Prematurely stripping aircraft for corrosion inspection or maintenance purposes causes excess pollution in the form of hazardous air pollutants (HAP), volatile organic compound (VOC) emissions, Resource Conservation Recovery Act (RCRA) waste, and carcinogenic chromates. The recently developed infrared reflectance imaging technique (IRRIT) can be used to reduce these waste streams. IRRIT utilizes mid-wave infrared (MWIR) (3-5 micrometers of light) to image corrosion through coatings. By stripping coatings only when IRRIT inspection indicates that corrosion is present, pollution from premature aircraft stripping can be minimized.

The objective of this project was to conduct a demonstration/validation (dem/val) of the capability of IRRIT to detect corrosion through aircraft coating systems versus visual corrosion inspection. Specific objectives were to:

• Compare IRRIT with current visual inspection techniques to assess corrosion
• Collect and analyze dem/val data
• Determine cost/waste reductions from a reduction in premature aircraft stripping by conducting a cost-benefit analysis
• Develop recommendations for technology transfer

The IRRIT system was evaluated against visual inspection on aircraft from several services, including the U.S. Air Force, U.S. Coast Guard, and U.S. Navy. Examined aircraft included the A-10, B-52, KC-135, P-3, and HU-25. Both aircraft exteriors and interiors (outer mold line [OML] and inner mold line [IML], respectively) were examined to assess the various coating systems used and the geometric effects for these areas. The dem/val procedure was to visually inspect the target area, collect IRRIT images, strip the paint system, and visually validate all reported corrosion.

Results were as follows:

• IRRIT was confirmed as an improved method of corrosion inspection compared to current visual inspection methods with 70-80% accuracy obtained during demonstrations, significantly higher than the 5-25% accuracy of the visual inspection method.
• IRRIT scan rate during the dem/val was shown to be approximately 150 sq ft per hour, depending on corrosion density. It is anticipated that more ergonomic camera designs will yield an increased scan rate.
• IRRIT limitations were determined, including limitations based on coating thickness and type, surface cleanliness, and line-of-sight requirements.
• Potential cost/waste reductions resulting from reduced aircraft strip and repaint maintenance operations were calculated based on the ability of IRRIT use to prevent premature aircraft stripping. Calculations indicate that maintenance deferment of a single medium-sized aircraft (using a P-3 Orion as a baseline) could include:

    VOC and chromate reductions approaching 3,000 lb and 25 lb, respectively

    HAZMAT reductions approaching 11,000 lb

    Cost savings approaching $130,000, greater than the cost of a single     IRRIT camera system.

The IRRIT system consistently identified corrosion through coatings more accurately than an unassisted visual inspection. The contributing factor for such a large deviation of inspection results between visual and IRRIT was due to the detection methods utilized for each technique. The IRRIT method directly images corrosion by-product through the paint system due to reflectance contrast differences of the substrate. The visual method relies on the identification of paint surface irregularities/blistering (i.e., paint degradation) as a result of substrate volume changes associated with corrosion formation.

Primary end users for the IRRIT system consist of in-service depot-level maintainers of fielded aircraft weapon systems and their associated support equipment in the sustainment community. Other end users could include inspectors, quality assurance specialists, and engineers in applicable maintenance and engineering departments of the Department of Defense.

IRRIT system procurement may be performed as individual component purchases later integrated by the user community or through IRRIT System Kits produced and provided by Northrop Grumman Technical Services (Bethpage, New York), including operating instructions and support for the IRRIT MWIR camera plus all required accessories.