Infrared Thermography and its Applications: An Overview

Table of Content

• What is Infrared Thermography?
• Types of Infrared Thermometers
• How to use Infrared Thermography?
• Infrared Thermography Assessment Criteria
• Interpreting Infrared Data Correctly
• Infrared Thermography Testing Techniques
• Advantages of Infrared Thermography
• Disadvantages of Infrared Thermography
• Key Takeaways

Infrared Thermography, a revolutionary technique used in Non-destructive Testing, employs specialized cameras to detect the imperceptible and invisible infrared energy emitted by objects. This thermal energy, which is beyond the scope of human vision, serves as a tangible representation of heat in the electromagnetic spectrum. Unlike visible light, the infrared spectrum encompasses all objects emitting infrared energy, even those seemingly cold, like ice cubes. 

What is Infrared Thermography?

Infrared thermography uses thermal imagers, to unveil the invisible thermal radiation emanating from objects, converting it into temperature data and projecting it to a visual representation of the temperature distribution, commonly referred to as Thermograms. These thermal images act like a unique lens, exposing heat-producing objects that are imperceptible to the naked eye. 

Infrared thermography is a pivotal tool in various NDT Industries and is widely employed in predictive maintenance and condition monitoring. Its applications span diverse industries, including machine condition monitoring, building diagnostics for moisture, roof inspections, and energy-loss assessments, as well as medical imaging for conditions like peripheral vascular disease and metabolic abnormalities. Given that all objects emit thermal infrared energy above absolute zero, thermal imagers effortlessly capture and display infrared wavelengths irrespective of ambient light conditions. A parallel can be drawn with night-vision goggles, showcasing the versatility of infrared thermography in detecting objects in darkness. 

While infrared imagers are user-friendly, decoding the generated data requires a nuanced understanding of their operation, coupled with baseline knowledge of radiometry and heat transfer processes. Inspecting mechanical equipment through infrared thermography reveals a wealth of insights, but effective interpretation necessitates a holistic comprehension of the technology for NDT Services.

Types of Infrared Thermometers

Infrared thermometers, integral to contemporary temperature measurement, encompass various configurations tailored to specific applications. These devices, which operate without direct contact, rely on a lens to focus infrared thermal radiation onto a detector, translating radiant energy into a color-coded signal. Here are three common types of Infrared Thermometers:

1. Spot Infrared Thermometers (Pyrometers)

Resembling handheld radar guns, spot infrared thermometers precisely measure temperatures at specific points on a surface. Ideal for hard-to-reach structures or those in extreme conditions, they find applications in HVAC diagnostics, bearing inspections, electrical room monitoring, and energy audits. Parameters like field of view (FOV) and distance-to-spot ratio (D:S) ensure accurate measurements, with higher ratios indicating superior resolution.

2. Infrared Scanner Systems

Designed for scanning larger areas, these systems prove beneficial in manufacturing plants with conveyors or web processes. Common applications include scanning objects on conveyor belts or monitoring sheets of glass or metal leaving an oven.

3. Infrared Thermal-Imaging Cameras

Representing an advanced form of radiation thermometers, thermal-imaging cameras measure temperatures across large areas, creating two-dimensional thermographic images. These cameras are more software- and hardware-based than spot thermometers and offer real-time imaging. They can be connected to specialized software for enhanced evaluation, accuracy, and report generation. Features such as multiple color palettes, fusion blending, and color alarms provide versatility in deciphering temperature differences.

Key considerations when choosing a Thermal-imaging Camera include detector resolution, thermal sensitivity, and temperature range. Resolutions in the range 160x120, 320x240, and 640x480 pixels are commonly available. Thermal sensitivity indicates the camera's ability to detect minimal temperature differences, while the temperature range specifies the minimum and maximum temperatures measurable. In order to ensure the optimal performance of these Thermal-Imaging Cameras across diverse applications, detector resolution, and thermal sensitivity should be carefully controlled.

How to use Infrared Thermography?

Infrared thermography stands as a cornerstone in condition monitoring and preventive maintenance, offering a non-intrusive, real-time approach to detecting thermal abnormalities in machinery. The efficiency of Thermal Inspections depends on the judicious application of three primary methods: comparative thermography, baseline thermography, and thermal-trending thermography.

1. Comparative Thermography

Comparative thermography helps in assessing the temperature of similar components under comparable conditions. This method reveals the hidden issues by analyzing variations in temperature. Thermographers can opt for either quantitative or qualitative approaches.

Quantitative inspections, conducted by highly trained thermographers, precisely measure temperature or temperature distribution. On the other hand, qualitative inspections emphasize temperature differences rather than absolute values. While 90 percent of industrial applications lean towards qualitative measurements, a strategic combination of quantitative and qualitative data aids in gauging both the severity and nature of detected issues.

2. Baseline Thermography

Baseline thermography establishes a reference point for material identification by capturing temperature readings under optimal conditions. It serves as a benchmark for subsequent thermal images, allowing early identification of potential issues. Conducting baseline measurements on critical assets, especially when new or recently repaired, is advisable. This method lays the groundwork for proactive maintenance strategies, enhancing the overall efficiency of the monitoring process.

3. Thermal-Trending Thermography

Thermal-trending thermography examines how temperature evolves within a component or asset over extended periods. Particularly useful for analyzing mechanical equipment with intricate thermal signatures or gradual thermal developments, this method shines in scenarios where a slow, subtle shift in temperature signifies a potential concern. For instance, monitoring high-temperature refractory insulation in a boiler over time assists in formulating a maintenance schedule that minimizes downtime.

In essence, mastering the art of infrared thermography involves selecting the most apt method based on the equipment type and the desired data. Comparative thermography uncovers hidden anomalies, baseline thermography establishes reference points, and thermal-trending thermography provides insights into evolving temperature patterns. Together, these techniques empower practitioners to navigate the complexities of machinery diagnostics, ensuring a proactive and comprehensive approach to condition monitoring.

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Infrared Thermography Assessment Criteria

In the dynamic realm of condition monitoring through infrared thermography, the establishment of severity criteria emerges as a pivotal practice. These criteria, delineated either in general categories for temperature levels or tailored to specific machines and components, evolve over time, shaped by a meticulous accumulation of data. Best practices dictate the development of criteria specific to each equipment category, considering factors such as design intricacies, operational dynamics, installation specifics, maintenance characteristics, criticality, and potential failure modes.

1. Individualised Severity Criteria

Crafting severity criteria for individual machines or components involves a multifaceted analysis, considering temperature rise against historical data. The rate of deterioration, time to failure, and the machine or component's criticality to the overall process and safety are crucial factors.

Thermographers often focus on temperature rises in critical machines, mechanical components, bearings, and electrical supply units to classify temperature severity and pinpoint mechanical abnormalities.

2. Relative Temperature Criteria

One approach to severity criteria involves categorizing temperature rises into advisory, intermediate, serious, and critical categories. For instance, a machine may fall under the advisory category if its temperature rises 10 degrees above a reference or baseline temperature. The critical category, on the other hand, might entail a temperature rise exceeding 104 degrees above the baseline. This relative approach provides a nuanced understanding of severity based on distinct temperature thresholds.

3. Absolute Temperature Criteria

Thermographers may opt for material or design criteria derived from published data, focusing on either the machine's material or design. Design criteria, encompassing material considerations, are often preferred for reliability monitoring. Material criteria become particularly relevant when measuring the heating of multiple adjacent components, with the lowest temperature specification serving as the "alarm criteria." This approach ensures a comprehensive assessment considering both material and design aspects.

4. Profile Assessment Criteria

Profile assessment involves comparing temperature differences and patterns across surfaces. A precursor to this is a severity assessment, determining absolute and differential temperatures to categorize the machine or component as either "as new" or "failed." Key areas of focus in a profile assessment include temperature gradients, historical changes, localized differences, and the absolute temperatures or location of abnormalities.

This comprehensive approach illustrates the condition of the machinery, aiding in timely interventions. Understanding and implementing infrared thermography assessment criteria are vital for effective condition monitoring. This practical guide empowers practitioners to navigate the intricacies of temperature variations, ensuring a proactive and tailored approach to maintaining critical assets. The evolution of severity criteria over time becomes a testament to the continuous improvement and precision achievable through this indispensable tool in the realm of preventive maintenance.

Interpreting Infrared Data Correctly

The widespread adoption of infrared thermography in preventive maintenance can be attributed to its user-friendly nature. However, effective interpretation of the data and a thorough understanding of imager capabilities are imperative to avoid common pitfalls.

Here are key aspects to consider to ensure accurate and insightful infrared data interpretation:

1. Understanding Resolution

Infrared thermography images come with inherent limitations in their ability to perceive and measure. It's essential to grasp these resolution limitations before acquiring an infrared imager. Knowing the device's capabilities ensures that the data collected aligns with the precision required for diagnostic accuracy. This foundational understanding prevents misinterpretation and aids in harnessing the full potential of the technology.

2. Discounting Ambient Conditions

Environmental factors such as wind, rain, ambient air temperature, and sunlight exert a tangible influence on the final temperature measurement. To avoid inaccuracies, meticulous attention to ambient conditions is paramount. Accounting for elements like wind and rain in reporting is crucial. Additionally, inspecting surfaces away from direct sunlight helps mitigate abnormal temperature readings, enhancing the reliability of the data collected.

3. Disregarding Cold Spots

While the focus is often on identifying hot spots, neglecting cold spots can lead to oversight, particularly in electrical or steam systems. Cold spots may signify issues such as the absence of electrical current in a capacitor or a malfunctioning steam trap. A comprehensive approach to thermography involves scrutinizing both hot and cold anomalies, ensuring a thorough assessment of potential concerns.

4. Solely Focusing on Surface Temperature

Ambient factors inherently impact the accuracy of thermal imaging in displaying absolute temperatures. Consequently, prioritizing differences in thermal patterns rather than fixating on apparent temperatures proves more effective. In a comparative analysis of multiple components using infrared thermography, the one diverging from the thermal norm likely signals an underlying issue. This nuanced approach provides a more reliable indication of potential problems, guiding maintenance efforts more precisely.

In essence, the effectiveness of infrared thermography lies not only in its simplicity but also in the astute interpretation of the data it yields. By acknowledging and mitigating common misinterpretations related to resolution, ambient conditions, cold spots, and surface temperatures, practitioners can harness the full potential of infrared technology for robust and proactive preventive maintenance.

Infrared Thermography Testing Techniques

In the expansive landscape of infrared thermography, testing techniques play a pivotal role in unraveling the mysteries of machinery health and performance. The choice of technique hinges on various considerations, encompassing the desired data set and the specific nuances of the monitoring task at hand. Given below are some of the most prevalent infrared thermography testing techniques, shedding light on their applications and advantages.

1. Passive Thermography

This method involves capturing thermal images while the machine is operational or immediately after shutdown. Operating without an external energy source or necessitating machine downtime, passive thermography allows for seamless data collection, providing insights into temperature patterns and potential abnormalities.

2. Active Thermography

For a more dynamic approach, active thermography takes the stage. This technique relies on an external energy source to induce temperature variations in components, influenced by internal materials and defects. By showcasing how heat flows through a component during operation, active thermography serves as a valuable tool for pinpointing abnormalities and potential issues.

3. Flash Thermography

Flash thermography employs pulses of light to illuminate gaps, inclusions, or obstructions hindering heat flow into a component. This rapid, high-energy approach facilitates the swift identification of anomalies, offering a snapshot of the component's thermal integrity.

4. Vibrothermography

Introducing an acoustic dimension, vibrothermography injects acoustic waves into a machine or component. This technique adeptly identifies potential cracks in the material. Acoustic energy disrupts the surfaces flanking a crack, generating friction and subsequent heat. The infrared camera captures this heat, unravelling the hidden complexities within the material.

5. Lock-in Thermography

In scenarios demanding a deeper penetration, lock-in thermography emerges as a method of choice. Requiring an external energy source—be it light, sound, or heat—lock-in thermography unveils abnormalities below the component's surface. Precision is paramount, necessitating knowledge of the abnormality's depth, size, location, and material properties for accurate results. While it demands more time than other techniques, lock-in thermography is adept at navigating components with thicker walls.

Each of these infrared thermography testing techniques brings a unique set of capabilities to the diagnostic arena. From seamless data collection with passive thermography to the dynamic insights offered by active thermography and the precision of flash, vibrothermography, and lock-in techniques, the choice depends on the specific demands of the monitoring task. As technology continues to evolve, these techniques stand as beacons, guiding practitioners toward a proactive and comprehensive understanding of machinery health.

Advantages of Infrared Thermography

1. No Contact Required:

Infrared thermography eliminates the need for physical contact with components or machines during testing.

This non-contact nature enhances safety and efficiency, allowing for inspections without disrupting normal operations.

2. Real-time Output:

One of the defining features is the ability to obtain real-time output. Infrared thermography provides instantaneous data, facilitating quick decision-making and timely interventions based on the most up-to-date information.

3. Large Surface Area Coverage:

The technology allows for the simultaneous capture of data on large surface areas. This capability is particularly valuable in industrial settings, enabling a comprehensive assessment of machinery and systems in a single scan.

4. Easy-to-read Visual Images:

Infrared cameras produce visual images that are easy to interpret. These images provide a clear visualization of temperature variations, making them accessible to both experts and non-experts, facilitating effective communication of findings.

5. Data Analysis Software Integration:

The data collected can be seamlessly uploaded to software for further analysis. This integration with analysis tools enhances the depth of insights, allowing for detailed examination and trend analysis over time.

6. Great Mobility:

Infrared cameras offer exceptional mobility, allowing practitioners to navigate diverse and complex environments. This flexibility is particularly advantageous in industrial settings with intricate machinery configurations.

7. No Downtime or Production Interruptions:

A significant advantage is the absence of downtime or production interruptions during testing. Infrared thermography allows for non-intrusive inspections, ensuring continuous operations without the need to halt production.

Disadvantages of Infrared Thermography

In the realm of preventive maintenance, infrared thermography stands as a powerful ally, revolutionizing the landscape with its non-contact, real-time diagnostics. While the advantages are substantial, it's crucial to navigate the potential pitfalls and costs associated with this cutting-edge technology.

1. Equipment Cost

The upfront cost of infrared equipment can be a significant investment. It's essential to consider not only the equipment cost but also the associated expenses, including time and labor. The savings derived from early detection warnings need to be weighed against the initial investment.

2. Limitations in Detecting Through Non-Transparent Materials

Infrared technology faces limitations when components are separated by non-transparent materials like glass covers. Such materials appear non-transparent when viewed through an infrared imager, rendering them opaque to temperature detection.

3. Expertise Requirement for Data Evaluation:

Interpreting infrared data demands significant expertise and an extensive knowledge base. Evaluating imaging results requires a thorough understanding of thermodynamics, material properties, and the intricacies of the specific machinery being inspected. The advantages of infrared thermography are transformative in preventive maintenance, offering efficiency, real-time insights, and non-intrusive assessments.

However, the investment considerations and the expertise required for accurate data interpretation underscore the need for a thoughtful and strategic approach to maximize the benefits of this advanced technology. The exploration of infrared thermography unveils a realm where the imperceptible becomes tangible, empowering industries across diverse sectors.

The transformative potential of this revolutionary technique lies in its ability to capture and decode the invisible language of heat, opening new dimensions in preventive maintenance and diagnostics. From the fundamental understanding of infrared energy emission to the intricate workings of thermographic cameras, the journey traverses the complexities of temperature measurement.

Infrared thermography, with its non-contact, real-time capabilities, emerges as a cornerstone in condition monitoring, offering advantages that range from large surface area coverage to easy-to-read visual images. The spectrum of infrared thermometers, from spot devices to thermal imaging cameras, underscores the adaptability of this technology to varied applications.

Each type plays a unique role, redefining temperature measurement precision and efficiency across industries. The characteristics of infrared thermography equipment, marked by its capacity to capture temperature distributions in real-time from a distance, reinforce its status as a technological marvel. Its role in setting severity criteria for condition monitoring further solidifies its place as an indispensable tool in the pursuit of operational excellence. However, the journey is not without challenges. The nuanced interpretation of infrared data demands expertise, and the investment considerations, though outweighed by the benefits, necessitate strategic planning.

Key Takeaways

• Infrared Thermography employs specialized cameras to detect thermal energy emitted by objects, converting it into visual temperature data. 
• This technology visualizes heat patterns imperceptible to the naked eye, aiding in diagnostics and anomaly detection. 
• Its uses span various sectors, from predictive maintenance in industries to building diagnostics, medical imaging, law enforcement, and more. 
• It aids in identifying thermal anomalies, monitoring electrical systems, and even medical conditions like peripheral vascular disease.
• There are various types of thermometers including spot thermometers, scanner systems, and Thermal-Imaging Cameras, each tailored for specific applications, offering different resolutions and features.
• Setting severity criteria is crucial for effective monitoring. Criteria can be individualized or categorized based on temperature rises, profiles, or material design considerations.
• Understanding resolution limitations, accounting for ambient conditions, and scrutinizing both hot and cold anomalies enhance the reliability of thermal imaging results. 
• Different techniques like passive, active, flash, vibrothermography, and lock-in thermography offer varied insights into machinery health, each with distinct applications and advantages.
• Infrared Thermography offers real-time, non-contact assessments, large surface area coverage, and easy-to-read visual images. However, there are associated costs, limitations in detecting through non-transparent materials, and a requirement for expertise in data interpretation.

References

1. Reliable Plant
2. TSI Energy Solutions
3. Sapphire Technologies
4. Munich Re
5. SOS electronic