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Passive Inter-Modulation RF Emissions Utilized for Identifying Galvanic Corrosion in Metal Structures


Corrosion is a major concern that causes premature deterioration or failure at damage sites in metal structures thereby necessitating monitoring, maintenance, repair or replacement. PIM emissions are a known problem for ships and land-based cellular systems where metal structures simultaneously receive RF radiation on two or more different signal frequencies. The received RF signal frequencies may then cause RF currents to flow in metal structures that can be non-linearly mixed together in metal-to-metal contacts in the structures affected by galvanic corrosion. These RF currents may then generate additional new intermodulation RF emissions from the structures due to sum and difference harmonic mixing of the two or more original frequencies. PIM may occur in a variety of areas from coaxial connectors to cables, rusty bolts, or any metallic structure joint where dissimilar metals or similar metals in an electrolyte occur. Corrosion sites could include poor, loose, or contaminated connectors, junctions between dissimilar metals, and mechanical connections that have become oxidized, or contaminated with typical corrosion chemicals found in missile defense systems. Demonstrate that PIM RF emissions have the capability to accurately detect and characterize degradation arising from galvanic corrosion processes in metal structures. Areas of emphasis include determining if various conditions of corrosion severity found at points on a metal structure can be accurately and repeatedly identified to determine where and when a particular corrosion site is an issue for concern. Furthermore, the information gained by the preceding effort should be evaluated for its capability to support corrosion degradation monitoring, corrosion modeling and determining applicable acceleration factors for galvanic and other combinational corrosion processes. Also desired from this effort is to determine whether the RF currents that circulate due to RF radiation impinging on the metal structures increase the PIM emissions. Resolve how RF radiation affects or accelerates existing galvanic corrosion processes in the structures. PHASE I: Demonstrate a proof-of-concept for detecting PIM RF emissions from metal structures and provide analysis of how effectively the measurements are employed to detect and locate the corrosion points at sites on metal structures. Identify prototype equipment items, develop a preliminary equipment design and document developed techniques. PHASE II: Perform testing of a PIM detection prototype to obtain information on PIM emission “signatures” of corrosion sites with known differing metallurgical characteristics. Demonstrate that the results are accurate and repeatable enough to provide a basis for degradation monitoring, corrosion modeling and determination of corrosion model acceleration factors. Develop a library of repeatable signatures of corrosion to include metallurgical characteristics at corrosion sites such as joint contact pressure, surface topology, current density and area of the contact point. PHASE III: Develop a final equipment design and hardware and transition to the government. This phase is to obtain improved capability for identifying the presence and progression of underlying galvanic corrosion in metal-to-metal contacts. This effort offers significant cost avoidance for missile defense applications. Positive results from this project have great potential to improve system reliability, and to reduce the costs of metal structure corrosion from material and systems functional loss within the DoD, and on a national commercial level. Commercialization: In the U.S., total direct cost of corrosion is estimated at about 300 billion dollars per year; which is about 3.2% of domestic product. Corrosion also interferes with human safety, disrupts industrial operations and presents dangers to the environment. Positive results from this project have great potential to improve system reliability and to reduce the costs of metal structure corrosion within the DoD and on a national commercial level.
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