Nondestructive Testing of Corrosion Under Coatings

WP-1137

Objective

Project Graphic

Application of infrared reflectance technology to the aircraft part coated with green primer (left) revealed corrosion underlying the primer surface (right).

Surface corrosion on aluminum aircraft skins and around joints and fasteners is often the precursor to buried corrosion. Aircraft paints are routinely removed to reveal the presence of corrosion on the surface of metal structures, and the aircraft is subsequently repainted. Aircraft painting and repainting operations result in significant emissions of volatile organics, organic and inorganic hazardous air pollutants, and hazardous waste.

The objective of this project is to develop nondestructive evaluation (NDE) techniques to detect the presence of corrosion under an organic film in order to reduce the amount of painting and depainting that is normally performed.

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Technical Approach

Inspection and measurement techniques to be developed include (1) a spectral NDE technique employing an optical reflectance probe in the near/mid infrared (IR) region combined with Directional Hemispherical Reflectance (DHR) and Fourier Transform Infrared (FTIR) integrated detector; (2) Wide-Area Spectral Imaging (WASI) using spectral filters and high-resolution focal plane cameras to allow rapid initial assessment of sub-paint corrosion; and (3) a Scanning Kelvin Probe (SKP) electrochemical method employing a calibrated capacitance probe to indirectly measure corrosion potential across a surface. Challenges to be overcome include probe positioning and electrical noise. Baseline measurements of unexposed coatings and typical corrosion products were performed to establish a database of standards. Aged aircraft components then were evaluated. Measuring systems will be optimized at varying levels of corrosion and modified for field use. Prototypes will be verified in conjunction with the Naval Air Warfare Center Aircraft Division (NAWCAD). Finally, a transition plan for cost-effective applications will be prepared.

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Results

A portable IR Reflectance Camera System has been developed to detect corrosion under military and commercial aerospace coatings up to 12 thousandths of an inch in thickness. The system is also capable of detecting fatigue cracks of approximately 0.030 thousandths of an inch in length emanating from fastener holes and corrosion pits down to 0.001 of an inch under coatings. IR images of high fidelity were produced in real time on a television monitor for instant observation with the capability of storing the data as a movie (i.e., MEPG file) or capturing the data in the form of a picture, as a JPEG or TIFF file.

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Benefits

By minimizing the number of times the aircraft exterior coatings are stripped and reapplied, substantial pollution prevention and cost saving opportunities are provided. The NDE techniques developed in this project will be able to target and map specific areas that require maintenance due to corrosion, allowing for a migration from schedule-based to condition-based maintenance. In addition, verification of the condition of the primer and surface preparation once the topcoat has been removed will eliminate a portion of the rework that now routinely occurs.

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Project Documents

Points of Contact

Principal Investigator

Mr. John Weir

Northrop Grumman Corporation

Phone: 516-575-5422

Fax: 516-346-3670

Program Manager

Weapons Systems and Platforms

SERDP and ESTCP

Project Documents

Document Types

  • Fact Sheet - Brief project summary with links to related documents and points of contact.
  • Final Report - Comprehensive report for every completed SERDP and ESTCP project that contains all technical results.
  • Cost & Performance Report - Overview of ESTCP demonstration activities, results, and conclusions, standardized to facilitate implementation decisions.
  • Technical Report - Additional interim reports, laboratory reports, demonstration reports, and technology survey reports.
  • Guidance - Instructional information on technical topics such as protocols and user’s guides.
  • Workshop Report - Summary of workshop discussion and findings.
  • Multimedia - On demand videos, animations, and webcasts highlighting featured initiatives or technologies.
  • Model/Software - Computer programs and applications available for download.
  • Database - Digitally organized collection of data available to search and access.