Infrared Thermography: Mechanical and Fluid-System Scanning

What Infrared Thermography Measures

Every object above absolute zero emits infrared (IR) radiation proportional to its surface temperature. A thermal imaging camera detects that radiation and converts it into a false-color image called a thermogram. Warmer areas appear as bright yellows, oranges, or whites; cooler areas appear as blues and purples, depending on the color palette selected. Because heat is a byproduct of friction, electrical resistance, flow restriction, and mechanical stress, a thermal camera lets you see faults that are invisible to the naked eye — without stopping the equipment.

Why Thermography Matters for Industrial and Marine Maintenance

Rotating machinery and pressurized fluid systems are found throughout manufacturing plants and marine vessels. Bearings, motors, pump casings, steam traps, and hydraulic lines all run at characteristic temperatures under normal load. When something goes wrong — a bearing begins to fail, a steam trap sticks closed, a pump impeller cavitates, or a coupling misaligns — the surface temperature of the affected component rises above its normal baseline. Catching that temperature rise early is the core value of predictive maintenance (PdM): you schedule the repair before the failure causes unplanned downtime, secondary damage, or a safety event.

Key Concepts: Emissivity and Delta-T

Emissivity is the ratio of radiation emitted by a real surface compared with a perfect emitter (a blackbody) at the same temperature. Shiny metallic surfaces have low emissivity and can fool the camera into reading a falsely low temperature. Always check the camera's emissivity setting before scanning. Most industrial paints, oxidized metals, rubber hoses, and plastic housings have emissivity values close to 0.90–0.95 and can be measured reliably. When in doubt, apply a small piece of black electrical tape to a metal surface, let it reach thermal equilibrium, and use it as a reference spot.

Delta-T (ΔT) is the temperature difference between a suspect area and a reference baseline — either a similar component running under the same load, or a cool area on the same component. Delta-T is the number that drives your fault classification and urgency rating. A ΔT of a few degrees may call for increased monitoring frequency; a large ΔT — the specific thresholds vary by equipment type and the standard your site follows — typically calls for prompt corrective action. Always document both the hotspot temperature and the reference temperature so the delta-T is traceable.

Normal Thermal Gradients vs. Fault-Related Hotspots

Normal thermal gradients are gradual and symmetrical. A motor running at rated load will be warmer at the drive-end bearing than at the frame, and warmer at the frame than at ambient — a smooth ramp that follows heat-flow physics. A pump casing will show a warm inlet zone tapering toward the discharge.

Fault-related hotspots look different: they are localized, often asymmetrical, and hotter than the surrounding component by a noticeable margin. Common faults you will encounter include:

• Overloaded or failing bearing housing — a tight hot zone centered on the bearing race, often 20 °F or more above the opposite bearing on the same shaft.
• Blocked or failed steam trap — the trap body and downstream piping stay hot because live steam passes through instead of condensate only (failed-open), or the upstream piping backs up with condensate (failed-closed, which shows as an abrupt cool zone just before the trap).
• Hydraulic restriction or blocked filter — elevated temperature downstream of the restriction as fluid shears through a reduced opening.
• Motor winding or rotor fault — uneven heating across the motor frame or end bells.

Scanning Procedure — Step by Step

1. Don PPE before approaching the rig. Arc-flash rated face shield and voltage-rated gloves are required near energized panels; safety glasses, hearing protection, and close-fitting clothing with no loose items are required near rotating parts at all times. Never defeat a guard to get a better image.

2. Allow equipment to reach steady-state temperature — at least 30 minutes of operation under representative load before scanning.

3. Set camera emissivity to match the surface being measured. Record the setting on your scan log.

4. Establish a reference baseline. Locate an area of the same equipment that is known to be operating normally and note its temperature.

5. Capture at least ten images covering motor end bells, bearing housings, shaft coupling, pump casing, suction and discharge flanges, and all steam-trap or hydraulic-line sections assigned. Frame each image so the asset ID or a label is visible.

6. Log every image file name, camera orientation, and machine location on the scan log sheet as you go. Do not rely on memory.

7. Maintain safe working distance from rotating parts. Use the camera's zoom rather than stepping closer.

Reviewing Images and Writing the Report

In the camera software, open each image and apply spot-temperature and area-measurement tools. Compare hotspot readings to your reference baseline and calculate ΔT. Flag any image where ΔT exceeds the threshold defined in your site standard or the instructor's rubric.

Your formal inspection report must include: asset ID, date, ambient temperature and relative humidity (ambient conditions affect readings), annotated thermograms with measurement markers, the calculated ΔT for each flagged area, a fault classification, a corrective action recommendation (repair, monitor, replace), and a recommended follow-up interval. Use the instructor-provided template — the format mirrors what industry clients and CMMS systems expect.