Understanding Thermography (Infrared Analysis)

1. Definition: What is Thermography?

Thermography, or Infrared (IR) Analysis, is a non-contact, non-destructive testing technology that detects and visualizes thermal energy (heat) emitted from an object. It uses a specialized infrared camera to capture this thermal energy and convert it into a visual image, called a thermogram. In this image, different colors represent different temperatures, allowing a trained thermographer to instantly identify hot spots or cold spots that are invisible to the naked eye.

In a maintenance and reliability context, thermography is used to find temperature anomalies that are often the first sign of a developing problem. It is a key technology in a Condition-Based Maintenance (CBM) program and is highly complementary to vibration analysis and oil analysis.

2. How Does It Work?

All objects with a temperature above absolute zero emit thermal energy in the infrared spectrum. An infrared camera has a special detector that is sensitive to this radiation. The camera focuses the infrared energy onto the detector, which then creates a detailed temperature pattern called a thermogram.

It is important to understand that a thermogram is a map of emitted thermal energy, not a direct measurement of temperature. To get an accurate temperature reading, the thermographer must account for two key properties of the surface being measured:

• Emissivity: A measure of how effectively a surface emits thermal energy. A dull, black surface has a high emissivity (near 1.0), while a shiny, reflective surface has a low emissivity (near 0.0).
• Reflectivity: A shiny surface will not only emit its own heat but will also reflect the heat from surrounding objects (including the thermographer’s own body).

A trained thermographer knows how to adjust the camera for emissivity and how to position themselves to avoid reflections to ensure accurate and meaningful data.

3. Applications in Machinery and Plant Maintenance

Thermography is a versatile technology with a wide range of applications:

a) Electrical Systems

This is one of the most common and valuable applications. Overheating is almost always the first sign of a problem in an electrical component.

• Finding Loose Connections: A loose or corroded connection in a motor control center (MCC), breaker panel, or switchgear will have a higher resistance, causing it to heat up under load. This appears as a distinct hot spot in the thermogram.
• Detecting Overloaded Circuits: An overloaded circuit breaker or cable will appear warmer than similar, correctly loaded components.
• Identifying Unbalanced Loads: In a three-phase system, a significant temperature difference between the phases can indicate an unbalanced load.

b) Mechanical Systems

• Bearings: An overheating bearing can be a sign of improper lubrication (too much or too little) or advanced wear. Thermography can often confirm a suspected bearing fault found with vibration analysis.
• Couplings: Misaligned couplings can generate significant heat due to friction and stress.
• Gearboxes and Pumps: Abnormal temperatures can indicate incorrect oil levels, internal friction, or flow blockages.
• Belts and Sheaves: Misaligned belts or improper tension can cause sheaves to become hot.

c) Other Applications

• Steam Systems: Detecting failed steam traps that are blowing through and wasting energy.
• Refractory/Insulation: Finding areas where refractory lining in a furnace or insulation on a pipe has failed.
• Tank Levels: The liquid level in a large tank can often be “seen” due to temperature differences between the liquid and the vapor space above it.

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