Cost-effective thermography

According to FLIR Systems, thermographic inspection using advanced infrared camera technology has never been more affordable!


The potential for thermal imaging as a flexible and powerful technology is finding favour in the aerospace industry, where its huge scope can range from standard predictive maintenance right up to non-destructive testing (NDT) and stress analysis in AOG applications.

Needless to say, not all applications can be addressed by a single type of camera. Broadly speaking, the technology falls into two camps: cooled for scientific research and development applications and uncooled, typically used for predictive maintenance work and automated infrared inspection in the manufacturing sector.

In recent years however this definition has become a little blurred as the gap between cooled and uncooled cameras has narrowed considerably in terms of sensitivity. This is good news for those involved in aerospace production and means that relatively sophisticated inspection applications can now be addressed by a commercially priced, uncooled, industrial grade camera. In other words thermography has become an extremely cost-effective choice for all manner of quality control, predictive maintenance and even NDT applications.

Shannon Aerospace is one such company that is proving the point. As a fully-owned subsidiary of Lufthansa Technik, Shannon Aerospace caters for the airframe maintenance requirements of over 50 commercial airlines and charter operators. The company is located at Shannon Airport in a facility that includes five heavy maintenance bays, painting bays and workshops and stores. Although the airline customers are not based at Shannon Airport, they fly their aircraft there specifically for checks, maintenance and repairs.

Shannon Aerospace specialises in the heavy airframe overhaul of narrow body aircraft types, performing structural maintenance checks on Airbus, Boeing and McDonnell Douglas aircraft. For the Airbus A319, A320 and A321 models, it provides a range of services including D-Checks and C-Checks, and among the work undertaken is NDT. An important and relatively recent addition to this speciality is the thermographic inspection of elevators (the moving component on the rear of the aircraft tail which is used to adjust the climb and descent of the aircraft).

At its commercial aircraft maintenance facility in Ireland, Shannon Aerospace uses a FLIR Systems P-Series predictive maintenance infrared camera to detect for moisture in the ‘honeycomb' composite used in Airbus elevators. This is in response to Airbus adding thermal imaging to the mandatory inspection requirements for elevators on its narrow body aircraft.

The inspection is designed to catch moisture build-up early and reduce the cost of repairs which involve removing the external surface of the elevator panels. The FLIR P-Series camera captures images that show the temperature differences between moisture and the composite materials inside the elevator.

The Airbus elevators consist of an upper and lower panel which tapers to a point at the trailing edge. Between the two panels is a structural framework of about 20cm depth. The panels themselves have two surfaces, one facing outwards to the airflow and one internal and adjacent to the structural framework. Between the two surfaces of each panel is a honeycomb composite about 3cm thick. Thermographic inspection is used to detect moisture inside the honeycomb.

During the inspection process, the elevators are removed manually and put into an oven inside the composite shop at the Shannon facility. The oven is heated to a predetermined temperature for long enough that all materials - whatever their molecular structure - will heat to the same point. The elevators are removed and stand for eight minutes at room temperature during which time any water present in the honeycomb composite will cool at a different rate to the composite itself, creating a temperature differential that shows up on the FLIR P-Series infrared camera.

The inspectors view the camera display in inverted grey/black, moving the camera unit over the static Airbus elevator by hand. The lights are then switched off - not to make the display easier to see, but because the camera is so sensitive that it will register the heat from electric lights and even sunlight through windows. The inspectors are trained to interpret external heat sources, including their own bodies, and are looking for different shades that indicate moisture inside the airframe.

If an elevator contains moisture, this must be removed. The location of the ingress is identified so the surface of the panel can be removed and the moisture extracted according to the Airbus structural repair manual.

Kieran Patton, senior NDT engineer at Shannon Aerospace, explains: “Most of the inspection work performed here is to minimise the cost of repairs. In relation to the elevators, the undetected moisture would later require delamination and therefore a larger repair or replacement of the elevator.”

Airbus has determined that thermography is the best approach to elevator moisture inspection. Patton says radiography would have been ruled out for this type of inspection because, with two panels on the elevator (each with two surfaces and a honeycomb composite centre), radiography would show through them both and that makes it difficult to determine which panel contains the moisture. “With thermography you can look from both sides,” he notes.

The FLIR P-Series uses a highly sensitive, uncooled detector, considered to be one of the most advanced infrared camera technology in the world. This long wave detector provides thermal sensitivity of 80mK at 50Hz, enabling the camera to detect very subtle temperature differences that lower performance cameras would miss. Its 50Hz operation allows the operator to scan moving objects or scan with a moving camera without image smear or distortion.

Shannon Aerospace rented a FLIR P-Series to carry out the first inspections while Patton researched the business case for buying. He concluded there would be a 2.5 year return on investment for the FLIR systems unit. “That is an excellent ROI in our industry because typically we see 3-5 years,” he reveals.

The return on investment figure illustrates how thermographic inspection is becoming increasingly affordable - a fact that has led to rapid uptake in other industries where heat differentials provide the basis for mission-critical measurement processes. Speed of payback is also increased with every application to which the camera is applied.

The main benefit of a thermal imaging camera is its flexibility across a range of inspection requirements. This means that the cost saving potential of the technology in aerospace manufacturing is immense.

www.flir.com/thg

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