N121-064 TITLE: Terahertz Imaging for Detection of Corrosion and Defects Under Hull Coatings

TECHNOLOGY AREAS: Ground/Sea Vehicles, Materials/Processes

ACQUISITION PROGRAM: PEO-SUBS VIRGINIA Class Submarine Program

OBJECTIVE: The object is to develop a Terahertz (THz) imaging system suitable for in-situ defect detection in commonly used ship hull coatings and rapid, non-destructive detection of corrosion, hull coating delamination, and hull surface gouges recessed into the hull metal through still-attached hull coatings/panels.

DESCRIPTION: THz imaging is an evolving technology currently in niche markets in industry with the potential to transition into Non-Destructive Evaluation (NDE) testing in many markets.

The Navy employs hull coatings, which present inherent difficulties for more traditional forms of non-invasive imaging such as ultrasound. Traditional methods for detecting corrosion defects under hull coatings involve costly removal and replacement of the coatings for visual inspection of the underlying surface. THz imaging could provide a potential alternative to current imaging technology because of its ability to penetrate hull coatings (as it is electromagnetic radiation) with much finer spatial resolution than possible with microwave-frequency electromagnetic imaging options. THz imaging (a pulsed technology) has many advantages when compared to somewhat faster millimeter-wave and sub-millimeter-wave imaging (non-pulsed, continuous-wave technologies), including multiple-decade higher signal-to-noise-ratio (SNR) across a broad bandwidth resulting in finer resolution due to penetration at higher frequencies for a given target material/coating and highly accurate depth measurement capability to better define volume and interface (delamination) defect location. These significant advantages over the previous technology may enable detection of defects that were not possible up to now.

THz imaging research has shown promise with Navy-relevant materials, specifically in characterizing the THz absorption coefficient and refractive index as an important step toward allowing corrosion inspection of ships without removal of the hull coatings. If this topic is successful, the technology developed could save the Navy millions of dollars per ship inspection, which is in line with the Navy�s Reduction of Total Ownership Cost (RTOC) initiatives.

This topic focuses on development of technologies that will support a system that can image corrosion and defects through coatings rapidly enough to support a statistically sampled portion of a submarine hull. The system should be man-portable, support sufficiently rapid data acquisition to support a survey of the entire hull or portions of interest, be capable of expected system movement without need for recalibration more frequently than once annually, be resilient to shipyard environmental factors (i.e., salt air ambient), and deliver sufficient (maximum) SNR for normal-incidence surface imaging.

PHASE I: Develop a system concept approach for THz imaging suitable for detection of defects defined as hull surface corrosion, hull surface gouges, and various coating material volume/interface defects (bubbles, improper material-material and material-metal interface adhesion, pockets of improperly cured material, and unintentional foreign objects) through coatings on a submarine hull without removal of the coatings to meet with unrestricted operation (URO) maintenance requirement card (MRC) specifications. If an URO MRC specification does not exist for a particular defect, a "good faith" effort shall be made to provide detection capability of that defect for the smallest defect size possible. Detection of a defect is defined herein as the ability to accurately distinguish the defect from surrounding regions which do not contain the defect and display the location and size of the defect in a software image. Demonstrate the feasibility of the concept to detect these defects through hull coatings. Demonstrate the feasibility of developing the concept into technology that can be used by the Navy for detecting these defects. Concept feasibility will be supported by appropriate analyses and laboratory experiments. Provide a Phase II development plan that includes performance goals and key technical milestones.

PHASE II: Based on the results of Phase I and the Phase II development plan, develop prototype suitable for evaluation. Evaluate the performance of the prototype with regard to the goals defined in Phase I on submarine hulls or representative structures. Based on the results of the evaluation, refine the prototype into a conceptual design. Prepare a Phase III development plan to transition the technology into a system that can be acquired by the Navy. The Phase III plan should include testing, validation, certification, and qualification for Navy use.

PHASE III: If Phase II is successful, the small business will be expected to support the Navy in transitioning the technology to Navy use should a Phase III award be made. Based on the Phase II results, develop a THz hull defect detection system for testing onboard a submarine. Support the Navy in testing, validating, certifying, and qualifying the system for Navy use.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The results of this effort should lead to improved inspection of submarine hulls for corrosion and defects under coatings, and should have applicability to other types of ship hulls as well. Resulting THz system SNR and speed performance improvements should benefit all applications which use the same region of the THz spectrum including space shuttle fuel tank hull and insulated pipe corrosion inspections.

REFERENCES:
1. Robert F. Anastasi, Eric I. Madaras, and Jeffrey P. Seebo, Stephen W. Smith, Janice K. Lomness, Paul E. Hintze, Catherine C. Kammerer, William P. Winfree, and Richard W. Russell, "Terahertz NDE Application for Corrosion Detection and Evaluation under Shuttle Tiles." Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2007 (Proceedings of SPIE Volume: 6531), http://spie.org/x648.html?product_id=690256&origin_id=x4318&event_id=725046

2. Robert F. Anastasi and Eric I. Madaras, "Terahertz NDE for under paint corrosion detection and evaluation." The 4th International Workshop on Ultrasonic and Advanced Methods for Nondestructive Testing and Material Characterization, June 19, 2006 at UMass Dartmouth, N. Dartmouth, MA (published in www.ndt.net).

3. NAVSEA T9081-AE-MMO-010 - URO MRC SSN 774 Class

KEYWORDS: Terahertz; imaging; corrosion; defects; hull coatings; nondestructive evaluation

** TOPIC AUTHOR (TPOC) **

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