Document No.
GIS 22-201
Applicability
Group
Date
Draft 21 March 2006
Guidance on Industry Standard for
API 537 Flare Details
GIS 22-201
BP GROUP
ENGINEERING TECHNICAL PRACTICES
Draft 21 March 2006
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
Foreword
This is the first issue of Engineering Technical Practice (ETP) BP GIS 22-201. It is based on API Std 537
“Flare Details for General Refinery and Petrochemical Service” and available documents of three merged
companies: BP, Amoco, and Arco.
In addition, reference is made to other standards and reports that provide guidance in use of heritage
documents or similar documents.
Normative references are mandatory to extent that they are referenced and not superseded by this guide.
British Petroleum
RP 44-3
Design Guidelines for Relief Disposal System.
Amoco
A FE-FLR-00-E
A FE-FLR-00-G
A FE-STK-00-E
A FE-STK-00-G
A PC-PRD-00-E
A PC-PRD-00-G
PSS#6
Fabricated Equipment—Flares—Engineering Specification.
Fabricated Equipment—Flares—Guide.
Fabricated Equipment—Stacks—Engineering Specification.
Fabricated Equipment—Stacks—Guide.
Process Control-Pressure-Relief Devices-Device Selection and System
Design Specification.
Process Control-Pressure-Relief Devices Guide.
Flare, Blowdown, Pressure Relief, Vent, and Drain Systems for Process
Units.
GOMDW
1400-20-PR-RP-2002-13 Flare System Design Guideline.
1400-20-ME-SP-2510 Flare Stack, Tip, and Igniter.
PTA
PTA FE-FLR-00-P
Fabricated Equipment Vertical Elevated Flares Procurement Specification.
Copyright  2006,
2005, BP Group. All rights reserved. The information contained in this
document is subject to the terms and conditions of the agreement or contract under which
the document was supplied to the recipient’s organisation.
organization. None of the information
contained in this document shall be disclosed outside the recipient’s own organisation
organization
without the prior written permission of Director of Engineering, BP Group, unless the
terms of such agreement or contract expressly allow.
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Table of Contents
Page
Introduction...................................................................................................................................11
Introduction...................................................................................................................................11
1. Scope........................................................................................................................................11
1. Scope........................................................................................................................................11
2. Referenced publications............................................................................................................12
2. Referenced publications............................................................................................................12
3. Definition of terms.....................................................................................................................13
3. Definition of terms.....................................................................................................................13
3.9 Coanda flare............................................................................................................................13
3.9 Coanda flare............................................................................................................................13
3.30 Flare......................................................................................................................................13
3.30 Flare......................................................................................................................................13
3.31 Flare burner or flare tip..........................................................................................................14
3.31 Flare burner or flare tip..........................................................................................................14
3.54 Pin actuated device...............................................................................................................14
3.54 Pin actuated device...............................................................................................................14
3.60 Smokeless capacity...............................................................................................................14
3.60 Smokeless capacity...............................................................................................................14
3.69 Combustion support..............................................................................................................14
3.69 Combustion support..............................................................................................................14
3.70 Flare boom...........................................................................................................................14
3.70 Flare boom...........................................................................................................................14
3.71 Flare stack............................................................................................................................14
3.71 Flare stack............................................................................................................................14
3.72 Flare system.........................................................................................................................14
3.72 Flare system.........................................................................................................................14
3.73 Flare vendor.........................................................................................................................15
3.73 Flare vendor.........................................................................................................................15
3.74 Purge gas rate......................................................................................................................15
3.74 Purge gas rate......................................................................................................................15
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3.75 Maximum flaring rate............................................................................................................15
3.75 Maximum flaring rate............................................................................................................15
3.76 Maximum smokeless rate.....................................................................................................15
3.76 Maximum smokeless rate.....................................................................................................15
3.77 Operating range....................................................................................................................15
3.77 Operating range....................................................................................................................15
3.78 Marine or sea flare................................................................................................................15
3.78 Marine or sea flare................................................................................................................15
3.79 Low pressure tip...................................................................................................................15
3.79 Low pressure tip...................................................................................................................15
3.80 High pressure tip..................................................................................................................15
3.80 High pressure tip..................................................................................................................15
3.81 Variable orifice......................................................................................................................15
3.81 Variable orifice......................................................................................................................15
3.82 Water injection......................................................................................................................15
3.82 Water injection......................................................................................................................15
3.83 Water curtain........................................................................................................................15
3.83 Water curtain........................................................................................................................15
3.84 Radiation shield....................................................................................................................15
3.84 Radiation shield....................................................................................................................15
3.85 Operational flaring load........................................................................................................15
3.85 Operational flaring load........................................................................................................15
3.86 Emergency flaring loads.......................................................................................................16
3.86 Emergency flaring loads.......................................................................................................16
3.87 FPSO...................................................................................................................................16
3.87 FPSO...................................................................................................................................16
3.88 FSO......................................................................................................................................16
3.88 FSO......................................................................................................................................16
3.89 Jin pole.................................................................................................................................16
3.89 Jin pole.................................................................................................................................16
4. Flare equipment overview .......................................................................................................16
4. Flare equipment overview .......................................................................................................16
4.1 System purposes.....................................................................................................................16
4.1 System purposes.....................................................................................................................16
4.2 Types of flares.........................................................................................................................16
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4.2 Types of flares.........................................................................................................................16
4.2.1 Vertical and inclined flare......................................................................................................17
4.2.1.1 Self-supported (see Figure 1)............................................................................................17
4.2.1.2 Guyed (see Figure 2).........................................................................................................18
4.2.1.3 Derrick supported..............................................................................................................18
4.2.1.4 Boom and tower mounted flares .......................................................................................18
4.2.1.5 Marine flares/remote flares................................................................................................19
4.2.2 Horizontal or pit flares...........................................................................................................20
4.2.3 Enclosed flame flares...........................................................................................................20
4.2.4 Single point and multi burner................................................................................................21
4.2.4.1 Single point flares..............................................................................................................21
4.2.4.2 Multi burner staged flares..................................................................................................21
4.2.4.3 Multi burner ground flares..................................................................................................23
4.2.5 Smokeless and non smokeless flares...................................................................................23
4.2.5.1 Smokeless flares...............................................................................................................23
4.2.6 Endothermic (fuel gas assisted) flares..................................................................................24
4.3 Selection considerations..........................................................................................................24
4.3 Selection considerations..........................................................................................................24
4.3.2 Interrelationships..................................................................................................................26
4.4 Major components...................................................................................................................26
4.4 Major components...................................................................................................................26
4.5 Mechanical design basis.........................................................................................................27
4.5 Mechanical design basis.........................................................................................................27
4.6 System design criteria.............................................................................................................27
4.6 System design criteria.............................................................................................................27
4.6.1.1 Reliable effective burning..................................................................................................29
4.6.1.2 System hydraulics.............................................................................................................30
4.6.1.3 Liquid removal..................................................................................................................30
4.6.1.4 Air infiltration......................................................................................................................33
4.6.1.4.1 Flashback prevention......................................................................................................33
4.6.1.4.2 Gas purge.......................................................................................................................34
4.6.1.4.3 Liquid seals.....................................................................................................................35
4.6.1.4.4 Buoyancy seals (molecular seals)..................................................................................37
4.6.1.4.5 Flame arresters..............................................................................................................37
4.6.1.5 Flame radiation..................................................................................................................37
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4.6.1.5.1 Height of flares...............................................................................................................37
4.6.1.5.2 Calculation methods for flare thermal radiation...............................................................38
4.6.1.5.3 Thermal radiation levels..................................................................................................39
4.6.1.5.4 Restricted access zone (sterilisation zone).....................................................................40
4.6.1.6 Smoke suppression...........................................................................................................40
4.6.1.7 Flare gas recovery.............................................................................................................43
4.6.1.8 Noise and visible light........................................................................................................45
4.6.1.9 Other design considerations..............................................................................................45
5. Elevated flare equipment components.......................................................................................45
5. Elevated flare equipment components.......................................................................................45
5.1 Flare burner.............................................................................................................................45
5.1 Flare burner.............................................................................................................................45
5.1.1 Purpose................................................................................................................................46
5.1.2 Unassisted pipe flare............................................................................................................46
5.1.3 Steam assisted pipe flare.....................................................................................................47
5.1.4 Pipe flare with internal steam/air eductor tubes....................................................................47
5.1.5 Air assisted smokeless flares...............................................................................................47
5.1.6 High pressure smokeless flares............................................................................................48
5.1.7 Mechanical details of flare burners.......................................................................................48
5.1.7.1 Flare burner dimensions and connections.........................................................................48
5.1.7.2 Flange ratings....................................................................................................................48
5.1.7.3 Flare burner handling and lifting lugs.................................................................................48
5.1.7.4 Materials............................................................................................................................49
5.1.7.5 Welding requirements........................................................................................................50
5.1.7.6 Flare burner piping............................................................................................................51
5.1.7.7 Hydro testing for flare burners...........................................................................................51
5.1.7.9 Wind shields for flare burners............................................................................................51
5.1.7.10 Muffler for flare burners...................................................................................................51
5.1.7.11 Refractory for flare burners..............................................................................................51
5.1.7.12 Maintenance issues.........................................................................................................52
5.1.8 Operations............................................................................................................................52
5.2 Pilots.......................................................................................................................................52
5.2 Pilots.......................................................................................................................................52
5.2.1 Purpose................................................................................................................................52
5.2.2 General description..............................................................................................................53
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5.2.3 Mechanical details................................................................................................................54
5.2.5 Maintenance.........................................................................................................................54
5.3 Ignition equipment...................................................................................................................54
5.3 Ignition equipment...................................................................................................................54
5.3.1 Purpose................................................................................................................................54
5.3.2 General description..............................................................................................................55
5.3.3 Mechanical details................................................................................................................55
5.3.3.1 Spark ignition at pilot tip.....................................................................................................55
5.3.3.3 Compressed air flame front generator...............................................................................55
5.3.3.4 Self inspirating flame front generator.................................................................................56
5.3.4 Operation..............................................................................................................................56
5.3.4.2 Compressed air flame front generators.............................................................................57
5.3.4.4 Operator training................................................................................................................57
5.3.6 Troubleshooting....................................................................................................................57
5.4 Flame detection equipment.....................................................................................................57
5.4 Flame detection equipment.....................................................................................................57
5.4.1 Purpose................................................................................................................................57
5.4.2.2 Flame ionisation...............................................................................................................58
5.4.2.3 Optical systems ................................................................................................................58
5.4.2.4 Acoustic systems...............................................................................................................58
5.4.3 Mechanical details................................................................................................................59
5.4.3.1 Thermocouples..................................................................................................................59
5.4.4 Operation..............................................................................................................................59
5.4.4.4 Acoustic systems...............................................................................................................59
5.4.5 Maintenance.........................................................................................................................59
5.4.5.1 Thermocouples..................................................................................................................59
5.4.5.2 Flame ionisation................................................................................................................59
5.5 Purge gas conversion seals.....................................................................................................59
5.5 Purge gas conversion seals.....................................................................................................59
5.5.1 Purpose................................................................................................................................59
5.5.3 Mechanical details................................................................................................................60
5.5.4 Maintenance.........................................................................................................................60
5.6 Elevated flare equipment components support structure.........................................................60
5.6 Elevated flare equipment components support structure.........................................................60
5.6.1 Piping...................................................................................................................................60
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5.6.2 Aircraft warning lighting........................................................................................................60
5.6.3 Platforms and ladders...........................................................................................................61
5.6.4 Structural design...................................................................................................................62
5.6.4.1 General..............................................................................................................................62
5.6.4.2 Design loads......................................................................................................................64
5.7 Knock-out drums and liquid seals............................................................................................65
5.7 Knock-out drums and liquid seals............................................................................................65
5.7.1 Knock-out drum....................................................................................................................65
5.7.2 Liquid seal............................................................................................................................65
5.8 Blowers and drivers.................................................................................................................65
5.8 Blowers and drivers.................................................................................................................65
5.8.1 General description..............................................................................................................65
6 Multi-burner, staged flare equipment components......................................................................66
6 Multi-burner, staged flare equipment components......................................................................66
6.2 Pilots......................................................................................................................................66
6.2 Pilots......................................................................................................................................66
6.8 Operations...............................................................................................................................66
6.8 Operations...............................................................................................................................66
7. Enclosed flame flares................................................................................................................66
7. Enclosed flame flares................................................................................................................66
7.1 Purpose...................................................................................................................................66
7.1 Purpose...................................................................................................................................66
7.2 General description.................................................................................................................67
7.2 General description.................................................................................................................67
7.2.1 Combustion chamber size and shape...................................................................................67
7.2.2 Burners.................................................................................................................................68
7.2.5 Operational and safety controls............................................................................................68
7.2.7 Guarantees...........................................................................................................................69
7.2.8 Other requirements...............................................................................................................69
7.3 Mechanical details...................................................................................................................69
7.3 Mechanical details...................................................................................................................69
7.3.1 Combustion chamber ..........................................................................................................69
7.3.2 Burners.................................................................................................................................70
Appendix B
(Informative)
Bibliography..........................................................................................................................71
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Annex C
(Normative)
H.W. Husa’s correlation formulae..........................................................................................72
Annex D
(Normative)
BP purchasing requirements.................................................................................................74
D.1 Conflict resolution ..................................................................................................................74
D.1 Conflict resolution ..................................................................................................................74
D.2 Vendor responsibilities............................................................................................................74
D.2 Vendor responsibilities............................................................................................................74
D.3 Exceptions, variances, and substitutions................................................................................74
D.3 Exceptions, variances, and substitutions................................................................................74
D.4 Inspection and testing.............................................................................................................75
D.4 Inspection and testing.............................................................................................................75
D.4.1 General............................................................................................................................75
D.4.1 General................................................................................................................................75
D.4.2 Welding............................................................................................................................75
D.4.2 Welding................................................................................................................................75
D.4.3 Access.............................................................................................................................75
D.4.3 Access.................................................................................................................................75
D.4.4 Materials..........................................................................................................................75
D.4.4 Materials..............................................................................................................................75
D.4.5 Quality assurance............................................................................................................75
D.4.5 Quality assurance................................................................................................................75
D.5 Shipment and storage.............................................................................................................76
D.5 Shipment and storage.............................................................................................................76
D.5.1 General............................................................................................................................76
D.5.1 General................................................................................................................................76
D.5.2 Preservation and storage.................................................................................................76
D.5.2 Preservation and storage.....................................................................................................76
D.5.3 Loadout and transport......................................................................................................76
D.5.3 Loadout and transport..........................................................................................................76
D.5.4 Identification and tagging.................................................................................................76
D.5.4 Identification and tagging.....................................................................................................76
D.5.5 Skid packages..................................................................................................................76
D.5.5 Skid packages.....................................................................................................................76
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Annex E
(Normative)
Documentation......................................................................................................................77
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Introduction
a.
Guidance for flare details is based on API Std 537, 2003.
b.
Guidance statements of this GIS are modifications to API Std 537.
c.
Modifications to API Std 537 are identified as Add, Modify to Read, or Delete.
d.
Paragraph numbers in this GIS correspond to API Std 537.
e.
Paragraphs of API Std 537 that are not revised remain applicable.
f.
In this GIS, term “approve”, as applied to BP, is used if BP does not wish design to proceed
unless certain features have been agreed upon in writing with Vendor. This does not imply that
all details of a document have been considered by BP and does not affect design
responsibilities of Vendor.
g.
Throughout this document, words “will”, “may”, “should”, and “shall”, if used in context of
actions by BP or others, have specific meanings. For the purposes of this GIS, the following
terms and definitions apply:
1.
Will: used normally in connection with action by BP, rather than by Vendor.
2.
May: used if alternatives are equally acceptable.
3.
Should: used if a provision is preferred.
4.
Shall: used if a provision is mandatory.
h. In application of this GIS, BP may select options or waive requirements, depending on
nature of project concerned. This may involve any requirement stated in this GIS.
By necessity, API Std 537 provides more flexibility than required by BP. API Std 537
does not include specific BP experience. This GIS adds the requirements that BP has
found are necessary for safe and cost effective operation.
This GIS may refer to certain local, national, or international regulations, but
responsibility to ensure compliance with legislation and any other statutory
requirements lies with user. User should adapt or supplement this GIS to ensure
compliance for specific applications.
1.
Scope
Add to First Paragraph
a.
This GIS provides general requirements for procurement of equipment and materials for flare
systems to be used in general refinery, petrochemical, and offshore marine environments.
b.
This GIS defines minimum requirements for procurement of flare systems for design,
materials, fabrication, inspection, testing, documentation, and preparation for shipment as
proposed in data sheets and specifications.
c.
Guidelines added in this GIS are based on BP operating experience, preferences, and project
execution requirements.
d.
Flares for the following facilities are within the scope of this GIS:
1.
Refineries.
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2.
Chemical plants.
3.
Terminals.
4.
Offshore installations (shallow and deepwater).
5
Crude oil and natural gas gathering and processing centres.
6
Pipelines: buried, aboveground, or subsea.
7.
Storage installations.
8.
Floating production systems.
9.
Well testing.
10. Liquefied natural gas (LNG) facilities (plants and terminals).
Add to Third Paragraph
The following types of flares are within the scope of this GIS:
d.
Pit flares.
e.
Marine or sea flares.
f.
Oil production platform boom flares.
g.
Portable/temporary flares.
Add to Fourth Paragraph
a.
API Std 537 provides equipment data sheets in Appendix A. Equipment data sheets are not
included in this GIS. Equipment data sheets and instructions for use of data sheets are in
DS 22-201. Equipment data sheets can be selected with SI units or U.S. customary units.
b.
Vendor shall be fully acquainted with bid specifications and clarify all questions before bid
submittal. BP or its representative will issue clarifications or responses to questions in form of
addendum to these documents. Clarifications will be provided to Vendors.
Add
2.
a.
API Std 537 and this GIS do not include issues associated with design of system for relieving
gases by venting into atmosphere.
b.
API Std 537 does not include issues associated with procurement and warranty. These
requirements are in Annex D of this GIS.
Referenced publications
API
Add
Std 673
Centrifugal Fans for Petroleum, Chemical and Gas Industry Services.
ASME
Add
B16.47
Large Diameter Steel Flanges: NPS 26 Through NPS 60.
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ASTM
Add
ASTM C155
Standard Classification of Insulating Firebrick.
ASTM C401
Standard Classification of Alumina and Alumina-Silicate Castable Refractories.
Add
BP
GN 22-XXX
BP Safety Critical Equipment Definition for PI.
DS 22-201
Data Sheet for Flares.
BS
6651
Code of Practice for Protection of Structures against Lightning.
CONCAWE
Report No. 2/79
ISO
3.
13705
Fired Heaters For General Refinery Service.
23251
Petroleum, Petrochemical and Natural Gas Industries - Pressure Relieving and
Depressuring Systems.
Definition of terms
Modify to Read
Terms used in this Standard as they relate to flares are defined in 3.1 through 3.89.
3.9
Coanda flare
Modify to Read
Flare tip that uses Coanda effect.
Coanda effect is aerodynamic skin adhesion effect in which gas follows the profile of a
curved surface, entraining air up to 20 times its own volume.
Flares of this type generally use pressure of gas to achieve smokeless performance.
3.30
Flare
Modify to Read
Term used to designate device or system to safely dispose of relief gases in an environmentally
compliant manner through combustion. System may be flare stack, flare boom, ground flare, or
enclosed flare.
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Flare burner or flare tip
Add
Flare burner includes all auxiliaries as attached to supporting stack or boom.
3.54
Pin actuated device
Add
3.60
a.
These devices can be reset in place without breaking flange and may be considered as
alternates for rupture disc devices.
b.
Pin actuated valves are more costly and some offered valves might have questionable
operating characteristics.
Smokeless capacity
Add
Requirements are defined by local regulations, such as UK Clean Air Act 1956, Section 34(2), and
U.S. EPA CFR 60.18.
Add
3.69
Combustion support
Addition of fuel gas to effluent to be flared for any of the following reasons:
3.70
a.
To increase fuel concentration to make effluent flammable and achieve required combustion
destruction efficiency.
b.
To increase volume of effluent in order to increase flare tip velocity to avoid:
1.
Burn back in flare tip.
2.
Flame lick outside flare tip.
3.
Lazy flame situation that could damage adjacent flare tip.
c.
To maintain adequate slot velocity in flare tip using Coanda effect.
d.
To increase flame stability during high wind conditions (only as temporary solution until flare
flame instability is resolved).
Flare boom
Horizontally displaced or inclined boom, together with other items listed for flare stack.
3.71
Flare stack
Elevated stack (either self supported, guyed, or structure supported), flare tip, pilot burners, igniters,
smoke suppressing devices, flame heat radiation suppressing devices, service pipes, and
miscellaneous auxiliaries.
3.72
Flare system
Whole closed disposal system for fluids discharged from pressure relief valves, other pressure
relieving devices, control valves, or manually operated valves, terminating in one or more flares.
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Flare vendor
Contractor who undertakes design, supply, and erection of flare.
3.74
Purge gas rate
Rate of flow of inert or combustible gas required to prevent oxygen concentration exceeding
specified level at specified location in flare stack or supply ducting if oxygen egress is undesirable.
3.75
Maximum flaring rate
Maximum rate of flow to flare calculated in accordance with specified blowdown and relief
philosophy for plant.
3.76
Maximum smokeless rate
Maximum rate of flow to flare that is required to be burned smokeless.
3.77
Operating range
Range of gas flows and conditions for which flare is required to operate.
3.78
Marine or sea flare
Flare remotely located from drilling or production platform. Typically used in shallow water
platforms.
3.79
Low pressure tip
Flare tip that operates at low differential pressure across flare tip.
3.80
High pressure tip
Flare tip that operates at medium and high differential pressure across flare tip.
3.81
Variable orifice
Flare tip that continuously changes size of exit orifice to maintain higher exit velocities contributing
to better mixing between air and gas achieving higher nonsmoking rates.
3.82
Water injection
System that provides water injection into flare combustion zone, achieves flame temperature
reduction, and also lowers heat radiation rates emitted by flare flames.
3.83
Water curtain
Systems consisting of numerous spray nozzles that provide water curtain protection from intensive
heat radiation emitted by flare flames.
3.84
Radiation shield
Structure, typically steel plate or other heat resistant materials, that provides personnel or critical
equipment protection from intensive heat radiation emitted by flare flames.
3.85
Operational flaring load
Load results from process vent to normal safety valve leakage and main activities.
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Emergency flaring loads
Load results from emergency flare pressure relief devices (relief from upset and/or emergency
blowdown system is activated).
3.87
FPSO
FPSO: floating production storage and offloading. Ship used to store and offload hydrocarbon oil
and gas production.
3.88
FSO
FSO: Floating storage and offloading. Ship without hydrocarbon processing facilities used to store
and offload hydrocarbon liquids.
3.89
Jin pole
Jin poles and lifting cables are provided with derrick supported flare stack to facilitate removal of
flare burner.
4.
Flare equipment overview
4.1
System purposes
Add
The following are general requirements for flare Vendor related to supply of flare system:
4.2
a.
Vendor design shall be based on process information provided in data sheets.
b.
Required equipment and accessories necessary for proper system operation shall be provided
by Vendor.
c.
Calculations that demonstrate sufficiency of proposed design shall be submitted and shall be
subject to BP approval. Calculations shall be presented in logical manner and demonstrate
consideration given for different operating scenarios.
d.
Sufficient information shall be provided to clarify computerised calculation based on inhouse
computer programs or list titles of commercial programs used to perform design calculations.
e.
Flare riser and support structure design assembly and flare burner and accessories for flare
system may be furnished by separate Vendors.
f.
Vendor shall confirm adequacy of all BP presized process equipment in its detail design and
provide all process warranties as stipulated in data sheets and specifications.
g.
Recommendation in regard to any special problem or alternate design shall be included in
proposal.
h.
Requirements for inspection and maintenance for flare system and specific impact on plant
operations shall comply with BP specifications.
Types of flares
Add
BP will specify general type of flare system and configuration for installation in data sheet.
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Modify Title to Read
4.2.1
Vertical and inclined flare
Modify to Read
The following are general requirements for flare Vendor related to supply of vertical and inclined
flare system:
4.2.1.1
a.
Vendor providing flare burner and accessories shall confirm adequacy of height of flare stack.
b.
Vendor supplying riser and flare support structure shall perform structural design calculation
as outlined in specifications.
c.
Flare structures shall be designed to withstand loads imposed by known environmental
conditions, such as wind, ice, and temperature, that will be specified by BP.
d.
In addition to environmental loadings, structure shall be designed to withstand thrusts from
liquid slugs (if there is risk that these can occur), gas discharging from flare tips, and imposed
structural and equipment loads.
e.
Structural plans indicating complete arrangement, including flare foundation requirements,
manner of reinforcements, ladders, and platforms, shall be provided.
f.
Structure shall be analysed for rhythmical oscillations and ensure adequate structural design.
g.
Structure shall be designed for maintenance loads, such as supporting spare flare tip during tip
replacement, additional scaffolding, lifting beams, tools, and personnel.
h.
Guidelines or recommendations for transportation to site and for installation of stack shall be
provided.
i.
Minimum flare height shall be 7,6 m (25 ft). Shorter flare stacks are allowed, provided that
flaring does not impose excessive thermal radiation or other safety hazards in vicinity.
j.
Due to lower overall installation cost, elevated flares should be guy supported or self
supported, if practical, unless special requirements call for another type.
k.
If two or more services with dedicated tips are installed on single stack, the following issues
shall be addressed:
1.
Flame impingement from tip to tip.
2.
Combined heat radiation rates and noise.
3.
Difficulty to schedule maintenance work.
Self-supported (see Figure 1)
Modify to Read
a.
Flare riser pipe shall provide structural support for all flare components.
b.
This type of flare should be used for short and medium height flares, typically from 9 m to
30 m (30 ft to 100 ft), but can be designed for up to 76 m (250 ft) if minimum ground area is
available.
c.
In same cases, base of stack can incorporate water seal drum.
This kind of flare is well suited for air assisted flare.
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Guyed (see Figure 2)
Modify to Read
4.2.1.3
a.
Guided stack should be used for heights up to 107 m (350 ft).
b.
Since guyed supported structure requires large plot area, minimum allowance for deadman
radius and anchor points for support of vertical flare stack shall be proposed.
c.
Guy wires are typically positioned in triangular plan and shall be anchored by buried concrete
block foundations.
d.
Proposal for detail design of guyed structure shall outline all design scenarios to be considered
and shall include load types, load directions, and stack conditions for design.
e.
If more than four levels of guys are required to support stack, derrick supported structure
should be proposed as alternate.
f.
Vendor shall list and recommend maintenance procedures, recommended frequency for non
destructive testing (NDT), inspection, special tools required, such as hydraulic tensioners, and
lubricants required for guy ropes. This will allow maintaining guyed wire ropes and prevent
corrosion that could extend facility life.
Derrick supported
Add to First Paragraph
a.
Documentation to verify structural design and other general requirements for transportation of
structure to final site shall be provided.
b.
Fixed derrick structure on offshore facilities shall have davit provision for tip removal or
maintenance.
Generally fixed derrick supported structure for flare riser is typically used for FPSO
and FSO facilities.
c.
Design alternate may be quoted, subject to BP approval.
Add
4.2.1.4
Boom and tower mounted flares
Except for structural details, sizing of this type of flare is similar to elevated flare
commonly used for onshore installations. Heat radiation limits imposed by platform
design criteria have important influence on flare boom length and on overall cost of
platform. Use of heat radiation reduction options, such as inclined tip orientation,
water injection, water curtains, and radiation shields, may be cost effective solutions
resulting in boom length reduction and significant savings in overall platform cost.
a.
BP will specify or flare Vendor may propose flare as tower or boom type, either on offshore
platform or FPSO/FSO.
b.
High pressure (HP) flare, low pressure (LP) flare, and atmospheric vent shall, if possible, be
located on common flare stack on typical offshore production platform.
c.
HP flare should be low radiation sonic tip. Other types of HP flare tips may be proposed. HP
system collects pressure safety valve (PSV) discharges from vessels designed for 700 kPag
(100 psig) maximum allowable working pressure (MAWP) or greater.
d.
LP flare may be standard pipe tip flare and collect PSV discharges from equipment with low
design pressures less than 700 kPag (100 psig) but not less than 14 kPag (2 psig).
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Atmospheric vent
1.
Atmospheric vent is unlit open end pipe and services tanks or other equipment designed
for operating pressure less than 14 kPag (2 psig).
2.
Atmospheric vent may terminate midway up flare boom or at end of flare boom and point
away from boom structure.
3.
Atmospheric vents shall have flame snuffing system to prevent vents from burning (if
vents are accidentally ignited) that may result in flare boom structural damage.
f.
In addition to radiation heat concerns, design of flare structure shall take into consideration,
possibility and effect of liquid carryover and dispersion and location of hot gas plume.
g.
If several flare tips have to be sited in close proximity (i.e., high pressure and low pressure
service), attention shall be given to possibility of interactive thermal damage to flare tips.
h.
Maintenance and inspection
1.
Access to flare tips may be required for maintenance and inspection.
2.
Maintenance platform, if used, shall be capable of withstanding heat produced by flare
flame and anticipated loads.
3.
If platform is not needed, alternative method for access to flare tips should be provided.
4.
Mechanical system may be provided to allow removal and replacement of flare tip.
5.
As alternate to mechanical system, helicopter or barge based crane is effective but costly
to provide mechanical system for tip installation or replacement.
i.
Flare structure, riser, and flare tip shall be constructed of materials suitable for both operating
temperatures and marine environment.
j.
Materials for structure will be specified by BP or shall be subject to BP approval if specified
by others.
k.
Except for instruments required to be located at flare tip, instruments shall be accessible for
testing, repair, and replacement without shutdown.
Marine flares/remote flares
a.
Flare systems shall preferably be on platform.
b.
The following are general requirements for flare Vendor related to supply of marine flare
system:
1.
If amount of gas to be flared is so high that flare on platform is not practical or if local
statutory regulations require, remote flare facilities shall be provided.
2.
Specific attention shall be given in design of system to include:
3.
a)
Subsea equipment (lines and risers, knockout drum).
b)
Condensate removal methods.
c)
Maintenance and repair (no hoists or cranes permanently available).
d)
Provision to avoid liquid accumulation from carryover, vapour condensation, or
seaspray into flare line.
Location of bridge linked flare shall be chosen to prevent wind from carrying hot flared
gas and any unburned gas to affect personnel and equipment on main platform.
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4.
Fully remote flares typically are HP flare only.
5.
LP flare pressure may be sufficient to allow mounting on bridge linked structure.
Otherwise, facilities for LP flaring should be provided on main platform.
Modify Title to Read
4.2.2
Horizontal or pit flares
Add
a.
Although this type of flare has been used in BP and other company facilities, due to potential
for negative environmental impact, such as flue gas dispersion and ground water
contamination, future use shall be limited or completely eliminated.
b.
Horizontal flares may be required to allow operation of temporary installations in remote
locations and are subject to BP approval.
c.
If horizontal flare is considered, the following general requirements for flare selection and
design shall be addressed:
1.
Local regulations.
2.
Spacing requirements.
3.
Smoke formation.
4.
Dispersion of combustion produced gases.
5.
Flare tip life expectancy.
6.
Pilot ignition system life expectancy.
7.
Need for use of assisting media.
d.
Flare lines leading to flare header shall not be buried.
e.
The following design enhancement options could be considered in existing or new pit flare
design:
1.
Tip location: Consider installation of tip on upwind side of prevailing wind direction.
Wind will then carry flame away from flare tip. Because these flares are typically
operated at low tip pressure, gas exit velocities are low, allowing wind at lower release
rates to blow air inside tip causing internal combustion and premature tip mechanical
failure.
4.2.3
2.
Tip heat protection: Consider use of additional tip protection from heat or burning flash
fires caused by presence of liquids. Options may include selection of higher metallurgy
for tip, refractory protection of tip, and use of heat shields.
3.
Use of retractable pilots: Retractable pilots can significantly increase flare safety and
availability by allowing onstream pilot repair and replacement.
Enclosed flame flares
Add
a.
BP or its representative will propose use of enclosed ground flares. Vendor may, however,
propose alternate for BP approval.
b.
If enclosed flame flare is considered, the following general requirements for flare selection and
design shall be addressed:
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1.
Performance guaranteed to meet all operating conditions specified in data sheets shall be
provided.
2.
If facilities are located close to populated areas, Vendor shall provide explanation on how
flare design and operation will ensure that waste stream is continuously ignited and shall
provide guarantee for maximum emissions limits.
3.
Wall or fence to cut off direct route for light and noise to surroundings shall screen air
inlet at bottom of box.
4.
Plenum height shall be specified and provided by Vendor and shall be subject to BP
approval.
Adequate plenum height is required to avoid wind causing downdrafts that force flames
outside bottom of flare.
5.
If vent stream to be burned is low BTU gas, it is important to have stable and complete
combustion especially if toxic gases are present.
6.
Flare gases or hazard shall have adequate dispersion if combustion products are toxic or
in event of flameout.
7.
Exhaust gas temperature shall be optimised to suit site and operating conditions.
8.
Auxiliary elevated flare shall be used for emergency flaring to provide supplemental
capacity to enclosed flame flare.
9.
Noise levels shall comply with general requirements specified in data sheets and, in
addition, shall be sufficiently low so as not to cause nuisance to local residents.
10. Potential maintenance problems with enclosed flame flares should be identified at early
stage in project.
4.2.4
Single point and multi burner
4.2.4.1
Single point flares
Add
The tip used for single point flares can be a low pressure type, such as utility or open
pipe type, or tips that operate at medium or high differential pressure across the tips.
The majority of the tips that are currently being offered by flare Vendors are either a
“generic” type design for relatively simple service applications or proprietary designs
for more demanding operating characteristics/performances.
4.2.4.2
Multi burner staged flares
Add
Multi burner staged flares may have tips located near grade or on elevated
structures/stack.
If use of multi burner staged flare is considered, the following general requirements for flare
selection and design shall be addressed:
a.
Performance guaranteed to meet all operating conditions specified in data sheets shall be
provided.
b.
Vendor may quote multi burner staged flare installation that uses staged operation to provide
smokeless operation as specified in data sheets.
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Purge gas shall be carefully considered for these types of flares that use flow staging, such as:
1.
Proper purge gas rates are maintained at all times to avoid internal combustion in raisers
and header.
2.
At low flow rates, only first stage of multi tip array should be open to atmosphere, and
this stage is only one that needs to be included in purge rate calculations.
d.
Provisions for adding purge gas in all stages shall be provided to avoid internal combustion if
control valve in one or more stages develops a leak.
e.
Purge gas requirements and estimate of service life of burners at normal and at minimum
purge rates shall be provided.
f.
Potential noise problem should always be considered. The following are additional flare noise
requirements:
1.
Flare Vendors, in their quotations, shall provide information on noise emission from flare
at maximum emergency flow and at maximum smokeless flaring rate.
2.
Noise emission data shall be provided as test report containing sound power levels in
octave bands from 31 Hz to 8 kHz.
3.
Flare shall be sited such that noise at positions normally accessible to personnel, at
maximum emergency flow should not exceed 115 dB(A), except with BP approval. BP
may specify lower noise limit to be applied in a particular case, e.g., offshore platform
ground flare.
4.
To reduce noise in specific areas, siting of flare, if possible, should be such that flare is
not in direct line of sight from area.
The high kinetic energy and velocity needed to produce smokeless combustion also
creates a higher level of noise than might be expected from a tip not using forced air or
steam for assistance.
The main contributor to the noise in a smokeless flare is the steam jet noise. Therefore,
in general, the lower the ratio of steam to flared gas, the quieter the flare.
This noise may not be a problem in isolated areas, in shielded ground installations, or
on elevated stacks of sufficient height.
g.
h.
Gas flow control
1.
Gas flow to flare stages shall be controlled by main control logic housed in control panel
enclosure that is usually located near staging manifold.
2.
Control logic shall be integrated into plant control system.
3.
Control valves shall be located at end of main flare header.
4.
As header protection from overpressure, in case of control valve(s) or control system
malfunctions, rupture disk or pin valve bypass lines shall be installed for each stage.
Vendor shall outline maintenance procedures, provide estimates for annual cost, and list all
special tools and spare parts requirements.
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Add
4.2.4.3
Multi burner ground flares
In addition to general requirements outlined for multi burner staged flares, the following are
additional requirements that are specific to multi burner ground flares:
a.
Proper number of pilot burners shall be provided on flare to maintain stable source of ignition
for discharged gases.
b.
Radiation protection
c.
1.
Multi burner ground flares provide visible flames at grade level. Therefore, installations
located in areas adjacent plants and close to public facilities shall be surrounded by
radiation fence.
2.
Radiation shielding may be limited to stage manifold area or may be required around
entire area.
3.
If radiation shields are used, care shall be taken in design to ensure sufficient airflow to
burners.
4.
Radiation fence shall normally be approximately 3,7 m (12 ft) high. Height of fence shall
be determined by specific shielding requirements for each particular installation.
5.
If radiation protection is not required, some normal fencing of area should be undertaken
to restrict unauthorised access to flare area.
Burners shall be designed with stainless steel casting instead of lower cost fabricated designs,
which will reduce maintenance and extend life of burners.
4.2.5
Smokeless and non smokeless flares
4.2.5.1
Smokeless flares
Modify to Read
Smokeless flares shall be designed and operated in accordance with GP 44-80, Section
8.6. However, some of the mechanical aspects and flare components of smokeless flares
are addressed in various sections of this GP.
The following are additional requirements that are specific to smokeless flares:
a.
Smokeless flares eliminate noticeable smoke over specified range of flows.
b.
Smokeless combustion shall be achieved by using gas, air, steam, pressure energy, or other
means to create turbulence and entrain air within flared gas stream.
c.
Smoking shall be defined by Ringelmann numbering scale (#1 Ringelmann is 20% opacity,
Ringelmann 0 is clear).
d.
Smokeless flaring requirement may be achieved by any of the following methods:
1.
Inspirating additional air into combustion zone with fuel gas.
2.
Inspirating additional air into combustion zone by tip design/Coanda effect. The
following are options that should be considered for this application:
a)
Slots may be fixed or variable.
b)
Slots should be wide enough to not get blocked by impurities in gas
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3.
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c)
With variable slots, mechanism should be robust and well protected against ambient
conditions.
d)
Additional protection from system overpressure, such as use of bypass with rupture
disk or pin type valve, should be considered.
e)
Steam may be used in Coanda effect to draw in air for mixing with gas in single
large units.
Providing highly turbulent condition within flame by using energy of incoming gas or
turbulence caused by steam or air injection.
e.
Flow rates for both smokeless and non smokeless flaring will typically be specified by BP.
f.
Vendor may propose flow rates, which will be subject to BP approval.
Endothermic (fuel gas assisted) flares
Add
a.
If other means, such as steam, air assisting, or high differential pressure across flare tip, are not
available or are not economical solutions, fuel gas assisted flare design can be used for flare
smoke suppression.
b.
If flare gas LHV is less than 150 to 200 BTU/ (scf), this may be the only viable option to
achieve complete combustion of flare gas. This option will generally be proposed by BP and
confirmed by Vendor. Fuel assist gas supply requirement for design shall be listed Vendor.
4.3
Selection considerations
4.3.1
Add
4.3.1.1
a.
BP or its representative will select type of flare to be used for application.
b.
This requirement will be specified in data sheets and specifications.
c.
Design alternates may be quoted by Vendor.
Add
To select and implement the most cost effective solution and to minimise the effect on
the environment, the environmental considerations for all releases should be discussed
thoroughly with regulatory authorities at an early stage of process design.
The following issues shall be addressed by Vendor during flare design:
a.
Safety and well being of all personnel in vicinity (both onsite and offsite) under all conditions
of flare operation. This shall include startup, purging, operational and emergency flaring,
shutdown, inspection, and maintenance of all or parts of system.
b.
Protection of plant and equipment in vicinity of flare system under all conditions.
c.
Protection of flare system from damage by external events, e.g., fires.
d.
Inherent safety of flare system itself, especially with respect to the following:
1.
Flammable or explosive mixtures.
2.
Blockages or flow restrictions.
3.
Toxic components.
4.
Chemical reactions.
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5.
Mechanical damage.
6.
Corrosion, erosion, and hydrogen embrittlement.
7.
Flare flame stability.
8.
Security of ignition.
9.
Security of pilots.
10. Change over to another flare
e.
Flare as disposal device shall be evaluated to determine if it can be classified as “Safety
Critical Equipment”.
f.
Evaluation can be performed in accordance with “BP Safety Critical Equipment Definition For
PI” document.
This document will be added as a reference document in ETP Library.
g.
4.3.1.2
4.3.1.3
Guidance in assessing consequences and impact of secondary hazards shall be obtained from
BP.
Add
To determine overall cost of flare installation, Vendor shall review and address the following major
requirements that heavily influence system design and performance:
a.
Safety and environmental requirements (dispersion, smoking limits, radiation limits, noise,
etc.).
b.
Type and quantities of released gases and nature of flaring event (toxic or non toxic fluids,
emergency and routine flaring, etc.).
c.
Type of enclosed disposal system selected (single or multi service system, etc.).
d.
Disposal device selection (elevated flare, ground flare, enclosed flare, marine and platform
flare, etc.).
e.
Site and plant requirements (distance from unit to flare, additive effect of radiation from
multiple flare installation, possibility of burning liquid droplets, etc.).
f.
Construction materials requirements (seawater environment, corrosive products of
combustion, high heat flame intensity, intermittent operation, multiple tips in close vicinity,
etc.).
g.
Utilities availability and cost (steam, air, high pressure gas, electricity, etc.).
h.
Accessibility (marine flare, boom flare, site with multiple flares, multiple tips on common
stack, remote site location, etc.).
i.
Climate conditions (artic, desert, offshore, etc.).
j.
Alternates to this GIS that may result in improved safety or economy for design may be
quoted.
Add
BP will typically provide design and requirements data for flare design. Data will be specified in
flare data sheets and include the following information:
a.
Flare gas flowrate.
b.
Flare gas composition.
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c.
Molecular weight.
d.
Flare gas temperature.
e.
Frequency and duration of process streams discharging into flare system at any one time.
f.
Inherent restrictions imposed, e.g., allowable backpressure, solids deposition.
g.
Depressuring flow rates especially if depressuring is activated because of fire or if due to
utilities failure that might cause all depressuring valves to open simultaneously (all fail open
depressuring valves).
Interrelationships
Add
Issues that are related to interrelationship are not discussed in one particular section of this GIS.
They are instead imbedded into numerous sections covering flare system design requirements.
4.4
Major components
Add
4.4.1
a.
BP will select major flare components for each installation.
b.
Vendor shall provide only components as outlined in this GIS.
c.
Vendor may, however, recommend optional component in its proposal and itemise associated
cost for each option.
Modify to Read
Major and optional components for elevated flare are:
a.
Flare burner with or without smoke suppression capability.
b.
Pilot(s).
c.
Retractable pilot(s) (optional).
d.
Pilot igniter(s).
e.
Pilot flame detector(s).
f.
Retractable thermocouple(s) (optional).
g.
Buoyancy or velocity seal (optional).
h.
Support structure.
i.
Knockout drum (optional).
j.
Flame/detonation arrestor (optional).
k.
Liquid seal (optional).
l.
Piping.
m.
Smoke suppression control system (optional).
n.
Blower(s) (optional).
o.
Ladders (caged or with safety climbing system) and platforms (optional).
p.
Davit for tip removal (optional).
q.
Aircraft warning lights and painting (optional).
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r.
Radiation heat shields (optional).
s.
Rain shields (optional).
t.
Flashback prevention (optional).
u.
Purge system.
v.
Isolation system (optional).
w.
Gas sampling system (optional).
x.
Oxygen analyser (optional).
y.
Flow, temperature, and level measurements and alarms (optional).
z.
Pumpout facilities for drum (optional).
aa. Fire protection (optional).
bb. Flame snuffing system (optional).
cc. Insulation (optional).
dd. Heating and heat tracing (optional).
ee. Cold liquid/vapour vaporisation and heating system (optional).
ff.
4.5
Flare gas recovery system (optional).
Mechanical design basis
Add
a.
Protection of flare system from damage by external events, e.g., fires.
b.
Material selection suitable for operational temperatures, corrosion, erosion, hydrogen
embrittlement, temperature cycling embrittlement, etc.
c.
Material selection should take into consideration special issue associated with potential
autorefrigeration from depressuring.
d.
Typical operating conditions (e.g., flare that is exposed to low flow operating condition for a
long period of time might result in flames sitting well down in tip causing damage; therefore,
range of operating conditions needs to be fully considered in deriving mechanical design).
e.
Vendor shall be responsible for mechanical design of flare system.
f.
Mechanical design bases are provided in data sheet and specifications.
g.
Presized equipment information provided in data sheet shall be confirmed by Vendor.
4.6
System design criteria
4.6.1
Modify to Read
Note that issues that are related to system design are imbedded into numerous sections
of this GIS.
BP or its representatives will perform general system design criteria development for
the flare system. Vendor shall typically verify if BP proposed system would meet all
requirements. Vendor may quote alternate system design that would provide overall
improvement to the flare system design resulting in improved safety, operability, and
reliability.
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The following are major system design criteria that are outlined, in greater detail, in
GP 44-80:
a.
•
Choice of disposal system (GP 44-80, Section 5).
•
Closed systems (GP 44-80, Section 7).
•
Flare system design (GP 44-80, Sections 8.1, 8.3, 8.6, 8.7, 8.12, and 8.16).
•
Liquid removal (GP 44-80, Section 9).
The following additional points shall be given specific attention in overall design of flare
system:
1.
Required life of flare system components.
2.
Philosophy to be adopted on inspection and maintenance of flare system and impact of
these requirements on plant operation (flare system sparing requirements).
3.
Meteorological and any other relevant environmental conditions pertaining to site.
4.
National and local regulations, particularly concerning smokeless burning, flare visibility,
pollution and noise restrictions.
5.
Need for winterisation, especially of liquid seals.
6.
Need for segregation of relief headers for reasons of temperature, toxicity, corrosive
materials, etc.
BP Safety Critical Equipment Definition For PI Segregation is particularly required to
prevent freezing of water wet streams, solidification of viscous materials, or reactions
that could lead to plugging of lines.
7.
Handling systems for safe disposal of condensed hydrocarbons and sour water from both
knockout and seal drums.
8.
Secure supply of seal fluid to seal drum with provision to prevent overfill to flare, header,
and knockout drum(s).
9.
Plot space/layout considerations.
10. Requirement for cold liquid/vapour vaporisation and heating system in situations where
cold flare cannot be justified.
b.
The following is a checklist of possible hazards that should be considered in the design of flare
systems.
1.
Flammable/explosive mixtures in flare system. These may result from air entering the
system by any of the following mechanisms:
a)
Down draft due to buoyancy effects, loss of purge gas flow, failure of purge
reduction (molecular) seal.
b)
Condensation of vapours in flare system can cause air to be sucked in at flare tip or
through open vents or drains. This can be a very serious problem, since capacity of
flare pipework to absorb heat can lead to very large and rapid contraction in
volume.
c)
Cooling of hot vapours discharged into cold flare system can also lead to air being
sucked into system.
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d)
Buoyancy of light gases can create subatmospheric pressure in low level flare
pipework. Resultant pressure differential may induce air to enter system through
any openings, vents, drains, etc.
e)
Vacuum systems connected to flare can cause air to be sucked in. Especially high
integrity segregation mechanisms are required to prevent this.
f)
Process air may enter flare due to loss of control in oxidation plants or uncontrolled
air purging.
g)
Blockages/flow restrictions.
h)
Freezing of liquid seals or condensate in flare lines or molecular seals or steam
condensing, freezing in flare tip during low steam flow in winter condition, due to
low ambient temperatures, low temperature discharges, or autorefrigeration.
i)
Polymerisation products, hydrates, waxes, corrosion products.
j)
Solids carried forward from plants, catalyst, polymers etc.
k)
Liquids trapped through faulty drains, bad design, and level control failure.
l)
Valves incorrectly closed or failing closed.
Toxic components
a)
Streams containing more than 10% H2S or other highly toxic material should be run
in separate line to flare (as required by and preferably coupled to main flare gas
stream near flare tip to minimise exposure of main flare pipework to corrosive
effects of H2S).
b)
Careful consideration should be given to disposal of foul liquid effluents from flare
seals, drains, etc.
3.
Chemical reactions within flare system, scales, acetylenes, peroxides, etc.
4.
Mechanical damages, hydraulic surge of liquid slugs, propulsion of solid ice slugs,
hydrates, impact, low temperature embrittlement through autorefrigeration, external fire
damage, burn back at flare tip, flame lick, venting of high temperature gases into flare
system.
Reliable effective burning
Modify to Read
a.
Reliable effective burning shall be achieved by proper system design.
b.
Design criteria and specifications will be provided by BP.
c.
Alternate design and quote as options may be proposed.
d.
BP may request testing of flare burners to performed by Vendor for simulated tested operated
conditions at designated test facility.
e.
Minimum heat content of flare gas shall be maintained as required by U.S. Environmental
Protection Agency (EPA) document AP 42, Volume 1 and Chapter 13.5. Minimum heat
content of flare gas should be 11,250 kJ/m3 (300 Btu/ft3) to ensure high combustion efficiency
for flare. Concentrations below 9300 kJ/m3 (250 Btu/ft3) shall require addition of fuel gas for
complete combustion.
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System hydraulics
Modify to Read
BP or its designated representative will typically perform hydraulic design for the flare
system. Flare Vendor may, however, be requested to review and confirm the proposed
design. The basis and methods to be used for determining system pressure losses shall
be subject to BP approval.
The following are general considerations required if providing hydraulic design for flare system:
a.
Total allowable pressure loss through flare system, including stack, flare tip, liquid seal (if
any), knockout drums, and piping is normally dictated by back pressure limitation on critical
relief valves, and shall be subject to BP approval. Evaluations shall take account of:
1.
Potential relief, depressurising, and process venting conditions as specified in data sheets.
2.
Pipe roughness consistent with pipe material and operating conditions.
3.
Final piping configuration details, including fittings and entrance losses.
Pressure drop limitations may dictate the flare stack diameter and flare tip size.
b.
Flare Vendor shall refer calculated flare tip exit velocity to BP, which shall be subject to
approval. Velocity shall be chosen to satisfy requirements for flame stability, noise, and
dispersion.
The latest designs of pipe flare tips permit smokeless flaring at velocities above 0.2
Mach No., but if this velocity is exceeded, experience of satisfactory operation of the
design should be examined. For emergency flaring, 0.5 Mach No. is generally accepted
as a maximum. Above that figure, the flame could become unstable and lifts off,
resulting in the risk of flame extinction. A Sonic flare tip, 1.0 Mach No., can, however,
be specified for offshore flare applications.
4.6.1.3
c.
Relief header shall be sized using pipe roughness of 0,46 mm (0.018 in) instead of normally
adopted value for clean steel pipe of 0,046 mm (0.0018 in). This reflects BP experience of
increased roughness in relief headers.
d.
If back pressure is not significant and governing factor is fluid velocity, flare line shall be
sized to limit maximum velocity to 0.5 Mach No., as long as relief valve pipes supports is
assured adequate. Allowable Mach No. may be increased to 1.0 for offshore application.
e.
Relief header shall be self draining towards knockout drum. Header upstream of flare tip shall
similarly drain back to drum.
Liquid removal
Modify to Read
The flare knock drums are used for removal of the bulk of the liquid carryover. A drum
shall be provided in all cases where significant quantities of liquid can be relieved from
within the battery limit.
An onsite knockout drum should normally be provided within the battery limit of each
plant or group of plants served by the flare system. The offsite knockout drum is
typically located in the flare area.
The offsite and onsite knockout drums have similar design requirements.
The choice between a horizontal and a vertical drum should be made on economic
considerations, taking into account the vapour flow rate, the liquid storage required,
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and the necessary slope of the flare header. BP will, however, typically select the type
of drum for each service.
a.
BP or its representatives will size flare knockout drum, which will typically be supplied by
others.
b.
Flare Vendor may be requested to confirm size of knockout drum, even if it is not included in
Vendor scope of supply.
c.
The following are specific considerations/requirements for design and sizing of knockout
drums:
1.
Offsite knockout drum (onshore)
a)
Each flare system shall have offsite knockout drums.
b)
Drums shall be located as close as practical to flare, taking account of access
requirements and potential use of liquid seals that shall be located downstream of
drum.
c)
Calculation method shall comply with API RP 521.
d)
Onsite knockout drums shall be designed for full vacuum and maximum allowable
working pressure of at least 3,5 barg (50 psig).
e)
Liquid storage capacity of drum shall allow for minimum of 20 min holdup at
maximum liquid inflow to drum. Capacity shall be provided between maximum
normal liquid level (i.e., pump trip in level) and maximum level allowable in drum.
f)
Offsite knockout drum, typically referred to as flare drum, shall be sized to remove
liquid droplets above 600 µm at maximum emergency gas flow to flare and above
150 µm from gas flow equivalent to maximum smokeless capacity of flare. In
exceptional cases, for flares that are capable of burning larger sized droplets,
waiver of these requirements may be accepted, subject to BP approval.
g)
Any flashing of relieved liquid at knockout drum pressure.
h)
Because of potential for blockage from scale or waxy deposits, use of demister pad
to limit size of drum should be avoided. Applications shall be restricted to clean
systems if there is no practical alternative.
i)
Unless specified otherwise, knockout drum shall have automatic hydrocarbon liquid
removal.
Since the liquid in the KO drum may be toxic or flammable or have toxic or flammable
material dissolved in it, particular care should be taken in the design and operation of
any drain points. If there is any risk of toxic materials being released, the drain should
be routed to a closed system. If there is any risk of the materials freezing, a second
valve in series is required as a minimum.
j)
If appropriate, separate facilities for water or heavy hydrocarbon removal shall also
be provided - these may be automatic or manual. Disposal route and facilities for
these liquids shall be subject to BP approval. Particular attention should be paid to
prevent creation of hazard due to release to atmosphere of flammable or toxic
materials from drain points.
k)
Instrumentation and control systems for the drum shall comply with data sheets
provided by BP.
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l)
Piping systems entering and leaving drum shall comply with BP piping
specifications.
m) If specified on BP data sheet, winterisation shall be provided.
n)
Personnel protection shall be provided in accordance with BP data sheet
requirements.
o)
Facilities shall be provided, if specified on BP data sheet, for isolation, venting and
purging, inspection, maintenance, and cleaning of drum.
p)
Specific attention shall be given to requirements of inspection, maintenance, and
cleaning if associated plants cannot be shutdown. Proposals shall be subject to BP
approval..
q)
Specific attention shall be given to liquid removal facilities in flare systems that are
required to dispose of both “cold” and “wet” streams.
In this context, a “cold” stream is defined as a stream at a temperature below 0°C
(32°F) that could cause freezing of water in a knockout drum or on mixing with a
stream containing free or dissolved water. The situation is most likely to occur in plants
handling liquefied gases or gas streams at high pressure.
If practical, cold streams shall have separate systems, with segregation maintained
until the streams become compatible. Flare Vendor proposals shall be subject to BP
approval.
r)
Cold liquid collection drums may require vaporisation facilities. Cold vessel
material of construction shall be appropriate for minimum design temperature.
s)
Attention shall also be given to presence of other materials that freeze or are highly
viscous at temperatures above 0°C (32°F).
t)
Attention is drawn to special sealing provisions for cold service. Seal provision in u)
is generally followed.
u)
Water seals shall only be used if temperature of vapour cannot fall below 0°C
(32°F). To guard against freezing in cold weather, seals shall be fitted with
automatic heating, either electrical or steam coil, as specified by BP.
Some chemicals can raise the freezing point of water above 0°C (32°F). If such
chemicals could be relieved, suitable adjustments should be made to water seal or seal
liquid.
v)
2.
For cold service, glycol or other suitable material shall be used, either pure or with
water, depending on anticipated temperature of vapours.
Knockout drum (offshore facility)
The liquid removal facilities should be designed to remove entrained droplets (which
may carryover as burning hydrocarbons) from the gas flow and provide sufficient liquid
holdup capacity to collect any surges of liquid.
a)
Holdup capacity should be based on longest estimated time required to isolate
incoming flow. Typically, for most offshore platforms, isolation time may be 1.5
min.
b)
Maximum use should be made of surge capacity within process area to
accommodate liquid relief.
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c)
4.6.1.4
Devices that provide warning (and if necessary execute shutdown action) shall be
fitted to all relief valves which can discharge liquids to flare.
Air infiltration
Modify to Read
4.6.1.4.1
Flashback prevention
a.
Reliable method of flashback prevention shall be incorporated into flare system design. The
following methods may be used, either singly or in combination (choice of method shall be
subject to BP approval):
1.
Gas purge
2.
Liquid seals
3.
Efflux velocity accelerators
The above methods are primarily intended to prevent diffusion of air into the flare
stack. Note that gas seals, i.e., molecular seals are not sufficient by themselves to
prevent flashback. If flare gas recovery is used, both gas purge and liquid seals should
be installed.
b.
Use of flame arrester shall be considered only if none of methods in a. are suitable and shall be
subject to restrictions in a.
c.
The following conditions conducive to formation of flammable mixtures within flare system
shall be evaluated and addressed if:
1.
Vacuum systems are linked to flare.
2.
Lighter than air gases, particularly hydrogen, are being flared.
3.
Condensation or rapid cooling can occur within flare system.
It may be possible to reduce or even prevent condensation by heating and insulating the
flare line. However, such measures may be expensive to install and difficult to maintain
in a reliable condition.
d.
4.
Flashback velocity may be reduced by addition of inert gases to flammable mixture. Best
location for addition of inert gas is as close to flare tip as possible, compatible with good
mixing of gases before burning at tip.
5.
Care shall be taken to ensure flare gas heat value is above minimum allowed at all phases
of operation. Otherwise, pilot and main flames can be extinguished.
6.
BP will specify if it is necessary to keep flare lit.
7.
Velocity accelerators and inert gas addition may be used in combination.
Method of calculating flashback velocity
1.
Method of calculating flashback velocities for some gases commonly occurring in flare
systems when mixed with nitrogen, carbon dioxide, or both has been developed by Van
Krevelin and Chermin and reported in transactions of Seventh International Symposium
on Combustion, 1959, pages 358-368.
2.
This method may be used to calculate inert gas flow corresponding to peak flashback
velocity of gas mixture. Excess inert gas flow of 25% above calculated value should
provide ample margin of safety to compensate for measuring errors and minor flow
disturbances.
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Gas purge
a.
Inert gas (e.g., nitrogen), fuel gas, or natural gas from reliable source shall be continuously
introduced as purge into vapour disposal systems. Choice should primarily be evaluated on
cost. If economically viable, inert gas shall be used.
b.
Purge gas supply shall be from high reliability source approved by BP.
c.
If necessary to achieve overall acceptable reliability, automatic backup supplies should be
used.
d.
Purge system shall be designed such that loss of single purge gas source or injection point does
not allow hazardous conditions to occur.
e.
Maximum calculated purge rate shall be established to required purge rate to balance
flashback and efflux velocities for variety of relief flow rates.
f.
Minimum purge gas velocity or flow rate shall be maintained at flare tip to:
1.
Minimise air ingress due to wind effects.
2.
Prevent burn back inside flare tip.
g.
Larger of the two flow rates shall be used.
h.
Minimum purge rate to minimise air ingress due to wind effects shall be calculated using
H.W. Husa’s correlation formulae given in Annex C. Purge rate shall be such that oxygen
content in flare gases 8 m (25 feet) down from top of flare shall be less than 6%.
Note that the Husa correlation applies if typical wind speeds do not exceed
approximately 13,4 m/s (30 mph). Locations where prevailing winds can often exceed
this wind speed may need somewhat higher purge rates.
i.
If either purge gas or flare gas is low molecular weight (e.g., containing high concentrations of
hydrogen), maximum oxygen content shall not exceed:
1.
Maximum oxygen of 5 volume percent for flare gases with MW greater than 6 but not
exceeding 8.
2.
Maximum oxygen of 4 volume percent for flare gases with MW greater than 4 but not
exceeding 6.
3.
Maximum oxygen of 3 volume percent for flare gases with MW less than or equal to 4.
j.
Minimum purge required to prevent burn back inside non refractory lined flare tips shall be
specified by Flare Vendor. Flow velocity shall be verified, based on selected proprietary flare
tip or molecular seal design. If tip is refractory lined, purge rate only needs to be based on that
required to prevent air ingress due to wind effects.
k.
Required purge rate using gas mixture heavier than air shall be calculated using nitrogen
parameters in Husa equation in Annex C.
For flammable purge gases heavier than air, the minimum purge rate could
theoretically be achieved with very low flow rates. This may result in burning inside the
tip, resulting in higher tip temperatures and shorter tip life or flame extinguishment.
l.
Minimum flow rate required shall be adequate to maintain flare alight, while problem of
internal burning shall be economically evaluated against the following alternatives:
1.
To increase purge gas velocity at tip to typical velocities of between 0,15 m/s and 0,3 m/s
(0.5 f/s and 1.0 f/s).
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2.
To upgrade material specification for flare tip.
3.
Provided there is alternative relief route during flare shutdown, to replace tip more often.
4.
To provide additional cooling for flare tip.
m.
Unless specified otherwise, flares shall have oxygen monitoring.
n.
Oxygen monitoring system shall comply with the following:
1.
Oxygen monitoring equipment shall ensure that, if minimum purge rate is used, explosive
atmosphere does not result. Monitoring equipment should also highlight spurious ingress
of oxygen due to operating deviations, e.g., suck back.
2.
If inert gas is being used for flashback prevention and system is of high integrity, oxygen
monitoring may not be required.
3.
Oxygen sampling probe shall be located 8 m (25 ft) or 15 diameters, whichever is
smaller, below tip exit.
4.
Oxygen analysing installation should be located at base of stack or at boundary of
restricted access zone. If located in area where radiation level may exceed 4,73 kW/m2
(1500 Btu/ft2h), oxygen analysing installation shall have suitable shielding.
5.
Sample gas shall be withdrawn by diaphragm type vacuum pump, fitted upstream with
liquid knockout pot and returned to stack above sample point. This is required to avoid a
fluctuating pressure in sampling line, due to changes in pressure drop through stack
induced by changes in flow rates.
6.
Portion of sample gas shall be taken through regulating needle valve to oxygen analyser
of type specified by BP and exhausted to atmosphere. Local and control room indications
and alarms shall be provided as specified by BP.
Liquid seals
Liquid seals may be employed for prevention of air ingress into the flare header
network due to most thermal contraction events and for diversion of vapour flows (e.g.,
for flare gas recovery systems). (See ISO 23251 or API RP 521).
Liquid seals may not prevent flashback in cases where a large volume of gas is relieved.
Incidents have shown the flame can propagate back through a continuous flow of
bubbles. Hence, a continuous purge or other method should be used to ensure the flare
header is air free.
a.
If used, liquid seals should be incorporated in relief disposal systems as close as practical to all
elevated flares.
b.
Liquid seals should normally be used in conjunction with continuous gas purging.
c.
If more than one flare is connected to relief header and automatic pressure actuated valves are
used, full capacity backup route to flare shall be provided via liquid seal or another BP
approved alternative that ensures “open” relief route.
d.
If liquid seals are impractical, another system shall be required that provides both guaranteed
emergency relief route and guaranteed protection against air ingress to flare and header
systems.
e.
Water seals normally should be used if either ambient temperature or temperature of relief
streams cannot fall below 0°C (32°F). To guard against freezing in cold weather, seals shall be
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part of winterisation program and shall be fitted with automatic heating, either electrical or
steam coil, as specified by BP.
Some chemicals can raise the freezing point of water above 0ºC (32ºF). If such
chemicals could be relieved, suitable adjustments should be made to water seal or seal
liquid.
f.
For cold service, glycol or other suitable material shall be used, either pure or with water,
depending on anticipated temperature of vapours.
g.
Fluid shall be compatible with all fluids that can enter flare header.
h.
Liquid seals shall be designed in accordance with the following:
1.
Vertical leg of flare header inlet shall form vacuum leg of adequate length above liquid
level in drum for maximum vacuum expected in header due to cooling and/or condensing
of hot vapours.
a)
Leg shall be minimum 3 m (10 ft) high, which corresponds to approximately -0,3
barg (-4 psig) of vacuum protection.
b)
Minimum submergence depth of inlet downcomer shall be 100 mm (4 in) in
accordance with ISO 23251 or API RP 521. However, volume of liquid in seal drum
above level of top of submerged weir shall be sufficient to fill 3 m (10 ft) vacuum
leg.
See “Liquid Seal Drums” in ISO 23251 or API RP 521 for further details.
To avoid flow pulsations that can cause rumbling type noise, use of a more effective
system based on separate dip legs of different sizes, sometimes with side slots (see ISO
23251 or API RP 521) should be considered. This system allows that each release route
have a progressively larger flow without any noticeable pulsation.
2.
Dip leg should be surrounded by anti splashing perforated baffle sheath.
3.
Diameter of baffle sheath should be 1.8 to 2.0 times diameter of dip leg, with 13 mm (0.5
in) diameter holes on 75 mm (3 in) diagonal centres.
4.
Maximum depth to which inlet pipe may be submerged shall be based on maximum exit
back pressure allowable in relief or flare header.
5.
To prevent surges of gas flow to flare, free area for gas flow above liquid should equal at
least 3 times inlet pipe cross section area.
6.
Details of dip leg design shall be subject to BP approval. Design shall be capable of
flowing all quantities from maximum emergency flow down to 1/3000th of that flow
without causing flow pulsations that cause nuisance.
7.
Minimum pressure of 3,5 barg (50 psig) shall be used for design of seal drum.
8.
All necessary equipment shall be provided to maintain design seal level. Makeup lines
shall be sized to replace seal within 10 min.
9.
Design of seal system shall provide for:
a)
Prevention of hydrocarbon build up.
b)
Prevention of displacement of seal liquid.
c)
Maintaining correct seal liquid level over operating pressure range.
d)
Continuous purging of seal water to prevent build up of H2S and CO2.
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10. Flare header shall slope from top of vacuum leg back to offsite knockout drum.
11. If water is used for seal, design of disposal system for excess water shall take into
account likely contamination with relieved materials, e.g., H2S. Alternatively,
recirculating system may be provided with capacity to allow for makeup and for checking
liquid inventory. Latter option should be provided for seal systems containing antifreeze.
If makeup requirements are not significant (i.e., static liquid seals), antifreeze systems
may be used.
4.6.1.4.4
Buoyancy seals (molecular seals)
a.
Labyrinth type gas seals and flow restriction type seals are not recommended but may be used,
subject to BP approval.
There are two main types of gas seals: labyrinth type and flow restriction type.
Though called seals, neither stop the reverse flow completely, only reduce it. They are
both installed immediately below the flare tip. However, if volumetric condensation or
cooling rate of vapour in the relief system exceeds purge rate plus incoming gas
volume, air entry can no longer be precluded, and a risk of an explosion exists.
Due to the ingress of rain water and potential for condensation, labyrinth gas seals
require drains. These can block with ice or carbon or with refractory, if any, dislodged
from the flare tip, and therefore such seals are not recommended.
b.
4.6.1.4.5
Due to fact that benefits of use of either type of seal is not possible to quantify, no reduction in
purge flow should be used.
Flame arresters
Flame arresters are another way of preventing flashback. These are not very commonly
used but could be effective against flashback. Their disadvantage comes from the fact
that they can easily become blocked by dust, carryover, corrosion products, materials
liable to polymerisation, etc. A flame arrester should be considered only if there is no
other viable or economic alternative.
4.6.1.5
a.
Flame arresters shall be used only in clean systems, where plugging, scale buildup, dust, or
other accumulation cannot occur during any phase of operation (startup, normal, shutdown,
emergency, etc.) and if there are no practical alternatives. Their use shall be subject to BP
approval.
b.
Provision shall be made for periodically checking condition of flame arresters and maintaining
flame arresters.
c.
It shall be possible to maintain or replace flame arresters without shutting down plant.
Flame radiation
Modify to Read
4.6.1.5.1
Height of flares
Height of flare shall be determined by the following considerations:
a.
Maximum allowable thermal radiation levels as specified in 4.6.1.5.3.
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b.
Adequate dispersion of flammable and/or toxic gases, even with flare extinguished, such that
their concentration shall not cause significant impact to personnel and property and shall be
acceptable to local regulations.
c.
Dispersion analysis should not only consider flare design flowrate but also other scenarios
representing other conditions that may increase potential severity of impact (e.g., higher
molecular weight vapour at lower velocity may reach grade level, buildings, process, and
breathing air intakes or platforms while flammable).
d.
CIRRUS, PHAST, or other BP approved dispersion model shall be used to determine
concentration versus distance and possible consequences if flare is extinguished.
e.
Calculations of ground level concentrations shall be subject to BP approval. Acceptable
concentrations shall be based on period over which conditions leading to release can be
sustained and health hazard that they represent.
f.
Local or national height restrictions, e.g., for aircraft movements, shall be considered.
Calculation methods for flare thermal radiation
a.
ISO 23251 or API RP 521 or another similar, BP approved method can be used to estimate
preliminary thermal radiation levels at grade level, elevated platforms, and buildings.
ISO 23251 or API RP 521 method can be used for initial rough calculations but it is
significantly inaccurate at fewer than 2 flame lengths. Most Flare Vendors have
developed proprietary programs that are empirically based for their specific flare tips.
The fraction of heat radiated used in their models may not be interchangeable with that
used in ISO and API. Flare Vendor thermal radiation model is generally preferred .
b.
If Flare Vendor proprietary program is used, Vendor shall indicate basis for calculations,
including flame emissivity and shall supply calculated results for flame length, flame shape,
and emission. BP will specify points where flare radiation calculations are required and
environmental and operating conditions.
c.
Positions critical to flare radiation calculations, particularly offshore, are:
d.
1.
Base of flare boom.
2.
Nearest edge of platform.
3.
Helideck.
4.
Crane cabs.
5.
Monkey board (drilling derrick).
6.
Radio mast (includes fittings).
7.
Drillers pipe rack.
Environmental conditions that should be used in thermal radiation calculations are:
1.
No wind.
2.
32 km/h to 50 km/h (20 mph to 30 mph) wind.
Higher wind speed can be evaluated as required but the user should recognise that
there is better cooling at higher wind speed that would mitigate the heat radiation.
e.
Plant or process areas containing high thermal radiation levels (fired heaters, exothermic
reactors, etc.) shall be considered in relation to and shall be additive to expected thermal
radiation rates from both operational and emergency flaring events.
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f.
Duration of and additive effect from radiation of any other elevated flare(s) located onsite that
would flare simultaneously with flare under design shall also be considered.
g.
If flaring continuously, effects of solar radiation should be included in overall radiation rates.
Thermal radiation levels
a.
Maximum permissible design level of radiation for exposure of personnel at maximum
emergency flaring shall be based on the following:
1.
Continuous full shift
exposure (offsite public location,
1,6 kW/m2
(500 Btu/ft2h)
outside plant boundary where
public can be present)
2.
Operational blowdown
-
(1000 Btu/ft2h)
(maximum 30 min)
3.
60 s peak exposure
-
20 s peak exposure
(escape time to safe haven)
4,7 kW/m2
(1500 Btu/ft2h)
(escape time to safe haven)
4.
3,2 kW/m2
-
6,3 kW/m2
(2000 Btu/ft2h)
b.
In general, 3,2 kW/m2 (1000 Btu/ft2h) threshold is used where personnel can be normally
working and 4,7 kW/m2 (1500 Btu/ft2h) is used where personnel are not normally working.
c.
Average peak solar radiation value of 1,0 kw/m2 (312 Btu/ft2-hr) should be used for solar
radiation allowance unless specific measured values are available for site.
Notes
•
The figures given assume at least single layer whole body working clothing and
hard hat.
•
For flaring where the peak radiation load is intermittent, solar radiation can be
excluded. For flare where the peak radiation load is continuous, solar radiation
should be included. An appropriate allowance, dependent on latitude, should be
made when determining permissible flare radiation.
•
Metal surfaces irradiated at any of the time/level ratios given may produce burns on
contact with bare skin.
•
For offshore flares, it may not be possible to satisfy some of the requirements.
Access to some areas may therefore have to be restricted, e.g., the flare structure,
the bridge for a linked flare, and the drilling tower. It should be possible for any
vital work in these areas to be performed under specified and controlled conditions.
•
If necessary, these design levels may be achieved by the use of displacement or
shielding. The requirements for any shielding system, and the type of system to be
employed shall be agreed with BP at an early stage.
•
On towers or other elevated structures where rapid escape is not possible, ladders
shall be provided on the side away from the flare such that the tower or structure
can provide some degree of shielding where necessary.
•
In tower supported multiple flare systems, all access requirements shall be
considered. Shielding shall be provided if specified by BP.
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4.6.1.5.4
•
A maximum ground level radiation will be specified by BP, either where access
across a restricted access zone without shielding is required or where the ground
covering may be ignited, e.g., grass or peat.
•
The effect of flaring on equipment in the vicinity shall be considered, using the same
design level above, from the following aspects:
•
High temperature from radiation.
•
Large temperature gradients between exposed and non exposed surfaces.
•
Corrosive action of pollutants.
•
Possibility of burning of unignited droplets.
•
Effect of hot gases.
Restricted access zone (sterilisation zone)
a.
To minimise risk of injury to personnel through thermal radiation or related heat exhaustion,
volumetric zone around flare flame within which radiation may exceed levels specified in
4.6.1.5.3 shall be designated restricted access zone. At places where it may be possible for
personnel to enter this zone (usually at ground level but also possibly via elevated structures),
access shall be restricted by warning notices located in prominent positions.
b.
Equipment may be located within restricted access zone, provided that:
c.
4.6.1.6
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1.
It is designed such that it will not be damaged by highest levels of thermal radiation to
which it could be exposed.
2.
Equipment requires no regular operator attention or maintenance while flare is in
operation.
3.
It is possible to perform emergency maintenance without risk of injury from thermal
radiation to personnel (wearing protective clothing or using radiation shields if
necessary).
Restricted access zone shall be specified around flare tip unless approved otherwise by BP.
Radius of this zone shall be defined by larger of distances calculated as follows:
1.
Operational (for periods of one shift or more). Distance from flare tip beyond which
thermal radiation level does not exceed 1,6 kW/m2 (500 Btu/ft2h) at maximum
operational flaring rate and wind speed determined by local environmental conditions.
2.
Emergency (for periods up to 60 s). Distance from flare tip beyond which thermal
radiation level does not exceed 4,7 kW/m2 (1500 Btu/ft2h) at maximum flaring rate and
wind speed determined by local environmental conditions.
3.
Blowdown (for periods up to 30 min). Distance from flare tip beyond which thermal
radiation level will not exceed 3,2 kW/m2 (1000 Btu/ft2h) for more than 30 min.
Smoke suppression
Modify to Read
a.
Refer to other clauses within this GIS for mechanical details on design, operation, and
maintenance of a smoke suppression system used on flaring devices. This clause is addressing
selection and design issues associated with application of a smoke suppression system.
Requirement for smokeless operation is normally the overriding requirement if
designing a burner for a flare system.
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Smokeless flares eliminate noticeable smoke over a specified range of flows.
Flow rates for both smokeless and non smokeless flaring will typically be specified by
BP. Vendor may propose flow rates, which will be subject to BP approval.
Smoking is defined by Ringelmann numbering scale (#1 Ringelmann is 20% opacity,
Ringelmann 0 is clear).
Smokeless combustion can be achieved by supplying an adequate amount of air and
adequate mixing within flare flame. This can be achieved by using gas, air, steam,
pressure energy, or other means to create turbulence and entrain air within the flared
gas stream.
b.
Provision for smokeless flaring shall be made to comply with national or local regulations
applicable to site.
c.
BP will specify or Flare Vendor shall propose, subject to BP approval, flowrates for both
smokeless and non smokeless flaring.
d.
Proposed design alternates for smokeless operation shall be listed separately in bid document.
e.
Vendor shall review flue gas properties in data sheets or specifications and provide comments
regarding tendency for gas to smoke.
Typically, the smoking tendency is a function of the gas calorific value and the bonding
structure of the hydrocarbons. The paraffinic series of hydrocarbons have the lowest
tendency to produce smoke, whereas olefins, dioleffins, and aromatics series of
hydrocarbons have a much higher tendency to produce smoke.
e.
If calorific value of vented gases is not adequate to provide complete incineration in an open
air environment by maintaining critical combustion temperature, an incinerator should be
used.
f.
Primary emphasis shall be given for design where inlet gas supply pressure is used to
minimise smoking of flared gas.
g.
Multiple burner heads that are staged to operate and provide smokeless flare operation may
also be considered.
h.
Utility consumption estimates for proposed design shall be provided.
i.
Design shall provide smokeless flaring for:
1.
All cases of operational flaring, i.e., controlled release of fluid to flare system for
continuous period exceeding 30 min.
2.
Most credible flaring scenario or 10% to 20% of maximum flaring capacity.
j.
Requirements for smokeless flaring may be relaxed by agreement with BP for periods of non
normal operation, e.g., initial commissioning, startup, and shutdown.
k.
Smokeless flaring by using fuel gas as mixing media may be considered.
In this method, gas jets are used to aspirate air and mix with the fuel. This type of tip
may be used in ground flares (multi burner staged flares and pit flares), where other
means of smoke suppression system cannot be used. The system requires adequate gas
pressure and has a poor turndown ratio. This method requires additional fuel gas
consumption that will increase the cost of flaring, increase radiation, and increase
emissions. The reliability of this kind of flares is poor.
l.
Inspirating additional air into combustion zone by tip design/Coanda effect.
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Guidance on Industry Standard for API 537 Flare Details
This method can utilise the aerodynamic skin adhesion effect known as the Coanda
effect, in which steam, high pressure gas, or air flowing from a narrow slot follows the
profile of a curved surface, entraining air up to 20 times its own volume and
introducing oxygen and turbulence required for complete combustion.
Slots may be fixed or variable. Slots should be wide enough not to get blocked by
impurities in the smoke suppressing media. With variable slots, the mechanism should
be robust and well protected against ambient conditions.
Steam may be used in Coanda or other flare tips to draw in air for mixing with gas in
single large units.
Additional protection from system overpressure, such as use of bypass with rupture disk
or pin type valve, should be considered.
m.
Providing highly turbulent condition within flame.
Highly turbulent conditions within the flame, required for smokeless combustion, may
be achieved by:
•
Using energy of incoming gas (multi ports tips).
•
By steam injection.
•
Air injection.
•
Water injection.
Steam injection may be achieved either by the discharge or multiple steam jets into the
combustion zone, which inspirates air thereto or by a high velocity steam jet centrally
placed in the tip, which entrains air and creates enough turbulence to attain efficient
mixing of fuel and air. Both of these methods may be combined in one tip.
Table 10 of API RP 521 provided steam injection rates into the flared gas in order to
promote smokeless burning. Vendors should be consulted in steam rate requirements
for their specific tip design.
n.
o.
If using steam for smoke suppression, the following points shall be observed:
1.
System shall be designed to provide dry steam at flare tip with steam pipework suitably
insulated.
2.
System shall be provided to avoid introduction of steam condensation to flare tip,
resulting in extinguishing pilots or causing mechanical damage.
3.
Drainage, with steam traps, shall be provided at low points, and steam lines shall be frost
protected.
4.
Unless specified otherwise by BP, steam flow shall be automatically controlled either in
relation to gas flow or by characteristics of flame. Latter method is preferred.
5.
Steam lines should be suitably filtered as close to flare base as practical but upstream of
flow control valve.
6.
To cool pipework at tip, minimum flow of steam shall be maintained by a bypass round
steam control valve.
7.
Expansion loops shall be installed in steam riser as required.
Automatic smoke control
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1.
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
If specified by BP, smokeless flares using smoke suppression may have automatic control
systems that will apportion suppressant to flare gas to produce clean burning without
excess flow.
Excessive suppressant flow is not only costly but also increases flare noise.
2.
p.
Four main types of control system that may be used are:
a)
Ground mounted optical flare radiation sensor.
b)
High level flare radiation sensor.
c)
Based on measurement of flowrate of flare gas.
d)
Based on pressure measurement of flare gas.
The following are general requirements/system descriptions for use of automatic smoke
control system:
(Note that these requirements are somewhat of a generic nature and are also applicable
for systems that use other means of smoke suppression media, such as steam or gas
assisting.)
4.6.1.7
1.
Systems 1 and 2 should measure radiation rate from a smoking flame. Measuring of
radiant heat energy from portion of flame may be achieved either by optical monitor
located at ground level at moderate distance from base of flare stack and focused on base
region of flame or by radiation sensors spaced around stack located just below flare tip.
2.
Optical monitor shall be rugged telescope with restricted field of view, equipped with
photocell sensitive to near infrared radiation. Telescope shall be of waterproof design and
allow regular cleaning of lenses. Optical monitors have fast response time.
3.
Optical monitor should be located at ground level such that monitor can be checked and
maintained at any time.
4.
In system 2, high level radiation sensors, non optical type sensors shall be used. These
sensors shall be strongly constructed and maintenance free because they cannot be
reached during flares operation.
5.
For both types of radiant heat measurement, compensation for ambient variations
(night/day, sun/cloud) may be required. Signals from monitor shall operate smoke
suppressant media via appropriate converters, adjustable for range and zero. Manual
control shall also be provided.
6.
In system 3, measurement of flowrate of flare gas should be used. Flow measuring device
shall not obstruct line or reduce its capacity. Flow measurement should be by flow
sensing elements inserted into blowdown line. Elements should be removable and
serviceable while flare is in service. Density measurement and compensation need only
be considered if flared gas accounting is necessary and to provide corrections that allow
more suppressant for heavier hydrocarbon gases.
Flare gas recovery
Modify to Read
Note that various process equipment Vendors are currently offering the flare gas
recovery system/equipment as complete system (kit or skid based). The system includes
all required components. In some cases, the system is a proprietary design and
patented.
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Guidance on Industry Standard for API 537 Flare Details
a.
If specified by BP or its representative, Flare System Vendor shall investigate feasibility of
installing flare gas recovery system.
b.
Installation of flare gas recovery may be for economic or environmental reasons.
c.
If flare gas recovery system is installed, free path to flare (e.g., liquid seal drum or rupture
disk), independent of instrumentation, shall be provided to allow for failure of recovery
system.
d.
The following are requirements for flare gas recovery systems design:
1.
Recovery equipment capacity should be typically selected to handle normal or routine gas
flows to flare, with spare capacity to manage smaller releases from blowdown
valves/pressure safety valves.
2.
Flare gas recovery system should be installed downstream of flare knockout drum.
3.
Isolation valve should be provided to close gas flow to flare and diverts flow to flare gas
recovery system. For safety reasons, rupture disc or pin valve shall be installed in parallel
with this valve.
4.
During larger releases, recovery system should be isolated from flare system and full
flow is diverted to flare. Diverted gas to flare needs to be ignited and burned by flare.
5.
If flare gas recovery is implemented, flare stack will be left without flow. Therefore,
stack should have some kind of purge gas flow, either by gas or inert gas, to avoid air
egress into flare stack.
6.
During gas recovery operation, flare pilots may or may not be left in service. However,
decision to shut down pilots shall be evaluated by performing risk analysis and evaluation
of pilot ignition system availability and reliability.
7.
Some Vendors have developed and are offering flare ignition system without use of
conventional combustion based pilot design or have need to continuously operate these
pilots if they are used. Any eventual decision not to use continuously operated pilots shall
be checked against operating permit and/or local government imposed requirements.
In many cases, the operating permit requires that pilots be in service all the time and
loss of pilot flame is considered as environmental incident, which could result in fines.
Another important economic and safety benefit from having the flare gas recovered and
not being continuously flared is that the expected life of the flare tips and pilots is
increased. This is due to the fact that most flares are designed for the anticipated
maximum flow rates. However, the typical or routine flaring rates are substantially
lower. Low flaring rates, in most cases and applications, may be below minimum rates
for flare tip design, resulting in the tip mechanical damage and short tip life.
e.
Two basic types of flare gas recovery systems are being currently used in flare gas recovery
and compression: ejector system and compressor based system. Choice of equipment is
dependent on process design and installation specifics and shall be assessed individually in
each case.
The compressor based system is superior from an energy efficiency viewpoint and
provides larger system capacity. The ejector based system offers very high rate of
availability and is virtually maintenance free. However, it requires a high rate (due to a
low overall efficiency) of high pressure motive gas that, in many cases, limits its
application. The choice of equipment is dependent on the process design and
installation specifics and needs to be assessed individually in each case.
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4.6.1.8
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
Noise and visible light
Modify to Read
Noise sources include gas exit velocity, combustion produced noise, and noise from any
assist utilities used as a smoke suppression. In some cases, noise produced by
components located upstream of the flare can be carried along flare header
contributing to increase of overall noise emitted by the flare.
The tip design can incorporate some features, such as use of low noise injectors,
mufflers, and careful distribution of suppressant media at the tip.
4.6.1.9
a.
Unless local government or operating permit set requirements, flare shall be sited such that, at
maximum emergency flow rate, noise level at positions normally accessible to personnel
should not exceed 80 dB(A). BP may specify lower noise limit to be applied in a particular
case, e.g., offshore platform, ground flare. Deviations from this shall be subject to BP written
approval.
b.
Flare Vendors, in their quotations, shall provide information on noise emission from flare at
maximum emergency flow and at maximum smokeless flaring rate. Noise emission data shall
be provided as test report containing sound power levels in octave bands from 31 Hz to 8 kHz.
All measurements shall be made in accordance with CONCAWE report 2/79.
Other design considerations
Add
a.
Thermal movement of flare lines shall preferably be accommodated by providing flexibility in
piping layout or alternatively by expansion loops.
b.
Sliding expansion joints shall not be used.
c.
Any use of piping bellows shall be subject to approval by BP.
If flaring streams likely to contain H2S or water vapours, bellows should only be used if
essential.
5.
5.1
d.
Flare lines should slope all the way towards knockout drums at 1 in 400 minimum. If this is
not possible, drainage pots shall be provided at low points. Pots shall have level gage,
automatic pumpout facilities, and frost protection (where required).
e.
Horizontal sections of line to accommodate potential flow in either direction shall not be
acceptable.
f.
Pipe stressing and anchor and support design shall allow for thermal expansion or contraction,
two phase flow, slugs of liquid, ice formation in cold service, and fire protection, if any. To
avoid expensive over design, flare header mechanical design should be based on realistic
evaluation of maximum temperatures and durations of each relief situation and not simply
maximum specified relief temperatures.
g.
Consideration shall be given to need for hydrotesting after construction. If hydrotesting is
required, all components, particularly foundations and supports, shall be designed for this
condition.
Elevated flare equipment components
Flare burner
Term flare burner shall be interchangeable with term flare tip.
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5.1.1
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
Purpose
Add
a.
Flare capacity and mechanical design requirements will be specified by BP in equipment data
sheets.
b.
Flare tips shall be designed to burn with stable flame for full operating range at all anticipated
wind speeds.
c.
BP will specify design flow and available pressure drop for burner design. Vendor may quote
its proprietary burner design with adequate documentation for BP to review. Vendor
calculations shall include:
1.
Burner pressure drop requirements versus flow.
2.
Radiation contour curve at points designated in the specifications.
3.
Fuel gas and air rate for pilots.
4.
Calculations estimates for the minimum required purge rates.
5.
Estimated service life for burners at normal and minimum rates for purging.
d.
Flare tip shall not be over/under designed on capacity. Specified flare capacity should
represent actual anticipated operating conditions.
e.
Design should not be based on conditions that rarely occur during life of flare while sacrificing
all other design criteria, such as reliability and flexibility.
f.
Flare shall be operated within operating range that is specified in flare design.
Minimum flow to all internal parts of the tip should be maintained during flaring to
provide adequate internal cooling and eliminate potential for internal burning.
5.1.2
g.
Smokeless capacity and total capacity of flare tip(s) shall be specified or shall be subject to BP
approval.
h.
Flare tips shall be designed for minimum maintenance such that no maintenance is needed
between regular scheduled unit shutdowns.
i.
Flare tip design and materials selection shall comply with the following:
1.
Potential damage to tip and ancillaries due to high temperature and corrosion shall be
minimised.
2.
Selected materials shall not sustain embrittlement or lose critical physical properties
under anticipated operating conditions.
3.
Selected flare tip materials shall be suitable to survive flame lick and thermal cycling.
4.
If possible, tip components metal temperature shall be controlled to be below 482°C
(900ºF).
Unassisted pipe flare
Add
The term Pipe Flare is interchangeable with term Utility Flare Tip.
The following are additional requirements for pipe flare tips:
a.
Unassisted pipe flares shall typically be used only for duties if there are no restrictions on
radiation and production of smoke.
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Draft 21 March 2006
5.1.3
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
b.
Unassisted pipe flare design exit velocity for new flare should be selected in range of 0.2
Mach to 0.5 Mach for all operating conditions.
c.
Velocities up to 0.8 Mach may be allowed for emergency or blowdown conditions in retrofit
projects or rating of existing flare. However, exit tip velocity selection is primarily influenced
by gas composition and permit requirements for VOC emissions.
d.
Vendor may optionally quote its own proprietary design if cost benefits can be achieved from
reduced stack height, at specified supply pressure, and if other design specifications can also
be met.
Steam assisted pipe flare
Add
Steam assisted flares may be external, internal, combined steam jet type, or Coanda
type. If there is risk that freezing of condensate in flare could occur, only the external
type should be used unless prevention methods are implemented.
a.
Detail evaluation for using steam assist flare shall be subject to preapproval by BP.
Due to high energy cost, steam assist flare applications are becoming more restricted.
5.1.4
b.
Estimated steam supply rates shall be quoted for Vendor design.
c.
To reduce steam consumption, Vendor may quote optional controls, such as infrared sensors,
that sense flame characteristics and adjust steam flow automatically for smokeless operation.
d.
If using steam for smoke suppression, steam piping components at tip shall be of adequate
metallurgy, typically similar used for other tip components, to withstand thermal fatigue,
elevated temperature, and corrosive flue gas effluent characteristics.
e.
Steam supply piping shall have design provisions as outlined in 4.6.1.6.
Pipe flare with internal steam/air eductor tubes
Add
5.1.5
a.
Vendor shall quote steam and air supply rates for its design.
b.
Internal steam tubes should be designed as pipe in accordance with piping specifications
requirements.
c.
Steam tubes should be reinforced at exit. High alloy casting materials are preferred for these
reinforcements.
d.
Steam tubes should be internally supported to prevent failure from vibration.
e.
Air tube inlet should be Venturi type.
f.
Noise mufflers with ceramic fibre insulation are preferred.
g.
Steam supply piping shall have design provisions as outlined in section 4.6.1.6.
Air assisted smokeless flares
Add
Air may be used as the assisting fluid if this is either a more convenient or more
economical means than using steam, high pressure gas, or water.
Air assist is primarily used within facilities that do not have steam available for flare
system.
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Guidance on Industry Standard for API 537 Flare Details
The use of air assist will generally be uneconomical at high flare design capacities.
5.1.6
a.
If smokeless combustion of a gas stream is required and if this requirement can only be
satisfied by use of assisting fluid, air can be considered.
b.
Means by which air is provided will be specified by BP or shall be proposed by Flare Vendor.
c.
Vendor shall quote air blower motors that comply with noise requirements specified in BP
provided flare data sheets.
High pressure smokeless flares
Add
a.
High pressure flares should be considered if it is advantageous to minimise heat radiated from
flare, such as on offshore drilling production platforms, where this could allow for reduction in
flare stack height or length of flare boom.
b.
High pressure system design may also reduce flare header pipe size, reduce knockout drum
size requirement, and may overall provide for more economical design.
5.1.7
Mechanical details of flare burners
5.1.7.1
Flare burner dimensions and connections
Add
5.1.7.2
a.
Piping shall be provided in accordance with BP referenced pipe specifications.
b.
Joints between flare stack and flare tip, such as tip joint, utilities (steam, air, water, pilot gas,
etc.), and flame front generator (FFG) piping, regardless of size, shall be flange joint type.
c.
Except for electrical conduits, joints shall not be threaded.
Flange ratings
Add
5.1.7.3
a.
Flange rating shall be provided in accordance with data sheets.
b.
Piping interface connections shall be flanged.
c.
Process gas inlet flange size less than and including DN 600 (24 in) shall have ANSI B16.5,
Class 150 raised face dimensions.
d.
Process gas inlet flange size larger than DN 600 (24 in) shall comply with ANSI B16.47 or
equivalent.
Flare burner handling and lifting lugs
Add
a.
Three lifting lugs on 120 degree centreline shall be supplied.
The lifting lugs are not reusable after the tip has been in service. Consideration for
removal of old flare tip may include:
•
Cutting off the old lifting lugs and welding on new ones if feasible.
•
Vendor to provide predesign alternate to using lifting lugs to facilitate tip removal,
i.e., securing lifting chains around tip to allow removal.
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Draft 21 March 2006
5.1.7.4
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
b.
If height of flare is such that mobile lifting facilities available at site are stated by BP as not
adequate for removing and replacing tip, flare stack shall have derrick support structure
equipped with Jin poles and lifting cables to facilitate removal of flare tip.
c.
In normal flaring operations, lifting beam shall be lowered below level of top platform or
below bottom of inverted gas seal, if fitted, to position where it will not be affected by flare. It
shall be stored in a manner such that full load testing is not required before subsequent reuse.
d.
Suitable lifting tackle shall be provided to raise lifting beam to lifting position. Wire ropes
used for lifting beam on tip, and seal, if fitted, shall be replaced by reeving lines and removed
to storage.
e.
Lifting beam anchor system and all associated lifting equipment shall be designed for
temperatures to which they will be subjected during flaring without significant deterioration.
System shall also be capable of operation after exposure to these temperatures.
Materials
Add
a.
Materials of construction for tips shall be suitable for full range of metal temperatures to be
encountered.
b.
Materials selection shall take in consideration the following:
1.
Tip type used.
2.
Tip design.
3.
Flare gas composition.
4.
Flowrate.
5.
Cooling effect of smoke suppressing steam or air.
6.
Burn back at low flows or purge flow.
c.
Materials for tip and related components shall be subject to BP approval.
d.
Flare tip shall be constructed of materials specified on equipment data sheets. BP may,
however, consider change in material selection proposed by Vendor if safety and reliability of
flare tip are not compromised and proposed change provides cost savings for BP.
e.
Unless approved otherwise, minimum material grade for flare tip shall be Type 310S SS for
upper 3 m (10 ft).
g.
Flare tip pilots, igniters, and steam ring
h.
1.
Flare tip pilots, igniters, and steam ring (if steam is smoke suppressant) shall be Type 321
SS as a minimum.
2.
Materials for these components should be of same material grade as flare tip.
3.
Type 316 SS should not be used, and Type 316L SS is not recommended, both because of
potential for catastrophic oxidation.
Bolting
1.
Typical material used for bolting flanges shall be cadmium plated A-193-B16 Studs and
A-194-2H Nuts.
2.
Bolting of grades B and M and Class 2 of B and T should be avoided because of stress
corrosion cracking.
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5.1.7.5
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
i.
Gaskets shall typically be Flexitallic Style CG or equivalent, Type 304 SS filled with filament
materials, and with Type 304 SS gage ring if Style CG is used.
j.
Materials for flare tip flanged joint and remainder of flare tube/body, lower than 3 m (10 feet),
may be carbon steel but shall be compatible with flaring stream (corrosion, cryogenic stream,
etc.).
k.
Components that are made of carbon steel shall have minimum corrosion allowance 3 mm (1/8
inch) for unlined flare tube/body and 1,5 mm (1/16 inch) for refractory lined flare tube/body.
l.
Pilot piping between pilot gas filter, located at the base of flare stack, and flange near flare tip
shall be either carbon steel or Type 304 SS.
m.
Piping from base of tip to pilot shall be of higher grade metallurgy, typically Type 310S,
schedule 40S, minimum.
n.
Igniters piping, flame front Generator piping, up to flange near flare tip may be carbon steel.
o.
Remainder of piping to pilot shall be of higher grade metallurgy, typically Type 310S,
schedule 40S, minimum.
p.
Refractory
1.
If damaging burn back inside tip cannot be prevented or is anticipated, refractory lining
of tip should be considered.
2.
Type of refractory and method of application is discussed in 5.1.7.11 and shall be subject
to BP approval.
3.
As an alternative to use of refractory, use of higher grade of metallurgy for tip material
may be considered.
q.
Material of domestic origin is preferred, although Vendor may request, in writing, approval to
use foreign material prior to commencement of fabrication.
r.
All materials and components for flare system shall be new, unused, and free of mill scale and
rust. If material from Vendor existing inventory is proposed, BP or its representative reserves
right to inspect and approve subject material prior to commencement of fabrication.
Welding requirements
Add
a.
Welding procedures shall be subject to BP for approval prior to start of fabrication.
b.
Number of welds exposed to high temperatures shall be minimised to reduce potential for
cracking due to thermal stresses.
Cracking of the weld joints can also cause gas leaks, which increases flame
impingement that will result in high temperature corrosion damage.
c.
Butt welds shall be full penetration welds.
d.
Butt welds in flare body and piping shall be 100% radiographed.
e.
Radiographic procedures and acceptance criteria shall comply with ASME B31.3.
f.
Welds joining components of type 310S SS to same or to carbon steel materials shall be made
with 309 filler rods.
g.
Welding procedure and filler metal for welding of all dissimilar metal joints shall be obtained
from BP prior to the start of fabrication.
Page 50 of 78
Draft 21 March 2006
h.
5.1.7.6
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
Welders’ Qualification Certificates shall be subject to review and approval by BP or its
representative before commencement of fabrication.
Flare burner piping
Add
Requirements using steam for smoke suppression shall comply with 5.1.3.
5.1.7.7
Hydro testing for flare burners
Add
a.
If practical or specified by BP, Vendor shall perform hydrotesting of flare burner components.
Requirements for hydrotesting will be included in flare data sheets.
The decision on the acceptability of pneumatic or hydraulic testing should be taken at
an early stage in the design and cannot be left until the line is constructed.
5.1.7.9
b.
Vendor shall notify BP or its representative, a minimum of 7 working days prior to all
pneumatic, hydrostatic, and functional testing.
c.
Test chart of all hydrostatic tests shall be provided if requested by DS 22-201. Duration of
tests shall comply with DS 22-201.
Wind shields for flare burners
Add
5.1.7.10
a.
Continuous flare operation under all operation wind conditions shall be guaranteed.
b.
Vendor may also propose wind shield, as alternate, for its proprietary flare tip design to further
ensure stable operation under maximum wind condition.
c.
Wind shield, if provided, shall be:
1.
Externally mounted on tip.
2.
Complete with floor plate or solid type cooling gap design to prevent flame lick at tip.
Muffler for flare burners
Add
a.
Vendor design shall comply with noise specification requirements. Design provisions may
include muffler to limit noise from flaring.
b.
For installation on offshore platform, Vendor may consider seawater injection at flare tip for
noise and radiation reduction.
If water is injected into a high pressure gas discharge, shock associated noise is
significantly reduced.
5.1.7.11
Refractory for flare burners
Add
a.
Vendor shall ensure that burner internals can withstand maximum temperature that may result
if internal burning occurs at minimum turndown flow rates.
b.
Internal lining may be proposed to protect burner from thermally induced stress due to high
temperatures that may occur.
Page 51 of 78
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GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
Thermally induced stress is the dominant cause for burner metallurgical failure. A thin
layer of refractory can reduce the burner metal temperature significantly with flame
impingement.
c.
Recommended refractory lining should include refractory mixed with stainless steel fibres.
Addition of stainless steel fibre in refractory has proven to be effective in preventing
micro cracks that develop under thermal stress and propagate into visible cracks that
could cause premature burner failure.
d.
With certain refractory, repair or replacement of lining may be considered specialist task.
e.
Refractory curing
f.
5.1.7.12
1.
If possible, refractory curing should be performed in Flare Vendor shop in which much
better curing conditions can be achieved.
2.
Instructions of refractory manufacturer should be followed rigorously.
After installation, tip refractory shall be protected from wet conditions before setting or frost
after setting.
Maintenance issues
Add
5.1.8
a.
Flare tips shall be designed for minimum maintenance such that no maintenance should be
needed between unit overhauls.
b.
If specified by BP, Vendor shall provide ladders and maintenance platform for access to flare
tip.
c.
Special tools required for removal or installation of flare burner shall be listed by Vendor as an
addition.
d.
If weight of flare burner is significantly increased by refractory installations, Vendor shall note
requirements for special design provision for local lift at flare platform or davits to allow
removal or inspection of tip.
e.
Flare tip assembly shall be compact and lightweight to facilitate removal. Arrangements of
ancillaries shall allow adequate space for access and maintenance of all system components
without removal of any major assembly.
f.
Piping, unions, and valves shall be flexible and easily accessible for operation and
maintenance.
Operations
Add
Complete sets of operating manuals for flare system shall be provided in accordance with Vendor
data request forms provided by BP or its representative.
5.2
Pilots
5.2.1
Purpose
Add
a.
Pilot burners shall be ignited by reliable ignition system capable of operating under relevant
ambient conditions.
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GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
b.
Flare pilots shall burn continuously whether flare burner is ignited or not.
c.
Pilots should be of energy efficient design proved by at least 2 yr of operation in similar use.
d.
Pilot shall be mounted to outside of flare stack such that assembly is externally removable.
e.
If there is long history of pilot malfunctions that are not attributed to poor pilot design or
selection or if periods between scheduled flare outages are too long, use of retractable pilot(s)
should be considered.
f.
Use of retractable pilot arrangement should be also considered in severe duty applications,
such as toxic gases and wet corrosive environments.
Some operating permits require continuous monitoring of flare pilot operation. Loss of
pilots flame indication is qualified as environmental incident, even though pilots remain
lit. These events shall be reported, and potential citations may follow.
g.
Pilot head assemblies should be manufactured from high nickel alloy to ensure long service
life.
h.
Flame retention devices and wind shrouds should be used to achieve reliable ignition and
stable pilot flames.
i.
Pilot wind shield should be capable to control outside wind, up to 241 km/hr (150 mph),
prevent downdraft, and operate efficiently in heavy rains.
j.
Pilot gas supply
1.
Pilot gas supply shall be from high reliability source approved by BP.
Typically, natural gas is used. Pilot gas can be taken directly from plant fuel gas main if
available.
2.
Pilot gas supply line shall be by top mounted branch, with two filters in parallel or dual
filter at the base of flare.
3.
BP may require an automatic backup gas supplies if necessary to achieve acceptable or
required overall reliability and availability of pilots.
4.
Vendor shall confirm that pilot gas provided by BP will work satisfactorily in flame front
pilot ignition system without adjustment to air and gas flows (pilot gas molecular weight
and calorific value range).
It is extremely important to provide Vendor with accurate data on the gas that will be
flared and on gas that will be used for pilot operation. Flare Vendor will alter the
material selection from standard if necessary and appropriate.
5.2.2
5.
Differential pressure gage shall be fitted across filter to check pressure drop through
filter.
6.
Pilot gas pressure reducing valve shall be provided. Valve shall be self operating type,
placed downstream of filters.
7.
Control system shall provide contacts for pilot flame failure and panel lights for pilot
flame on and pilot gas on.
General description
Add
Due to their complexity, compressed air pre mix pilots should be limited to installations that operate
in very harsh environmental conditions.
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5.2.3
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
Mechanical details
Add
5.2.5
a.
Refer to 5.1.7.4 for reference on tip pilot components and pilot piping material selection.
b.
Use of stainless steel piping material for pilot gas supply from plant gas system connection,
typically located at base of flare structure due to cost, is not mandatory, but its use is highly
recommended. Vendor shall provide cost, as a separate line item in proposal, of material
upgrade from standard carbon steel to stainless steel material.
c.
Strainers for prevention from pilot gas orifice plugging shall be used in close vicinity of tip, as
well as at base of flare stack. If stainless steel is used for pilot gas risers, from base of stack to
pilot tip, only one strainer, located at base of stack, could be used.
d.
Electronic/electrical igniters and flame front generator piping connection shall form integral
part of pilot heads.
e.
Pilot flame failure detector should be fitted to each pilot burner. This device is normally dual
thermocouple or flame ionisation probe.
f.
Rain shields around air intakes on pilot mixer should be used to prevent water intake into pilot
combustion zone during rain.
Maintenance
Add
Vendor shall provide training and outline preventative maintenance guidelines for flame pilots in
maintenance and operating procedure manual.
5.3
Ignition equipment
5.3.1
Purpose
Add
a.
Flare tip or burners shall have pilot burners capable of igniting flare gas under all relevant flow
conditions and ambient conditions.
b.
Pilots shall have ignition system capable of igniting pilot gas under all relevant flow
conditions and ambient conditions.
c.
Automatic ignition system shall be primary means of ignition. Independent manual backup is
recommended. Use of flare gun shall not be acceptable as independent manual backup system.
d.
Ignition system components shall be suitable for surrounding zone classification.
e.
Ignition panel shall, if possible, be located in non-hazardous classification area.
Note that, in offshore installations and other compact, restricted ventilation areas, the
location of the ignition panel in a non-hazardous classified area is unlikely to be
practical. Regardless of the panel location relative to the tip, care should be given to
compliance with manufacturer’s recommendations regarding pipe routing between the
panel and the flare tip to be ignited.
f.
Igniters fuel gas system shall be designed such that it is not in itself a source of hazard.
g.
Igniters shall form integral part of pilot heads.
h.
With BP approval, novel ignition systems, such as ABB Gas Technology and UMOE
incendiary pellets, may be considered.
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Draft 21 March 2006
5.3.2
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
General description
•
Compressed air flame front generator
Add
a.
Flame front generator shall provide remote ignition of flare pilots from generator panel
mounted at grade.
b.
Electronic igniter for flame front generator system, if used as primary ignition source, shall be
automatic and self monitoring with automatic relight capabilities.
c.
Flame front generator (FFG), manual or automatic, shall be used as backup for spark ignition
pilot system.
d.
Vendor may propose alternate arrangement of the pilot and igniters gas and air supply system
as shown in corresponding section in Figure 10 of API Std 537 or as ,e.g., a packaged unit.
•
ABB Gas Technology and UMOE ballistic ignition systems
Add
5.3.3
Mechanical details
5.3.3.1
Spark ignition at pilot tip
Add
5.3.3.3
a.
Each pilot shall have a dedicated igniter rod and panel switch.
b.
Flare igniter panel shall be enclosed in weatherproof NEMA 4 panel or shall comply with area
classification requirements specified in data sheets.
c.
External panel preparation shall comply with requirements specified in data sheets.
d.
Flame front generator (FFG), manual or automatic, shall be used as backup for spark ignition
pilot system.
e.
Local ignition panel shall indicate location and type of failure.
Compressed air flame front generator
Add
a.
Each pilot shall have dedicated flame front line.
b.
One manifold that connects these lines with necessary valve to accommodate ignition of one
pilot at the time shall be provided.
c.
Use of one front flame line to simultaneously ignite more than one pilot shall not be allowed.
d.
Flame front generator shall be mounted in self supporting steel panel of carbon steel
construction, complete with rain shield suitable for typical installation in Class I, Group D,
Division 2, area.
e.
Flame front generator panel shall contain:
1.
Manual fuel gas bypass valve.
2.
Automatic electronic solenoid control valve.
3.
Removable fuel gas metering flow control orifice.
4.
Fuel gas pressure gage.
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Guidance on Industry Standard for API 537 Flare Details
5.
Compressed air inlet with manual bypass valve.
6.
Removable air metering flow control orifice and pressure gage.
f.
Flame front line shall have drain provision since humid moist air will enter unused flame front
line, where it cools, and will result in water buildup in line. This can cause malfunction of
flame front generator.
g.
Flame front generator piping should have no pockets upstream of control panel. Line shall be
of constant diameter and free from constriction or enlargements.
h.
Ignition panel shall also contain, on both gas and air lines, stop valves, regulating needle
valves, pressure gages and nonreturn valves. Downstream of mixer and the ignition chamber,
means shall be provided to direct flame front to each of pilots in sequence.
i.
Flame front generator panel shall also contain:
1.
Power ON/OFF switch.
2.
Manual/Automatic selector switch.
3.
Manual spark control pushbutton.
4.
Pilot indicator lights for each pilot..
j.
Ignition chamber shall have continuous electronic sparking device and sight port.
k.
Generator panel shall include power transformer that shall deliver power to solid start sparking
device.
l.
Vendor shall review fuel gas characteristic and determine if heat tracing and insulation of
flame front line is required at minimum ambient operating conditions.
In cold weather conditions, the flame front line can cause flame out from cooling the
flammable mixture as it flows to the pilot. The flammable characteristic of the fuel gas
may also change in the line if cooling causes dew point fallout of heavy hydrocarbon
components.
m.
5.3.3.4
Ignition of gas-air mixture in ignition chamber shall be by spark plug, which shall be energised
by main transformer. Backup ignition by piezoelectric means shall be provided. Ignition may
be manual or fully automatic as specified by BP.
Self inspirating flame front generator
Add
Self inspirating flame from generator shall only be used in locations where compressed air is
unavailable or if service application is preapproved by BP.
5.3.4
Operation
Add
a.
Flare system shall be purged until oxygen content is less 2% before ignition of flare pilots.
In case of a major unignited gas release, it may be considered safer to extinguish all
sources of ignition in the facility, including the flare pilots.
b.
Prior to facility shutdown, flare pilots shall be extinguished before reducing purge gas flow
rates below minimum requirement, since oxygen could enter flare and detonation could take
place if ignition source is present.
Page 56 of 78
Draft 21 March 2006
c.
5.3.4.2
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
As a minimum, common trouble alarm shall be sent to control room to alert operator of any
failure on flare system.
Compressed air flame front generators
Add
5.3.4.4
r.
Pressure requirements for gas and air may change due to variations in gas composition or
changes in ambient temperature and pressure. Adjustable pressure regulators for air and fuel
gas supply shall be provided.
s.
If fully automatic, ignition system for flame front generator shall perform the following:
1.
On press button initiation, open flow of ignition gas and air, and fire sparking plug to
ignite first pilot.
2.
Monitor, through thermocouples installed in pilots, whether pilots are on.
3.
If pilot is not on, make three attempts to relight that pilot. If this fails, give an alarm.
4.
As each pilot is ignited, turn distributing valve and repeat actions to ignite second pilot,
and so on until all pilots are lit.
5.
In addition, full manual operation shall be provided.
Operator training
Add
Operator training assistance during initial startup and commissioning of flare system shall be
included as an addition in Vendor quote.
5.3.6
Troubleshooting
Add
Vendor shall provide troubleshooting guide for flare system as part of operating manual.
5.4
Flame detection equipment
5.4.1
Purpose
Add
a.
All flares shall have continuous pilots with flame detection and provision for remote pilot
reignition.
b.
Continuous pilots are typically mandatory for all flare system with hazardous or toxic waste.
Local regulations shall be reviewed early in project design phase.
c.
Each pilot shall have flame failure detection, which is required to perform the following
functions:
d.
1.
Alarm to indicate detector fault.
2.
Alarm on pilot flame failure.
3.
Indicate “pilot on”.
Common alarm in control room shall be activated for any of failures detection listed in c.
Local ignition panel shall indicate location and type of failure.
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Guidance on Industry Standard for API 537 Flare Details
Although, in practice, pilot flame failure detection thermocouples are not reliable, there
is currently no reliable alternative. Development in alternate monitoring systems, such
as acoustic monitoring and optical monitoring, has shown improved reliability in actual
service applications and may be considered as alternative to use of thermocouples.
5.4.2.2
e.
Pilot sensor shall be electrically insulated from metal structures to protect it from possible
damages caused by lighting.
f.
On BP request, retractable thermocouple system to facilitate thermocouple removal while flare
is in service shall be quoted as an extra.
Flame ionisation
Add
a.
Each pilot shall have its own dedicated monitoring and control circuits.
b.
Flame ionisation system shall have backup power provision.
The flame ionisation monitoring is a very reliable pilot flame monitoring technique. The
instant that the flame is lost an open circuit is detected by the control system, allowing
the control system to immediately switch to the reignition mode to attempt to reignite
the pilot. The ionisation detector typically has a direct spark ignition system at the flare
pilot. The electrode used in the pilot nozzle is typically a rugged rod design system that
will have a much longer service life than a thermocouple. The rod is insulated along the
entire length of the pilot by a high temperature ceramic rod.
5.4.2.3
Optical systems
Add
a.
Sensor shall be located as close to flare as practical to minimise false alarms and facilitate
installation and maintenance.
b.
Alarm delay shall be added to minimise false alarm that may result from temporary blocking
of flame sensor due to clouds or rain.
c.
Sensors shall be located outdoors, since flame detection may be affected by a standard glass
window.
The optical sensor can determine the presence of a pilot flame by computing the radiant
energy emitted by the flame from IR or UV spectral band. Optical lenses are used to
focus the energy emitted from the pilot flame onto the infrared or ultraviolet detector.
Optical sensors will have a maximum pilot enclosure operating temperature. Direct
sunlight may raise the internal pilot enclosure by 8ºC (15ºF). With typical
recommended ambient temperature of 49ºC (120ºF), the optical sensor enclosure may
require cooling provision and heat shield protection.
5.4.2.4
Acoustic systems
Add
a.
Acoustic flare monitor sensor shall be located at grade to facilitate inspection and
maintenance.
b.
Sound conveying piping shall be straight with few fittings.
c.
Acoustic system shall have backup power supply.
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Guidance on Industry Standard for API 537 Flare Details
5.4.3
Mechanical details
5.4.3.1
Thermocouples
Add
a.
Thermocouples bimetallic junction shall be placed directly in pilot flame tip or in contact with
portion of pilot flame, where it can detect heat being produced by pilot.
b.
Thermocouple shall be positioned inside pilot nozzle such that it is protected from false signals
due to main flare burner, other pilots, external crosswinds, and external flame impingement.
Type K thermocouple is generally used for flare pilot operational sensor. Type K
thermocouple consists of nickel-chromium vs. nickel-aluminium metals, which has
temperature range -200ºC to 1 250ºC (-328ºF to 2 282ºF).
c.
Thermocouple sheath material shall be 310SS for flares in normal sweet pilot gas service and
446 SS for flare service that contain hydrogen sulphide in pilot gas or main flare gas stream.
d.
Thermocouple measuring junction shall be in electrical contact with sheath or thermowell.
This will extend service life of thermowell, especially in corrosive environments.
5.4.4
Operation
5.4.4.4
Acoustic systems
Add
a.
Moisture buildup in sound sensor piping from flare pilot shall be avoided. Moisture could
result in dampening pilot sound and may lead to false alarms.
b.
Drains on piping should require periodic checking to ensure no liquids are present.
c.
In cold climate, potential plugging of flame ignition line due to freezing shall be addressed.
5.4.5
Maintenance
5.4.5.1
Thermocouples
Add
If necessary, special tools to facilitate maintenance for system shall be provided.
5.4.5.2
Flame ionisation
Add
Unit shall have backup monitoring system or retractable pilot system to allow for emergency repair.
5.5
Purge gas conversion seals
5.5.1
Purpose
Add
Refer to 4.6.1.4.2 for more information on purge gas conversion seals.
Page 59 of 78
Draft 21 March 2006
5.5.3
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
Mechanical details
Add
These purge seals are usually propriety in design and, if requested by BP, individual Vendors shall
submit mechanical design details for review.
5.5.4
Maintenance
Add
If required, special tools required for maintenance repairs shall be provided by purge gas seal
Vendor.
5.6
Elevated flare equipment components support structure
5.6.1
Piping
Add
a.
Required auxiliary flare piping for plant facility tie-ins shall be provided where required for
flare operation.
b.
Such piping may include:
1.
Pilot gas line.
2.
Flame front igniters line to each pilot.
3.
Steam line to main smoke suppression system, if used.
4.
Steam line to auxiliary system.
5.
Oxygen sampling lines.
6.
Assist gas, if used.
7.
Electrical conduit.
8.
Instrumentation conduit.
c.
Piping shall be design in accordance to attached BP reference pipe specification.
d.
In elevated flare, piping shall be flanged at base of tip for ease of tip removal, with suitable
flanges for spading points at base of stack.
e.
Location of connecting joints and type of joints at grade will be specified by BP
f.
Differential thermal expansion of auxiliary flare piping shall be specifically allowed for in
design.
g.
Piping in elevated flares shall preferably be anchored at top of stack in vicinity of bottom of
tip and guided along length of stack, with expansion taken up by flexing of sufficient
horizontal length of connecting piping at ground level.
h.
In potentially high temperature environment, galvanised and stainless steel pipe and fittings
shall not be in contact with each other.
5.6.2
Aircraft warning lighting
5.6.2.1
Add
Lighting provisions shall comply with requirements of local government, as well as state or federal
government.
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5.6.2.2
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
Add
Vendor shall provide, as a separate item, price for retractable aircraft warning lighting.
5.6.3
Platforms and ladders
Add
a.
Unless specified otherwise, structural material shall be ASTM A36, galvanised.
b.
Stair treads should be open type metal, similar in pattern to main flooring, with visible slip
resistant front edges and hot dipped galvanised finish.
c.
Platforms and ladders on flare stacks should present minimal wind resistance.
d.
Elevated flares shall have ladders and platforms to provide:
e.
1.
Access for maintenance and inspection of tip.
2.
Inspection of guy attachment points on guyed flares.
Access platforms shall be provided for:
1.
Elevated manways on process equipment.
2.
High level fixed fire monitors.
3.
Instrument locations.
4.
Manifold locations.
5.
Inspection of flare structure.
f.
First platform shall be located approximately 4,5 m (15 ft) above grade, with remainder of
platforms at interval of 9 m (30 ft), maximum.
g.
Permanent ladders from ground level should, if possible, be directly supported from plant or
its supporting structure and kept clear of paving to avoid effects of settlement and corrosion at
ground level. If ladder bases bear on soil supported paving, allowance should be made for
settlement of paving.
h.
360 degree top work platform near tip flange shall be provided.
i.
Ladders shall extend from first platform to flare top work platform.
j.
Ladders shall have safety cages and hand rails in accordance with presiding regulating codes.
In the UK, permanent ladders for industrial use should comply with BS 5395, and
stairway treads should comply with BS 4592. EEMUA Publication 105 gives
recommendations and typical details for the design and general construction of
stairways, ladders, access platforms, ramps, and handrails.
Hand railing shall comply with to BS 6180.
In the U.S., hand railing shall comply with OSHA standards.
k.
Safety cages shall be of circular shape in plan.
l.
Self closing gates should be provided at platform exits to all vertical ladders.
m.
Gate should open inwards towards platform and hinge from outer edge of platform. Self
closing safety bars may be considered in lieu of gates. Safety chains shall not be permitted.
n.
Ladder rung (steps) design shall be based on an 890 N (200 lb) concentrated live load.
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Guidance on Industry Standard for API 537 Flare Details
o.
Ladder connections shall be designed for minimum total load (dead plus live) of 4,4kN (1 000
lb).
p.
If chequer plate flooring is used to fulfil structural task, thereby stabilising compression flange
of beams, fixing should comply with structural requirements. Corrosion should be allowed for
if developing such a detail.
q.
If two or more stacks are within 150 m (490 ft) of each other, access ladder shall be placed
such that stack shields ladder from heat radiation from other stacks.
5.6.4
Structural design
5.6.4.1
General
Add
a.
Structural design of elevated flares, whether guyed, mast (self supported), or tower supported,
shall be performed by specialists in this field with proven record of experience.
b.
Single Vendor should be responsible for design, detailing, supply, and erection. Materials of
construction, standards for fabrication, inspection, and nominated fabricator shall be subject to
BP approval.
c.
Self supporting stack for facilities located within North America Region shall be designed in
accordance with API Std 560.
d.
Facilities located outside of North America Region shall be designed in accordance with
ISO 13705.
e.
Unless specified otherwise, to lengthen period between inspections, the following
constructional requirements shall be satisfied:
1.
Load carrying connections shall be bolted.
2.
Steelwork and bolting shall be galvanised or aluminium sprayed after fabrication.
3.
Design of flare stack shall take into account proposed method of transportation and
erection.
4.
Specification for bolting of flanges shall take fatigue into consideration.
f.
Structural calculations shall be submitted to BP for review and shall demonstrate that in
proposed design Vendor addresses design requirements that are listed in equipment data
sheets.
g.
The following are some aspects of design that shall require consideration:
1.
Static wind loading.
2.
Dynamic effect of wind, including effect of wind turbulence on dynamic response of
structure.
3.
Earthquake loads.
4.
Internal pressure and sudden internal pressure.
5.
Vortex shedding phenomenon.
6.
Dynamic response of guys, including “galloping” response.
7.
Ice loading on structure and its effect on static and dynamic response.
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8.
Local stress at guy attachment points and local stress due to choice of structural element,
i.e., in the case of tubular joints, punching shear stress.
9.
Radiant heat and its effect on riser, guys, upper guy fixings, and upper members in the
case of a structure.
10. Effect of fatigue. Analysis shall be performed in accordance with Department of Energy
guidance notes - Offshore Installations: Guidance on design and construction - using n/N
no greater than 0,5 for design life. Fatigue design shall take into account full extent of
allowable misalignment of circumferential seams.
11. Shell and strut buckling for static and dynamic loads.
h.
i.
j.
Foundations
1.
Foundation design should be by main civil contractor to loads and moments specified by
supporting structure designers.
2.
If guys are used, specific attention shall be paid to possibility of differential settling of
main foundation and those of concrete block foundation.
3.
Earthing (grounding) of flare structure and riser shall be independent of foundation
reinforcement and piling.
4.
Templates for anchor bolts shall be supplied and delivered to site in a timely manner to
enable associated civil works to commence.
5.
Templates for anchor bolts and design details of concrete block foundation shall be
provided by Vendor to site in time for foundation construction. This requirement shall be
written into contract of supply to ensure compliance.
Guylines and terminations
1.
Radiation shield in type 321 SS shall be provided if effect of incident heat flux will
reduce termination efficiency by more than 5%.
2.
Sufficient articulation shall be provided in connections between guy rope terminations at
one end and rigging screws at other end to ensure that no bending moment is transmitted
to their respective attachment points.
3.
In light of experience, guys and associated equipment (i.e., shackles, turnbuckles, anchor
points) should be checked and regreased every 4 yr to 5 yr.
4.
Guys should be retensioned after first year of operation and every 4 yr to 5 years
thereafter.
Effect of temperature
1.
Structural components shall be designed to ensure that allowable stresses will not be
exceeded at temperatures that may be reached due to thermal radiation, hot gas flow, and,
if applicable, flame impingement.
2.
In performing this analysis, specific attention should be given to wind effects. Analysis
should address:
a)
Flame tilt due to high winds and radiation levels on structures below height of tip.
b)
Radiation levels on guy supported structure and guy ropes on downwind side of
flare.
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Guidance on Industry Standard for API 537 Flare Details
c)
k.
5.6.4.2
Account should be taken of minimal wind speed case if flame is vertical or near
vertical, and incident radiation on flare tip and structure is usually higher than in
high wind speed case.
Flanges for guyed flares
1.
Flanges for risers of guyed flares shall be of forged weld neck type with flat faces.
2.
Jointing faces of flanges should be machined after welding flanges to pipe.
3.
Accuracy shall be such that, after assembly, deviation of centreline from vertical shall not
be greater than 30 mm in 100 m (0,36 in in 100 ft).
4.
Gas inlet to guyed flares should be of same size as riser and may be in form of either
“tee” branch or bend.
5.
In both cases, sufficient reinforcement shall be provided to transmit vertical loads in riser
from above inlet to below inlet without exceeding allowable stress levels.
6.
Near atmospheric pressure in riser does not demand use of raised face flanges.
7.
Full face gaskets with supporting inner and outer rings should be used.
Design loads
Add to First Paragraph
a.
b.
Structure or part of structure shall be designed to resist applicable dead and live loading,
including the following:
1.
Structure dead loads (including fireproofing and insulation).
2.
Imposed loads.
3.
Weight of process contents of test fluids, also process contents resulting from credible
maloperation.
4.
Lifting equipment, including dynamic effects.
5.
Dynamic or periodic loads resulting from operating machinery.
a)
Wind, snow, and ice loading.
b)
Seismic loading.
c)
Settlement.
d)
Thermal loading - particularly for structures subject to high temperature variation
and long structures.
e)
Pipe anchor and surge condition loads.
f)
Loads arising during construction and erection.
g)
Lack of fit.
h)
Flare platform shall be sized and structurally suitable for maintenance activities.
The following imposed loads shall be used in design of structures:
1.
Platforms, walkways and stairways (not supporting any equipment and not intended as
working platforms): 2,5 kN/m2 (36 750 psi).
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Guidance on Industry Standard for API 537 Flare Details
2.
Working platforms and platforms over which heavy equipment may be transported or
stored: 5,0 kN/m2 (73 500 psi) or the actual superimposed equipment load, whichever is
the heavier.
3.
Earthquake loads.
1.
If appropriate, seismic loads shall be calculated in accordance with national standards or
codes applicable to site of works.
2.
If such standards or codes do not exist or, with approval of BP, are considered
inappropriate or if these do not refer to specialised and hazardous items of plant, a study
shall be performed to determine potential risk and level of seismic activity, to determine
appropriate design loading.
3.
For loading combinations with seismic load, increase in permissible stresses may be
allowed. However, proposals shall be submitted and shall be subject to BP approval.
Add
i.
Special loads
Add
Unique design problems, such as transportation loads during shipping, shall be taken into
account.
5.7
Knock-out drums and liquid seals
5.7.1
Knock-out drum
Add
Refer to 4.6.1.3.
5.7.2
Liquid seal
Add
Refer to 4.6.1.4.3.
5.8
Blowers and drivers
5.8.1
General description
Add
a.
If approved by BP, forced draft air can be used to achieve smokeless flaring. Two speed air
blower or multiple blowers shall be provided as follows:
1.
Low speed shall be for continuous operation.
2.
High speed shall be actuated by pressure switch from flare header, with manual override.
3.
Damper on blower discharge can be used for flow variation requirements.
4.
Blower unit shall include inlet screen, removable for maintenance.
b.
Air intake for fan shall be ducted from safe area.
c.
Ducting shall be sized and provided by Vendor.
d.
Sound pressure level shall not exceed 85 dBA if measured 1 m (3 ft) from blower motor.
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6
6.2
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
Multi-burner, staged flare equipment components
Pilots
Add
6.8
a.
Flare shall have proper number of pilot burners to maintain stable source of ignition for
discharged gases.
b.
Pilots shall be able to light main gas burners on commencement of gas flow and during all
operating conditions.
c.
Ground flares shall have minimum of two pilots/burners per stage to ensure safe and reliable
light up of main gas burners.
d.
If only two pilots are used per stage, they should be installed on first and last burner in row.
e.
Precise number of pilots should be determined in accordance with layout of burners, number
of stages used, and climate conditions (wind direction, ambient temperature, etc.).
Operations
Add
7.
7.1
a.
Once flare is commissioned, control unit should monitor operations and operate sequencing.
No operator intervention should be required. However, it is recommended that operations of
flare system be observed to ensure that preselected pressure and control parameters/settings
operate satisfactorily.
b.
Sweeping combustibles from system for shutdown
1.
If shutting down system, it may be necessary to sweep all combustible gas from headers.
Inert gas injection into flare header, at point farthest from flare, can be used.
2.
Inert gas flow should continue until some time after flare is extinguished to sweep away
all combustibles remaining in system.
3.
Pilots should remain in service during sweep operation.
4.
If plant personnel are scheduled to enter flare area for any reason, all stage headers shall
be purged.
Enclosed flame flares
Purpose
Add
5.
To achieve high thermal destruction efficiency that cannot be achieved in open flame
environment.
6.
To safely dispose low BTU value gas that is not possible to achieve with open flame type of
flare, such as tank farm gas blanketing, terminals loading/unloading activities, and purging
with inert gases. In some applications, supplementary firing may be required to maintain
desired combustion chamber temperature.
7.
To provide temporary service (mobile unit) as backup unit for facility flare.
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7.2
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Guidance on Industry Standard for API 537 Flare Details
General description
Add
a.
Two basic enclosed flame flare designs should be considered: bottom fired units and side fired
units.
b.
Bottom fired units should be selected for the following service applications:
c.
d.
e.
7.2.1
1.
For light gases or gases that will not smoke and in very low flow applications.
2.
If liquid carryover is not possible.
3.
For waste gases with high allowable pressure drop across the burner.
4.
For applications where flow is high or constant and staging is not required.
Typical applications of bottom fired enclosed flame flare are:
1.
Gas plants with high pressure gas.
2.
Landfill gas distraction.
3.
Loading terminal vapour control.
4.
Applications for which temperature control in a chamber is required for destruction of
waste gases.
Side fired units, are normally selected for the following service applications:
1.
If liquid carryover is possible.
2.
If allowable pressure drop is very low.
3.
If large turndown is required.
4.
If gases being burned are heavy and produce smoke.
Typical applications of side fired enclosed flame flare are:
1.
Refinery flares systems.
2.
Ethylene plants flare system.
3.
FPSO offshore flare system.
4.
Chemical plants flare systems.
5.
Heavy gas processing facilities.
6.
Very large capacity flares units.
Combustion chamber size and shape
Add
a.
Enclosed flame flare chamber shall be designed to operate at temperature sufficient to allow
complete combustion of all incoming gases and hydrocarbon fuels.
b.
Required chamber temperature and residence time shall be provided by enclosed flame flare
Vendor and shall be subject to BP approval.
c.
Combustion of waste gases shall be completed within combustion chamber without any flames
issuing from flare stack.
d.
Proposed height for enclosed flame flare shall be subject to BP approval.
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7.2.2
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Guidance on Industry Standard for API 537 Flare Details
e.
Exit area of enclosed flame flare shall provide for adequate dispersion of all combustion
products exiting flare.
f.
Use of cylindrical combustion chamber design for enclosed flame flare is recommended.
Burners
Add
a.
Enclosed flame flare gas burner(s) shall be capable of stable firing within specified range of
gas flow and composition.
b.
Gas jets in main burners shall be sized sufficiently to remain free from blockage during all
operating conditions and with all potential gas conditions.
c.
Burners should be capable of turndown from maximum flare gas flow to minimum purge gas
requirements.
d.
To allow for greater turndown, burners may be divided into zones coming consecutively into
operation.
e.
If selected, division of burners into zones should address the following:
1.
Some groups may be smokeless, others non smokeless.
Smokeless operation may sometimes not be specified but may, however, be implicit with
complete combustion, since smoking is a common factor for indicating poor
combustion.
7.2.5
2.
Control shall be automatic and may be by means of valves.
3.
If valves are used, liquid seals, rupture disks, or pin valves shall be installed in parallel to
retain full flaring capacity in event of primary control system failure.
4.
Vendor design shall ensure that premix pilots are at base of stack and are designed to fire
continuously and ignite supplied waste gases.
5.
Combustion of gases shall take place within refractory lined stack.
Operational and safety controls
Add
a.
Each main flame zone of enclosed flame flare shall be individually monitored with flame
detector capable of discriminating between adjacent flame zones, including pilot flames.
b.
Alarms shall be provided to indicate loss of main flame.
c.
As a minimum, facilities shall be provided for permanent monitoring of enclosed flame flare
flame status, chamber temperature, and draught.
d.
If burner staging is used, on/off tight shutoff valve shall be used.
e.
Proposal to prepurge enclosed flame flare with air shall be subject to BP approval. Fans
provided for this purpose shall have anti vibration mounts and comply with API Std 673 for
centrifugal fans of more than 20 kW (27 hp).
f.
If used, flare pilots shall have continuous flame. Each pilot shall have flame failure detection,
which is required to perform the following functions:
1.
Alarm to indicate detector fault.
2.
Alarm on pilot flame failure.
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Draft 21 March 2006
3.
g.
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
Indicate “pilot on”.
Common alarm in control room shall be activated for any of the failures in f. Local ignition
panel shall indicate location and type of failure.
Add
7.2.7
Guarantees
a.
Typically flare Vendor shall provide the following performance guarantee for enclosed flame
flare:
1.
Performance of flare hydraulically, mechanically, and electrically.
2.
Capacity of flare for specified composition range.
3.
Smokeless capacity range.
4.
Turndown ratio.
5.
Minimum purge gas requirement for each burner.
6.
Emission levels over specified operating range.
7.
Noise levels over specified operating range.
8.
That flame envelope will be contained within confines of flare chamber.
9.
That flare lining will not suffer deterioration/degradation between anticipated overhauls.
10. Combustion efficiency at design flow.
11. Noise at design flow.
b.
7.2.8
Guarantees shall apply to both summer and winter operation.
Other requirements
a.
Recommendations for method to be used for field test to determine actual emissions rates shall
be provided.
b.
Vendor shall advise whether dispersion modelling should be performed to ensure that material
release is below acceptable ground concentrations if personnel exposure could be expected.
7.3
Mechanical details
7.3.1
Combustion chamber
Add
a.
Structural steel shall be designed to permit lateral and vertical expansion of all enclosed flame
flare parts.
b.
Casing plate shall be seal welded to prevent air and water infiltration.
c.
Materials of structures and accessories shall be adequate for all load conditions at lowest
specified ambient temperature if flare is not in operation.
d.
Ladders and platforms, including bolting and other attachments, shall be hot dip galvanised.
e.
Protection shall be provided against lightning.
f.
Earthing (grounding) of structure shall be as recommended by BS 6651 or equivalent national
standards.
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Draft 21 March 2006
g.
Surfaces of flare that may come into contact with corrosive gases shall be given protective
coating against acid attack resulting from potential downwash of gases, in addition to
protection from atmospheric corrosion.
h.
Ladders and platforms shall have acid resistant protection in addition to galvanising.
i.
Type of coating selected by Vendor shall be subject to BP approval.
j.
Lining
1.
Enclosed flame flare shall be lined with acid resistant material.
2.
Lining shall be capable of:
3.
7.3.2
GIS 22-201
Guidance on Industry Standard for API 537 Flare Details
a)
Withstanding, without damage, temperature of 165°C (300°F) above normal
maximum flue gas operating temperature.
b)
Withstanding rapid change in temperature during excursion periods.
c)
Fast warmup.
Furnace refractory shall comply with relevant grade in ASTM C401 or C155.
k.
Consideration shall be given to possibility of low temperature conditions occurring,
particularly below acid dew point level, and potential effects of resultant condensation within
enclosed flame flare.
l.
If air and flare gas velocities are suitable, ceramic fibre blanket system, due to its low cost,
should be considered as a preferred material for enclosed flame flare lining.
m.
If ceramic fibre construction is used, casing shall have internal protective coating to prevent
corrosion, and vapour barrier shall be required.
n.
If multilayer linings are used, expansion joints shall not be continuous throughout adjacent
layer.
o.
Access doors shall be protected from direct radiation by material of at least same quality as
adjacent liner.
p.
If liquid carryover may occur, floor shall be gravel.
Burners
Add
a.
Burner material shall provide reliable and long service.
b.
Burners shall typically consist of 310 SS materials.
c.
Due to possibility of failure in event of fire, burner pressure parts and their associated
supports, bolts, nuts, springs, etc., shall not consist of brittle materials (e.g., cast iron,
spheroidal graphite cast iron, malleable iron) and low melting point materials (e.g., copper or
aluminium and their alloys, plastics).
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Guidance on Industry Standard for API 537 Flare Details
Appendix B
(Informative)
Bibliography
Add
BP
[1]
GIS 22-101
design).
Guidance on Industry Standard for ISO 13705 Fired Heaters (API 560) (for stack
[2]
GP 22-20 Guidance on Practice for API 537 Flare Details.
[3]
GP 44-70 Guidance on Practice for Overpressure Protection Systems.
[4]
GP 44-80 Guidance on Practice for Relief Disposal Systems.
API
[5]
RP 520
Recommended Practice for Sizing and Installation of Pressure Relieving Devices in
Refineries.
British Standards (BS)
[6]
BS 4592, Specification for Open Bar Grating.
[7]
BS 5395, Code of Practice for the Design of Industrial Type Stairs, Permanent Ladders and Walkways.
[8]
BS 6180, pCode of Practice for Barriers In and About Buildings.
Engineered Equipment and Materials Users Association (EEMUA)
[9]
Publication 105, Factory Stairways, Ladders and Handrails (Including Access Platforms and Ramps).
ISO
[10]
9001Quality Management Systems - Requirements.
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Guidance on Industry Standard for API 537 Flare Details
Add
Annex C
(Normative)
H.W. Husa’s correlation formulae
a.
Husa correlation shall be used to calculate minimum purge gas flow rates for gases lighter than
air.
b.
If purge gas mixture is heavier than air, purge rate based on nitrogen shall be used.
c.
Husa correlation may be expressed in either U.S. customary units or metric units as follows:
In U.S. customary units:
Q = 0.07068D 3.46
1  20.9   n 0.65 
 ∑ Ci K i 
ln
y  O2   i

where:
Q = purge gas rate, SCFH
D = flare stack diameter, in
y = column depth at which the oxygen concentration (O2) is to be predicted, ft
O2 = oxygen concentration, volume percent
Ci = Volume fraction of component i
Ki = Constant for component i.
Typical values for Ki are:
Hydrogen:
K = +5.783
Helium:
K = +5.078
Methane:
K = +2.328
Nitrogen:
K = +1.067 (No wind)
Nitrogen:
K = +1.707 (Wind 15 to 20 MPH or 6.7 to 8.9 m/s)
Ethane:
K = -1.067
Propane:
K = -2.651
CO2:
K = -2.651
C4+:
K = -6.586
In metric units:
Q = 201.66 D 3.46
1  20.9   n 0.65 
 ∑ Ci K i 
ln
y  O2   i

where:
Q = purge gas rate, m3/hr
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Guidance on Industry Standard for API 537 Flare Details
D = flare stack diameter, m
y = column depth at which the oxygen concentration (O2) is to be predicted, m
O2 = oxygen concentration, volume percent
Ci = Volume fraction of component i
Ki = Constant for component i (see above)
d.
Note that steam or other condensable is not a suitable purge gas.
e.
These equations can be simplified using standard criteria of limiting oxygen concentration to
volume % 25 ft (7,6 m) down flare stack (note that lower oxygen concentrations should be
used for certain compounds, such as hydrogen - refer to 10.1.c):
In U.S. customary units:
Q = 0.0035283 D3.46 K
where:
Q = purge gas rate, SCFH
D = flare stack diameter, in
K = constant (see above)
In metric units:
Q = 33.0292 D3.46 K
where:
Q = purge gas rate, m3/hr
D = flare stack diameter, m
K = constant (see above)
g.
Values of Ki for gases lighter than air are determined from:
Ki =
h.
exp (0.065 (29-MWi))
Values of Ki for gases heavier than air are determined from an amended Husa correlation,
where (MWi-29)) is substituted for MWi as follows:
Ki =
exp (0.065 (MWi-29))
Where:
MWi = molecular weight of the i th component of n components.
Note: It should be recognised that Husa correlation was derived
under calm or no wind conditions and is generally applicable for
wind speeds up to approximately 13,4 m/s (30 mph). Locations
where prevailing winds can often exceed this wind speed may
need somewhat higher purge rates.
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Add
Annex D
(Normative)
BP purchasing requirements
D.1 Conflict resolution
a.
If any conflict occurs as a result of applying these specifications, the more stringent
requirement shall be applied.
b.
If level of stringency is undeterminable, discrepancy shall be resolved as follows:
c.
1.
Inquiry or purchase order.
2.
Specification data sheets.
3.
This GIS.
4.
API Std 537.
Vendor shall however contact BP or its representative in writing before proceeding with
effected work and with proposed resolution for applying discrepancy following order of
precedence.
D.2 Vendor responsibilities
a.
Detailed design of flare system shall be total responsibility of Vendor.
b.
Vendor shall furnish all labour and equipment and perform all operations in accordance with
attached specifications.
c.
Design information enclosed in attached specification defines minimum requirements for
design, materials, fabrication, assembly, testing, and preparation for shipment of proposed
flare system.
d.
Drawings and related documents supplied in attached specifications shall be used by Vendor
as a guideline for requirement and for location of flare system components.
e.
Vendor shall perform detail analysis and calculations to establish optimum configurations for
system.
f.
Review of Vendor submitted bid documents by BP or its representative shall not relieve
Vendor from complete compliance with drawings and specifications. Nothing contained in any
of the specifications or data sheets shall be deemed to relieve Vendor of any warranty,
expressed or implied.
D.3 Exceptions, variances, and substitutions
a.
At bid submittal stage, all exceptions taken to this GIS, all variances from this GIS, and all
substitutions of operating capabilities or equipment called for in this GIS shall be listed in
writing and forwarded to BP or its designated representative.
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Guidance on Industry Standard for API 537 Flare Details
b.
Any such exceptions, variances, or substitutions that are not listed at time of bid and which
subsequently are identified by BP or its representative in submittal shall be grounds for
immediate disapproval without comment.
c.
No fabrication shall begin until approval drawings have been approved and stamped approved
for construction by BP or its designated representative.
D.4 Inspection and testing
D.4.1
D.4.2
D.4.3
D.4.4
D.4.5
General
a.
BP or its representative will appoint an inspector to periodically inspect work being done at
Vendor facility, as well as inspect materials being proposed for fabrication.
b.
BP shall be notified 7 working days prior to all hydro testing and functional testing.
Welding
a.
BP reserves right to require Vendor to remove sections containing completed welds or any of a
finished weld and prepare specimens and deliver such specimens to BP for testing.
b.
All costs for this requirement will be borne by BP.
c.
Repairs required by test results not meeting specifications shall be to Vendor’s account.
d.
BP reserves right to use destructive testing methods.
Access
a.
BP’s inspector shall have full entry at reasonable times to such parts of Vendor facility as may
concern assembly and manufacture of flare facility.
b.
Approved office space shall be provided for use by BP inspectors. Such office space shall be
located at Vendor facility where flare facilities are fabricated and assembled.
c.
If BP inspectors or representatives are in or about Vendor facility in course of their
employment, they are deemed to be invitee of Vendor.
Materials
a.
All materials furnished shall comply with materials requirements, including tolerances, if any
are shown in specification documents.
b.
If BP inspector finds materials or finished product in which material are used or work
performed are not in accordance with specifications, work or materials shall be removed or
otherwise corrected by Vendor at its own expense.
Quality assurance
a.
Vendor shall be responsible for carrying out provisions of specifications at all times and for
control of quality of materials and workmanship.
b.
Vendor shall submit a copy of its quality assurance manual with proposal.
c.
Vendor QC program shall have comprehensive documentation, including material
certification, mill tests, purchase specifications, fabrication, and inspection and testing history
for each part, component, assembly, or complete items.
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d.
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Guidance on Industry Standard for API 537 Flare Details
Inspection or observation of performed work by BP or its representative does not relieve
Vendor of its obligation to meet all specifications requirements for scope of work. Adequate
safety measures shall be provided and maintained at all times during the development and
execution of the project.
D.5 Shipment and storage
D.5.1
General
Throughout duration of work, BP or its representative shall be kept informed of any changes that
may affect equipment delivery.
D.5.2
D.5.3
D.5.4
D.5.5
Preservation and storage
a.
Vendor shall be solely responsible for adequacy of equipment preservation provision
employed with respect to materials application.
b.
Equipment preservation shall be suitable for minimum of 18 mo of outdoor storage.
Loadout and transport
a.
Loadout of equipment from Vendor facility shall be performed under supervision of BP
representative. However responsibility for loadout shall remain with Vendor.
b.
Vendor shall load out, tie down, and secure equipment on Vendor furnished transport.
c.
Vendor shall be responsible for transport to BP’s designated receiving location.
d.
Removal from transport upon arrival at designated receiving location shall be by BP and
designated agent.
Identification and tagging
a.
Each major component shall be properly identified with item and serial numbers.
b.
Material shipped separately shall be properly tagged or marked with item and serial number
for which it is intended.
c.
Small, easily damaged parts shall be removed from shipping. Part removed and location from
which part was removed shall both be identified with securely attached 316 SS metal tags,
with 316 SS wire indicating instrument and tag number.
d.
Items that can be damaged by water shall be securely wrapped in waterproof paper before
placed in wooden crates.
Skid packages
Assembled equipment skid packages, ready for interconnection, startup, and commissioning, shall
be provided.
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Add
Annex E
(Normative)
Documentation
a.
Detailed operating procedure and maintenance manuals shall be developed for each flare
system.
Typical Vendor supplied procedures and manuals are not usually sufficient because
they tend to be of a “generic” nature and, in many cases, lack plant and system
specifics for the particular application.
b.
c.
The operating procedure should include the following major topics:
1.
Detailed system description.
2.
Operating range and operating limits.
3.
Operating logs that may include data on flow to flare measurements, assisting media flow
measurements, purge gas flow measurements, and pilot operational status.
4.
Flame observation permit requirements (opacity requirements, remote camera operation,
visual observation, aviation lights status, etc.).
5.
Flare operational data required by permit (smoking severity and duration of smoking
event, venting volumes, pilot operational status report, etc.).
6.
Operator training requirements and training frequency.
The following shall be included in great detail for each flare system:
1.
Pilot operation aspects.
2.
Pilot ignition aspects.
API Std 537 provides comprehensive operating instructions for various types of ignition
systems. These instructions could be included in Operating Manuals and Training
Manuals for particular type of flare ignition used in facility flare system.
d.
3.
Blowers and drivers.
4.
Blower staging and control equipment.
5.
Pressure staging equipment.
6.
Multi burner staged flare.
7.
Enclosed flame flares.
The following API Std 537 tables should be included in whole or in parts that are applicable
for particular installation:
1.
Table 3, Troubleshooting Pilots.
2.
Table 4, Troubleshooting Ignition Systems.
3.
Table 5, Troubleshooting Flame Detection Systems.
4.
Table 6, Troubleshooting Purge Gas Conservation Seals.
5.
Table 7, Troubleshooting Blower Systems.
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e.
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Guidance on Industry Standard for API 537 Flare Details
6.
Table 8, Troubleshooting Blower Staging and Control Equipment.
7.
Table 9, Troubleshooting Pressure Staging Equipment.
8.
Table 10, Troubleshooting Enclosed Flame Flare Systems.
Complete documentation/information, including flare drawings provided by Vendor, shall be
accessible to personnel who will conduct inspection and maintenance work on the following:
1.
Pilots and pilot system.
2.
Flare ignition components.
3.
Flare blowers and drivers.
4.
Flare blower staging and control equipment.
5.
Flare pressure staging equipment.
6.
Multi burner staged flare.
7.
Enclosed flame flares.
Page 78 of 78