OIL & GAS EQUIPMENT | Updated May 2026 | 8 min read
What You’ll Learn in This Guide
- How to diagnose smoke during normal operation and turndown on an air assisted flare
- How to identify VFD blower control loop tuning problems
- How to troubleshoot flame instability, lift-off, and intermittent blowout
- How to find and resolve blower mechanical issues — bearings, belts, vibration, motor faults
- How to handle pilot loss-of-flame and ignition system failures
- Why OOOOb monitor signals are the best leading indicator of trouble
- Common air assisted flare operating mistakes and how to avoid them
An air assisted flare that started up commissioned and certified at 98% Destruction and Removal Efficiency does not stay there automatically. Field problems show up over time: a flare that smokes only during the 6 AM turndown, a blower that vibrates more than it used to, a pilot that drops out every few weeks during weather changes, a combustion-zone monitor that throws a deviation alarm every other Tuesday. Every one of those symptoms has a specific root cause, and most of them are catchable before they become OOOOb deviation events if operators know what to look for. This guide walks through the most common air assisted flare troubleshooting scenarios and the diagnostic workflow for each.
Hero Process Solutions, founded in 2011 and headquartered in Kellyville, Oklahoma with operations in Midland, Texas, supports air assisted flare customers across the United States with field troubleshooting, parts, and aftermarket support. This guide draws on the operating issues the field services team sees most often on installed A+ Series units.
DIRECT ANSWER: Air assisted flare troubleshooting starts with reading the OOOOb continuous monitor data — pilot flame, combustion zone, and vent-gas flow — across the period when the problem occurred. Smoke is almost always a VFD blower air-to-gas ratio problem, either from wrong tuning, slow response to flow excursions, or a stuck/drifted flow measurement. Flame instability is usually a tip wear or pilot weakness issue. Blower vibration and motor faults are mechanical wear. Pilot loss is fuel pressure, ignition transformer drift, or weather exposure. The right diagnostic answer comes from matching the symptom to the data, not from guessing.
1. Smoke During Normal Operation and Turndown
Visible smoke from an air assisted flare during normal operation almost always traces back to the air-to-gas mass ratio at the tip. EPA 40 CFR 60.18 limits flares to no more than five minutes of visible emissions during any consecutive two-hour period, and OOOOb tightens that for affected sources. Any smoke is a deviation risk.
The diagnostic workflow has four steps. First, pull the OOOOb continuous monitor data for the smoke period and verify the vent-gas mass flow reading at the time. A spike in actual flow that the VFD did not respond to within seconds is a flow-measurement or VFD-tuning problem. Second, verify the blower speed and confirm the VFD is actually responding to its calculated setpoint. A blower stuck at low speed during a high-flow excursion produces guaranteed smoke. Third, check the air-to-gas ratio computed by the control logic against the design ratio for the actual gas composition. A ratio set for design composition that is now lower than required for actual (heavier or olefin-rich) composition produces smoke at all flows. Fourth, inspect the tip for combustion zone erosion, partial blockage of air injection ports, or thermal damage that has changed the effective tip geometry.
Smoke specifically during turndown — but not at peak flow — is almost always VFD minimum-speed limit set too high. The blower over-supplies air at low waste-gas flow, cools the flame, and the resulting incomplete combustion produces smoke. Lower the minimum speed (or relax the minimum-flow cutout) with appropriate testing.
KEY INSIGHT: Smoke only during turndown and never at peak flow is one of the most diagnostic patterns in air assisted flare operation — it tells you the problem is in the low-speed end of the VFD control range, not in the tip geometry or composition. Tune the minimum speed and the low-flow control logic, not the hardware.
2. VFD Blower Control Loop Tuning Problems
The VFD control loop is the brain of the air assisted flare. When it is tuned correctly, the blower responds to vent-gas flow changes within seconds and holds the air-to-gas ratio across the full operating envelope. When it is tuned poorly, the flare oscillates between over- and under-air conditions and produces a noisy, unstable flame at best — and OOOOb deviation events at worst.
Three tuning problems appear most often. PID gains too aggressive produce hunting — the blower ramps up to chase a flow spike, overshoots, ramps back down, undershoots, and cycles. Smoke and DRE drops appear during the undershoot. The fix is reducing proportional gain or adding integral filter. PID gains too sluggish produce delayed response — the blower ramps too slowly during real flow excursions, smoke appears for 10 to 30 seconds during the lag, then clears. The fix is increasing proportional gain or shortening the integral time. Slew rate limits set too restrictive prevent the blower from ramping fast enough during large step changes; relax the slew limit and re-test.
Tuning is verified by step-change testing during commissioning and after any major change. If tuning has not been re-verified in years, that is often the root cause of slowly worsening performance.
3. Flame Instability, Lift-Off, and Intermittent Blowout
A stable flame sits on the tip with a defined inner cone and a turbulent outer envelope. An unstable flame wanders around the tip exit, lifts off and drops back, or extinguishes briefly and reignites from the pilot. Each pattern points to a different cause.
Flame lift-off (the flame anchor point rises above the tip exit) usually means exit velocity is too high for the current gas composition — either the blower is over-supplying air, the waste-gas flow is above design, or the gas composition has shifted lighter and the resulting higher exit velocity has exceeded stability limits. Verify air-to-gas ratio first, then composition.
Intermittent blowout (the main flame extinguishes and the pilot relights it within seconds) is almost always a pilot weakness — the pilot is too small or too unstable to hold ignition during a brief main-flame loss. Inspect the pilot ignition system for fuel pressure, ionization rod erosion, or weather damage to the pilot housing.
Wandering flame anchor with the inner cone shifting around the tip circumference points to uneven air distribution across the tip — partial blockage of air injection ports, asymmetric flow from the blower discharge, or a damaged Coanda profile. Tip inspection during the next scheduled outage is the right next step.
4. Blower Mechanical Issues — Bearings, Belts, Vibration, Motors
The blower is the one piece of rotating equipment on an air assisted flare, and rotating equipment wears. Five mechanical issues account for most blower-related troubleshooting on installed units.
Bearing wear appears as elevated vibration on quarterly inspection rounds and audible high-frequency noise from the bearing housings. Catching this on vibration data before it becomes audible saves the bearing and prevents collateral damage to the shaft. Belt slippage (for belt-driven blowers) appears as a blower speed lower than the VFD setpoint and is detectable by comparing the VFD speed reference to the actual measured blower RPM. Motor faults — winding insulation degradation, capacitor weakness on smaller VFDs, ground faults — typically appear first as motor current irregularities visible on the VFD diagnostic page.
Loose blower foundation bolts and resonance issues cause vibration that worsens at specific operating speeds and improves at others — diagnostic by varying VFD speed during inspection. Air filter fouling on the blower intake increases motor amp draw and reduces effective air delivery; clean or replace per the maintenance schedule.
CRITICAL RULE: Never bypass a vibration trend that is rising even if it has not crossed an alarm threshold yet. Bearing failure on a flare blower can take the flare offline for days waiting on parts and replacement labor. Schedule the bearing change at the next planned outage, not at the next emergency.
5. Pilot Loss-of-Flame and Ignition System Failures
A pilot loss-of-flame event on an air assisted flare is a logged OOOOb deviation and requires root cause analysis. The four most common causes follow a predictable diagnostic order.
Pilot fuel pressure drop is the most common cause. Check the pilot fuel regulator output pressure, the fuel gas supply pressure at the regulator inlet, and any solenoid valves between the supply and the pilot. A regulator that has drifted, a solenoid that is sticking partially closed, or upstream supply pressure that has dropped below the regulator dropout will all kill the pilot.
Ionization rod erosion or wet ionization rod (after weather) produces intermittent loss-of-flame signals even when the pilot is actually still lit. Clean or replace the rod; if the loss-of-flame events correlate with rain or fog, the pilot housing needs better weather protection.
Ignition transformer drift causes failed relight attempts after a real loss-of-flame event. Test the transformer output during a scheduled outage and replace if the pulse strength is below spec.
High-wind blowout is more common than operators expect on coastal or open-prairie sites; if loss-of-flame correlates with wind data, the pilot housing needs a wind shield or the pilot itself needs to be upgraded to a high-stability design.
6. OOOOb Continuous Monitor Signals as Leading Indicators
The continuous parametric monitoring required by 40 CFR 60 Subpart OOOOb is the best leading indicator of air assisted flare problems — well before visible smoke or pilot loss appear. Three signals deserve specific operator attention.
Combustion-zone thermocouple temperature drift trends downward over weeks before a tip wears out enough to lose DRE performance. Set a trend alarm on the rolling average, not just the instantaneous reading. Pilot flame detector signal strength dropping over weeks means the ionization rod is eroding or the pilot fuel mixture is drifting — schedule a pilot inspection. Vent-gas flow meter calibration drift can be detected by comparing measured flow against process material balance; if the flow meter has not been calibrated in a year, that drift is probably the root cause of any unexplained DRE swings.
Visit the EPA OOOOb compliance resource for the full monitoring and recordkeeping requirements.
7. Common Operating Mistakes
| Mistake | Symptom | Fix |
|---|---|---|
| VFD minimum speed limit set too high | Smoke during turndown, fine at peak flow | Lower minimum speed and re-tune low-flow control logic |
| Aggressive PID gains causing blower hunting | Oscillating flame, intermittent smoke spikes | Reduce proportional gain or add integral filter |
| Skipping quarterly blower vibration trend reviews | Bearing fails between scheduled inspections | Trend vibration data, address rising trends at next planned outage |
| Ignoring slow downward drift of combustion-zone thermocouple | Tip wears out unnoticed, DRE drops | Set rolling-average trend alarm, schedule tip inspection at threshold |
| Treating pilot loss-of-flame as routine without root cause analysis | Repeated OOOOb deviation events, audit risk | Document root cause and corrective action on every event |
| Not re-verifying VFD tuning after a major maintenance event | Slowly worsening performance over months | Step-test the control loop after any blower or tip work |
Frequently Asked Questions
Why does my air assisted flare smoke during turndown but not at peak flow?
Smoke during turndown only is almost always caused by the VFD minimum-speed limit being set too high. At low waste-gas flow, the blower over-supplies combustion air, cools the flame, and produces incomplete combustion. The fix is lowering the VFD minimum speed and re-tuning the low-flow control logic, then verifying smokeless operation by step-test across the turndown range.
What does it mean when the air assisted flare flame lifts off the tip?
Flame lift-off means exit velocity at the tip exceeds the stability limit for the current gas composition. Three causes: the blower is over-supplying air (check air-to-gas ratio control), the waste-gas flow rate is above design (check vent-gas mass flow), or the gas composition has shifted lighter (verify composition against design envelope). Resolve the air-to-gas ratio first because that is most often the controllable variable.
How often should the VFD blower control loop be retuned?
Retune after any major maintenance event affecting the blower, tip, instrumentation, or control system. Otherwise, verify tuning at least annually using step-change tests during the OOOOb annual performance verification window. Slowly worsening performance over months is often a sign that the original tuning has drifted from optimal and is overdue for re-verification.
What causes repeated pilot loss-of-flame events on an air assisted flare?
The four most common causes in diagnostic order are pilot fuel pressure drop (regulator drift, solenoid issues, upstream supply problems), ionization rod erosion or wet rod after weather (intermittent false loss signals), ignition transformer drift (failed relight after a real loss event), and high-wind blowout on exposed sites. Document the root cause of every event because OOOOb compliance requires it.
How do I tell whether a problem is in the tip or in the controls?
Control problems show patterns tied to flow rate, composition, or VFD speed and clear when the operating point changes. Tip problems persist across operating points and show in the combustion-zone monitor as a downward DRE drift over time. If the issue clears when you change the VFD setpoint or the gas composition, it is in the controls. If the issue is constant or trending, it is in the tip — schedule an inspection.
Does Hero Process Solutions provide field troubleshooting support?
Yes. Hero’s field services team supports installed A+ Series air assisted flares with remote and on-site troubleshooting, parts diagnosis and supply, VFD tuning verification, pilot and ignition system service, and OOOOb performance test support. Many operating issues can be diagnosed remotely from the continuous monitor data before a field visit is dispatched.
