Thermal Imaging: An NDT technology that is evolving rapidly

Thermal Imaging An NDT technology that is evolving rapidly By Joe Escobar Photos courtesy of Thermal Wave Imaging, 2001 November 2001 In the day to day routine of aircraft inspection, non-destructive testing (NDT) plays a vital...

Seeing the big picture
Some of the aircraft structures that can be inspected by thermal imaging can be fairly large. But the area that can effectively be inspected on each image shot is only around one square foot. In the past, a person using a pulsed thermography system would have to take the images one at a time until the whole surface was inspected. For every shot taken, the inspector had to analyze that shot, make a decision, then move on to the next one. If he wanted to get a big picture of the entire component, he would have to put together a patchwork quilt of the images using all those single shots.
Thermal Wave Imaging has recently improved it’s pulsed thermography system with the addition of their MOSAIQ software. With MOSAIQ, the inspector gets the whole picture of the structure, with the benefit of a greatly enhanced view of subsurface features. Basically, just a little input is required by the inspector.
Dr. Shepard explains, "All the technician has to do is tell the computer what inspection path he is going to take. Once he gives it the pattern and tells it how many shots he anticipates taking, the software knows exactly what to do. It uses advanced signal processing techniques we have developed to compile all the images into one complete image and remove the blurring normally associated with thermography, so that a precise image of the subsurface structure of the entire part is created."

Thermal imaging has several advantages. First of all, it is non-invasive. Unlike X-ray where you need access to the back side of the part, an inspection can be done without any disassembly.
It is also a clean inspection. No couplants or penetrants are needed. In addition, it is a relatively fast process where large areas can be inspected in a matter of minutes.
Another advantage is being able to get the complete picture of the structure, especially with the new MOSAIQ software. Other NDT methods rely on point-to-point inspection and that can be time consuming.

As with any type of NDT inspection method, thermal imaging has its limitations. It relies on the ability of the part being inspected to absorb heat. If the material is shiny, such as an un-painted aluminum skin, the heat will not be absorbed, but merely reflected. In this case, it is sometimes possible to apply a water-based temporary coating on top of the metal for the inspection.
Rubber-coated surfaces, like leading edges with de-ice boots, are impossible to inspect due to rubber’s insulating properties. In addition, very thick parts like landing gear are difficult, if not impossible, to inspect using thermal imaging.
Thermal imaging has seen increased use and greater acceptance in recent years. With the abilities it offers in widening our NDT capabilities, it is likely to see even more use in our industry in the future.

The Source
Additional resources....

American Society for Nondestructive Testing

Nacelles and Thrust Reversers Division
6911 N. Whirlpool Drive
Tulsa, OK 74117
(918) 878-4504

Thermal Wave Imaging Inc.
845 Livernois St.
Ferndale, MI 48220
(248) 414-3730

NDT Listing
The following is a listing of companies that provide NDT products and services.
Please contact them directly for more information.

AEI North America Inc.
Old Mill Bldg., 10 Orange St., Marcellus, NY 13708, (315) 673-0164,
Manufacturer and distributor of remote visual inspection systems that include rigid borescopes, flexible fiberscopes, videoscopes, pole/pushcams, crawlers and related accessories such as fiber-optic illumination, video monitoring and recording systems.

Cardinal Electronics Inc.
4405 Wagon Wheel, Lansing, MI, 48917, (800) 344-9469 or (517) 321-6618
Cardinal Electronics Inc.'s Digital Optical Tachometer works like a camera inside or outside the cockpit. Unit looks like a propeller and displays speed to 1 rpm accuracy and resolution once per second. It is self-contained, easy to use, works on singles and twins, works to 15ft. and adds nothing to the propeller.

Centurion NDT
707 Remington Rd., Ste. 9, Schaumburg, IL 60173, (847) 884-4949,
Centurion NDT designs, manufactures, markets, and services eddy current and ultrasonic test instrumentation. The Model ED-520 is among the most recognized and used eddy current flaw detectors in the aviation industry.

Command Electronics Co.
Box 17842, Kansas City, MO 64134, (816) 761-3514,
Manufactures and distributes digital and analog airdata testers. Digital Model 803 is only tester whose accuracy can be verified right in shop. Traceable to N.I.S.T. Also can be calibrated in-house.

Everest VIT
199 Hwy 206, Flanders, NJ 07836, (888) 332-3848 or (973) 448-0077,
Introducing the new 60 watt light source (ELSV-60) with video pass through. The high intensity light box attaches to borescopes and fiberscopes to provide bright, white light and true-to-life color for better detection of cracks or corrosion during inspections.

Foerster Instruments Inc.
140 Industry Dr., RIDC Park West, Pittsburgh, PA 15275, (800) 635-0613,
Non-destructive testing electrical equipment for crack detection, electrical conductivity measurement and determination of material properties. Foerster's equipment is portable, easy to operate, and highly sensitive.

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