow to the oily water
disposal tube.
The sump tank shall be fitted with level gauges (one per compartment), and a high level alarm
in the oil-rich compartment (above pump cut-in level) lighting and sounding in the installation
main control room.
8.5.2 Oily water disposal tube
The oily water disposal tube is a caisson.
Disposal tube top part shall be gas tight and vented to atmosphere.
Disposal tube bottom part shall be open to sea, to disperse and dispose of drainage water into
the sea. It shall also allow any accidental, gross oil spillage to be returned into the sump tank.
The oily water disposal tube shall receive all disposal waters with the exception of oil-free
water (OD3) which can be discharged directly to sea (via the clean water drains). Main
incomers are:
• From non-hazardous areas: the unclassified open drains.
• From hazardous areas: the sump tank(s) water discharge(s), the cellar deck drains (see
section 8.5.1).
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• Additional specific water treatment if not compatible with open oily waste water shall be
disposed in a different caisson.
Incoming lines from hazardous (e.g. from the sump tank) and non-hazardous areas (i.e. from
unclassified drains) shall be independent (no interconnections, even for maintenance
purposes).
Water from the sump tank(s) shall enter the caisson via downcomers (e.g. between the inner
wall and a weir) which shall extend to be permanently submerged. Sufficient water depth shall
be provided to minimise turbulence at entry (8 m below Lower Astronomical Tide is a typical
depth for high wave activity locations), and to prevent suction in disposal tube pump (2 m
below pump suction is a minimum).
Water from unclassified drains shall be piped at the same depth or below the depth of the
sump tank water downcomer.
The disposal tube shall be provided with an atmospheric vent, preferably not connected to
other degassing vents. The risk for the formation of a flammable atmosphere in the vapour
space which depends on oil density, ambient temperature, and wave activity shall be reviewed:
if deemed significant, consideration should be given to the provision of a permanent nitrogen
purge in the vapour space. The vapour space should be inerted with nitrogen before any
maintenance intervention on one of the disposal tube equipment (i.e. oil recovery pump).
The height of the disposal tube above the water shall be such that even full of oil, the level of
the liquid inside the tube shall not touch the top of the caisson at highest tide. Oil separated in
the upper part of the caisson main compartment shall be pumped back to the sump tank. A
permanent pump shall be installed and started from a local control station. Disposal tube pump
piping shall be arranged to recycle back to the caisson and to enable visual checks via a sight
glass for oil presence. A sample point shall also be provided at pump discharge.
The bottom of the oily water disposal tube (at least 15 meters and up to 30 meters below the
Lower Astronomical Tide level) shall be open, ending with a restriction to maximise dispersion. It
shall be positioned so that the platform seawater pump intakes (particularly potable water maker
intakes) are at maximum distance and across normal tidal currents. It shall also be at a different
depth from other disposal caissons (e.g. drilling).
8.5.3 Design for accidental spillage
It is COMPANY policy to contain as far practicable any credible accidental spillage within the
offshore open drain system. Therefore the combined sump tank and caisson volume shall be
capable of containing the accidental spillage volume as calculated in section 6.2.5.
8.6 Minimum installations
This section highlights specific requirements applicable to offshore minimum installations.
Apart from the issues addressed in this section, the requirements set out for the design of the
open drains on offshore installations shall apply to the minimum offshore installations.
Appendix 3, Figure 3D illustrates the points made in this section. Refer to chapter 0 for the
definition of minimum installations.
On an offshore minimum installation, the decks supporting hydrocarbon equipment are
assumed to be wholly classified “hazardous”.
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Drip pans shall drain and be sealed into an atmospheric drum called the open drain drum,
which may be emptied periodically to a boat provided with adequate storage facilities. The open
drain drum shall not be used as, nor connected to the closed drain drum.
The closed drain drum shall be an independent vessel. It shall be fitted with an overflow to the
oily water disposal tube.
The hazardous decks (outside the drip pans) shall drain and be sealed into the oily water
disposal tube. A permanent skimming pump is not mandatory.
The requirement for an oily water disposal tube may be waived in very shallow water areas
(e.g. swamps), with COMPANY’s approval. If there is no oily water disposal tube, the
hazardous decks (outside the drip pans) may drain directly to sea, but the effluent from
hazardous deck and non-hazardous deck drainage shall not be mixed.
The non-hazardous, clean decks shall be piped directly to sea, below the cellar deck level. As
an exception to this rule, clean water (firewater, rainwater) may be discharged directly
overboard on single deck platforms.
9. High volatility hydrocarbon liquids
9.1 Containment of accidental spillage
This chapter is intended to set out COMPANY requirements to collect and contain accidental
spillage in areas where high volatility hydrocarbon liquids are processed.
As stated in chapter 4, the general rule is that high volatility hydrocarbon liquids shall not be
intentionally drained directly to atmosphere, but collected only in a closed drains system
(refer to chapter 5).
An open drainage system is required however to collect and contain accidental spillage from
the facilities handling the high volatility hydrocarbon liquids.
For the design of bunds which contain accidental spillage from storage facilities:
• LPG storage: GS EP SAF 341 shall be followed.
• LNG storage: ISO 14620, is available. ISO/EN 1473 shall be followed.
9.2 Onshore process areas: paving and impounding basins
The points made in this section are illustrated in Appendix 3, Figure 3H.
Drainage of high volatility hydrocarbon liquid spillage shall involve only those devices that
are permanently vented to atmosphere e.g. open ditches, channels, and impounding basins.
No pipes and generally no totally enclosed devices shall be used.
The general objective shall be to ensure good run-off of the liquefied hydrocarbons in process
areas, away from the process equipment, towards impounding basins designed and located
such as to:
• Minimise the risk of hydrocarbon gases drifting to potential sources of ignition
• Minimise the risk for a BLEVE if such liquids catch fire.
Paving processing plants handling high volatility hydrocarbon liquids is required to collect
spillage and prevent infiltration of hydrocarbon into the soil (see section 7.2). Clean water
collection shall be minimised. Gravel shall not be used in areas prone to collect liquefied
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hydrocarbons because gravel increases considerably the rate of vaporisation: generally heat
exchange should be minimised in drainage of liquefied hydrocarbons (use of colloidal concrete
is recommended for paving and impounding basins).
The paving slope shall be adequate to provide good run-off away from the process inventories
towards a impounding basin. The required slope depends on the paving material but should
not be less than 2% where practicable and shall never be less than 1%. A ditch should be
provided to channel liquefied gas spillage to the impounding basin, provided that it is designed
to prevent turbulent flow (to avoid excessive vaporisation). Ditches shall be covered by grating
(plain covers are prohibited).
Wherever facilities containing high volatility hydrocarbon liquids are present on both sides of
a plant, the recommended design is to provide a high point approximately in the centre of the
paved area such that water and spillage run-off to peripheral impounding basins.
Plant paving shall be divided into sub-catchment areas (each provided with its independent
impounding basin), based on the inventory present in the catchment area and the feasibility of
trenching high depth impounding basins. Kerbs of at least 0.15 m height (e.g. pre-cast in the
concrete slab) shall divide the sub-catchment areas.
Rectangular-shaped channels, covered with easily removable gratings (no plain cover) shall
direct spilled liquid to impounding basin. Local regulation shall be identified and applied. In
absence of these, the impounding basin capacity shall be designed on a case by case
analysis, based on type of process, leak size scenario and time to detect and take corrective
action to isolate. As examples, for process areas the impounding basin should have a liquid
capacity of 110% of the largest vessel at high liquid level (LAH). In addition adequate height
shall be provided for foam and free board. For transfer areas the loading/offloading pump
maximum capacity should be used for a period of time of 2 minutes.
Vaporisation between the spillage point and the basin should however be taken into
consideration. The length of the basins should be the length of the catchment or sub-catchment
area that it serves. Where practicable, the width of impounding basins should be limited to 2
meters and laid cross the prevailing wind, so that evaporation rate is minimised and foam
durability is not compromised (note that 1 m is regarded as the minimum to allow internal
inspection).
The depth of the impounding basin shall accommodate: the dimensioning liquid spill plus 1 m
of blanketing foam layer plus 0.3 m freeboard.
Temperature sensors to detect water/LNG/LPG/NGL presence in and hydrocarbon gas
detection above each impounding basin shall be provided. They shall alarm in the plant main
control room (permanently manned control centre).
Water shall not be allowed to remain in the impounding basins: it shall be pumped out after
each rainfall event. Pumping may be achieved with mobile units. In areas with regular periods of
very frequent/continuous rains however (such as the monsoon areas), fixed pumping units
should be provided. Where snow is anticipated to be a likely occurrence, this shall be taken into
consideration at design stage.
Provision shall be made for foam blanketing in all impounding basins.
• In LNG plants, application of foam shall be automatically initiated on low-low temperature
detection (detection of LNG spillage, as opposed to low temperature detection used for
detection of LPG spillage in areas where both LNG and LPG are present).
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• In LPG plants, application of foam shall be initiated on fire detection only, manually
(operator decision) or automatically. Routing LPG effluents from impounding basins to a
remote impounding basin provided with foam protection may be considered. Routing
shall be via ditches, not pipes. The decision of installing an impounding basin shall be
taken on a case by case basis, only after balancing the risk of spreading LPG vapours
against the risk of keeping LPG close to process units.
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Appendix 1
Appendix 1
Accidental spillage flow rate calculation
The accidental spillage flow rate should be calculated with the following formula:
Qa = 0.6 x Ah x (2 x (P – Pa) / ρ)0.5
Where:
Qa = Liquid flow rate (m3/s)
Ah = Hole cross section (m2)
P = Vessel pressure (ignoring hydrostatic head) (N/m2)
Pa = Atmospheric pressure (N/m2)
ρ = Liquid density (kg/m3)
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Appendix 2
Appendix 2
Run-off water rates (onshore) (Informative)
This appendix provides guidelines to determine the rain water run-off rates in an onshore plant
for the design of the open drain systems. The method presented below is known as the
Rational Method. The rational formula used to determine the design flow is as follows:
Q=CIA
Where:
Q = Peak flow rate at the particular point in the drain system under consideration (m3/min.)
C = Run-off coefficient for the catchment or sub-catchment area. This is the ratio of the
amount of run-off flowing from the catchment to the total amount of rainfall that falls on the
catchment area, dimensionless
I = Design rainfall intensity for the calculated time of concentration, (m/min.)
A = Size of the catchment area contributing run-off to the drains, (m2)
Run-off coefficient ©
Typical values are listed below:
Nature of Catchment area
C
Asphalt or concrete paving, roof
0.95
Brick roads, tiled areas, paving with large joins
0.70
Stone roadways, bare offsite areas (depending on soil)
Grassed areas, clay soils
Grassed areas, sandy soils
0.40 to 0.70
0.50
0.1 to 0.30
Design rainfall intensity (I)
A typical storm shows an initial rapid increase in rainfall intensity, followed by a gradual
reduction. When the intensity is at its highest, only areas immediately adjacent to the sewer
contribute to the flow. As the storm continues, more areas contribute to the flow, but at a
reduced intensity. The concept of “time of concentration” Tc accounts for this, in conjunction
with rainfall intensity data to develop the design rainfall intensity. Tc is estimated by calculating
the time required to flow overland to the inlet to the drains and the time of flow in the open drain
system to the end design point (treatment/disposal facility). Tc should not be less than 10
minutes for developed areas, or the maximum hourly rate of rainfall may be applied as a “flat”
rate for I.
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Appendix 3
Appendix 3
Liquid drainage (informative)
Important note : The drawings and figures contained in this specification are illustrative only
and should not be regarded as detailed engineering documents. They illustrate some of the
points made in the specification and should be used as a basis for the preparation of detailed
engineering drawings.
Figure 3A – Onshore oil or condensate storage tank bottom drainage
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Appendix 3
HAZARDOUS AREAS
HAZARDOUS AREAS
NON HAZARDOUS AREAS
NON HAZARDOUS AREAS
Hydrocarbon processing
Liquid hydrocarbon
storage
Away from oil
and gas processes
Clean areas e.g.
Office, undeveloped
areas, greenbelt
Associated gas
Oil
Oil and Gas Process
Oil or
Condensate
Storage
Water
Wellhead
Drip pan
Drip pan
Cellar
Workshop
Warehouse
Utilities
Tank bottom
Water
Paved
areas
Office area
OR
Bund
OD I
CD
OD I
PW
OD II
OD I
OD II
OD II
OD III
LEGEND :
PW
PRODUCTION (Reservoir) WATER
CD
CLOSED DRAINS
PRODUCTION WATER TREATMENT
TO LP PROCESS (or oily water treatment), VIA CLOSED DRAIN DRUM
OD
OPEN DRAINS
OILY WATER TREATMENT + OBSERVATION BASIN
PUBLIC WATER
OBSERVATION BASIN (overflow to storm basin)
PUBLIC WATER
Direct discharge to
PUBLIC WATER
OD I : PERMANENTLY OIL CONTAMINATED WATER
OD II : ACCIDENTALLY OIL CONTAMINATED WATER
OD III : OIL FREE WATER
NOTE :
- No interconnection (even for maintenance) between : CLOSED AND OPEN DRAIN PIPING
: hazardous and non hazardous area drain piping
Figure 3B – Onshore oil plant drainage schematic (oily water)
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Appendix 3
Figure 3C – Offshore platform drains schematic
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Appendix 3
HAZARDOUS DECKS
NON-HAZARDOUS DECKS
TEST
SEPARATOR
VENT TO
ATMOSPHERE
MAIN
DECK
CLEAN WATER
DRAINS
NOTE 3
DRIP PAN
VENTS TO
ATMOSPHERE
DECK
FLAME
ARRESTER
CLOSED DRAINS
SLOPE
DRIP PANS
SLOPE
LP VENT HEADER
LP VENT & CLOSED DRAIN
OVER
FLOW
OVER
FLOW
OPEN DRAIN DRUM
DRUM
BOAT LANDING
200mm MIN
200mm MIN
200mm MIN
FROM
DECK DRAINS
200mm MIN
CELLAR DECK
BOAT LANDING
BELOW
CELLAR
DECK
NOTES :
SEA
NOTE 1
NOTE 2
2m
1 - DRAIN HEADER OUTLETS PERMANENTLY SUBMERGED
IN WATER.
2 - THE SKIMMING PUMP IS OPTIONAL. IF PROVIDED,
MINIMUM DIFFERENTIAL HEIGHT BETWEEN HEADER
DRAIN OUTLET AND PUMP SUCTION IS 2M.
3 - LP VENT & CLOSED DRAIN SYSTEMS TO BE DESIGNED
FOR INTERNAL EXPLOSION.
DISPOSAL
TUBE
Figure 3D – Offshore minimum installation drains schematic
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Appendix 3
Figure 3E – Process platform drains collection
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Appendix 3
Figure 3F – Offshore deck classified open drains collection
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Appendix 3
FROM CLASSIFIED OPEN DRAINS
VENT TO ATM
VENT TO ATM
SYPHON BREAKER
NORMAL LIQUID LEVEL
LAH
SUMP
TANK
LT
SEAWATER
PURGE
1000mm MIN
LI
LAL
SC
VENT
TO
ATM
SG
200mm MIN
200mm MIN
FO
INERT
GAS
PURGE
OIL RICH OUTLET
TO CLOSED
DRAIN DRUM
WATER RICH OUTLET
CELLAR DECK
CLASSIFIED
OPEN DRAINS
UNCLASSIFIED
OPEN DRAINS
DISPOSAL
TUBE
PUMP
LEGEND :
TIDE EL 0.0m
GAUGE
8m
SC : SAMPLE CONNECTION
SG : SIGHT GLASS
MCC : MOTOR CONTROL CENTER
2m
H
FLAME ARRESTER
OILY WATER
RUNNING
XLA
HS
LOCAL INSTRUMENT
STOPPED
ESD
MCC
STOP
HS
START
DISPOSAL TUBE
XLS
CENTRAL CONTROL
ROOM INSTRUMENT
DRAINS DISCHARGE
EL -15.0m to -30.0m
Figure 3G – Offshore sump tank and disposal tube
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Appendix 3
SUB-CATCHMENT AREA DRAINAGE
GRATING
NOTES :
1 - External impounding basin capacity designed for maximum hydrocarbon liquid spillage.
2 - Paved area general slope is 2% minimum.
3 - Draining ditch is optional.
4 - Rainwater pump may be a mobile unit.
Figure 3H – Paved area for high volatility hydrocarbon liquid process plant
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Appendix 3
HAZARDOUS AREA
NON HAZARDOUS AREA
ASSOCIATED GAS
LP VENT HEADER
NOTE 3
CLOSED DRAINS HEADER
TEST
SEPARATOR
LP VENT &
CLOSED DRAIN
DRUM
NOTE 1
PROCESS LIQUIDS
NOTE 2
NOTE 1
NOTES :
SEAL POT
API SEPARATOR
OBSERVATION BASIN
1 - MOBILE LIQUID DISPOSAL FACILITY.
2 - FLAME ARRESTER.
3 - LP VENT & CLOSED DRAIN SYSTEMS TO BE DESIGNED
FOR INTERNAL EXPLOSION.
Figure 3I – Onshore minimum installation drains schematic
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Appendix 4
Appendix 4
The collection of the drainage effluent in onshore
process and utility areas (prescriptive)
This Appendix is a part of the chapter 7 (see section 7.4).
Drain collection points
There are two main types of collection points for effluent entering the drain system:
• Tundishes
• Gullies.
Tundishes (see Figure 4B) are basically open pipe connections that collect drips from
“equipment drains”: hydrocarbon pump glands and bearings, sample draw-off points, instrument
drains and generally all point-type sources of oily drips and spillage. The lip of the tundishes
should be located 50 mm minimum above ground level to prevent flooding of the oily water
drain systems with rain/fire water.
Gullies (see Figure 4B) are open devices used as a single point to collect surface drainage.
Their size and shape depends on the volumes of effluents which have to be collected; gullies
designed to collect large flows of fire and/or rainwater are referred to as catch basins (see
Figures 4B and 4C).
Gullies collecting oily water shall be designed so as to contain a permanent layer of water.
Manholes (see Figure 4C) are access points to a drain header. They also act as junction boxes
between drain headers. They shall be normally enclosed and in most cases buried.
Equipment drip pans (OD1 and OD2)
Figure 4A of this Appendix shows the typical layout of an oil/condensate processing plant
collection system.
Refer to the section 4.3.3, which states the requirement for drip pans under process and utility
equipment. One drip pan should be dedicated to only one item of equipment. Only small,
closely grouped independent items handling compatible fluids (e.g. very small pumps) may
share the same drip pan.
The equipment drip pans shall be permanently connected to the appropriate oily water drains
via tundishes and/or gullies:
• Equipment processing hydrocarbon liquids: connection to OD1 drains
• Equipment not handling hydrocarbon liquids: connection to OD2 drains (e.g. engines, tools,
utility pumps and compressors).
Such drip pans are not to be confused with the bunded areas installed around the
hydrocarbon liquid storage facilities, designed for the containment of a major accidental
spillage and connected to the open drains via a normally closed valve.
The equipment delivered in skids shall be provided with drip pan in factory, the drip pan being
connected to the installation open drains during on-site installation.
The kerbs and plates (or truncated pipes) used around the perimeter of the drip pans shall be
no less than 100 mm high.
One given drip pan shall cover at least the ground plan of the item of equipment it serves.
Further allowance for collection of drips and minor spillage shall be decided on a case by case
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Appendix 4
basis, depending on the type of equipment and associated operations. Ideally any leakage of
liquids from one facility should not be directed under any other facility before reaching a
drainage system.
All items within the drip pan which are point-type sources of oily drips during routine operation
should be pointing directly to a tundish, or should be piped to above a gully located within the
drip pan.
As far as practicable, each drain intake within a drip pan shall be connected directly to a
manhole, sealed on entry by submerging the inlet pipe a minimum of 300 mm below the water
level in the manhole (see Figure 4C). The distance between a tundish/gully and its manhole
should not exceed 15 metres.
Closely grouped drip pans or catchment basins may be connected to the same header when
individual connection to a manhole is not practical.
For effective surface drainage of drip pans, those shall be sloped at a gradient no less than 1%
to a gully located as far as practicable from the sources of pollution within the drip pan.
Figure 4D of this Appendix shows the configuration of a pig receiver drip pan for liquid
hydrocarbon pipelines.
Paved areas: general requirements
Process plants handling hydrocarbon liquids shall be paved to avoid infiltration of hydrocarbons
into the soil. All areas within a minimum of 1.5 meter from the kerb or drip pan of a hydrocarbon
process facility shall be paved (see Figure 4A). Paved areas shall be surrounded by a
continuous kerb of minimum 150mm height, for containment of accidental spillage, in
accordance with section 4.10.
Beyond this, the extent of paving shall be strictly limited to the collection of oily water to prevent
the unnecessary collection of clean rainwater. Paths between process units may be gravelled to
allow percolation of clean water into the soil.
As far as practicable, OD1 and OD2 drains from different fire zones (see definition in
GS EP SAF 253) should not be collected in the same headers: drains from process paved
areas and hydrocarbon storage areas, drains from independent process trains, drains from
process paved areas and furnaces should be collected separately.
Paved areas: lay-out and drainage
Refer to Figure 4A of this Appendix which shows the typical layout of an oil/condensate
processing plant collection system.
Plants are divided into paved areas which then should be sub-divided into smaller subcatchment areas arranged so as:
• To handle the rain/fire water design flows
• To prevent flooding
• To prevent the spread of fire and flammable liquids from one sub-catchment area to
another
Paving shall be sloped to the nearest gully at a gradient of not less than 1%. The maximum
slope shall be 4%.
Outside the equipment drip pans, gullies in paved areas collect primarily rainwater and
firewater: they are referred to as “catch basins” in this specification. They shall be capable of
draining the design flows without flooding of their sub-catchment area occurring.
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Appendix 4
Catch basins are recessed into the paving. Grating (flush with the paving surface) shall cover
them and allow easy removal.
Each catch basin should normally be connected directly and sealed into a manhole. Where
this is not practical, it shall be sealed with a dip pipe into the next catch basin: the minimum
seal depth shall be 300 mm (see Figure 4C). In paved areas, there should not be more than
three catch basins in series.
In areas where water run-off is likely to carry sediments, sand or other solids prone to silt,
gullies and catch basins shall be fitted with sediment/sand traps.
Catch basins should have adequate provision for rodding of the drainage underground pipes.
The maximum drainage area for one catch basin shall be 400 m2.
The flow accommodated by one gully/catch basin should not exceed 120 m3/h. The maximum
travel of liquid to a gully/catch basin should be 20 meters.
Paved areas shall be designed so that liquids do not accumulate beneath the pipeways. Gullies
and catch basins shall not be located beneath process equipment or pipeways. They shall not
be located closer than 10 m to fired heaters or other permanent ignition source. They shall not
be made of plastic.
Manholes
Manhole typicals are shown in Figure 4C in this Appendix.
In addition to the construction (structural) requirements, manholes shall be provided in sufficient
numbers to properly seal and vent the drainage underground pipes.
Manholes should be provided and located as required in GS EP CIV 202:
• Every 70 m of drainage pipe of 24” diameter and less
• Every 100 m of drainage pipe greater than 24” diameter
• At each junction point between sub and main headers
• At each point where there is a change in header diameter, direction or elevation (depth).
All manholes carrying effluents containing flammable gases or liquids shall be vented and
sealed with water on entry, with a 300 mm depth as a minimum.
The seal should generally be achieved by installing dip pipes in water. For very large drain pipes
(16” diameter and above) or manholes with two or more inlets, manholes should be fire sealed
by an isolation baffle (split manhole with two vents).
The only exceptions to the requirement for entry seals are: manholes that are necessary only
for a change in pipe direction or structural reasons, and with no additional influent pipes
connected. There shall be however a sealed manhole at least every 300 m of main drainage
header.
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Appendix 4
Venting shall be to a local vent, or to a process vent system designed for venting atmospheric
capacities. The manhole vent discharge point shall be located at least 3 m above ground and
the following minimum safety distances shall apply:
• Distance to building window or air intake: 5 m
• Distance to the edge of a roadway in plant restricted area: 5 m
• Distance to a permanent source of ignition: 15 m
• Distance to combustion chamber air intake: 15 m
• Distance to a public road: 30 m
The vent diameter shall be 3” or 4” (upper limit is to prevent gas accumulations, install two vents
if necessary).
Manholes are usually made of concrete. They shall be waterproof and adequately protected
externally and internally (e.g. by lining against corrosion, chemicals).
Manholes shall be closed with covers removable for routine inspection. An appropriate sealant
shall be used to prevent gas leaks from the manholes located:
• In or adjacent to potential sources of ignition in areas classified non-hazardous, or
• Near roadways.
For manholes intended to be used as an access point for internal inspection of the drainage
network, the size of the cover shall be:
• Minimum diameter: 600 mm for circular covers
• No side less than 500 mm for rectangular covers.
They shall be sized such as to prevent overflowing and overpressures. The following minimum
sizes shall apply:
• Diameter/side: 1 meter
• Outlet pipe diameter: 6” (8” for the last manhole upstream an oil trap or primary
treatment unit).
Important note : The drawings and figures contained in this specification are illustrative only
and should not be regarded as detailed engineering documents. They illustrate some of the
points made in the specification and should be used as a basis for the preparation of detailed
engineering drawings.
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Appendix 4
Figure 4A – Onshore oil plant paved areas
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Appendix 4
Figure 4B – Onshore open drain ancillary equipment
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Appendix 4
Figure 4C – Onshore manholes and catch basins
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Appendix 4
Figure 4D (1) – Pig receiver drainage (onshore and offshore)
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Appendix 5
Appendix 5
The collection of the drainage effluent in offshore
process and utility areas (prescriptive)
This Appendix is a part of the chapter 8 (see section 8.2).
This Appendix assumes that the offshore installation is fixed. For F(P)SO, the detail design may
be slightly different to make up for vessel movement.
Drain collection points
Appendix 5, Figures 5A, 5B and 5C illustrate the points made in this section.
There are two main types of collection points for effluent entering the drain system:
• Tundishes
• Gullies.
Onshore tundishes have been described in Appendix 4, offshore tundishes serve the same
function.
Gullies are open devices used as a single point to collect surface drainage, either on deck or in
drip pans. Their size and shape depend on the volumes of effluents, which have to be
collected. Gullies for rainwater collection are channels recessed into the deck. All gullies shall
be covered by grating at deck level. Gratings shall be arranged for easy removal and fitted such
as to prevent trip hazards.
The gullies of the classified and unclassified open drains shall be designed so as to contain
a permanent layer of water. They should be made short to minimise the risk of spread of fire
due to flammable liquids and vapours in the channel; they should typically be 1.5 meter long.
There should be at least 3 gullies per 100 m2 of deck surface.
Overloading of gullies in open drainage shall be catered for by provision of freeboard above the
design flow level. This freeboard should not be less than 100 mm. For gullies provided with
firewater overflows, the freeboard shall be between the design flow level and the lip of overflow
tundish level.
Gullies shall be designed to slope towards the open drain pipe intake, with a 2% minimum
slope. Use of weirs in gullies should be avoided.
Presence of sand or other solids prone to silt shall call for purposely designed sand/sediment
traps in gullies (e.g. removable strainers).
Drip pans
Drip catchment areas underneath offshore equipment are commonly called drip pans or drip
trays. They are generally referred to as drip pans for offshore installations.
Offshore equipment drip pans follow the same design, installation and operation rules as
detailed in Appendix 4 and in section 4.3.3. Drip pan specificities for offshore installations are
given below. Provisions for accidental spillage, outside of the drip pan, should be implemented
in accordance with requirements given in section 4.10.
Equipment drip pans shall be permanently connected to the appropriate oily water drains via
tundishes and gullies:
• In hazardous areas: connection to the classified drains
• In non-hazardous areas: connection to the unclassified drains.
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Appendix 5
Drip pans shall be designed to slope towards a gully, with a 2% minimum slope.
Classified open drains
Every gully and tundish shall be collected independently to a sub-header. Piping from every
such item shall incorporate a siphon of 300 mm minimum seal depth.
There shall be at least one horizontal sub-header per module or per deck level, connecting and
sealing into a classified open drains main vertical header running directly into the sump tank.
Seal pots (see Figure 5D) shall be used in preference to piping siphons to seal a drain subheader to the vertical main header. The seal pots should have a seal depth at least twice the
seal depth of the siphons provided at drainage intake points. The seal depth shall be no less
than 600 mm. The diameter of the seal pot should be no less than 5 times the diameter of the
inlet drain sub-header.
Seal pots shall be connected to vents or vent headers so that trapped gas is safely vented and
pressure fluctuations in one drainage sub-header cannot adversely affect another sub-header
(the recommended diameter of an individual vent is 2”). Vent outlets shall be diverted away from
sources of ignition (refer to GS EP SAF 216).
Under abnormal conditions of firewater surge flow, drainage shall be diverted away from the
classified open drain headers. This shall be achieved by incorporating two offtakes in gullies
(see Figure 5A).
Provided that firewater/rainwater surge flows are not taken by the classified open drains, the
classified open drains system shall be sized based on:
• The washdown case (refer to section 6.2.) or as far as practicable
• The accidental spillage case (refer to section 8.5.3)
Unclassified open drains
Every gully and tundish shall be collected independently to the horizontal sub-header. Piping
from tundishes and gullies should incorporate a siphon (seal depth of 50 to 300 mm depending
on service).
There should be at least one sub-header per deck level. Each horizontal sub-header is
connected to a main vertical header running directly into the oily water disposal tube, where it
is submerged permanently below the caisson liquid level.
The unclassified open drains pipes are usually sized based on the washdown case (refer to
section 6.2. (“design flows”)). Rainwater is normally not dimensioning i.e. units draining into the
unclassified open drains are not deluged and are usually roofed.
Clean water drains
This is a piped drain system collecting oil-free water from gullies to headers leading to an
outboard discharge point located below the cellar deck.
The clean water drain headers shall also accommodate all firewater/rainwater overflows from
the hazardous areas. The greater of the firewater and rainwater cases shall be selected for
the sizing of this system (they shall not be added, refer to section 6.2.. (“design flows”)).
All drainage outfalls to sea shall be located so that the platform seawater pump intakes,
particularly those feeding the potable water maker if any, are at maximum distance and across
normal tidal current direction.
This document is the property of Total. It must not be stored, reproduced or disclosed to others without written authorisation from the Company.
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Appendix 5
Exceptions to the rules set out in this section:
• Single deck platforms (such as in river deltas): discharge of excess rainwater/firewater
overboard to sea or river is acceptable
• Multi-deck platforms: if on a deck very large rainwater (not firewater) flows associated
with severe, rare storms resulted in the need for very large diameter lines, routing of this
run-off water over the deck plates and discharge overboard could be considered. Overflow
points at the edge of the platform shall be identified and the consequence of the potential
carry-over of oil to the lower deck assessed. All overboard discharges shall be kept away
from equipment, personnel, escape routes and lifeboats on lower decks. Such design
requires derogation to this specification, duly approved by COMPANY.
Important note : The drawings and figures contained in this specification are illustrative only
and should not be regarded as detailed engineering documents. They illustrate some of the
points made in the specification and should be used as a basis for the preparation of detailed
engineering drawings.
This document is the property of Total. It must not be stored, reproduced or disclosed to others without written authorisation from the Company.
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Rev: 03
Appendix 5
Figure 5A – Offshore open drain ancillary equipment
This document is the property of Total. It must not be stored, reproduced or disclosed to others without written authorisation from the Company.
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Appendix 5
Figure 5B – Offshore platform rainwater collection (1)
This document is the property of Total. It must not be stored, reproduced or disclosed to others without written authorisation from the Company.
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Rev: 03
Appendix 5
Figure 5C – Offshore platform rainwater collection (2)
This document is the property of Total. It must not be stored, reproduced or disclosed to others without written authorisation from the Company.
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GS EP SAF 228
Appendix 5
Figure 5D – Gas seals / Fire breaks
This document is the property of Total. It must not be stored, reproduced or disclosed to others without written authorisation from the Company.
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