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Page 2 of 37 ABU DHABI GAS INDUSTRIES LTD. (GASCO) DRAINAGE DESIGN BASIS

TABLE OF CONTENTS

1.

GENERAL .................................................................................................................................................................. 4

1.1 1.2 1.3 1.4

INTRODUCTION........................................................... ................................................................. ................................. 4 PURPOSE ..................................................................................................................................................................... 4 DEFINITIONS ................................................................................................................................................................ 4 CROSS-REFERENCES ...................................................................................................................................................... 5

2.

CODES AND STANDARDS.......................................................................................................................................... 5

3.

REFERENCE DOCUMENTS ......................................................................................................................................... 6

4.

DOCUMENT PRECEDENCE ........................................................................................................................................ 7

5.

SPECIFICATION DEVIATION/CONCESSION CONTROL ................................................................................................ 7

6.

QUALITY ASSURANCE/QUALITY CONTROL ............................................................................................................... 7

7.

DESIGN REQUIREMENTS .......................................................................................................................................... 8

7.1 7.2 8.

REFERENCE CODES AND STANDARDS ................................................................................................................................ 8 MEASUREMENT ............................................................................................................................................................ 8

SITE SURVEY AND SOIL REPORTS .............................................................................................................................. 8

8.1 8.2 9.

SITE SURVEYS ............................................................................................................................................................... 8 SOILS REPORT ............................................................................................................................................................... 8

DESIGN OF DRAINAGE STRUCTURES ........................................................................................................................ 8

10.

10.1 10.2 10.3

EFFLUENTS ........................................................................................................................................................... 8

EFFLUENT SOURCES ....................................................................................................................................................... 8 EFFLUENT CLASSIFICATION .............................................................................................................................................. 9 EFFLUENT ROUTING ...................................................................................................................................................... 9

11.

CATCHMENT AREAS ........................................................................................................................................... 10

12.

DRAINAGE NETWORKS ....................................................................................................................................... 10

12.1 12.2 13.

13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 14.

14.1

OFF PLOT NETWORKS .................................................................................................................................................. 10 ON PLOT NETWORKS .............................................................. ................................................................. .................... 12 NETWORK COMPONENTS .................................................................................................................................. 13

MANHOLES, SUMPS AND CATCH BASIN DETAILS............................................................................................................... 13 UNDERGROUND PIPING ............................................................................................................................................... 13 OPEN CHANNELS ........................................................................................................................................................ 14 CULVERTS....................................................... ........................................................................................................................ ................................................................. .......................................... 14 FIRE AND SAND TRAPS ............................................................ ................................................................. .................... 14 CLOSED DRAIN TRENCHES ............................................................................................................................................ 15 TREATMENT FACILITIES DESIGN ...................................................................................................................................... 15 AREA CLASSIFICATION .................................................................................................................................................. 17 SAFETY ..................................................................................................................................................................... 17 MATERIALS......................................................................................................................................................... 18

UNDERGROUND PIPING ............................................................................................................................................... 18

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TABLE OF CONTENTS

1.

GENERAL .................................................................................................................................................................. 4

1.1 1.2 1.3 1.4

INTRODUCTION........................................................... ................................................................. ................................. 4 PURPOSE ..................................................................................................................................................................... 4 DEFINITIONS ................................................................................................................................................................ 4 CROSS-REFERENCES ...................................................................................................................................................... 5

2.

CODES AND STANDARDS.......................................................................................................................................... 5

3.

REFERENCE DOCUMENTS ......................................................................................................................................... 6

4.

DOCUMENT PRECEDENCE ........................................................................................................................................ 7

5.

SPECIFICATION DEVIATION/CONCESSION CONTROL ................................................................................................ 7

6.

QUALITY ASSURANCE/QUALITY CONTROL ............................................................................................................... 7

7.

DESIGN REQUIREMENTS .......................................................................................................................................... 8

7.1 7.2 8.

REFERENCE CODES AND STANDARDS ................................................................................................................................ 8 MEASUREMENT ............................................................................................................................................................ 8

SITE SURVEY AND SOIL REPORTS .............................................................................................................................. 8

8.1 8.2 9.

SITE SURVEYS ............................................................................................................................................................... 8 SOILS REPORT ............................................................................................................................................................... 8

DESIGN OF DRAINAGE STRUCTURES ........................................................................................................................ 8

10.

10.1 10.2 10.3

EFFLUENTS ........................................................................................................................................................... 8

EFFLUENT SOURCES ....................................................................................................................................................... 8 EFFLUENT CLASSIFICATION .............................................................................................................................................. 9 EFFLUENT ROUTING ...................................................................................................................................................... 9

11.

CATCHMENT AREAS ........................................................................................................................................... 10

12.

DRAINAGE NETWORKS ....................................................................................................................................... 10

12.1 12.2 13.

13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 14.

14.1

OFF PLOT NETWORKS .................................................................................................................................................. 10 ON PLOT NETWORKS .............................................................. ................................................................. .................... 12 NETWORK COMPONENTS .................................................................................................................................. 13

MANHOLES, SUMPS AND CATCH BASIN DETAILS............................................................................................................... 13 UNDERGROUND PIPING ............................................................................................................................................... 13 OPEN CHANNELS ........................................................................................................................................................ 14 CULVERTS....................................................... ........................................................................................................................ ................................................................. .......................................... 14 FIRE AND SAND TRAPS ............................................................ ................................................................. .................... 14 CLOSED DRAIN TRENCHES ............................................................................................................................................ 15 TREATMENT FACILITIES DESIGN ...................................................................................................................................... 15 AREA CLASSIFICATION .................................................................................................................................................. 17 SAFETY ..................................................................................................................................................................... 17 MATERIALS......................................................................................................................................................... 18

UNDERGROUND PIPING ............................................................................................................................................... 18

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15.

DESIGN PARAMETERS FOR DRAINAGE NETWORKS ............................................................................................ 18

15.1 15.2 15.3 15.4 15.5 15.6 15.7 15.8 16.

GENERAL ................................................................................................................................................................... 18 CONTROLLED FLOODING............................................................................................................................................... 19 RAINFALL PEAK FLOW / ACCUMULATED FLOW ................................................................................................................. 19 RUN-OFF COEFFICIENT ................................................................................................................................................ 20 RAINFALL INTENSITY .................................................................................................................................................... 20 TIME OF CONCENTRATION/ENTRY/FLOW......................................................... .............................................................. . 20 FIRE FIGHTING WATER (FFW) ...................................................................................................................................... 21 INDIRECT FLOWS......................................................... ................................................................. ............................... 21 HYDRAULIC CALCULATI ONS ................................................................................................................................ 21

16.1 16.2 16.3 16.4 17.

GENERAL ................................................................................................................................................................... 21 HYDRAULIC GRADIENTS ........................................................... ................................................................. .................... 22 SUMP LOSSES AND WEIR LOSSES ................................................................................................................................... 25 COMPUTER PROGRAMS ............................................................................................................................................... 26 MISCELLANEOUS ................................................................................................................................................ 26

17.1 18.

THE INSTALLATION OF UNDERGROUND PIPES .............................................................. ..................................................... 26 ATTACHMENTS ................................................................................................................................................... 27

18.1 18.2 18.3 18.4 18.5 18.6 18.7 18.8 18.9 18.10

ATTACHMENT 1: EFFLUENT CLASSIFICATION AND ROUTING ................................................................................................ 28 ATTACHMENT 2: TYPICAL TANK COMPOUND DRAINAGE........................................................... .......................................... 29 ATTACHMENT 3: TYPICAL PIPETRACK DRAINAGE/SAND TRAP/FIRE TRAP DETAILS ................................................................... 30 ATTACHMENT 4: TYPICAL PROCESS AREA SURFACE WATER DRAINAGE.............................................................. .................... 31 ATTACHMENT 5: RAINFALL INTENSITY/DURATION CURVES FOR VARIOUS RECURRENCE PERIODS ............................................... 32 ATTACHMENT 6: TIME OF ENTRY (OVERLAND FLOW) .............................................................. .......................................... 33 ATTACHMENT 7: SCHEMATIC LAYOUT LIQUID FILLED UNDERGROUND DRAINAGE NETWORK ..................................................... 34 ATTACHMENT 8: C VALUES FOR OPEN CHANNELS (COLEBROOK) ......................................................................................... 35 ATTACHMENT 9: TYPICAL DRAINAGE LAYOUT OF LPG STORAGE AREA.............................................................. .................... 36 ATTACHMENT 10: TYPICAL TANK BOTTOM DRAIN FUNNEL ............................................................... ............................... 37

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1.

GENERAL

1.1

Introduction

This specification outlines the minimum requirements for the design and engineering of drainage networks. 1.2

Purpose

This specification contains the minimum criteria for the design and engineering of site drainage runoff and collection systems including all hydraulic calculations for rainfall and fire fighting capabilities. 1.3

Definitions

1.3.1

General Definitions

COMPANY ABU DHABI GAS INDUSTRIES LTD. (GASCO) and its successors in interest and assignees. CONCESSION REQUEST A deviation requested by the CONTRACTOR, usually after receiving the contract package or purchase order. Often, it refers to an authorisation to use, repair, recondition, reclaim, or release materials, components or equipment already in progress or completely manufactured but which does not meet or comply with COMPANY requirements. A CONCESSION REQUEST is subject to COMPANY/ PMT approval. CONTRACTOR The party which carries out all or part of the design engineering, procurement, construction and commissioning or management of the project. MANUFACTURE The service organization which actually manufacturers the material/product in question. DESIGNER The Engineering Division of the CONTRACTOR or the Consultant which performs the design of the element in question. PROJECT (To be defined) PROJECT MANAGEMENT The COMPANY -authorized party responsible for the overall TEAM (PMT) day-to-day execution of the Project. PMT is to serve as a liaison between COMPANY and the CONTRACTOR(S) on the Project. SHALL Indicates a mandatory requirement. 1.3.2

Abbreviations

AOC : Accidentally Oil Contaminated COC : Continuously Oil Contaminated TDS : Total Dissolved Solids CWS : Clean Water Sewer OD : Open Drain SS : Sanitary Sewer SW : Sour Water SDM : Solvent Drain MDEA (Amine) GD : Glycol Drain BWS : Boiler Water Sewer LNG:

Liquefied Natural Gas

LPG:

Liquefied Petroleum Gas

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1.4

CS:

Carbon Steel

GRE:

Glass Reinforced Epoxy

CD:

Closed Drain

CCTV:

Closed Circuit Television

OEM:

Original Equipment Manufacturer

Cross-References

Where cross-references to other parts of this specification are made, the referenced section number is shown. 2.

CODES AND STANDARDS

The following Codes and Standards, to the extent specified herein, form a part of this specification. When an edition date is not indicated for a Code or Standard, the latest edition in force at the time of the contract award shall apply. Where there are conflicts between the requirements of different Codes and Standards the most stringent criteria shall apply. Alternate codes, standards and specifications meeting the requirement of the referenced codes, standards and specification may be used with approval by the COMPANY. OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION (OSHA)

Code of Formal Regulation, Title 29 AMERICAN SOCIETY OF CIVIL ENGINEERS (ASCE) ASEC Manual Practice No. 77

of

Design and Construction of Urban Storm water Management Systems

U.S. DEPARTMENT OF TRANSPORTATION – FEDERAL HIGHWAY ADMINISTRATION (FHWA) FHWA-EPD-86-102

Design Charts for Open Channel Flow (Hydraulic Design Series No. 3)

FHWA-NHI-01-019

Introduction to Highway Hydraulics (Hydraulic Design Series No. 4)

FHWA-NHI-01-020

Hydraulic Design of Highway Culverts (Hydraulic Design Series No. 5)

FHWA-NHI-01-021

Urban Drainage Design Manual (Hydraulic Engineering Circular No. 22)

BRITISH STANDARDS (BS) BS EN 752

Drain and Sewer Systems Outside Buildings

BS EN 1295-1

Structural Design of Buried Pipelines Under Various Conditions of Loading – General Requirements

BS EN 1610

Construction and Testing of Drains and Sewers

INTERNATIONAL ORGANISATION FOR STANDARDIZATION (ISO)

ISO 9001

Quality Management Systems -Requirements

ISO 9004

Quality Management Systems – Guidelines for Performance Improvements

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3.

REFERENCE DOCUMENTS

Design General Specifications: DGS 1782-001

Civil Design Basis

DGS 1882-001

Structural Design Basis

DGS 2010-001

Architectural Design Basis

DGS 00-001

Basis Engineering Design Data

DGS 1482-002

Sanitary / Storm Sewer Systems and Culverts

DGS 1783-001

Concrete Supply

DGS 1783-002

Concrete Construction

Standard Drawings: STD-1481-001-001

Culvert Details for Unlined Ditch

STD 1481-001-002

Headwall Details

STD-1481-001-003

Details of Ditches and Swales

STD-1481-001-005

Drainage Ditch and Road Crossings – Fire Traps Types A & B

STD-1481-001-006

Tank Bund Outlet – Fire Type C

STD-1481-001-007

Sanitary Sewer & Storm Water Manhole and Catch Basin Details

STD-1481-001-008

Oily Water & Accidentally Oily Water Manhole Details

STD-1481-001-009

Accidentally Oil Contaminated & Oily Water Double Compartment Manhole

STD-1481-001-010

Vents for Manholes

STD-1481-001-011

Typical Tank Foundations – Bund wall and Internal Bund finish – Condensate Tanks

STD-1481-001-012

Electrical or Instrumentation Cable Trenches in Paved Areas

STD-1481-001-012A STD-1481-001-013

Electrical Cable Trenches or instrumentation Cable Trenches in Paved Areas – Sheet 2 Road Crossing Conduits for Electrical or Instrumentation Cables

STD-1481-001-014

Pressurised System – Standard Valve Pits

STD-1481-001-015

Fire System Pillar Hydrant – Typical Installation

STD-1481-001-016

Fire System Monitor Hand Operated Typical Installation

STD-1481-001-017

Road and Paving Details

STD-1481-001-018

Ground Finishes – Typical Requirements

STD-1481-001-019

Traffic Signs and Road Marking Details

STD-1481-001-020

Fence Types and Details

Drawing Attachments: Attachment 1:

Effluent Classification And Routing

Attachment 2:

Typical Tank Compound Drainage

Attachment 3:

Typical Pipetrack Drainage/Sand Trap/Fire Trap Details

Attachment 4:

Typical Process Area Surface Water Drainage

Attachment 5:

Rainfall Intensity/Duration Curves For Various Recurrence Periods

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4.

Attachment 6:

Time Of Entry (Overland Flow)

Attachment 7:

Schematic Layout Liquid Filled Underground Drainage Network

Attachment 8:

C Values For Open Channels (Colebrook)

Attachment 9:

Typical Drainage Layout Of LPG Storage Area

Attachment 10:

Typical tank bottom drain funnel

DOCUMENT PRECEDENCE It shall be the CONTRACTOR’S responsibility to be, or to become, knowledgeable of the requirements of any referenced Codes and Standards.

The CONTRACTOR shall notify the COMPANY of any apparent conflict between this specification, the related data sheets, the Codes and Standards and any other specifications noted herein. Resolution and/or interpretation precedence shall be obtained from the COMPANY in writing before proceeding with the design/manufacture. In case of conflict, the order of precedence shall be:

5.



Purchase Order or Contract



Design Drawings



Design General Specifications and Standards



Industry Codes and Standards

SPECIFICATION DEVIATION/CONCESSION CONTROL

Any technical deviations to the Purchase Order and its attachments including, but not limited to, the Design General Specifications shall be sought by the CONTRACTOR only through CONCESSION REQUEST format. CONCESSION REQUESTS require PMT’s review/approval, prior to proposed technical changes being implemented. Technical changes implemented prior to PMT approval are subject to rejection. 6.

QUALITY ASSURANCE/QUALITY CONTROL

Quality Management Systems shall comply with the applicable requirements of ISO 9001 “Quality Management Systems-Requirements”. The CONTRACTOR shall ensure that the MANUFACTURER/VENDOR shall have in effect at all times, a QA programme, which clearly establishes the authority and responsibilities of those responsible for the quality system. Persons performing quality functions shall have sufficient and well-defined authority to enforce quality requirements that they initiate or identify and to recommend and provide solutions for quality problems and thereafter verify the effectiveness of the corrective action. Quality System and Quality Control requirements shall be identified and included in the CONTRACTOR’s Purchase documentation. Based on these requirements, the MANUFACTURER/VENDOR will develop a QA/QC programme, which shall be submitted to the CONTRACTOR for review and concurrenc e. The MANUFACTURER/VENDOR’s QA/QC programme shall extend to SUBVENDORs. COMPANY/CONTRACTOR reserves the right to inspect materials and workmanship standards at all stages of manufacture and to witness any or all tests. The MANUFACTURER/VENDOR, 30 days after award but prior to the pre-inspection meeting, shall provide the CONTRACTOR with a copy of its Manufacturing and Inspection Plan for review and inclusion of any mandatory COMPANY/CONTRACTOR witness or hold points.

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7.

DESIGN REQUIREMENTS

7.1

Reference Codes And Standards

All civil engineering design shall be within the parameters of the documents listed in Sections 2.0 and 3.0 above, and these documents shall be considered as a part of this design basis. 7.2

Measurement

All dimensions, quantities, and units of measurement shown on drawings, or used in specifications and calculations, shall be given in metric units, except one. This exception is pipe size and it may be given in inches. 8.

SITE SURVEY AND SOIL REPORTS

COMPANY accepts no liability for the information contained in the Site Surveys and the Soil Reports and the CONTRACTOR shall carry out any additional works deemed necessary to perform the work covered in this specification. 8.1

Site Surveys

A topographic survey of the site has to be conducted by an independent consultant. All design shall be in accordance with the horizontal and vertical controls contained in the survey report prepared by the survey consultant. 8.2

Soils report

A geotechnical evaluation of the site has to be conducted by an independent consultant. All design shall be in accordance with the recommendations contained in the soils report prepared by the geotechnical consultant. 9.

DESIGN OF DRAINAGE STRUCTURES

For all design requirements, refer to Structural Design Specification DGS 1882.001. Design and construction of drain and sewer system shall conform to BS EN 752 or BS EN 1610 or ASCE (Manual of Practice No. 77) or FHWA (Hydraulic Engineering Circular No. 22) as applicable. 10.

EFFLUENTS

Dependent upon source, type and level of contamination, effluents shall be classified into various categories. Each category shall be used to define the required drainage network and treatment facility. The segregation of all effluent streams shall start at the source. 10.1

Effluent Sources

The following are sources of effluents:            



Rainwater Fire fighting water Wash/flush water Cooling water blowdown / filter backwash Equipment drains Sampling points Desalter drains Accidental process spillages Amine network Maintenance operations (e.g. exchanger bundle pulling) Domestic sewers

Substation transformer pens/enclosures Floor/roof drains

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10.2

Effluent Classification Atmospheric non-hazardous drainage effluents are classified as belonging to one of the following categories: 







Entirely clean rain water draining to the Clean Water Sewer (CWS) drain – This is applicable exclusively to areas where surface rain water cannot be contaminated by hydrocarbons or chemicals. Accidentally Oil Contaminated water draining to AOC drain – This system collects storm water or fire water run-off from roads and paved equipment areas divided into AOC catchment areas. These streams are normally envisaged to meet the water effluent specifications, but could on occasion be contaminated. Oil drips from pump trays and equipment oily water drains routed to the atmospheric open oily water drain (OD) or otherwise known as continuously oil contaminated drain (COC) – This system collects effluent water with possible hydrocarbon content that exceeds the required effluent water specifications. Domestic sewage draining to the sanitary sewer (SS).

Except for AOC and OD / COC drains, the majority of the other effluents drains into free draining gravity flow systems; partially filled but mainly dry. However, the AOC and OD / COC systems are to be flooded systems. Upstream flushing need to be ensured to maintain the above as flooded systems. Additional underground hazardous Process Effluent Streams, comprising largely of pure hydrocarbons or chemicals which are routed to closed systems: 



Process water effluents such as Sour Water (SW) draining to a closed drain connecting to a below ground vessel with pump-out to the effluent treatment plant. Hydrocarbon drain from vessel drain down draining to the plant Closed Drain (CD) system connected to dedicated collection vessel and recovery.



Amine discharge draining to a closed Amine drain (SDM)



Glycol discharge draining to a closed Glycol drain (GD)



Boiler blowdown and emergency water dumping (BWS)

The Process Closed drains are dedicated buried closed drainage systems, carrying discharge collected via flanged closed drain hubs to buried collection vessel/s. These are designed as per respective piping specifications. The collected discharges are pumped via above ground drain headers to the designated units for processing. Closed drain hubs are flanged (and generally pressurized) systems which are distinct from atmospheric open drain hubs. These are listed here to ensure appropriate space allocation and integration with other underground services, but are not otherwise addressed in this DGS. 10.3

Effluent Routing Effluents shall be routed by means of separate drainage networks to selected treatment facilities and / or discharge points. The segregation of the drainage networks shall be done based on the contamination criteria as identified in Section 10.2. The selection of the routing of drainage networks shall be determined in conjunction with the plant layout requirem ents. Typical destinations for effluents are as follows: 



Storm Sewer, AOC run-off within Process and Utility Areas catch-pits / manholes shall be directed to AOC sump / interceptor(s) for first flush volume treatment. Volume in excess of the first flush volume shall be directed to site evaporation pond(s). Atmospheric open oily water drains (OD) collected in the OD / COC catch-pits and manholes shall be directed to oily water sump / interceptor(s).

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



Oil-free runoff outside of Process and Utility Areas, shall be directed to offsite discharge / site evaporation pond(s). Domestic Sewage, direct to a sewage treatment facility

All other effluent drainage networks are covered in the piping and process specifications. For a diagrammatic summary of typical effluent classification and routing, see Attachment 1. In this figure, the final source is labeled public water which has the following meanings: 





11.

Oil-free runoff shall be discharged offsite/into the site evaporation pond(s). If the treated water is high in TDS, it will be reinjected into the aquifer. Maximum particle size of suspended solids in such treated water shall be agreed with Company prior to aquifer injection If the treated water is low in TDS, (i.e., treated sewage and boiler blowdown), it will be discharged to a holding tank for irrigation purposes.

CATCHMENT AREAS

A catchment area is defined as an area in which a number of effluent streams have a common discharge point. For calculation and identification purposes catchment areas shall be numbered and may be further divided into sub-catchment areas. 12.

DRAINAGE NETWORKS

Each network shall be capable of collecting and handling the design flows of the specific effluents. The most efficient and practical routing of the networks to the 'end-of-pipe'treatment facility shall be taken. 12.1

Off Plot Networks

12.1.1

Tank Compounds All surface water run offs within a tank compound (rain water, fire fighting water used for cooling) shall be collected and discharged by means of surface drain channels to an AOC network outside the tank compound bunded area. A sand trap shall be provided at the discharge point of the drain channels within the bunded area. A fire trap between the compound area and the external AOC network shall be provided by means of a sump within the compound area, a liquid filled discharge pipe under the bund wall and a sump at the tie-in with the extern al AOC network. Each compound shall have a dedicated discharge line which shall be valve controlled. The valve shall be kept 'normally-closed', shall be located outside the bunded area and shall have safe and easy accessibility for operation purposes. A tank compound shall not be drained via an adjacent tank compound It should however be noted that the applicable run-off factor will be affected by the selection of the surface finishes. A typical arrangement of tank compound drainage is shown in Attachment 2. Water settling down in a storage tank shall be drained via a separate drainage system to COC drainage network. A tank bottom water drainage system shall consist of a manual outlet valve and funnel. Directly under the funnel an additional valve shall be installed for the purpose of shutting off the funnel from the system when the tank is not being drained. Where a branch of the system leaves the tank compound, an isolating valve shall be installed at the outside of the bunded area. A typical arrangement of a tank bottom drain funnel is shown in Attachment 10.

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Floating roof tanks are normally provided with roof drains to discharge the rain water from the floating roof into the tank compound. For LNG/LPG facilities Potential liquefied gas spills shall be drained away from equipment as quickly as possible to a safe distance where the liquefied gas shall be allowed to evaporate in a collection basin or open ditch (liquid gas trap). Spills shall not be allowed to enter any closed drainage network, and to prevent ingress of liquefied gas entering the underground flooded drainage network, gas seals shall be constructed at the connection of gas traps to the underground drainage system. Paved areas of liquefied gas processing, storage and loading facilities shall be divided into subcatchment areas of approximately 30 m x 40 m. The areas shall be finished with concrete paving sloping at 1:100 towards the perimeter drain channels. Potential hydrocarbon liquid spills which may not evaporate at ambient conditions, shall be held inside the bund until emergency procedures to dispose of the spilled liquid are carried out. In any case, the contained liquid hydrocarbons shall not be drained to the AOC or the COC drainage network. 12.1.2

AOC Network

The AOC Drainage Network shall be comprised of all paving areas in Process and Utilities Units and routed underground to a collector sump or tank before treatment. 12.1.3

Oil Free Network The oil free drainage system is for the collection and dispersal of uncontaminated surface water runoff from building roofs, unpaved (gravel finish) areas and paved areas permanently clear of process equipment and all sources of contamination. The discharge will be collected in concrete or gravel lined swales/soakaways located at the perimeter of the relevant discharge areas, these swales shall be utilized as carriers to locations where uncontaminated run off can discharge into the ground or evaporation pond. Where oil free drainage run off has to cross roads between units a piped flooded culvert with reinforced concrete chambers and sand trap shall be constructed in accordance with the standard detail drawings.

12.1.4

Impounding Basins

Impounding basins, where required, shall be identified on the drawings. Where pumping facilities are required to pump out any rainwater accumulated in the basins, the discharge of from said pumps shall be directed to AOC drainage network. 12.1.5

Domestic Sewage Network Domestic sewage networks shall be directed to the sewage treatment facility. Design shall be based on the sewage capacities given in the contract documents.

12.1.6

Pipetrack Drainage

All pipetracks surface finishes shall have a free run-off towards a pipetrack drain channel and shall be constructed with a minimum slope of 1:200 to one side. The high point of the pipetrack finished level shall be 250mm below the top of the pipe sleepers. For wide pipetracks a central high point should be provided with surface finishes sloping to both sides to drain channels. To prevent pollution of the subsurface soil, the surface finish of pipetracks in areas where spills or leakages can be expected should be provided with concrete paving. This will facilitate cleaning, maintenance and washdown operations in the event of a spill having occurred.

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Recommended surface finishes for pipetracks are as follows: Pipetracks containing light product lines: concrete blinding Pipetracks containing heavy product lines: gravel or stone chippings The design of open drain channels at pipetracks shall comply with the requirements of Section 13.3. For typical details of pipetrack drainage, see Attachment 3. 12.1.7

Miscellaneous Roads and car parks Storm water collected from roads and car parks area is normally free from contamination and can be discharged directly to CWS system. For locations where possible contamination may occur, such as loading / unloading areas, AOC system shall be established to prevent the effluent collected from the area from directly entering the offsite discharge. Slug catcher area Effluents collected from the slug catcher areas can be contaminated with hydrocarbons and shall be treated properly. Effluents collected from the areas shall be routed via COC network(s) to ensure the effluents will receive proper segregated treatment. Pump and metering stations Surface runoff from pump and metering station area can be contaminated with hydrocarbons, which shall be routed to AOC drainage system. For locations where connection to AOC drainage system is difficult, proper measures shall be taken to prevent soil, groundwater and water contamination.

12.2

On Plot Networks

12.2.1

New Designs For on-plot drainage networks, two main segregated systems shall be considered. They are the Accidentally Oil Contaminated (AOC) system for all surface water flow and the Continuously Oil Contaminated (COC) system for oil drips, equipment drains, etc. Sewage from Process buildings shall be directed to the sewage treatment facility.

12.2.1.1

AOC Network The AOC Drainage Network shall comprise of all paving areas in Process and Utilities Units and be routed underground to a collection sump located between the process and utility areas and the evaporation pond. The surface water run-off from these paved areas shall be collected mainly by perimeter drain channels with additional area catch basins (if required) and directed to the collection sump via distribution chambers and underground headers.

In normal operation (rain water, wash water) AOC water is discharged directly to the collection sump via the distribution chamber and then lifted to the oily water surge tank. In the event of a high AOC water flow rate, (storm water, fire water), the first flush, which is the most contaminated, is routed to the collection sump via the distribution chamber as before and lifted to the oily water surge tank. When the collection sump is full and the lift pumps are not able to cope with the incoming flow rate, the effluent is routed by overflowing from the distribution chamber to the evaporation pond. Evaporation pond shall be lined with impervious material (e.g. HDPE membrane). Paved areas shall have a slope of 1:100 minimum towards the perimeter drain channels and catch basins. Paving slopes shall wherever possible be directed away from equipments to reduce the risk of further spill contamination or escalation of fire. Catch basins, if provided, shall be such that one catch basin serves a catchment area of 600 m 2 maximum. To satisfy the requirements for the fire fighting water design condition it is necessary to provide additional kerb areas and/or additional catch basins located such that accidental spills or spills of effluents which could be on fire, can be quickly collected in the underground system. Any spill shall not travel more than 15 m over the surface of the paved plant area.

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The main perimeter drain channels, at the edge of the paved areas shall be provided with heavy duty grating covers and shall slope to collection sumps at a maximum of 50m centres. These sumps in turn discharge to the main underground pipe headers located under and parallel with the surface drain channels.

All on-plot AOC network drainage piping shall be liquid filled. 12.2.1.2

Continuously Oil Contaminated System (COC) The Continuously Oil Contaminated (COC) system is for the collection of discharge, via drain hubs, from equipment drains, floor drains at equipment rooms within buildings and controlled discharge at transformer pens. COC drainage discharge is collected in sumps from where it is pumped / conveyed to the waste water treatment unit for processing. General design requirements for COC s ystem shall be similar to those for AOC system.

13.

NETWORK COMPONENTS

The design aim is to achieve improved surface water run-off and provide better segregation of effluents at source, thus reducing the risk of contaminating cleaner effluent streams with dirtier streams. In line with this aim the following design parameters shall apply. 13.1

Manholes, Sumps And Catch Basin Details Refer to applicable standard drawings as listed in Section 3.0 – Reference Documents. The bottom of each manhole, sump and catch basin shall be at least 200 mm below the bottom of the lowest connected pipe. In order to transport the free oil and to avoid accumulation of hydrocarbons, self-skimming buckets or upturned elbow at the down streamside shall be Provided within each manhole, as per the design requirement. Wherever possible manholes shall be provided with open steel grating cover in order to have proper ventilation and prevent the accumulation of hydrocarbon vapors in the manholes. Where sealed manholes and sumps are used , the ventilation shall be provided by means of suitably sized pipe (76 mm diameter minimum) routed to a safe area. Entry points in open manholes in COC drainage networks to be designed to prevent surface water run-off entry into the COC network.

13.2

Underground Piping To prevent the propagation and accumulation of hydrocarbon vapors and/or fire through an AOC / COC drainage network, underground pipes shall be laid horizontally and designed such that they are kept flooded (liquid-filled) at all times. A minimum liquid head of 100 mm, measured from the inside top of the pipe, shall be maintained.

Underground piping in drainage service should have a minimum diameter of 100 mm. The minimum soil cover above the underground piping shall be 0.50 meter (as per design requirements).

Underground piping shall not be installed underneath spread footings or foundations. No pipe work shall pass through a foundation. In the event that any existing / new foundation interferes with new / existing underground pipe work, the pipe work shall be re-routed to clear the foundation. Where it is unavoidable to re-route pipes to avoid foundations, said pipes shall be installed within a pipe sleeves.

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13.3

Open Channels

The size of open drain channels shall be determined by hydraulic calculation for the actual design condition applicable. The cross sectional profile of open drain channels may be rectangular or hydraulically shaped. All permanent ditches shall have a trapezoidal cross section. Side slopes shall be 1:1.5 for lined ditches and 1:3 for unlined ditches unless soil conditions permit otherwise. A slope of 1:300 shall be used for drains up to 0.6 m wide and a slope of 1:500 shall be used for drains up to 0.9 m wide. For oil free networks slopes of up to 1:1000 may be used if construction methods can be executed which avoid low spots and possible ponding. Open channels may be constructed in-situ or by utilizing precast sections. The minimum width of rectangular channel shall be 300 mm, and the minimum depth for all channels shall be 150 mm. Large open channels (greater than 900 mm wide) shall be provided with a central dry weather flow channel. No piping and/or pipe supports shall be installed directly over or across open channels. Open channels shall be covered with grating only at those places where operator/maintenance access is required. Open channels located at the toe of an embankment shall be provided with a 'walking strip'(minimum 350 mm wide) for maintenance access. 13.4

Culverts

13.4.1

A minimum culvert diameter of 18 inches shall be used.

13.4.2

Culvert minimum gradients shall be determined using the design flow rate. Culverts shall be sized so as to prevent headwater depths that will cause flooding within the plant facilities. In general, a minimum gradient of 0.30 percent shall be provided where possible. Otherwise, the slope of the upstream or downstream channel should be matched.

13.4.3

The culvert at a road intersection should be aligned with the ditch and located as nearly perpendicular to the road as possible.

13.4.4

Culvert headwalls shall be used where required for flow and erosion control. Plain or flared-end culverts may be used with consideration given to traffic and hydraulic design.

13.5

Fire And Sand Traps

Fire traps and sand traps shall be installed at road crossings and/or fire breakers within pipetracks and as required to isolate the inlet separator units from the rest of the Process Area. The minimum requirements for fire trap sumps shall be the same as those specified for the drainage sumps. The minimum distance between two interconnecting fire trap sumps shall be 9 m and the connecting underground pipe shall always be liquid-filled. Sand traps shall be provided upstream of a fire trap and at the lowest point in an open drain channel system where this enters a sump. Sand traps shall have the same width as the drain channel, shall have a minimum length of 2 m and shall have a minimum depth of 0.50 m. Applicable standards to be developed by CONTRACTOR. Typical details of a sand/fire trap together with the recommended level difference between drain channel inverts and sand trap overflow are shown in Attachment 3. Fire trap design shall comply with the following additional requirements with respect to compound drainage networks.

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



The location of the (outlet) valve sump shall be such that safe access is possible even under fire-fighting conditions. Where a tank compound drainage valve discharges directly into an open channel a splash wall shall be provided. The lowest invert of the open drain channel inside the tank compound at the sand trap shall always be 50 mm higher than: a) The invert level of the drain outside the tank compound receiving the tank compound discharge. b) The static water level of the liquid-filled system serving also the tank compound drainage.

13.6

Closed Drain Trenches Closed drain concrete trenches housing closed drain pipes shall be backfilled with clean, dry sand to prevent the collection of gas within the trench and shall have removable covers.

13.7

Treatment facilities design

13.7.1

Introduction The effluent from AOC and COC drainage networks, collected in catch basins and drainage channels, shall be routed by underground liquid sealed drain lines to the interceptor / sump, for hydrocarbon removal. The sump / interceptors are to be designed like simplified atmospheric oil-water gravity separation facility, consisting of various compartments such as 

Oil / water receiving and separation compartment,



Oil compartment,



Effluent water compartment.

The bottom of each compartment shall be sloped to facilitate sediment or sludge removal. 13.7.2

Interceptor design considerations The oil / water separation compartment shall be designed to receive the incoming drain flow (by gravity) and will be the section where oil-water separation takes place. The volume of the compartment shall allow a minimum retention time of 12 minutes based on the maximum continuous incoming flowrate. The baffle / weir configuration should be designed to allow basic clean water to flow under the baffle and over the weir into the effluent water compartment. The surface area of the basin shall be designed to yield an overflow rate of 0.005 m/sec. Any oil droplet with a rising velocity equal to or greater than the overflow rate will reach the surface under ideal conditions and can be skimmed off. The baffle / weir of the basin shall allow the velocity under the baffle of 0.008 m/sec. An adjustable oil skimmer shall be located at the end of the basin, to skim the separated oil from the surface and rout the skimmed oil to the oil compartment. The effluent water compartment for system shall be provided with pumps to route the treated water to the secondary treatment facility. The pumping capacity should based on the available intake capacity of the downstream facility. The pumping capacity should also consider the need to sufficiently empty the compartment to receive the next first flush. The compartment shall also be provided with an emergency overflow to the evaporation pond. The invert level of the overflow pipe should be located as high as possible to maximise the storage volume within the interceptor. The invert level will need to be verified to ensure that no reverse flow is possible and that the overflow system is either liquid filled or liquid sealed. The oil compartment shall also be provided with pumps to route the skimmed oil to the slop facilities. The oil pumps should be carefully selected to suit the expected viscosity of the oil slops. The oil compartment capacity shall be determined on the basis of a minimum pump running time of 9 to 10 minutes, and the pump capacities shall be selected based on the capacity of of the downstream facility. Covers shall not be used on the interceptors without the approval of the COMPANY.

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However, in COC service, in some cases partial covers may need to be installed due to various reasons (proximity to road, pump installation footprints, maintenance issues, etc.). In such cases, size of openings shall be capable of limiting the overpressure due to confined space explosion within the sump (if any) to within the design limits of the concrete cover. Also, where necessary, the covers shall be designed to limit sand / rain water ingress into the interceptor from outside. Design should also ensure that the sump contents are visible from outside.

Broadly, the design of the treatment facility should consider the following aspects:

13.7.3



Hand-railing and grating for operator safety and access.



Easy access to skimmers, pumps and filters.



Proper ventilation for depressed locations.



Perimeter lighting.



Surface drainage of surrounding paved areas.



Kerbs around pump foundations.



Maintenance access for gulley sucker, vacuum truck, mobile crane.

Pumps design The pumps are recommended to be vertical centrifugal type and shall be provided with access for inspection purposes (manhole and step irons). Access shall be possible without the removal of pumps. Installation of spare pumps are recommended but maybe reviewed subject to space availability. The level control of the pump and installed spare unit shall be set for automatic start and stop. The installed spare should have an HH-on level control and the LL control of both pumps shall be protected by a low level alarm and switch off. Causes for overloading of the pumps should be avoided. The pumps should trip under any kind of overload conditions. The key design issues for the pumps are as follows: 



Maintain water supply from assured external source for flushing and / or pump seal cooling at all times when the pump is running. Provide proper monitoring and surveillance of the pumps to prevent catatrophic failures of the anti-friction bearings or coupling.

Proper maintenance practices should also be maintained for the pumps.

13.7.4



Twice per day the pump should be checked for any unusual signs of noise and vibration.



The pump and motor bearings should be re-greased on regular intervals.



The couplings should be inspected at regular intervals.



Specific OEM requirements for assembly / maintenance should be followed.

Operational instructions and requirements It is important that regular skimming of the free oil is carried out, recommended to do at least twice a week. Setting the adjustable skimmer in a continuous skimming position is an alternative, but is not recommended as it often r esults in skimming more water than oil. Pump start and stop functions (level switches and manual) to be tested once a week. Since the interceptor configuration is recommended to be an open structure, dirt and sand will find its way into the sump and will settle at the bottom. The bottom profile is to be designed with a slope towards a cleaning channel, where the collected dirt can be removed by means of a vacuum truck / gulley sucker.

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13.7.5

Housekeeping instructions and requirements Preventive maintenance and good housekeeping shall be practiced at the source of all drainage networks and shall continue through the systems and treatment facilities upto and including the outfall to the public waters. Regular maintenance, housekeeping and inspection activities shall be considered as a safety and environmental care item. The responsibility for housekeeping and maintenance of drainage networks, treatment facilities and any other related disposal activities shall be assigned to plant personnel or departments qualified and trained for these particular duties. The overall coordination shall be allocated to a supervisor, who shall maintain a complete record of the overall networks and treatment facilities updating these as necessary to include as-built situations. Records shall be kept of all cleaning and other related activities (spill control), to establish upgrading and cleaning / maintenance schedules. Recommended maintenance and housekeeping intervals are as follows:

ITEM

RECOMMENDED INTERVALS

Sumps, manholes

6 months

Channels and underground piping

6 months

Inspection for sludge cleaning

3 months

Tank compound (valve controlled)

Every 6 months & after every major rainstorm

However, it is also to be noted that sludge build-up in the sump is a gradual process and so a proper condition based maintenance program should be developed to address the issue of preventive maintenance for sump cleaning. 13.8

Area Classification For area classification, primary water treatment facilities shall be considered as hydrocarbon containing equipment and their location shall be subject to the minimum safety distances noted as follows: 

Distance to the edge of public roads : 30 m



Distance to the edge of main roads : 15 m



Distance to a fixed source of ignition : 15 m

Prevailing winds and meteorological conditions shall be taken into consideration when choosing the location and orientation of the treatment facility. For sumps / manholes that may contain flammable liquid or hydrocarbon, minimum safety distance shall be 15 m away from any ignition source. The distance maybe reduced for manholes with tight seal cover, but hydrocarbon gases need to be vented to a safe area. 13.9

Safety Drainage systems at operating facilities shall be designed to ensure that plant safety is not impaired by the drainage systems and that the systems primarily do not contribute to the possibility of propagation of fire from one area to the next should a plant fire break out. Operation and maintenance effort for drainage system may involve work in confined spaces. Operations and maintenance staff shall make sure that all working procedures shall comply with HSE regulations regarding work in confined space. Human access into underground drainage components shall be considered as the last option. Wherever possible, unmanned operation, e.g., by means of CCTV shall be adopted for inspections or facilities shall be designed to enable maintenance activities to be accessible from above ground.

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Operational and maintenance staff responsible for interceptors and controlled drainage facilities needs adequate access and walkways to undertake their tasks in a safe manner. The designer should always consult with operations and maintenance personnel on the specific requirements of safety in design. Use of nitrogen for purging into the confined spaces to be avoided due to asphyxiation hazards. 14.

MATERIALS

Drainage networks and components should be of leak-proof design. System tightness shall be controllable and measurable, even after a long period of operation. 14.1

Underground Piping

Piping material for storm and domestic sewer drainage networks shall comply with Specification for Sanitary/Storm Sewer Systems and Culverts, DGS 1482.002. Piping material for all other drainage network shall be as per Process and Piping drawings and specifications. The following general design parameters shall apply to the design of underground drainage piping: 





Pipe connections and materials shall be selected such that the underground pipes and sewers in plant areas can easily be installed and will not give rise to leakage or collapse due to e.g. settlement of subsoil, shock loads of aggressive oils/chemicals released accidentally or during plant shutdown (polluted effluent), cleaning of pipes by rodding, the use of low-pressure steam of 3.5 bar and/or the insertion of high pressure jetting water of approximately 10 bar. Pipes passing through walls of manholes, sumps, etc., shall be provided with a puddle flange or hydrophilic sealant as indicated on the standard drawings. In instances where differential settlement or differential expansion between pipe and sump can be expected, a flexible connection shall be applied.

15.

DESIGN PARAMETERS FOR DRAINAGE NETWORKS

15.1

General

The following minimum requirements shall be applicable to designs in order to achieve functional drainage networks. 15.1.1

MAXIMUM VELOCITIES Maximum Flow Velocities Shall Be As Follows:

Pipes & Culverts 2.50 m/sec Paved Ditches 3.66 m/sec Unpaved Ditches 0.91 m/sec This velocity may be exceeded only under the fire fighting design condition. 15.1.2

The Use Of Concrete And Steel All concrete and steel used in t he design of drainage systems shall comply with the requirements of Specifications for Structural Design Basis DGS 1882 001 and Specifications for Concrete Supply DGS 1783 001.

15.1.3

Design Flow Drainage networks shall be designed to convey without flooding the maximum flow resulting from the greater of the following load combinations:

Rainfall (Qrain) + any other known contributing continuous 'dry weather flow'. Fire water (Qfire) + any other known contributing continuous 'dry weather flow'. 15.1.4

The maximum effluent temperature within any drainage network shall not exceed 45°C. COMPANY environmental standards in this connection shall be followed.

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15.2

Controlled Flooding

Temporary storage of effluent in pipetracks is allowed, provided that the safety and environmental requirements are met. The maximum allowable effluent level during any surcharging condition shall not be higher than 150 mm below the top of the pipe sleeper. Flooding is not permitted in any other area. 15.3

Rainfall Peak Flow / Accumulated Flow

Peakflow calculations will determine the design of drainage collection systems. 15.3.1

Rainwater Peakflow Design Parameters Rainfall 'Intensity-Frequency-Duration' curves shall form the basis of any hydraulic calculations. Drainage Design Curve is as follows: Peak intensity 40mm/hr (10 mm for 15 min. period), 16mm/hr (16 mm for 1 hour period). CONTRACTOR shall refer to Attachment 5. Drainage design curve described above is similar to the rainfall depth of a storm with a two (2) year return period, i.e. a storm with a two year return period would give approximately 9.5 mm of rainfall in 15 minutes (0.25 hour) and approximately 16 mm of rainfall in 1 hour. CONTRACTOR shall use more stringent requirement (10 mm for 15 min. period). Calculations for establishing the run-off values shall be carried out using established and proven methods. One method most frequently used is the Rational Method. The information below is from this method. Another acceptable method would be the Colebrook-White equation.

=

CiA

Qrain

=

quantity of rainwater run-off in m3/hr

C

=

run-off coefficient

i

=

design rainfall intensity (m/hr) based on the time of concentration (T c)

A

=

catchment area under consideration in m2.

Qrain Where:

The Rational Method assumptions and design parameters are as follows: 1.

The maximum run-off resulting from particular rainfall intensity occurs if the duration of rainfall is equal to or greater than the time of concentration (T c). The time of concentration is defined as the time required for water to flow from the most distant point of the catchment area under consideration to the point of flow measurement (investigation).

2.

The maximum run-off resulting from a particular rainfall intensity, whose duration is equal to or greater than the time of concentration, is directly proportional to the rainfall intensity.

3.

The frequency of occurrence of the peak discharge is the same as that of the rainfall intensity from which it was calculated.

4.

The peak discharge per unit area decreases as the drainage area increases, and the intensity of rainfall decreases as its duration increases.

5.

The coefficient of run-off remains constant for all storms on a given watershed.

6.

The method may only be applied for surface water run-off by gravity for an area not larger than 2

approximately 40 hectares (400,000 m ). For areas greater than 40 hectares, the total area should be sub-divided into smaller catchment areas. For each individual catchment area, the Rational Method may then be applied.

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15.3.2

Accumulated Rainfall Design Parameters Accumulated rainfall data is available in the form of tables from local weather stations, indicating rainfall 'depths' in mm for a range of durations and recurrence periods. These tables are plotted as graphs indicating the accumulated rainfall for given time periods (see Attachment 5).

15.4

Run-Off Coefficient

The permeability of surface finishes and in some instances the evaporation of rainwater affect the quantity of rainwater/firewater which enters a drain system. Table 1 lists some typical run-off coefficients which have been selected for drainage network design for various types of surface finishes. TABLE 1 RUN-OFF COEFFICIENTS

A

Plant area/utility area Roofs, concrete, asphalt and other paved areas Evaporation/percolation coefficient (see note below)*

1.0

B C D

Graveled and other unpaved areas Manifold and pump slab areas Roads and road shoulders Brick roads/tiled areas Pipe tracks (general) Pipe track concrete finish Bundwalls (average) Bundwalls with seepage prevention Tank roofs Tank compounds areas (unpaved) Tank compound areas with seepage prevention Grassed areas (sandy soil, flat)

0.25 1.0 0.95 0.75 0.50 0.90 0.55 0.90 1.0 0.3 0.9  0.1

E F G H

* Note: For densely built up plant areas where significant heat is generated by equipment and plant piping, this run-off coefficient may be reduced to 0.7. 15.5

Rainfall Intensity

For drainage network designs, curves representing a 'one in two year storm'return period shall be used. See Attachment 5. 15.6

Time Of Concentration/Entry/Flow

The time of concentration (Tc) shall be used to determine the applicable rainfall intensity which, when used in the Rational Formula, will determine the peak flow values at the point of measurement in the system. The time of concentration (Tc) shall be 10 minutes minimum. The time of entry or 'overland flow'(Te) shall be taken as the time required for one rain droplet to enter a drain channel in the drainage network. The time of overland flow within typical refinery areas normally varies between 5 and 25 minutes. Attachment 6 shows typical Te values for various surface slopes and finishes. The time of flow (T f) shall be taken as the time required for the effluent to flow through the drainage network or an element thereof. For open drain channels and for non-liquid-filled pipes, the time of flow (T f) is the time required for the effluent to flow through the relevant channel length, i.e. length divided by the velocity. For liquid-filled pipes the time of flow should be taken as the time required for the system to reach stable flow conditions and is referred to as T df. Typically, this value can vary between 2 and 5 minutes.

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Thus, for drainage networks the following Tc values should be used: For open drain channels and for non-liquid-filled pipes:

Tc = Te +Tf For liquid-filled pipes only:

Tc = Te +Tdf For a combination of liquid-filled pipes and open drain channels the overall network calculations should be simplified using the formula:

Tc = Te +Tf 15.7

Fire Fighting Water (FFW)

15.7.1

General Design Parameters The quantity of fire fighting water to be collected and discharged through a drainage network shall be determined based on the assumption that there will only be one major fire at any one time.

Design of the drainage network shall be based on fire scenario to be established by the Safety Department of CONTRACTOR. Under the FFW design condition all available drainage networks may be used to discharge fire fighting water and the parameters governing the velocities in the individual drainage network elements are not applicable. Normally, FFW design condition will govern design of upstream networks, whereas the rainfall design condition will govern downstream networks. 15.7.2

Off-Plot Areas (Tank Compounds)

For tank compounds the following shall apply: Where automatic spray water systems are installed, these will be used to cool adjacent tanks in the event of a tank on fire. The drainage network and outlet valve shall be designed such that the water level inside the tank pit will not exceed a height of 0.3m above the lowest tank pad during a fire fighting condition. A practical valve size is 12 inches. If the design requires a larger outlet, additional outlet valves should be selected rather than increasing the valve diameter. 15.8

Indirect Flows

The design of drainage networks shall consider the maximum use of indirect flows to reduce endof-pipe treatment capacity. Indirect flows can be achieved by buffering of rainwater at defined areas during a rain storm and releasing the buffered effluents only after treatment of the direct run-off effluents has been completed. The buffering of rainwater can be achieved by keeping the valve controlled outlet of the tank compound closed during a rainstorm. Sequential release of buffered rainwater shall take place within a maximum period of 6 hours after a given storm. The compound shall have adequate buffer volume such that the level of buffered rain shall not reach the level of the underside of the tank base. 16.

HYDRAULIC CALCULATIONS

16.1

General

Hydraulic calculations shall be prepared to achieve an economical and effective drainage network design. All drainage piping, sewers and open drain channels shall be designed in accordance with FHWA (Hydraulic Design Series No. 3, 4 & 5 and Hydraulic Engineering Circular No. 22) or in accordance with accepted standard formulae and calculation methods, including sump influences

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(losses), weir overflow losses, and friction coefficients which take into account the anticipated future condition of the drainage network. Although there are many 'empirical' formulae which can be used, the formulae given in Sect. 16.2, should be used in order to simplify and standardize the design method and presentation. The design of drainage networks should be based on gravity flow where the installed depth of the underground pipes relates directly to the weir level at the main outlet point, e.g. treatment facility. See Attachment 7. At locations where the available positive head is insufficient to achieve a gravity flow condition, pumping facilities shall be provided. 16.2

Hydraulic Gradients

The hydraulic gradient (I) can be determined by using Chezy's formula:

V

I =

2

2

C R Where: V

=

velocity [m/s] 0.5

C

=

Chezy coefficient [m /s]

R

=

hydraulic radius, or hydraulic mean depth [m]

I = hydraulic gradient or incline [m/m] R is the relationship between the amount of liquid being conveyed and the contact area between this liquid and the inside of the channel. R = cross sectional area of flow divided by the wetted perimeter The Chezy coefficient can be calculated using the simplified Colebrook formula:

18 log 10

C =

[

12 R k

]

Where 0.5

C

=

Chezy coefficient [m /s]

R

=

hydraulic radius [m]

k =

Nikuradse wall roughness factor [m]

The value k is independent of the diameter of the drainage pipeline. Table 2 gives k values for various materials. Note that for GRE material the influence of the boundary layer in the calculations of the Chezy coefficient has been taken into account. The influence of the boundary layer can be disregarded for k values of 0.5 mm and greater. TABLE 2 NIKURADSE WALL ROUGHNESS FACTOR "k" FOR VARIOUS M ATERIALS Material

k (mm)

Concrete

2

steel (non corroded)

0.5

steel (corroded)

5

GRE

0.2 (Includes influence of boundary layer)

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16.2.1

Open Channels

For a rectangular drain channel, R is given by:

C values for open drain channe ls, based on the Colebrook formula, are shown in Attachment 8. If precast drain channels are used, Manufacturer's design charts may be used to establish I, V and C. All reference documentation shall be enclosed in any design packages prepared. 16.2.2

LIQUID-FILLED PIPES For 100% liquid filled drainage pipes, Chezy's formula can be simplified as follows: 2

V C 2 R

I =

(1)

For liquid filled drainage pipes, the hydraulic radius (R) will be:

(2)

 D

R=

2

/ 4

D =

 D

4

V is derived as follows:

Q

V =

(3)

(D



2

/ 4)

Inserting (2) and (3) into (1) gives:

64 Q

I =

2



2

5

x D x C

2

The relationship between I and Q can be written as: I=αxQ

2

Where I = incline (slope) [m/m] 3

Q = flow [m /s]

α = ALPHA 64

α =

2



5

x D x C

2

α is related to the pipe material. The ↑ factors are shown in Table 3, using C values calculated with Colebrook's formula.

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TABLE 3 "C" VALUES AND "ALPHA" VALUES FOR LIQUID FILLED PIPES (based on Chezy-formula)

Diameter (m)

GRE

Concrete

Steel

Corroded steel

K = 0.2 mm

k =2 mm

k = 0.5 mm

k = 5 mm

C

alpha *10-3

c

alpha *103

c

alpha *10-3

c

alpha *10-3

0.10

57.2

198 403.47

39.2

422 650.13

50.0

259 312.5

32.0

632 991.41

0.15

60.3

23 454.36

42.3

47 636.18

53.2

30 198.59

35.2

69 011.59

0.20

62.6

5 173.04

44.6

10 192.73

55.4

6 596.52

37.4

14 467.73

0.25

64.3

1 604.42

46.3

3 093.20

57.2

2 031.65

39.2

4 327.94

0.30

65.8

617.13

47.8

1 170.00

58.6

777.24

40.6

1 619.31

0.35

67.0

275.34

49.0

515.00

59.8

345.25

41.8

706.62

0.40

68.0

136.92

50.0

253.23

60.8

171.06

42.8

344.99

0.50

69.8

42.65

51.8

77.48

62.6

52.97

44.6

104.37

0.60

71.2

16.46

53.2

29.49

64.0

20.35

46.0

39.39

0.70

72.4

7.36

54.4

13.05

65.2

9.07

47.2

17.30

0.80

73.4

3.67

55.4

6.44

66.3

4.51

48.3

8.50

0.90

74.3

1.99

56.3

3.46

67.2

2.43

49.2

4.54

1.00

75.2

1.15

57.2

1.98

68.0

1.40

50.0

2.59

1.10

75.9

0.70

57.9

1.20

68.8

0.85

50.8

1.56

1.20

76.6

0.44

58.6

0.76

69.4

0.54

51.4

0.99

1.30

77.2

0.29

59.2

0.50

70.1

0.36

52.1

0.64

1.40

77.8

0.20

59.8

0.34

70.6

0.24

52.6

0.44

1.50

60.3

0.23

71.2

0.17

53.2

0.30

1.60

60.8

0.17

71.7

0.12

53.7

0.21

1.70

61.3

0.12

72.2

0.09

54.2

0.16

1.80

61.8

0.09

72.6

0.07

54.6

0.12

1.90

62.2

0.07

73.0

0.05

55.0

0.09

2.00

62.6

0.05

73.4

0.04

55.4

0.07

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16.3

Sump Losses And Weir Losses

Sump losses can be determined by using the following simplified formulae:

Where: V = velocity (m/s) P = sump head loss (m) g = acceleration due to gravity (m/s2)

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Weir overflow losses can be determined by using the following simplified formulae: The liquid depth over a weir may be calculated as follows:

Where 3

Q = flow [m /s] L = length of the weir [m] h = liquid depth over the weir [m] z = liquid depth over the weir [m] 16.4

Computer Programs

Computer programs used for design purposes shall take into account that the design of underground piping networks as required by this specification are principally laid horizontally and liquid filled. The programs shall be identified during the basic design stage and all required documentation shall be supplied to demonstrate their accuracy and applicability. 17.

MISCELLANEOUS

17.1

The Installation Of Underground Pipes

Underground pipes for drainage systems shall be installed in accordance with the following: 





Excavation and backfill required for drain system installation shall comply with the appropriate requirements laid down in Specification for Excavation and Backfill for Underground Installations, 1486.002. Installation and testing for storm and domestic sewer drainage networks shall comply with the Specification for Sanitary/Storm Sewer Systems and Culverts, DGS 1482.002. Structural design of buried pipelines shall conform to BS EN 1295-1

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18.

ATTACHMENTS Attachment 1:


Attachment 2:


Attachment 3:


Attachment 4:


Attachment 5:

Rainfall Intensity/Duration Curves For Various Recurrence Periods

Attachment 6:


Attachment 7:


Attachment 8:


Attachment 9:


Attachment 10:

Typical tank bottom drain funnel

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18.1

Attachment 1:

DGS 1482-001 REV 2


Rev.

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18.2

Attachment 2:

DGS 1482-001 REV 2


Rev.

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18.3

Attachment 3:

DGS 1482-001 REV 2


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18.4

Attachment 4:


Process Drip/Drain System is covered in Piping Specifications.

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Page 32 of 37 ABU DHAB I GAS INDUSTRIES LTD. (GASCO) DRAINAGE DESIGN BASIS

18.5

ATTACHMENT 5: Rainfall Intensit y/Duration Curves For Various Recurrence Periods

24. 0

12. 0

6. 0

3. 0

2. 0

1. 5

) S R U O H ( N O I T A R U D

1. 0

0. 5

GRAPH DEPTH - DURATI ON - FREQUENCY RELATI ONSHI P FOR ABU- DHABI I NTERNATI ONAL AI RPORT ( 1982- 1989) 0. 25

100

90

80

70

60

50

40

30

20

15

10

9

8

7

6

5

RAI NFALL DEPTH ( mm)

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Page 33 of 37

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18.6

Attachment 6:


1 = paved surface (n = 0.02), slope 1:200 2 = paved surface (n = 0.02), slope 1:1000 3 = bare surface (n = 0.15), slope 1:200 4 = bare surface (n = 0.15), slope 1:1000

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18.7

Attachment 7:




Maximum velocity of 0.9 m/s applies to AOC network only (2.5 m/s for clear water)



Minimum height of weir above inside “top of pipe shall be 100 mm (instead 50 mm)

DGS 1482-001 REV 2

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18.8

Attachment 8:

DGS 1482-001 REV 2


Rev.

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18.9

Attachment 9:

DGS 1482-001 REV 2


Dgs 1482-001 Rev 2 Drainage Design Basis

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