A furnace hotspot is a local shell-temperature elevation relative to a suitable baseline. It may indicate refractory wear, an insulation gap, a joint or anchor bridge, material penetration, changed operation or a measurement artefact. Thermography becomes diagnostic only when emissivity, viewing conditions, equipment state and trend history are controlled.
First principle: apparent temperature is not automatically true temperature
An infrared camera estimates surface temperature from detected radiation. The result depends on emissivity, reflected apparent temperature, atmosphere, viewing angle, distance and camera setup.
Shiny or changing steel surfaces are especially sensitive to reflected radiation. A bright patch can therefore be a real thermal condition, an emissivity difference or both.
Pattern-based interpretation
|
Observed pattern |
Possible explanations |
Verification step |
|
Small local hotspot |
Local wear, crack, missing insulation, penetration or reflected source. |
Check from another angle; compare visual condition, history and neighbouring zones. |
|
Horizontal or circumferential band |
Slag line, charge line, burner zone, ring condition or layer transition. |
Match the band to internal geometry and operating stage. |
|
Vertical seam or repeating grid |
Panel joints, anchors, stiffeners or construction pattern. |
Compare with drawings and installation records. |
|
Broad temperature rise |
Higher load, longer cycle, worn lining, ambient change or general insulation decline. |
Normalise operating conditions and compare trend data. |
|
Rapidly expanding hotspot |
Active wear, penetration or insulation failure. |
Escalate under site safety procedure; increase monitoring frequency. |
A repeatable thermography workflow
- Define fixed scan zones and camera positions on an equipment drawing.
- Record equipment state: time in cycle, load, internal temperature, burners, cooling and ambient conditions.
- Set or verify emissivity using the site’s approved method; record camera settings.
- Capture thermal and visible images together, including scale and location reference.
- Trend maximum, average and representative spot temperatures—do not retain only colour images.
- Escalate against plant-specific limits and confirm findings with inspection or other measurements.
What thermography can and cannot establish
|
Thermography can support |
Thermography cannot prove alone |
|
Finding abnormal surface-temperature patterns. |
Exact remaining refractory thickness without a validated correlation. |
|
Comparing like-for-like zones over time. |
The precise internal defect type in every case. |
|
Prioritising inspection and maintenance areas. |
Energy savings from one image without heat-flux and operating data. |
|
Verifying whether an insulation retrofit changed the shell pattern. |
Safety to continue operating when site limits or alarms are exceeded. |
Turning scans into an insulation decision
If a repeatable hotspot aligns with a joint, penetration or locally damaged zone, a targeted repair may be appropriate.
If the entire shell trend rises as the lining wears, the issue may require a redesigned backup layer or changed wear allowance.
If the thermal pattern changes only with operating practice, the best intervention may be process control rather than material replacement.
Reporting format for credible results
A useful report states the equipment, zone, date, camera, lens, distance, emissivity, reflected temperature assumption, ambient conditions, operating stage and temperature statistics.
Before-and-after figures should use consistent scales where possible. Include uncertainty and label images as apparent surface temperatures unless the measurement method supports stronger wording.
Lanexis service perspective
Lanexis describes a workflow of thermal assessment, material selection, precision installation and performance monitoring.
Thermography can connect these stages: it identifies candidate loss areas, informs thermal modelling, checks installation outcomes and creates a campaign trend.
Its strongest use is as part of an engineering record, not as a standalone promotional image.
Frequently asked questions
What causes a furnace shell hotspot?
Possible causes include refractory wear, insulation gaps, open joints, penetration, anchors, changed firing or reflected radiation. The pattern must be verified in context.
Can thermography measure refractory thickness?
Only when a validated model or correlation exists for that equipment and operating condition. It is not a universal direct thickness measurement.
Should two thermograms use the same colour scale?
For visual comparison, a consistent scale is highly useful. Also compare numerical maximum, average and selected spot values.
When is a hotspot an emergency?
Follow the equipment manufacturer’s and plant’s approved temperature limits and escalation procedure. A rapidly changing or limit-exceeding hotspot requires immediate site assessment.
