Corrosion Damage Assessment Using Infrared Thermography: A Historical Overview - Essay Example

After detecting the radiation, these cameras then produce images of the found radiation. Through the use of objects' temperatures, thermography makes it possible to view objects with or without visible illumination; objects can be seen at nighttime with thermography although they may not be visible by basic eyesight. The amount of radiation which an object emits increases with temperature "therefore thermography allows one to see variations in temperature, hence the name." ("Wikipedia", 2006).

Thermographic imaging is commonly used in military and security services, and forms of it are also used by firefighters, power lines maintenance technicians, and building construction technicians (to name a few). Thermal imaging cameras are also often installed in certain luxury cars, to aid the driver. A modern day thermographic camera is similar to a camcorder in appearance, but instead of CCD sensors a thermographic camera uses microbolometer arrays. Much more expensive than their so-called counterparts, thermographic cameras also require much more attention in regards to monitoring and maintaining it as a form of equipment.

Infrared imaging has the potential of rapidly inspecting large areas at video frame rates to provide an early warning for many areas of topic in the world. Recent advances in thermography have been used in nondestructive inspections (NDI) of aluminum airframes and concrete bridge decks. The effects of corrosion on metallic aircraft structures really only began to be appreciated in the 1970s when it became easily apparent that many transport aircraft would be flown well beyond their original design lives.

"These aircraft have been designed in such a way that the majority of defects should be found by inspection while the aircraft is still strong enough to carry normal flight loads. At the time, the interactive aspects of fatigue failure were also recognized and manufacturers were required to address multiple crack initiation, redistribution of loading following a fatigue failure, and concurrent failure of multiple load path elements." (Ford, 1999, pp.249-254). There are various forms of corrosion to which metallic aircraft structures are prone.

These forms are: uniform; galvanic; pitting, crevice and filiform; intergranualar and exfoliation. Uniform corrosion is the most common form, and this type of corrosion most times produces large areas of damage "and providing the area affected is accessible for visual inspection, it can usually be detected fairly early and remedial action taken." (Ford, 1999, pp.249-254). Galvanic corrosion occurs when the metals in question are in contact with a corrosive medium. Prime examples of sites in which galvanic corrosion would take place are battery compartments or toilet and galley areas.

Crevice corrosion occurs when a corrosive liquid accesses into crevices and "is usually associated with small volumes of solution trapped between gasket surfaces or lap joints, or, for example, in crevices under bolt or rivet heads. Pitting is similar to this form of corrosion, in that it refers to local contamination by highly corrosive substances. Intergranular corrosion most often affects the grain boundary regions in a polycrystalline metal. Corrosion and cracking of the metal surface occurs, and the very