Technologies
- NDT and Asset Reliability
  - Conventional NDT

Thermography

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Thermography

Thermography uses a camera containing large numbers of infrared sensors, which can detect and measure small temperature differences. The image showing these differences can be downloaded to and displayed on a PC, normally as a colour or grey-scale map.

There are two basic types of thermography – passive and active. In passive thermography, the camera is simply pointed at the test piece and from the thermal image a temperature map is constructed. Active thermography involves heating the surface of the object rapidly using an external heat source and observing how the temperature decays with time. Flaws in the material show up by variations in the temperature decay rate.

TWI's Thermography Resource

TWI owns state-of-the-art systems of both types:

Passive thermography - Fluke Ti30 infrared camera
Active thermography – Thermal Wave Imaging EchoTherm™ Pulsed Thermography (PT) system

Passive Thermography

Although the Fluke Ti30 is passive - having no method of inducing a thermal pulse - the data collection system can record temperature changes with time. An application of thermography is to study heat flow during joining.

TWI has used the Fluke Ti30 camera to study electro-fusion welds in polyethylene pipe. A potential defect in such welds occurs when one of the pipes is not pushed fully home in the coupler (so-called short-stab or under-penetration). In such joints the temperature of the coupler in the underpenetrated region will be higher after welding and will decay more slowly.

Pulsed thermography (PT)

PT is an active thermography technique for the assessment of composite materials. It is a high-speed, portable, non-contact and large area inspection technique. The surface to be inspected is heated by an intense light source (~1kW) for periods of 1-25ms. Heat flow into the sample is altered by the presence of any sub-surface flaws (disbonds, voids or inclusions), creating a temperature variation at the surface, which changes with time. These changes are recorded by the infrared camera.