OIL & GAS EQUIPMENT | Updated May 2026 | 8 min read
What You’ll Learn in This Guide
- When a flare retrofit is the right answer vs replacing the entire stack
- How to assess an existing non-assisted or pre-OOOOb flare for retrofit feasibility
- What scope is included in a typical air assisted flare lift-and-bolt tip retrofit
- How to upgrade a fixed-speed blower system to OOOOb-grade VFD control
- How to add OOOOb-required continuous parametric monitoring to an existing flare
- What commissioning and performance test pathway brings a retrofit into OOOOb compliance
- Common air assisted flare retrofit mistakes and how to avoid them
EPA 40 CFR 60 Subpart OOOOb pulled forward an expensive question for every oil and gas operator with an existing flare on an affected source: replace the flare or retrofit it? Replacement is straightforward engineering but high cost and long shutdown. Retrofit is faster and cheaper but requires careful engineering to confirm the existing stack, foundation, headers, and instrumentation can support the OOOOb-grade air-assisted performance the rule demands. Most retrofits work. Some do not, and the engineering assessment up front determines which case you are in.
Hero Process Solutions, founded in 2011 and headquartered in Kellyville, Oklahoma with operations in Midland, Texas, manufactures retrofit air assisted flare packages designed for “lift and bolt” installation on existing stack connections. This guide walks through the retrofit decision, the typical scope, and the OOOOb compliance pathway from existing equipment to certified 98% DRE performance.
DIRECT ANSWER: An air assisted flare retrofit converts an existing non-assisted, steam-assisted, or pre-OOOOb air-assist flare to OOOOb-grade performance by replacing the tip with a Coanda-profile air-assist tip designed for the existing stack connections, replacing or upgrading the blower to VFD control with closed-loop air-to-gas ratio logic, adding the OOOOb-required continuous parametric monitoring instrumentation (pilot flame, combustion zone, vent-gas flow), and commissioning the retrofitted system with an initial OOOOb performance test demonstrating 98% Destruction and Removal Efficiency. Typical site downtime is days rather than weeks, with much lower CAPEX than full flare replacement.
1. When Retrofit Is the Right Answer
Retrofit is the right answer when the existing stack, foundation, and major site infrastructure are sound but the tip technology, blower control, or instrumentation cannot meet OOOOb requirements as installed. Retrofit is not the right answer when the existing structural elements have deteriorated past their service life, when the existing stack height or diameter is fundamentally undersized for the current waste-gas envelope, or when the original installation was so poorly engineered that piecemeal upgrades cannot reach OOOOb-grade performance.
The decision matrix is straightforward. If the stack is structurally sound (foundation, anchor bolts, ladders, platforms inspected within service life), the stack diameter is correct for the current peak relief flow at Mach 0.5 limits, the header capacity supports the current and projected relief load, and the existing utilities can supply the upgraded blower with electric power, then retrofit is viable. If any of those is not true, replacement is the better path.
A pre-retrofit engineering assessment typically takes one to two weeks and produces a definitive go/no-go answer plus a scoped retrofit package with cost and downtime estimates.
2. How to Assess an Existing Flare for Retrofit Feasibility
The retrofit feasibility assessment covers five areas. The first is structural — stack integrity, foundation condition, anchor bolt corrosion, ladder and platform compliance with current OSHA standards. A 30-year-old stack with no foundation cracking and intact anchor bolts is a strong retrofit candidate. A stack with foundation settling or visible corrosion at the base plate is a replacement candidate.
The second is dimensional — stack diameter against current peak relief flow at API 521 exit velocity limits, stack height against current property boundary radiation calculation, sample port locations for OOOOb Method 1 compliance. If the existing dimensions are correct or generous, retrofit proceeds. If they are undersized, the retrofit may need stack extension or replacement.
The third is utility — electric power available at the flare base for an upgraded VFD blower, instrument air available for any new instrumentation, fuel gas pressure and flow available for upgraded pilots. Many older flares were installed without anticipating VFD blower power requirements, and a power upgrade may be needed.
The fourth is the existing tip — type, condition, manufacturer, and flange connection geometry. Coanda-profile retrofit tips are designed for “lift and bolt” installation on standard stack connections, but the specific connection dimensions must match. The fifth is the existing instrumentation — what monitoring is already in place, what must be added for OOOOb compliance, and what integration is needed with the existing control system or historian.
KEY INSIGHT: The pre-retrofit assessment is the single most important deliverable in the project. A thorough assessment finds the surprises early — an undersized stack, a corroded foundation, missing electrical capacity — when they can still be addressed by changing the project scope rather than discovered mid-construction.
3. The Lift-and-Bolt Tip Retrofit
The core of an air assisted flare retrofit is replacing the existing tip with a Coanda-profile air-assist tip designed for the specific existing stack connection. “Lift and bolt” installation means the new tip arrives at site pre-assembled and ready to bolt onto the existing flange without stack modification.
The retrofit tip is custom designed to fit the existing flare stack connections, which avoids stack rework, shortens installation time, and reduces project risk. The new tip is sized for the current waste-gas envelope (which may have changed since original installation), the new air-to-gas ratio control logic, and OOOOb-grade DRE performance.
Site installation typically takes one to two days for the tip change itself, with the surrounding scope (blower, instrumentation, controls, commissioning) extending total project time to one to three weeks depending on complexity. Site downtime is the days the flare is offline during the tip change, not the full project duration.
4. Upgrading the Blower to OOOOb-Grade VFD Control
Most pre-OOOOb air-assist flares were installed with fixed-speed blowers because the prior NSPS (Subpart OOOOa) accepted 95% DRE and did not require variable air-to-gas ratio control. OOOOb requires 98% DRE across the full operating range, which is only achievable with VFD-controlled blower modulation. The retrofit therefore upgrades the blower system to VFD control.
The upgrade scope has three components. First, the VFD itself — a variable frequency drive sized for the existing blower motor, with the control logic needed for closed-loop air-to-gas ratio control. Second, a vent-gas mass flow meter on the inbound header if one is not already installed. Third, the control logic itself — programmed on the existing PLC or DCS, or installed on a new flare-dedicated controller, to modulate blower speed in real time based on measured vent-gas flow and the target air-to-gas ratio.
If the existing blower motor is undersized for the upgraded duty (a common finding in retrofits of older fixed-speed systems), the motor is replaced as part of the upgrade. If the blower itself is sound and correctly sized, only the VFD and control logic change.
5. Adding OOOOb-Required Continuous Parametric Monitoring
OOOOb requires continuous monitoring of pilot flame presence, combustion zone presence, and vent-gas flow during all periods of waste-gas flow. Most pre-OOOOb flares lack one or more of these monitors, so they are added as part of the retrofit.
Pilot monitoring uses redundant thermocouple plus ionization rod detection. Combustion zone monitoring uses a video flame monitor, combustion-zone thermocouple, or flame ionization detector. Vent-gas flow uses a Coriolis or ultrasonic meter on the relief header inlet. Data is logged at 15-second to 1-minute intervals, retained for five years, and reported through the EPA CEDRI portal.
Visit the EPA OOOOb compliance resource for the full continuous monitoring and recordkeeping requirements. The monitoring scope is non-negotiable for OOOOb compliance and must be included in every retrofit.
6. Commissioning and OOOOb Initial Performance Test
After tip retrofit, blower upgrade, and instrumentation installation, the retrofitted flare is commissioned and tested. Commissioning verifies that the VFD control loop holds the design air-to-gas ratio across the full operating range, the pilot system ignites and holds flame reliably, and the monitoring instrumentation reads correctly and feeds the historian or compliance system.
The OOOOb initial performance test follows commissioning. EPA Method 18 (gas chromatography) speciates the vent-gas inlet stream; Methods 25A or 25B measure total hydrocarbons at the flare outlet; the resulting Destruction and Removal Efficiency is calculated as the percentage of inlet vent-gas carbon destroyed in the combustion zone. The retrofitted flare must demonstrate 98% or greater DRE.
Hero’s field services team supports customers through commissioning and the initial OOOOb performance test, including pre-test verification of VFD control logic, pilot and combustion-zone monitor calibration, and sample-port verification to EPA Method 1.
CRITICAL RULE: Do not declare an OOOOb retrofit complete until the initial performance test has been passed and the test report is filed in the compliance documentation. A retrofitted flare that has been mechanically completed but not performance-tested is not yet OOOOb-compliant — and the operator carries the OOOOb compliance risk until the test report is in the file.
7. Retrofit vs Replacement Cost and Downtime Comparison
| Project Type | Typical Site Downtime | Typical CAPEX | When to Choose |
|---|---|---|---|
| Tip-only retrofit | 1 to 3 days | Lowest | Existing flare structurally sound, stack dimensions correct, only tip technology needs upgrade |
| Tip + blower upgrade | 1 to 2 weeks | Moderate | Existing tip and blower both need upgrade for OOOOb; stack and structure sound |
| Tip + blower + monitoring | 2 to 3 weeks | Moderate-high | Full OOOOb-grade upgrade on a structurally sound existing flare |
| Full flare replacement | 4 to 8 weeks | Highest | Existing stack or foundation past service life, or fundamentally undersized |
8. Common Air Assisted Flare Retrofit Mistakes
| Mistake | Why It Hurts | Fix |
|---|---|---|
| Skipping the pre-retrofit structural assessment | Foundation or stack issues discovered mid-installation | Run full structural assessment before scoping the retrofit |
| Assuming existing stack dimensions still match current waste-gas envelope | Undersized stack causes flow problems after retrofit | Verify Mach 0.5 exit velocity and API 521 radiation at current peak relief |
| Specifying a fixed-speed blower upgrade to save CAPEX | Fails OOOOb 98% DRE outside peak design flow | Specify VFD blower with closed-loop air-to-gas control |
| Adding monitoring instrumentation without sample-port verification | Cannot run EPA Method 1-compliant performance test | Verify sample-port locations meet Method 1 during the retrofit, not after |
| Skipping initial OOOOb performance test after retrofit | Operator carries OOOOb compliance risk indefinitely | Schedule and complete the initial performance test as part of project closeout |
| Treating retrofit as mechanical-only without controls re-tuning | VFD tuning not verified, slow performance degradation | Step-test the control loop during commissioning and document tuning parameters |
Frequently Asked Questions
When is an air assisted flare retrofit better than replacement?
Retrofit is better when the existing flare stack is structurally sound (foundation, anchor bolts, ladders, platforms intact), stack dimensions are correct for the current relief flow at API 521 exit velocity limits, and site utilities can support the upgraded blower. Replacement is better when those structural elements have deteriorated or were fundamentally undersized.
What is included in a lift-and-bolt tip retrofit?
The retrofit tip is custom designed to fit the existing flare stack flange and connection geometry, arrives at site pre-assembled, and bolts onto the existing connections without stack modification. The scope typically includes the new Coanda-profile air-assist tip, the VFD blower upgrade, OOOOb-required continuous parametric monitoring, control logic programming, commissioning, and the initial OOOOb performance test.
How long does an air assisted flare retrofit take?
Site downtime for the tip change itself is typically one to three days. Full project duration including blower upgrade, monitoring installation, controls programming, and OOOOb commissioning is typically one to three weeks. Site downtime is the days the flare is offline, not the full project duration.
Can I retrofit a fixed-speed blower to OOOOb-grade VFD control?
Yes. The retrofit installs a VFD on the existing blower motor (or replaces the motor if undersized), adds a vent-gas mass flow meter if one is not already installed, and programs the closed-loop air-to-gas ratio control logic on the existing PLC, DCS, or a new flare-dedicated controller. The result is OOOOb-grade 98% DRE across the full operating range.
Does a retrofit require a new OOOOb performance test?
Yes. The retrofitted flare must demonstrate 98% Destruction and Removal Efficiency on an initial performance test using EPA Methods 18, 25A, or 25B as applicable, with sample ports compliant with EPA Method 1. Annual recertification tests follow the same protocol thereafter. The initial test report becomes the foundation of the OOOOb compliance documentation file.
What if the pre-retrofit assessment finds the existing stack is undersized?
If the existing stack cannot meet API 521 exit velocity or radiation criteria for the current waste-gas envelope, the retrofit either extends the stack to add height or replaces it entirely. Hero’s engineering team scopes the right path during the assessment phase and provides cost and downtime estimates for each option so the operator can choose between extended retrofit and full replacement.
