Infrared Thermography (IRT)

Infrared Thermography (IRT) is a non-destructive testing (NDT) technique that uses infrared imaging to detect temperature variations on the surface of a component. These variations can indicate underlying defects, material inconsistencies, or abnormal operating conditions. It is widely used for condition monitoring, preventive maintenance, and quality assurance.

Overview

IRT relies on the fact that all objects emit infrared radiation proportional to their temperature. By capturing this radiation with a thermal imaging camera, inspectors can visualize temperature distributions across a surface. Abnormal hot or cold spots often correspond to defects, discontinuities, or operational issues. The method is fast, non-contact, and can be applied while equipment is in service.

Apparatus and Working

Apparatus

  • Infrared camera: Detects and converts infrared radiation into thermal images.
  • Computer/software: For image processing, analysis, and reporting.
  • Reference sources: Blackbody calibrators for accuracy checks.
  • Lighting/shielding: To minimize reflections and environmental interference.

Working Steps

  1. Preparation: Ensure the surface is accessible and free from obstructions.
  2. Imaging: Capture thermal images of the component using an infrared camera.
  3. Analysis: Identify abnormal hot or cold spots compared to expected patterns.
  4. Interpretation: Correlate temperature anomalies with possible defects or conditions.
  5. Reporting: Document findings with annotated thermal images.

Principle

Infrared Thermography is based on the principle that all objects above absolute zero emit infrared radiation. The intensity and wavelength distribution of this radiation depend on the object’s temperature and emissivity. Thermal cameras detect this radiation and convert it into a visual image (thermogram), where different colors or shades represent temperature variations. Defects or anomalies cause localized changes in heat flow, which appear as temperature contrasts.

Advantages and Disadvantages

Advantages

  • Non-contact and non-invasive method.
  • Can inspect large areas quickly.
  • Allows real-time monitoring while equipment is in operation.
  • Effective for preventive maintenance and condition monitoring.
  • Provides visual, easy-to-interpret results.

Disadvantages

  • Only detects surface temperature variations, not internal defects directly.
  • Accuracy depends on emissivity, surface condition, and environmental factors.
  • Requires skilled interpretation to avoid false indications.
  • High-quality infrared cameras can be expensive.

Applications

  • Electrical systems: Detecting overheating in connections, breakers, and transformers.
  • Mechanical systems: Monitoring bearings, motors, and rotating equipment for abnormal heating.
  • Building inspection: Identifying insulation defects, moisture ingress, and air leaks.
  • Process industry: Monitoring refractory linings, pipelines, and vessels.
  • Aerospace and automotive: Detecting delaminations, disbonds, and thermal anomalies in composites.

Welding Defects Detectable by IRT

  • Lack of fusion (near-surface): Causes localized heat flow anomalies.
  • Cracks (surface-breaking): Appear as hot or cold lines due to heat concentration.
  • Porosity clusters: May alter thermal conductivity, visible as irregular spots.
  • Incomplete penetration: Root defects affecting heat distribution.
  • Delaminations in overlays: Detected as thermal discontinuities.