Thermography Inspection: Guide for NDT Professionals

Thermography, also referred to as thermal imaging or thermal video, is a process that uses a thermal camera to capture and create an image of an object by using the infrared radiation emitted from that object. This process is a type of infrared imaging science.

How Does It Work?

Thermography works by detecting and visualising heat emitted from objects using infrared technology. Here's a breakdown of how it functions:

• Infrared Detection: Thermal cameras measure infrared radiation in the long-wave infrared range, typically between 9,000 and 14,000 nanometers (9–14 μm) which is invisible to the human eye.
  
  
• Temperature and Radiation: Every object with a temperature above absolute zero emits infrared radiation. The higher the temperature, the more radiation it emits.
  
  
• Thermal Imaging: These radiation levels are captured by the camera and converted into visual images, known as thermograms, which represent temperature differences.
  
  
• Heat Visualisation: Warmer objects appear brighter or in warmer colours on the thermal image, while cooler areas appear darker. This contrast helps highlight temperature variations clearly.
  
  
• Application Value: By mapping these differences, thermal cameras provide valuable insights into the condition of structures, equipment, and environments. This makes them indispensable tools for inspections, maintenance, surveillance, and more.

Types of Thermal Imaging

There are two types of thermography for intended uses.

• Passive thermography: It uses the infrared radiation that is naturally emitted by objects.
• Active thermography: It involves the use of an external stimulus to cause a temperature difference in an object which is then measured by the camera.

Key Components of a Thermal Imager

A thermal imager relies on several key components that work together to capture and analyse thermal data. Each component plays a vital role in ensuring accurate temperature measurement and high-quality thermal imaging.

By making it essential to understand how these elements function to achieve optimal results in various applications.

Lens

The lens in a thermal imager focuses infrared radiation onto the detector, allowing the camera to capture and produce clear thermal images. It plays a crucial role in determining the quality and resolution of the thermal data collected.

Detector

Two primary types of detectors, which are cooled and uncooled that play crucial roles in determining the performance and capabilities of the thermal imager. 

Cooled detectors represent the high-performance option, operating in extreme cryogenic conditions that range from a frigid 4 Kelvin (-269°C) up to just below room temperature. In practical use, they're typically maintained between 60K to 100K (-213°C to -173°C) through specialised cooling systems. This intense cooling enables remarkable sensitivity and rapid response times, making them ideal for demanding applications like military targeting systems or scientific research where precision is paramount.

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On the other end of the spectrum, uncooled detectors offer a more practical solution for everyday use. Designed to function at ambient room temperatures without any cryogenic support, these detectors sacrifice some sensitivity for significantly reduced size, power requirements, and cost. This makes them the go-to choice for commercial thermal cameras used in building inspections, security systems, and industrial maintenance.

Display

Shows the thermal image, often with colour scales that represent different temperatures.

Controls

Allow the user to adjust settings, such as focus, temperature scale, and colour palettes.

Advantages of Thermography

Thermography provides a non-destructive, real-time method to visually detect and compare surface temperatures, even in dark or hazardous areas. It helps identify potential problems by spotting high-temperature components before failure and can measure inaccessible or moving targets efficiently.

Provides a visual picture, allowing for temperature comparison over a large area. It can detect moving targets in real-time and be used in dark areas.

Identifies potential problems by finding components with higher temperatures before they fail. It can measure or observe areas that are inaccessible or hazardous for other methods, and is a non-destructive testing method.

Limitations and Disadvantages of Thermography

Although thermography inspection is an excellent tool for maintenance, it does have certain limitations that may discourage its use. Which is why many factors can influence thermal images, leading to misinterpretations:

• Requires professional training for proper use and interpretation of images.
• Reflections can lead to incorrect data.
• Some materials change temperature more slowly than others, requiring knowledge of the materials being inspected.
• Thermal gradients can affect the accuracy of readings.

Applications

Thermography is a versatile technology that finds applications across a wide range of industries, helping to identify issues that might otherwise go unnoticed. 

From predictive maintenance to safety inspections, thermal imaging provides valuable insights that enhance efficiency and minimise risks.

Industrial Applications

In industrial settings, thermography plays a critical role in maintaining operational efficiency and safety. 

By detecting temperature variations in equipment and infrastructure, thermal imaging helps prevent costly breakdowns, improve energy efficiency, and ensure the safe operation of machinery across various industries, including manufacturing, energy, and construction.

Predictive Maintenance

By identifying temperature changes before failures occur, it allows for timely maintenance, reducing unplanned downtime and improving the reliability of equipment:

• Finding overheating joints and sections of power lines.
• Inspecting electrical distribution equipment such as transformer yards and distribution panels.
• Identifying defects in shafts, pipes, and other metal or plastic parts.
• Monitoring motors, pumps, and gearboxes.

Process Control

It ensures that production processes remain within optimal conditions, helping to maintain quality and prevent issues that could disrupt operations:

• Monitoring furnaces, boilers, and heat exchangers.
• Checking for pipe blockages.
• Ensuring refractory quality in boilers and furnaces.
• Monitoring tank levels.

Quality Control

By identifying temperature discrepancies, they help detect defects or irregularities in products, enabling manufacturers to maintain high standards and avoid costly production errors:

• Inspecting welding robots.
• Checking uniformity of product temperature.

Building Inspections

Thermal imaging is a vital tool for building inspections, enabling professionals to identify hidden issues such as insulation gaps, water leaks, and structural defects. Visualising temperature differences allows for non-invasive assessments that improve the accuracy of inspections and help prioritise repairs.

Energy Audits

Detecting heat leaks and energy losses is crucial for improving a building's energy efficiency. Thermal cameras highlight areas where heat is escaping helping to pinpoint opportunities for energy savings and reducing overall heating and cooling costs:

• Inspecting insulation and detecting refrigerant leaks.
• Finding air leaks.

• Locating moisture in walls and roofs.

Structural Analysis

By detecting temperature variations in materials, it helps uncover hidden problems such as moisture intrusion, cracks and potential areas of weakness, enabling proactive maintenance and repairs to ensure the integrity of structures:

• Locating pest infestations.
• Analysing masonry walls.
• Checking for missing insulation.

Roof Inspections

Thermal imaging is highly effective in locating wet insulation and identifying structural issues within roofs. Detecting temperature anomalies helps uncover moisture accumulation, leaks, and areas of heat loss, providing a clear picture of a roof’s condition without the need for invasive methods.

Home Performance

Thermal cameras are essential for evaluating overall building performance by assessing heat distribution and identifying inefficiencies. They help pinpoint areas where energy is being wasted, from air leaks to insulation gaps, enabling homeowners to optimise comfort and reduce energy consumption.

Health

Thermography inspection is useful for monitoring physiological responses, such as detecting fever in humans and animals by identifying elevated body temperatures that may indicate infection. It also has applications in certain physiotherapy treatments.

Security and Defence

Thermal imaging is widely used in security and defense for surveillance, allowing operators to detect people or objects even in low-visibility conditions. By capturing heat signatures, thermal cameras provide critical insights for security personnel to monitor environments and respond to potential threats effectively.

Military Applications

In military applications, thermal imaging is crucial for detecting people and vehicles, especially when using unmanned aerial vehicles (UAVs). The technology enhances reconnaissance, providing real-time thermal data that helps improve situational awareness and decision-making on the battlefield.

Other Applications

Beyond traditional inspections, thermography inspection is practised across various industries for its ability to detect temperature anomalies that are invisible to the naked eye. 

From identifying energy inefficiencies in buildings to enhancing medical diagnostics and ensuring safety in industrial settings, thermal cameras provide invaluable insights. Some other key applications include:

• Inspecting photovoltaic power plants.
• Monitoring active volcanoes.
• Archaeological research.
• Equine thermography.
• Bird surveys.
• Physical password breaking via thermal sequence analysis.
• Automatic seed counting.
• Detection of delamination in bridge decks.

How to Perform a Thermographic Inspection

Performing a thermographic inspection requires more than just the right equipment as it demands knowledge, skill, and adherence to safety standards. 

By utilising thermal cameras to capture and analyse temperature variations, professionals can identify potential issues before they become costly problems. 

Whether you’re inspecting electrical systems, building structures, or mechanical equipment, understanding the steps and best practices for a thermographic inspection is key to ensuring accurate results and maintaining safety throughout the process.

Planning

Define the goals and objectives of the inspection. Identify the necessary equipment, configurations, and procedures. Establish inspection routes and timelines.

Baseline Inspection

The process involves capturing thermal images of all equipment under normal conditions, documenting all conditions, settings, and locations, and establishing acceptable temperature ranges and alarm thresholds.

During Inspection

To detect thermal anomalies, scan equipment, take images, be aware of environmental conditions, check electrical devices, ensure temperature difference, and adjust angle when inspecting reflective targets.

Analysis and Reporting

Utilise software to analyse thermal images, identify hot or cold spots, compare to baseline, and document findings in reports, including problem location, diagnosis, and suggested corrective actions.

Standards and Training

Adhering to established guidelines, gaining professional expertise, and prioritising safety ensures accurate and reliable thermographic inspections. 

Whether you're new to thermal imaging or looking to enhance your skills, understanding the importance of standards and certifications is crucial for achieving the best results while maintaining safety:

• Standards: Organisations such as ASTM International and SNT develop standards for thermographic inspection.
• Training: Professional training is essential for proper use and interpretation of thermal images. Training can range from short introductory courses to certification programs.
• Certification: Thermographers can be certified at different levels (Level I, II, and III), with higher levels requiring more training and experience.
• Safety: Thermographers should follow safety procedures and use personal protective equipment (PPE), especially when inspecting electrical systems.

Inspection Methods

These methods involve capturing and analysing infrared data in different ways, allowing for accurate assessments of temperature variations in objects or environments:

• Comparative Thermography: Comparing similar components under similar conditions to assess their condition.
• Baseline Thermography: Establishing a reference point using images of equipment operating under normal conditions.
• Thermal Trending: Comparing temperature distributions in the same component over time.

Final Thoughts 

Thermography inspection is a powerful, non-invasive tool that offers deep insights into the thermal performance of systems, structures, and equipment. With proper training, equipment, and methodology, thermographic inspections can detect issues early, reduce costs, enhance safety, and improve operational efficiency. 

As technology continues to advance, thermal imaging will remain an essential asset across industries, providing clarity where the human eye falls short.

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