The Department of Defense (DoD) has numerous high performance weapon platforms that require stringent monitoring of the structural integrity of the platforms owing to these structures' low tolerance for corrosion and/or cracks. The need to inspect the substrates of these platforms for corrosion, fatigue cracks, and other operationally induced damage is very time consuming and costly, often necessitating the removal and subsequent replacement of the coating system, not to mention the handling of the hazardous wastes associated with these materials and processes. The paint, stripping, and repainting process generates significant and costly pollutant streams such as volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). Environmental regulations limit emissions of VOCs and HAPs, and DoD efforts to attain compliance have identified removal and reapplication of coatings as major contributors to the emissions problems at DoD facilities. Developing realistic and practical nondestructive evaluation (NDE) technologies for "inspection-through-paint" is considered to be one means by which the DoD can extend the service life of coatings systems, extend the life of aging weapons systems, meet the increasingly stringent environmental requirements, and increase operational capability with limited assets.
The objective of this project was to develop and evaluate three technologies for their viability as NDE tools for the detection of cracks and corrosion under surface coatings.
The Naval Surface Warfare Center Carderock Division and the Naval Air Warfare Center Aircraft Division (NAWCAD), leveraging with prior Navy small business innovation research programs, investigated three NDE techniques, namely, real-time ultrasound imaging, thermal imaging, and near-field microwave imaging, for the detection of corrosion and fatigue cracks hidden under paint. These technologies were selected and developed for their potential to inspect areas rather than points, portability to the job site, overall projected economy to implement, and relative technological maturity.
Of the three innovative NDE technologies developed and evaluated, the real-time ultrasound imaging and pulse thermography system show the most promise for transition to the field. The through transmission approach to real-time ultrasound imaging has received considerable attention from the aerospace industry. In fact, Boeing/Vertol has accepted delivery of a through transmission unit to test composite components on the production line. The pulse thermography system is transitioning into the field because of successful demonstration of the abilities of the system to the aerospace community. Navy Depot Cherry Point NC has an older pulse thermography system that is currently used for limited applications. The system developed in this project will allow for an expansion of these applications owing to the greater sensitivity of the new system as well as to the increased portability. Other achievements include the publication of eight papers, the submission of four reports, and the presentation of nine technical talks at national and international conferences. In addition, Imperium, Inc. and NAWCAD have made an application for the issuance of a patent based on the oblique angle beam real-time ultrasound imaging system. This project was completed in FY01.
Early detection and quantification of corrosion and cracking without removing the paint system will enhance the life of structural platforms while significantly minimizing the environmental impact.