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Process & Utility Systems
Flare and Vent Systems
Flare and Vent Systems covers equipment that burns or releases gas away from people and plant: well test burner booms and burner heads, flare tips and stacks, pilots and ignition panels, knock-out drums, water screens and cold vent lines. On a drilling unit the burner boom and the mud gas separator vent are the main items. A used boom or flare is sized by a radiation study, not by its length alone.
How flares and vents work
During a well test, oil and gas lines run out along a burner boom to burner heads at its tip. The burners atomise the oil with compressed air and burn it with the gas. Water sprays around the burner and along the boom absorb radiant heat before it reaches the rig.
On a production facility, relief and blowdown gas collects in a header and passes a knock-out drum that removes liquid. It then rises to a flare tip lit by continuous pilots. A cold vent releases gas without burning it, at a height where the plume disperses before it reaches people or ignition sources. The mud gas separator vent on a drilling rig is a cold vent, usually run to the top of the derrick.
Configurations
- Well test burner booms, fixed to the hull or removable, with one or more burner heads
- Flare stacks, booms and ground flares for production facilities
- Pilot ignition by flame front generator, high-energy electric igniters or ballistic ignition
- Smokeless burners with air or water assist
- Cold vents with flame arrestors or snuffing where required
Key specifications
| Parameter | Why it matters | Typical classes or units |
|---|---|---|
| Gas and oil capacity | Must cover the test or relief case | MMscfd, barrels or m3 per day |
| Boom length or stack height | Sets radiation at the deck | Metres or feet |
| Number of burner heads | Sets oil burning capacity and turndown | Count, nozzle type |
| Ignition system | Must light reliably in wind and spray | Pilot type, igniter type |
| Water screen demand | Must match your firewater or seawater supply | Cubic metres per hour or gpm at bar or psi |
| Piping design pressure | Must exceed the upstream relief settings | psi or barg |
Radiation decides the size
API 521 gives the method for calculating radiant heat from a flame and the design levels at receptors. They are commonly quoted as follows.
| Radiation level | Exposure basis in API 521 |
|---|---|
| 1.58 kW/m2 (500 Btu/h ft2) | Continuous exposure of personnel in protective clothing |
| 4.73 kW/m2 (1,500 Btu/h ft2) | Emergency action lasting 2 to 3 minutes, without shielding but with appropriate clothing |
| 6.31 kW/m2 (2,000 Btu/h ft2) | Emergency action lasting up to 30 seconds, without shielding but with appropriate clothing |
| 9.46 kW/m2 (3,000 Btu/h ft2) | Locations where urgent emergency action is needed; plan shielding or special protective clothing |
Check whether your design basis adds solar radiation to these values. A boom that met the limits on one rig may be too short on yours, because the flow, wind and receptor positions all change. Ask for the original study and rerun it for your layout.
Standards and certification
API 521 covers flare and vent sizing, radiation, dispersion and knock-out drums. API 537 covers flare tips, pilots, ignition and burner details. Knock-out drums are pressure vessels, normally to ASME Section VIII. A removable boom is lifted equipment, so its lifting points and rigging need certification. Class rules on a mobile unit may add structural approval for the boom foundations.
Failure modes and inspection
- Burner heads and flare tips burn back, crack and distort from heat. Inspect them visually and measure nozzle wear.
- Boom structures crack at the pedestal, hinge points and section joints from wind and fatigue. Use magnetic particle testing on the welds.
- Piping thins from erosion and corrosion. Take ultrasonic thickness readings and review hydrotest records.
- Pilots and igniters fail from fouling and wet cables. Run a full ignition test.
- Water spray nozzles scale up and block. Flow test the water screen.
- Knock-out drum internals, level instruments and relief valves need their own inspection.
Documentation
- Radiation study for the original installation
- Structural calculations and the last NDT report for the boom
- Piping hydrotest and thickness survey
- Burner and ignition system manuals and test records
- Lifting certificates for removable booms
Integration and compatibility
A boom needs a foundation on your hull or deck, clearances from lifeboats and anchor handling areas, compressed air for the burners and water for the screen. Gas reaches it from gas separators or the well test equipment spread. Ignition panels need a power supply and gas detection interface that suits the zone.
Refurbishment and recertification
Burner heads and flare tips are wear parts, so budget for new nozzles or a new tip. A boom overhaul covers NDT of the structure, recoating, piping thickness checks and hydrotest, and an ignition function test. Used booms move between rigs for test campaigns, and they work well when your radiation study confirms their length.
FAQ
Frequently asked questions
What is a burner boom on an offshore rig?
A burner boom is a steel structure that carries oil and gas lines out from the rig to burner heads at its tip. It is used during well testing to burn produced fluids away from the rig. Water sprays around the burners cut the radiant heat that reaches the deck.
How long does a flare or burner boom need to be?
A flare or burner boom must be long enough to keep radiant heat at people and equipment within the API 521 design levels. The length depends on the flow being burnt, wind and the positions of people and plant, so it comes from a radiation study for your unit, not a standard figure.
What radiation limits does API 521 use for flare design?
API 521 commonly uses 1.58 kW/m2 (500 Btu/h ft2) for continuous exposure of personnel in protective clothing. It allows higher levels for short emergency actions in appropriate clothing, 4.73 kW/m2 for 2 to 3 minutes and 6.31 kW/m2 for up to 30 seconds. Check whether your design basis adds solar radiation.
What should I check on a used well test burner boom?
On a used burner boom, check the structure for fatigue cracks at the pedestal, hinges and section joints, with a recent magnetic particle report. Also check piping thickness and hydrotest records, burner head wear, the ignition system and the water screen nozzles.
What standards cover flare and vent systems?
API 521 covers flare and vent sizing, radiation, dispersion and knock-out drums. API 537 covers flare tips, pilots, ignition and burner details. Knock-out drums and other pressure parts are normally built to ASME Section VIII, and removable booms also need lifting certification.
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