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A DUAL-BAND infra-red (IR) corrosion-detection system is being tested on aircraft skins by scientists from the Lawrence Livermore National Laboratory (LLNL) in California in the hope of developing a non-destructive commercial system.
The IR system uses flash lamps to heat the metal skin with uniform thermal pulses, each lasting a few milliseconds. A dual-band scanner then images the resulting surface temperature changes for later analysis by computer. Areas, which show up as "hot spots" indicate potential corrosion.
The new system, the IR Computed Tomography Method, differs from conventional IR imaging systems, which work at only one wavelength, by retrieving images at two separate wavelengths. The developers claim that the system can show what metal, and how much of it, has corroded.
"We can also characterise the type of defects involved, such as gaps or areas with poor adhesive bonds, and its depth in three-dimensional space. This is particularly important for inspecting new composite materials used to repair parts of aircraft wings," says LLNL non-destructive evaluation programme's Nancy Del Grande.
The system can also be used to differentiate between real corrosion and conditions which could resemble it, such as fabrication ripples, surface roughness and uneven sealant in a lap joint. LLNL is analysing data collected in January, when the technique was tested on two Boeing 747s undergoing routine maintenance.
Arizona-based Garrett Aviation has begun using a new ComScan Backscatter Imaging System at its Van Nuys Jet Center in California, to detect corrosion in the aft pressure-bulkheads of Gulfstream II and III business aircraft.
The X-ray-based device is being used to help operators comply with Gulfstream bulletins, which require the inspection of all GIIs by 28 July, and all GIIIs by December 1996.
Source: Flight International
